Treatment Of Hexavalent Chromium Pollutants By Nanoscale Fe/Cu Bimetallic Particles

With the acceleration of industrial modernization in our country, problems caused by environmental pollution have become increasingly severe due to the significant emission of pollutants. Hexavalent chromium Cr(Ⅵ) is a kind of typical inorganic contaminants with extremely high eco-toxicity. As one of the largest chromium-production countries, emissions of chromium into our environment continue to increase with the further development of industrial use of chromium. Thus, effective measures need to be adopted to control the environmental contamination by chromium as soon as possible. In recent years, nanoscale zero valent iron-based materials have been widely used for environmental remediation due to their ultra high surface activity and reactivity. Researches show that nanoscale zero valent iron-based materials are able to effectively remove a variety of both organic and inorganic pollutants in environment, exhibiting a good potential of application in pollution treatment. In this study, nanoscale zero valent iron (NZVI) and Fe/Cu bimetallic nanoparticles were synthesized in the laboratory and were applied for treatment of Cr(Ⅵ) wastewater and contaminated soil. The effects of different environmental conditions on the removal of Cr(Ⅵ) by Fe/Cu bimetallic nanoparticles were investigated. The reaction kinetics and reaction mechanism of Fe/Cu nanoparticles and Cr(Ⅵ) were discussed.Moreover, the modification of Fe/Cu nanoparticles were also conducted to enhance their efficiencies in the Cr(Ⅵ) removal by reduction. The main conclusions are presented as follows:1) Characterization of nanoparticles were performed using TEM, BET and X-ray diffraction. Results indicated that the nanoparticles were successfully synthesized by reduction of FeCl3 using KBH4 in aqueous system. Cr(Ⅵ) were reduced to Cr(Ⅲ) by NZVI and Fe/Cu nanoparticles. Results showed that, the nano Fe/Cu bimetallic system had better Cr(Ⅵ) removal efficiency compared with NZVI, indicating that NZVI reactive activity could be enhanced by loading copper on the surface. Cr(Ⅵ) removal efficiency could be affected by different experimental conditions. When the copper loading of Fe/Cu nanoparticles was 3%, the dosing concentration was 0.2g/L and the initial concentration of Cr(Ⅵ) was 100mg/L,92.46% removal of Cr (Ⅵ) was obtained after 60 minutes.2) The Cr(Ⅵ) reduction process by Fe/Cu nanoparticles followed pseudo-first-order kinetics. When the copper loading of Fe/Cu nanoparticles was 3%, the nanoparticle dosage was 0.1 g/L, the initial concentration of Cr(Ⅵ) was 100mg/L and the initial pH was 3.5, the apparent rate constant kobs was 0.016mm-1. XPS were used to analyse the precipitate after the reaction between Fe/Cu nanoparticles and Cr(Ⅵ). Results showed Cr(Ⅵ) was reduced to Cr(Ⅲ) with Fe°oxidized to Fe(Ⅲ), followed by hydroxide precipitation and co-precipitation from the water.3) The contaminated soil with high concentrations of Cr(Ⅵ) obtained from the chemical plant in Hangzhou was selected as the test soil. The removal efficiency of water-soluble Cr(Ⅵ) in the soil by Fe/Cu nanoparticles was investigated. Results indicated that the water-soluble Cr(Ⅵ) could be removed efficiently by Fe/Cu nanoparticles and largest Cr(Ⅵ) removal efficiency was achieved when the copper loading of Fe/Cu nanoparticles was 5%. The water-soluble Cr(Ⅵ) removal rate could be 93.35% by adding 5% Fe/Cu nanoparticles into the soil with the ratio of soil quality and solution volume 1:10.4) Modifications of Fe/Cu nanoparticles were conducted by supporting them on bentonite and coating them with carboxymethyl starch(CMS), respectively. Results showed that higher removal efficiencies of water-soluble Cr(Ⅵ) in the soil by Fe/Cu nanoparticles were obtained after both two kind of modifications. The best mass ratio of bentonite and CMS to Fe/Cu nanoparticles was 1:1 and 3:1 individually. Cr(Ⅵ) removal rate was 98.58% and 97.77% by adding 2% bentonite-supported and CMS-coated Fe/Cu nanoparticles into the soil respectively.