In situ recovery of copper sulfide ores: Alternative process schemes for bioleaching application

There is a growing interest in exploring the application of bioleaching for treating copper sulfide ores of decreasing grade and located at larger depth by in situ recovery (ISR) for its potential savings in ore extraction, crushing, grinding and the avoidance of tailings. As copper sulfide ores are usually present in well consolidated rocks a crucial aspect for ISR to be successful is to increase the ore permeability in order to allow a good access of solution to the valuable metal values. However, in bioleaching an additional critical aspect is to guarantee an adequate supply of oxygen, the final electron acceptor in the reaction chain. Two alternative schemes to solve this issue are here characterized and compared using process simulation. One approach considers pre-treating the rock with hydrofracturing and/or confined blasting in order to create a network of cracks adequate for pumping the pressurized leaching solution into the ore bed in a saturated flow regime. In this scheme oxygen needs to be added in an external bioreactor where ferric iron is generated by bacterial oxidation of ferrous iron. A second approach considers pre-treating the ore by application of sublevel stopping techniques with partial removal of the rock to be able to irrigate the solution into the ore bed under an unsaturated flow regime. In this scheme oxygen can be directly supplied into the ore bed enabling in situ generation of ferric iron by the oxidative action of microorganisms present in the ore. The influence of irrigation rate, leaching solution concentration, bacterial population and ore bed dimensions on copper recovery and bioreactor requirements was assessed for these two process schemes. Some economic aspects of these two alternatives are discussed.