Copper can be extracted from low-grade ore (CuFeS2) by means of bacterial leaching.

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Copper can be extracted from low-grade ore (CuFeS2) by means of bacterial leaching. The low-grade ore and tailings are put onto an area of impermeable ground. This is then covered in an acidic leeching solution that contains the bacteria, T. ferro-oxidans and T. thio-oxidans. These bacteria are best suited to an acidic environment. All the bacteria need are Fe2+ ions or S2- ions, oxygen, carbon dioxide and bacterial nutrients containing phosphorus and nitrogen. The final result is that the bacteria convert the insoluble chalcopyrite into a solution containing Cu2+, Fe2+, Fe3+ and SO2- ions. The solution carrying the copper ions can be straightforwardly drained off as it is on an impermeable base layer. The Cu2+ is removed from the solution by ligand exchange solvent extraction. This is where the ligand, a compound with a lone pair of electrons, binds to metal ions. A complex is then formed with the metal ion in the centre surrounded by the lignads. The Fe2+ and Fe3+ ions are left behind in the aqueous solution. A compound that is a good ligand for copper ions is dissolved in an organic solvent immiscible in water, such as kerosene. When this solution is mixed with the copper