Resin Supported Nanoscale Zero-valent Iron For Effective Removal Of Arsenite Through Simultaneous Oxidation And Adsorption

Arsenic contaminant in groundwater and wastewater greatly affects the health of millions of people worldwide.So developing and applying efficient techniques to control and remedy arsenic pollution has become the focus of water research.Zero-valent iron(ZVI)oxidation and adsorption is regarded as one of the most promising technologies for arsenic removal.However,in practical application ZVI nanoparticles will cause excessive pressure drops and it is hard to separate them from the system due to its tiny particle size.To overcome this bottleneck,a propriety process was employed to fabricate a novel type of polymeric hybrid material,D201-ZVI,by encapsulating nanoscale ZVI(nZVI)into a porous polystyrene anionic exchanger(D201).The removal of arsenite by the D201-ZVI in the presence of O2 and H2O2,and the underlying mechanisms were investigated.The effect of ZVI distribution and aging on the reactivity of the hybrid composite was investigated by comparing the As(?)removal performances of freshly synthesized and aged D201-ZVI composites.This work may shed light on designing and improving nanocomposites for arsenic removal.nZVI was loaded onto the anionic exchanger D201 through ion exchanging and chemical reduction.Arsenic removal by the as-prepared D201-ZVI was examined in batch and column tests.The results demonstrate that As(?)and As(?)could be efficiently sequestrated by the D201-ZVI.The removal of As(?)and As(?)by the D201-ZVI fitted the Langmuir isotherm with the maximum capacities of 121 mg/g and 125 mg/g,respectively.The capacity of arsenite removal depends on pH.The arsenite removal efficiency followed the sequence of pH 5>pH 7>pH 9>pH 3.The Cl-?NO3-?CO32-and SO42-anions had slightly negative effect on As(?)removal even at high concentration levels,whereas PO43-and SiO32-,especially PO43-,significantly reduced the removal efficiency under similar conditions.Column sorption results suggest that the sequestration on the D201-ZVI could result in a significant decrease of As(?)from 500 ?g/L to less than 10 ?g/L with the treatment volume up to 400 BV(Bed Volume)even in the presence of the commonly encountered anionic competition.The As(?)removal in the D201-ZVI/H2O2 system was investigated.Both the oxidation and removal of As(?)was enhanced by the introduction of H2O2.The effect of 2-propanol on the oxidation indicates that the oxidation might proceed mainly through a non-Fenton mechanism.H2O2 was directly converted into O2 and H2O by a series of 2e-transfer reactions in the cycling of Fe[IV]/Fe[?]on the surface.The removal rate of As(?)were increased with increasing D201-ZVI dose and initial arsenite concentration.The effect of pH on As(?)oxidation in the D201-ZVI/H2O2 system was obvious.The As(?)removal increased with increasing solution pH.Besides,there was an optimal H2O2 concentration for As(?)removal.The effect of ZVI distribution and aging on the reactivity of the hybrid composite was investigated by comparing the As(?)removal with freshly synthesized and aged D201-ZVI composites.The hybrids with more uniform ZVI distribution exhibited higher removal efficiency and faster reaction rate.After aging in aerated water for 24 h and 96 h,the ZVI distribution in the aged composites did not change significantly.However,both the Fe(0)content and the As(?)removal efficiency were decreased as the aging time increased.The composite with a peripheral ring-like shell-core structure was more severely oxidized than the homogeniously distributed counterpart.The results demonstrates that the starting composition of the particles is important for the aging and the As(?)removal performances.Based on the study of the arsenic removal by the D201-ZVI in the presence of O2,X-ray photoelectron spectroscopy(XPS)analysis was performed to further reveal the As(?)removal mechanisms.The reasonable mechanism consists of two steps:(1)oxidation of As(?)to As(?)and(2)adsorption of the resultant As(?),that is,in the presence of O2,the ZVI on-going corrosion in water not only caused As(?)oxidation to As(?)but also supplied a continuous source of surface sites for arsenic adsorption.Moreover,due to excellent As(?)adsorption capacity of D201,the resultant As(?)was not left in solution but ion exchanged onto the surface of D201-ZVI through the electrostatic interaction between the arsenic group and quaternary ammonium group.D201 plays multiple roles,acting not only as a supporter(a dispersant of nZVI),but also as an adsorbent of anion.