Assessment of Optimal Iron Concentration in the Precipitation of Jarosite and the Activity of Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is one of the most important microorganism in bioleaching. During this process, biooxidation of iron leads to precipitation of jarosite. Jarosite decreases copper bioleaching efficiency. The aim of this study was to investigate the iron concentration in the precipitation of jarosite and the activity of Acidithiobacillus ferrooxidans. Acidithiobacillus ferrooxidans was cultivated in 9k medium containing ferrous sulfate (Fe2+) with concentrations of 5, 10, 20, 30, and 50g/100ml and also jarosite seed medium with concentrations of 5 and 10g/l. The iron concentration was assessed by atomic absorption. Jarosite was analyzed by Fourier-transform infrared spectroscopy (FTIR) and X-ray crystallography (XRD) methods. Findings: The cell count of Acidithiobacillus ferrooxidans, in Fe2+ concentrations of 5, 10, 20, 30, and 50g/100ml was 5×107, 2.5×108, 1.5‍×107, 10×107, and 7×107cell/ml, respectively. The jarosite precipitation rate in concentrations of 5, 10, 20, 30, 50g/100ml was 1.80, 6.09, 10.90, 16.65, and 28.8g. The minimum rate of jarosite precipitation was in 10g/100ml of Fe2+ concentration. Jarosite precipitation rate increased by increment of Fe2+ concentration and it was parallel with decrease of Acidithiobacillus ferrooxidans cell count in concentrations of 5 and 10g/l of jarosite seed; the jarosite precipitation rate was 3.13 , 3.68g. However the growth of Acidithiobacillus ferrooxidans was better than the absence of jarosite seed. The optimal concentration of Fe2+ in 9K medium is 10g/100 ml. In this condition, the maximum growth rate of Acidithiobacillus ferrooxidans and minimal precipitation of jarosite exist.