Alkaline fusion–hydrothermal synthesis of Losod zeolite from industrial waste for CO ₂ capture

Abstract This work studies the hydrothermal synthesis of zeolitic materials from three types of industrial waste (granite cutting sludge; slate cutting sludge and aggregate washing sludge), which are regarded as low-cost materials. The synthesis was carried out through acid pretreatment with aqua regia to minimize iron content, followed by alkaline melting at 600°C followed by a hydrothermal crystallization stage at 180°C for 12 h. Characterization of the three synthesized zeolite materials by X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed that the methodology used induced the formation of LOS (Losod) zeolite (Na 12 Al 12 Si 12 O 48 · x H 2 O) as the predominant phase in all products, regardless of the waste used as the raw material. The end-products have a significant amorphous fraction (33–43 wt.%) and a zeolitic crystalline fraction (51–66 wt.%) and are enriched in Na and Al, and they have Si/Al and Na/Al ratios ranging from 1.27 to 1.39 and from 0.58 to 1.05, respectively, characteristic of low-silica zeolites. The synthetic zeolites showed reduced CO 2 adsorption capacities at room temperature (0.50–0.55 mmol g –1 ) compared to commercial zeolites such as 13X (3.45 mmol g –1 ).