A SELECTIVE COLLECTOR FOR PHOSPHATE FLOTATION
FINAL REPORT
Jan D. Miller
Principal Investigator
with
Xuming Wang and Minhua Li
THE UNIVERSITY OF UTAH
Salt Lake City, Utah 84112
Prepared for
FLORIDA INSTITUTE OF PHOSPHATE RESEARCH
1855 West Main Street
Bartow, Florida 33830 USA
Contract Manager: Patrick Zhang
FIPR Project Number: 00-02-142R
August 2002
DISCLAIMER
The contents of this report are reproduced herein as received from the contractor. The
report may have been edited as to format in conformance with the FIPR Style Manual.
The opinions, findings and conclusions expressed herein are not necessarily those of the
Florida Institute of Phosphate Research, nor does mention of company names or products
constitute endorsement by the Florida Institute of Phosphate Research.
PERSPECTIVE
Patrick Zhang, Research Director - Beneficiation & Mining
Phosphate companies in Florida as well as in many parts of the world all use the
Crago “Double Float” process to upgrade phosphate. In the conventional "Double Float"
(Crago) process, about 30-40% by weight of the sands in the feeds are floated twice, first by
fatty acid, and then by amine. This Crago process is therefore inefficient in terms of
collector utilization. The theoretical fatty acid collector efficiency in phosphate flotation
was estimated to be only about 5%. The rest of the fatty acid is wasted primarily due to
silica or clay. One of the major drawbacks of this process is the deoiling process. Deoiling
consumes a significant amount of sulfuric acid, which calls for special safety precautions
and equipment maintenance. Insufficient deoiling, which is not an infrequent phenomenon,
often causes loss of phosphate and poor concentrate grade. Deoiling also causes loss of fine
phosphate particles, amounting to more than 1% of the phosphate in the original feed in
most operations. Another problem with the Crago process is with the amine flotation step.
Not only are amines more expensive than fatty acids, but also very sensitive to water
quality, particularly to the slime content in water.
University of Utah has recently developed a suite of flotation collectors based on
alkyl hydroxamic acids, some of which showed exceptional performance in flotation of
phosphate from sands. At their April 2000 meeting, the FIPR Board of Directors
approved funding in the amount of $10,000 for a preliminary lab-testing program for
developing a one-step flotation process using the Utah reagent. As is shown in the table
below, the new collector could achieve single-stage flotation with both coarse and fine
flotation feeds.
Lab Testing Results Using the New Collector
Conc. % P2O5
31.12
31.02
31.42
29.01
30.14
P2O5 % Recovery
95.18
94.36
93.88
85.42
85.11
Water Type
Tap
Plant
Plant
Tap
Plant
Feed
Deslimed coarse feed
Deslimed coarse feed
As-received coarse feed
Fine feed
Fine feed
The above results were considered very encouraging technically. However, the
economic feasibility and the environmental impact of the reagent system remained
unclear, which prompted funding for in-plant evaluation of this reagent. Due to some
logistic problems, the testing was eventually conducted in a pilot plant. Pilot testing
showed similar results as lab testing, achieving about 95% and 85% recoveries in one
step flotation, at concentrate grades of 31.5% and 29.6% P2O5 for coarse and fine feeds,
respectively. As expected, economic analysis of the new flotation chemistry with the
new collector shows a strong dependence on the reagent price. If the cost of reagent could
be reduced to $1.80/lb the single-stage flotation of coarse phosphate with the alkyl
hydroxamic acid/alcohol collector would be very competitive with the traditional double
float process using fatty acid, fuel oil and amine.
iii
ABSTRACT
It has been discovered that water insoluble alcoholic solutions of alkyl
hydroxamic acids serve as selective collectors for the flotation of phosphate mineral
resources (Miller and others 2000). Critical aspects of the composition and structure of
these new collectors have been considered with respect to their effectiveness in phosphate
flotation using microflotation techniques. The wetting characteristics of the new collector
at fluorapatite, francolite, dolomite and quartz surfaces have been examined by contact
angle measurements and high speed video experiments. The new collector is
commercially available from Cytec as AERO 6493.
The effectiveness of the new collector chemistry is demonstrated by the results
from single-stage bench-scale flotation experiments with AERO 6493 for feed material
from plants in Florida, North Carolina, and Utah. In the best case, from experiments with
low grade (5% P2O5) coarse feed (16x35 mesh) from central Florida, a single-stage
phosphate recovery of 95% was achieved with a concentrate grade of 31% P2O5. Such a
separation efficiency could not be achieved using the traditional fatty acid/fuel oil
collectors as is evident from comparison of the respective grade/recovery curves. AERO
6493 has been evaluated for use by the Florida phosphate industry in pilot-plant studies at
Jacobs Engineering and the experimental results, which confirm results from laboratory
experiments, show improved separation efficiency especially for coarse phosphate
flotation feed from the Cargill SFM plant.
As expected, economic analysis of the new flotation chemistry with AERO 6493
shows a strong dependence on the reagent price. If the cost of AERO 6493 could be
reduced to $1.80/lb, the single-stage flotation of coarse phosphate with the alkyl
hydroxamic acid/alcohol collector would be competitive with the traditional double float
process using fatty acid and fuel oil.
The environmental impact regarding use of the hydroxamic acid collector in
phosphate flotation was considered with respect to water quality. Literature review and
experimental results indicate that there is no significant environmental impact from the
utilization of the new collector.
v
ACKNOWLEDGMENTS
The Principal Investigator and all researchers involved in this project want to
express their thanks for the financial and technical support from FIPR and also would like
to recognize
Arr-Maz Products, LP
Cargill Fertilizer, Inc.
CF Industries, Inc.
Cytec Industries, Inc.
Eriez Inc.
IMC-Agrico
Jacobs Engineering
PCS Phosphate
SF Phosphates
for their participation, support, and contribution to the completion of this project.
vi
TABLE OF CONTENTS
PERSPECTIVE.................................................................................................................. iii
ABSTRACT.........................................................................................................................v
ACKNOWLEDGMENTS ................................................................................................. vi
EXECUTIVE SUMMARY .................................................................................................1
INTRODUCTION ...............................................................................................................3
COLLECTOR CHEMISTRY..............................................................................................5
Materials and Methods.............................................................................................5
Mineral Samples ..........................................................................................5
Reagents.......................................................................................................5
Microflotation ..............................................................................................6
Contact Angle and Collector Attachment ....................................................6
Results and Discussion ............................................................................................6
Collector Dosage and Flotation pH..............................................................6
Collector Composition ...............................................................................10
Wetting Characteristics..............................................................................14
Analysis of High Solids Conditioning .......................................................18
Summary ................................................................................................................18
BENCH-SCALE FLOTATION.........................................................................................21
Materials and Methods...........................................................................................21
Flotation Samples.......................................................................................21
Reagents.....................................................................................................21
Bench-Scale Flotation................................................................................22
Results and Discussion .........................................................................................22
Efficiency of Separation ............................................................................22
Collector Addition .....................................................................................22
High Solids Conditioning ..........................................................................23
vii
TABLE OF CONTENTS (CONT.)
Particle Size ...............................................................................................29
Effect of Plant Water .................................................................................30
North Carolina Phosphate ..........................................................................31
Utah Phosphate ..........................................................................................31
Summary ................................................................................................................32
PILOT PLANT TESTING.................................................................................................33
Preparation for Pilot Plant Testing.........................................................................33
Supplemental Bench-Scale Experiments ...............................................................33
In-Plant Trial at PCS Plant with Column Flotation ...............................................34
Pilot Plant Testing at Jacobs Engineering..............................................................37
Flotation with Cargill SFM Fine Feed .......................................................42
Flotation with Cargill SFM Coarse Feed ...................................................42
Summary ................................................................................................................42
ECONOMIC CONSIDERATIONS..................................................................................45
Sources of Data ......................................................................................................45
Economic Analysis ................................................................................................45
ENVIRONMENTAL IMPACT.........................................................................................49
Literature Review...................................................................................................49
Experiments on Water Quality...............................................................................50
Water Quality in Open-Cycle Testing .......................................................50
Water Quality in Locked-Cycle Testing ....................................................52
Summary ................................................................................................................55
CONCLUSIONS................................................................................................................57
REFERENCES ..................................................................................................................59
APPENDIX A
Data from Pilot-Plant Flotation Tests ......................................... A-1
viii
LIST OF FIGURES
Figure
Page
1.
Microflotation Recovery of Fluorapatite, Francolite, Dolomite and
Quartz as a Function of AERO 6493 Addition at Natural pH 6.5,
with DI Water ..............................................................................................7
2.
Microflotation Recovery of Francolite and Dolomite (35x100 Mesh) as a
Function of FA/FO (7:3 Ratio by Volume) Addition at Natural pH
6.5, with DI Water .......................................................................................8
3.
Microflotation Recovery of Fluorapatite, Francolite, Dolomite and
Quartz as a Function of pH at an AERO 6493 Addition of 1200 g/t
with DI Water ...............................................................................................9
4.
Microflotation Recovery of Francolite as a Function of Collector Addition
at a Natural pH of 6.5. In the Case of Collector Addition as an
Alcoholic Solution, an Isodecanol Solution Containing 20%
Hydroxamic Acid Was Used ......................................................................11
5.
Effect of Octyl Hydroxamic Acid Content in Isodecanol Solution on
Phosphate Recovery for Various Levels of Total Collector Addition at
Natural pH of 6.5 for Microflotation of Pure Francolite ............................12
6.
Microflotation for Coarse Phosphate Feed from IMC-Agrico Four Corners
Plant in Central Florida, as a Function of Alcohol Hydrocarbon Chain
Length for Collector Solutions Containing 20% Octyl Hydroxamic
Acid at a Total Reagent Dosage of 800 g/t .................................................13
7.
Insoluble Collector Drop at a Mineral Surface in Water .................................14
8.
Relaxation of Hydroxamic Acid Collector (AERO 6493) Drop Contact
Angle at Fluorapatite and Dolomite Surfaces with the Captive-Drop
Method in DI Water at Natural pH of 6.5...................................................15
9.
High-Speed Video Photographs Showing the Spreading Characteristics
of a Drop of Hydroxamic Acid Collector (AERO 6493) at the
Fluorapatite Surface in DI Water of pH 6.5, and 220 C .............................16
10.
High-Speed Video Photographs Showing the Spreading Characteristics
of a Drop of Hydroxamic Acid Collector (AERO 6493) at the Dolomite
Surface in DI Water of pH 6.5, and 22oC ...................................................17
ix
LIST OF FIGURES (CONT.)
Figure
Page
11.
X-Ray CT Image of Aeroflocs Formed by Francolite Particles, Air
Bubbles During Flotation with the Hydroxamic Acid Collector ................19
12.
Comparison of Grade/Recovery Curves Obtained with the New
Hydroxamic Acid Collector (AERO 6493) and the Traditional FA/FO
Collector for Single-Stage Flotation of Coarse Feed (16x35 Mesh,
5.65% P2O5) from the IMC-Agrico Four Corners Plant, Central Florida
(Miller and others 2001) .............................................................................23
13.
Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (16x35 Mesh,
5.6% P2O5) Received from IMC, Central Florida.......................................24
14.
Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (12x80 Mesh,
15.1% P2O5) Received from Cargill, Central Florida .................................25
15.
Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (20x200 Mesh,
16.4% P2O5) Received from PCS, North Carolina .....................................26
16.
Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (16x325 Mesh,
26.7% P2O5) Received from SF Phosphates, Utah .....................................27
17.
Single-Stage Flotation Response as a Function of Percent Solids During
Conditioning with 1000 g/t AERO 6493 for Coarse Feed from the
Cargill Plant ...............................................................................................28
18.
Single-Stage Flotation Grade/Recovery Curves for Different Sizes of
Phosphate Feed from the Cargill Plant at Natural pH 7.5, 75%
Conditioning Solids. Data Points Represent Different Levels of
Collector Addition ......................................................................................30
19.
