Bio leaching of copper, nickel and cobalt from copper converter slag by Thiobacillus Ferroxidens

Bioleaching of the converter slag was studied on bench scale using Thiobacillus Ferroxidens, an iron oxidising bacteria for recovery of valuable metals at room temperature. Parameters such as particle size, pH, pulp density, Fe (II)/Fe(III) ratio and amount of Fe(II), additives etc., were optimised to treat the slag. In bioleaching with samples-1, 98.0% Cu in 50 days, 60.0% Ni in 75 days and 80.0% Co in 75 days were recovered but in experiments without bacteria the recoveries were 66.0% Cu in 50 days, 18.0% Ni in 75 days and 18.0% Co in 90 days. The recoveries of metals from another sample-2 under the sterile and bio-assisted leaching conditions were found as 80.0% and 99.0% Cu in 80 days, 18.0% and 22.0% Ni was mainly due to association of valuable metals in the fayalite, magnetite and copper metal/oxide phase. Based on these studies it may be concluded that the microorganism oxidised the iron available in the solution which accelerated the dissolution of the valuable metals by indirect mechanism.