Zeolite Synthesis and Steam: Preliminary data Using coal fly ash as raw Material

Despite the wide range of industrial applications for ash and slag waste, the actual utilization rate of ash disposed at Ukrainian TPPs is close to zero. Dry ash from electrostatic precipitators is used in the production of construction materials to a very limited extent. An analysis of the possibility of producing commercial materials from ash and slag using hydrochemical methods shows that these methods are mainly used in laboratory practice. Taking into account the content of silica in TPP fly ash, which is more than 50% by weight, it is of practical interest to use it to produce zeolite-like materials that have pronounced adsorption properties and can be used in water and gas purification processes. The known processes for obtaining sorption materials based on fly ash involve alkaline treatment of raw materials and hydrothermal synthesis at temperatures of about 100 °C. At the current stage of development of this technology, the main problem is to increase the synthesis capacity to ensure the profitability of production on an industrial scale. In recent years, in many fly ash-producing countries, the most widespread synthesis has been the one involving the high-temperature fusion of fly ash with sodium hydroxide, but this process is practically unfeasible from a technical and economic point of view, as it requires the use of huge furnaces. The methods of ultrasonic processing and hydrodynamic cavitation can be a possible alternative to high-temperature synthesis, and the conditions provide significant economic advantages for potential production. This paper systematically considers the problems of large-scale synthesis of zeolites from fly ash of thermal power plants and discusses the factors that determine the efficiency of hydrothermal synthesis processes in terms of quality and specific yield of product zeolite. Critical analysis of typical technological processes for the synthesis of zeolites based on TPP`s fly ash from showed that hydrothermal synthesis requires the minimum energy consumption and forms very small amount of by-products that require disposal. Unlike fusion synthesis (about 500 °C), the hydrothermal process is possible at much lower temperatures. Also, hydrothermal synthesis enables replacing pure water with less expensive recycled water to save resources. Recommendations are given that may be useful in the development of appropriate production of zeolite materials based on fly ash. Keywords: fly ash, scaling, technological parameters, technical and economic indicators, waste utilization.

Due to the large quantity of fly ash produced during the combustion of coal, it has become necessary to give greater applicability to this residue of low commercial value. The residue contains inorganic oxides which can act on the crystalline structure of zeolites, namely silicon and aluminum oxide. The coal ash was submitted to physical and chemical treatments with the aim of potentiating the silicon and aluminum extraction from the residue. The pure ash and the treated ashes were characterized by: X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FTIR). By means of the carried out characterizations it was observed that the treatments were effective for the extraction of aluminosilicates from the matrix. The treatments did not affect the morphology, the crystalline phases and neither the chemical composition of the ashes. Seeing this, the coal ash and its treatments showed to be a precursor for the synthesis of zeolites.

Synthesis of zeolites from coal fly ash: an overview

Enhancing CO2 adsorption capacity through Fe2O3/CaO ratio engineering in simulated fly ash-derived zeolite synthesis through gradient oxide modulation.

Mechanism study on green high-efficiency hydrothermal activation of fly ash and its application prospect

The coal fly ash (CFA) is produced on large scale in India by thermal power plant. CFA is the waste material having aluminosilicate as the major portion. Zeolite is the aluminosilicates microporous crystalline material. So CFA can be used as a source material for the synthesis of ZSM5 zeolite. In the present study ZSM5 zeolite is synthesized from CFA by reflux method. The synthesized zeolite is characterized by XRD, IR, SEM, EDAX and TG-DTA.

Synthesis of Na-zeolites from fly ash

Using synthetic zeolite from fly ash to treat high concentration phosphorus wastewater does not only improve the utilization of fly ash as solid waste but also reduce the environmental pressure caused by eutrophication. A synthetic zeolite was prepared from coal fly ash by one-step hydrothermal synthesis and applied for phosphorus adsorption from industrial wastewater (∼8,000 mg-P/L), and its adsorption characteristics and performance were studied. The results indicated that the product was a well-crystallized Na-P1 zeolite with typical morphology of plate- and rod-shaped crystals. Compared with the original fly ash, the specific surface area and average pore volume of the synthetic zeolite were nine and six times larger than the fly ash, reaching 43.817 m 2 /g and 0.122 cm 3 /g. The results from phosphorus adsorption onto the synthetic zeolite showed that the synthetic zeolite had good phosphorus adsorption properties. The adsorption process highly conformed to the pseudo-second-order kinetic model with the regression coefficient R 2 of 0.998. Phosphorus adsorption on the synthetic zeolite was fitted to the Langmuir monolayer adsorption model, and the regression coefficient R 2 was 0.989. The maximum phosphorus adsorption capacity was 84.4 mg-P/g-zeolite.

The Earth has relatively abundant coal resources, and a large amount of solid fly ash waste is generated with the development of industry. The synthesis of zeolites from waste coal fly ash has become an increasingly promising remedy for the crisis of coal fly ash production and disposal. The results of the study showed that the zeolite molecular sieve derived from fly ash exhibited good activity in the adsorption and removal of ammonia nitrogen from wastewater. The synthesized zeolite molecular sieves were characterized by XRD, SEM, TEM, TG analysis, EDS image mapping, and low‐temperature nitrogen adsorption/desorption isotherms. Furthermore, the influences of time, pH, temperature, type of competing cation in solution, and initial concentration of ammonium chloride on the adsorption experiment were also explored. The catalysts exhibited good catalytic reactivity superior to other commonly used aluminosilicate catalysts. In addition, the recyclability experiment indicated that the molecular sieve derived from coal fly ash displayed recyclability.

