Preparation of polymeric aluminum ferric chloride (PAFC) coagulant from fly ash for the treatment of coal-washing wastewater

Fly ash-based polymeric aluminum ferric chloride (PAFC) was prepared from fly ash leached with acid; the PAFC was used as a coagulant to treat coal-washing wastewater. The effects of pH, reaction temperature, and reaction time on coagulant performance were investigated, with optimal conditions determined using response surface methodology. The coagulation mechanism of PAFC was explored by comparing its performance with commercially available polyaluminum chloride (PAC), using scanning electron microscopy and infrared spectroscopy analyses. Results showed that the optimum PAFC preparation conditions were at a pH of 3.60, a reaction temperature of 92°C, and a reaction time of 2.30 h. Under these conditions, the removal of suspended solids and chemical oxygen demand in treated coal-washing wastewater reached efficiencies of over 81 and 70%, respectively. This means that the prepared PAFC is an effective coal-washing wastewater treatment technique, combining the advantages of polyaluminum and polyferric coagulants.