Red mud-based polyaluminium ferric chloride flocculant: Preparation, characterisation, and flocculation performance

Abstract

In this study, red mud was used as a raw material to extract Al and Fe using hydrochloric acid. A highly efficient polyaluminium ferric chloride (PAFC) flocculant was prepared by adjusting the pH of a leaching solution, the molar ratio of Al to Fe, and the polymerisation temperature. The effects of synthesis and flocculation conditions on the flocculation performance of aged landfill leachate were investigated. The results confirmed that PAFC flocculant prepared at a polymerisation pH of 2.5, Al/Fe molar ratio of 8, and polymerisation​ temperature of 70 °C had the optimum effect. The effect of PAFC and commercial polyaluminium ferric chloride flocculants used under different flocculation conditions were compared. The chemical oxygen demand, UV 254 , chroma, total organic carbon, and PAFC settlement height at a flocculant concentration of 1.2 g/L and solution pH of 6 were 72.2%, 79.2%, 82.9%, 82.6%, and 9.5 cm (within 90 min), respectively. The PAFC performed excellently at flocculation and can be used as a simple and potentially low-cost wastewater treatment agent in industrial applications. • Red mud was used to synthesise polyaluminium ferric chloride (PAFC) flocculant. • The COD and TOC of PAFC to landfill leachate were 72.2% and 82.6%, respectively. • PAFC have advantages over commercial PAFC in settlement velocity and TOC removal efficiency.