Dermatas Dimitris, Chrysochoou Maria, Grubb Dennis G, Xu Xuanfeng
W.M. Keck Geoenvironmental Lab., Stevens Inst. of Technology, Hoboken, NJ 07030, USA.
J Environ Qual. 2008 Jan 4;37(1):47-56. doi: 10.2134/jeq2007.0151. Print 2008 Jan-Feb.
Phosphate treatment of lead (Pb)-contaminated soils relies on the premise that Pb converts to the thermodynamically stable, insoluble mineral class of pyromorphites. Recent research showed that treatment performance is kinetically controlled and strongly dependent on soil pH; this study employed an acidic phosphate (P) form, monobasic calcium phosphate (MCP), to investigate treatment performance of Pb occurring in an alkaline-buffered and an acidic firing range soil. The results of leaching, X-ray powder diffraction (XRPD), and modeling analyses showed that P and Pb dissolution in the alkaline soil and transformation reactions were kinetically controlled, so that: (i) TCLP (toxicity characteristic leaching procedure) and SPLP (synthetic precipitation leaching procedure) results were poor to marginal even at high MCP dosages; (ii) brushite (Ca(HPO(4)).2H(2)O) and cerussite (PbCO(3)) persisted in XRPD patterns; and, (iii) geochemical modeling failed to predict leaching and phase assemblages. In the acidic soil, Pb-P reactions promoted further soil acidification, improved TCLP performance, and generated better agreement with the equilibrium-based model; however, SPLP and modeling results showed that Pb concentrations could not be reduced below 15 microg/L mainly due to the low soil pH. The marginal or inadequate Pb immobilization was observed in both soils despite the elevated MCP dosages, which were well in excess of the pyromorphite stoichiometric ratio (P/Pb = 0.6). Additionally, P leaching concentrations and rates were extremely high (>300 mg/L), under both SPLP and deionized (DI) water extraction conditions, and as predicted by thermodynamic equilibrium. The performance and sustainability of phosphate-based treatment therefore seem questionable.
用磷酸盐处理铅（Pb）污染土壤的前提是铅会转化为热力学稳定的不溶性磷氯铅矿矿物类别。最近的研究表明，处理性能受动力学控制，且强烈依赖于土壤pH值；本研究采用酸性磷酸盐形式的磷酸二氢钙（MCP），来研究在碱性缓冲和酸性焙烧范围土壤中铅的处理性能。浸出、X射线粉末衍射（XRPD）和建模分析结果表明，碱性土壤中磷和铅的溶解以及转化反应受动力学控制，因此：（i）即使在高MCP剂量下，毒性特性浸出程序（TCLP）和合成沉淀浸出程序（SPLP）的结果也很差或处于边缘水平；（ii）透钙磷石（Ca(HPO₄)·2H₂O）和白铅矿（PbCO₃）在XRPD图谱中持续存在；并且，（iii）地球化学建模未能预测浸出和相组合。在酸性土壤中，铅-磷反应促进了进一步的土壤酸化，改善了TCLP性能，并与基于平衡的模型产生了更好的一致性；然而，SPLP和建模结果表明，主要由于土壤pH值较低，铅浓度无法降低到15微克/升以下。尽管MCP剂量有所提高，且远远超过磷氯铅矿化学计量比（P/Pb = 0.6），但在两种土壤中均观察到铅固定效果不佳或不足。此外，在SPLP和去离子（DI）水提取条件下，磷的浸出浓度和速率都极高（>300毫克/升），这与热力学平衡预测的一致。因此，基于磷酸盐的处理性能和可持续性似乎值得怀疑。
