Characterizing the impact of MnO(2) addition on the efficiency of Fe(0)/H(2)O systems

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.