Removal of Zn ions from mine water by coagulation precipitation

Based on the distinguishing feature of mine water from Tongkeng Mine in south China, a complex coagulation method was selected to treat the mine water. Through single-factor and orthogonal tests, the effects of some factors, such as coagulants, coagulant aid content, pH values, stirring speed, and stirring time, on removing Zn²⁺ in the mine water were studied and the best level of each factor was determined. The best synergistic effect can be achieved when the volume ratio of polyaluminium chloride (PAC) to polyacrylamide (PAM) is 2:1, and the best treatment effect is obtained when the pH value is 9, the stirring speed is 80 r·min^-1 and the stirring time is 10 min. The results of actual water treatment tests show that the removal rate of Zn²⁺ reaches 93.9%, and the mass concentration of Zn²⁺ in the discharged water can meet the national emission standards of China.