Minerals Engineering 18 (2005) 371–374
Technical note
This article is also available online at: www.elsevier.com/locate/mineng
Bioflotation of Sarcheshmeh copper ore using Thiobacillus Ferrooxidans bacteria T.R. Hosseini a, M. Kolahdoozan a, Y.S.M. Tabatabaei b, M. Oliazadeh a, M. Noaparast a, A. Eslami c, Z. Manafi c, A. Alfantazi d,* a Department of Mining Engineering, Tehran University, Tehran 11365, Iran Department of Biotechnology, Tehran Medical Sciences University, Tehran 11365, Iran c R&D Division––Sarcheshmeh Copper Complex of Iran, Iran Department of Metals and Materials Engineering, The University of British Colombia, Vancouver BC, Canada V6T 1Z4 b
d
Received 30 September 2003; accepted 10 June 2004
Available online Abstract Thiobacillus Ferrooxidans bacteria are commonly used for bio-leaching and recently in biobeneficiation of sulfide minerals. In this study, the effect of Thiobacillus Ferrooxidans on the froth flotation behavior of Sarcheshmeh copper ore in Iran has been investigated. Pure strains of Thiobacillus Ferrooxidans were used to promote surface chemical changes in pyrite and chalcopyrite, and thus influence their flotation behavior. In the presence of Thiobacillus Ferrooxidans, and xanthate as collector, pyrite was depressed, whereas chalcopyrite and other sulfide minerals were unaffected at natural pH. The present investigation shows that the surface chemical properties of bacteria can be manipulated successfully to achieve the desired effects on the flotation process. The results showed that recovery of pyrite in the presence of a depressant (Thiobacillus Ferrooxidans) is 50% lower than in the absence of any bacteria, demonstrating the depressing effect of bacteria on pyrite. It was concluded that the use of Thiobacillus Ferrooxidans would decrease the recovery of pyrite but would not changed the floatability of chalcopyrite. 2004 Elsevier Ltd. All rights reserved Keywords: Biotechnology; Froth flotation; Non-ferrous metallic ores
1. Introduction Thiobacillus Ferrooxidans is a gram negative, chemolithotrophic bacteria. Its ability to oxidize Feþ2 to Feþ3 ions and elemental sulfur in acidic solution is well known. Although bioleaching of low-grade ores is a well established application of bacteria in mineral processing, the use of bacteria in flotation is relatively new and few studies have been reported in the literature so far (Sharma et al., 1999; Nagaoka et al., 1999; Kawatra and Eisele, 1999; Somasundaran et al., 2000; Devasia et al., 1993; Bryner et al., 1996). In the present work, an attempt was made to use chemolithotrophic bacteria, namely Thiobacillus Ferrooxidans, as a pyrite depressant in the flotation of Sarcheshmeh copper ore. Since chemolithotrophs derive
energy by dissolving sulfide minerals, this could change mineral surface properties. The growth kinetics of T. Ferrooxidans are slow, and a fully-grown culture of T. Ferrooxidans can be obtained after about 48 h, the bacterium surface properties depending on the growth conditions (Nagaoka et al., 1999; Bryner et al., 1996; Lyalikova and Lyubavina, 1986). The chemical components of the bacterial surface play an important role in adhesion behavior (Bryner et al., 1996). Since flotation depends largely on the chemical properties of mineral surfaces, any changes in the surface chemistry could affect the flotation process.
2. Experimental 2.1. Materials and methods
* Corresponding author. Tel.: +1-604-822-8745; fax: +1-604-8223619. E-mail address:
[email protected] (A. Alfantazi).
0892-6875/$ - see front matter 2004 Elsevier Ltd. All rights reserved doi:10.1016/j.mineng.2004.06.005
Two samples of porphyry copper ore, one sample each of pure pyrite and chalcopyrite from Sarcheshmeh
372
T.R. Hosseini et al. / Minerals Engineering 18 (2005) 371–374
Table 1 Chemical analysis of the two sulfide copper samples Elements
CuT
CuO
Fe
SiO2
S
Al2 O3
Mo
Sample A Sample B
1.5 1.01
0.16 0.13
4.54 9.00
60.92 59.34
4.00 5.86
14.94 16.22
0.029 0.017
mine, in the southern part of Iran, were used in this study (samples A and B). Table 1 shows the chemical analysis of the two sulfide copper samples. The collector sodium isopropyl xanthate (Z11 ) and frother methyl–isobotyl carbonyl (MIBC) used at Sarcheshmeh, were from the Dow Company. All other reagents were obtained from Merck-Schuchardt.
