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.