Remediation of hexavalent chromium contamination in chromite ore processing residue by sodium dithionite and sodium phosphate addition and its mechanism

JOURNAL OF ENVIRONMENTAL MANAGEMENT

卷:192

Article

Li, Yunyi^1,2  Cundy, Andrew B.²  Feng, Jingxuan³  Fu, Hang¹  Wang, Xiaojing¹  Liu, Yangsheng¹ 

[1] Peking Univ, Coll Environm Sci & Engn, Beijing Key Lab Solid Waste Utilizat & Management, Beijing 100871, Peoples R China

[2] Univ Southampton, Sch Ocean & Earth Sci, Southampton 5014 3ZH, Hants, England

[3] Ctr Environm Educ & Commun, Minist Environm Protect, Beijing 100029, Peoples R China

关键词: Cr(VI);    Na2S2O4;    Na3PO4;    COPR;    Remediation;    Reductive precipitation;   

DOI  :  10.1016/j.jenvman.2017.01.031

来源: Elsevier

【 摘 要 】

Large amounts of chromite ore processing residue (COPR) wastes have been deposited in many countries worldwide, generating significant contamination issues from the highly mobile and toxic hexavalent chromium species (Cr(VI)). In this study, sodium dithionite (Na2S2O4) was used to reduce Cr(VI) to Cr(III) in COPR containing high available Fe, and then sodium phosphate (Na3PO4) was utilized to further immobilize Cr(III), via a two-step procedure (TSP). Remediation and immobilization processes and mechanisms were systematically investigated using batch experiments, sequential extraction studies, X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). Results showed that Na2S2O4 effectively reduced Cr(VI) to Cr(III), catalyzed by Fe(III). The subsequent addition of Na3PO4 further immobilized Cr(III) by the formation of crystalline CrPO4 center dot 6H(2)O. However, addition of Na3PO4 simultaneously with Na2S2O4 (via a one-step procedure, OSP) impeded Cr(VI) reduction due to the competitive reaction of Na3PO4 and Na2S2O4 with Fe(III). Thus, the remediation efficiency of the TSP was much higher than the corresponding OSP. Using an optimal dosage in the two-step procedure (Na2S2O4 at a dosage of 12x the stoichiometric requirement for 15 days, and then Na3PO4 in a molar ratio (i.e. Na3PO4: initial Cr(VI)) of 4:1 for another 15 days), the total dissolved Cr in the leachate determined via Toxicity Characteristic Leaching Procedure (TCLP Cr) testing of our samples was reduced to 3.8 mg/L (from an initial TCLP Cr of 112.2 mg/L, i.e. at >96% efficiency). (C) 2017 Elsevier Ltd. All rights reserved.

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