Bacterial Leaching

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Bacterial Leaching

Blue green streams of liquid found running from tailing dumps which left brown streaks of copper over iron implements at the Rio Tinto mine, Spain led to the discovery of micro-organisms by a team of microbiologists in 1947. These bacteria Thiobacillus ferro-oxidans and Thiobacillus thio-oxidans obtained the energy they needed to live by oxidising Fe2+ ions and S2- ions, respectively. In doing so these bacteria release copper bonded or trapped in compounds with Fe and S. This new breakthrough is known as Biohydrometallurgy. In use waste left from traditional copper mining is piled up on top of impermeable ground. It is sprayed with an acidic leaching solution, which contains the t. ferro-oxidans and T. thio-oxidans. Working best in an acidic environment of ph2 they oxidise Fe2+ ions S2- ions releasing Cu2+ ions in to the solution.

4CuFeS2 + 17O2 + 4H+ ==> 4Cu2+ + 4Fe3+ + 8SO42- + 2H2O

The solution Is then drained of from the bottom of the pile, so that the copper ions can be removed by the process of ligand exchange solvent extraction, in this a compound which is a good ligand for copper is dissolved in a solvent which is immiscible