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Секция 2. Биотехнологии
Section 2. Biotechnology Секция 2. Биотехнологии
Zaynitdinova Lyudmila Ibrahimovna, Kukanova Svetlana Ivanovna, Aripov Tahir Fatihovich Institute of Microbiology, Tashkent, Uzbekistan, doctoral candidate
E-mail: zajn-lyudmila@yandex.ru
Application of methods of bacterial leaching for gold-sulphide ores of Uzbekistan
Abstract: Possibility of application of bacterial leaching for ores of Kokpatas deposit was established. It was determined that at heap bioleaching of ores during 150 days sulphides are oxidized to 80-87% and extraction of gold reaches 70%. Synthetic polymer on basis of polyvinylpyrrolidone (P-1) was used for intensification of the process of bioleaching and its application promoted to additional 8-10% of gold extraction.
Keywords: Acidithiobacillus ferrooxidans, heap bioleaching, sulphide ore
Sulphide ores is source of many precious metals, though their treatment by modern hydrometallurgical methods is complicate. Search for new modern and non-traditional approaches to solution of this problem allow rationally use reserves of sulphide ores and fully extract valuable components. It explains the growing attention to bacterial intensification of processes of metal leaching from ores and concentrates. Application of biotechnology in hydrometallurgical processes limits environmental pollution and promotes to involvement into processing ofores, extraction ofmetals from which by traditional methods is not economically reasonable, and also involve into production wastes of hydrometallurgical enterprises. Climatic and mining-and-geological conditions of Uzbekistan suppose possibility of application of biotechnological methods for extraction of a number of metals, such as gold, uranium, copper and so on [1,2].
Uzbekistan possesses considerable reserves of gold-sulphide ores, which in the nearest future may be drawn in processing with preliminary biooxidation or bacterial intensification of the process. In these regards, there is necessity to study influence of microorganisms on substrate, direct application of bacterial population, biogeochemial reactions taking place in system microorganism-ore.
It is known, that adaptability to leaching product and ions of metals at Acidithiobacillus ferrooxidans varies within wide range and depends on strains’ features,
specific character of ore that are leached, which stipulates importance of selection and adaptation of the culture to processed product. As result of study we have selected the most active cultures for processing of Zarmitan concentrate by method of tank leaching (A.ferrooxidans B-12), for heap leaching of gold from ores of Kokpatas deposit (A.ferrooxidans К-1), and also for use in underground leaching of uranium from uranium ores of the Kizil-Kum uranium geological province (A.ferrooxidans 564).
For gold-sulphide ores of Uzbekistan both heap leaching and processing of gold-sulphide float-concentrates is prospective. Possibility of use of ores for heap leaching was proved both in laboratory experiments, at which during 150 days sulphides were oxidized to 80-87% and 70% of gold was extracted, and in experimental-industrial conditions, where gold extraction was between 40 and 75%.
It is know that introduction of bacteria to ore after heap’s acidification plays significant role in creation of optimum conditions for activity of cells of Acidithiobacillus ferrooxidans. The important peculiarity of microorganisms is their ability to stick to solid surface. At presence of solid phase over 90% of cells of A. ferrooxidans usually stick to present solid surfaces, inert surfaces (jarosite — precipitated at oxidation of iron protoxide) or to surface of minerals. The main condition is ability of cells to stick on surface of minerals to prevent cells of geochemically active microorganisms from washing-out in these conditions [3].
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Section 2. Biotechnology
Brierley et al have used synthetic polymer for agglomeration of cells and ore, which gave a positive result and promoted to development of the agglomeration method of microorganisms and ore with content of carbonates less than 2.5% [4, 5]. There is need for preliminary acidification of ore with the higher content of carbonates and only after this microorganisms are applied with irrigation solution. But, in the filtration mode the number of stuck cells may vary between 20 and 60%, depending on the height of the heap. In these regards, jointly with the Institute of chemistry and physics of polymers, search for polymers soluble in cultural broth of these microorganisms was conducted, their influence on vital functions and geochemical activity of microorganism was studied, possibility of increasing the degree of bacteria attachment to the surface of ore (biocapsulation) was investigated and
optimal concentrations of the polymer, which do not decrease oxidizing activity of bacteria, were determined. As result of this work synthetic polymer on basis of polyvinylpyrrolidone (P-1) was selected [6].
