Treatment of manganese, in the presence or absence of iron, in acid and neutral mine drainage using raw vs half-calcined dolomite

Abstract

Efficient removal of Mn from mine drainage is complex because of its high solubility minerals, especially in the presence of Fe. This study evaluates the comparative efficiency of raw and half-calcined dolomite for Mn removal in synthetic and real contaminated neutral drainage (CND) as well as in real acid mine drainage (AMD). Batch isotherms were used to evaluate the removal of Mn by raw and half-calcined dolomite, in the presence or the absence of Fe, in synthetic CND and in synthetic AMD. Batch kinetics tests were also performed, only for synthetic CND, in the absence of Fe. Raw dolomite showed limited efficiency in batch tests. Hence, only the half-calcined dolomite was used in column tests. Removal of Mn from synthetic CND (pH 6.84; 46.1 mg/L Mn) was effective for 106 days. For the following 119 days of monitoring, Mn was treated ≥95%. For Mn removal in real AMD (pH 2.40; 22.8 mg/L Mn and 679 mg/L Fe), half-calcined dolomite proved less effective. After 1 week, Mn, Ni and Zn were no longer treated, whereas after 3 weeks, the pH and the concentration of Cu in the final effluent were also no longer conform to the Canadian discharge criteria. In the same time, Co, Cr and Fe were still removed even after 8 weeks. For the real CND, Mn concentration decreased by >90% (0.65 mg/L at the inlet and 0.05 mg/L at the exit) with half-calcined dolomite. Therefore, half-calcined dolomite seems highly promising for the treatment of Mn in CND.