水中硫代钨酸盐的形成及其形态转化

基于紫外-可见分光光度法定量测试了模拟的不同天然水环境条件下硫代钨酸盐的含量变化，探讨了其对硫代钨酸盐的形成和形态转化过程的影响.结果表明：偏酸性-中性条件是水中大量形成一、二、三、四硫代钨酸盐（特别是三、四硫代钨酸盐）的必要前提，且在偏酸性条件下（pH=5）钨酸盐硫代程度更高.在偏酸性条件下，当硫化物与总钨的摩尔浓度比（S （Ⅱ）/W）为10：1时，硫代钨酸盐成为钨的主要存在形式；S （Ⅱ）/W为20：1时，钨酸盐全部转化为硫代钨酸盐，且钨的主要形态是WO₃S^2-；S （Ⅱ）/W为30：1和40：1时，钨的主要形态分别是WO₂S₂^2-和WOS₃^2-.在偏酸性条件下，离子强度的增加对钨酸盐的硫代过程有明显抑制作用；而在中性条件下，离子强度变化对钨的形态变化的影响甚微.

Formation and species transformation of aqueous thiotungstates

The concentrations of thiotungstates formed under various experimental conditions simulating natural aquatic environments were quantitatively determined by an ultraviolet/visible spectrophotometer, with their effects on the formation and species transformation of thiotungstates being evaluated. The results demonstrate that weakly acidic to neutral pH values were necessary for the substantial formation of mono-, di-, tri-, and tetra-thiotungstates, especially tri-and tetra-thiotungstates, and the thiolation of tungstate to the highest degree occurred at pH=5. Under acidic conditions, thiotungstates were prone to be the major species of tungsten even at relatively low molar ratios of sulfide to tungsten (e.g. S(Ⅱ)/W ratio=10:1).With an increase of S(Ⅱ)/W ratio to 20:1, complete thiolation of tungstate was observed, and the dominant species of tungsten became mono-thiotungstate WO₃S^2-. At S(Ⅱ)/W ratios of 30:1and 40:1, di-and tri-thiotungstates WOS₃^2- predominated in the solutions, respectively. Moreover, for the acidic solutions, the increase of ionic strength obviously inhibited the thiotungstate-forming reactions. In contrast, the variation of solution ionic strength had little effect on the tungsten speciation under neutral conditions.