... the solution occured naturally through the work of micro-organisms. There were two types: Thiobacillus ferro-oxidans - which oxide the Fe2+ ions; and thiobacillus thio-oxidans - the S2-. Biotechnologists soon discovered that spraying the low-grade ores with the micro-organisms could be used to extract copper. The low- grade ore and tailings left from any previous mining is piled up (1). The ground below is impermeable, allowing the solutions to drain away. The pile is then sprayed with the micro- organisms, who thrive in the acidic environment. The bacteria convert the insoluble sulphide materials into a solution containing Cu2+, Fe2+, Fe3+ and SO42- ions (2). The solution containing copper ions is drained away, and then separated by the process of ligand exchange solvent extraction. This process transfers the copper ions from the leaching solution (low concentration) to the organic solvent (high concentration). This whole process depends on the pH. Figure 1 shows the reaction ...

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