TP 1906
Trans. Indian Inst. Met.
Vol.57, No. 5, October 2004, pp. 485-490
BIOFLOTATION OF THE LOW GRADE
SARCHESHMEH COPPER SULFIDE
M. Kolahdoozan1, S.M Tabatabaei Yazdi2 , W.T.Yen3, R. Hosseini Tabatabaei4,
A.R Shahverdi2, M. Oliazadeh1, M. Noaparast1, A. Eslami5, Z. Manafi5
1 Dept. of Mining Eng., University of Tehran, Tehran, 11365, Iran.
2 Dept. of Biotech., Tehran Medical Sciences University, Tehran, 11365, Iran.
3 Dept. of Mining Eng., Queen’s University, Kingston, Ontario, Canada, K7l 3N6.
4 M.Sc Graduate, Dept. of Mining Eng., University of Tehran, Tehran, 11365, Iran.
5 Mineral Processing Expert, Sarcheshmeh R & D Division, Sarcheshmeh, Kerman.
Email: [email protected]
(Received 10 March 2004 ; in revised form 29 June 2004)
ABSTRACT
Application of Thiobacillus ferrooxidans bacteria in the flotation of Sarcheshmeh low-grade sulfide copper ore
was studied. Sarcheshmeh low-grade ore contains pyrite that cause some problems in flotation process of
copper minerals. In this study, pure strain of T.Ferrooxidans was used to bring about surface chemical changes
of pyrite and sulfide copper ores, and consequently their flotation behavior. In presence of Thiobacillus
ferrooxidans and xanthate as collector, pyrite was depressed whereas chalcopyrite and other sulfide minerals
were unaffected. Also the pulp pH remained unchanged. It was shown that the surface chemical properties of
bacteria can be manipulated successfully to achieve desired effects in flotation process. The results showed that
recovery of pyrite in the presence of bio-depressant is 50% lower than the time when no bacteria applied. At
the same time recovery of chalcopyrite was not affected.
1. INTRODUCTION
Thiobacillus ferrooxidans is a gram negative,
chemolithotrophic bacteria that grows in acidic
drainage water of mines 1. It’s ability to oxidize
Fe+2 to Fe+3 ions and elemental sulphur in acidic
solution is well established.
Although, bioleaching of low-grade ores is being
practiced for a long time, application of bacteria to
flotation is relatively new and few studies have been
reported 2-7.
Sarcheshmeh copper deposit is the major producer
of copper and molybdenum of the country located in
south eastern Iran, 160 km from the city of Kerman.
Pyrite is the main gangue mineral and for long it has
been depressed by lime while floating copper. In
present work, an attempt was made to use
chemolithotrophic bacteria such as Thiobacillus
ferrooxidans as a depressant for pyrite in flotation of
Sarcheshmeh copper ore. The growth kinetics of
Thiobacillus ferrooxidans is slow and its fully-grown
culture can be achieved after 48 hours. The bacterium
surface properties depend on the growth
conditions 3,7,8. The chemical components of bacterial
surface play an important role in its adhesion on the
mineral surface 7. Since flotation is dependent on
the surface properties of minerals, any changes in
this property can introduce direct effects on the whole
process of bacteria application.
2. EXPERIMENTAL
2.1 Materials and Methods
A representative sample of low-grade sulfide copper
ore, pure pyrite and chalcopyrite from Sarcheshmeh
were collected and used in this study. Table 1 shows
the chemical composition of the sample. Also sodium
TRANS. INDIAN INST. MET., VOL. 57, NO. 5, OCTOBER 2004
isopropyl xanthate (Z 11 ) and Methyl Isobutyl
Carbonyl (MIBC) were used as the collector and
frother respectively.
