Features of ferric sulfate precipitates formed by different cultivations of Acidithiobacillus ferrooxidans

Abstract This study focused on the ferric sulfate precipitates formed during the culture of Acidithiobacillus ferrooxidans (A. ferrooxidans) in a modified 9K medium by applying a potential control on the electrode. X-ray diffraction (XRD), environmental scanning electron microscope (ESEM), Raman spe...
Ausführliche Beschreibung

Abstract This study focused on the ferric sulfate precipitates formed during the culture of Acidithiobacillus ferrooxidans (A. ferrooxidans) in a modified 9K medium by applying a potential control on the electrode. X-ray diffraction (XRD), environmental scanning electron microscope (ESEM), Raman spectroscopy (Raman) and Fourier Transform Infrared spectroscopy (FTIR) were carried out to characterize and identify the precipitates which were formed, respectively, in the electrochemical cultivation with a fixed cathode potential (bias-experiment) and in the conventional batch cultivation without cathode potential control (no-bias-experiment). The results indicated that K-jarosite presented in both experiments while $ NH_{4} $-jarosite and schwertmannite were only found in the no-bias-experiment. The formation of different precipitates could be attributed to the different growth statuses and rates of A. ferrooxidans and the different concentrations of $ Fe^{3+} $. In the bias-experiment, external electrons reproduced $ Fe^{2+} $ and promoted the growth of A. ferrooxidans, thus resulting in the low $ Fe^{3+} $ concentration and the rapid depletion of $ NH_{4} $+ as the nitrogen source, in which K-jarosite was preferentially formed. In the no-bias-experiment, the lower concentration of A. ferrooxidans was observed, which was due to the continuous consumption of $ Fe^{2+} $ by bacteria, thus resulting in the relatively higher $ Fe^{3+} $ and the $ NH_{4} $+ concentration in culture. The high concentration of $ Fe^{3+} $ favored the precipitation of the solid solution of K-$ NH_{4} $-$ H_{3} $O jarosite, and led to the formation of schwertmannite after $ K^{+} $ and $ NH_{4} $+ were depleted. Ausführliche Beschreibung