– 19 –
Flotation of Oxide Copper and Copper Cobalt
Ores
19.1
INTRODUCTION
Flotation practice of oxide copper minerals dates back to almost 60 years ago, and has been
applied in Central Africa (Congo) by Union Miniere (Belgium). The process involves two
basic flotation methods: (a) fatty acid flotation of oxide copper minerals from siliceous ore,
and (b) sulphidization of oxide copper minerals followed by flotation using sulfhydryl
collectors, such as xanthate [1] from carbonate ores. In the past 50 years, extensive research
has been carried out on a variety of oxide copper minerals, and only a few of the many
innovative processes have been introduced into operating plants. It was not until recently
that new technology has been developed and introduced into some operating plants around
the world. One of the major problems with flotation of oxide copper minerals, at industrial
scale, is that the floatability of oxide copper minerals from natural ores depends largely on
the mineralogy of the ore and the gangue composition. The floatability of oxide copper
minerals that are present in the ore containing carbonaceous and dolomitic gangue is
significantly different from the flotation properties of oxide copper containing siliceous
gangue minerals.
The presence of various types of clay slimes also has a significant effect on flotation
properties of oxide copper minerals [2].
19.2
OXIDE COPPER ORES AND MINERALS
More than 120 oxide-containing minerals have been identified, mainly from the Central
and South African regions, but only a few of these minerals have any economic value.
Some of the most important copper oxide minerals are listed in Table 19.1.
In most cases, oxide copper ores contain more than one copper oxide mineral, and also
contain mixtures of sulphide and oxide copper minerals. From a processing point of view,
the oxide copper ores can be divided into the following five groups:
Oxide copper ores. In oxide ores copper is predominantly malachite with significant
quantities of cobalt oxides. According to the mineral composition, these ores can be
47
48
19.
Flotation of Oxide Copper and Copper Cobalt Ores
Table 19.1
List of economically valuable copper oxide minerals
Mineral
Chemical formula
Cu content (% Cu)
Specific gravity (SG)
Colour
Cuprite
Tenorite
Malachite
Azurite
Brochantite
Atacamite
Antlerite
Chrysocolla
Chaecantite
Cu2O
CuO
Cu2(OH)CO3
Cu3(OH)2(CO3)2
Cu4(OH)6SO4
Cu2(OH)2Cl
Cu3(OH)2SO4
CuO · SiO2
CuSO4 · 5H2O
88.8
80.0
57.4
55.3
56.6
44.6
54.0
10–36
25.5
5.9
6.5
3.9
3.7
3.9
3.8
3.9
2–2.4
2.2
Brick red
Black
Green
Blue
Emerald green
Green, blue
Emerald green
Blue
Deep blue
sub-divided into two main groups: (a) oxide ore that contains carbonaceous gangue
minerals (carbonate, dolomite) with little or no silica; and (b) oxide ore, where silica is
the predominant gangue mineral. The gangue composition of the ore plays a decisive role
in selection of reagent scheme for beneficiation of the ore.
These ores also contain cobalt minerals, mainly carrollite (CoCuSO4) and cobaltite
(CoAsS).
Copper oxide mixed ore – Type 1. The main copper minerals found in these ores include
malachite, pseudo-malachite, chrysocolla and some tenorite. These ores also may
contain mainly siliceous gangue minerals, including spherocobaltite as the main cobalt
minerals. The carbonaceous types also contain an appreciable amount of clay slime
minerals.
Copper oxide mixed ore – Type 2. In contrast to Type 1, this ore type contains cuprite,
malachite and azurite as the main copper oxide minerals. This ore type predominantly
contains carbonaceous gangue, and usually, significant amounts of clay-like slimes.
Mixed copper sulphide oxide ores. These contain varieties of both sulphide and oxide
minerals, and are the most complex copper-bearing ores from a beneficiation point of view.
The major copper minerals present in this ore type include bornite, chalcocite, covellite,
malachite, cuprite and chrysocolla. In some cases, significant amounts of cobalt minerals
are also present in this ore.
Copper oxide gold ores. Although this ore type is not abundant, they are of significant
value because they contain gold. Only a few deposits in Brazil and Australia are known.
The copper in these ores is represented by cuprite, native copper, antlerite and tenorite. The
gold is associated with cuprite, as an auricupride and several sulphosalts. The major
problem associated with treatment of this ore type is the presence of large amounts of
clay slimes in the form of iron hydroxide and illite.
Most of the oxide copper deposits are located in the former Republic of Zaire (Katanga)
and Zambia. Only a few deposits are located in Chile, Peru, Canada and the United States.
