Soluble Catalysts for Copper Recovery from Low Grade Primary Copper Sulfide Ores

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Roughly 80% of the world's copper comes from the copper sulfide mineral chalcopyrite, CuFeS2. Typically, chalcopyrite ores are concentrated and subsequently smelted to obtain high purity copper. However, the grades of these primary copper ores have been steadily decreasing, which renders this route less than economical for many of today's low-grade ores. A potential low-cost alternative to process low-grade copper ores is heap bioleaching. However, chalcopyrite is notoriously difficult to leach due to mineral passivation, and commercial application of heap bioleaching has thus far been limited to secondary copper sulfide (chalcocite, Cu2S) ores. Heap bioleaching of low-grade chalcopyrite ores (combined with solvent extraction and electrowinning, or SXEW) has been the “holy grail” of hydrometallurgy for many years, and several methods have shown some promise, including the use of extreme thermophilic microbes in hot heaps where pyrite is first oxidized to generate heat, and the use of chloride as a catalyst. However, hot heaps are unreliable and difficult to control, and chloride is extremely corrosive.******Recent work at UBC suggests that it is possible to catalyse the leaching of chalcopyrite with certain soluble species. Electrochemical tests on a chalcopyrite electrode showed that small amounts of a proprietary (albeit inexpensive and readily available) soluble organic compound (which will be referred to as MFD) depassivated the electrode. Preliminary results from column and tank leaching experiments show that MFD is a powerful catalyst in ferric leaching. Adding MFD prevented passivation and enhanced the leaching rate significantly. Also, a column of ore which had stopped leaching began to leach rapidly again upon addition of MFD.******These results are very promising. If MFD can depassivate chalcopyrite under heap leaching conditions, then this could render chalcopyrite ores as easy to heap leach as chalcocite ores. This would be a major breakthrough which fundamentally alters the economics of copper mining.******The proposed research will focus on developing a viable heap bioleaching process for chalcopyrite ores using MFD. Specific objectives include:*** 1 Conduct column bioleaching experiments with MFD to determine optimum process conditions*** 2 Culture iron and sulfur oxidizing bacteria to be resistant to MFD at the levels required*** 3 Refine analytical methods for measuring MFD concentrations in leach solutions*** 4 Determine the impact of MFD (if any) on copper SXEW*** 5 Measure the reaction kinetics of MFD-catalyzed leaching*** 6 Develop a comprehensive mathematical model of heap bioleaching with MFD*** 7 Develop a parallel technology for stirred tank bioleaching of chalcopyrite ores and concentrates*** 8 Determine the fundamental mechanism of the catalytic effect of MFD*** 9 Test alternative organic compounds which share the same functional groups as MFD***10 Test MFD on other important sulfide minerals**