Slow Formation and Dissolution of Zn Precipitates in Soil: A Combined Column-Transport and XAFS Study

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• 作者：Andreas Voegelin ; Andreas C. Scheinost ; Karin Bü ; hlmann ; Kurt Barmettler ; and Ruben Kretzschmar
• 刊名：Environmental Science & Technology
• 出版年：2002
• 出版时间：September 1, 2002
• 年：2002
• 卷：36
• 期：17
• 页码：3749 - 3754
• 全文大小：130K
• 年卷期：v.36,no.17(September 1, 2002)
• ISSN：1520-5851

文摘

Recent spectroscopic studies have demonstrated theformation of layered double hydroxides (LDH) andphyllosilicates upon sorption of Zn²⁺, Ni²⁺, and Co²⁺ toclay minerals and aluminum oxides at neutral to alkalinepH and at relatively high initial metal concentrations (>1mM). The intention of the present study was to investigatewhether such phases also form in soil under slightlyacidic conditions and at lower metal concentrations.Columns packed with a loamy soil were percolated withaqueous solutions containing 0.1 or 0.2 mM Zn, Ni, Co, andCd in a 10 mM CaCl₂ background at pH 6.5. Metalbreakthrough curves indicated a rapid initial sorptionstep, resulting in retarded breakthrough fronts, followedby further slow metal retention during the entire loadingperiod of 42 days (7000 pore volumes). Total metal sorptionand the contribution of slow sorption processes decreasedin the order Zn > Ni > Co > Cd. Leaching the reactedsoil with 10 mM CaCl₂ at pH 6.5 remobilized 8% of the totalretained Zn, 15% of Ni, 21% of Co, and 77% of Cd.Subsequent leaching with acidified influent (pH 3.0)remobilized most of the remaining metals. X-ray absorptionfine-structure (XAFS) spectroscopy revealed that slowZn sorption was due to the formation of a Zn-Al LDHprecipitate. Although Ni, Co, and Cd concentrations weretoo low for XAFS analysis, their leaching patterns suggestthat part of Ni and Co were also incorporated in solid phases,while most sorbed Cd was still present as exchangeablesorption complex after 42 days. A small but significantpercentage of the sorbed metals (2-5%) remained in thesoil, even after leaching with more than 3000 porevolumes at pH 3.0, which may suggest micropore diffusionor incorporation into more stable mineral phases.