Background and purpose: Presence of heavy metals in water resources is of great concerns due to adverse effects on human health. The aims of this study were to evaluate the efficiency of coagulation process using Polyaluminum Silicate Chloride (PASiC) in removal of hexavalent chromium and Cadmium from aqueous solutions and comparing that to the standards.

Materials and methods: Experiments were carried out by Jar test using PASiC coagulant. The applied pH range in this study was 4 to 11, and different PASiC dosage (15 to 187.5 mg/l), heavy metal concentrations (5 to 100 mg/l), and settling times (10 to 90 minutes) were investigated. All experiments were repeated three times for accuracy and precision.

Results: The optimum conditions for chromium removal was in PASiC dose of 150 mg/l, pH= 5, and settling time= 45 minutes, which decreased the chromium concentration (from 10 mg/l initial concentration) to 3.118 ± 0.29 mg/l and this was more than the standard levels of wastewater discharge into receiving water. The PASiC in 75 mg/l could reduce the cadmium level to 0.019 ± 0.01 mg/l (from 5 mg/l) in optimum condition (pH= 8 and settling time= 30 minutes). This level of cadmium removal was less than the standard levels of wastewater discharge into the receiving water.

Conclusion: The PASiC coagulant was found to be more effective in removing cadmium than chromium from aqueous solutions and could be applied for cadmium removal from water and wastewater.