Multiple factor design for reactive mixture selection for use in reactive walls in mine drainage treatment

Sulfate-reducing reactive walls installed in situ in the path of acid mine drainage contaminated groundwater, present a promising passive treatment technology. However, a rigorous and methodical selection of the most appropriate reactive mixture composition still needs to be investigated. The aim of this study was the selection of the most reactive medium using a multiple factor design and the modeling of the sulfate-reduction rate. Reactivity of 17 mixtures was assessed in batch reactors (in duplicates) using a synthetic AMD. Results indicate that within 41 days, sulfate concentrations decreased from initial concentrations of 2000–3200 mg/l to final concentrations of <90 mg/l. Metal removal efficiencies ranged between 51–84% for Ni and 73–93% for Zn. Generated sulfate-reduction rate predictive models which had very satisfactory parameters (R2=0.86, F=62.38 (p-level <10−13) and R2=0.90, F=62.30 (p-level <10−13)) identified poultry manure and two other carbon sources as the critical variables for sulfate-reduction rate.