Column Flotation System at the PCS Phosphate White Springs Plant
North Florida...............................................................................................35
20.
Photograph of Flotation Column at PCS White Springs Plant .......................36
21.
Pilot Plant Testing Flowsheet ..........................................................................38
x
LIST OF FIGURES (CONT.)
Figure
Page
22.
Photograph of Single-Stage Flotation Pilot Plant ............................................39
23.
The Results of Particle Size Analysis for Fine Flotation Feed, Concentrate, and Tailing from Pilot Testing at a Feed Rate of 900 Lb/Hr. and
74% Conditioning Solids ............................................................................40
24.
Results of Particle Size Analysis for Coarse Flotation Feed, Concentrate, and Tailing from Pilot Testing at a feed Rate of 700 Lb/Hr. and
74% Conditioning Solids ............................................................................41
25.
Effect of Collector Addition on Single-Stage Pilot Plant Flotation of
Cargill Fine Feed at a Feed Rate of 900 Lb/Hr. and 74% Conditioning
Solids..........................................................................................................43
26.
Effect of Collector Addition on Single-Stage Pilot Plant Flotation of
Cargill Coarse Feed at a Feed Rate of 700 Lb/Hr. and 71% Conditioning Solids ....................................................................................................44
27.
Open-Cycle Single-Stage Flotation Procedure Without Recycled Water .......51
28.
Locked-Cycle Single-Stage Flotation Procedure With Recycled Water .........53
xi
LIST OF TABLES
Table
Page
1.
Other Chemicals Used .....................................................................................22
2.
Evaluation of the New Collector (AERO 6493) vs. Fatty Acid/Fuel
Oil for Fine Feed from IMC-Agrico Four Corners Plant, Central Florida
(Single-Stage Flotation, Collector 800 g/t, Tap Water).............................29
3.
Test Results for Deslimed Coarse Feed from the IMC-Agrico Four Corners
Plant with New Collector (AERO 6493) Using Tap Water and Plant
Water (Single-Stage Flotation, Collector 1250 g/t, Na2CO3 400g/t,
Na2SiO3 400g/t, pH 8.6) .............................................................................31
4.
Results from Single-Stage Phosphate Flotation of Feed from the PCS
North Carolina Plant Using the New Hydroxamic Acid Collector
(AERO 6493 900 g/t)..................................................................................31
5.
Results from Single-Stage Phosphate Flotation of Feed from the SF
Phosphates Utah Plant Using the New Hydroxamic Acid Collector
(AERO 6493, 1200 g/t)...............................................................................32
6.
Results from Single-Stage Phosphate Flotation of Feed from the Cargill
SFM Plant Using the New Hydroxamic Acid Collector (AERO 6493).
No Other Reagents were Added .................................................................34
7.
Results from Single-Stage Phosphate Flotation of Feed from the IMC
FTG Plant Using the New Hydroxamic Acid Collector (AERO 6493).
No Other Reagents Were Added.................................................................34
8.
Results from In-Plant Trial at the PCS White Springs Plant with
Column Flotation (-16 Mesh Fraction) .......................................................37
9.
Results from Single-Stage Pilot Plant Phosphate Flotation of Feed from
the Cargill SFM Plant Using the New Hydroxamic Acid Collector
(AERO 6493) ..............................................................................................42
10.
Pilot Plant Flotation Results and Reagent Schedule for Single-Stage
Flotation with AERO 6493 .........................................................................46
11.
Typical Flotation Results and Reagent Costs for Coarse Feed Using
Traditional Double Float Process (FA/FO and Amine)..............................47
xiii
LIST OF TABLES (CONT.)
Table
Page
12.
Typical Results from the Economic Performance Analysis (Assuming
4 Million Tons Per Year of Capacity)..........................................................48
13.
Analytical Results for Open-Cycle Flotation of Cargill Feed (12x80
Mesh) and Discharge Water Quality without Water Recycle Using
AERO 6493 as Collector. Flotation with Tap Water at pH 7.41 ................52
14.
Analytical Results for Locked-Cycle Flotation Products of Cargill Feed
(12x80 mesh) with 100% Water Recycle Using AERO 6493 as
Collector. Flotation with Tap Water at pH 7.41 .........................................54
15.
Analytical Results for Locked Cycle Flotation of Cargill Feed (12x80
Mesh) and Discharge Water Quality from the Last Cycle (Cycle 3)
Water Recycled Using AERO 6493 as Collector. Flotation with Tap
Water at pH 7.41 ..........................................................................................54
16.
Average Analysis of Plant Water Samples from Central Florida .....................55
17.
Results from Single-Stage Pilot Plant Phosphate Flotation of Feed from
the Cargill SFM Plant Using the New Hydroxamic Acid Collector
(AERO 6493) ..............................................................................................58
A-1.
Pilot Testing Performed on Fine Feed from Cargill SFM Plant .................... A-1
A-2.
Pilot Testing Performed on Coarse Feed from Cargill SFM Plant ................ A-2
A-3.
Analytical Results from Pilot Testing for Fine Feed from Cargill SFM
Plant.......................................................................................................... A-3
A-4.
Analytical Results from Pilot Testing for Coarse Feed from Cargill
SFM Plant................................................................................................. A-4
xiv
EXECUTIVE SUMMARY
Flotation with oily, water insoluble collectors is frequently governed by selective
wetting/spreading phenomena and the formation of aeroflocs; complex aggregates of air,
water, the liquid collector phase, and mineral particles. Traditional phosphate flotation is
a classic example of this type of flotation, which involves aerofloc formation with the
insoluble fatty acid/fuel oil collector. It seems that selective phosphate flotation with
water insoluble alcoholic solutions of alkyl hydroxamic acid collectors functions in a
similar manner but with greater selectivity. The new collector is commercially available
from Cytec as AERO 6493. High solids conditioning is preferred to achieve the creation
of stable aeroflocs of sufficient buoyancy for flotation. In this study collector
composition, wetting/spreading characteristics and other surface chemistry considerations
are discussed as part of the development of these hydroxamic acid collectors for
phosphate flotation.
Traditional reagent chemistry for the flotation of sedimentary phosphate rock
involves use of the insoluble fatty acid/fuel oil (FA/FO) collector. Generally the
separation is not sufficiently selective and the phosphate rougher concentrate must be
treated further in a second stage by reverse flotation of quartz contaminants from the
rougher phosphate concentrate with amines. Bench-scale flotation results for plant feeds
from Florida, North Carolina, and Utah have demonstrated that single-stage selective
flotation of coarse phosphate can be achieved using water insoluble alcoholic solutions of
alkyl hydroxamic acid collectors. For example, when the grade/recovery curve for the
rougher flotation with FA/FO collector is compared with AERO 6493 collector for coarse
feed from plants in Central Florida it is evident that the separation efficiency has been
significantly improved. In the case of coarse feed (15% P2O5) from the Cargill SFM
Plant in Central Florida the concentrate grade reached 34% P2O5 with 93% recovery from
single-stage bench-scale flotation experiments. AERO 6493 has been evaluated for use
by the Florida phosphate industry in pilot-plant studies at Jacobs Engineering and the
experimental results, which confirm results from laboratory experiments, show improved
separation efficiency especially for coarse phosphate flotation feed from the Cargill SFM
plant. The results from pilot plant testing are summarized in the following table.
Initial economic analysis of the new flotation chemistry with AERO 6493 shows a
strong dependence on the reagent price. If the cost of AERO 6493 could be reduced to
$1.80/lb, the single-stage flotation of coarse phosphate with the alkyl hydroxamic
acid/alcohol collector would be competitive with the traditional double float process
using fatty acid and fuel oil.
The environmental impact of the hydroxamic acid collector in phosphate flotation
was considered with respect to water quality. Literature review and experimental results
indicate that there is no significant environmental impact from the utilization of the new
collector.
1
Table 1. Results from Single-Stage Pilot Plant Phosphate Flotation of Feed
from the Cargill SFM Plant Using the New Hydroxamic Acid Collector
(AERO 6493).
Feed
Fine Feed
Coarse Feed
Condition
Product
Wt %
P2O5 %
Recovery %
Dosage 850 g/t
Concentrate
27.96
29.6
85.94
Conditioning
Tail
72.04
1.88
14.06
Solids 74%
Feed
100.00
9.63
100.00
Dosage 1200 g/t
Concentrate
38.80
31.55
94.88
Conditioning
Tail
61.20
1.08
5.12
Solids 71%
Feed
100.00
12.9
100.00
2
INTRODUCTION
Froth flotation for the separation of phosphate minerals from other gangue
minerals has been practiced by fatty acid flotation with pine oil as frother since as early
as 1928 (Gieseke 1985; Houot 1982). Many flotation strategies for the processing and
concentration of phosphate ores have been developed since then. The conventional
phosphate flotation process for the Florida resources is the "double float" process, i.e.,
anionic flotation fatty acid/fuel oil of the phosphate minerals at alkaline pH, followed by
cationic "reverse" flotation of silica from the initial phosphate concentrate with amine.
The Florida phosphate industry, with few exceptions, still uses the standard method
(Moudgil and Somasundaran 1986). During the past decade much research has been
carried out to develop a more efficient flotation technology for the processing of Florida
phosphate resources (Zhang 1994, Lu and others 1999, Zhang 1999, El-Shall 1999, Gu
and others 1999, Miller 1999, Wiegel 1999, Gruber 1999). Development of technologies
to improve the efficiency of phosphate flotation in order to reduce requirements for plant
space, energy, water, and chemicals and to improve the efficiency of dolomite separation
have been important FIPR research priorities (FIPR 1998). Specifically it is desired to
achieve the following objectives:
(1) Eliminate the double float process so that phosphate recovery can be achieved
in one step.
(2) Improve the flotation recovery of coarse phosphate.
(3) Develop efficient flotation technology for the recovery of phosphate from
dolomite resources.
These objectives have been identified to be of high priority and considerable research
effort will be required if they are to be realized.
One approach that offers some promise to achieve these objectives is the
identification of new reagent chemistry, particularly a selective collector to improve the
efficiency of phosphate flotation. Recent research indicates that hydroxamic acid has
been identified as a selective collector which can achieve these objectives, increase the
separation efficiency, and simplify the standard flowsheet. A research program at the
University of Utah was proposed to develop this phosphate collector. In May 2000 FIPR
granted funds to the University of Utah (FIPR #00-02-142R) as a research project to
evaluate the hydroxamic acid collector.
In order to achieve these objectives the research program was organized into the
following tasks:
(1) Collector Chemistry Study
3
(2) Bench-Scale Flotation
(3) Pilot-Plant Testing
(4) Economic Consideration and Environmental Impact
The results from this research program are described in the following sections of this
final report.
4
COLLECTOR CHEMISTRY
MATERIALS AND METHODS
Mineral Samples
Polycrystalline francolite was provided by the Florida Institute of Phosphate
Research (FIPR). The sample which contains 32.41% P2O5, 4.74% Insoluble, 0.4% MgO,
and 46.11% CaO was identified by X-ray diffraction as carbonate-fluorapatite. The
sample was sized and the 35x100 mesh fraction was used for microflotation experiments.
Natural single crystals of yellow apatite, from Durango, Mexico, were identified
by X-ray diffraction as fluorapatite. A crystal about 10x20 mm was polished for contact
angle measurements and bubble attachment experiments. Other crystals were crushed
and ground in a mortar and sized to 35x100 mesh for microflotation tests.
A high purity dolomite sample from Florida was supplied by FIPR and a 35x100
mesh size fraction was used for microflotation experiments. U.S. Silica provided a high
quality quartz sample and the 35x100 mesh fraction was used for microflotation
experiments. A polycrystalline dolomite rock was obtained from Silver Zone Pass, NV
and polished for contact angle measurements.
Reagents
Hydroxamic Acids: alkyl hydroxamic acids and potassium salts of alkyl
hydroxamic acid were synthesized in our laboratory at the University of Utah. The
method of synthesis is similar to the method reported in the literature (Peterson and
others 1966). Unless otherwise specified the octyl acid and/or salt was used in the
formulation of the collector.
