Differences in coagulation efficiencies between PACl and PICl

Abstract

Laboratory preformed inorganic polymer flocculants—polyaluminum chloride (PACl) and polyiron chloride (PICl)—were compared for their coagulation efficiency according to various basicity (B) values. Conventional jar tests were combined with electrophoretic mobility (EM) measurements. After dosing, some preliminary experiments were also carried out on coagulant speciation analysis by ferron assay. The results show fundamental differences in coagulation between PACl and PICl. Basicity has a significant effect on coagulation behavior. Particle destabilization efficiency and charge neutralization ability, as shown by the effect of dosage on residual turbidity (RT) and EM, increases for PACl but decreases for PICl as their basicities are raised. A coagulation‐stability diagram, showing the quantitative relationship between the change in zeta potential and the coagulating species, is plotted to more clearly illustrate the differences between PACl and PICl. Differences between the mechanisms of coagulation for PACl and PICl are also discussed. Suggestions for further development of inorganic polymer flocculants are proposed.