Investigations of attached and unattached cells during bioleaching of

chalcopyrite with Acidianus manzaensis at 65℃℃℃℃

H. Zhou *, L. Zhang, Y. Guo, J. Peng, M. Wei, J. Ding, G. Gu and G. Qiu

School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan Province, 410083, China; Tel: +86-731-8877216; Fax: 86-0731-8710804; Email:

zhouhb@mail.edu.cn

Keywords: attach, Acidianus manzaensis, passivating layer, cooperative action Abstract. For the purpose of investigations of the different situations when the cells of Acidianus manzaensis can or can not attach the surface of the chalcopyrite. Three experiments were carried out in the modified shake flasks, and in one of the experiments the cells could not attach the surface of the chalcopyrite, but could participate in the solution chemistry of the process. The redox potential, pH, cell density, copper, ion and thiosulfate concentration in the solution were monitored in the experiments, and the morphological feature and chemical composition of the leached residues were analyzed by SEM and XRD. The most leach effiency of Cu and Fe was reached in the experiment that the Acidianus manzaensis could attach the surface of the chalcopyrite. However, the unattached Acidianus manzaensis could also leach the chalcopyrite, but it was less actively than attached cells. There was no precipitation of jarosite in the leached residues of the three experiments, but there was sulfur in the leached residues when the cells could not attach the chalcopyrite. So the surface passivating layer of sulfur can be removed only when the Acidianus manzaensis can attach the surface of the chalcopyrite. From these results it become apparent that the leach of the chalcopyrite is the cooperative action of the attached and unattached Acidianus manzaensis.

Introduction

Chalcopyrite is both the most abundant and the most refractory of the copper sulfide, but it can be dissolved at convenient rates in the presence of thermophilic microorganisms such as Sulfolobus metallicus, Acidianus brierley or Metallosphera sedula [1].There is considerable interest today in applying themophiles to bioleach chalcopyrite in stirred tank reactors and in bioheap leaching. So it is important to do research on the themophiles. The Acidianus manzaensis used in the experiments is a novel thermoacidophilic Archaeo of Acidianus genus, firstly isolated from a fumarole in Manza by Naoki Yoshida [2] in 2006, which could survive under the temperature of 60-90℃ and pH 1.0-5.0. It is able to oxidize ferrous iron and sulfur compounds to obtain energy for growth, such energetic metabolism is responsible for metal solubilization [3].The traditional hypothesis, that bacteria oxidize sulfides by either a direct mechanism or an indirect mechanism, has evolved into a complex chemical/electrochemical/biochemical description of the interactions of baceria with sulfide minerals. It is proposed that the term “contact” leaching be used in place of “direct” leaching because it described the association of bacteria with a surface rather than the means of attack [4]. So it is important to do research on the attachment between the bacteria and the sulfide minerals. This paper is to investigate the different situations when the cells of Acidianus manzaensis can or can not attach the surface of the chalcopyrite.

Advanced Materials Research Vols. 71-73 (2009) pp 377-380Online available since 2009/May/19 at www.scientific.net© (2009) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.71-73.377

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 128.59.222.12, Columbia University Library, New York, USA-15/11/14,04:42:15)

Materials and Methods

Mineral.The pure chalcopyrite used in the experiments was passed through a sieve with a pore size of 75 µm, it contained 32.19% Cu, 32.33% Fe and 32.47% S. Bacterial Strain and Growth Conditions The pure strain of Acidianus manzaensis used in the experiments was isolated and conserved by our laboratory, and it was grown in medium 9K containing (NH4)2SO4: 3 g/L, MgSO4.7H2O: 0.5 g/L, K2HPO4: 0.5 g/L, KCl: 0.1 g/L, Ca (NO3)2: 0.01 g/L and Yeast Extract: 0.2 g/L with initial PH of 1.5 and 65℃. The inocula was obtained by centrifugation and washed twice in distilled water adjusted to 1.5 with sulfuric acid. The cells then were suspended in basal salts medium without energy sources. Experimental procedure The experiments were carried out in a modified shake flask. There were two parts of the flask, a big cylinder with a small cylinder in it. The end of the small cylinder was sealed with a 0.15µm millipore filter, which was immersed in the solution of the big cylinder. Chalcopyrite particles were contained in the big cylinder and microorganisms inoculated in the small cylinder participated in the solution chemistry of the process, but were prevented from reaching chalcopyrite surface during the leaching process. Flasks were maintained at 65℃ and shaken at 150rpm.There were 100 ml basal medium and 1 g chalcopyrite in the big cylinder, and there are 40 ml basal medium in the small cylinder. Redox potential and pH were measured daily, while the levels of copper and iron in solution were analyzed by atomic absorption spectrophotometry every 2 days. The cell density in solution was determined by direct microscope counting. Once the experiments were finished, the leached residues were filtered and dried using a freeze drier. The morphological feature and chemical composition of the leached residues were analyzed by SEM and XRD. The experiments were carried out under three different conditions: experiment (A)both of the cylinders were inoculated with Acidianus manzaensis ;experiment(B)only the small cylinder was inoculated with Acidianus manzaensis ;experiment(C)neither of the cylinders was inoculated.