Tests were carried out with two different dosages of collector and some tests were also performed in the absence of both bacteria and depressant. All tests were conducted at the natural pH of the respective minerals.
2.2. Bacterial strain and adaptation
3.1. Adhesion of T. Ferrooxidans to sulfide minerals
A pure strain of T. Ferrooxidans, which was isolated from the acidic water drainage of Sarcheshmeh mine, was used in this study. T. Ferrooxidans was cultured and maintained in 9 k medium (3 g/l (NH4 )2 SO4 , 0.5 g/l MgSO4 Æ 7H2 O, 0.5 g/l K2 HPO4 , 0.1 g/l KCl and pH of 1.9) (Silverman and Lundgren, 1959). A 10% active cell culture was added to the medium and incubated in a rotary shaker at 150 rpm at 32 C. The cells were harvested from the culture at the beginning of the stationary phase of their growth. Cells grown in ferrous and elemental sulfur were filtered through Whatman filter paper to remove the suspended solid material. The liquid containing the cells was then filtered through biological filter paper and washed twice with acidic water (pH 1.9). During the tests, the cells were counted using a Petroff-Hauser counter, this method being rapid and convenient.
In all samples except chalocopyrite, T. 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, followed in descending order by sample B, A and chalcopyrite. The results showed that when T. Ferrooxidans cells were added to pyrite, adhesion increased almost linearly, in the case of samples B and A the trend was almost the same, but with the chalcopyrite sample the adherent cells were not increased and did not depend on the number of cells adhered. This proved that T. Ferrooxidans bacteria do not have any motion for adhering to sulfide copper minerals, although it was evident from the results that T. Ferrooxidans selectively adhered to pyrite.
2.3. Adhesion experiment
The flotation results, using ferrous and sulfur grown T. Ferrooxidans, with increasing cell concentration and at two different xanthate concentrations are shown in Fig. 2a and b for sample A, Fig. 3a and b for sample B
Adhesion experiments were carried out on all four samples (A, B, pyrite, chalcopyrite). In each case 0.5 g of sample was added to 2 ml cell suspension (0.5–3.5 · 107 cells/ml). The suspension was then shaken for 1 min by a vortex shaker and allowed to settle for 5 min. The optical density of the supernatant was then measured to determine the cell density. The number of adherent cells was determined by subtracting the number of cells in the supernatant from the number initially added.
3. Results and discussion
3.2. Flotation results
2.4. Flotation tests The mineral flotation tests were carried out in 2.5-l Denver laboratory flotation cell, using 820 g of mineral samples. The mineral samples were first conditioned with predetermined bacteria for 15 min and then the collector and MIBC were added and conditioned for 5 min and floated for 6 min. The influence of initial cell concentration on the flotation of sulfides was examined.
Fig. 1. Number of cells adhering to 0.5 g of each ore and mineral sample as a function of added cells.
T.R. Hosseini et al. / Minerals Engineering 18 (2005) 371–374
Fig. 2. Recovery Fe (a) and Cu (b) from ore sample A in the presence of ferrous (Fe) and sulfur (S) grown T. Ferrooxidans (TF) at xanthate concentrations of 100 and 200 g/t.
