Significance of Oxygen Supply in Jarosite Biosynthesis Promoted by Acidithiobacillus ferrooxidans

Jarosite [(Na+, K+, NH4+, H3O+)Fe3(SO4)2(OH)6] is an efficient scavenger for trace metals in Fe- and SO42--rich acidic water. During the biosynthesis of jarosite promoted by Acidithiobacillus ferrooxidans, the continuous supply of high oxygen levels is a common practice that results in high costs. To evaluate the function of oxygen in jarosite production by A. ferrooxidans, three groups of batch experiments with different oxygen supply levels (i.e., loading volume percentages of FeSO4 solution of 20%, 40%, and 70% v/v in the flasks), as well as three groups of sealed flask experiments with different limiting oxygen supply conditions (i.e., the solutions were not sealed at the initial stage of the ferrous oxidation reaction by paraffin but were rather sealed at the end of the ferrous oxidation reaction at 48 h), were tested. The formed Fe-precipitates were characterized via X-ray powder diffraction and scanning electron microscope-energy dispersive spectral analysis. The results showed that the biosynthesis of jarosite by A. ferrooxidans LX5 could be achieved at a wide range of solution loading volume percentages. The rate and efficiency of the jarosite biosynthesis were poorly correlated with the concentration of dissolved oxygen in the reaction solution. Similar jarosite precipitates, expressed as KFe3 (SO4) 2(OH)6 with Fe/S molar ratios between 1.61 and 1.68, were uniformly formed in unsealed and 48 h sealed flasks. These experimental results suggested that the supply of O2 was only essential in the period of the oxidation of ferrous iron to ferric but was not required in the period of ferric precipitation.