EFFECT OF BACTERIAL ADAPTATION ON KINETICS AND MECHANISMS OF BIOLEACHING FERROUS SULFIDES

Thiobacillus ferrooxidans bacteria were used in this work to study the effect of bacterial adaptation on bioleaching of three iron-bearing sulfide minerals, namely, pyrite (FeS2), chalcopyrite (CuFeS2), and arsenopyrite (FeAsS). It was found that bacterial adaptation prior to bioleaching, enhanced the degree of sulfide leaching 2-4 fold over non-adapted bacteria. Also the bacterial activity was enhanced by 2-4.8 fold. The pH of leaching solution was decreased by the increase in both adaptation period and bioleaching time. A mechanistic model for bioleaching of sulfides with T. ferrooxidans is described. The model explains the role of bacteria in direct and indirect biochemical leaching reactions. It also reconciles such observed behaviors and phenomena as lag time, adaptation, pH increase during lag time, and electrochemistry of bioleaching. The model shows how direct and indirect biochemical interactions are involved in bioleaching of ferrous sulfides.