Enhancing electrochemical preparation of polyaluminum chloride by a magnetic field

A novel effective method for preparing polyaluminum chloride (PAC) with high content of Al₁₃ polymer through conventional electrolysis coupled with rare earth Nd-Fe-B magnetic field was introduced. The content of Al₁₃ polymer in PAC synthesized by this method was highly influenced by the electrobath voltage (E), the magnetic flux density (B), the current density (i) and the distance between the two adjacent electrodes (d_adj). A total aluminum concentration (Al_T) in the PAC solution of 0.8 mol l⁻¹ was obtained when the E, B and i was 2.2 V, 0.4 T and 3.2 A dm⁻², respectively. The optimum d_adj and circulating flow (Q_f) were 20 mm and 23.7 l h⁻¹. With accelerated mass transfer rate by external magnetic field and high Q_f, this process had the advantages of forming more Al(OH)₄⁻ as the precursor of Al₁₃ polymer and inhibiting the concentration polarization more obviously than conventional electrolysis process. Under the optimum conditions, the amount of Al₁₃ polymer in PAC accounted for 82.3% of the Al_T (Al_T = 0.8 M, basicity = 2.2), which was higher than that of PAC prepared by other methods.