Biohydrometallurgy Of Copper Modern Developments

Transcription

1 Lecture 12 Biohydrometallurgy Of Copper Modern Developments Keywords: Developments In Heap, Thermophile Leaching, Chalcopyrite Leaching. Bioleaching of chalcopyrite Most of the research has been done using chalcopyrite concentrates and little information is available on its heap bioleaching aspects. As mentioned before, chalcopyrite is a refractory mineral not readily amenable to bioleaching using acidophilic mesophiles. The leaching rate can be significantly enhanced at higher temperatures at controlled redox potentials. Appropriate control of iron chemistry and ore preparation are essential to achieve desirable copper extraction from chalcopyrite ores. Beneficial role of fine grinding of chalcopyrite concentrates before bioleaching has been assessed. Heap bioleaching of chalcopyrite ores need several controls such as Knowledge of indigenous microflora and factors that promote their growth and activity. If the heap need be operated at high temperatures, inoculation with a consortia of thermophiles. Proper irrigation methods and nutrient addition Agglomeration of fines using inoculum. A number of methods have been suggested for generation and maintenance of heat in heaps. Use of hot water while acid curing and also heap heating. Promoting exothermic reactions through external addition of sulfides. Proper heap insulation and prevention of evaporation. Control heat transfer Humidity and aeration control. 1

2 Heap (bio) leaching of copper ores is a practical technology. Robust and proven under different climatic conditions for oxides and secondary sulphides. Flexible-heap engineering and management can accommodate site peculiarities in remote localities; suited to small deposits Simple-a technology that can be communicated to non-scientific personnel. Low cost-stacking, irrigation, aeration, solution collection are all basic. Efficient heap bioleaching requires the indigenous presence of effective and appropriate bacterial population. Bacterial inoculation with the leach liquor cannot be effective, since many organisms are naturally adherent to the ore particle surfaces and do not penetrate to the interior depths. The StickBugs TM process, currently being developed, is capable of generation of sufficient population of desirable bacteria and to facilitate attachment to inner depths of heaps. Bacterial activity can thus be enhanced following effective inoculation. The above StickBugs TM process prevents the desirable bacterial population from remaining at the top of the heap and facilitate their penetration into the heap. Bacteria lose their adhesion tendency if deprived of an essential nutrient. Generation of micro non-adherent bacteria find application in plugging of permeable subterranean strata, in oil recovery. Ultra-micro-bacteria (UMB) are generated through nutrient starvation. UMBs do not attach to mineral surfaces in the absence of nutrients, but can be revived by re-introduction of the missing nutrient. Assaying methods for microbial population (both planktonic and sessile) in bioheaps have been developed. Qualitative and quantitative estimation of the microorganisms that colonise the ore surfaces and as available in the liquid phase within a heap can be performed using newly developed molecular biology techniques. Attached organisms can be dislocated from the solid phase through successive washes with detergents and acidified water and the cells then enumerated. Genetic DNA can be isolated. 2

3 Microbial identification can be achieved through restriction endonuclease analysis of the 16S rrna genes, and also as 16S rrna gene sequencing. Thermophile bioleach status Successful batch bioleaching of chalcopyrite (98%), enargite (98%), and sphalerite (95%) achieved in laboratory. Established A 1 3 bioleach pilot plant in January 1998 for continuous thermophile bioleaching of a Chilean chalcopyrite concentrate, Successful bioleaching of copper concentrate achieved on continuous basis yielding > 99% copper recovery at economic residence times. Continuous operation of bioleaching mini plant treating copper/cobalt concentrate yielded 98% copper and cobalt recovery. Limited dissolution of chalcopyrite owing to mineral surface passivation. Slow kinetics for enargite. Require high redox potentials and high temperatures. Require long residence times for metal dissolution. Difficult to attain complete sulphide oxidation. Precious metals recovery may be problematic. Bac Tech/Mintek process (using moderate thermophiles) Successful bioleaching of Mount Lyell copper concentrate in Fully integrated circuit consisting of 200 litre mini plant with return raffinate from SX. Achieved 96% copper dissolution on Mount Lyell concentrate. Geocoat Process The GEOCOAT process incorporates two successful and commercially amenable technological concepts heap leaching and biooxidation. Sulfide ores can be concentrated by flotation and thickened. The resulting slurry coated onto crushed, screened support rock, stacked on a lined pad, and bioleached. Coating achieved by spraying concentrated slurry onto the support rock. 3

