Experimental Studies on Metal Extraction Improvement in Bacterial leaching

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Bacterial leaching has the advantages of low energy consumption and operation costs over abiological conventional processes, and is now used commercially to recover copper from low-grade sulfide ore which would otherwise be waste. However, the leaching rate is generally slow and metal extraction is incomplete. To achieve higher leaching rates and metal recovery, it is important to establish the factors influencing leaching behavior. The authors have investigated the effects of extracellular phospholipids and polyoxyethylene sorbitan monolaurate on bacterial leaching of chalcopyrite by Thiobacillus ferrooxidans.Phosphatidylglycerol and phosphatidylethanolamine are main phospholipids detected in the cultures of iron-oxidizing bacteria. The former depressed chemical leaching of chalcopyrite with ferric sulfate and ferrous oxidation by T.ferrooxidans. The final copper extraction in bacterial leaching decreased with increasing phosphatidylglycerol addition.On the other hand, phosphatidyleth … More anolamine accelerated slightly the chemical leaching and had no effect on the ferrous oxidation. The copper extraction in bacterial leaching was not affected by phosphatidylethanolamine.Polyoxyethylene sorbitan monolaurate is a nonionic surfactant. Without the surfactant, most cells of T.ferrooxidans adhered to chalcopyrite surfact and soluble iron was dominantly present in ferrous form. The surfactant depressed the cell adhesion to the mineral surface and number of cells in the liquid phase increased with increasing addition. When adding 20 to 50 g/m^3 of the surfactant, the cells in the liquid phase rapidly oxidized ferrous ions to ferric ions and chalcopyrite was chemically oxidzed by the ferric ions, as a result the amount of extracted copper increased markedly. However, the excessive addition depressed the bacterial ferrous oxidation and the chemical leaching of chalcopyrite with ferric ions, consequently copper extraction was decreased.Moreover, the authors have developed a simple and rapid cell growth estimation method for T.ferrooxidans. Less