Enhanced Cr(VI) stabilization in soil by carboxymethyl cellulose-stabilized nanosized Fe0 (CMC-nFe0) and mixed anaerobic microorganisms

Abstract

A collaborative system of carboxymethyl cellulose stabilized nanosized zero-valent iron (CMC-nFe0) and microorganisms was set up to enhance the stabilization of Cr(VI) in soil. In comparison with an aqueous-bound Cr(VI) removal of 18.9% in the nFe0 system, a higher Cr(VI) removal of 68.9% was achieved in the nFe0 and microorganisms system after 14 d remediation because the microorganisms on the nFe0 surface promoted nFe0 corrosion and enhanced abiotic and biotic Cr(VI) stabilization by generating highly active minerals such as magnetite, lepidocrocite and green rust on the nFe0 surface. As a stabilizing agent for nFe0 and an organic substrate for microorganisms, CMC on the nFe0 surface not only enhanced the dispersion of nFe0, but also boosted the activity of microorganisms, resulting in a promotion of 0.9 and 0.5 times higher aqueous-bound Cr(VI) removal via the improvement of nFe0 and microorganisms respectively, thus a total 4 times higher aqueous-bound Cr(VI) removal of 95.3% was achieved in the CMC-nFe0 and microorganisms system as compared to the nFe0 system. After 14 d remediation, easily available species of Cr(VI) and Crtotal, such as water soluble (WS), exchangeable (EX) and bounded to carbonates (CB), were mainly transformed to less available Fe–Mn oxides-bounded (OX) and residual (RS) species because of the production of ferrochrome precipitates (CrxFe1-xOOH or CrxFe1-x(OH)3). Besides, the stabilization of Cr(VI) in the CMC-nFe0 and microorganisms system was pH-dependent and it increased with CMC-nFe0 dosage. Due to excellent Cr(VI) stabilization and Cr immobilization, coupled CMC-nFe0 and anaerobic microorganisms process is of great potential in remediating Cr(VI)-containing soil.