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.

In this paper, 27Al NMR was used to measure the Al13 polymer in PAC. The amount of Al13 polymer in PAC reached up to 80% of AlT. Meanwhile, we used reversal electrodes to modify the conventional electrolysis, the concentration polarization and cathodes polarization were inhibited successfully.Figure optionsDownload as PowerPoint slideHighlights
► Using electrolysis with reversal of electrodes to prepare PAC, dispersing catholic polarization.
► External high Qf had more advantage of forming Al(OH)4− and inhibiting concentration polarization.
► Al13 of PAC prepared by this method counted for 85.4% of AlT for aging 96 h.
► PAC prepared by this method is suitable for on-line production because of inhibiting polarization.