Results and Discussion

The most leach effiency of Cu was reached in experiment (A) after 16 days leach.The leach effiency of Cu of experiment(B) was about 48% of the experiment(A),which was a little more than the leach effiency of Cu of experiment(C). So the unattached Acidianus manzaensis can also leach the chalcopyrite. In other words, the leach of the chalcopyrite is the cooperative action of the attached and unattached Acidianus manzaensis.

The solution pH of A and B increased to about 1.6 then started to decrease after 2 days, while the solution pH of C increased all the time to about 2.3. The Eh of A reached about 570 mV at the end of the experiments, and the Eh of B only reached about 480 mV, but the Eh of C decreased all the time. In experiment (A) the density of microorganisms in the small cylinder increased during the first 4 days, but in experiment (B) the density of microorganisms in the small cylinder decreased all the time. It indicated that the number of the unattached cells can increase only when some cells can attach the surface of the chalcopyrite.

SEM images of the leached residues are shown in Figure 1. From the figure (a) we can see that

378 Biohydrometallurgy 2009

the chalcopyrite was heavily etched in experiment (A), and there are lots of attachment of cells in the etched pits, but this could not be seen in experiment (B) and (C).From the figure (b) and (c) we can find an interesting thing that the surface is smooth and there are some cracks on it, this can not be seen in figure (a). It demonstrated that there was passivating layer on the surface of the leached residues of the experiment (B) and (C), it may be sulfur or jarosite. This can be clear from the X-ray diffraction result of the leached residues .The jarosite was not detected in the leached residues of the three experiments, but the sulfur was detected in the leached residues of the experiment(B) and (C) but (A). So the layer on the leached residues of the experiment (B) and (C) is composed of sulfur. From this we can conclude that the layer composed of sulfur can be dissolved by attached cells, but unattached cells can not do this.

(a) (b)

(c)

Figure 1.SEM images of leached residues: (a) leached residue of experiment (A); (b) leached residue of experiment (B); (c) leached residue of experiment (C)

Conclusions The leach of the chalcopyrite is the cooperative action of the attached and unattached Acidianus manzaensis. The number of the unattached cells can increase only when there are some attached cells, and they grow out of the oxidation of soluble sulfur compounds and ferrous ion in the solution. The surface passivating layer of sulfur can be dissolved only when the Acidianus manzaensis can attach the surface of the chalcopyrite. Acknowledgments

This research was supported by the National Nature Science Foundation of China (No. 50621063), the National Basic Research Program of China (“973” Program, 2004CB619204), and the State Oceanic Administration of People’s Republic of China (No. 200805032).

Advanced Materials Research Vols. 71-73 379

References

[1] M.B. Stott, H.R. Watling, P.D. Franzmann, D.C. Sutton and A.J. Parker. In: Ciminelli V.S.T. and Garcia Jr O. (Eds.), Biohydrometallurgy, Elsevier Science (2001), 207-215.

[2] Y. Naoki, N. Masanori, O. Naoya, et al: Current Microbiology Vol. 53 (2006), p. 406

[3] D. E. Rawlings, D. Dew and C. du Plessis: Trends. Biotechnology. Vol. 21 (2003), p. 38

[4] H. Tributsch: Hydrometallurgy Vol. 59 (2001), p. 177-

380 Biohydrometallurgy 2009

Biohydrometallurgy 2009 10.4028/www.scientific.net/AMR.71-73 Investigations of Attached and Unattached Cells during Bioleaching of Chalcopyrite with Acidianus

Manzaensis at 65°C 10.4028/www.scientific.net/AMR.71-73.377

DOI References

[3] D. E. Rawlings, D. Dew and C. du Plessis: Trends. Biotechnology. Vol. 21 (2003), p. 38

doi:10.1016/S0167-7799(02)00004-5 [4] H. Tributsch: Hydrometallurgy Vol. 59 (2001), p. 177-

doi:10.1016/S0304-386X(00)00181-X