Analysis of key factors in the coagulation of metal salts based on the calculation of hydrolysis-precipitation distribution

Hydrolysis and precipitation are the key processes that determine the coagulation performance of inorganic metal salts. The valence and concentration of metal salts, ligands, and solution pH all influence the coagulation performance. In order to get a full picture on the pros and cons of various inorganic metal salts as coagulants, this paper conducted thermodynamic equilibrium calculations and coagulation experiments to analyze and verify the hydrolysis-precipitation areas and speciation of four inorganic metal salts (aluminum, iron, titanium, and zirconium) in the absence and presence of ligands. In addition, the contributions of polynuclear hydrolysates in the hydrolysis and precipitation of the four metal ions were quantitatively described. Furthermore, the underlying mechanisms of the effects of common aquatic ligands on coagulation performance were discussed from the perspective of solution chemistry. The above results provide a theoretical basis for the development and application of inorganic metal salt coagulants, and are of great significance for understanding the coagulation performance and mechanisms accurately.