Study Of Native Micro Organisms In Bioleaching Processes Of Refractory Auriferous


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Study Of Native Micro Organisms In Bioleaching Processes Of Refractory Auriferous

  1. 1. Study of Native Micro organisms in Bioleaching Processes of Refractory Auriferous Minerals and its Use as a Tool for Bio-regeneration Francisco Gordillo Espinosa, Víctor Sanmartín, José Torracchi. Fabián Carrión. Bac-Min 2004 Congress. Contact: Fabián Carrión. Zip. Cod: 11-01-608 Tlf: 593-7-2570275 Fax: 593-7-2584893 1
  2. 2. Study of Native Micro organisms in Bioleaching Processes of Refractory Auriferous Minerals and its Use as a Tool for Bio-regeneration Francisco Gordillo Espinosa, Víctor Sanmartín, José Torracchi, Fabián Carrión. Universidad Técnica Particular de Loja. San Cayetano s/n Zip.code: 11-01-608 Loja-Ecuador ABSTRACT The broad biodiversity of our country is manifested through several different biological forms. From the villages of Portovelo and San Gerardo in the southern part of Ecuador, some samples of water and rocks were taken in order to identify the native micro-organisms which take part in the natural processes of leaching of sulphurous minerals. It’s been achieved to determine the presence of Spp. Thiobacillus ferrooxidans and a fungi sample which has not been determined yet. These have been isolated, grown, experimented and conserved in appropriate cryogenic environments. The present research intends to study the individual and group adaptation of the bacteria and the fungi upon suitable systems of agitation and ventilation, in which has been placed several different concentrations of refractory auriferous samples. These come from the recovery processes of gold through traditional methods and test their affectivity as pre- treatments upon the cyaniding processes. Also the capability of these bacteria to develop in minerals with high concentrations of cyanide has been studied for the possibility of using the bacteria as a method for the biodegradation of cyanide. The presence of Thiobacillus ferrooxidans in acid conditions has already been tested in advance, however, the presence of fungi species in these conditions are studied to prove their efficiency as another alternative for the bioleaching of refractory auriferous minerals, 2
  3. 3. INTRODUCTION In Ecuador, a lot of wastes with some Some bacteria have been discovered which refractory characteristics have been are able of rusting from the elemental accumulated for several industrial plants sulphur to the sulphuric acid (14) and the and for mining craftsmen. The contents of influence of certain species of bacteria in gold of these wastes are, in some cases, the oxidation and decomposition of more than of 20 gram per ton sulphuric minerals, in particular the pyrite (PRODEMINCA, 2001 Programa de (14). These methods have been determined desarrollo minero y capacitaciòn as processes of catalytic action in the ambiental del Ecuador). Moreover, with dissolution of mineral components through these characteristics, these deposits are not the direct and indirect action of bacteria. feasible of benefiting by traditional processes of concentration or dissolution One of the micro-organisms that have which impede to get bigger percentages of favoured these studies is the recovering. Chemolithotrophic mesophilus Thiobacillus ferrooxidans. It possess the The problem of refractivity has placed the capability of catalyse reduced components pyrite and the arsenopyrite as the most of sulphur and ferric ion, using oxygen as important minerals that encapsulate and electric acceptor and generating sulphuric make refractivity on some metals such as acid as a final product. (12). gold (3). This makes the method of recovering through cyanide a little The microbiologic leaching is a natural optimum and it applies only the recovering process of dissolution that results from the of native gold and electrum (1) action of a group of bacteria (basically bacteria from Thiobacillus), with The transcendence of the micro-organisms capability of rusting sulphuric minerals, in the physical and chemical formation which allow to release the metallic values and transformation of the minerals with an contented. (7) enormous interest in those which present natural oxidations and dissolutions The selected samples for the essay were provoked by the action of the samples that taken from galleries of closed mines in the obtain the energy for their metabolism 50s in the place Zoroche Unificado of rusting the present iron and the sulphur. Portovelo and new deposit of the mine of 3
