金属溶剂萃取的热力学研究(Ⅶ)——2-乙基己基膦酸单(2-乙基己基)酯-硫酸钻-硫酸铜体系

本文提出了具有相同电荷的同号离子间作用力相等的假定, 简化了Pitzer的电解质溶液活度系数计算公式, 用此公式, 计算了H_2SO_4-CoSO_4-CuSO_4水相体系各单个离子活度系数以及水的渗透系数。本文还应用由作者提出的工作参考态法, 应用改进的Scatchard-Hildebrand模型计算了EHEHPA-CoSO_4-CuSO_4萃取体系中有机相各组分的活度系数以及萃取反应热力学平衡常数.

THERMODYNAMICS OF SOLVENT EXTRACTION OF METALS (Ⅶ) EHEHPA-CoSO4-CuSO4 System

The system for metal solvent extraction is a complicated one, which deals with electrolyte solution, non-electrolyte solution, phase equilibrium and chemical reaction simultaneously. It is interesting and important to establish an extraction thermodynamic model in hydrometaliutgy based on the modern theories of solution. In recent years the extraction thermodynamic model on one-metal system has been presented by authors1-5].The two-metal extraction system in which cobalt and copper, are co-extracted from sulfuric acid solution by 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHEHPA) has been investigated in this paper.The aqueous phase contains H_2SO_4, CoSO_4 and CuSO_4, mixed electrolytes with dissociation equilibrium. The activity coefficients for all ions are calculated by computer based on the Pitzer′s electrolyte theory with some assumptions and approximations made. The mean relative deviation between the experimental and calculated pH values is less than 0.02. The calculated results show that the simplified Pitzer′s equtions work very well for the aqueous phase with dissociation equilibrium.Form the experimental equilibrium data in both phases and the activity coefficient of diluent determined by the gas-chromatography, the activity coefficients for HEHPA, Co(HR_2)_2, CU(HR_2)_2 and the thermodynamic extraction equilibrium constants K_(Co) and K_(Co) are obtained through “working reference state” proposed by the authors. The values of K_(Co) and K_(Co) keep constant respectively in the region of 0.6168-1.079 mol L~(-1) (the initial concentrations of extractant). Combining the improved Scatchard-Hildebrand theoretical model with the “working reference state”, the calculated values of activity coefficient for all components in the organic phase are obtained which are consistent with the experimental data. These results show that the “working reference state” is very useful for the two-metal extraction system and it seems to be possible to establish theoretical model for two-metal extraction equilibria in place of empirical ones.