From most of the south and North American deposits, oxide copper is recovered using a
hydrometallurgical method.
19.3
19.3
Flotation Properties of the Individual Copper Minerals and Mixtures
49
FLOTATION PROPERTIES OF THE INDIVIDUAL COPPER MINERALS
AND MIXTURES
The flotation characteristics of the oxide copper minerals from natural ore are dependent on
several main factors, some of which include the following:
• Chemical composition and physical structure of the oxide copper minerals and the ionic
composition of the slurry phase play important roles in the floatability of various oxide
minerals. The oxide copper minerals are often porous, and in some cases, water soluble.
Some of the oxide minerals tend to slime during grinding, and flotation of fine oxide
minerals is rather difficult.
• The gangue constituents and their nature are sometimes determining factors in selection
of a treatment process for beneficiation of oxide copper ores. Highly weathered ores
usually contain a fairly large amount of slimes, which has a negative effect on the
floatability of oxide copper minerals. Also, there is an appreciable difference in
floatability between oxide minerals from carbonaceous and siliceous ores.
• The mechanical strength of the surface layers of many of the oxide copper minerals is
weak. Therefore, flotation of oxide copper ores using sulphidization method, can
improve by reducing turbulence and attrition within the flotation cell [3].
Floatability of malachite is one of the most important oxide copper minerals for
production of copper from oxide ores using flotation. Extensive research has been carried
out by a number of researchers [4–7] in which various flotation methods were examined.
Hydroxamaic acid flotation has been established from laboratory research work, which
has the chemical formula as shown in Figure 19.1.
R1
Figure 19.1
N
C
R2O
OH
Hydroxamaic acid formula.
where R1 is organic ligand (alkyl benzyl, etc.) and R2 may be organic or inorganic, and is a
suitable malachite collector. It was found that the effectiveness of hydroxamaic acid was
dependent on flotation pH and collector concentration. Figure 19.2 shows the relationship
between malachite recovery and flotation pH. It has been proposed that chelation mechan­
ism involves CuOH+, where hydroxamate has a high chemsorption specifically for copper.
Although good metallurgical results have been obtained in the laboratory, it has not found
any plant application to date.
The sulphidization process, which was first successfully applied on a commercial scale
on lead carbonate ores, is currently the most popular method used during treatment of oxide
copper ores that contain malachite and carbonaceous gangue. The commonly used sulphi­
dizers are Na2S · 9H2O and NaHS, with xanthate or xanthate ester.
50
19.
Flotation of Oxide Copper and Copper Cobalt Ores
100
Copper recovery (%)
80
60
40
20
0
4
5
6
7
8
9
10
11
12
Flotation pH
Figure 19.2 Effect of pH on malachite recovery using hydroxamic acid as collector.
Carboxilic acid flotation of malachite has been commercially used for over 70 years.
This collector is prepared by heating a mixture of hydrolysed palm oil (or oleic acid) and
fuel oil in a 3:1 ratio. This mixture is manly used for recovery of malachite from siliceous
ores. The use of carboxylic acid for malachite flotation from carbonaceous ores resulted in
both reduced concentrate grade and recovery.
Cationic flotation of malachite, using mono- and diamines in alkaline pulp, was also
examined. Malachite floats readily using mono-amines under laboratory conditions.
Figure 19.3 illustrates the floatability of pure malachite with different amines. It should
be pointed out that there are several varieties of malachite, Cu4(PO4)2(OH)4·OH. Pseudomalachite is difficult to float, and it is well known that pseudo-malachite can be floated
with anionic collectors, but responds poorly to the sulphidization method.
In a number of oxide ores, cuprite (Cu2O, Cu = 88.8%, SG = 5.9) is present as secondary
minerals together with sulphides, malachite and tenorite. Cuprite can be floated using either
sulphidization or anionic flotation methods. The flotation properties of cuprite are some­
what different from that of malachite. For example, using a sulphidization method for
flotation of cuprite requires higher dosages of sulphidizer.
Some ore deposits contain cuprite as the principal mineral. Typically, these deposits
contain appreciable amounts of slimes and clay minerals. The laboratory studies conducted
on these types of ore indicated that improved metallurgical results can be achieved using
the sulphidization method with ester-modified xanthate [8].
Tenorite (CuO; Cu = 80%, SG = 6.5) is usually present in mixed copper oxide and
sulphide ore. The flotation properties of tenorite are similar to that of cuprite.
