Study on the removal effect and influencing factors of nitrobenzene reduction by iron carbonate precipitates

To investigate the activity of iron carbonate precipitates produced by long-term operation of Fe⁰ permeable reactive barriers, three kinds of precipitates, namely Fe₆(OH)₁₂CO₃, Fe₂(OH)₂CO₃, and FeCO₃, were prepared to reduce the pollutant nitrobenzene. We studied the reduction effects of these iron carbonate precipitates on nitrobenzene by considering three factors, namely the initial nitrobenzene concentration, initial pH, and precipitate dosage, and established the kinetic degradation using pseudo-first-order kinetics model. The results showed that all three precipitates can reduce nitrobenzene, and the order of reducing capability is Fe₆(OH)₁₂CO₃ > Fe₂(OH)₂CO₃ > FeCO₃; moreover, the removal efficiency values of nitrobenzene are 68.08, 53.00, and 50.29%. A high initial nitrobenzene concentration and high pH value are beneficial to nitrobenzene reduction, and removal efficiency was increased when pH was increased from 4 to 9. In addition, the increased precipitate addition in the Fe₆(OH)₁₂CO₃ and Fe₂(OH)₂CO₃ systems increased removal efficiency. Furthermore, the dosage did not significantly influence the removal rate in the FeCO₃ system. Fe₆(OH)₁₂CO₃ and Fe₂(OH)₂CO₃ mainly relied on the precipitate itself with the structural Fe(II) to reduce nitrobenzene, and FeCO₃ mainly relied on the dissolved Fe²⁺. The reaction of all three precipitates in reducing nitrobenzene followed the first-order reaction kinetics.