Impact of the copper solvent extraction reagent LIX 984N on the growth and activity of selected acidophiles

The effects of the copper extractant LIX 984N 20% v/v in Shellsol 2046 on the abilities of Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans to catalyse copper extraction from a chalcopyrite concentrate and to oxidise ferrous ion to ferric ion were compared and the possible role of Acidiphilium cryptum in ameliorating the effects of the SX reagent was examined. The SX reagent up to 250 mg/L was found to have little impact on the extraction of copper from a chalcopyrite concentrate using At. ferrooxidans. In contrast, with S. thermosulfidooxidans, copper extraction was reduced to about one third in the presence of 50 mg/L SX reagent and at 250 mg/L SX reagent, was barely more than for an abiotic test. The SX reagent strongly inhibited ferrous ion biooxidation by several bacterial species in contrast to At. ferrooxidans. The presence of 50 mg/L SX reagent caused oxidation rates to drop to between 0 and 12% of those in controls in approximately 40-hour tests. The most toxic component of the SX reagent was found to be 4-nonylphenol. A. cryptum tolerated 250 mg/L SX reagent but did not utilise it as an energy source. Bioleaching of chalcopyrite concentrate was not enhanced significantly when A. cryptum was added to test inocula. It is proposed that A. cryptum utilises fungal biomass as an energy source in managed heaps with solution recycle via solvent extraction plants. While it shares the environment with iron- and sulfur-oxidising acidophiles, it does not contribute directly to copper extraction from sulfide minerals.