19.4
Cobalt and Copper Cobalt Oxide Ores
51
100
monoamine
Malachite recovery (%)
90
diamine
7 EtO
80
monoamine
2 EtO
monoamine
7 EtO
monoamine
11 EtO
70
60
1
4
7
10
13
16
Collector concentration (mg/L)
Figure 19.3
Floatability of malachite with C-18 mono- and dialkylamines at pH 8.5–9.0.
Azurite (Cu3(OH2)(CO2)2, Cu = 55.3%, SG = 3.7) usually appears in small quantities
together with malachite in a number of deposits in Zambia and Congo. From plant and
laboratory data, azurite has similar flotation properties as malachite.
Atacamate (Cu2(OH2)Cl; Cu = 44.6%, SG = 3.8) is common to the Atacoma desert in
Chile, for which this mineral was named. As an individual mineral, it does not have any
significant economic value. No data on the floatability of this mineral are known.
Chrysocolla (CuOxSiO2; Cu = 10–36%, SG = 2–2.4) is the most studied mineral of all
the oxide minerals. Extensive laboratory studies have been conducted by numerous
researchers [9–11]. The laboratory research work indicates that chrysocolla can be floated
using the sulphidization method, as shown in Figure 19.4, or by hydroxamate collectors.
However, none of these processes have been applied at an industrial scale.
In a number of operations, chrysocolla has been recovered using a hydrometallurgical
technique.
The flotation properties of bronchantite, antlerite and chalcantite were not examined.
These oxide minerals are contained in an altered sulphide ore in some deposits in South
America and Zambia.
19.4
COBALT AND COPPER COBALT OXIDE ORES
In the deposits where oxide cobalt is present, it is common to have oxide copper minerals .
The cobalt is, therefore, recovered in a bulk copper–cobalt concentrate that is processed
using a hydrometallurgical technique to produce separate copper and cobalt metals. Oxide
52
19.
Flotation of Oxide Copper and Copper Cobalt Ores
100
Recovery (%)
80
dixanthogen
emulsion
+ 10 mg/L AmX
60
40
20
aqueous
dixanthogen
emulsion
aqueous
benzene
emulsion
0
0
100
200
300
400
500
Concentration of Na2S•9H2O (mg/L)
Figure 19.4
Effect of Na2S concentration on the flotation of chrysocolla.
cobalt minerals belong to the heterogenite group, which consists of complex hydrated
cobalt oxides of various compositions and degrees of crystallization. In view of the
complex mineralization, oxide cobalt minerals are known to be rather difficult to float.
The floatability of oxide cobalt minerals is strongly influenced by the presence of small
amounts of copper in its crystalline structure. From the point of view of flotation properties,
the cobalt minerals can be classified in two main groups: (a) crystalline varieties with
compositions closely responding to the formula CoO·OH. Cobalt is trivalent and only
minor amounts of impurities enter the structure. This is the most difficult variety of cobalt
to float using conventional reagent schemes; and (b) crypto crystalline or amorphous
varieties that contain various amounts of copper–nickel–iron and also bivalent cobalt.
Their formula is of the form (χCo2O3·γCoO·ZCuO)H2O + n% hygroscopic H2O. These
varieties of cobalt can be floated using reagent schemes used to float oxide copper minerals.
19.5
FLOTATION PRACTICE IN BENEFICIATION OF OXIDE COPPER
MINERALS
Selection of a reagent scheme for beneficiation of oxide copper ores depends on many
factors; some of the more important ones being
• Type of oxide copper minerals present in the ore.
• Type of gangue minerals – some ore types contain silicate gangue free of slimes, which
are the most amenable to flotation. Ores with dolomitic gangue can be beneficiated
19.5
Flotation Practice in Beneficiation of Oxide Copper Minerals
53
using sulphidization only. These ores usually contain an appreciable amount of clay
slimes that have a detrimental effect on flotation. Some oxide ores contain talc, iron
hydroxides and iron oxides. In general, each ore type requires the selection of different
reagent schemes.
• Degree of liberation – the relatively fine-grained ores are more amenable to flotation
than the disseminated ores, which require finer grinding.
• Chemical composition and physical structure of the copper minerals play an important
role in the floatability of oxide copper minerals [12]. Oxide copper minerals are often
porous and aqueous soluble. Because of that, they tend to slime during grinding.
During the past two decades, there has been an appreciable amount of research work
conducted mainly on the application of hydroxamates for oxide copper flotation. These
reagents have yet to find industrial application.
In recent years, a new class of collectors, consisting of xanthated fatty acids (TY
collector), and monoester-modified xanthate (PM230) have found industrial applications
with improved metallurgical results. From plant practice, treating oxide copper and copper
cobalt ores, two basic flotation methods are practiced: (a) sulphidization flotation method,
and (b) anionic flotation method.