Alcohol: C6-C13 aliphatic iso-alcohols were obtained from Exxon Mobil
Chemical. The alcohol products were colorless, transparent liquids.
Collector: In some cases the Cytec reagent AERO 6493, a water insoluble
alcoholic solution of hydroxamic acid was used. In other cases the collector was
prepared in our laboratory from synthesized hydroxamic acids and selected alcohols.
When comparison is made with the traditional fatty acid/fuel oil (FA/FO) collector, the
reagents used were those obtained from a phosphate plant in Central Florida. The fatty
acid was an industrial mixture from Westvaco and the fuel oil was #5 fuel oil from
International Petroleum.
5
Microflotation
Experiments were conducted with a 150 cc Hallimond tube. Generally a 2 gram
sample with particle size of 35x100 mesh was conditioned at 65% solids for 2 minutes
with reagents. Then the suspension was transfer into the Hallimond tube and diluted to
about 15% solids. The flotation was carried out at a constant air flowrate of 50 cc/min.
The float and sink products were filtered, dried and weighed to determine the flotation
recovery of the mineral being studied.
Contact Angle and Collector Attachment
The captive-drop method was used to measure the contact angle of the collector
droplet (typically an alcoholic solution of alkyl hydroxamic acid) at selected mineral
surfaces. The polished and cleaned mineral surface was immersed in DI water for 15
minutes then a collector drop, with size of about 3 mm in diameter, was introduced by a
microsyringe through a U shaped needle underneath the mineral surface. Relaxation of
the contact angle was recorded as a function of time. Before every measurement the
mineral surface was polished with Harrick #600 (<0.05 µm) fine polishing compound to
obtain a fresh surface which was washed with acetone and subsequently with DI water.
The attachment of the collector droplet to the substrate was observed using a
high-speed video camera (Kodak Ektapro 1000 High-Speed Video System). The
procedure for cleaning and surface preparation was the same as for contact angle
measurements.
RESULTS AND DISCUSSION
Collector Dosage and Flotation pH
The selectivity of the hydroxamic acid collector for phosphate flotation with
respect to dolomite and quartz is revealed by the results from microflotation experiments
with selected mineral samples (35x100 mesh). Figure 1 shows the flotation recovery of
single minerals, fluorapatite, francolite, quartz and dolomite as a function of collector
dosage at pH 7.5. It can be seen from Figure 1 that when the total reagent dosage
increased to 400 g/t, the recovery of the coarse phosphate minerals reached 95% while
the recovery of dolomite and quartz was insignificant (about 2%).
Such selectivity in coarse particle flotation is not achieved for fatty acid/fuel oil
(FA/FO) with the same experimental procedure under similar conditions as shown in
Figure 2. As is frequently the case, even in plant operations, effective flotation of coarse
phosphate is difficult with FA/FO (Moudgil 1992). Note that there is poor selectivity
with respect to dolomite and that high levels of the FA/FO collector addition are
necessary to realize complete flotation.
6
Most importantly, flotation with the hydroxamic acid collector is not particularly
sensitive to pH, for pH values between 6 and 9 as shown in Figure 3. These results for a
dosage of 1200 g/t suggest that the selective flotation of phosphate rock can be achieved
without pH adjustment.
100
90
80
Fluorapatite
Francolite
Dolomite
Quartz
Recovery %
70
60
50
40
30
20
10
0
0
200
400
600
800
1000
Collector Dosage g/t
Figure 1. Microflotation Recovery of Fluorapatite, Francolite, Dolomite and
Quartz as a Function of AERO 6493 Addition at Natural pH of 6.5,
with DI Water.
7
120
100
Recovery %
80
60
40
Francolite
Dolomite
20
0
0
1000
2000
3000
4000
FA/FO (g/t)
Figure 2. Microflotation Recovery of Francolite and Dolomite (35x100 Mesh) as
a Function of FA/FO (7:3 Ratio by Volume) Addition at Natural pH
6.5, with DI Water.
8
100
90
80
Recovery %
70
Fluorapatitel
Francolite
Dolomite
Quartz
60
50
40
30
20
10
0
2
4
6
8
10
Conditioning pH
Figure 3. Microflotation Recovery of Fluorapatite, Francolite, Dolomite and Quartz
as a Function of pH at an AERO 6493 Addition of 1200 g/t with DI
Water.
9
Collector Composition
The necessity of an alcohol carrier for the hydroxamic acid is revealed by typical
results presented in Figure 4. In this case the results for an isodecanol solution containing
20% octyl hydroxamic acid (OHA) are compared to the results for an aqueous solution of
OHA. Flotation was carried out at a natural pH of 6.5. It can be seen that when the
alcohol solution of octyl hydroxamic acid was used as the collector the effectiveness of
phosphate recovery improves significantly at high solids conditioning. Such is not the
case if conditioning is done at low percent solids (Miller and others 2001). It is clear that
the alcoholic solution of OHA is preferred. Without the alcohol carrier more than 10
times the collector dosage is required. Many other carriers have been examined for
phosphate rock experiments none of which were found to be satisfactory. These results
reveal the importance of high solids conditioning and the significance of the
wetting/spreading phenomena.
Another important issue that must be considered is the composition of the
alcoholic solution. The effect of octyl hydroxamic acid content on the flotation of
francolite is presented in Figure 5 at various levels of collector addition. It is very clearly
seen that as the hydroxamic acid content increases the flotation recovery increases
sharply and when the hydroxamic acid percentage reaches 20-30% by weight the
recovery reaches a maximum. It should be noted that the solubility limit of octyl
hydroxamic acid in isodecanol is about 30%. Further it should be mentioned that the acid
form of the hydroxamate is preferred again because of solubility considerations.
Finally with respect to collector composition the nature of the alcohol was
studied. Experimental results show that normal alcohols are not suitable carriers for
hydroxamic acid apparently due to solubility limitations. In this regard branched chain
isomers of aliphatic alcohols are preferred and the effect of carbon number on the
flotation response is revealed in Figure 6. The flotation recovery increases with an
increase in chain length. Of course it is well known that the hydrophobicity generally
increases with an increase in carbon number. It is evident that greater hydrophobicity is
achieved when the octyl hydroxamic acid is mixed with long chain alcohols.
10
100
Francolite Recovery %
80
60
Alcoholic Solution
Aqueous Solution
40
20
0
2.0
2.5
3.0
3.5
4.0
4.5
Collector Addition (g/t)
Figure 4. Microflotation Recovery of Francolite as a Function of Collector Addition
at a Natural pH of 6.5. In the Case of Collector Addition as an Alcoholic
Solution, an Isodecanol Solution Containing 20% Octyl Hydroxamic Acid
Was Used.
11
100
90
Francolite Recovery %
80
70
60
50
40
Total Collector 5000 g/t
Total Collector 2000 g/t
Total Collector 1600 g/t
Total Collector 1200 g/t
30
20
10
0
0
10
20
30
40
50
60
70
80
90
100
Octyl Hydroxamic Acid Content (%)
Figure 5. Effect of Octyl Hydroxamic Acid Content in Isodecanol Solution on
Phosphate Recovery for Various Levels of Total Collector Addition at
Natural pH of 6.5 for Microflotation of Pure Francolite.
12
Grade (%P2 O5) and Recovery (%)
100
Recovery
Grade
80
60
40
20
0
5
6
7
8
9
10
11
12
13
14
Alcohol Hydrocarbon Chain Length
Figure 6. Microflotation for Coarse Phosphate Feed from IMC-Agrico Four
Corners Plant in Central Florida, as a Function of Alcohol Hydrocarbon
Chain Length for Collector Solutions Containing 20% Octyl
Hydroxamic Acid at a Total Reagent Dosage of 800 g/t.
13
Wetting Characteristics
Flotation with oily, water insoluble collectors is frequently governed by selective
wetting/spreading phenomena and the formation of aeroflocs; complex aggregates of air,
water, the liquid collector phase, and mineral particles. Traditional phosphate flotation is
a classic example of this type of flotation, which involves aerofloc formation with the
insoluble fatty acid/fuel oil collector. The significance of the wetting/spreading
phenomena and the necessity of high solids conditioning have not received sufficient
attention but preliminary results and discussion have been reported (Lu and others 1997).
Flotation using water insoluble collectors such as FA/FO requires high solids
conditioning to insure dispersion and wetting of francolite particles by the insoluble
collector mixture.
Wettability is most often described by the contact angle of a drop resting at a
surface as shown in Figure 7. A small contact angle (θ) means high wettability and a
large contact angle means poor wettability.
Mineral
θ
Collector
Water
Figure 7. Insoluble Collector Drop at a Mineral Surface in Water.
Presented in Figure 8 are the results of contact angle relaxation measurements for
the hydroxamic acid collector (AERO 6493)/water/mineral systems. Drop attachment did
not occur at quartz surfaces. However it can be seen that the collector spreads very well
on the fluorapatite surface as indicated by the contact angles from 20-40o after an
appropriate equilibration time. Dolomite shows some affinity for the collector as
indicated by contact angles of 40-60o after longer times of equilibration. The relaxation
of the collector at the mineral surfaces also indicates that spreading of the collector drop
is a relatively slow process and that the three phase contact line is unstable for several
minutes at the fluorapatite and dolomite surfaces during spreading.
The kinetics of collector drop spreading at the fluorapatite surface was observed
using a high-speed video system as shown in Figure 9. The fluorapatite sample was
immersed in the DI water, a collector drop was introduced, and attachment at the mineral
surface was examined. The spreading of the collector drop was recorded at a rate of 50
frames/sec by the high-speed video system. The collector drop spreads significantly faster
at the fluorapatite surface (4 seconds) as shown in Figure 10 than at the dolomite surface
(8 seconds). These results are consistent with the contact angle measurements.
14
Air bubble attachment on the surfaces of fluorapatite and quartz was observed
using the high-speed video system. The fluorapatite and quartz surface were smeared
with the hydroxamic acid collector (AERO 6493) and rinsed with 30 ml DI water to
remove the extra or residual reagent. Then fluorapatite and quartz samples were
immersed in the DI water and an air bubble was then introduced at the mineral surface
the events being recorded at a rate of 1000 frames/sec. The results indicate that film
rupture occurs after about 37 milliseconds at the francolite surface followed by film
displacement and bubble attachment. No air bubble attachment occurs at the quartz
surface. The results imply that the thin collector film formed at the quartz surface is
extremely unstable and is removed during rinsing DI water. The quartz surface remains
hydrophilic. In contrast to the quartz surface the thin collector film formed at the
fluorapatite surface is very stable and the hydrophobic surface state is sustained.
AERO 6493 Drop Contact Angle (Degrees)
160
140
120
Dolomite
100
Apatite
80
60
40
20
0
0
100
200
300
400
Equilibrium Time (Sec)
Figure 8. Relaxation of Hydroxamic Acid Collector (AERO 6493) Drop Contact
Angle at Fluorapatite and Dolomite Surfaces with the Captive-Drop
Method in DI Water at Natural pH of 6.5.
15
0 sec
4 sec
30.48 sec
15 sec
Figure 9. High Speed Video Photographs Showing the Spreading Characteristics of
a Drop of Hydroxamic Acid Collector (AERO 6493) at the Fluorapatite
Surface in DI Water of pH 6.5, and 220 C.
16
0 sec
8 sec
17 sec
33 sec
Figure 10. High Speed Video Photographs Showing the Spreading Characteristics
of a Drop of Hydroxamic Acid Collector (AERO 6493) at the Dolomite
Surface in DI Water of pH 6.5, and 22oC.
