title: Reduction and immobilization of chromate in chromite ore processing residue with nanoscale zero-valent iron.
abstract: Chromite ore processing residue (COPR) poses a great environmental and health risk with persistent Cr(VI) leaching. To reduce Cr(VI) and subsequently immobilize in the solid matrix, COPR was incubated with nanoscale zero-valent iron (nZVI) and the Cr(VI) speciation and leachability were studied. Multiple complementary analysis methods including leaching tests, X-ray powder diffraction, X-ray absorption near edge structure (XANES) spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to investigate the immobilization mechanism. Geochemical PHREEQC model calculation agreed well with our acid neutralizing capacity experimental results and confirmed that when pH was lowered from 11.7 to 7.0, leachate Cr(VI) concentrations were in the range 358-445mgL(-1) which contributed over 90% of dissolved Cr from COPR. Results of alkaline digestion, XANES, and XPS demonstrated that incubation COPR with nZVI under water content higher than 27% could result in a nearly complete Cr(VI) reduction in solids and less than 0.1mgL(-1) Cr(VI) in the TCLP leachate. The results indicated that remediation approaches using nZVI to reduce Cr(VI) in COPR should be successful with sufficient water content to facilitate electron transfer from nZVI to COPR.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Du
authors.forename: Jinsuo
authors.initials: J
authors.lastname: Lu
authors.forename: Qiong
authors.initials: Q
authors.lastname: Wu
authors.forename: Chuanyong
authors.initials: C
authors.lastname: Jing
mesh_terms: D002857:Chromium / Q000737:chemistry*; D017608:Chromium Compounds / Q000737:chemistry*; D052918:Environmental Restoration and Remediation / Q000379:methods; D019652:Extraction and Processing Industry; D007220:Industrial Waste; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D033362:Powder Diffraction; D012037:Refuse Disposal / Q000379:methods; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D017608:Chromium Compounds; D007220:Industrial Waste; D002857:Chromium; C074702:chromium hexavalent ion; D007501:Iron