TREATMENT OF WATER FROM AN OPEN-PIT COPPER MINE USING BIOGENIC SULFIDE AND LIMESTONE - A FEASIBILITY STUDY

A bench-scale biogenic sulfide and limestone treatment system was used to treat acidic metal-contaminated water from the Berkeley Pit, an abandoned open-pit copper mine in Butte, Montana. Hydrogen sulfide was generated in a sulfate reduction bioreactor and was used to precipitate metal sulfides from the mine water in a separate reactor. The metal-depleted, sulfate-rich mine water then passed through a limestone-filled reactor to raise its pH before entering the bioreactor. The treatment process removed more than 99% of the initial concentrations of Fe, Cu, Zn, and Al (620, 178, 530, and 278 mg l(-1), respectively) in the mine water. The process also removed 91% of the initial Mn concentration (191 mg l(-1)). Copper and Zn concentrates were selectively recovered from the mine water based on the pH-dependent dissociation of the added H2S. The limestone used to raise the pH was eventually passivated, possibly by the precipitation of gypsum, silica, clay minerals, and aluminum hydroxide. A modification of this biogenic sulfide/limestone treatment system has the potential to treat Berkeley Pit water to within discharge standards, and could generate saleable metal sulfide concentrates to partially offset treatment costs.