SELECTION OF REACTIVE MIXTURES FOR USE IN PERMEABLE REACTIVE WALLS FOR TREATMENT OF MINE DRAINAGE

Porous, permeable, geochemically reactive walls, installed in situ in the path of migrating groundwater, present a promising passive treatme nt alternative for remediating metal-contaminated groundwater derived from oxidized mine wastes. Contaminants are removed from the groundwat er as a result of bacterial sulfate reduction and the subsequent preci pitation of sparingly soluble sulfide solids. The permeability and rea ctivity of eight organic-carbon reactive mixtures were assessed. The p ermeability ranged between <10(-4) and 10(-2) cm/s. Batch tests conduc ted using simulated mine drainage indicated that, within 40-70 days, S O4 concentrations decreased from initial concentrations of 1200-4800 m g/L to final concentrations of <10 mg/L in four mixtures. Iron concent rations decreased from initial concentrations of between 105 and 1400 mg/L to concentrations between 0.1 and 50 mg/L within 0.1-65 days. Con centrations of 480 mg/L Ni and 135 mg/L Cd decreased to below 0.05 mg/ L within 10 days, pH and alkalinity values increased from initial pH v alues of <6 to values of 6.5-7 and alkalinity values (as CaCO3) of <15 mg/L to >1000 mg/L Geochemical model calculations suggest precipitati on of Fe and Zn sulfide phases and the Mn carbonate phase rhodochrosit e. The reactivity of the mixtures varied with those containing several organic sources being most reactive. Results obtained from these stud ies indicate that levels of reactivity and permeability suitable for r emediating tailings-impacted groundwater can be attained.