Speciation stability of inorganic polymer flocculant–PACl

The speciation distribution, physico-chemical properties of coagulants, and principles for their further species transformation under various water and wastewater treatment conditions are of paramount importance in coagulation processes. In this paper, the effect of various factors on the speciation transformation of typical inorganic polymer flocculants (IPFs)–polyaluminum chloride (PACl) was investigated by ferron assay. Dilution and co-existing electrolyte exhibit little effect on the speciation distribution of PACl after dosing. Solution pH has significant effect on the species transformation, depending mainly on OH/Al ratio (denoted as B value). The lower the B value, the more significant the effect pH exhibits. A large amount of Alb, i.e. rapid reactive species by ferron assay, could form for alum and PACl0 in the weak acidic pH range, which transforms quickly into Alc after aging. PACl, at high B values, maintains high speciation stability under the various conditions investigated. The ferron method provides a measure to explain the reactivity of different species with ferron. The classification of three kinds of aluminum hydrolysis species based on kinetic differences needs further modification.