Reactor Bioleaching And Developments In Bioleaching Of

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1 Lecture 5 Reactor Bioleaching And Developments In Bioleaching Of Concentrates Keywords:, Reactor Leaching, Bioleaching Of Metal Concentrates, Recent Developments Metal sulfide concentrates are generally bioleached in stirred tank reactors (agitation leaching). Several designs of bioreactor configurations are available (Fig.5.1) Feed Air Input Air Agitated Tank Reactor Pachuca Reactor Fig. 5.1: Typical bioreactor designs 1

2 Bioleaching of base metal concentrates A number of companies have developed biooxidation processes for use in metal extraction. Some of these have found commercial application while others are still in the experimental or pilot plant stages: Newmont Mining BIOPRO Process heap leaching of refractory gold ores Gold Fields, Ltd BIOX Process agitated tank oxidation of refractory gold ores BHP Billiton, Ltd. BioCOP Process agitated tank oxidation and leaching of copper sulfides BioNIC Process agitated tank oxidation and leaching of nickel sulfides BioZINC Process agitated tank oxidation and leaching of zinc sulfides BacTech Enviromet BacTech/Mintek Process agitated tank oxidation and leaching of copper sulfides GeoBiotics, Inc. GEOCOAT Process heap leaching sulfide mineral concentrates BacTech Enviromet Corp., in conjunction with Mintek, has developed proprietary technologies for the high temperature leaching of copper concentrates. Working in conjunction with Industrias 2

3 Penoles SA de CV, they operated a 2.2-metric tons per day (mt/d) stirred-tank copperconcentrate bioleach demonstration plant in Monterrey, Mexico during BHP Billiton and Codelco, in a joint venture, Alliance Copper Ltd., constructed a demonstration plant at Chuquicamata, Chile, to produce 20,000 tons of cathodes a year starting in 2003 using Billiton s patented BioCOP process, to treat dirty concentrates containing high levels of arsenic (enargite, Cu 3 AsS 4 ). The following process developments are note-worthy: The GEOCOAT Process A heap leaching process capable of bioleaching base metal and refractory sulfidic gold concentrates. The concentrate slurry is coated onto a support rock, or substrate material, and stacked in a bioxidation heap. The ratio of support rock to concentrate is in the range of 5:1 to 10:1 by weight. The heap can be inoculated with thermophilic bacteria and a process leach solution consisting of sulfuric acid, ferric iron and nutrients applied to the heap. Low-pressure blowers provide air supply through a system of perforated pipes placed under the heap. The exothermic nature of the oxidation reaction increases the heap temperature to at least 50 C. The BioCOP Process Carried out in a stirred reactor containing sulfuric acid into which air is blown. Thermophilic microorganisms are used at a temperature between 60 C and 90 C. Limestone is used to maintain the ph of the solution and to provide carbon dioxide for bacterial growth. Copper concentrate is fed to the reactor. Pregnant solution containing grams per liter is sent to solvent extraction electrowinning. Retention time is about 10 days. The BacTech/Mintek Process Countercurrent reactors used. Two proprietary bioreactors were tested in Mexico; - (a) the Circox bioreactor developed for the biotreatment of municipal sewage and industrial waste water and licensed from Paques Bio Systems B.V. of the Netherlands. The Circox bioreactor used an airlift to circulate 3

4 the solids within the reactor, and (b) the BAR (BacTech Aerated Reactor). Thermophilic microorganisms used at temperatures between 25 C and 55 C. A ph of 0.5 to 2.5 is maintained. Nutrients are added to the leach liquor. Retention time is about of 30 days. Bioleaching parameters and developments: Parameters influencing bioleaching are illustrated in table 5.1. Table 5.1: Factors and parameters influencing bacterial mineral oxidation (Adapted from H.Brandl; Microbial leaching of metals ( Physicochemical parameters Temperature ph redox potential oxygen, carbon dioxide Mass transfer, nutrients, Ferrous concentration Microbiological factors Microbial diversity Population diversity and density Spatial distribution Metal tolerance and toxicity Whether adapted or not Mineral properties Mineral type and composition Mineral dissemination, porosity Surface area, galvanic interactions Processing parameters Leaching mode (in situ, heap, dump, or tank) Pulp density Stirring rate (in case of tank leaching operations) Heap geometry (in case of heap leaching) 4