17
Analysis of High Solids Conditioning
Flotation with oily, water insoluble collectors is frequently governed by selective
wetting/spreading phenomena and the formation of aeroflocs; complex aggregates of air,
water, the liquid collector phase, and mineral particles. Traditional phosphate flotation is
a classic example of this type of flotation, which involves aerofloc formation with the
insoluble fatty acid/fuel oil collector. Shown in Figure 11 is the X-ray CT Spectroscopy
image of cross section of aeroflocs formed with francolite particles, air bubbles and the
new collector. The significance of the wetting/spreading phenomena and the necessity of
high solids conditioning have not received sufficient attention but preliminary results and
discussion have been reported (Lu and others 1997). Flotation using water insoluble
collectors such as FA/FO requires high solids conditioning to insure dispersion and
wetting of francolite particles by the insoluble collector mixture.
It seems that the need for high solids conditioning is related to the wetting
characteristics of apatite and quartz as reported by Lu and others 1997. The oily, water
insoluble collectors have a strong tendency to spread at a fluorapatite surface and a weak
tendency to spread at a quartz surface as indicated from contact angle measurements and
high-speed video observations. High solids conditioning enhances particle collector drop
particle interaction and therefore increases the probability for collector film rupture, drop
attachment, and spreading at preferred phosphate mineral surfaces. The thin layer of the
hydroxamic acid collector is stable at fluorapatite surfaces but unstable and shrinks to
form lenses at the quartz surface. Thus it is not surprising that during the interaction
between a quartz particle and a fluorapatite particle that the collector drop will be forced
mechanically and thermodynamically to be transferred and preferentially spread at the
fluorapatite surface. When these two particles are forced apart, a major portion of the
collector drop transfers to the fluorapatite surface. The small portion of the collector
remaining at the quartz surface will shrink to form a smaller drop (lens). This procedure
happens again and again during high solids conditioning. In this way any collector
initially at the quartz surface will be transferred to the surface of the fluorapatite. Thus
the extent to which high solids conditioning improves both recovery and selectivity in
phosphate flotation depends on the wetting characteristics of the collector used.
SUMMARY
It has been found that excellent flotation selectivity is achieved when pure mineral
samples are conditioned at high percent solids with water insoluble alcoholic solutions of
alkyl hydroxamic acids as collectors. The results from contact angle and high-speed
video studies indicate that the hydroxamic acid collector has different spreading
characteristics at the surfaces of fluorapatite, dolomite and quartz. It is evident that
collector composition is an important variable which influences the flotation response.
Long branched chain alcohols increase the hydrophobicity and reduce reagent
consumption. Understanding of the mechanism of collector attachment and spreading is
still unclear and surface chemistry research is in progress to further understand the
phenomena involved in the flotation of phosphate minerals with insoluble alcoholic
solutions of hydroxamic acids.
18
Figure 11. X-Ray CT Image of Aeroflocs Formed by Francolite Particles, Air
Bubbles during Flotation with the Hydroxamic Acid Collector.
19
BENCH-SCALE FLOTATION
MATERIALS AND METHODS
Flotation Samples
Samples of coarse flotation feed and/or fine flotation feed were taken from IMCAgrico's Four Corners Plant in Central Florida, Cargill's South Fort Meade plant in
Central Florida Plant, PCS's North Carolina Plant, and SF Phosphates’ Utah Plant. In the
case of the IMC-Agrico sample from the Four Corners Plant, approximately 10 gallons of
plant water and samples of fatty acid and fuel oil were also collected and shipped to
laboratories at the University of Utah. The results from X-ray diffraction indicated that
the phosphate minerals in the sample from IMC-Agrico Four Corners Plant were
carbonate-fluorapatite, and carbonate-hydroxylapatite. The particle size was determined
to be in the range of 12x80 mesh for the coarse feed sample and 20x150 mesh for the fine
feed sample.
For the sample from Cargill's Central Florida Plant, the phosphate minerals were
found to be similar to the sample from the IMC-Agrico Four Corners Plant containing
carbonate-fluorapatite and carbonate-hydroxylapatite. The particle size was determined to
be in the range of 12x80 mesh for the coarse feed, 12x150 mesh for intermediate feed and
20x200 mesh for the fine feed.
The X-ray diffraction results show that the phosphate mineral in the sample from
the PCS North Carolina Plant was carbonate-hydroxylapatite. The particle size was in the
range of 12x150 mesh. The +20 mesh fraction was removed by wet screening and the
20x150 mesh fraction was used as flotation feed.
The sample from the SF Phosphates Utah Plant was taken from rougher flotation
feed. The results from X-ray diffraction analysis indicated that the sample contained
dolomite, fluorapatite, calcite and quartz. The phosphate minerals in this feed had been
reported to be carbonate-apatite minerals with the chemical formula
Ca5(PO4CO3OH3(F.OH) (Allen 1993). The particle size of the sample was determined to
be in the range of 20x200 mesh.
Reagents
The collector used was Cytec’s AERO 6493, a 30% alcoholic solution of
hydroxamic acid, unless otherwise indicated. Other reagents are listed in Table 1.
21
Table 1. Other Chemicals Used.
Reagent
Fatty Acid
Fuel Oil
Sodium Carbonate
Sodium Hydroxide
Sodium Silicate
Formula
CH15-17H27-35COOH
#5 Fuel Oil
Na2CO3
NaOH
Na2SiO3
Supplier
Westvaco
Int. Petroleum
Mallinckrodt
Aldrich
Fluka
Purity/Grade
Industrial Mixture
Industrial Mixture
Analytical Grade
ACS Reagent
Solution
Bench-Scale Flotation
The flotation tests were conducted in 1 liter Denver flotation cells for both the
fatty acid/fuel oil collector and the new collector. Unless otherwise indicated, the feed
material was conditioned at 70-75% solids for 2 minutes. Then the slurry was transferred
into the flotation cell and diluted to about 20% solids with tap water or plant water. The
flotation products were filtered, dried, and weighed before acid digestion and analysis by
ICP.
RESULTS AND DISCUSSION
Efficiency of Separation
Single-stage flotation efficiency was evaluated for the coarse feed sample (16x35
mesh) from the IMC Four Corners Plant in Central Florida, using the new hydroxamic
acid collector. Significant improvement in separation efficiency is clearly evident from
the grade/recovery curves comparing the new collector with the traditional fatty acid/fuel
oil (FA/FO) collector as presented in Figure 12. The results indicate that a high
separation efficiency is obtained with the new collector. Notice the significant difference
in concentrate grade. An excellent concentrate product (31% P2O5) was achieved at 95%
recovery with the new collector in single-stage flotation.
Collector Addition
Shown in Figures 13 to 16 are the flotation response as a function of collector
addition for flotation feeds from Central Florida, North Carolina, and Utah. Typically the
recovery increases with an increase in collector addition. Generally the results indicate
that flotation recovery and/or concentrate grade have been improved significantly when
the new collector AERO 6493 is compared with the traditional FA/FO collector. It
seems from these bench-scale results that a dosage of 800 to 1200 g/t will be required to
achieve satisfactory flotation results. Although recent results from water recycle testing
suggest that the collector demand can be reduced.
22
High Solids Conditioning
The critical feature of high solids conditioning is revealed by the data for coarse
feed from the Cargill plant presented in Figure 17. Note that the recovery decreases
significantly when the percent solids drops below 70% whereas the concentrate grade
decreases slightly from 34% to 32%. As discussed in other contributions (Lu and others
1997; Miller 2001) high solids conditioning seems to be necessary for oily, water
insoluble collectors in order to achieve adequate distribution and selective spreading at
the surface of phosphate minerals.
35
30
Grade, % P2 O5
25
20
15
AERO 6439
FA/FO
10
5
0
75
80
85
90
95
100
Phosphate Recovery %
Figure 12. Comparison of Grade/Recovery Curves Obtained with the New
Hydroxamic Acid Collector (AERO 6493) and the Traditional FA/FO
Collector for Single-Stage Flotation of Coarse Feed (16x35 Mesh,
5.65% P2O5) from the IMC-Agrico Four Corners Plant, Central
Florida (Miller and others 2001).
23
Grade (%P2 O5 ) and Flotation Recovery (%)
100
80
60
40
20
0
700
900
1100
1300
1500
Collector Addition (g/t)
Recovery with AERO 6493
Recovery with Fatty Acid/Fuel Oil
Grade with AERO 6493
Grade with Fatty Acid/Fuel Oil
Figure 13. Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (16x35 Mesh,
5.6% P2O5) Received from IMC, Central Florida.
24
Grade (%P2 O5 ) and Flotation Recovery (%)
100
80
60
40
20
0
500
700
900
1100
1300
1500
Collector Addition (g/t)
Recovery with AERO 6493
Recovery with Fatty Acid/Fuel Oil
Grade with AERO 6493
Grade with Fatty Acid/Fuel Oil
Figure 14. Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (12x80 Mesh,
15.1% P2O5) Received from Cargill, Central Florida.
25
Grade (%P2 O5 ) and Flotation Recovery (%)
100
80
60
40
20
0
700
800
900
1000
1100
1200
Total
TotalReagent
CollectorAddition
Addition(g/t)
(g/t)
Recovery with AERO 6493
Recovery with Fatty Acid/Fuel Oil
Grade with AERO 6493
Grade with Fatty Acid/Fuel Oil
Figure 15. Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (20x200 Mesh,
16.4% P2O5) Received from PCS, North Carolina.
26
Grade (%P2 O5 ) and Flotation Recovery (%)
100
80
60
40
20
0
400
800
1200
1600
Collector Addition (g/t)
Recovery with AERO 6493
Recovery with Fatty Acid/Fuel Oil
Grade with AERO 6493
Grade with Fatty Acid/Fuel Oil
Figure 16. Single-Stage Flotation Recovery and Concentrate Grade as a Function of
Collector Dosage at Natural pH 7.5 for Phosphate Feed (16x325 Mesh,
26.7% P2O5) Received from SF Phosphates, Utah.
27
Grade(P2 O5 %) and Flotation Recovery %
100
80
Grade
Recovery
60
40
20
0
20
30
40
50
60
70
80
90
Percent Solids during Conditioning
Figure 17. Single-Stage Flotation Response as a Function of Percent Solids During
Conditioning with 1000 g/t AERO 6493 for Coarse Feed from the
Cargill Plant.
28
Particle Size
Typically, the efficient recovery of phosphate from coarse flotation presents a
major problem in industrial practice. In this regard the effectiveness of the hydroxamic
acid collectors for coarse phosphate flotation is quite impressive as demonstrated by the
data presented in Figures 13 to 15. In similar fashion the flotation of fine feed is
improved with hydroxamic acid collectors when compared to the traditional FA/FO
collector as shown by the results presented in Table 2 for low grade fine feed from the
IMC-Agrico Four Corners Plant. In this case a 30% P2O5 grade was achieved in a single
stage at 85% recovery with the new collector. The traditional fatty acid/fuel oil collector
does not provide for such a high selectivity. However compared with the results from the
flotation of coarse feed, the recovery from the flotation of fine feed is lower with the new
collector.
Table 2. Evaluation of the New Collector (AERO 6493) vs. Fatty Acid/Fuel
Oil for Fine Feed from IMC-Agrico Four Corners Plant, Central
Florida (Single-Stage Flotation, Collector 800 g/t, Tap Water).
Collector
FA/FO
AERO 6493
Product
Wt. %
P2O5 %
P2O5 Recovery %
Concentrate
19.42
17.68
91.03
Tail
80.58
0.42
8.97
Feed
100.00
3.77
100.00
Concentrate
10.68
30.14
85.11
Tail
89.32
0.63
14.89
Feed
100.00
3.78
100.00
Samples of phosphate feed from Cargill were tested in order to evaluate the effect
of particle size on flotation efficiency. The results in Figure 18 indicate that an excellent
separation was achieved for both the coarse and intermediate size flotation feed and that
the separation efficiency decreases with a decrease in particle size. As might be
expected, the single-stage grade and recovery from fine feed with an insoluble collector is
less than from coarse feed. This effect is evident from the results obtained for both the
IMC and Cargill samples. The reason for this sensitivity to particle size is that fine
particles consume collector and are more easily entrapped in the aeroflocs that form
during flotation with insoluble collector oils (Miller and others 2001).
