M(Ⅱ)-S-H₂O体系的热力学平衡

来源期刊：有色金属科学与工程2012年第5期

论文作者：柴立元 王海棠 尤翔宇 王庆伟 舒余德

文章页码：8 - 13

关键词：重金属废水； S-H₂O系； M-S-H₂O系； 热力学；硫化沉淀法

Key words：heavy metal waste water, S（Ⅱ）-H₂O system, M（Ⅱ）-S-H₂O system, thermodynamics equilibrium

摘    要：根据配位化学热力学平衡原理，绘制了298.15 K时S-H₂O系含硫物种的离子分率αn-pH 图，以及 4 种重金属离子（Cu、Pb、Zn、Cd）-S-H₂O体系的硫化平衡pM-pH图．αn-pH图指出了不同pH值下水溶液中硫的存在形式，当pH>12.5时，溶液中逐渐出现S^2-，pH值达到16以上时，溶液中的S主要以S^2-的形式存在，其离子分率达到了98.61 %．pM-pH图指出了4种重金属硫化物在溶解平衡时，总离子浓度与pH值的关系．pH值分别在7.75、8.87、8.36、9.83时，CuS、PbS、ZnS、CdS的溶解度最小．同时对热力学计算结果进行了实验验证，结果表明：在一定的金属浓度下，pH值分别为8.2、8.7、8.3、10.3时，溶液中金属离子浓度达到最小值，基本符合热力学分析结果．这些热力学研究具有较高的实用价值，为硫化沉淀法处理重金属废水提供了理论依据．

Abstract: Diagrams for the distribution of S（Ⅱ）species αn-pH in S（Ⅱ）-H₂O system, the concentration of four kinds of heavy metal ions（Cu2+、Pb²⁺、Zn²⁺、Cd²⁺）pM-pH in M（Ⅱ）-S-H₂Osystem are drawn, respectively. The various existing forms of S（Ⅱ）in S（Ⅱ）-H₂O system at different pH are illustrated in αn-pH diagram. The concentration of S^2- occurs at pH>12.5. The dominant S（Ⅱ）species is S^2- at pH=16 with the percentage 98.61 %. The pM-pH diagram indicates the relationship between the equilibrium concentration of total heavy metal ions and pH in M（Ⅱ）-S-H₂O system, when dissolution of metal sulfide is in equilibrium. The solubility of CuS, PbS, ZnS, CdS is at the minimal level at pH 7.75, 8.87, 8.36, 9.83, respectively. Meanwhile, the thermodynamic results were verified by a series of experiments. The results show that the total Cu²⁺, Pb²⁺, Zn²⁺, Cd²⁺, concentrations reach the minimum value when pH is 8.2，8.7，8.3，10.3，respectively under a certain concentration，which was largely in line with thermodynamic calculation. The thermodynamics study is of greater practical value and can offer theoretical foundation for treatment of heavy metal wastewater by sulfide precipitation.