[Removal of Hg in wastewater by zero-valent iron]

Kinetic characteristics of mercury ion (Hg2+) removal in wastewater by zero-valent iron (ZVI) and the influence factors were studied, and the reaction mechanism of ZVI and Hg2+ was preliminarily discussed. The removal rate of Hg2+ in wastewater reached 94.5% under the optimal removal conditions, i. e. the initial concentration of Hg2+ was 0.10 mg x L(-1), the initial pH was 5, the ZVI dosage was 0.050 g, and the temperature was 25 degrees C. There was a rapid removal process for Hg2+ in wastewater by ZVI, which could be described by the pseudo first-order reaction kinetic equation, and the rate constant was 0.010 min(-1). The removal mechanism of Hg2+ may mainly be attributed to the oxidation-reduction of ZVI, and the adsorption and flocculation precipitation of iron oxides and hydroxides. However, the passivation of FeOOH and Fe2O3-Fe3O4 on ZVI surface may be the main reason for the decrease in the removal rate of Hg2+. Humic acid (HA) in wastewater could not only form Fe-HA complex with the Fe2+ and Fe3+ produced by ZVI reduction, which increased the ratio of soluble iron and relieved ZVI passivation, but also stabilize fine iron oxide and iron hydroxide colloid, and thus enhance the adsorption of Hg2+ in wastewater.