Use of the GEOCOAT™ process for the recovery of copper from chalcopyrite

In this study, the GEOCOAT™ process was evaluated as a low cost altemative for chalcopyrite bioleaching.The effect of temperature, leach solution composition, silver addition, and type of microorganisms inoculated were investigated in laboratory tests. Experiments were carried out at moderate temperature (35–45 °C) using a mixed mesophilic bacterial culture, and at elevated temperature (70 °C) using thermophilic archaea (extreme thermophiles).Chalcopyrite concentrate was coated onto inert support for the moderate temperature experiments, and onto low-grade chalcopyrite ore for the elevated temperature experiment. The rates of copper leaching were determined by analysis of leach solutions from small temperature-controlled columns. The extent of total copper removal was determined by residual copper analysis. The use of thermophilic archaea at 70 °C resulted in 94% extraction of the concentrate copper, and 86% of the total copper, in 90 days. The improved leaching at elevated temperatures supports the contention that chalcopyrite bioleaching at lower temperatures is limited by the formation of a heat labile passivation layer. The best result at moderate temperature was 97% copper removal achieved with the addition of 0.1% silver sulfate, compared to 19.2% without silver. This result agrees with previous reports which found that silver enhanced chalcopyrite bioleaching at moderate temperatures. The GEOCOAT™ process can be used to leach high yields of copper from chalcopyrite concentrates over a wide range of copper grades. In addition, substantial copper recoveries may be achieved in as little as 90 days.