PAC with high content of Al13 polymer prepared by electrolysis with periodical reversal of electrodes

An effective method for preparing polyaluminum chloride (PAC) with high content of Al13 polymer through modified electrolysis with periodical reversal of electrodes was introduced. The content of Al13 polymer in PAC synthesized by this method was highly influenced by the electrobath voltage (Em), the current density (i), the cycle of reversing electrodes (Trev), the distance between the two adjacent electrodes (dadj) and out-circulating flow (Qf). A total aluminum concentration (AlT) in the PAC solution of 0.4 mol l−1 was obtained when the Em, i and Trev was 3.0 V, 3.8 A dm−2 and 6 s, respectively. The optimum Qf and dadj were 35 l h−1 and 25 mm. For periodical reversal of the adjacent electrodes, the ions gathering around the cathodes were dispersed, and the asymmetric current density caused by over-dissolving fixed anodes was solved effectively. With accelerated mass transfer rate by external high Qf, 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 84.5% of the AlT (AlT = 0.4 M, basicity = 2.2) after aging for 72 h, which was higher than that of PAC prepared by other methods.