An alternative method for preparation of polyaluminum chloride coagulant using fresh aluminum hydroxide gels: Characterization and coagulation performance

摘要

The drawbacks, high energy consumption, rigorous preparation condition and high impurity contents, have been well-recognized in the preparation of widely-used polyaluminum chloride via conventional methods in industrial scale. In order to overcome the drawbacks, the fresh aluminum hydroxide gels were proposed to prepare the polyaluminum chloride (PAC(G)) in this study. The optimal preparation condition of PAC(G) was obtained by optimizing the preparation conditions including temperature, time and acid concentration. The contents of the small/middle polymeric aluminum (Al-b) in an optimized PAC(G) could reach 80%. During preparation, high temperature significantly reduced the preparation time but led to a poor stability Lower rate constants of reaction between hydroxyl-Al and Ferron, k(b1) and k(b2), were almost equal at high basicity value. It implied that the middle polymeric aluminum (Al-b2) was dominant in Al-b. Besides, the pseudo-first-order kinetics equation was rearranged. Coagulation by PAC(G2.0) was found to be the most effective for low-turbidity water treatment but limited to a narrowest optimum range of dosage compared with other PAC(G). The residual aluminum concentration of the water after coagulation by the PAC(G2.5) with fresh aluminum hydroxide gels was always low even overdosing. Charge neutralization was not the predominant coagulation mechanism in this treatment. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.