The coupling reaction of Fe bio-oxidation and resulting Fe hydrolysis drastically improve the formation of iron hydroxysulfate minerals in AMD.

The oxidation of Fe by () in acid mine drainage (AMD) is often accompanied by formation of iron hydroxysulfate minerals, such as schwertmannite and jarosite. This study reported that 80 mmol L of Fe could be completely oxidized by LX5 within 48 h, but only 27.7% of the resultant Fe precipitated to form schwertmannite. However, the conversion efficiency to jarosite was much higher (54.5%). The formation of jarosite lasted 120 h, while only 24 h when conversed to schwertmannite. By constructing a cyclic process of 'Cu-reducing coupled with bio-oxidization', the total Fe in AMD could be fully converted into mineral precipitates. The resultant mineral specie could be regulated simply by control the K concentration. Thermodynamically, Fe cannot hydrolyze spontaneously to form schwertmannite due to the positive Gibbs free energy ( = 6.63 kJ mol) of the reaction. However, if Fe were biologically oxidized by , the resultant Fe could spontaneously form schwertmannite because the aforementioned coupling reaction has a negative Gibbs free energy ( = -34.12 kJ mol). Even though Fe itself could hydrolyze to form jarosite spontaneously with  = -22.20 kJ mol, the coupling reaction of Fe bio-oxidation followed by Fe hydrolysis in the presence of K could easily promote the formation of jarosite, which exhibited a great negative Gibbs energy ( = -67.45 kJ mol).