Equilibrium of hydroxyl complex ions in Pb2+-H2O system

The thermodynamics equilibrium principle was used to construct the diagrams for the concentration of complex ions (pc) vs pH, the distribution ratio of lead hydroxyl complex ions (αn) vs pH, and the conditional solubility product of Pb(OH)2 vs pH in the Pb2+-H2O system. The relationship between the equilibrium concentration of each kind of lead hydroxyl complex ions in equilibrium with Pb(OH)2(s) and pH value was shown in the system. The minimum solubility of lead is at the pH value of 10.096–10.997. The distribution ratio of each kind of the lead hydroxyl complex ions is determined as a function of the pH value and the total lead concentration ([Pb]T). The diagram for the conditional solubility product, pKSP vs pH, shows that each kind of lead hydroxyl complex ions existing in the system is dependent upon an optimized pH value at the established concentration of [Pb]T, and that pKSP reaches the minimum at the pH value of 10.3–11.2. The results can provide a theoretical basis for removing lead ions from wastewater by the neutralization and hydrolyzation technology.