29
36
34
Grade, %P2 O5
32
30
28
26
Coarse(12x80 Mesh)
Intermediate(12x150 Mesh)
24
Fine(20x200 Mesh)
22
20
50
60
70
80
90
100
Phosphate Recovery %
Figure 18. Single-Stage Flotation Grade/Recovery Curves for Different Sizes of
Phosphate Feed from the Cargill Plant at Natural pH 7.5, 75%
Conditioning Solids. Data Point Represent Different Levels of
Collector Addition.
Effect of Plant Water
The issue of plant water was considered and these results are presented in Table 3
for coarse feed from the IMC-Agrico Four Corners Plant. The influence of plant water
on the effectiveness of the new collector does not seem to be significant.
30
Table 3. Test Results for Deslimed Coarse Feed from the IMC-Agrico Four Corners
Plant with New Collector (AERO 6493) Using Tap Water and Plant Water
(Single-Stage Flotation, Collector 1250 g/t, Na2CO3 400g/t, Na2SiO3 400g/t,
pH 8.6).
Collector
Tap Water
Plant Water
Product
Wt. %
P2O5 %
P2O5 Recovery %
Concentrate
17.32
31.12
95.18
Tail
82.68
0.33
4.82
Feed
100.00
5.66
100.00
Concentrate
17.39
31.02
94.36
Tail
82.61
0.39
5.64
Feed
100.00
5.71
100.00
North Carolina Phosphate
The sample from the PCS North Carolina Plant was evaluated with the
hydroxamic acid collector and the results are presented in Table 4. Excellent recovery
was achieved with the new collector. Compared with the results from the single-stage
flotation of other samples from Florida and Utah, the concentrate grade is slightly lower
in quality. See Figure 15. The significant improvement in recovery is revealed from the
results comparing the new collector with the traditional fatty acid/fuel oil collector as
presented in Figure 15.
Table 4. Results from Single-Stage Phosphate Flotation of Feed from the PCS
North Carolina Plant Using the New Hydroxamic Acid Collector
(AERO 6493, 900 g/t).
Product
Wt. %
P2O5 %
Recovery %
Concentrate
57.32
27.52
96.35
Tail
42.68
1.40
3.65
Feed
100.00
16.37
100.00
Utah Phosphate
The sample from the SF Phosphates Plant near Vernal Utah was tested to
determine the effectiveness of the new hydroxamic acid collector. The single-stage
flotation results presented in Table 5 indicate that a high quality phosphate concentrate
(32% P2O5), containing less than 0.3% MgO, can be made at more than 85% recovery
31
from the rougher flotation feed. The improved flotation recovery is clearly demonstrated
by the results comparing the new collector with the traditional fatty acid/fuel oil collector
shown in Figure 16.
Table 5. Results from Single-Stage Phosphate Flotation of Feed from the SF
Phosphates Utah Plant Using the New Hydroxamic Acid Collector
(AERO 6493, 1200 g/t).
Product
Wt. %
P2O5 %
MgO %
Recovery %
Concentrate
70.88
32.26
0.28
85.74
Tail
29.12
13.08
0.94
14.26
Feed
100.00
26.67
0.47
100.00
SUMMARY
In general, based on these bench-scale flotation results with a water insoluble
alcoholic solution of hydroxamic acid (AERO 6493) it seems that a single-stage
phosphate recovery of 90-95% with a concentrate grade of 31% P2O5 is possible for
coarse feed from the IMC-Agrico Four Corners Plant. As is the case for the traditional
phosphate flotation, high solids conditioning is necessary with the hydroxamic acid
collector. Conventional plant practice using traditional fatty acid/fuel oil collector (1,200
g/t) results in only 75-80% recovery at a grade of 31% P2O5 after multiple flotation stages
in different flotation circuits (double flotation). In the case of coarse feed from the
Cargill Plant, the concentrate grade reached 34% P2O5 with 93% recovery in single-stage
bench-scale flotation with the new collector. Also significant improvements in flotation
were achieved with plant samples from North Carolina and Utah. The results indicate that
the hydroxamic acid collector is more effective for the flotation of coarse feed than for
the flotation of fine feed.
Experimental results show that the hydroxamic acid collector (AERO 6493) can
be blended with fuel oil (#5 fuel oil) without much of a decrease in recovery, from 93.9%
to 90.7%.
No excessive foaming was observed during acid digestion of the flotation
concentrate obtained using the new collector.
32
PILOT PLANT TESTING
PREPARATION FOR PILOT PLANT TESTING
Preparation for pilot plant testing included supplemental bench-scale experiments
at Arr-Maz Products’ laboratory in Winter Haven Florida, organization of the plant test
campaign with industrial sponsors, and reagent procurement for plant testing.
Another hydroxamic reagent, AERO 6494 from Cytec Industries, Inc., was tested
in bench-scale flotation experiments. The results indicated the selectivity is not as good
as AERO 6493. Some new unclassified rock samples from CF Industries were tested. It
was found that the classified sample resulted in a better separation and a higher recovery
than the unclassified sample.
Organization for the pilot plant test was completed. Reagent companies Cytec
Industries, Inc. and Arr-Maz Products agreed to participate. On this basis meetings were
held in Florida with selected phosphate mining companies and with the participation of
Andy Poulos, Business Manager-Industrial Minerals, Cytec Industries Inc.; and Bill
Cook, Vice President-Mining and Fertilizer Chemicals, Arr-Maz Products. These
meetings and/or demonstrations were held with the following companies:
30 July 2001
CF Industries − David Gossett and Mark Waters
31 July 2001
IMC-Agrico − Leon Seale and Chaucer Hwang
1 August 2001
Cargill Fertilizer − Karen Lulf and Ray Ellis
The meetings were generally successful. All three phosphate mining companies
expressed interest in the test campaign. After further discussion with the reagent
suppliers it was decided that perhaps only one or two locations would be selected for
plant testing. Subsequently the contract was modified, because of reagent availability, to
do pilot-plant testing at Jacobs Engineering. In this regard a commitment to supply the
hydroxamic acid collector (AERO 6493) for pilot plant testing was obtained from Cytec
Industries, Inc.
SUPPLEMENTAL BENCH-SCALE EXPERIMENTS
A series of bench-scale flotation experiments were conducted at the Arr-Maz
laboratory with the assistance of, and collaboration with, Arr-Maz engineers and using
fresh samples from Cargill SFM and IMC Fort Green plants. Experiments were done by
both University of Utah researchers and Arr-Maz researchers. The typical results from
bench-scale flotation experiments with fine feed and coarse feed are summarized in Table
6 and 7. The results are consistent with previous bench-scale flotation results. Again, the
greater selectivity in single-stage phosphate flotation was demonstrated by the bench-
33
scale flotation experiment using fresh samples from Cargill SFM plants and IMC FTG in
Central Florida.
Table 6. Results from Single-Stage Phosphate Flotation of Feed from the Cargill
SFM Plant Using the New Hydroxamic Acid Collector (AERO 6493).
No Other Reagents Were Added.
Feed
Condition
Product
Wt %
P2O5 %
Recovery %
Concentrate
20.65
30.46
87.08
Conditioning Solids
Tail
79.35
1.17
12.92
75.7 %
Feed
100.00
7.23
100.00
Concentrate
33.77
31.99
95.88
Conditioning Solids
Tail
66.32
0.70
4.12
76%
Feed
100.00
11.27
100.00
Dosage 1.2 kg/t
Fine Feed
Dosage 1.5% kg/t
Coarse Feed
Table 7. Results from Single-Stage Phosphate Flotation of Feed from the IMC Fort
Green Plant Using the New Hydroxamic Acid Collector (AERO 6493).
No Other Reagents Were Added.
Feed
Product
Wt %
P2O5 %
Recovery %
Concentrate
15.08
30.10
84.51
Conditioning Solids
Tail
84.92
0.98
15.49
74.0 %
Feed
100.00
5.37
100.00
Concentrate
30.69
30.04
91.07
Tail
69.31
1.30
8.93
Feed
100.00
10.12
100.00
Condition
Dosage 1.0 kg/t
Fine Feed
Dosage 1.3% kg/t
Coarse Feed Conditioning Solids
75.2 %
IN-PLANT TRIAL AT THE PCS WHITE SPRINGS PLANT WITH COLUMN
FLOTATION
A plant trial was conducted with ERIEZ's pilot scale column flotation system at
the PCS Phosphate, White Springs Plant in North Florida. The feed was taken from a
hydrocyclone underflow which was discharged into a drum conditioner. A metering
pump was used to add the Collector (AERO 6493) into the conditioner. The slurry was
then diluted and fed to the flotation column. The overflow and underflow from the
column were taken for analysis. The column flotation system is shown in Figures 19 and
20.
34
Due to the unusually cool weather, the reagent was difficult to deliver to the
system. The experimental results were not as good as expected as shown in Table 8.
Hydrocyclone
Metering Pump
Water
Flotation
Column
Drum Conditioner
Tailing
Concentrate
Figure 19. Column Flotation System at the PCS Phosphate White Springs Plant.
35
Figure 20. Photograph of Flotation Column at PCS White Springs Plant.
36
Table 8. Results from Testing Trial at the PCS White Springs Plant with Column
Flotation (-16 Mesh Fraction of Flotation Products).
Test No.
1
2
Product
Wt. %
P2O5 %
Recovery %
Concentrate
23.01
27.68
55.38
Tail
76.99
6.66
44.62
Feed
100.00
11.50
100.00
Concentrate
19.78
27.25
51.43
Tail
80.22
6.34
48.57
Feed
100.00
10.48
100.00
The results from flotation of PCS feed with AERO 6493 differed from the results for
other feed with a recovery of only 50% compared to 90%. Further study of this material
is necessary. Based on these results testing at the PCS White Springs Plant was
terminated.
PILOT PLANT TESTING AT JACOBS ENGINEERING
Pilot plant testing was carried out at the Jacobs Engineering pilot plant facility in
Lakeland, Central Florida. The pilot flotation system is shown in the Figure 21. The feed
material was loaded by a front end loader into a screw feeder and pulped by tap water.
The slurry was pumped into a screw classifier to dewater to 70-75% solids. Then the
slurry was discharged into a vertical conditioning tank with impeller and the new
collector was added. The conditioning time was about 2-3 minutes. After conditioning
the slurry was diluted and fed to the flotation circuit which consisted of two flotation
cells (DECO Flotation machine, total active volume 5 ft3). Flotation products and feed
samples were taken every 20 minutes. Three samples were combined and taken as a
sample for analysis. Shown in Figure 22 are the photographs of the pilot flotation plant.
The flotation variables considered were the collector dosage and conditioning
percent solids. The pilot plant testing used the flotation feed from Cargill SFM plant.
Two flotation feeds, fine flotation feed and coarse flotation feed, were tested. The size
distribution for fine feed and coarse feed is shown in Figures 23 and 24. Figures 23 and
24 also show the results of particle size analysis for flotation feed, concentrate and tailing
used in the pilot plant testing. The feed rate was about 700-900 lbs/hr.
37
Water
Feed Sample
Feed Pump
Water
Collector
Dewatering
Conditioning
Concentrate
Tail
Flotation
Figure 21. Pilot Plant Testing Flowsheet.
38
Feed Loading and Feed Pump
Dewatering and High Solids Conditioning
Single-Stage Flotation
Figure 22. Photographs of Single-Stage Flotation Pilot Plant.
39
100
90
Feed
Concentrate
Tailing
80
70
Wt%
60
50
40
30
20
10
0
20
35
60
100
150
-150
Particle Size (Mesh)
Figure 23. The Results of Particle Size Analysis for Fine Flotation Feed,
Concentrate, and Tailing from Pilot Testing at a Feed Rate of
900 Lb/Hr. and 74% Conditioning Solids.
40
70
60
Feed
Concentrate
Tailing
Wt.%
50
40
30
20
10
0
20
35
60
100
150
-150
Particle Size (Mesh)
Figure 24. Results of Particle Size Analysis for Coarse Flotation Feed, Concentrate,
and Tailing from Pilot Testing at a Feed Rate of 700 Lb/Hr. and 74%
Conditioning Solids.