2.1.1 Bacterial strain & adaptation
A pure strain of Thiobacillus ferrooxidans isolated
from acidic water drainage of Sarcheshmeh mine
was used in this study. Thiobacillus ferrooxidans
was cultured and maintained in 9k medium (3g/l
(NH4)2SO4, 0.5g/l MgSO4.7H2O, 0.5g/l K2HPO4,
0.1g/l KCl and pH 1.9) given by Silverman and
Lundgren. A 10% active cell culture was added to
the medium and incubated in rotary shaker at 150rpm
and 320C. The cells were harvested from the culture
just at the beginning of the stationary phase of their
growth. Cell 5 grown in the presence of ferrous ions
and elemental sulfur, were filtered through Whatman
filter paper to remove cells from the suspended solid
material. The liquid containing the cells then filtered
through biological filter paper and washed twice with
acidic water (pH of 1.9). During tests, cells were
counted by Petroff-Hauser counter as this method is
comparatively quick and convenient.
2.1.2 Adhesion experiments
Adhesion experiments were carried out on all three
samples (low-grade sulfide copper ore, pyrite and
chalcopyrite). In this case 0.5g of each sample was
added to 2ml cell suspension (0.5-3.5 *107 cells/
ml). The suspension was then shaken for 1 min with
a vortex shaker and allowed to settle for 5 min. At
that point, the optical density of the supernatant was
measured to determine the cell density. The number
of adherent cells was determined by subtracting in
the number of cells in the supernatant from the
number initially added.
2.1.3 Determining Parameters of Bioflotation
In bioflotation process, there are important parameters
that should be determined carefully before doing
any bioflotation tests. These parameters are as
follows:
z
Degree of grinding of minerals
z
Dosage of collector
z
Retention time in conditioning stage
z
Speed of rotation in conditioning stage
One of the important stages in bioflotation process
is its conditioning stage. In this stage mineral sample
first conditioned with predetermined bacteria that
time of conditioning and speed of rotation should be
determined carefully.
2.1.4 Flotation tests
The flotation tests were carried out in 2.5-liter Denver
laboratory cells. 820g of low-grade sulfide copper
ore sample was used in each test. The mineral sample
was first conditioned with predetermined bacteria
for 15 min and then the collector and frother were
added and conditioned for 5 min after which floated
for 6 min. The effect of initial cell concentration on
the flotation of low-grade sulfide copper ore was
examined. Tests were carried out in two different
dosage of collector and some tests were also
performed in the absence of bacteria and without
any depressant. All tests were performed at natural
pH.
3. RESULTS AND DISCUSSION
3.1 Adhesion of Thiobacillus ferrooxidans to sulfide
minerals
In case of low-grade sulfide copper ore and pyrite
mineral samples Thiobacillus ferrooxidans adhesion
increased with the number of cells added, although
there were significant differences in the affinity of
the bacteria for the samples (Fig. 1). By far the
largest number of cells adhered to pyrite. The results
showed that when Thiobacillus ferrooxidans cells
were added to pyrite, adhesion increased almost
linearly and in the case of low-grade copper sample
Table 1
CHEMICAL COMPOSITION OF SAMPLE
Element Cu(Total)(%)
Sample
1.01
CuO(%)
Fe (%)
SiO2 (%)
S (%)
Al2O3 (%)
Mo (%)
0.13
9.00
59.34
5.86
16.22
0.017
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KOLAHDOOZAN, et.al., : BIOFLOTATION OF THE LOW GRADE SARCHESHMEH COPPER SULFIDE
Fig. 1 : Number of cells adhering to 0.5 g of each sample
the trend was almost the same. However in the case
of chalcopyrite the adherent cells were not increased
and it did not show any dependence on the number
of cells adhered. It is concluded that bacteria cells
do not attach on the surface of copper ore.
3.2 Flotation Parameters
Results, shown in Fig. 2, demonstrate that the finer
the sample, the more will be the degree of attachment
of bacteria on the surface of pyrite. However as the
slime will also be increased it produces some
problems in flotation. The optimized grinding
condition was evaluated as 70 percent -200 mesh
size.
3.2.1 Grinding
3.2.2 Collector Dosage
To optimize this parameter low-grade copper sulfide
ore samples were grind in different percentage of
ore less than 200 mesh (65–85 %< 200 mesh).
