Bio-assisted leaching of copper, nickel and cobalt from copper converter slag

Bioleaching of the converter slag was studied on bench scale using Thiobacillus ferrooxidans, 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. The recoveries of metals from the slag under the sterile and bio-assisted leaching conditions were found as 80.0% and 99.0%Cu in 1920 h, 18.0% and 22.0% Ni in 1680 h and 16.0% and 30.0%Co in 1200 h respectively. The variance in leach recoveries 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.