Synthesis of zeolite NaA membrane from fused fly ash extract

Abstract

Zeolite-NaA membranes were synthesized from an extract of fused South African fly ash on a porous titanium support by a secondary growth method. The influence of the synthesis molar regime on the formation of zeolite NaA membrane layer was investigated. Two synthesis mixtures were generated by adding either aluminium hydroxide or sodium aluminate to the fused fly ash extract. The feedstock material and the synthesized membranes were characterized by X-diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). It was found by XRD and SEM that the cubic crystals of a typical zeolite NaA with a dense intergrown layer was formed on the porous Ti support. The study shows that the source of Al used had an effect on the membrane integrity as sodium aluminate provided the appropriate amount of Na(+) to form a coherent membrane of zeolite NaA, whereas aluminium hydroxide did not. Morphological, the single hydrothermal stage seeded support formed an interlocked array of zeolite NaA particles with neighbouring crystals. Also, a robust, continuous and well-intergrown zeolite NaA membrane was formed with neighbouring crystals of zeolite fused to each other after the multiple stage synthesis. The synthesized membrane was permeable to He (6.0 × 10(6) L m(-2)h(-1) atm(-1)) and CO2 (5.6 × 10(6) L m(-2)h(-1) atm(-1)), which indicate that the layer of the membrane was firmly attached to the porous Ti support. Membrane selectivity was maintained showing membrane integrity with permselectivity of 1.1, showing that a waste feedstock, fly ash, could be utilized for preparing robust zeolite NaA membranes on Ti support.

Synthesis of zeolites Na-A and Na-X from tablet compressed and calcinated coal fly ash

“…We then characterized the chemical composition of synthesized Na-A and Na-X samples with XRF. The result of XRF on Na-A sample indicates that it contains 44.64% SiO 2 , 37.29% Al 2 O 3 , 18.22% Na 2 O, 3.80% CaO, 3.36% Fe 2 O 3 , 3.06% TiO 2 , 0.55% MgO and 0.41% K 2 O and the corresponding Si/Al molar ratio is 1.48 and is typical for commercial Na-A, while that for the Na-X sample is 5.12 [ 30 , 61 , 62 ]. The high Si/Al molar ratio of Na-X is due to the introduction of silica sol to get phase-pure Na-X [ 60 ].…”

“…We then characterized the chemical composition of synthesized Na-A and Na-X samples with XRF. 48 and is typical for commercial Na-A, while that for the Na-X sample is 5.12 [30,61,62]. The high Si/Al molar ratio of Na-X is due to the introduction of silica sol to get phase-pure Na-X [60].…”

The steric influence of extra-framework cations on framework flexibility: an LTA case study

“…20 19 2 (12) iron for example, which may influence the zeolite crystallisation process. [3][4][5][6][7][8][9] Cations are known to play an essential part in the zeolite crystallisation process and influence the type of zeolite structure formed. This is due to the limited structure directing effect of cations in aqueous solutions.…”

The Behaviour of Rare Earth Elements from South African Coal Fly Ash during Enrichment Processes: Wet, Magnetic Separation and Zeolitisation

“…Other applications include CFA utilisation for mine back-filling, as well as agricultural remediation of soil and water treatment using modified CFA [17,23]. Another major area of research in CFA valorisation is the production of value-added, porous materials such as zeolites (i.e., zeolitisation) as well as metal extraction/recovery [24][25][26][27][28][29][30][31][32][33][34][35]. As South Africa is largely reliant on coal for energy production [15], CFA research and the development of various CFA valorisation technologies remain major priorities.…”

“…It was reported that the glassy, aluminosilicate phase of CFA contained the majority of the REE content and a process involving size classification, magnetic separation and hydrothermal treatment was proposed as a method of enriching the REE content of CFA [42]. Zeolitisation is a common method utilised in the transformation of the Si and Al content in CFA into a crystalline, porous material with high industrial value [24][25][26][28][29][30][31][32][33][34]. The distributional fate of elements found in CFA during the process of zeolitisation by two different methods (a two-step process and solid fusion-assisted process) was previously reported in literature [26].…”