Iron and Trace Metal Retention in Net Alkaline Co2-Rich Mine Waters via Aerobic Processes

Abstract

Aerobic iron removal is a well-documented treatment process for netalkaline mine waters. In this study, on-site field mesocosm experiments were conducted to evaluate effective oxidative removal of iron and trace metals from a lead-zinc mine discharge in the former were conducted in 40-L containers and water quality was analyzed over 24 hours to evaluate the effects of aeration and degassing on homogeneous and heterogeneous iron removal mechanisms. All treatments were established in triplicate. Iron concentrations decreased rapidly and significantly in the aerated treatments (180 mg/L to < 10 mg/L), with the addition of iron precipitate to the initial treatment having no significant impact on rates or final concentration. Iron concentrations also decreased significantly in the open buckets, but not as greatly (to ~170 mg/L), and decreased slightly (but not significantly) in the closed treatments (to ~190 mg/L).Zinc, nickel, arsenic, cadmium and lead concentrations also decreased significantly in the aerated treatments. Despite the production of proton acidity from iron hydrolysis, pH increased significantly in the aerated treatments (from ~6 to ~8) and slightly in the open treatments (~6 to ~6.1). The pH did not change in the closed treatments. Increased pH with increased iron removal indicates the major importance of CO 2 degassing by aeration, thus impacting both iron and trace metal concentration changes.