Siberian Federal University

The paper examines the physicochemical regularities of coagulation and selective crystallization processes in the multicomponent aqueous salt system K, Ca, Al//SO 4–H2O in order to improve water purification efficiency and ensure the rational use of dissolved salt components. The object of the study is the daily regulation reservoir of a water-supply station in Dushanbe, which receives water from the derivation canal of the Varzob River. Aluminum sulfate and potassium alum KAl(SO4)2·12H2O were used as coagulants. The density of solutions, alkalinity, transparency, suspended solids content, and residual aluminum were determined. It was shown that increasing the dose of a 1 % alum solution leads to a gradual decrease in water turbidity: from an initial value of 142 mg/L to a minimum of 22 mg/L. It was established that the optimal coagulant concentration should be selected with regard to transparency, alkalinity, and the amount of suspended particles. The influence of temperature and the ratio of K⁺, Ca²⁺, and Al³⁺ ions on phase transformations in the system was also studied. The possibility of selectively separating gypsum CaSO 4·2H2O and alum KAl(SO4)2·12H2O based on their solubility differences was substantiated. The proposed approach combines water purification with the recovery of valuable salt products and the recycling of the mother liquor into the technological cycle