Recycling of Waste Solution after Hydrothermal Conversion of Fly Ash on a Semi-Technical Scale for Zeolite Synthesis

Abstract

Nowadays, using fly ash for zeolites production has become a well-known strategy aimed on sustainable development. During zeolite synthesis in a hydrothermal conversion large amount of post-reaction solution is generated. In this work, the solution was used as a substrate for Na-A and Na-X zeolites synthesis at laboratory and technical scale. Obtained materials were characterized using particle size analysis, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR), and nitrogen adsorption/desorption isotherm. Produced zeolites revealed high purity (>98%) and monomineral zeolitic phase composition. The SiO2 content was in the range 39–42% and 40–38%, whereas Al2O3 content was 23–22% and 25–26% for Na-X and Na-A, respectively. TEM and BET analyses revealed Na-X zeolite pores were almost identical to commercial 13X with SBET in the range 671–734 m2/g. FTIR indicated slight differences between materials obtained at laboratory and technical scale in Si-O-(Si/Al) bridges of the zeolitic skeleton. The results showed good replicability of the laboratory process in the larger scale. The proposed method allows for waste solution reusability with a view to highly pure zeolites production in line with circular economy assumptions.

Simultaneous Removal of Pb2+ and Zn2+ Heavy Metals Using Fly Ash Na-X Zeolite and its Carbon Na-X(C) Composite

“…It can be found that Na-X(C) has high Si/Al molar ratio. The Si/Al molar ratio values highly correspond to the results obtained by other researchers [ 18 , 19 ]. Boycheva, with coworkers, determined a similar Si/Al molar ratio (1.37–1.60) for Na-X zeolite synthesized from coal fly ash by hydrothermal reaction and with preliminary fusion step [ 35 ].…”

“…Moreover, in the case of the carbon composite, there is a small fraction volume of 250–500 µm (5.44%), which corresponds to results obtained by other researchers [ 19 ]. Pure Na-X zeolite has a very fine particle size of 2–20 µm (61.88%), which is very similar to the value received by Panek et al [ 18 ]. This material is also characterized by the highest content of the finest fraction 0.01–2 µm, constituting 10.64%, and a small content of larger fractions: 16.31% for 20–50 µm, 6.58% for 50–100 µm and 4.35% for 100–250 µm.…”

“…The carbon–zeolite composite was created in the hydrothermal reaction of fly ash (25 kg) with a 3 M aqueous sodium hydroxide solution (90 L) on the technological line for the synthesis of ash zeolites for 48 h in 80 °C [ 19 ]. On the other hand, Na-X was obtained from a waste solution rich in silicon and aluminum (formed during the synthesis of Na-X(C)) according to the procedure contained by Panek et al [ 18 ]. Briefly, this waste solution was mixed with a sodium hydroxide solution containing Al foil and then subjected to a hydrothermal reaction.…”

“…The adsorbents used in the experiments were manufactured in the process of hydrothermal conversion of high-carbon fly ash (HCFA) [ 18 , 19 , 20 ]. This byproduct is accounted for 65–95% of total waste produced in the energy sector.…”

A Short Review on the Utilization of Incense Sticks Ash as an Emerging and Overlooked Material for the Synthesis of Zeolites

“…Therefore, ISA could act as a potential candidate for the synthesis of zeolites as few works have reported its chemical composition unlike CFA and kaolin or red mud. However, it has been most underestimated in the scientific community, limiting its application to our daily life [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”