Recovery and Re-Use of Aluminium Coagulants from Coagulation Sludge by Liquid-Ion Exchange

Abstract

The residual Al/Fe content in clarifier sludge resulting from coagulant use is a valuable resource. Chemical conditioning is carried out in previous years to recover the Al/Fe coagulants. However, the major problem associated with the use of the recovered coagulants in potable water treatment is the contamination of the recovered coagulants by heavy metals, colour-causing natural organic matter and manganese. This paper describes the research conducted to evaluate the applicability of liquid-ion exchange to Al ion recovery and the coagulation performance of the recovered coagulants for water treatment. A range of factors affecting the liquid-ion exchange efficiency have been studied including the type and concentrations of extracting agents, mixing strength and retention time and the type and concentrations of stripping agents. A jar test experimental procedure was used to evaluate the coagulation performance of the recovered coagulants in comparison with the commercial aluminium sulphate (AS). The results have shown that the liquid-ion exchange process will recover more than 95% of the Al from influent sludge and the recovered AS can be of the same quality and concentration as commercial AS. and can perform as well as the commercial AS for potable water treatment