Characterizing the impact of MnO2 addition on the efficiency of Fe0/H2O systems

Abstract The role of manganese dioxide (MnO 2 ) in the process of water treatment using metallic iron (Fe 0 /H 2 O) was investigated in quiescent batch experiments for t ≤ 60 d. MnO 2 was used as an agent to control the availability of solid iron corrosion products (FeCPs) while methylene blue (MB) was an indicator of reactivity. The investigated systems were: (1) Fe 0 , (2) MnO 2 , (3) sand, (4) Fe 0 /sand, (5) Fe 0 /MnO 2 , and (6) Fe 0 /sand/MnO 2 . The experiments were performed in test tubes each containing 22.0 mL of MB (10 mg L −1 ) and the solid aggregates. The initial pH value was 8.2. Each system was characterized for the final concentration of H + , Fe, and MB. Results show no detectable level of dissolved iron after 47 days. Final pH values varied from 7.4 to 9.8. The MB discoloration efficiency varies from 40 to 80% as the MnO 2 loading increases from 2.3 to 45 g L −1 . MB discoloration is only quantitative when the operational fixation capacity of MnO 2 for Fe 2+ was exhausted. This corresponds to the event where adsorption and co-precipitation with FeCPs is intensive. Adsorption and co-precipitation are thus the fundamental mechanisms of decontamination in Fe 0 /H 2 O systems. Hybrid Fe 0 /MnO 2 systems are potential candidates for the design of more sustainable Fe 0 filters.