The coupling of sand with ZVI/oxidants achieved proportional and highly efficient removal of arsenic

The coupling of zero-valent iron(ZVI)with common oxidants has recently achieved very rapid and highly efficient removal of Heavy metals from wastewater.However,the uniform activation of ZVI throughout the column and the proportional removal of target contaminants are urgently required for the prevention of premature filter clogging and the extension of the effective column operational time.In this study,we successfully achieved this objective by simply doping granular sand with ZVI at appropriate weight ratios.When pure ZVI packed column was spiked with oxidants,the majority of As trapping occurred between the column inlet and the first sampling point.In a packed column with a 1:20 mixture of ZVI and sand,the average As removal efficiency was 36(1st),13.1(2nd),18.5(3rd),19.2(4th)and 5.9%(5th outlet).The overall arsenic removal performance of the composite filling system of ZVI/sand was equally as efficient as that of the previous pure ZVI-packed system.Moreover,the leaching of Fe was significantly reduced with an increased sand ratio,resulting in clearer water with less turbidity.The results of X-ray photoelectron spectroscopy(XPS)demonstrated that more than 54%of the arsenic was reduced to As(III).X-ray diffraction(XRD)and scanning electron microscopy(SEM)confirmed the extensive corrosion of the ZVI surface,which resulted in various species of iron oxyhydroxides responsible for the highly efficient sequester of arsenic through reduction,adsorption,and coprecipitation.

Rapid and long-effective removal of broad-spectrum pollutants from aqueous system by ZVI/oxidants

Zero-valent iron(ZVI)technology has recently gained significant interest in the efficient sequestration of a wide variety of contaminants.However,surface passivation of ZVI because of its intrinsic passive layer would lead to the inferior reactivity of ZVI and its lower efficacy in contaminant removal.Therefore,to activate the ZVI surface cheaply,continuously,and efficiently is an important challenge that ZVI technology must overcome before its wide-scale application.To date,several physical and chemical approaches have been extensively applied to increase the reactivity of the ZVI surface toward the elimination of broad-spectrum pollutants.Nevertheless,these techniques have several limitations such as low efficacy,narrow working pH,eco-toxicity,and high installation cost.The objective of this mini-review paper is to identify the critical role of oxygen in determining the reactivity of ZVI toward contaminant removal.Subsequently,the effect of three typical oxidants(H2O2,KMnO4,and NaClO)on broad-spectrum contaminants removal by ZV1 has been documented and discussed.The reaction mechanism and sequestration efficacies of the ZVI/oxidant system were evaluated and reviewed.The technical basis of the ZVI/oxidant approach is based on the half-reaction of the cathodic reduction of the oxidants.The oxidants commonly used in the water treatment industry,i.e.,NaClO,O3,and H2O2,can be served as an ideal coupling electron receptor.With the combination of these oxidants,the surface corrosion of ZVI can be continuously driven.The ZVI/oxidants technology has been compared with other conventional technologies and conclusions have been drawn.