4 The support rock is uniform sized, in the range of 6 to 30 millimeters and the concentrate coating is less than one millimeter in thickness. The weight ratio of support rock to concentrate is in the range of 5 10 : 1. The hydrophobic nature of the concentrate assists in the coating and no binding agents required. Depending on the desired temperature of operation, the heap is inoculated with naturally occurring sulfide oxidizing bacteria, such as the mesophiles; Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans or moderate thermophiles; Acidithiobacillus caldus, Sulfobacillus thermosulfidooxidans or extreme thermophiles; Acidianus brierleyi, Acidianus infernus, Metallosphaera sedula, Sulfolobus acidocaldarius, Sulfolobus shibatae and sulfolobus metallicus. Nutrients added to the heap through recirculating solution. As biooxidation progresses, the sulfide minerals in the concentrate are oxidized and the solubilized metal ions, iron and sulphate are recovered from the heap and stripped solution recirculated. Chalcopyrite ores or flotation concentrates can be bioleached using thermophiles using the Geocoat process. (fig. 12.1) Fig.12.1: Schematic representation of chalcopyrite coating on a support rock in a heap configuration. Typical pilot plant operations for chalcopyrite concentrate reactor bioleaching and for high temperature heap bioleaching are illustrated in figs 12.2 and

5 Fig 12.2: Pilot Plant consisting of Regrinding, Agitated Bioleaching, Iron Removal, Copper-SXEW and Zinc Precipitation, to treat Polymetallic Chalcopyrite Concentrate. (Kind courtesy from MINTEK, P.J.van Staden, manager, Biotechnology Divn.MINTEK) (Permission from MINTEK thankfully acknowledged) Fig. 12.3: Pilot Plant for High Temperature Heap Bioleaching Showing the first of three 20,000 t cells stacked. (Kind courtesy from MINTEK, P.J.van Staden, manager, Biotechnology Divn.MINTEK) (Permission from MINTEK thankfully acknowledged) 5

6 Heap bioleaching tests on Iranian low grade chalcopyrite ores The Darehzar Copper Mine located in the Kerman province of Iran, belongs to the National Iranian Copper Industries Company (NICICO). Temperatures, higher than those normally attained in the heap bioleaching of secondary sulphide copper ores, are required to obtain faster copper leach kinetics from the hypogene ore of the Darehzar Mine in Iran. Through mathematical modeling, it could be established that certain blends of the hypogene and supergene ores could become amenable to heap bioleaching. Three independent pilot heaps, each of about 25,000 tones, were constructed on site at the Sarcheshmeh copper mine. Copper extraction, bacterial activity and acid consumption were monitored as a function of time. Mintek developed the control strategy. The Darehzar ore deposit has been estimated at around 50 to 80 million tonnes assaying 0.6% copper, with up to 143 million tonnes assaying 0.44% copper. Chalcopyrite amounts to 79% of the copper content in the hypogene, for 24% of the copper in the supergene, and for 54% of the copper in a 70:30 blend. The pyrite content is about 4%. About 0.6% copper as average could be achieved through a 70:30 blend. Laboratory test work and analysis were carried out to establish the mineralogy and chemistry of ore for a period of an year. Effect of particle size, temperature, ph and redox potential on copper and iron recovery as well as acid consumption. Agglomeration characteristics with various binders and admixtures. Establishment of conditions amenable to bacterial activity and sulfide oxidation. Bacterial action and sustainability in the heap. Effect of temperature, oxygen, carbon source, nutrients and solution chemistry on bacterial growth and activity. Control of iron precipitation in the form of jarosites. Control of segregation and migration of fines during stacking and leaching. Initial test runs were carried out in columns 6

