Conversion of Harmful Fly Ash Residue to Zeolites: Innovative Processes Focusing on Maximum Activation, Extraction, and Utilization of Aluminosilicate

Abstract

Reuse of the solid residue from coal fly ash alumina extraction (FAAE) by acid leaching is problematic. Conversion of this solid residue into aluminum-rich zeolite (13X) and silicon-rich zeolite (ZSM-5) was investigated in this research. The FAAE residue was activated by alkali roasting with Na 2 CO 3 powder (110% mass fraction) at 890 °C for 60 min. Silicon and aluminum were mainly present as two mineral phases, Na 2 SiO 3 and NaAlSiO 4 , respectively, in the product obtained after roasting. The roasted product was dissolved in water (liquid/solid ratio of 2) after 20 min at 100 °C. The water-leaching liquor was investigated for total conversion to aluminosilicate zeolites without external aluminum or silicon addition. Hydrothermal synthesis of aluminum-rich zeolite 13X was successful after fine tuning of the conditions, although the filtrate had an unusually high SiO 2 /Al 2 O 3 molar ratio. Production of 13X consumed a large amount of aluminum, which increased the Si/Al ratio to a level suitable for synthesis of ZSM-5. The synthesis of ZSM-5 from the mother liquor of 13X was proved feasible. The FAAE residue was transformed into high-value zeolite products by nearly 100%. Additionally, the tail liquid of this process, mainly containing Na 2 CO 3 , was completely recycled. This process could be used to realize high-efficiency and high-value utilization of similar aluminosilicate solid wastes.

Beneficial properties of zeolite

“…Zeolite can activate antioxidant enzymes (peroxidase, catalase, and superoxide dismutase) (Huidong, 2022), which was reported in many animals. For example, dietary supplementation of rats with zeolite provided antioxidant protection after hepatectomy.…”

Fly Ash Derived FAU Zeolite Synthesis and Characterization

“…Coal y ash was pretreated by calcination at 850ºC for 2 hours, to remove volatile materials present in the y ash and the unburned carbon. The calcination was followed by acid treatment in 20% HCl solution (10 ml HCl/g Ash) to dealuminate the y ash and remove iron for the activate the aluminosilicate minerals (Liu, 2022). The acid treated and calcined y ash was then mixed with NaOH at varying NaOH / y ash weight ratios (0.8 to 1.6) and fused in a stainless-steel tray at 550ºC for 1 h before it was cooled to room temperature.…”

Desulfurization of Gasoline and Diesel by Fly Ash‐Derived FAU Zeolite

“…A promising technology that could complement HD for further and selective removal of sulfur compounds in petroleum fuels is adsorptive desulfurization (AD) by zeolite sorbent, which selectively removes sulfur compounds at ambient temperature and pressure without adsorbing aromatics and olefins present in the fuel [13][14][15]. Yang et al [9] found that zeolite sorbents usually bond with sulfur adsorbates via a ᴨ-complexation mechanism.…”

“…The influence of temperature and adsorbent's chemical composition on desulfurization performance was evaluated by varying the desulfurizing temperature (25-100 °C), zeolite Si:Al ratio (1, 2, and 3), and cationic exchanging the starting zeolite with Cu + , Ag + , and K + . To modify the Si:Al ratio, the starting zeolite material was contacted with a known amount of silica (Na 2 SiO 3 ) or alumina source (Al 2 (SO 4 ) 3 ), depending on whether more silicon or aluminum was required, in alkaline conditions with mild heating, followed by washing, filtration, and drying [13,14]. The cationic exchange was achieved by contacting the starting zeolite with an appropriate amount of aqueous AgNO 3 , CuSO 4 , and KCl to source Ag + , Cu 2+ , and K + cations, respectively.…”