Column adsorption of Rhodamine 6G over Na–P/SOD zeolite synthesised from aluminosilicate secondary waste

Abstract

Waste stream management for the conversion of coal fly ash into potential value-added aluminosilicate products has attracted intensive research in recent years. However, these valorisation processes generate secondary solid and liquid waste, thereby challenging the efficient recycling process, environmental sustainability, and industrial scalability. This study successfully utilised the secondary waste recovered after the extraction process of nanosilica from coal fly ash to synthesise Na–P/SOD zeolite adsorbent. The secondary solid waste was composed mainly of SiO2>Na2O > Al2O3 with mineral phases of thenardite, burkeite, and sodium carbonate sulphate. Upon thermal treatment of the secondary solid and liquid wastes, a high fraction of zeolite Na–P phase was formed and the characterised Si–O–Si or Si–O–Al bonds increased with increasing treatment period. Fixed-bed column studies were conducted for the adsorption of Rhodamine 6G over the synthesised adsorbents. High efficiency (71%) of Rhodamine 6G removal was achieved over the adsorbent with the highest fraction of Na–P/SOD zeolite phases. This adsorbent exhibited an extended utility before ultimate breakthrough and exhaustion time, which only occurred after prolonged uptake of the dye. The column adsorption data fitted the Thomas and Adams-Bohart model, thus, confirming the suitability of the adsorbents for the removal of dye from wastewater.