Reciprocal interferences of heavy metal and dissolved organic matter on their immobilizations by modulating the interfacial interactions with nanoscale zero-valent iron

With the increasing application of nanoscale zero-valent iron (nZVI) in environmental remediation, exploring the reciprocal effects of heavy metals (HMs) and dissolved organic matter (DOM) on their immobilizations by nZVI is crucial for predicting carbon dynamics and contaminant behavior in the environment. By using manifold analyses, the reciprocal effects of HMs (Cr(VI) and Cd(II)) and humic acid (HA) on their immobilizations by modulating the interfacial interactions with nZVI were systematically investigated. It was found that the previous interaction of HA especially its contained nonfluorescent substances (i.e., lipids, polysaccharides, and lignin) with nZVI improved the immobilization of HMs on nZVI; the previous interaction of Cd(II) with HA or nZVI promoted the sequestration of organic carbon (up to 1.8-fold) especially the aromatic carbon and humic-like fluorophores of HA by nZVI, but Cr(VI) had no such effect. The oxidized iron complexes on nZVI dominated the ultimate immobilizations of HA and HMs. The increased immobilizations of unsaturated hydrocarbons and quinone ketones by the formed nZVI-HM complexes decreased the reduction capability but enhanced the photochemical stability of the residual aqueous HA. These findings are of significance to understanding nZVI interactions with DOM and HMs and the effects on the carbon cycle and HM immobilization in the environment.