19.5.1
Sulphidization flotation method
This method is the most commonly used in beneficiation if oxide copper-bearing ore. The
reagent schemes used to treat oxide copper ores, mixed copper sulphide oxide ores and
oxide copper cobalt ores varies from one ore type to the next, mainly by type of collector
and sulphidizer used.
The choice of reagent scheme depends largely on the type of natural ore to be treated.
The three main groups of reagents used in beneficiation of oxide copper and copper cobalt
ores include (a) sulphidizers, (b) collectors and (c) modifiers and depressants.
Choice of sulphidizer and effect on flotation
The most preferred sulphidizer used in flotation of oxide copper minerals is Na2S · 9H2O.
Other sulphidizers used in operating plants include NaHS and (NH4)2S. Actually, the
selection of a sulphidizer is based on the consumption required for flotation of oxide
copper from particular ore types. For example, in some cases the consumption requirement
of NaHS is much higher than for Na2S. Figure 19.5 shows the effect of different levels of
sulphidizer on the recovery of malachite using xanthate collector.
From the data generated, higher dosages of NaHS are required to achieve activation of
malachite. From plant and laboratory experience [13], the sulphidization method using
xanthate collector is sensitive to the following, major factors:
• Rate of sulphidizer additions must be carefully controlled to obtain optimum
sulphidization and prevent excess SH– ions that may cause depression.
• Sometimes higher additions of sulphidizer are required, especially if the ore contains
excessive amounts of slimes.
54
19.
Flotation of Oxide Copper and Copper Cobalt Ores
100
Na2S•9H2O
Copper recovery (%)
80
NaHS
60
40
(NH4)2S
20
0
0
500
1000
1500
2000
2500
Activator additions (g/t)
Figure 19.5 Effect of levels of different sulphidizers on copper flotation from the Kolwezi open pit
ore (Congo, Africa).
The consumption rate of sulphidizer also depends on the type of collector used. When
using xanthate only, the sulphidizer rate is much higher than when using certain secondary
collectors, such as dithiophosphates.
Choice of depressants
In a large number of oxide flotation plants, sodium silicate (Na2SiO3) is used as a gangue
depressant. In the past two decades, a new line of depressants has been developed and
introduced into a number of operating plants. Some of these depressants include (a) a
mixture of sodium phosphate and lignin sulphonate (i.e. depressant 3XD), (b) a mixture of
a low-molecular-weight acrylic acid and sodium silicate (depressant 2D) and (c) hydrosol
based on the reaction of sodium silicate with alumina sulphate (depressant SD). These
depressants were extensively examined on copper oxide ores from the Nchanga mine in
Zambia.
Figure 19.6 shows the grade–recovery relationship using different depressant combina­
tions. Depressants 3XD and 2MD have shown excellent gangue depression.
The presence of clay in the ore has a detrimental effect on copper oxide flotation. Results
from experimental development test conducted on various clay containing ore types using
AQ depressants showed that in the presence of these depressants, the results improved
markedly using the sulphidization flotation method.
19.5
Flotation Practice in Beneficiation of Oxide Copper Minerals
55
100
Depressant
Type
Copper recovery (%)
80
60
2MD
40
3XD
800 g/t
sodium
silicate
20
none
0
0
5
10
15
20
25
30
35
Copper concentrate grade (%)
Figure 19.6 Effect of levels of various depressants on copper grade–recovery relationship from
Nchanga open pit ore.
Table 19.2 shows the effect of these depressants on oxide copper metallurgical results.
The ore used in these studies was from Dima (Shaba Province, Congo) underground oxide
ore. The results obtained demonstrated that the type of gangue depressant plays a sig­
nificant role in achieving good results. Research on gangue depressants has been conducted
by numerous researchers [16,17]. It has been proven that sodium silicate does not depress
calcite or dolomite using the sulphidization flotation method. It requires much higher
additions (i.e. up to 2000 g/t) to depress dolomite. Using Cataflot P39 (a modifying
agent developed by Pierrefitte-Abibu) showed excellent calcite depression at lower addi­
tion rates. The pilot plant results obtained on a Morrocan oxide copper ore (Table 19.3)
showed significant increase in copper recovery with the use of Cataflot 39 over that of
sodium silicate.
Other depressants examined included polysaccharides, polyacrylamides, polyphosphates
and carboxymethylcellulose. None of these depressants are found in industrial application.
