title: Electro-migration of heavy metals in an aged electroplating contaminated soil affected by the coexisting hexavalent chromium.
abstract: Cr(VI) was often reported to oxidize soil organic matter at acidic environments due to its high ORP, probably thus changing cationic metal species bound to soil organic matter, and influencing their electro-migration patterns. However, such an effect on the electro-migration was not confirmed in most previous studies. Therefore, this study applied a fixed voltage direct current field on an aged electroplating contaminated clayed soil, with a special interest in the direct or indirect influence of Cr(VI) on the electro-migration of other coexisting metals. After 353 h electrokinetic process, 81% of Zn, 53% of Ni and 22% of Cu in the original soil were electro-migrated into the electrolyte, and most of the remaining concentrated near the cathode. The Cr(VI) oxidized some soil organic matter along its migration pathway, with a pronounced reaction occurred near the anode at low pHs. The resulting Cr(III) reversed its original movement, and migrated towards the cathode, leading to the occurrence of a second Cr concentration peak in the soil. Metal species analyses showed that the amount of metals bound to soil organic matter significantly decreased, while a substantial increase in the Cr species bound to Fe/Mn (hydro-)oxides was observed, suggesting an enhancement of cationic metal electro-migration by the reduction of Cr(VI) into Cr(III). However, the Cr(VI) may form some stable lead chromate precipitates, and in turn demobilize Pb in the soil, as the results showed a low Pb removal and an increase in its acid-extractable and residual fractions after electrokinetic remediation.
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-sen University, University Town, Guangzhou, China. zhangwh5@mail.sysu.edu.cn
authors.forename: Weihua
authors.initials: W
authors.lastname: Zhang
authors.forename: Luwen
authors.initials: L
authors.lastname: Zhuang
authors.forename: Lizhi
authors.initials: L
authors.lastname: Tong
authors.forename: Irene M C
authors.initials: IM
authors.lastname: Lo
authors.forename: Rongliang
authors.initials: R
authors.lastname: Qiu
mesh_terms: D002857:Chromium / Q000302:isolation & purification*; D004595:Electroplating / Q000295:instrumentation* / Q000379:methods; D052918:Environmental Restoration and Remediation / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019216:Metals, Heavy / Q000302:isolation & purification*; D012987:Soil / Q000032:analysis*; D012989:Soil Pollutants / Q000302:isolation & purification*
chemical_list: D019216:Metals, Heavy; D012987:Soil; D012989:Soil Pollutants; D002857:Chromium; C074702:chromium hexavalent ion