Reduction of Cr(VI) in simulated groundwater by FeS-coated iron magnetic nanoparticles

FeS-coated iron (Fe/FeS) magnetic nanoparticles were easily prepared, characterized, and applied for Cr(VI) removal in simulated groundwater. TEM, XRD, and BET characterization tests showed that FeS coating on the surface of Fe-0 inhibited the aggregation of Fe-0 and that Fe/FeS at a S/Fe molar ratio of 0.207 possessed a large surface area of 62.1 m(2)/g. Increasing the S/Fe molar ratio from 0 to 0.138 decreased Cr(VI) removal by 42.8%, and a further increase to 0.207 enhanced Cr(VI) removal by 63% within 72 h. Moreover, Fe/FeS inhibited the leaching of Fe, reducing the toxicity of the particles. Mechanistic analysis indicated that Fe-0, Fe2+, and S2- were synergistically involved in the reduction of Cr(VI) to nontoxic Cr(III), which further precipitated as (CrxFe1-x)(OH)(3) and Cr(III)-Fe-S. The process of Cr(VI) sorption by Fe/FeS (S/Fe = 0.207) was fitted well with a pseudo-second-order kinetic model, and the isotherm data were simulated by Langmuir isotherm model with a maximum sorption capacity of 69.7 mg/g compared to 48.9 mg/g for Fe-0. Low pH and initial Cr(VI) concentration favored Cr(VI) removal. Continuous fixed bed column studies showed that simulated permeable reactive barriers (PRB) with Fe/FeS was considerably effective for in situ removal of Cr(VI) from ground water. This study demonstrated the high potential of Fe/FeS for Cr(VI) immobilization in water, groundwater, and soil. (C) 2017 Elsevier B.V. All rights reserved.