Effective strategy for Cr(VI) removal from water in evolution process of ferroan brucite by redox and intercalation

Abstract

Cr(VI)-contaminated wastewater treatment is of great significance to ecological environment and human health. In this work, ferroan brucite with different Fe2+ doping amounts (Mg1-XFeX(OH)2, x = 0.1–0.8) were synthesized for the removal of Cr(VI) from wastewater. The effect of Fe content, initial concentration of Cr(VI), reaction time, co-existing ions and pH for Cr(VI) removal performance were examined. As Fe2+ content increased, the removal efficiency initially increased and then decreased, Mg0.4Fe0.6(OH)2 exhibited the maximum removal amount of 494.63 mg/g. Kinetic studies showed Cr(VI) removal well fitted pseudo-second-order model and achieved equilibrium at approximately 40 min. Isotherm data was well described by Langmuir model. The coexisting ions except CO32− had negligible effect, while pH had a significant influence on Cr(VI) removal since different dominated form of Cr(VI) existed at different pH. The removal mechanism towards Cr(VI) under different pH values was explored. At acidic environment, most Cr(VI) in Cr2O72− was reduced to Cr(III) by Fe2+ resulting in the precipitation of (Fe,Mg)(Cr,Fe)2O4, the remaining part was immobilized by interlayer of reaction product LDHs, and the intercalation amounts of Cr2O72− were 114.05 mg/g and 106.78 mg/g at pH of 3 and 6. While under alkaline conditions, most CrO42− entered the interlayer of LDHs with amounts of 262.3 mg/g at pH = 11, and the rest was absorbed on the surface. Furthermore, the reaction product could be recovered as chromite with recovery rate of 83.94 %. The excellent removal performance suggested a promising strategy in sewage water remediation.