  4. 4. San Antonio in San Gerardo. The stones weathering of the mineralised stones, present high degrees of weathering especially in the plains of structural (oxidation) in these places. contact, characteristic for the presence of stalactites and stalagmites. The craft auriferous Ecuadorian mining uses inappropriate quantities of cyanide, Some samples were taken from water and without any technical principle rocks that were placed in sterile flasks of (Prodeminca, 2001). This process 120 ml. They were carried in isolated generates highly dangerous levels of soil thermic boxes. and water pollution on these areas. A bacterial screening in the studied areas The solid culturing was done in Petri allowed demonstrating the growth of spp. dishes, using volume 125ml. of FeTSB pseudomonas with an important rate of medium (11). And the pH was adjusted to survival in the water containing important 2 with concentrated sulphuric acid. amounts of cyanide. Erlenmeyer flasks of 125 ml were used in the liquid cultivations. A volume of 50 ml The present study will permit to determine of 9K medium (11) and the pH was the bacterial behaviour at different adjusted at 2, likewise with concentrated concentrations of mineral, for verifying its sulphuric acid. It was agitated at 150 growing, the oxidation degree from Fe+2 to Fe+3 and the appropriate solid-liquid rev/min in orbital shaker (THERMOLYNE) during 15 days. percentage of pulp for the bio-oxidation as a pre-treatment to the lixiviation with cyanide, in addition, the capability of the The cultivation in both cases was done in bacteria found when degrading important aseptic conditions using the laminar flowing chamber (ESCO) and the quantities of dissolved cyanide. materials were sterilized (121 ºC, 20 minutes) and subjected at 20 minutes of MATERIALS AND METHODS radiation ultra violet light before the Isolation, cultivation and conservation inoculation. The samples were taken form 50 and 100 The conservation of selected frozen meters deep at those zones of mineral samples is done in cryotubes. A galleries that show high degrees of cryoprotector solution of glycerol at 10% 4
  5. 5. vacuum filtrated, plus a solution of 9K Mineralogical characterization medium, the glycerol-9Kmedium solution were sterilized (121ºC, 15 minutes). The mineralogical composition was determined by optic microscopy (NIKON The micro-organisms for freezing are EPIPHOT) of reflected light in polished cultivated in leaning agar tubes. The sections as seen on the Table 1. cryoprotector solution is added in the agar tubes and liquid medium. The cultivation Chemical analysis is re-suspended by scraping the colonies and agitating respectively. The reading for each basic metal was done for Spectrophotometry of atomic Determining bacterial growing absorption (PHILIPS-PYE-UNICAM). A permanganate solution of potassium The precious metals were determined by was prepared for determining the fire assay, acid desegregation of the gold transformation from Fe+2 to Fe+3. It titrates pearl and the reading for over 5 ml. of extracted solution from the spectrophotometer of atomic absorption. tests of examination. The results as seen on the Table 2 The bacterial growing is determined taking Physical analysis 15 µl of culture. It is added 5 µl of blue lacto phenol. For the bacteria of the The specific weight was determined by the mineral pulp and blue of methylene for method of pycnometer and the control of those which grow on cyanide. They are pH with pH meter (THERMO ORION). mixed in a micro tube. The solution is The results are shown on the Table 3. The placed in a chamber of re-counting granulometric analysis was done by dry (NEUBAUER) and the bacteria are and wet via in sieve shaker (RETSCH) counted in five fields. with a passing from the 80 to 190 mesh. The resulting re-estimating value gives us Experimenting the approximated number of bacteria per millilitre of cultivation. Fifty samples were done for evaluating the ranges of concentration of pulp, from 5
