The Influence Of Microplastics On Heavy Metal Remediation By Nano Zero-valent Iron(nZVI)

Nano zerovalent iron(nZVI)is one of the most broadly applied nanomaterials in the fields of groundwater remediation which benefits from its high reactivity for pollutants.However,its successful application faces challenges due to its tendency to agglomerate or form passive(oxy)hydroxide corrosion.With the emerging microplastics(MPs)pollution in groundwater system in recent years and considerable data vacancy on its potential physicochemical and ecological effects,it complicates the situation for groundwater remediation.Hereby,we investigated the effects on metal removal by nZVI in groundwater in the presence of various MPs.The removal capacity of Cu(II),Cr(VI),Pb(II)and Zn(II)by nZVI was found to be inhibited to different degrees in the presence of MPs.Desorption of metallic ions was observed dependent on various metal species,with the highest desorption rate in Zn(II).Amongst all MPs investigated,including polystyrene(PS),polyethylene(PE),polyethylene terephthalate(PET),and polyvinyl chloride(PVC),PVC poses the most adverse impact on metal desorption,attributing to its promotion of nZVI aging through electrostatic attraction.This study focused on the impact of MPs to metal remediation,beyond the general aspect of MPs hazard such as its toxic effects or delivery of contaminants.Moreover,groundwater was investigated to make a useful supplement to the research of MPs which primarily focuses on surface water.After finding that MPs can promote aging and inhibit the removal of heavy metals by nZVI,in order to find solution to overcome the inhibition of MPs,we chose sulfidation modification of nZVI to deal with problems caused by MPs,because according to previous studies,sulfidation can enhance the surface conductivity and electron transfer ability from iron core and improve electron selectivity.Batch experiments were carried out,indicating polyvinyl chloride(PVC)inhibited the metal sequestration efficiency of nZVI and resulted in desorption of metals(especially in Zn(II)system).After sulfidation,however,such inhibition on Zn(II)from PVC was only observed before equilibrium,while inhibition completely disappeared on the other metals.With the employment of S-nZVI,Cu(II),Pb(II),Zn(II)could reach a complete(100%)removal within 24 h even under the interference of PVC.Therefore,sulfidation assisted to overcome the inhibition of PVC on nZVI,which was attributed to the improved reducing,adsorbing ability,higher affinity of metals with Fe S layer and the anti-ageing capacity of S-nZVI.These findings found sulfidation to be a promising measure to overcome the inhibition of PVC,had a clearer insight of the interaction mechanism between S-nZVI and metal ions,and the mechanism of PVC inhibition,which also brought insights to promote heavy metal removal using S-nZVI in the face of intricate surrounding environment.