Removals of Cr(VI) and Cd(II) by a novel nanoscale zero valent iron/peroxydisulfate process and its Fenton-like oxidation of pesticide atrazine: Coexisting effect, products and mechanism

Abstract

Nowadays, inorganic and organic pollutants always coexist in the environment, thus an economic and efficient treatment is urgently required. In this paper, a novel nanoscale zero valent iron (AMD-nZVI) produced from the reaction of acid mine drainage (AMD) with NaBH4 was combined with peroxydisulfate (PDS) for the simultaneous removals of Cr(VI), Cd(II) and atrazine (ATZ) in water. Results demonstrate that the reactivity of AMD-nZVI/PDS process toward Cr(VI) removal was superior to that of AMD-nZVI/HCl or AMD-nZVI/H2O2 process. The coexisting species inculding PO43-, HCO3−, NO3 and humic acid exhibited obvious suppression on the Cr(VI) removal. The simultaneous removal efficiencies of Cr(VI), Cd(II) and ATZ by AMD-nZVI/PDS process were high up to 90% within 40 min. Most of Cr(VI) species were converted to Cr2O3 and Cr(OH)3, whereas both Cd(OH)2 and CdO were main Cd(II) species. The radical quenching tests affirmed that SO4− was the primary radical species for ATZ degradation. A total of five intermediate products of ATZ were sucessfully identified, and the degradation of ATZ was achieved through dealkylation, dechlorinatione and hydroxylation processes. A possible reaction mechanism involving in Cr(VI) reduction, Cd(II) precipitation and ATZ Fenton-like oxidation by AMD-nZVI/PDS process therefore was proposed.