ABSTRACT

Biooxidation................................................................................................ 202 7.12 Ladle Slag and EAF Slag as Neutralising Agents in Continuous

Biooxidation................................................................................................ 203 7.13 Conclusion .................................................................................................. 203 References ............................................................................................................. 204

Biomining is the extraction of metal values from sulphidic ores and mineral concentrates using microorganisms. Microorganisms are well known for their active role in the formation and decomposition of minerals in the Earth’s crust since the beginning of life on Earth. The utilisation of naturally available microorganisms for mineralisation of mineral deposits is an age-old process used in the Roman times during the rst century BC, and probably by the Phoenicians before that. At its inception, microbial-mediated methods were used to leach copper without any knowledge of the microorganisms involved in the process. The discovery of the microbial world unravelled the hidden mysteries lying behind microbial processes involved in day-to-day human endeavours, out of which microbe-mediated mineral dissolution was well studied and developed with time. In recent years, remarkable achievements have been made in developing biomining to cater to the interest of the mineral industry to match the global demand for metals in the twenty-rst century. Depletion of high-grade mineral deposits makes the traditional pyro-metallurgical process uneconomical for metal recovery. The search for alternative metal-recovery processes to achieve an economical advantage over conventional methods motivated the use of the biohydrometallurgical process, which in turn has accelerated the willingness of the metal industries to use low-grade minerals (Rawlings et al., 2003). Biomining is mostly carried out either by continuous stirred-tank reactors or heap reactors. Continuous stirred-tank reactors are used for both bioleaching and biooxidation processes collectively termed as biomining. Stirred-tank biooxidation processes are mostly applied on high-grade concentrates for the recovery of precious metals such as gold and silver, whereas the stirred-tank bioleaching process is used for the recovery of base metals such as cobalt, zinc, copper, and nickel from their respective sulphides, and uranium from its oxides. Continuous stirred-tank reactors are advantageous and widely used due to the following reasons (Rawlings and Johnson, 2007):

• The continuous ow mode of operation facilitates continual selection of those microorganisms that can grow more efciently in the tanks, where the more efcient microorganisms will be subjected to less wash out leading to a dominating microbial population in the tank reactor.