低温酸性条件下白钨矿的不一致溶解动力学

Incongruent Dissolution Kinetics of Scheelite under Low Temperature and Acid Conditions

在75℃和pH=1.04～2.46时采用间歇型实验方法测定了天然白钨矿在HCl溶液中的溶解速率,揭示了溶解反应的动力学机理。结果表明,Ca的释放速率随反应时间保持稳定,并随pH降低而增大。W的释放行为则更为复杂,在反应初期与Ca呈一致溶解,之后由于钨酸表面层(中间产物)的形成,W的释放量和释放速率明显下降。这说明白钨矿的溶解作用由早期的表面化学反应转变为化学反应-扩散控制过程,从而导致W、Ca呈不一致溶解。pH越小,不一致溶解出现的时间越早。酸性溶液中白钨矿的溶解速率方程为v=k[H+]n,以W和Ca计算的速率常数k分别为0.65×10-5mol/m2s和1.04×10-5mol/m2s,反应级数n则分别为1.20和1.26。结合他人研究结果,白钨矿的溶解反应相对于H+可能为一级反应。

Dissolution rates of natural scheelite were studied using batch type experimental method at 75 ℃ and pH between 1.04 and 2.46 of HC1 solutions, and the kinetic mechanism of dissolution reaction was also outlined. The results show that the release rates of calcium almost keep constant at certain pH during reaction and increase with decreasing pH. While the release behavior of tungsten is much complicated. In the early stage the dissolution reaction of scheelite is congruent with respect to tungsten and calcium. After that the release amount and rate of tungsten decrease substantially due to the formation of the surface layer ofttmgstic acid. It suggests that the kinetic mechanism is changed from the surface chemical reaction in the early stage to chemical reaction-diffusion controlling progress, which results in the incongruent dissolution of ttmgsten and calcium. The lower the pH is, the earlier the incongruent dissolution occurs. The rate equation of scheelite dissolution in acid solutions is described as v = k[H^＋]n. The rate constants, k, are 0.65×10-5 tool/m2 s and 1.04× 10-5 mol/m2 s with respect to tungsten and calcium, while the reaction orders, n, are 1.20 and 1.26, respectively. Combined with other research results, the dissolution reaction ofscheelite may be in the first order with respect to hydrogen ion.