Abstract:The diagrams for the concentration of complex ions pc—pH, the ratio of cadmium hydroxy complex ions αn—pH and the conditional solubility product of Cd(OH)2 to pH value in Cd2+-H2O system were drawn, respectively. The relationship between the equilibrium concentration of total cadmium ions and pH value was shown in Cd2+-H2O system, when the dissolution of Cd(OH)2 is in equilibrium. The solubility of Cd(OH)2 is the least at pH value of 9.84−13.31. The diagram for pKS—pH shows that each hydroxy complex ion existing in this system is dependent upon an optimized pH value. The diagram for the conditional solubility product pKS—pH indicates that the pKS reaches the minimum value at pH value ranging from 9.5 to 10.5. The results can provide a theoretical basis for the technology on removal of cadmium ion from the wastewater by neutralized hydrolyzation method.

Key words: Cd2+-H2O system; cadmium wastewater; complex ions; pc—pH diagram; conditional solubility product; complex ions ratio