Red mud is a waste produced in very large quantities by the aluminum industry. This study relates to a process of transformation of red mud, by treatment in hydrochloric pickle liquor of bauxite, into a novel composite inorganic coagulant that is usable for phosphate removal. The optimum conditions for preparing the composite coagulant with red mud and hydrochloric pickle liquor of bauxite were studied. The effect of various factors such as pH. ionic strength and water temperature on performance of the prepared coagulant was investigated. The coagulation performance of the composite coagulant by treating biologically pre-treated municipal sewage and eutrophic water was evaluated. The leaching potential of heavy metals from the coagulant was also investigated. The results showed that the prepared coagulant could reduce the phosphate in values lower than 0.02 mg/L Compared with commercial polyaluminum chloride coagulant (PACl), it could promote phosphate removal efficiency from 4.9% to 10.4%. Overall, it is suggested that the composite coagulant is an efficient coagulant and it can be possibly considered as a promising option for tertiary treatment of wastewaters and removing nutrients in eutrophic water, especially for the removal of phosphate. It exhibits better coagulation performance than commercial polyaluminum chloride coagulant. (C) 2011 Elsevier B.V. All rights reserved.