Choice of collectors
As mentioned earlier in this chapter, the choice of collector is very much dependent on the
type of copper minerals, as well as the type of gangue minerals present in the natural ore. If
the ore contains siliceous gangue minerals, then various fatty acid modifications can be
used as the principal collector in plant practice. Ores containing carbonaceous and dolo­
mitic gangue minerals, where sulphidization method is used, xanthate collector is used as
56
19.
Flotation of Oxide Copper and Copper Cobalt Ores
Table 19.2
Effect of AQ depressants on oxide copper results
Depressant
No depressant
650 g/t Na2SiO3
650 g/t AQ2
650 g/t AQ3
Product
Weight (%)
Copper cleaner concentrate
Copper combined tail
Head (calc)
Copper cleaner concentrate
Copper combined tail
Head (calc)
Copper cleaner concentrate
Copper combined tail
Head (calc)
Copper cleaner concentrate
Copper combined tail
Head (calc)
13.92
86.08
100.00
12.49
87.51
100.00
14.50
85.50
100.00
17.58
82.42
100.00
Assays (%)
% Distribution
CuT
CoT
CuT
CoT
23.98
1.73
4.67
28.30
1.47
4.82
27.02
0.81
4.61
26.42
0.71
5.23
–
–
–
1.74
0.21
0.40
1.55
0.18
0.37
1.96
0.20
0.51
71.5
28.5
100.0
73.3
26.7
100.0
85.0
15.0
100.0
88.8
11.2
100.0
–
–
–
54.2
45.8
100.0
59.4
40.6
100.0
67.6
32.4
100.0
Table 19.3
Effect of Cataflot 29 on oxide copper flotation
Depressant
Head (% Cu)
Tail (% Cu)
Concentrate (% Cu)
Recovery (% Cu)
Na2SiO3
Cataflot P39
2.16
2.15
0.38
0.29
34.5
35.0
82.5
87.8
the primary collector. Mercaptan and/or dithiophosphates are used as secondary collectors,
when the ore contains cobalt minerals.
The fatty-acid-based collectors have been employed for the past 60 years for flotation of
oxide copper/cobalt minerals from Congo, a company formerly owned by Union Minera
(Belgium).
The fatty acid modification was used in operating plants at Kolwezi, Koumbore and
Kakanda. The fatty acid used was hydrolysed palm oil prepared as a mixture consisting of
75% hydrolysed palm oil/21% gas oil/4% Unitol.
This mixture is passed through a colloidal mill in the presence of 0.5% soda ash solution.
The fatty acid prepared in this manner does not produce voluminous froth and is more
selective than ordinary fatty acid mixtures. Experimental laboratory testwork conducted on
the Kolwezi siliceous ore [18] with the above-mentioned mixture, with different degrees of
dispersion showed substantial differences in metallurgical results (Table 19.4). Poor results
were achieved when there was no dispersion of the mixture. The best results were obtained
when the mixture was treated for 10 min in an ultrasonic mixer. In each case, the mixture
was dissolved in a 0.5% soda ash solution.
19.5
Flotation Practice in Beneficiation of Oxide Copper Minerals
57
Table 19.4
Effect of degree of fatty acid mixture dispersion on Cu/Co flotation from siliceous Kolwezi open
pit ore – laboratory-locked cycle tests
Ultrasonic mixture pretreatment
time (min)
0
5
10
Head assays
(%)
Tailing
assays (%)
Concentrate
assays (%)
% Recovery
Cu
Co
Cu
Co
Cu
Co
Cu
Co
4.50
4.60
4.61
0.60
0.59
0.60
1.50
1.35
0.85
0.47
0.31
0.19
20.1
23.3
25.2
1.28
2.20
2.65
72.0
75.1
84.3
34.5
55.2
68.1
Xanthated fatty acid mixture is a new line of collectors, specifically designed for
beneficiation of oxide copper ores that contain dolomitic and carbonaceous gangue miner­
als [19]. This collector was developed after extensive laboratory development testwork.
The effectiveness of this collector was compared to a standard xanthate collector in a series
of continuous locked cycle tests (Table 19.5).
Using TY3 collector improved the copper recovery by 10%, while the cobalt recovery
remained unchanged. The consumption of sulphidizer in the presence of TY3 was sig­
nificantly reduced.
Based on the encouraging results obtained from laboratory testing, a plant test was
conducted at the Kolwezi concentrator, during which a number of important factors in
preparation of the fatty acid xanthate emulsion were discovered, some of which included:
• High-power mixture for emulsion preparation was required to obtain a stable emulsion
of fatty acid and xanthate mixture.
• The collector emulsion was more stable when using potassium xanthate instead of
sodium xanthate.
