Preparation and characterization of polyaluminum chloride containing high content of Al13 and active chlorine

This paper introduces a new electrochemical method for preparation of polyaluminum chloride (PACl) which contains high content of Al13 and active chlorine and presents integrated properties of flocculation with oxidation. E-PACl (PACl prepared by electrolysis process) samples were successfully prepared in an electrochemical reactor, which used Ti/RuO2–TiO2 anodes and Ti cathodes. Anode potential was the key electrochemical parameter that needed to be controlled at 1.5 V to ensure the maximal current efficiency of main reactions in electrolysis process. Analyses by ferron colorimetric method and 27Al NMR spectroscopy indicated that Al13 was the predominant species in the final product when total Al concentration (AlT) was in the range of 0.1–1.5 mol/L. The amount of active chlorine was in inverse proportion to AlT. Contents of the most active component, Al13 and active chlorine could respectively reach 90.9% and 5650 mg/L with AlT = 0.51 mol/L and basicity (B, OH/Al molar ratios) = 2.23 in the liquid product of PACl (E-PACl2). In E-PACl2, the sulfate precipitate of Al13 was the unique material detected by X-ray diffraction patterns and clusters of small spheres that might be the aggregates of Al13 were observed on the surface of its air-dried sample by atomic force microscopy. Results of dynamic light scattering showed that the particle size distributions of E-PACl were related with the Al species distributions and ageing time. The active chlorine in E-PACl2 performed well on disinfection of raw water.