Results are shown in Fig. 3. Different collector
dosages (50-300 gram per ton) were examined and
the optimum condition achieved at 150 gram per
Fig. 2 : The effect of grinding on the recovery of Cu & Fe
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TRANS. INDIAN INST. MET., VOL. 57, NO. 5, OCTOBER 2004
Fig. 3 : The effect of collector dosage on recovery of Cu & Fe
tons which presented the highest recover for copper.
However with increasing the dosage of collector
beyond this point the recovery dropped as a result
of hemi micelle formation.
3.2.3 Retention Time and Rotation Speed in
Conditioning Stage
Results are shown in Figs. 4 and 5. These two
parameters are quiet important in bioflotation and
should be determined accurately. Results demonstrate
that with increasing the retention time and speed of
rotation from adequate point in conditioning stage
the bacteria can not depress pyrite and recovery of
pyrite were increased since it destroys bacteria’s
wall and increases shear stress (in increasing speed
of rotation). Results show that these parameters play
a vital role in bioflotation that even their little
fluctuations cause considerable consequences in
outcome of the operation.
3.2.4
Flotation results
The flotation results obtained by using increasing
cell concentrations of ferrous and sulfur grown
Thiobacillus ferrooxidans at two different xanthate
concentrations. Results are shown Figs. 6 and 7.
Fig. 4 : The effect of retention time in conditioning stage on the recovery of Cu and Fe
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KOLAHDOOZAN, et.al., : BIOFLOTATION OF THE LOW GRADE SARCHESHMEH COPPER SULFIDE
Fig. 5 : The effect of rotation speed in conditioning stage on the recovery of Cu and Fe
Fig. 6 : The effect of collector concentration on the recovery of Fe. In presence of sulfur & ferrous grown Thiobacillus
ferrooxidans
Fig 7 : The effect of collector concentration on the recovery of Cu. In presence of sulfur & ferrous grown Thiobacillus
ferrooxidans
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These figures show the recovery of Fe and Cu
respectively. For this sample, flotation recoveries of
Cu and Fe at higher xanthate concentration (200
gram per ton) were 62% and 65% respectively
compared to 55% and 64% at lower xanthate dosage
(100 gram per ton). The preconditioning of minerals
with bacterial cells prior to the addition of collector
reduced the floatability of pyrite, but it did not affect
the floatability of copper minerals. The sulfur grown
cells, depressed more pyrite compared to the ferrous
ion grown cells. The ferrous grown cells decreased
the pyrite recovery at two different collector
concentrations (200 and 100 gram per tons) from
65% to 40% and 42% but in sulfur grown cells the
drop in recovery of pyrite was higher. Results
demonstrated that recovery of copper minerals is not
a function of their growth conditions i.e. bacterial
cells do not attach on the surface of copper therefore
do not have any depressing effect on copper minerals
(Fig. 7).
can be adsorbed on the surface of sulfide copper
minerals promoting hydrophobicity.
5. ACKNOWLEDGMENTS
This work was conducted under financial support of
Research and Development Division of Sarcheshmeh
copper complex as well as The Research Department
of the University of Tehran, Faculty of Engineering.
Authors wish to express their sincere appreciations.
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4. CONCLUSIONS
It was shown that the selective flotation of copper
sulfides from pyrite is possible by interaction of
minerals with both ferrous and sulfur grown
Thiobacillus ferrooxidans. Thiobacillus ferrooxidans
bacteria do not have any motion for adhering to
chalcopyrite. However it could selectively adhere to
pyrite surface hindering its floatability and therefore
Thiobacillus ferrooxidans can be used as a depressant
for pyrite during the flotation of copper sulfides.
This is because bacterial cells obtain their energy by
oxidizing iron ion and elemental sulfide and therefore
the cells might have strongly adsorbed on pyrite
surface and xanthate could not replace the adsorbed
cells. However in the case of chalcopyrite, the copper
ions are toxic to the cells and bacteria do not adhere
on the mineral surface. Therefore collector species
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