FeS2/H2O2 mediated water decontamination from p-arsanilic acid via coupling oxidation, adsorption and coagulation: Performance and mechanism

Aromatic organoarsenic compounds (AOCs), comprising both inorganic and organic moieties, are widely used as animal feed additives. AOCs are ubiquitous in swine and poultry effluents as well as surrounding natural waters, though it is hard to efficiently remove AOCs from water due to the high stability and mobility. Herein, we utilize pyrite (FeS2)/H2O2 to decontaminate water from p-arsanilic acid (p-ASA), a representative AOC. The center dot OH radicals produced in FeS2/H2O2 transform p-ASA into As(III) and finally As(V), meanwhile considerable amount (60-90%) of the generated As(V) are adsorbed onto the newly formed iron (oxy)hydroxides. FeS2/H2O2 enables 92-100% removal of p-ASA in 2 h in a wide pH range 3-7, because the process releases massive H+ and changes solution pH to 3-4 rapidly, whereas classic Fenton (Fe2+/H2O2) exhibits> 90% p-ASA removal only at pH 3.0. The synergistic effects between %OH oxidation and adsorption are verified by reactive oxygen species quenching tests. The remaining As, mainly present as As(V), are further reduced to several mu g/L by subsequent coagulation with the dissolved Fe3+. The S(0)/S-n(2-) passivation layer formed on FeS2 surface is steadily eliminated by Fe2+/H2O2, while crystalline structure of the used FeS2 mineral remains unchanged, enabling its repeated use with constant decontamination efficiency. Besides, FeS2/H2O2 and Fe2+/H2O2 reduce p-ASA in contaminated lake water to <10 mu g/L and similar to 700 mu g/L, respectively, demonstrating the great potential of FeS2/H2O2 in practical water decontamination.