Application Of Carbon Modified Nano-zero-Valent Iron In Treatment Of Chromium Pollution

Nano zero-valent iron(nZVI)is widely used in the treatment of Cr(VI)in water and soil,but its development in pollution treatment is limited due to its disadvantages such as easy aggregation.Many studies have shown that loading nZVI on a stable carrier can effectively improve its defects.In this paper,a novel carbon-modified nZVI was prepared by the two-step of hydrothermal synthesis and liquid-phase reduction method.The synthesis mechanism was explored through characterization.The materials were applied to the treatment of Cr(?)in water and soil,and the application properties of the materials were investigated,and removal mechanism of Cr(?)was explored.The main conclusions of this study are as follows:(1)A modified activated carbon(MAC)was prepared by hydrothermal synthesis and a new carbon modified nZVI material was synthesized by liquid phase reduction in polyethylene glycol-water solution system.This material with surface of a fungus-like structure has a maximum surface area of 141.85 m2·g-1,and the pore volume of 0.202 cm3·g-1.The nZVI particles embedded in the fungus-like structure of material are spherical and chain-like,with a particle size of about 30?40 nm,and a body-centered cubic structure;X-ray diffraction,X-ray photoelectron spectroscopy and other characterization analysis showed that the structure of the fungus-like structure is a polyalcohol crystal in which depolymerization of the polyethylene glycol component in the synthesis system produces small molecules and recombination takes place on the MAC.(2)By examining the effect of removing Cr(VI)from carbon-modified nZVI material in water,it is found that the optimal iron-carbon ratio of the material is 1.5 g·g-1,and the optimal parameters for Cr(VI)-contaminated wastewater treatment are:The initial concentration was 40 mg·L-1.The pH value of the solution was 4 and the material dosage was 4 g ·L-1.The material had better removal effect for the solution with 80?200 mg·L-1 Cr(VI)concentration,and removal rate is close to 100%.And in alkaline conditions,the removal rate remains high.The removal process is in accordance with the pseudo-secondary adsorption kinetic equation and the apparent first order reaction kinetics equation.(3)By examining the effect of carbon-modified nZVI materials on Cr(VI)soils,it was found that the effect of repairs increased with the increase of the material dosage,and decreased with increasing of soil-water ratio.When the dosage was 0.5%,the best repair effect was 89%.The repair process basically reached equilibrium at 5 h,and with the progress of the reaction,the removal rate had a slight downward trend.(4)The removal mechanism of Cr(VI)by carbon-modified nZVI materials was explored:on the surface of material,nZVI reduces Cr(VI)to Cr(III),iron ions and Cr(III)form iron chromium hydroxide or iron chromium oxyhydroxide deposits on the surface of the material.Fungus-like structures constitute microdomains with high H+ concentrations to ensure the reaction under alkaline conditions.Cr(VI)soil remediation also includes desorption of Cr(VI)by soil particles,and the desorption process is a rate-control step.