Halim Cheryl E, Short Stephen A, Scott Jason A, Amal Rose, Low Gary
ARC Centre for Functional Nanomaterials, School of Chemical Engineering and Industrial Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia.
J Hazard Mater. 2005 Oct 17;125(1-3):45-61. doi: 10.1016/j.jhazmat.2005.05.046.
A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key compounds and provides information on leachate and precipitate speciation. The model was able to predict the leaching of Pb, Cd, As, and Cr from cement in the presence of both simple (0.1 and 0.6M acetic acid) and complex municipal landfill leachates. Heavy metal complexation by the municipal landfill leachate was accounted for by the introduction of a monoprotic organic species into the model. The model indicated Pb and As were predominantly incorporated within the calcium silicate hydrate matrix while a greater portion of Cd was seen to exist as discrete particles in the cement pores and Cr (VI) existed mostly as free CrO4(2-) ions. Precipitation was found to be the dominant mechanism controlling heavy metal solubility with carbonate and silicate species governing the solubility of Pb and carbonate, silicate and hydroxide species governing the solubility of Cd. In the presence of acetic acid, at low pH values Pb and Cd acetate complexes were predominant whereas, at high pH values, hydroxide species dominated. At high pH values, the concentration of As in the leachate was governed by the solubility of Ca3(AsO4)2 with the presence of carbonate alkalinity competing with arsenate for Ca ions. In the presence of municipal landfill leachate, Pb and Cd organic complexes dominated the heavy metal species in solution. The reduction of As and Cr in municipal landfill leachate was crucial for determining aqueous speciation, with typical municipal landfill conditions providing the reduced forms of As and Cr.
利用美国地质调查局的公共领域PHREEQC地球化学软件包开发了一个浸出模型，以模拟胶凝废物中铅、镉、砷和铬的浸出情况。该模型利用了关键化合物的动力学项和平衡热力学，并提供了关于渗滤液和沉淀形态的信息。该模型能够预测在简单（0.1和0.6M乙酸）和复杂的城市垃圾渗滤液存在下，水泥中铅、镉、砷和铬的浸出情况。通过在模型中引入一种单质子有机物种来考虑城市垃圾渗滤液对重金属的络合作用。该模型表明，铅和砷主要结合在硅酸钙水合物基质中，而大部分镉以离散颗粒的形式存在于水泥孔隙中，铬（VI）主要以游离的CrO4(2-)离子形式存在。发现沉淀是控制重金属溶解度的主要机制，碳酸盐和硅酸盐物种控制着铅的溶解度，碳酸盐、硅酸盐和氢氧化物物种控制着镉的溶解度。在乙酸存在下，在低pH值时，乙酸铅和乙酸镉络合物占主导地位，而在高pH值时，氢氧化物物种占主导地位。在高pH值时，渗滤液中砷的浓度受Ca3(AsO4)2溶解度的控制，碳酸盐碱度的存在与砷酸盐竞争钙离子。在城市垃圾渗滤液存在下，铅和镉的有机络合物在溶液中的重金属物种中占主导地位。城市垃圾渗滤液中砷和铬的还原对于确定水相形态至关重要，典型的城市垃圾填埋条件提供了砷和铬的还原形式。
