磷酸盐分解钼酸钙的热力学

Thermodynamic analysis on phosphate decomposition of calcium molybdate

针对磷酸盐分解钼酸钙的过程,根据同时平衡原理和质量守恒定律,绘制了25℃时Ca-Mo-P-H2O体系溶解组分的lgC-pH图,以及不同总磷浓度条件下溶液中总钙、总钼的lgC-pH图和钼酸钙稳定区.结果表明,在溶液中总磷浓度一定的条件下,随着pH的增大体系中会依次出现H2MoO4(s)、CaMoO4(s)、Ca5(OH)(PO4)3(s)和Ca(OH)2(s)稳定存在的区域.总磷浓度直接影响到钼酸钙的分解过程,随着总磷浓度的增加,钼酸钙的稳定区域不断减小甚至消失,使得钼酸钙更加易于分解,因此溶液中总钼浓度不断增大,而总钙浓度不断降低;但总磷浓度过高会导致溶液中残留游离含磷离子过高.从热力学角度来看,在钼酸钙分解过程中,添加磷酸盐比碳酸盐更加有利于钼酸钙的分解.

According to the laws of simultaneous equilibria and mass conservation, the logarithm concentration-pH diagram of a Ca-Mo-P-H2O system, the logarithm eoncentration-pH diagrams of total calcium and total molybdenum at different total phosphate concentrations, and the stabile area of calcium molybdate at 25 ℃ were obtained on the basis of thermodynamic data. The results show that the stabile areas of H2 MoO4 （s）, CaMoO4 （s）, Ca5 （ OH ） （ PO4 ） 3 （ s ） and Ca （OH） 2 （ s ） are distinguished orderly with increasing pH values at a constant total phosphate concentration. Calcium molybdate can be easily decomposed since the stabile area of calcium molybdate shrinks or even disappears with increasing total phosphate concentration; at the same time, the total molybdenum concentration increases, and the total calcium concentration decreases. However, high phosphate concentration is unnecessary for calcium molybdate can be decomposed at a very low phosphate concentration. Compared to carbonate, phosphate is more propitious to the decomposition of calcium molybdate.