Table 19.5
Comparison of results using xanthate and TY3 collector using dolomitic oxide Cu/Co ores
Test conditions
Plant
SNBX
3300 g/t NaHS
Laboratory-locked cycle
SNBX
2600 g/t NaHS
Laboratory-locked cycle
TY3 collector
1990 g/t NaHS
Product
Copper concentrate
Copper combined tail
Head (calc)
Copper concentrate
Copper combined tail
Head (calc)
Copper concentrate
Copper combined tail
Head (calc)
Weight (%)
13.01
86.97
100.00
11.96
88.04
100.00
16.76
83.24
100.00
Assays (%)
% Distribution
Cu
Co
Cu
Co
31.84
1.68
5.61
32.57
2.13
5.77
28.96
1.03
5.71
–
–
–
1.34
0.12
0.27
0.97
0.12
0.26
74.0
26.0
100.0
67.5
32.5
100.0
85.0
15.0
100.0
–
–
–
60.3
39.7
100.0
60.0
40.0
100.0
58
19.
Flotation of Oxide Copper and Copper Cobalt Ores
Table 19.6
Average plant results obtained with TY collector – 30-day plant test
Collector
TY3
SNBX
Product
Weight (%)
Copper concentrate
Final tailing
Head (calc)
Copper concentrate
Final tailing
Head (calc)
Assays (%)
14.27
85.73
100.00
13.80
86.20
100.00
% Distribution
Cu
Co
Cu
Co
23.73
0.82
4.09
22.94
1.14
4.15
2.23
0.21
0.50
2.04
0.20
0.45
83.0
17.0
100.0
76.3
23.7
100.0
64.0
36.0
100.0
62.5
37.5
100.0
The plant trial emulsion consisted of 70% amyl xanthate, 20% hydrolysed palm oil and
10% fuel oil. The average results obtained in the plant are compared in Table 19.6.
A significant improvement in copper recovery was realized with the use of the TY3 collector
in the Kolwezi plant. Nowadays, TY3 is used in a number of operating plants in Africa.
Collectors from the PM series are a mixture of xanthate/mercaptans, modified with esters
or surfactants, specifically developed for flotation of mixed copper oxide ores and copper
cobalt oxide ores. There are several collectors from the PM series, including PM230,
PM250 and PM270. Experimental laboratory work was conducted on the mixed copper
oxide sulphide ores from the Komoto plant in Chile using collectors from the PM series
[20]. The effect of these collectors on copper grade–recovery relationship is illustrated in
Figure 19.7. The results indicated that both grade and recovery can be significantly
improved, compared to the results obtained with xanthate.
100
MM 290
210 g/t
PM 250
200 g/t
Na amyl
xanthate
250 g/t
Copper recovery (%)
90
80
Collector
Type
70
60
50
5
10
15
20
25
30
35
40
Copper concentrate grade (%)
Figure 19.7
Effect of collectors from the PM series on the copper grade–recovery relationship.
19.6
Industrial Practice in Flotation of Oxide Copper and Copper-Cobalt Ores
19.6
59
INDUSTRIAL PRACTICE IN FLOTATION OF OXIDE COPPER AND
COPPER-COBALT ORES
Most operating plants that treat oxide copper and copper-cobalt ores are found in Central
Africa and Southern Africa regions. A few operations exist in Chile, Brazil and Peru, where
they treat mixed oxide sulphide ores or oxide copper gold ore.
In general, the reagent schemes used in these plants depend largely on the type of ore
being treated. The following sections describe the operating practices of the major plants
that treat oxide and mixed oxide sulphide copper ores.
19.6.1
Kolwezi concentrator (Kongo) – Oxide siliceous ore
For many years this plant has treated an oxide siliceous ore using the hydrolysed palm oil
mixture. The palm oil–fuel oil mixture is heated to about 60°C in the presence of soda ash
and then passed through a colloidal mill before it is added to the copper conditioner. A
typical reagent scheme used to treat the Kolwezi siliceous ore is shown in Table 19.7. The
soda ash and sodium silicate are added to the grinding mills and the palm oil emulsion to
the copper conditioner.
The addition of soda ash is quite important, as the water used in the plant contains an
appreciable amount of calcium and magnesium, where the soda ash acts as a water softener.
The flowsheet used in this plant (Figure 19.8) consists of a rod mill–ball mill grinding
system and a copper rougher–scavenger flotation circuit, followed by two cleaning stages.
Initially, the plant used a rake classifier, but now the rake classifiers have been replaced by
cyclones.
