Sulfidation enhanced reduction of polybrominated diphenyl ether and Pb(II) combined pollutants by nanoscale zerovalent iron: Competitive reaction between pollutants and electronic transmission mechanism

Abstract Sulfidated nanoscale zerovalent iron (S-nZVI) has showed higher reactivity towards organic pollutants and metal ions than nZVI. However, the competitive reaction and electron transport mechanism of organic-metal ions with S-nZVI in one-pot need further clarification. In this study, the removal mechanism of Pb(II) and decabromodiphenyl ether (BDE-209) complex contaminants by S-nZVI was systematically investigated. Compared with nZVI, the removal kinetic constants of BDE-209 and Pb(II) by S-nZVI (S/Fe ratio=0.2) increased 7.29 and 5.15 times, respectively. Pb(II) can be immobilized to PbO, Pb0 and PbS by S-nZVI particles via various surface reactions as electrostatic adsorption, reduction reaction and co-precipitation process. The removal efficiencies of Pb(II) by S-nZVI did not change significantly with increasing BDE-209 concentration. But in low S-nZVI dosage system, S-nZVI could preferentially react with Pb(II) due to the stronger electrostatic adsorption between S-nZVI and Pb(II) than that of S-nZVI and BDE-209. It was the formation of a galvanic effect of Pb0 with Fe0 on S-nZVI surface rather than active hydrogen atom (·H) that enhanced the reductive rate of BDE-209 in the presence of Pb(II). Sulfidation could inhibit the passivation and corrosion process by water/dissolved oxygen and improve the storage time and lifetime of nZVI. Whereas, the presence of Pb(II) accelerated the corrosion of S-nZVI during the aged reaction even without BDE-209, which adversely affected the longevity of S-nZVI. The dual effects of Pb(II) on the treatment of compound pollutants of BDE-209 and metal ions by S-nZVI should be taken into account in real application.