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Effects of iron/potassium molar ratio on mass of biogenic Fe(Ⅲ) hydroxysulfate precipitates in the FeSO4-K2SO4-H2O system and their environmental implications

Keywords: Acidithiobacillus ferrooxidans,secondary iron minerals,K+,environmental implication

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In the FeSO4-K2SO4-H2O biological oxidation system facilitated by Acidithiobacillus ferrooxidans, secondary ferric hydroxysulfate minerals are able to be synthesized including schwertmannite, potassium jarosite, and their mixture. In our system, the initial concentrations of ferrous iron were designed as 20, 40, 80 and 160 mmol·L-1 and the Fe/K molar ratios for each ferrous iron concentration treatment were designed as 3 to 200. The results show that treatment with lower initial Fe2+ levels such as 20 mmol·L-1 or 40 mmol·L-1 only produces a small amount of the precipitate with no more than 0.38 g produced after 72 h of reaction. With the increase of initial Fe2+ and the decrease of Fe/K molar ratios in the solution, the total amount of the precipitate formed by Acidithiobacillus ferrooxidans is greatly increased. For example, 4.48 g of jarosite are precipitated from 250mL of solution when the initial Fe2+ is 160 mmol·L-1and Fe/K is 3. The XRD pattern indicated that the precipitate is gradually transformed to crystallized jarosite from poorly-crystallized schwertmannite, exhibiting a close relationship between the mass produced and the mineral phase. For example, the amount of the precipitates formed as crystalline jarosite is much higher than that as poorly-crystallized schwertmannite. Therefore, the amount of biogenic minerals formed in the biological oxidation system depends, to a great extent, on the initial Fe2+ concentration and Fe/K molar ratio. This phenomenon is of potential significance in the removal of soluble Fe and SO2-4 from acid mine drainage.


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