Effect of SO42-/Al3+ ratio and OH−/Al3+ value on the characterization of coagulant poly-aluminum-chloride-sulfate (PACS) and its coagulation performance in water treatment

A poly-aluminum-chloride-sulfate (PACS) was prepared at various experimental conditions. It was found that the coagulation performance of PACS in water treatment was affected by the PACS particle size distribution and zeta potential value. The experimental results indicated that the PACS particle size distribution and zeta potential value were highly influenced by SO42-/Al3+ molar ratio and bacicities (γ, γ = [OH]/[Al]) value. At a fixed γ value of 2.0, the average PACS particle size increased from 25 to 80 nm with the increase of SO42-/Al3+ ratio from 0 to 0.1. Further increase of the SO42-/Al3+ ratio resulted in acute increment particle size of PACS extremely, which can be attributed to its aggregation. At a fixed SO42-/Al3+ ratio of 0.0664, the largest average size of PACS occurred at γ = 2.0. It was also found that the zeta potential value of PACS was strongly influenced by the SO42-/Al3+ ratio, γ value and pH of the aquatic solution. The zeta potential value of PACS increased with increasing of SO42-/Al3+ ratio. At a fixed SO42-/Al3+ ratio of 0.0664, PACS achieved greatest zeta potential value at γ value of around 2.0. The maximum positive zeta potential value of PACS was found at pH 5.3. At a fixed γ value of 2.0 and SO42-/Al3+ ratio of 0.0664, the PACS achieved an optimum natural organic matter and turbidity removal efficiency.