Processes Contributing to the Removal of Manganese from Mine Drainage by an Algal Mixture

摘要

An aerobic bench-scale experiment utilized algae to raise the pH (from ～ 6 to above 8) and remove manganese from an anaerobic constructed wetland effluent (from >20 mg/L to <0.3 mg/L Mn). Additional laboratory experiments were conducted to further examine the manganese removal mechanisms that occurred in the bench-scale reservoirs. Sequential extractions of the algal mass found that the manganese was predominantly associated with the carbonate and Mn oxide phases, and the algae contained 30 mg Mn per dry gram. The biosorption of manganese by nonliving algae in high pH-high Eh aquatic environments was found to be minimal compared to the manganese removed from solution by precipitation as amorphous manganese oxyhydroxides. Limestone contained in one of the bench-scale reservoirs was found to contain 0.16 mg Mn per g limestone when the limestone surfaces were dissolved. Thus, the removal of manganese by the algal mixture contained in the bench-scale reservoirs was accomplished by the precipitation of manganese carbonates and oxides on the algal mass, the precipitation of amorphous oxyhydroxides, and the binding or precipitation of manganese on the limestone surfaces.