Does polyaluminum chloride coagulate with hydrolyzed coagulants?

Coagulation with hydrolyzing coagulants has been studied thoroughly, but the coagulation behavior of pre-hydrolyzed coagulants such as polyaluminum chloride (PACl), especially the coagulation mechanisms at various coagulant dosages and pH values of raw water, has not been systemically investigated and not been well understood , .

What is the difference between Alum and PACL coagulation?

The restabilization zone of PACl coagulation disappears at a higher final pH value than that of alum coagulation. Moreover, the charge neutralization and sweep coagulation zones of PACl are broader in the ranges of coagulant dosage (as Al) and pH value than those of alum.

Does pH affect coagulation efficiency and Floc property?

The dose ratio of primary and secondary addition was optimised. The effects of solution pH, floc breakage and dosing timing of coagulant aid of non-ionic polyacrylamide (NPAM) on coagulation efficiency and floc property were investigated. The results showed that two-stage addition of PACl showed less sensitivity with the variation of pH.

What is the optimal coagulation mechanism at final pH 7.0?

The optimal mechanism at final pH < 7.0 is charge neutralization. Satisfactory coagulation efficiency could be obtained with either charge neutralization coagulation or sweep coagulation at the final pH values from 7.0 to 10.0. The coagulation process of PACl and the formation of PACl precipitates have the same optimal pH value.

Why is non ionic Pam better than cationic PACL in flocculating?

The use of non-ionic PAM in flocculating has the advantage of being more effective than cationic PACl, probably because it may avoid re-stabilization of broken flocs by polymer adsorption driven by electrostatic attraction.

What is the optimal pH for coagulation with PACL?

At pH 6.0, the RT during sweep coagulation is obviously higher than that during charge neutralization, and the latter is higher than that at pH 7.0–10.0. This indicates that the optimal mechanism at pH 6.0 for PACl is charge neutralization and the optimal pH for coagulation with PACl is above 7.0.