Coal fly ash (CFA) sample produced in coalburning power plants contains significant quantities of oxides of aluminium, iron and other important elements such as magnesium, silicon and calcium for the production of coagulant for wastewater treatment. In order to synthesize a coagulant, the dissolution of these CFA elements was studied in sulphuric acid (H2SO4) solutions. The impacts of dissolution time, H2SO4 concentration, temperature and solid/liquid ratio were investigated for the leaching process. The treated CFA samples were characterized by PSD, XRD, XRF, FTIR and SEM. Thermodynamic feasibility was studied using Hydra/Medusa software. The dissolution efficiencies of aluminium, iron, magnesium, silicon and calcium were 33.86, 57.90, 73.21, 11.12 and 25.43%, respectively, in 1.5 M H2SO4, with a pH ranging from 0.5 to 3.9, at 300 rpm, 150 °C, a solid/liquid ratio of 0.20 and a leaching time of 6 hours. The PSD results revealed that particle size changes happened during the leaching process, XRD and FTIR showed the presence of the same mineral phases in the raw and treated CFA samples, and SEM indicated that both a porous structure and a stem-like structure were formed after leaching. The generated dissolution solution containing polymeric sulphates of aluminium, iron, magnesium, silicon and calcium can be utilized as coagulant in the treatment of wastewater. The process can be easily adopted to synthesize complex coagulant, therefore decreasing CFA pollution and producing a valuable coagulant.

Keywords : Synthesis; Pressure sulphuric acid-leaching; Coal fly ash; Coagulant; Wastewater