7 References (Lectures 10-12): 42. H. R. Watling, The bioleaching of sulphide minerals with emphasis on copper sulphides A review, Hydrometallurgy 84 (2006), N.Pradhan, K.C. Nathsarma, K.Srinivasa Rao, L.B. Sukla, B.K. Mishra, Heap bioleaching of chalcopyrite: A review; Minerals Engineering, 21 (2008), M.Gericke, J.W.Neale and P. J. Van Staden, A Mintek perspective of the past 25 years in minerals bioleaching, J.S.Aftican Inst. Min. Met, 109, (2009) C. L. Brierley, How will biomining be applied in future? Trans. Nonferrous met. Soc. China, 18, (2008), Anon, Penoles bio-leach demonstration plant. Bateman press release (2001). 47. J.A. Brierley, Heap leaching of gold-bearing deposits: theory and operational description. In: Rawlings, D.E. (Ed.), Biomining: Theory, Microbes and Industrial Processes. Springer, Berlin, (1997) M.E. Clark, J. Batty, C. Van Buuren, D. Dew, M. Eamonn, Biotechnology in Minerals processing: Technological Break throughs Creating Value. In: Harrison, S. T.L, Rawlings, D.E., Petersen. J (Eds.) Proc. 16 th Int. Biohydrometallurgy Symposium (Cape Town). IBS, Cape Town, (2005) D.G. Dixon, Heap leach modelling the current state of the art. In:Young, C.A, Alfantazi, A.M, Anderson, C.G, Dreisinger, D.B., Harris, B., James,A. (Eds.), Hydrometallurgy Volume 1: Leaching and Solution Purification. TMS. Warrendale. (2003), D. G. Dixon, J.Petersen, Comprehensive modelling study of chalcocite column and heap bioleaching. In: Riveros, P.A., Dixon, D., Dreisinger, D.B., Menacho,T. (Eds.), Copper- Cobro (Santiago) Volum VI-Hydrometallurgy of Copper (Book 2) Modeling, Impurity Control and Solvent Extraction. Canadian Instiute of Mining, Metallurgy and Petroleum, Montreal, (2003), D.G. Dixion, J.Petersen, Modelling the dynamics of heap bioleaching for process improvement and innovation. Hydro-Sulfides, Intl. Colloquium on Hydrometallurgical Processing of Copper Sulfides (Santiago). University of Chile, Santiago, (2004),

8 52. C. du Plessis, Delivery system for heap bioleaching. World Patent WO 2,003, 068, 999 (2003), 21 August. 53. T. Gehrke, R.Hallman, K.Kinzler, W.Sand, The EPS of Acidithiobacillus ferrooxidans a model for structure function relationships of attached bacteria and their physiology. Water Science and Technology 43, (2001), M. Gericke, A.Pinches, Bioleaching of copper sulphide concentrate using extreme thermophilic bacteria. Minerals Engineering 12, (1999), M. Gericke, A.Pinches, J.V. Van Rooyen, Bioleaching of chalcopyrite concentrate using an extremely thermophilic culture. International Journal of Mineral Processing 62, (2001), M.Gericke, H.H. Muller, J.W. Neale, A.E. Norton, F.K.Crundwell, Inoculation of heap leaching operations. In: Harrison, S.T.L., Rawlings, D.E., Petersen, J. (Eds.), Proc. Intl. Biohydrometallurgy Symposium (Cap Town). IBS, Cape Town, (2005), C. Hunter, Bioheap leaching of a primary nickel-copper sulphide ore. ALTA Nickel/Cobalt 2002 (Perth, WA). ALTA. Melbourne. (2002). 58. C.J. Hunter, T.L Williams, Adaptation of bacteria for leaching, world patent WO 02,066,689, (2002), 29 August. 59. D.E. Rawlings, The molecular genetics of mesophilic, acidophilic, chemolithotrophic, iron or sulfur-oxidizing micro-organisms. In: Amils, R., Ballester, A. (Eds.), Proc. Intl. Bio hydrometallurgy Symposium (Madrid, Spain), Part B. Elsevier, Amsterdam, (1999), D.E. Rawlings, The molecular genetics of Thiobacillus ferrooxidans and other mesophilic, acidophilic, chemolithotrophic, iron- or sulfur-oxidizing bacteria. Hydrometallurgy 59, (2001), A.I.M. Ritchie, Optimization of biooxidation heaps, In: Rawlings, D.E (Ed.), Biomining: Theory, microbes and Industrial Processes. Springer Verlag, Berlin, (1997), P.J.van Staden, B.Shaisaee, M.Yazdani, A collaborative plan towards the heap bioleaching of low grade chalcopyritic ore from a new Iranian mine. In: Harrison, S.T.L., Rawlings, D.E., Petersen J. (Eds.), Proc, 16 th Intl. Biohydrometallurgical Symposium (Cape Town). IBS, Cape Town, (2005),

9 63. M.Vasquez, R.T. Espejo, Chemolithotrophic bacteria in copper ores leached at high sulfuric acid concentration. Applied and Environmental Microbiology 63, (1997),