Evaluating the Coagulants of Polyaluminum Silicate Chlorides on Turbidity Removal

Polyaluminum silicate chloride (PASiC) is a new inorganic coagulant and has different characters from other cationic inorganic products used in water treatment. The optimal formulas and conditions to produce and use PASiC are not thoroughly well-known. PASiC can be formed by treating AlCl 3 solution with silicate compounds and the insoluble aluminum silicates are produced thereafter. It has been found that partially decreasing alum acidity with silicate would form a more stable solution than polyaluminum chloride (PAC). PASiC may enhance aggregation by the silicate in it to remove turbidity especially for the water of low turbidity and alkalinity. In this research, a series of PASiC coagulants were produced from the different basicities (B) and Al/Si molar ratios at the different aging temperatures and aging times. Accordingly, PASiCs prepared by the different basicities (B) and Si/Al molar ratios were added in a synthetic water with low turbidity and alkalinity to evaluate the efficiency of PASiC for colloids removal. Finally, the raw water from Min-Der water treatment plant (Miaoli, Taiwan) was used to evaluate the treatment efficiency of PASiC and Aluminum Sulfate Al 2 (SO 4 ) 3 . The results indicate that the PASiC with higher B value and lower Si/Al molar ratio has higher coagulation efficiency. We also found that under the aging temperature of 40°C will increase the aging rate, and the product of PASiC formed is more stable. PASiC evidently has higher turbidity removal efficiency than that of Al 2 (SO 4 ) 3 when equivalent doses were used for Min-der reservoir water.