One of the main problems associated with beneficiation of the Kolwezi siliceous ore is
the production of malachite and pseudomalachte slimes that have a relatively low flotation
rate. Most of the copper losses occurring in the plant are in the –15 µm fraction. Experi­
mental testwork conducted with a different palm oil emulsifier indicated that copper
recovery from the fine fraction can be significantly improved with the use of petroleum
sulphonate (Petrosol 845) as the emulsifier [21] for palm oil. Significant improvement in
copper recovery was realized in the fine fractions with the use of palm oil emulsified with
Petrosol 845.
Table 19.7
Reagent scheme used to treat the Kolwezi siliceous ore
Reagent
Depressants and modifiers
Soda ash
Sodium silicate
Collectors and frothers
Palm oil emulsion
Pine oil
Additions (g/t)
Grinding
Copper flotation
1500–2000
800–1200
–
–
–
–
–
–
2000–2500
30–40
60
19.
Flotation of Oxide Copper and Copper Cobalt Ores
Ore feed
Rod
mill
Ball
mill
u/f
Cyclones
o/f
Conditioning
Copper
rougher 1
Slimes
Copper
rougher 2
Cyclones
Sand
Copper
scalper
Tail
Copper
cleaner
Combined
tailings
Copper
recleaner
Copper cleaner
concentrate
Figure 19.8
Typical flowsheet used in treatment of dolomitic oxide ores.
Other plants that treat siliceous copper oxide ores include Panda and Kabolela
plants from the same area. The gangue in this ore is composed of argillaceous and
siliceous schist. Both plants essentially use the same flowsheet and reagent scheme, as
that described for the Kolwezi plant. Typical plant results during treatment of a
siliceous ore are presented in Table 19.8. These are average results achieved from
1980 to 1982.
19.6
Industrial Practice in Flotation of Oxide Copper and Copper-Cobalt Ores
61
Table 19.8
Kolwezi plant results during treatment of the siliceous ore
Product
Weight (%)
Copper concentrate
Copper tailing
Head (calc)
19.6.2
13.26
86.72
100.00
Assays (%)
% Distribution
Cu
Co
Cu
Co
26.65
1.00
4.40
2.51
0.25
0.55
80.3
19.7
100.0
60.3
39.7
100.0
Industrial practice in beneficiation of dolomitic oxide ores
Industrial plants that treat dolomitic ores include the Kolwezi concentrator (Kongo) and the
Nchanga concentrator (Zambia), along with several smaller plants in the Kolwezi district.
The reagent scheme generally used in these concentrators is presented in Table 19.9.
Sodium silicate is used as the common depressant, and also acts as a dispersant together
with the soda ash. In the majority of operating plants, Na2S · 9H2O is used as the principal
activator. Some operating plants in Zambia use NaHS as a sulphidizer. Sodium or potassium
xanthates are the principal collectors used, where mercaptans are used as secondary collectors.
In the 1980s, a new collector (i.e. fatty acid-modified xanthate) was introduced into the
Kolwezi concentrator with significant improvement in copper recovery. In 1995, collectors
from the PM series were tested in the Nchanga concentrate improving results. The plant
results obtained in the Kolwezi concentrate using xanthate and TY3 are compared in
Table 19.10. Collector TY3 also had a positive effect on cobalt recovery.
The flowsheet used to treat dolomitic oxide copper ores is somewhat different from that
used in the beneficiation of siliceous oxide copper ores. This is due to the fact that
dolomitic ore usually contains elevated amounts of slimes, in which case a split circuit
flowsheet has been adopted in a number of operations. The typical flowsheet used for
treatment of dolomitic ores is shown in Figure 19.8. Usually, the scavenger tailings are
deslimed and the sand fraction is retreated in a scalp copper flotation stage. When the ore is
deslimed before flotation, a large amount of fine copper is lost in the slime fraction.
Table 19.9
Reagent scheme used to treat dolomitic ores
Addition rate (g/t)
Depressants and modifiers
Activators
Collectors
500–1000 g/t Na2SiO3
Na2CO3 to pH 8–9.5
100–200 Guar
1500–300 Na2S
1200–3000 NaHS
150–300 xanthate
50–80 mercaptan
150–200 TY3
100–200 PM290
62
19.
Flotation of Oxide Copper and Copper Cobalt Ores
Table 19.10
Kolwezi plant results using xanthate and TY3 (1980–1982)
Collector
320 g/t SIPX
280 g/t TY3
Product
Copper concentrate
Copper tailing
Head (calc)
Copper concentrate
Copper tailing
Head (calc)
Weight (%)
15.57
84.43
100.00
12.56
87.44
100.00
% Distribution
Assays (%)
Cu
Co
Cu
Co
24.6
1.03
3.70
25.1
0.76
3.82
1.4
0.24
0.42
2.4
0.20
0.48
76.5
23.5
100.0
82.5
17.5
100.0
51.9
48.1
100.0
62.8
37.2
100.0
SIPX, sodium isopropyl xanthate.
