Coagulation of Iron Oxide with Alum

Coagulation of dilute iron-oxide suspensions with alum has been studied at different pH values and coagulant concentrations. Measurements of pH, mobility, and particle concentrations in different size ranges were made as functions of time for a period of 2 hr. A kinetic model in good agreement with the data has been proposed for the agglomeration of particles in size ranges of 1–2μm and 2–3μm. The constants in the model are correlated with pH and coagulant concentration in a way consistent with the chemical characteristics of the system. The mobility changes from positive to negative as pH increases from acidic to alkaline values, suggesting that metal hydroxides rather than metal ions are involved in the coagulations process under the experimental conditions investigated.