INFLUENCE OF PH ON MINERAL SPECIATION IN A BIOREACTOR SIMULATING ACID-MINE DRAINAGE

Mineral precipitates formed under conditions representative of acid mi ne drainage were prepared by oxidizing 0.1M FeSO4 . 7H(2)O solutions a t 24 degrees C and pH 2.3, 2.6, 3.0, 3.3 and 3.6 using a bioreactor an d a strain of Thiobacillus ferrooxidans. The oxidation of dissolved Fe 2+ was monitored colorimetrically and was completed within 90 to 120 h at all pHs. Schwertmannite, Fe8O8(OH)(6)SO4, was a major component of the precipitates and was the only phase formed at pH 3.0. Jarosite, ( H,Na,K)Fe-3(OH)(6)(SO4)(2), increased in abundance with decreasing pH whereas goethite, alpha-FeOOH, appeared at pH 3.3 and 3.6. A similar r elationship between pH and mineralogy has been reported in natural spe cimens of mine drainage ochres. Copyright (C) 1996 Elsevier Science Lt d.