title: Characterization of adsorbent composition in co-removal of hexavalent chromium with copper precipitation.
abstract: Mechanisms of hexavalent chromium co-removal with copper precipitation by dosing Na2CO3 were studied with a series of well-designed batch tests using solutions containing 150 mg l-1 Cu(II) and 60 mg l-1 Cr(VI). It was found that direct precipitation of chromium through formation of copper-chromium bearing precipitates (in the form of CuCrO4) was one of the main mechanisms contributing to chromium co-removal at pH close to 5.0, and adsorption of chromium at a higher pH by freshly formed copper-carbonate precipitates (adsorbent) contributed to further chromium co-removal. Since, according to solubility products, neither copper-carbonate nor copper-hydroxide precipitates can be produced at pH around 5.0 for a pure 150 mg l-1 copper precipitation, characterization of copper-carbonate precipitates (adsorbent) was carried out through developing pC-pH curves of the systems by both equilibrium calculations and MINEQL+ 4.5 (a chemical equilibrium modeling software), and also through laboratory determination of the precipitate composition, such as gravimetric analyses, inorganic carbon percentage and EDAX spectrum analyses. CuCO3.Cu(OH)2, or a combination of CuCO3.Cu(OH)2 (in majority) and Cu(OH)2 (in minority) were suggested to be the major constituent of the precipitates obtained from the copper solution with Na2CO3 dosing.
authors.affiliation: School of Environmental Science and Engineering, Tianjin University, No. 92, Weijin Road, Tianjin 300072, PR China. tju_jmsun@hotmail.com
authors.forename: Jing-Mei
authors.initials: JM
authors.lastname: Sun
authors.forename: Xin-Hua
authors.initials: XH
authors.lastname: Zhao
authors.forename: Ju-Chang
authors.initials: JC
authors.lastname: Huang
mesh_terms: D000327:Adsorption; D002274:Carcinogens, Environmental / Q000737:chemistry* / Q000302:isolation & purification*; D011232:Chemical Precipitation; D002857:Chromium / Q000737:chemistry* / Q000302:isolation & purification*; D003300:Copper / Q000737:chemistry*; D007220:Industrial Waste; D008669:Metallurgy; D018508:Water Purification / Q000379:methods
chemical_list: D002274:Carcinogens, Environmental; D007220:Industrial Waste; D002857:Chromium; C074702:chromium hexavalent ion; D003300:Copper