  6. 6. which 3 were selected of better growing (BURRELL) to 220 rev/min during 10 and were tested again but duplicated. days (14). RESULTS The samples were processed in containers of precipitation of 2000 ml at Bacterial growing concentrations from 5 to 60% respectively. The bacterial growing in the studied It was placed homogenized refractory minerals in three different concentrations mineral with a granulometry of 190 mesh (fig 1, 2, 3) is observed in a similar (0.78m). Distilled and demineralized water relationship until the second week, from was added to get a total solution of 1000 which it is distinguished differences in the ml from the isolated cultures were taken growing of the sample of San Gerardo. 100 µl of the sample with bigger kinetic of Possibly by the influence of the growing, to which was inoculated in the mineralogical characteristics. On the last solution. It was stirred at 175 rev/min an week, there is an accelerated growing until flasks shaker (PHIPPS & BIRD the day 21. STIRRER), the pH regulated periodically at 2 with concentrated sulphuric acid and pH Variation the temperature of the growing chamber was of 22ºC. Each sample was maintained The consume of sulphuric acid to regulate in agitation during 21 days (2). the pH is in direct function of the Degradation Test of Cyanide mineralogical composition, evidencing its stabilization from the second week with an The tests were done by triplication on average value of 2.5 as it is shown on the cyanide dissolution to evaluate the figure 4. adapting capability of the samples of bacterial broth that was found in the Iron concentration mining deposits. In Erlenmeyer flask, it was prepared 250 ml of cyanide The titling of iron for the indirect dissolution to 25 ppm at a pH of 9. The determination of the bacterial growing is temperature of the chamber of growing shown in the figures 5 and 6, in which was 22ºC and inoculated 500 µl of culture. from the second week its values increase It was stirred in an agitator of arms proportionally due to the time as well as the increasing the kinetic of bacterial 6
  7. 7. growing. It was determined that the iron formed during the bio-oxidation process. percentage increases in the pulp from the This constitutes like the indirect indicator 12th day for San Gerardo and the 14th for of the decomposition of calcite carbonated Portovelo’s samples. minerals. DISCUSSION. Likewise, a great adaptation of a Penicillium species was observed during Under controlled conditions the collected the microscopy observation. It was very bacterial samples adapt successfully in the sporulating and survives in strong acid cultivation environments in vitro and in conditions and without the presence of the tests with mineral pulp. The statistic carbohydrates. This contrasts the normal results show that the bacterial growing is growing of this micro-organism that are directly proportional at the pulp not even determined like direct concentrations especially from the 4 7% to participants of the process of bioleaching. 51% in controlled conditions of granulometry, pH, temperature and stirrer The analysis of fig 5 determines the (Fig. 8 and 9). However, when comparing bacterial capability to adapt approximately the figure 4 and the figure 9 are evident in five days to cyanided solutions and an that the bacterial growing tends to exponential growth in ahead. It evidently decrease for the low transference of adjusts to the ranks found in the reading of oxygen in the environment for the major determination of ppm of dissolved cyanide pulp concentration. (fig 6) in which was found precisely smaller cyanide levels when the growth During the first days, the non-metal tends at the maximum level. It is estimated mineral dissolution increases the values of that after 5 days the present cyanide levels pH which stabilizes with the time until in the tested solutions are smaller than achieving a constant value of 2,5. This 0, 07 ppm. suggests that microbiological metabolism produces sulfuric acid for auto regulation of the environment. (16) REFERENCES The observed samples by microscopy of 1. Avila, M, Díaz, Y, 2000. transmitted light present a great quantity Biodegradaciòn de cianuro: uso de of crystals of calcium sulphate that are 7
  8. 8. microorganismos inmovilizados, minerales pp 409 (Vneshtorgizdat: Quito Ecuador, in Beneficio del Moscú). Oro y Tratamiento de Efluentes Course, pp 1-12 (Universidad Politécnica Nacional: Ecuador, 6. Diaz, X, and Moya, L, 2003. Universidad Católica de Lovaina: Recuperación de Oro mediante Belgium) biolixiviación y tiocianato, in Seminario internacional de 2. Bañuelos, S, and Castillo, P, 1993. minería, metalurgia y medio Recuperación de metales preciosos asbiente, pp. 127-135 (Universidad a partir de sulfuros minerales Politécnica Nacional: Ecuador). refractarios, utilizando el proceso de lixiviación bacteriológica. 