41
Flotation with Cargill SFM Fine Feed
The new collector (AERO 6493) was tested with Cargill SFM fine flotation feed.
Shown in Figure 25 are the results from collector addition experiments. The conditioning
solids was about 74% at natural pH of 7. The results indicate that a recovery of 85% with
a concentrate grade of 30% P2O5 could be achieved at an addition of 850 g/t of new
collector in a single stage.
Flotation with Cargill SFM Coarse Feed
The results of flotation with coarse feed with the addition of different collectors
are shown in Figure 26. The conditioning was conducted at 71% solids and natural pH of
7. It can be seen from the results presented in Figure 26 that with 1200 g/t collector
dosage, a concentrate with a grade of 31.55% P2O5 and 94.88% recovery can be achieved
in single-stage pilot-scale flotation of Cargill coarse feed.
SUMMARY
Pilot-plant testing was carried out in order to evaluate the new collector in a
continuous flotation circuit. The feed rate for the pilot plant testing was about 900 lbs/hr
for fine feed and 700 lbs/hr for coarse feed. During the coarse feed flotation the feed rate
was reduced from 900 lbs/hr to 700 lbs/hr because the conditioning solids were difficult
to control and the flotation time appeared to be insufficient. The results from pilot testing
were consistent with the results from bench-scale flotation experiments. The best results
from pilot plant testing are summarized in Table 9.
Table 9. Results from Single-Stage Pilot Plant Phosphate Flotation of Feed from
the Cargill SFM Plant Using the New Hydroxamic Acid Collector
(AERO 6493).
Feed
Fine Feed
Coarse Feed
Condition
Wt %
P2O5 %
Recovery %
Dosage 850 g/t
27.96
29.6
85.94
Conditioning Solids
72.04
1.88
14.06
74 %
100.00
9.63
100.00
Dosage 1200 g/t
38.80
31.55
94.88
Conditioning Solids
61.20
1.08
5.12
71%
100.00
12.9
100.00
42
Flotation Grade(P2O5 %) and Recover (%
100
90
Cargill SFM Fine Feed
80
70
60
Grade
Recovery
50
40
30
20
10
0
600
650
700
750
800
850
900
Collector Addititon (g/t)
Figure 25. Effect of Collector Addition on Single-Stage Pilot Plant Flotation of
Cargill Fine Feed at a Feed Rate of 900 Lb/Hr. and 74% Conditioning
Solids.
43
Flotation Grade(P2O5 %)and Recovery(%
100
Cargill SFM Coarse Feed
90
80
70
60
Grade
Recovery
50
40
30
20
10
0
700
900
1100
1300
1500
1700
Collector Addition (g/t)
Figure 26. Effect of Collector Addition on Single-Stage Pilot Plant Flotation of
Cargill Coarse Feed at a Feed Rate of 900 Lb/Hr. and 74% Conditioning
Solids.
44
ECONOMIC CONSIDERATIONS
It has been documented in a recent workshop (Tavrides 1988) that beneficiation
of phosphate is a significant portion of the overall cost of phosphate production and the
flotation process was identified to be the most costly of all the beneficiation steps
including washer, flotation preparation, flotation, in-process storage and hydraulic station
operation. A matter of particular concern in the development of the hydroxamic acid
collector for phosphate flotation is the cost of the new collector chemistry relative to
current reagent costs for typical plant operations.
SOURCES OF DATA
Since AERO 6493 generally showed significant improvement in flotation
efficiency for coarse feed, flotation results used for this preliminary economic evaluation
were from coarse feed from the Cargill South Fort Meade Plant, Central Florida.
Specifically, data for the cost comparison of the new collector chemistry with the
traditional collector chemistry were from two sources:
(1) The typical single-stage pilot plant flotation results obtained using the
hydroxamic acid collector (AERO 6493).
(2) The typical flotation results using the traditional double float process with
fatty acid/fuel oil (FA/FO) and amine as collectors. Data for the traditional
process were obtained from several different references (Wang 1999; Wiegel
1999; Zhang and others 1997).
Flotation results and reagent costs are presented in Table 10 for single-stage
flotation with AERO 6493, and Table 11 for double-stage flotation (Crago Process) with
fatty acid/fuel oil (FA/FO) and amine chemistry.
ECONOMIC ANALYSIS
This preliminary economic analysis was carried out considering separation
efficiency and, in this regard, includes recovery, grade, reagent consumption and the
reagent prices. The analysis is based on the economic evaluation model developed by
Jacobs Engineering (El-Shall and others 2001) for phosphate mineral processing. In this
model, a scheme for penalizing lower grade rock has been developed and the economic
performance measure is defined as
M = CP – CfF – FCr
45
where
M = The economic performance measure, representing dollars earned per year ($/year)
Cp = Sales value of product: Cp = Price of 66% BPL rock x (BL/66)1.5 (BL = % BPL )
Price of 66% BPL rock (30% P2O5): $30/ton [73]
Cf = Sales value of feed:
Cf = Price of 66% BPL rock x (BL/66)1.5
Cr = Total reagent cost:
Cr ($/ton feed)
P = Product flowrate:
P = F( α /100)( ε /100)(100/ β ) (ton/year)
F = Feed solid flowrate:
F = 4,000,000 ton/year (assumed)
α = Feed P2O5 grade (see Tables 5.1, 5.2)
β = Concentrate P2O5 grade (see Tables 5.1, 5.2)
ε = Product recovery (see Tables 5.1, 5.2)
Table 10. Pilot Plant Flotation Results and Reagent Schedule for Single-Stage
Flotation with AERO 6493.
Process
Feed Grade
P2O5 %
(α)
Concentrate
Grade P2O5 %
( β)
P2O5
Recovery %
( ε)
9.6
29.6
86
12.9
31.55
95
Cargill South Fort Meade
Fine Feed , Single-Stage, pilot
Scale Flotation at AERO 6493
Consumption of 1.87 lb/t feed
Cargill South Fort Meade
Coarse Feed, Single-Stage, pilot
Scale Flotation at AERO 6493
Consumption of 2.65 lb/t feed
46
Table 11. Typical Flotation Results and Reagent Costs for Coarse Feed Using the
Traditional Double Float Process (FA/FO and Amine).
Process
Feed Grade
P2O5 %
(α)
Concentrate
Grade P2O5 %
( β)
P2O5
Recovery %
( ε)
Typical Double Float
Plant Scale
Flotation with FA/FO
8.00
31.5
85
Reagents
Reagent
(lb/t feed)
Price
($/lb)
Cost
($/t feed)
Na2SiO3
0.1-0.4
0.05
0.01-0.02
Na2CO3
0.8-1.4 (pH 9)
0.08
0.07-0.11
Fatty Acid
1.4-2.1
0.15-0.20
0.21-0.42
Fuel Oil
0.6-0.9
0.07
0.042-0.063
H2SO4
2 (pH 3.3)
0.03
0.06
Amine
1
0.25-0.30
0.25-0.30
Total
0.64-0.97
The preliminary results comparing the AERO 6493 collector with the traditional
double float process using fatty acid/fuel oil (FA/FO) are presented in Table 12 using
Jacobs Engineering’s model for economic performance. The results indicate that if the
price for AERO 6493 is less than $1.80/lb., the economic performance for AERO 6493 is
comparable with the traditional Double Float process.
47
Table 12. Typical Results from the Economic Performance Analysis (Assuming 4
Million Tons Per Year of Capacity).
Process
Reagent
Price
Reagent Cost
Product Flowrate
$/t Feed
Ton/Year
$/Lb
Economic
Performance
Million $/Year
Single-Stage
AERO 6493
1.6-1.8
1.93-2.17
1,445,324
7.55-8.51
0.63-0.73
0.64-0.97
1,295,238
7.41-8.73
Double Float
FA/FO
Amine
48
ENVIRONMENTAL IMPACT
LITERATURE REVIEW
The hydroxamic acid compounds, of structure R-CONHOH where R is an alkyl
group, are prepared by condensation of the appropriate carboxylic acid methyl ester with
hydroxylamine. With the particular concern regarding the environmental impact of these
flotation reagents, Addison and Cote (1973) and Fletcher and Addison (1972), from
Fisheries Research Board of Canada, Marine Ecology Laboratory, published two lectures
on the study of acute toxicity of saturated n-alkylhydroxamic acids to salmon. In the
study “Variation with chain length in acute toxicity of alkylhydroxamic acids to salmon
(Salmo salar) fry,” it was reported that toxicity was attributed to the hydroxamic acid (or
hydroxamate anion) rather than to dimethylamine or to hydroxylamine (a potential
decomposition product). The n-decano-hydroxamic acid, tested as its sodium salt, was
considerably more toxic than the flotation reagent itself and the acute toxicity of
alkylhydroxamic acids was found to increase with chain length. It was also found in this
research project that hydroxamic acids with chain lengths less than 6 carbon atoms were
not lethal at concentrations below 100mg/l within 90 hrs. Hydroxamic acids with chain
lengths higher than 10 carbon atoms were also not found to be lethal at concentrations of
10mg/l or above (Addison and Cote 1973). The authors confirmed their previous
suggestion that the toxic component of the flotation reagent was hydroxamic acid (or
hydroxamate ion). Neither the possibility of decomposition products, hydroxylamine or
nitrite was detected in the test solutions of hydroxamic acids. The acid C9H19CONHOH
was more toxic than the flotation reagent based on a mixture of 60% C7H15CONHOH and
30% C9H19CONHOH.
It was also revealed in the toxicity study for iron ore flotation that the reagent,
dimethyl ammonium alkyl hydroxamate (DMAH), was lethal to brook trout and
dimethylamine proved to be non-toxic (Addison and Cote 1973; Fletcher and Addison
1972). Hydroxylamine was as lethal as DMAH and the 10 carbon sodium salt was 5-10
times more toxic than hydroxylamine or DMAH.
E. D. Savilov, from The Novosibirsk Scientific Research Public Health Institute,
Russia published a report (Savilov 1977) of hygienic standards for flotation reagent IM50 and hydroxamic acid in water reservoirs. The report indicated that the threshold
concentration of the hydroxamic acids on the organoleptic properties of water ranged
from 5mg/L for C9 HA to 200mg/L for C7 HA. For flotation reagent IM-50 the threshold
of smell was 1mg/L. A quantitative determination over time showed that reagent IM-50
and its component hydroxamic acids (HAs) are stable substances in water. The threshold
concentrations for the HAs and for the IM-50 flotation reagent with respect to BOD20
were established at 0.1mg/L for each. The threshold concentration for foam formation
for the homologous series of C7-C10 hydroxamic acids and IM-50 is 2mg/L, and for C6
HA it is 1mg/L. The toxicity of reagent IM-50 lies between that of C7 and C8
hydroxamic acids. DL50 for white rats was found to be 1900mg/L for C6 HA and
20,750mg/L for C10 HA. This research report from Russia also confirmed that reagent
IM-50 and the HAs are similar to each other with regard to toxicodynamics. The sanitarytoxicology experiments were conducted by administering enanthic hydroxamic acid
(EHA) into the stomach of the rats with drinking water in amounts of 0.5, 5, and 50mg/L
49
for 6 months. The conclusions revealed from this study are that the ineffective dose of
EHA can be set at the 0.5mg/kg level (10mg/L), and the threshold level at 5 mg/kg
(100mg/L) (Savilov 1977).
The essential components of AERO 6493 are 5-6% caprylic acid (C7H15COOH),
60% dodecyl alcohol (C11-14 isomers), and 35% alkyl hydroxamic acids (R-C(O)NHOH,
where R is alkyl group having 7-8 carbon atoms). It can be expected that the toxicity of
AERO 6493 should be less than that of hydroxamic acid type flotation reagents
mentioned above since the lower concentration of alkyl hydroxamic acids and the shorter
hydrocarbon chain length in the product. According to the application of AERO 6493 in
the kaolin industry in Georgia, where AERO 6439 is used as a collector to remove
impurities from kaolin, environmental studies have shown that the reagent is
biodegradable and that the toxicity level LC50 is 2.5ppm for blue gill sunfish. The toxicity
of the flotation collector, AERO 6493, is of particular importance in the kaolin industry
because the kaolin flotation product must be FDA approved, a condition which has been
satisfied without any difficulty. The hydroxamic acid collector can not be detected in
water discharged from the plant operated by Thiele Kaolin.
