Preparation and performance of a high purity poly-aluminum chloride

Poly-aluminum chloride (PACl) is one of the common coagulants for water and wastewater treatment. A new Chinese national standard of PACl has been implemented, where the concentration of insoluble substances, iron and heavy metals is to be controlled strictly, then researches on the preparation of high-purity PACl are needed. This paper presents a novel method to prepare high-purity PACl which contains high aluminum oxide content (>10%), high basicity (>90%), and low insoluble substance (<0.04%), iron (<300 mg L−1) and heavy metals. Samples taken from the Huangpu River were used to evaluate the coagulation performance of high-purity PACl in comparison with conventional PACl. The results demonstrate that for the whole dose range studied, high-purity PACls removed more turbidity than conventional PACl. On the other hand, when the dose was greater than 4 mg L−1 as Al, the high-purity PACl showed great UV254-absorbance removal capacity; which was even much greater at high does (e.g., 10 mg L−1). This could be partly attributed to the charge effect where a relative high zeta potential in the test water was achieved by dosing high-purity PACl.