Effect of speciation transformation on the coagulation behavior of Al13 and Al13 aggregates

摘要

Flocculation of kaolin suspension with aluminium fractal polycations was investigated as anfunction of aluminium concentration and pH. Aluminium flocculants included Al13 and Al13naggregates with OH/Al ratio of 2.6 and 2.8, respectively. The flocculation kinetics and floc sizendistribution were monitored by light scattering. The characterization of flocculants showed thatnthe tridecatmer Al13 and bridged [Al13]n with out-sphere structure were the dominant species fornall flocculants in a wide pH range. The coagulation results indicated that the pre and in situ-nformed [Al13]n play a key role in removing particles. With the increasing concentration of [Al13]n,ncoagulation mechanisms were transformed from charge-neutralization, electro-patch coagulationnto bridge-aggregation. Moreover, sweep-flocculation was involved at higher dosage besides othernthree mechanisms when amorphous aluminium oxides formed. Hence, chemical interactionnbetween particles and flocculants evolved from surface adsorption to surface precipitation fornaluminium polycations by virtue of species transformation.