Synthesis, characterisation and CO2 adsorption potential of NaA and NaX zeolites and hydrotalcite obtained from the same coal fly ash

Supercritical hydrothermal synthesis of zeolites from coal fly ash for mercury removal from coal derived gas

The formation of an aluminosilicate gel structure made of alkali-activated materials (AAMs) was conducted through an alkali-activation reaction of the solid precursors (fly ash, metakaolin, and wood ash). Fly and wood ash are by-products of the burning process of coal and wood, respectively. Alkali-activated materials of aluminosilicate origin, made from the different ashes, fly and wood, are very attractive research targets and can be applied in various technological fields due to their thermal stability, resistance to thermal shock, high porosity, high sustainability, and finally, low energy loss during production. In this paper, we evaluate physico-chemical properties, microstructure, and radiological environmental impacts when wastes that contain elevated levels of naturally occurring radionuclides (NORs) such as fly ash and wood ash are made into "green cements" such as AAMs. The determination of radionuclide content was performed by means of gamma-ray spectrometry. Results showed that the AAMs have a lower value in the activity concentration of radionuclides than raw materials. The external absorbed gamma dose rate was 74.7-107.3 nGy/h, and the external radiation hazard index values were in range of 0.445-0.628 Bq/kg. The results of the activity concentration measurements for alkali-activated materials indicate the potential of their safe application in building construction. In terms of the structural characterizations, the obtained alkali-activated materials were examined using XRD, DRIFT, FESEM, and TEM analyses.

The paper presents the results of hydrothermal zeolitization of fly ash from hard coal combustion in one of the Polish power plants. The synthesis was carried out using various NaOH fly ash mass ratio (3.0, 4.0 and 6.0) and the effect of NaOH concentration in the activating solution on composition of synthesized sample was tested. The process was carried out under the following permanent conditions temperature: 90°C, time – 16 hours, water solution of NaOH (L)/fly ash (g) ratio – 0.025. In the studied fly ash the dominant chemical components were SiO2 and Al2O3, while the main phase components were mullite, quartz and hematite, and a significant share of amorphous substance (glass and unburnt organic substance). After hydrothermal synthesis, the presence of unreacted fly ash phases was found in the products, as well as new phases, the quality and quantity of which depend on the NaOH to fly ash mass ratio used for synthesis:  for ratio 3.0 – Na-LSX type zeolite and hielscherite,  for ratio 4.0 – Na-LSX type zeolite, hielscherite and hydrosodalite,  for ratio 6.0 – hydrosodalite and hielscherite. The grains in all products of synthesis are poly-mineral. However, it was found that the new phases, overgrowing the unreacted phase components of fly ash, crystallize in a certain order. Hielscherite is the first crystallizing phase, on which the Na-LSX type zeolite crystallizes then, and the whole is covered by hydrosodalite. In the products of synthesis, the share of sodium-containing phases (the Na-LSX type zeolite and hydrosodalite) increases with the increasing concentration of NaOH in the solution used for the process.

BACKGROUNDThe commercial production of zeolite A mainly involves costly synthetic chemicals. However, cheaper raw materials such as clay minerals, coal ashes, natural zeolites, solid wastes and industrial sludge have been tested. Based on this, the objective of the present study is synthesis of zeolite A from two sources of raw kaolins (Ansho and Bombowha) from Ethiopia and evaluation of its application in tannery wastewater treatment.RESULTSThe synthesis result indicated high crystallinity (>90%) of zeolite A using Ansho kaolin. Lower grade Bombowha kaolin yielded zeolite A with crystallinity of 80%. In the tannery wastewater treatment study, a real sample having chromium concentration of 2036 mg L−1 was treated, obtaining 99.8% removal and about 200 mg g−1 adsorption capacity of Cr(III) using 100 g L−1 and 5 g L−1 adsorbent dose, respectively. This indicated that the synthesized zeolite A has great potential for Cr(III) removal from tannery wastewater.CONCLUSIONIn this study, zeolite A has been synthesized from two sources of kaolin from Ethiopia and has been evaluated in tannery wastewater treatment. The synthesis result indicated the formation of crystals of zeolite A with optimum crystallinity of 91% and the material exhibited chromium removal efficiency of 99.8%. © 2017 Society of Chemical Industry

Geopolymer, also referred to as “alkali-activated material” or “zeocement”, is an emerging sustainable material to replace Portland cement-based binder. It requires a straightforward process and has the potential for large-scale waste valorisation and utilisation and a lower carbon footprint. Several aluminosilicate materials as geopolymer precursors have been explored, such as coal fly ash and metakaolin, among others. However, the characteristics of raw materials vary depending on the source. Hence, this study aims to synthesise geopolymer composite from raw materials that are available locally. Coal fly ash and nickel laterite mine spoils were explored as a potential geopolymer precursor. Optimal mix formulation of 50 % nickel laterite mine spoils / 50 % coal fly ash, sodium hydroxide to sodium silicate ratio of 1:2, and activator to precursor ratio of 0.44:1 yielded a 28 d compressive strength of 22.1 ± 4.4 MPa and a 180 d compressive strength of 32.3 ± 7.4 MPa. The result implies that this eco-friendly geopolymer material can be potentially used for pedestrian pavers, light traffic pavers, and plain concrete for levelling and structural applications. Before any field-scale application, investigating the leachability of material is imperative. Hence, the toxicity characteristic leaching procedure (TCLP) was employed to evaluate the leachability behaviour of both the raw materials and developed geopolymer composite in this study. The results revealed that the concentration of the trace metals released pose no significant environmental and leaching hazard into the soil, surface, and groundwater sources based on the threshold limit as defined by USEPA.