EXPERIMENTS ON WATER QUALITY
As described above, hydroxamic acids and flotation reagents containing
hydroxamic acid compounds are toxic at a certain dosage, although industrial application
activities have been conducted for many years. Therefore, the environmental impact of
the new collector, the alcoholic solution of the alkyl hydroxamic acid (AERO 6493), is an
important issue regarding the use of AERO 6493 in the phosphate industry. To assess
water quality that might be discharged two sets of flotation experiments were conducted
and samples of the discharged water were analyzed to obtain the preliminary estimate of
the environmental impact of AERO 6493.
The coarse feed from the Cargill South Fort Meade Plant, Central Florida was
used for this environmental assessment. The scope of the work was based on bench
laboratory testing to: (1) Establish the baseline conditions with open-cycle single-stage
flotation experiments without recycled water to evaluate the discharge water quality; (2)
conduct the locked cycle single-stage flotation experiments with recycled water to
estimate the steady state discharge water quality; and (3) compare the discharge water
quality using AERO 6493, with the analytical results from plant water samples.
Water Quality in Open-Cycle Testing
Figure 27 shows the open-cycle flotation procedure. In this test, tap water was
used. The sample was conditioned with the collector, AERO 6493, with a dosage of 800
g/t at 75% solids for 3 minutes. Then the slurry was transferred into the flotation cell and
diluted to 20% solids with tap water. After flotation the water from filtration of the
tailing and concentrate products was collected and analyzed. Whatman #4 coarse fast
filter papers were used for the filtration. The flotation and water analytical results are
listed in Table 13. These results are used as a baseline. Notice that the TOC content is
6.5mg/l, of which 35% or 2.275mg/l may be contributed from hydroxamic acids (C 7-8).
50
Cargill Coarse Feed
AERO 6493 800 g/t
Tap Water
75% Solids Conditioning, 3 min.
Tap Water
Flotation (One Liter Cell) @ 20% Solids
Tailing Filtration
Concentrate Filtration
Solid Tailing
Sampling for Analysis
Solid Concentrate
Sampling for Analysis
Discharge Water
Sampling for Analysis
Figure 27. Open-Cycle Single-Stage Flotation Procedure Without Recycled Water.
51
Table 13. Analytical Results for Open-Cycle Flotation of Cargill Feed (12x80 Mesh)
and Discharge Water Quality without Water Recycle Using AERO 6493
as Collector. Flotation with Tap Water at pH 7.41.
Grade
Recovery
P2O5%
%
30.98
93.36
TOC(5)
mg/L
COD(6)
mg/L
Hardness(1)
TSS(2)
TDS(3)
Turbidity(4)
mg/L
mg/L
mg/L
NTU
8.07
650
140
820
150
P(7)
mg/L
Ca(8)
Mg(9)
mg/L
F(10)
mg/L
Dissolved
Oxygen(11)
pH
mg/L
mg/L
6.5
240
15
170
54
9.1
10.82
The analytical methods used were all EPA-approved standard methods, with the code as
follows:
(1) as CaCO3, 2340B (2) 160.2 (3) 160.1 (4) 180.1 (5) 415.1 (6) HACH 8000
(7) as total P, 365.4 (8) 6010B (9) 6010B (10)340.1 (11) 360.1
Water Quality in Locked-Cycle Testing
Figure 28 shows the locked-cycle flotation procedure. In this test the tap water
was used for the first cycle of flotation. In the first cycle of flotation, a sample of 250
grams was conditioned with the new collector, AERO 6493, with a dosage of 800g/t at
75% solids for 3 minutes. Then the slurry was transferred to the flotation cell and diluted
to 20% solids with tap water. After the first cycle of flotation, water from the filtration of
tailing and concentrate was collected for the second cycle of flotation. In the second
cycle of flotation a second 250 gram sample was conditioned and diluted with the
recycled water from the first cycle flotation at the same reagent schedule, conditioning
and flotation conditions. After the second cycle of flotation the water from filtration of
tailing and concentrate was collected for the third cycle of flotation. After completing the
same procedure as used for the second cycle, the filtration water from the third cycle was
collected and analyzed. Whatman #4 coarse fast filter papers were used for the filtration.
Flotation results and the water analysis (essentially the third cycle water) are
listed in Tables 14 and 15. The results indicate that the recovery and grade of the
phosphate concentrate have stabilized in the third cycle. It also can be seen that there
was no significant change in water quality (most analytical results) from the open-cycle
results to the closed cycle. Notice that the total organic carbon (TOC) in closed cycle
increased from 6.5mg/l to 22mg/L, which in turn would correspond to be from 2.275ppm
to 7.7ppm in hydroxamic acid. The chemical oxygen demand (COD) also increased from
240 to 440 mg/L. This change may be due to a build up of the reagent in the closed
cycle. Usually in the closed cycle the reagent dosage would be reduced.
52
Cargill Coarse Feed
AERO 6493 800 g/t
100% Recycled Water
75% Solids Conditioning, 3 min.
Tap Water
Flotation (One Liter Cell) @ 20% Solid
Tailing Filtration
Concentrate Filtration
Solid Tailing
Sampling for Analysis
Solid Concentrate
Sampling for Analysis
If Cycle < 3
If Cycle = 3
Discharge Water
Sampling for Analysis
Figure 28. Locked-Cycle Single-Stage Flotation Procedure with Recycled Water.
53
Table 14. Analytical Results for Locked-Cycle Flotation Products of Cargill
Feed (12x80 Mesh) with 100% Water Recycle using AERO 6493 as
Collector. Flotation with Tap Water at pH 7.41.
Cycle
1
2
3
Products
Wt. %
Grade P2O5%
Recovery %
Concentrate
42.57
32.41
89.36
Tailing
57.43
2.86
10.64
Feed
100.00
15.44
100.00
Concentrate
45.94
30.07
95.12
Tailing
54.06
1.31
4.88
Feed
100.00
14.52
100.00
Concentrate
46.13
30.07
95.30
Tailing
53.87
1.27
4.70
Feed
100.00
14.56
100.00
Table 15. Analytical Results for Locked Cycle Flotation of Cargill Feed (12x80
Mesh) and Discharge Water Quality from the Last Cycle (Cycle 3)
Water Recycled Using AERO 6493 as Collector. Flotation with Tap
Water at pH 7.41.
Cycle
3
3
Hardness(1)
TSS(2)
TDS(3)
Turbidity(4)
mg/L
mg/L
mg/L
NTU
7.97
590
110
820
110
COD(6)
P(7)
Ca(8)
Mg(9)
F(10)
mg/L
mg/L
mg/L
mg/L
mg/L
Dissolved
Oxygen(11)
mg/L
440
13
150
52
16
10.81
Grade
Recovery
P2O5%
%
30.07
95.30
TOC(5)
mg/L
22
pH
The analytical methods used were all EPA-approved standard methods, with the code as
follows:
(1) as CaCO3, 2340B (2) 160.2 (3) 160.1 (4) 180.1 (5) 415.1 (6) HACH 8000
(7) as total P, 365.4 (8) 6010B (9) 6010B (10)340.1 (11) 360.1
54
SUMMARY
Shown in Table 16 are the average analytical data of 11 samples of plant water
taken from the flotation operations in Central Florida, published by Jacobs Engineering
Group, Inc. (1995) in a survey of phosphate beneficiation plants including the IMC
plants, and the Cargill plants Since the individual plant water analytical data is not
available a complete comparison can not be made. In general, all the analytical terms
listed in Table 13 and Table 15, including Total Suspended Solids (TSS), hardness (as
Ca2CO3), pH, and P (total P), have higher values for the discharge water from AERO
6493 bench flotation experiments than those for plant water samples, especially for TSS
and hardness. Six and three times over in TSS and hardness, respectively, when the data
from AERO 6493 flotation discharge water is compared with the data from operating
plants, which are using fatty acid/amine flotation chemistry. Apparently, the difference
in water quality is significant. However, the final conclusion on the environmental
impact of the new flotation chemistry using AERO 6493 still can not be made based only
on these results since many incomparable variables are involved in this comparison, such
as the time for water sampling after being discharged, filtration conditions for concentrate
etc. Especially, the analytical results from Table 13 and Table 15 suggest that the
hydroxamic acid collector, AERO 6439 addition could be reduced in a locked cycle
flotation to improve the accumulation of TOC content in discharged flotation water
without having a negative influence on the separation efficiency. Further environmental
evaluation regarding water quality should be made in plant testing.
Table 16. Average Analysis of Plant Water Samples from Central Florida
(Jacobs Engineering Group, Inc.).
TSS(1)
Hardness(2)
pH(3)
P(4)
15 ppm
129 ppm
7.6
2.7 ppm
(1)
EPA procedure for filterable residue
CaCO3, EDTA titrimetric procedure
(3)
pH meter
(4)
AOAC procedure for Spectrophotometric Molybdovanadophosphate
(2)
55
CONCLUSIONS
It has been found that excellent flotation selectivity is achieved when pure mineral
samples are conditioned at high percent solids with water insoluble alcoholic solutions of
alkyl hydroxamic acids as collectors. The results from contact angle and high-speed
video studies indicate that the hydroxamic acid collector has different spreading
characteristics at the surfaces of fluorapatite, dolomite and quartz. It is evident that
collector composition is an important variable which influences the flotation response.
Long branched chain alcohols increase the hydrophobicity and reduce reagent
consumption. Understanding of the mechanism of collector attachment and spreading is
still unclear and surface chemistry research should be continued to further understand the
phenomena involved in the flotation of phosphate minerals with insoluble alcoholic
solutions of hydroxamic acids.
Based on these bench-scale flotation results with a water insoluble alcoholic
solution of hydroxamic acid (AERO 6493) it seems that a single-stage phosphate
recovery of 90 - 95% with a concentrate grade of 31% P2O5 is possible for coarse feed
from the IMC-Agrico Four Corners Plant. As is the case for the traditional phosphate
flotation, high solids conditioning is necessary with the hydroxamic acid collector.
Conventional plant practice using traditional fatty acid/fuel oil collector (1,200 g/t)
results in only 75-80% recovery at a grade of 31% P2O5 after multiple flotation stages in
different flotation circuits (double flotation). In the case of coarse feed from the Cargill
Plant the concentrate grade reached 34% P2O5 with 93% recovery in single-stage benchscale flotation with the new collector. Also significant improvements in flotation were
achieved with plant samples from North Carolina and Utah. The results indicate that the
hydroxamic acid collector is more effective for the flotation of coarse feed than for the
flotation of fine feed. Pilot plant testing at a feed rate of 700-900 lbs/hr was carried out
in order to evaluate the new collector in a larger scale continuous flotation experiment.
The results from the pilot plant with single-stage flotation are summarized in Table 17.
For the coarse feed, in the best case a concentrate grade of 31.5% P2O5 and 95.0%
recovery was achieved. The average concentrate grade is about 31.4% P2O5 with 92.8%
recovery and 6.96% insol. The results from the pilot plant testing confirmed the results
from bench-scale flotation experiments.
The preliminary economic analysis of the new flotation chemistry with the
alcoholic solution of the hydroxamic acid collector, AERO 6493, indicates that the
economic performance is sensitive to the feed grade and reagent cost. Significant
economic effectiveness could be achieved under certain circumstances. For example, at a
plant capacity of 4 million tons per year, a marginal economic performance of 7.55-8.51
million dollars per year can be reached for a price of AERO 6493 at $1.6-1.8/lb, in
contrast to a price of $0.63-$0.93/lb for the existing traditional double float process with
FA/FO and amine. A price lower than $1.60/lb for AERO 6493 would give a much more
significant improvement in economic performance. The value of using AERO 6493
would be much more significant if other aspects involved in the entire flotation process
57
were counted, such as energy reduction, water quality, water consumption, equipment
investment, the cost of equipment maintenance, etc.
