BIOLOGICAL EXTRACTION OF METALS - THE RATE-CONTROLLING STEP

Although an enormous amount of work has been done in the area of biohy drometallurgy, the influence of the inert solid matrix on metal extrac tion, and consequently the rate-controlling mechanism have not been fu lly understood. Actually, most studies have mainly focused on the bioe xtraction of metals from high-grade mineral concentrates. Such an appr oach is important in elucidating the diffusion and reaction phenomena that are taking place on the surface of the mineral. In reality, howev er, the mineral is embedded within an inert solid matrix which will ha ve significant effects on diffusion and chemical reaction rate process es. In this work, a detailed experimental kinetic study was conducted to incorporate this factor in an attempt to quantify the rate-controll ing mechanism involved. The biological dissolution of pyrite in the pr esence of acidophilic Thiobacillus ferrooxidans was investigated in a batch experiments on three distinct mine waste rocks. The experiments were conducted on two particle sizes and at three operating temperatur es. Based on particle size and activation energies results, it was fou nd that intraparticle mass transfer resistances were solely the rate-c ontrolling mechanism for this process This new finding is different fr om that reported by other investigators who underestimated the importa nce of intraparticle mass transfer resistances. Also, because similar processes are ubiquitous in nature, this work should have broad applic ations.