5 Status of bioleaching for base metal and refractory gold-bearing concentrates. Commercial viability of bioleaching proven for refractory gold concentrates Mesophile bioleaching applied commercially for treatment of cobaltiferrous pyrite (Kasese, Uganda) Continuous high temperature thermophile bioleaching demonstrated at pilot scale for chalcopyrite and pentlandite. Construction of demonstration plants for treatment of copper concentrates. Bioleaching is technically feasible and economically viable as a process option for treatment of base metal and multimetal complex concentrates. Biological extraction of cobalt from pyritic concentrates was commercialized in (BRGM, France) at Kasese Project at the Kilembe mine in Uganda. An inoculum of mesophilic ironoxidizing bacteria used for bioleaching cobalt in a stirred-tank reactor system. The plant uses solvent extraction-electrowinning for recovery of the cobalt. The promising developments in bioleaching of cobalt and nickel may lead to immediate commercialization of Biohydrometallurgical processing of base metals other than copper. Details of cobalt bioreactor operations are given below: Recovery of cobalt from cobalti-ferrous pyrite Tonnage (t/d) : 241 Primary Reactor Size (m 3 ) : 1350 Start Date : 1998 Cobalt Content (%) : 1.4 Sulphide Content (%) : 41 Challenges for commercial development Slow leach kinetics and need for large reactors; High power consumption for oxygen supply; Confidence that high plant availability will be achieved; Economic recovery of precious metals. 5

6 New developments in Biohydrometallurgical reactor designs Aerated trough bioreactor Low energy bioreactor Falling laminar liquid film principle Inclined plate bioreactor Biorotor Future biotechnological initiatives Modelling, design and development of bioreactor assemblies-low energy-high efficiencystirred tank and Pachuca. o New type of reactor of systems Comprehensive study of microbial composition of both bioheap systems and stirred-tank reactors-interactions among various microflora Techniques to enhance biomass growth o Electrochemical, Bacfox, inert substrates, o Growth reactors-genetic engineering Development of metal-tolerant and substrate-adapted special strains o Genetically modulated super bugs! Rapid, accurate and simple techniques to monitor bacterial activity in bioleach systems. High temperature heap bioleaching (Inoculation of heaps) High temperature tank bioleaching using thermophiles Bioprocessing of dirty and complex ores and concentrates Leaching of silicate-matrix minerals and alkaline ores Agitated tank bioleaching for uranium concentrates Nano particles produced by microbes Biomaterials processing, Biomimetics. Surfactants (flotation reagents, flocculants) through microbes in mineral beneficiation Organic acid leaching using heterotrophic bacteria and fungi Sulfate reduction in metals recovery and effluent disposal - Biogenic sulfides Waste treatment (slags, ash, scrap) Bioleaching to recover values from wastes. 6

7 References (Lectures 3-5): 7. Brierley C.L, Bacterial succession in bioheap leaching, Hydrometallurgy, 59 (2001), Natarajan, K.A., 1998, Microbes, Minerals and Environment, Geological Survey of India, Bangalore. 9. Rossi, G., 1990, Biohydrometallurgy. McGraw Hill, New York. 10. Brierley, C.L., 1978, Bacterial leaching, CRC Critical Reviews in Microbiology, 4, pp Brierley, C.L., August 1982, Microbiological mining, Scientific American, pp Acevedo, F., Gentina, J.C. and Bustos, S., 1993, Bioleaching of minerals a valid alternative for developing countries, Journal of Biotechnology, 31, pp Brierley, C,L., and Brierley, J.A., 2001, Present and future applications of biohydrometallurgy, Hydrometallurgy, 59, pp Anon, May 31, 2002, Bioleaching Moves forward, Mining J., pp Miller, P.C., Rhodes, M.K., Winby, R., Pinches, A. and Van Stadan, P.J., 1999, Minerals and Metallurgical Processing, 16, pp Olson G.J, Brierley J.A and Brierley C.L, Bioleachng Review Part B: Progress in bioleaching: applications of microbial processes by the minerals industries, App. Microbiol. Biotechnol 63, (2003), Gericke M, Neale J.W and van P.J Staden-A.Mintek perspective of the past 25 years in minerals bioleaching, J.South African Inst. Min. Met., 109 (2009),