19.7 INDUSTRIAL PRACTICE IN BENEFICIATION OF MIXED SULPHIDE
OXIDE ORES
The mixed sulphide oxide ores usually contain two or more oxide minerals, including
cuprite, malachite and tenanntite. The sulphide copper minerals are represented by covellite
and bornite. Examples of this type of operation are located in the former Republic of Zaire
(Komoto, Dima 1 and 2 plants), and the Nchanga open pit plant in Zambia.
In general, this ore type is treated using two distinct circuits: sulphide copper flotation
followed by oxide copper flotation, manly using the sulphidization method.
The basic reagent scheme used in the concentrators varies and is dependent on the type
of copper minerals present in the ore, and the mineral composition of the gangue. The
reagent scheme used in the three main concentrators treating this ore type is presented in
Table 19.11.
There are only slight differences in the reagent schemes used to treat the mixed sulphide
oxide ores. The type of sulphidizier and collectors are the main variance in the reagent
Table 19.11
Reagent schemes used in beneficiation of mixed sulphide oxide ores
Concentrator
Reagent consumption (g/t)
Sulphide circuit
Komoto, Kongo Na2SiO3 = 300, CaO = 460
Ethyl xanthate = 100, frother 41G = 15
Dima, Kongo
Na2SiO3 = 200, Na2CO3 = 300
K-amyl xanthate = 60, frother 41G = 10
Nchanga,
PM290 = 15, Na-amyl xanthate = 30
Zambia
Pine oil = 10
Oxide circuit
Na2CO3 = 200, NaHS = 1350, fuel oil = 50
K-amyl xanthate = 210, frother 41G = 20
Na2SiO3 = 600, NaHS = 3000
Mineral oil = 90, frother 41G = 15
Na2CO3 = 300, Na2S = 1200, PM290 = 40
Na-amyl xanthate = 100, kerosene = 100
19.7
Industrial Practice in Beneficiation of Mixed Sulphide Oxide Ores
63
Ore feed
Rod
mill
Ball
mill
u/f
Cyclones
o/f
Copper sulphide
rougher
Copper sulphide
cleaner
Conditioning
Copper oxide
rougher
Copper sulphide
re-cleaner
Copper oxide
1st cleaner
Copper sulphide
cleaner concentrate
Copper oxide
2nd cleaner
Copper oxide
scavenger
Tail
Copper oxide
cleaner concentrate
Figure 19.9
Typical flowsheet used in treatment of mixed sulphide oxide ores.
schemes used. The generalized flowsheet used for treatment of mixed sulphide ores is
shown in Figure 19.9. Some operations use semi-autogenous mills for primary grinding
(Komoto, Dima) with grind finenesses ranging from 55% to 60% minus 200 mesh.
The plant metallurgical results achieved in these concentrators are presented in
Table 19.12. In most cases, the results obtained on mixed copper sulphide oxide ores are
better than those obtained on oxide ores. The floatability of oxide copper from mixed ore is
usually better than the floatability of copper from oxide ores.
An appreciable amount of the cobalt in these ores is represented by sulphide cobalt
minerals, mainly carrolite.
64
19.
Flotation of Oxide Copper and Copper Cobalt Ores
Table 19.12
Plant results from mixed copper sulphide oxide ores
Concentrator
Komoto (1,2)
Congo, Africa
Dima
Kongo, Africa
Nchanga
ZCCM, Zambia
Product
Weight (%)
Cu sulphide concentrate
Cu oxide concentrate
Cu flotation tail
Head (calc)
Cu sulphide concentrate
Cu oxide concentrate
Cu flotation tail
Head (calc)
Cu sulphide concentrate
Cu oxide concentrate
Cu flotation tail
Head (calc)
7.11
2.57
90.32
100.00
2.78
8.59
88.63
100.00
1.82
3.53
94.65
100.00
Assays (%)
% Distribution
Cu
Co
Cu
Co
43.6
22.0
0.93
4.50
55.31
21.24
0.82
4.09
47.5
37.0
0.72
2.80
3.61
1.52
0.06
0.35
2.23
1.58
0.16
0.34
–
–
–
–
68.83
12.55
18.62
100.0
37.65
44.64
17.71
100.0
30.3
45.8
23.9
100.0
74.26
11.30
14.44
100.0
18.24
39.84
41.92
100.0
–
–
–
–
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