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 (Al_T) was in the range of 0.1–1.5 mol/L. The amount of active chlorine was in inverse proportion to Al_T. Contents of the most active component, Al₁₃ and active chlorine could respectively reach 90.9% and 5650 mg/L with Al_T = 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.