Analysis of water from bench-scale flotation experiments and review of the
literature indicate that there is no significant environmental impact from utilization of the
new collector. In fact the AERO 6493 reagent is currently used in the kaolin industry and
is not detected in discharged water from these operations.
Table 17. Results from Single-Stage Pilot Plant Phosphate Flotation of Feed from
the Cargill SFM Plant Using the New Hydroxamic Acid Collector
(AERO 6493).
Feed
Fine Feed
Coarse
Feed
Condition
Wt %
P2O5 %
Recovery %
Dosage 850 g/t
27.96
29.6
85.94
Conditioning Solids
72.04
1.88
14.06
74 %
100.00
9.63
100.00
Dosage 1200 g/t
38.80
31.55
94.88
Conditioning Solids
61.20
1.08
5.12
71%
100.00
12.9
100.00
58
REFERENCES
Addison RF, Cote RP. 1973. Variation with chain length in acute toxicity of
alkylhydroxamic acids to salmon (Salmo salar) fry. Lipids 8(9):493-7.
Allen MP. 1993. The Vernal phosphate rock mill. In: El-Shall H, Moudgil BM, Wiegel
R, editors. Beneficiation of phosphate: theory and practice. Littleton (CO): Society for
Mining, Metallurgy and Exploration. p 85-91.
El-Shall H, Svoronos S, Abdel-Khalek NA. 2001. Bubble generation, design modeling
and optimization of novel flotation columns for phosphate beneficiation: final report.
Volumes I and II. Bartow (FL): Florida Institute of Phosphate Research. Publication nr
02-111-175.
FIPR. 1998. 1998-2003 strategic research, programmatic, & management priorities.
Bartow (FL): Florida Institute of Phosphate Research.
Fletcher GL, Addison RF. 1972. Some aspects of the chemistry and acute toxicity of the
iron ore flotation agent dimethyl ammonium alkyl hydroxamate and some related
compounds to brook trout. Environmental Contamination and Toxicology 1(2/3):147-57.
Gieseke EW. 1985. Phosphate rock. In: Weiss NL, editor. Mineral processing handbook.
Vol. 2. New York: SME/AIME. p 21:1 to 21:8.
Gruber GA. 1999. Anionic conditioning for phosphate flotation. In: Zhang P, El-Shall
H, Wiegel R, editors. Beneficiation of phosphate: advances in research and practice.
Littleton (CO): Society of Mining, Metallurgy and Exploration. p 303-13.
Gu Z, Gao Z, Zheng S. 1999. Beneficiation of Florida dolomitic phosphate pebble with
a fine-particle flotation process. In: Zhang P, El-Shall H, Wiegel R, editors.
Beneficiation of phosphate: advances in research and practice. Littleton (CO): Society
of Mining, Metallurgy and Exploration. p 155-62.
Houot R. 1982. Beneficiation of phosphoric ores through flotation: review of industrial
applications and potential developments. Int. J. Miner. Process. 9(4):353-84.
Jacobs Engineering Group, Inc. 1995. Understanding the basics of anionic conditioning
in phosphate flotation. Bartow (FL): Florida Institute of Phosphate Research. FIPR
Publication nr 02-090-121. p 4-11.
Lu Y, Drelich J, Miller JD. 1997. Wetting of francolite and quartz and its significance in
the flotation of phosphate rock. Minerals Engineering 10(11):1219-31.
Lu Y, Liu N, Wang X, Miller JD. 1999. Improved phosphate flotation with nonionic
polymers. In: Zhang P, El-Shall H, Wiegel R, editors. Beneficiation of phosphates:
59
advances in research and practice. Littleton (CO): Society for Mining, Metallurgy and
Exploration. p 3-19.
Miller JD, Wang X, Li M. 2001. Selective flotation of phosphate minerals with
alcoholic solutions of alkyl hydroxamic acid. Presented at Engineering Foundation
Conference, Beneficiation of Phosphates III; 2-7 Dec 2001; St. Petersburg Beach, FL.
Moudgil BM. 1992. Enhanced recovery coarse particles during phosphate flotation:
final report. Bartow (FL): Florida Institute of Phosphate Research. FIPR Publication nr
02-067-099.
Peterson HD, Fuerstenau MC, Rickard RS, Miller JD. 1966. Chelating agents—a key to
chrysocolla flotation. Mining Engineering 18(4):81-6.
Savilov ED. 1977. Substantiation of hygienic norms of the new flotation reagent IM-50
and hydroxamic acids in the water of reservoirs. Gig. Aspekty Okhr. Zdorov’ya
Naseleniya. Moscow (USSR): Mosk. Nauchno-Issled. Inst. Gig. im. F. F. Erismana. p
42-3. Translated from the Russian by the Ralph McElroy Co., Custom Division, P.O.
Box 4828, Austin, TX 78765 USA.
Tavrides, JG. 1988. Assessment of present phosphate mining and beneficiation practice
and the evaluation of alternative technology. Bartow (FL): Florida Institute of Phosphate
Research. FIPR Publication nr 04-031-068. Section 5, “Beneficiation.” p 5-1 to 5-7.
Wang X. 1999. Flotation of phosphate rock from central Florida with the air sparged
hydrocyclone [MS thesis]. Salt Lake City (UT): University of Utah.
Wiegel R. 1999. Phosphate rock beneficiation practice in Florida. In: Zhang P, El-Shall
H, Wiegel R, editors. Beneficiation of phosphates: advances in research and practice.
Littleton (CO): SME. p 271-5
Zhang J. 1995. Phosphate beneficiation--challenges and opportunities. In: Misra M,
editor. Separation processes: heavy metals, ions and minerals: proceedings of a
symposium; 1995 Feb 12-16; Las Vegas, NV. Warrendale (PA): The Minerals, Metals
& Materials Society. p 167-183.
Zhang P, Yu Y, Bogan M. 1997. Challenging the “Crago” double float process. II.
Amine-fatty acid flotation of siliceous phosphates. Minerals Engineering 10(9): 983-94.
60
APPENDIX A
DATA FROM PILOT-PLANT FLOTATION TESTS
A-1
2
5/20/02
4
5
6
5/20/02
5/20/02
5/20/02
3
1
5/20/02
5/20/02
Test
Date
Mass
(Lbs./Hr.)
910
258
654
894
208
707
867
255
645
885
249
666
886
260
655
893
235
672
Stream
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
5.30
5.70
5.68
5.70
4.73
5.43
Collector
(Gm/min)
74.0
74.0
76.0
73.5
73.5
72.5
Conditioner
35.7%
21.1%
36.0%
20.7%
38.0%
20.8%
35.6%
20.7%
33.2%
23.7%
32.0%
21.8%
Stream
% Solids
Table A-1. Pilot Testing Performed on Fine Feed from Cargill SFM Plant.
0.69
1.10
4.68
0.64
0.84
4.54
0.63
0.92
4.94
0.56
0.81
5.06
0.62
0.92
5.03
0.63
0.85
5.03
Stream
5.30
2.80
-5.00
2.80
-5.80
2.20
-5.80
2.00
-5.80
2.00
-5.80
2.00
--
Dilution
Water (USGPM)
5.99
3.90
4.68
5.64
3.64
4.54
6.43
3.12
4.94
6.36
2.81
5.06
6.42
2.92
5.03
6.43
2.85
5.03
Total
A-2
8
5/21/02
10
11
5/21/02
5/21/02
9
7
5/21/02
5/21/02
Test
Date
Mass
(Lbs./Hr.)
886
270
643
659
217
468
782
292
465
745
281
467
658
247
466
Stream
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
Feed
Concentrate
Tailing
7.53
7.00
7.20
7.10
6.17
Collector
(Gm/min)
71.5
71.4
71.8
70.8
Conditioner
71.5
24.9%
19.4%
26.9%
19.3%
28.5%
19.4%
24.7%
19.2%
26.5%
23.6%
Stream
% Solids
Table A-2. Pilot Testing Performed on Coarse Feed from Cargill SFM Plant.
Stream
0.71
1.50
4.16
0.54
1.33
3.93
0.61
1.46
3.86
0.60
1.53
3.91
0.53
1.48
3.86
Dilution
5.50
2.50
-5.50
2.50
-5.50
2.00
-5.80
2.00
-5.80
2.00
--
Water (USGPM)
Total
6.21
4.00
4.16
6.04
3.83
3.93
6.11
3.46
3.86
6.40
3.53
3.91
6.33
3.48
3.86
Analysis and Adjusted Data
Table A-3. Analytical Results From Pilot Testing for Fine Feed from Cargill SFM
Plant.
Analyzed Data
Test No.
1
2
3
4
5
6
Adjusted Data
(Minimized SSQ)
Product
Mass
(Lbs./Hr.)
P2O5
(%)
Insol
(%)
Mass
(Lbs/Hr.)
P2O5
(%)
Insol
(%)
Feed
910.00
9.94
70.85
910.67
9.73
71.26
Concentrate
258.00
28.38
17.61
257.36
28.43
17.46
Tail
654.00
2.24
92.84
653.31
2.37
92.45
Feed
894.00
9.89
70.57
883.30
10.37
70.65
Concentrate
208.00
30.55
11.19
218.57
30.56
11.64
Tail
654.00
3.70
88.62
664.74
3.73
90.05
Feed
867.00
10.13
70.11
878.02
9.83
69.53
Concentrate
255.00
29.68
13.73
244.08
29.61
13.26
Tail
645.00
2.38
92.39
633.94
2.21
91.20
Feed
885.00
10.22
69.91
895.03
9.67
70.19
Concentrate
249.00
30.24
12.37
239.12
30.26
11.75
Tail
666.00
2.11
93.16
655.91
2.17
91.50
Feed
886.00
10.03
70.40
895.69
9.63
70.34
Concentrate
260.00
29.61
14.1
250.43
29.60
13.56
Tail
655.00
1.91
93.74
645.26
1.88
92.38
Feed
893.00
10.13
70.13
897.68
10.02
69.92
Concentrate
235.00
30.71
11.00
230.37
30.68
10.82
Tail
672.00
2.97
90.83
667.31
2.88
90.32
* Calculated by using TECHBAL Material Balance Spreadsheet by G.H. Luttrell,
Department of Mining & Minerals Engineering
A-3
Table A-4. Analytical Results from Pilot Testing for Coarse Feed from Cargill SFM
Plant.
Analyzed Data
Test No.
7
8
9
10
11
Product
Adjusted Data
(Minimized SSQ)
Mass
(Lbs./Hr.)
P2O5
(%)
Insol
(%)
Mass
(Lbs./Hr.)
P2O5
(%)
Insol
(%)
Feed
886.00
12.01
64.77
895.01
11.70
64.37
Concentrate
270.00
32.30
6.55
261.06
32.25
6.18
Tail
643.00
3.37
89.20
633.95
3.25
88.33
Feed
659.00
12.01
64.82
667.72
10.86
66.44
Concentrate
217.00
31.39
8.82
208.62
31.58
7.59
Tail
468.00
1.02
95.83
459.10
1.44
93.18
Feed
782.00
12.28
64.00
773.64
12.90
63.03
Concentrate
292.00
31.60
8.17
300.16
31.55
9.19
Tail
465.00
1.16
95.53
473.43
1.08
97.16
Feed
745.00
12.30
63.88
745.99
12.65
62.56
Concentrate
281.00
31.74
7.92
279.92
31.58
8.33
Tail
467.00
1.54
94.45
466.06
1.28
95.13
Feed
658.00
12.41
63.55
676.38
11.44
63.18
Concentrate
247.00
31.45
8.48
228.95
31.36
6.96
Tail
466.00
1.43
94.82
447.43
1.25
91.95
* P2O5 and Insols analyzed by FIPR lab.
A-4