Pablo dos Santos Pina

Kinetics of Ferrous Iron Oxidation by Moderately Thermophilic Microorganisms

The biological oxidation of ferrous iron is an important sub-process in the bioleaching of metal sulphides and other bioprocesses such as the removal of H2S from gases, the desulphurization of coal and the treatment of acid mine drainage (AMD). Owing to the numerous potential applications of ferrous iron biooxidation, several works were carried out with mesophilic microorganisms, especially with Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, and only few studies were performed with moderately thermophilic and thermophilic microorganisms. The latter two have potential to be applied to the leaching of refractory sulphides such as chalcopyrite and requires a smaller degree of reactor cooling during bioleaching. The ferrous iron oxidation kinetics in the presence of Sulfobacillus thermosulfidooxidans (DSMZ 9293) was studied. The experiments were carried out in batch mode (2L CSTR) and the effect of ferrous iron concentration (2-20g/L) on the ferrous iron consumption and bacterial growth rate was studied. The Monod equation was applied to describe the growth kinetics of this microorganism and values of μ max and KS around 0.33 h -1 and 1.18g/L, respectively, were achieved, similarly to those reported for mesophilic microorganisms.

Tecnologia limpa para redução de impacto ambiental do cianeto na mineração de ouro

A study on metal cyanocomplexes sorption on polyacrylic ion exchange resins has been undertaken. Batch sorption experiments have shown that polyacrylic resins have a high affinity for zinc and iron cyanides compared to copper complexes. Elution studies performed in column experiments have also depicted that 1mo/L sodium thiocyanate solutions can successfully extract the three metals. Conversely, sodium nitrate solutions at the same concentration are not effective in eluting zinc cyanocomplexes. Based on elution figures, it is proposed that copper and iron can be selectively eluted with nitrate before the zinc, this latter being recovered afterwards with thiocyanate solutions. Both eluants were able to concentrate the cyanocomplexes in solution with a beneficial effect on the subsequent steps of cyanide recycling.