Effect of precipitant consumption and cation ratio on their coppecipitation in forms of barely soluble compounds from mixed solutions

Regularities in the separation of cations precipitated from a solution in the form of barely soluble compounds CdSO3x2H2O and ZnSO3x2.5H2O are studied using the model system Na+, Zn2+, Cd2+ parallel SO42-, SO32--H2O at 20 deg C. The investigation is performed by the method of residual ion concentrations depending on the precipitant relative consumption. Regularities observed in the separation precipitation can be explained by the nature of the precipitant proportionation on the binding of oppositely charged ions in barely soluble compounds of the same type, differing in the probability of binding a precipitant anion with oppositely-charged cations being precipitated. This probability is proportional to the cation concentrations and their chemical affinity to the precipitant anion (affinity is inversely proportional to the solubility of newly formed compounds)