Analysis of kinetic curves of oxidizing activity of bacteria in conditions of the heap leaching reveals that the maximum concentrations of oxidized iron in solution are observed on 40-60 days of leaching both in control and test variants. Addition of polymer into irrigation solution intensified the process of iron oxidation and its concentration was 20-25 g/l, whereas in control it was 16-20 g/l. Study of interaction of synthetic polymer P-1 and association of mesophilic and thermophilic microorganisms with gold containing ore revealed that irrigation of ore with such solution promoted to high oxidizing activity of bacteria and vigorous carry-over of metals into solution (figure 1).
Figure 1. Geochemical activity of bacteria in the process of filtrating leaching with use of polymer P-1.
It should be noted that during the first 20 days of irrigation the number of cells stuck with the aid of polymer in concentration 0.01% was 6x10 4 cells/g, whereas in control it was 2.5x10 4 cells/g. Later the number ofcells stuck with the polymer aid was increasing, and starting from 40 day it was stable at the level 6.0x10 5 cells/g, whereas in control the number of cells stuck on ore has reached its maximum only by 80 day and was 6.0x10 4 cells/g (figure 2).
It was established that application of polymer promoted to increased extraction of gold by 8-10%, and also to increase carry-over of such elements as cobalt, nickel, copper and zinc.
It is known that the first stage of interaction of A.ferrooxidans and other bacteria with sulphide mineral is adsorption of cells on surface, after which the process of biochemical impact on oxidizing product starts. Microorganisms on surface of minerals are adsorbed due to such peculiarities as stickness, adhesiveness. There are composite complexes of proteins and lipids on surface of cells, there are hydrophilic and hydrophobic sites, which are important for adhesion of bacteria by oxidized substrate. But even in the case, when large population ofbacteria sticks to sulphide, but there is low electrode potential in this system, the bacterial disintegration of
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Секция 2. Биотехнологии
sulphide minerals may not take place because adhesion of bacteria should be combined with adequate level of anode polarization of sulphides. Biocapsulation of microorganisms with natural polymer may establish
a process of adsorption stipulated by formation of chemical links in system microorganism-polymer-ore between surface structures of polymer and bacteria with elements of crystal lattice of ores.
Figure 2. Influence of polymer P-1 on attachment of bacteria to ore particles in the process of filtrating leaching.
Apparently, creation ofhigh electrode potentials at increased concentration of bacteria on surface of ore material creates conditions for more active disintegration of sulphides. Application of polymers in such conditions, especially at the initial phase of irrigation, creates conditions not only for biocapsulation of microorganisms, but also for clumping small ore particles.
Results of study testify possibility of wide application of methods of bacterial-chemical leaching in Uzbekistan.
References:
1. Sanakulov K. S. Scientific and technical basics ofprocessing of wastes of mining-and-smelting industry. Tashkent, FAN publishing house, 2009, 405 p.
2. Kucherskiy N. I. Modern technologies at reclamation of primary deposits of gold. Moscow, Ruda i Metally publishing house, 2007, 696 p.
3. Grudev S. N., Grudeva V. I., Spasova I. I. Extraction of gold and silver from oxide ores by means of a combined biological and chemical leaching./Biohydrometallurgy Technologies, ed. by A. E. Torma et all, 1993. - p.417-425.
4. BrierleyJ. A., Luinstra L. Biooxidation - heap concept for pretreatment of refractory gold ore./Biohydrometallurgy Technologies, ed. by A. E. Torma et all, 1993. - p.437-447.
5. Method of gold extraction from mine dumps. Newmont Gold Corporation, USA, Newmont Mining Corporation, USA, № 5052039/Т3 dated on 09.07.92, published on 20.08.96; registered in Russia, patent № 2065503 С. 22 В 11/08.
6. Rashidova S.Sh., Voropoeva N. L., Kukanova S. I., Zaynitdinova L. I., Ruban I. N. To the question of effective metals extraction by alkaline from the rock with the use of microorganisms, biocapsulated by water-soluble polymers./In the book of abstracts of XIth International BRG Bioencapsulation Workshop, Strasbourg, France. -25-27 May -2003.
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