7. Fowler, T, Holmes, P, Crundwell, Geomimet Magazine Nº 184, pp. F, 1999. Mechanism of pyrite 9-18. dissolution in the presence of Thiobacillus ferrooxidans, Applied 3. Chapaca, G, Ávila, M, 2003. and Environmental Microbiology, Evaluación de las causas de Vol. 65, pp 2987-2993. refractariedad de un mineral aurífero de la zona de Bella Rica, 8. Guerreo, J, 1998. Biotecnología en Seminario Internacional de la disolución y recuperación de Minería, Metalurgia y Medio metales, in Primer Congreso Ambiente. pp. 113-123. Peruano de Biotecnología y Bioingeniería, (Trujillo Perú). 4. Chiacchiarini, P. Lavalle, L. Tecnologías emergentes para la 9. Guevara, A, De la Torre, E. 2003. bioremediación de metales y su Importancia de los estudios relación con la enseñanza de la mineralógicos en el procesamiento Química, Universidad Nacional de de minerales auríferos refractarios, Comahue. Facultad de Ingeniería, in Seminario Internacional de Argentina. Minería, Metalurgia y Medio Ambiente 2003, pp 99-110 5. Dercach, V, 1982. Métodos (Universidad Politécnica Nacional: especiales de enriquecimiento de Ecuador) 8
  9. 9. 10. González, M, 2004. Engineering University of Nevada , Biorremediación y (Reno: Nevada). tratamiento de efluentes, Monografías.Com, Lucas 15. Razo, I, Lopez, S, Lara, C and Morea/Sinexi S.A. Monrroy, M. Study on the ability of isolated and collection strains to 11. Hartikainen, T. Ruuskanen, J. degrade cyanide: an application of Raty, K. Von Wright, A. and heap-leaching residues and Martikainen, P, 2000. Physiology effluents, Instituto de Metalurgia, and taxonomy of Thiobacillus U.A.S. L.P., San Luis Potosì, strain TJ330, which oxidizes Mexico. carbon disulphide (CS2), Journal of Applied Microbiology, vol. 89, pp. 16. Rossi, G. 2001. The design of 580-586. Bioreactor. Hidrometallurgy. Vol 59. 12. Hernández, R., Fernández, C. y Baptista, P, 1998. Metodología de 17. Smith, A and Mudder, T. The la Investigación, pp 105 – 112, 376 chemistry and treatment of – 395 (McGraw Hill: México). cyanidation wastes, pp 219-237 (Mining Journal books limited: 13. Johnson, B. Macvicar, J. Rolfe, S, London). 1987. A New Solid Medium for the Isolation and Enumeration of 18. Susuki, N. Asai, S. Konoshi, Y. Thiobacillus ferrooxidans and Tokushige, M, 2001. Cooper Acidophilic bacteria. Journal of Recovery from chalcopyrite Microbiological Methods. pp. 7- concentrates by acidophilic 18.. thermopile acidianus brierleyi in batch and continuous flow stirrer 14. Noel, D M, Fuerstenau, M C and tank reactors. Hydrometallurgy. Hendrix, J L, 1991. Degradation of Vol 59 Nº 2-3. cyanide utilizing facultative anaerobic bacteria, Department of 19. Thompson, L C. Developments in Chemical and Metallurgical mine waste bio treatment processes, Pintail Systems, Inc. 9
  10. 10. 11801 E. 33rd Ave. Suite C. (Aurora: Colorado) 20. Zelikman, A, Voldman, G, Beliaevskaya, L. 1981. Teoría de los procesos metalúrgicos. pp. 208- 213 (Vneshtorgizdat: Moscú). 10
  11. 11. TABLES LIST Table 1. Mineralogical analysis of the wastes Quantity, % Minerals Formula Portovelo San Gerardo Pyrite FeS2 19.1 15 Chalcopyrite CuFeS2 0.44 6.1 Esfalerita (ZnFe)S 0.95 -- Galena PbS 0.4 -- Arsenopyrite FeAsS -- 10 Ganga -- 79.11 68.9 Table 2. Chemical analysis of wastes Concentration Element Portovelo San Gerardo Cu (%) 0.14 2.5 Fe (%) 9.5 15.3 Pb (%) 0.45 0.03 Zn (%) 0.62 0.03 As (%) 0.08 7.84 S (%) 12.1 8.9 Au (g/ton) 9.2 19.98 Table 3. Physical analysis of the wastes Values Parameter Portovelo San Gerardo Specific weight, g/cm3 2.65 2.92 pH 6.5 7.5 ( 35% solids) 11
  12. 12. FIGURES LIST Figure 1. Bacterial growing at 25% of pulp Figure 2. Bacterial growing at 30% of pulp Figure 3. Bacterial growing at 35% of pulp 12
  13. 13. Figure 4. Bacterial growing at different concentrations of pulp [days] Figure. 5 Bacterial growing in cyanide Figure. 6 . Degradation of the potassium cyanide 13
  14. 14. Figure 7. Variation of pH in the pulp at 35% of concentration Figure 8. Redox in Portovelo`s wastes Figure 9. Redox in San Gerardo wastes 14
  15. 15. Figure 8. Pearson Correlation and regression analysis of bacterial growing on the pulp concentration CRECIMI vs. CONCENTR CONCENTR = .11182 + 0.0000 * CRECIMI Correlation: r = .92098 0.65 0.60 0.55 0.50 CONCENTR 0.45 0.40 0.35 0.30 0.25 Regression 0.20 3e7 5e7 7e7 9e7 1.1e8 1.3e8 1.5e8 95% confid. CRECIMI Figure 9. Curve Adjustment to relate mathematically the pulp concentration in the solution with bacterial growing Scatterplot (biolix.STA 7v*11c) y=-3.199e9+4.508e10*x-2.447e11*x^2+6.454e11*x^3-8.21e11*x^4+4.035e11*x^5+eps 1.5e8 1.3e8 1.1e8 CRECIMI 9e7 7e7 5e7 3e7 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 CONCENTR 15