Coagulation behaviour of polyaluminium chloride with different aluminium speciation

The coagulation behaviour of polyaluminium chloride (PACl) with different contents of aluminium species (Alm, Al13, Alu detected by 27Al NMR spectroscopy) was investigated by using the conventional jar test together with studying the rate of floc size development, the zeta potential of particles and turbidity removal efficiency. Results show that Al13 has higher charge neutralisation ability, while Alu species contribute to the formation of hydroxide precipitates which have a rather open structure for capturing particles. The charge neutralisation plays a less important role in coagulation after the coagulant dosage reaching a certain value, while precipitate formation improves coagulation significantly.