Fig. 3. Recovery Fe (a) and Cu (b) of ore sample B in the presence of ferrous (Fe) and sulfur (S) grown T. Ferrooxidans (TF) at xanthate concentrations of 100 and 200 g/t.
and Fig. 4a and b for demonstrating differences between two samples. For sample A, flotation recoveries of Cu
373
Fig. 4. Recovery Fe (a) and Cu (b) of the two ore samples A and B in the presence of ferrous (Fe) and sulfur (S) grown T. Ferrooxidans (TF) at higher xanthate concentration (200 g/t).
and Fe at higher collector concentration (200 g/t) were respectively 80% and 70% compared to 40% and 80% recoveries at lower collector dosage (100 g/t) (Fig. 2a and b) and for sample B, the recoveries at higher xanthate dosage were respectively 62% and 65% compared to 55% and 64% at a lower xanthate concentration (Fig. 3a and b). The preconditioning of minerals with bacteria cells prior to the addition of collector reduced the floatability of pyrite, but did not affect the floatability of the sulfide copper minerals and their recoveries almost remained the same. The sulfur grown cells depressed the pyrite better compared to the ferrous ion grown cells. The ferrous grown cells reduced the pyrite recovery of sample A from 70% to 48% and sample B from 65% to 40%, but in sulfur elemental grown cells the decrease in recovery of pyrite was greater. The results demonstrated that the recovery of sulfide copper minerals, irrespective of their growth conditions, remains the same. Fig. 4a and b show the differences of two samples, these figures clearly demonstrating that the affect of T. Ferrooxidans bacteria as depressant of pyrite on two different samples is almost the same. Thus, T. Ferrooxidans bacteria can be used as a depressant for pyrite during sulfide copper flotation. Since bacterial cells obtain their energy by oxidizing iron
374
T.R. Hosseini et al. / Minerals Engineering 18 (2005) 371–374
ion and elemental sulfur, the cells might have strongly adsorbed on the pyrite surface and xanthate collector could not replace the adsorbed cells, but in the case of chalcopyrite, the copper ions are toxic to the cells and bacterial cells do not adhere on its surface, left unoccupied by cells, xanthate collector can be adsorbed on the surface of sulfide copper minerals and can be floated easily. Bioflotation process could be used for many sulfide minerals with different grades of pyrite, with no effect on the process.
4. Conclusions The surfaces of T. Ferrooxidans cells depend on their growth conditions. Since T. Ferrooxidans cells derive energy from the solid by adhering to and oxidizing Feþ2 to Feþ3 , the bacteria change the properties of the solid surfaces and thus their flotation behavior. This investigation showed that the selective flotation of sulfide copper minerals from pyrite is possible by interaction of the minerals with both ferrous and sulfur grown T. Ferrooxidans. The selective flotation of the sulfide copper from pyrite can be enhanced by sulfur grown T. Ferrooxidans bacteria. The study also showed that the bioflotation process is very flexible and can accommodate fluctuations in the grade of the feed without negatively impacting the flotation process.
Acknowledgements This work was conducted with the support of Research and Development Division of Sarcheshmeh Copper Complex. References Bryner, L.C., Beck, J.V., Davis, D.B., Wilson, D.G., 1996. International Engineering Chemistry 46, 2587. Devasia, P., Natarajan, K.A., Sathyanarayana, D.N., 1993. Surface chemistry of Thiobacillus Ferrooxidans relevant to adhesion on mineral surfaces. Applied Environmental Microbial Journal 59, 4051–4055. Kawatra, S.K., Eisele, T.C., 1999. Depression of pyrite by yeast and bacteria. Minerals and Metallurgical Processing 16 (4), 1–5. Lyalikova, N.N., Lyubavina, L.L., 1986. On the possibility of using a culture of Thiobacillus Ferrooxidans to separate antimony and mercuric sulfides during flotation. In: Lawrence, R.W., Branion, R.M.R., Ebner, H.B. (Eds.), Fundamental and Biohydrometallurgy. Elsevier, New York, pp. 403–406. Nagaoka, T., Ohmura, N., Saiki, H., 1999. A novel mineral flotation process using Thiobacillus Ferrooxidans. Applied Environmental Microbial Journal 65 (8), 3588–3593. Sharma, P.K., Hanumanth Rao, K., Nataraja, K.A., Forssberg, K.S.E., 1999. Bioflotation of sulphide minerals in the presence of heterotrophic and chemolithotrophic bacteria. Proceeding of the XXI International Mineral Processing Congress Flotation––Kinetics and Modeling B8a, 94–101. Somasundaran, P.K., Deo, N., Natarajan, K.A., 2000. Utility of bioreagents in mineral processing. Minerals and Metallurgical Processing 17 (2), 112–115.
