Upscaling of Zeolite Synthesis from Coal Fly Ash Waste: Current Status and Future Outlook

Coal fly ash has been recognised as suitable feedstock for zeolite synthesis, and with this discovery, there has been much literature produced over the years on various synthesis processes with a view to address the disposal problems associated with fly ash wastes. The different synthesis processes can be divided into a pre‐synthesis activation with an alkali solution and a hydrothermal synthesis of heating the resulting aluminosilicate gel. However, the challenge lies in up scaling the synthesis to allow production on a commercial scale. The most common pre‐synthesis involving high‐temperature fusion of fly ash with sodium hydroxide may not be feasible in an economic context, given that a large‐scale furnace that would be needed. In this review, the successes recorded in the application of acoustic cavitation by using ultrasonication technique were discussed as a possible alternative to the fusion process on one hand. On the other hand, jet‐loop reactor system provides hydrodynamic cavitation, which may be relatively scalable compared to ultrasonication and may offer an economic advantage, if systematically explored, over fusion process for large‐scale synthesis of zeolites. It is also recommended that agitation is critical during the crystallisation process and the suitability of an impeller type that offers a minimum shearing to be explored during the hydrothermal process with respect to quality and yield of the zeolite produced. The understanding gleaned from these recommendations may be useful in designing an appropriate scale‐up operation for zeolite synthesis from coal fly ash

Effects of Film Thickness of ALD-Deposited Al2O3, ZrO2 and HfO2 Nano-Layers on the Corrosion Resistance of Ti(N,O)-Coated Stainless Steel

The goal of this stydy was to explore the potential of the enhanced corrosion resistance of Ti(N,O) cathodic arc evaporation-coated 304L stainless steel using oxide nano-layers deposited by atomic layer deposition (ALD). In this study, we deposited Al2O3, ZrO2, and HfO2 nanolayers of two different thicknesses by ALD onto Ti(N,O)-coated 304L stainless steel surfaces. XRD, EDS, SEM, surface profilometry, and voltammetry investigations of the anticorrosion properties of the coated samples are reported. The amorphous oxide nanolayers homogeneously deposited on the sample surfaces exhibited lower roughness after corrosion attack compared to the Ti(N,O)-coated stainless steel. The best corrosion resistance was obtained for the thickest oxide layers. All samples coated with thicker oxide nanolayers augmented the corrosion resistance of the Ti(N,O)-coated stainless steel in a saline, acidic, and oxidising environment (0.9% NaCl + 6% H2O2, pH = 4), which is of interest for building corrosion-resistant housings for advanced oxidation systems such as cavitation and plasma-related electrochemical dielectric barrier discharge for breaking down persistent organic pollutants in water

Isolation and characterisation of cellulose nanocrystal obtained from sugarcane peel

This work was aimed at developing efficient and stable cellulose nanocrystal (CNC) from sugarcane peel, which has been of growing concern as a potential for various industrial applications and providing a solution to the problem of indiscriminate disposal of peels of sugarcane, which creates nuisance in the environment. The alkaline treatment with sodium hydroxide and bleaching with acidified sodium chlorite were used to isolate cellulose from sugarcane peel, followed by acid hydrolysis which was done at 45o C for 45 min using 64% sulphuric acid to prepare the CNC. The chemical composition of the samples and their physicochemical properties were studied. The untreated and treated samples were characterised using various techniques, scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The CNC exhibited FT-IR spectra identified as cellulose structures. XRD showed that the CNC earmarked the structure of the cellulose nanocrystal with a crystallinity index of 99.2%. The SEM micrograph revealed fiber bundles separated into individualized CNC; the TEM image showed a needle-shaped CNC with a particle size of 20.57 nm and 153.05 nm in diameter and length, respectively. The TGA curve revealed a good thermal stability for the CNC. The results showed an effective synthesis of CNC from sugarcane peel

The use of factor analysis and acid base accounting to probe the speciation of toxic metals in gold mine waste

The generation of acidic drainage has become pervasive over the years and toxic elements are released due to exposure to oxidising agents, unforeseen circumstances, and human interactions. Uncontrolled acidic mine drainage release can result in substantial ecological disruption in sensitive and productive receiving waters. This study probes the element mobility of gold tailings with regard to various zones identified, based on possible phenomena such as the natural water medium, or acidic and alkaline media using sequential extraction and multivariate analyses. Factor analysis results, coupled with mineralogy, were corroborated with acid generation potential to identify various relationships that exist and establish the efficacy of the research towards predicting acid mine drainage generation potential. The statistical analysis was able to establish that pH or acidity, Fe ions, Ca2+ and Mg2+ played a major role in the released metals. Out of the four factors (80.8% accounted for) identified in factor analysis results for water fraction (WF), Fe contributed to three factors which showed the presence of Fe ions (assuming Fe2+ and Fe3+) responsible for the increased acidity of the tailings

Chemical, mineralogical and morphological investigation of coal fly ash obtained from Mpumalanga Province, South Africa

Abstract: Background and Objective: Coal fly ash generated from the combustion of coal by thermal power plant stations are enormous and the disposal there of is a big problem. In the present study, the chemical, mineralogical and morphological characterization of coal fly ash samples (CFAs) obtained from Mpumalanga province, South Africa were investigated. Materials and Methods: The CFAs were characterised by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), high resolution transmission electron spectroscopy (HRTEM) and the selected area electron diffraction (SAED) analytical technique. Result: Experimental results showed that the CFAs contain hematite, magnetite, calcite, lime, mullite and quartz. The CFAs are polycrystalline, could be categorized as class F fly ash and the particles are spherical in shape. Conclusion: The phase characterization suggested that CFA could be used for the synthesis of nanoparticles, as well as extraction of valuable metals, more so, the elemental composition of the CFAs suggested that the storage and disposal of CFAs could lead to the release of salts and toxic elements into the environment, thereby, contaminating surface and ground waters

Effects of film thickness of ALD-deposited Al2O3, ZrO2 and HfO2 nano-layers on the corrosion resistance of Ti(N,O)-coated stainless steel

The goal of this stydy was to explore the potential of the enhanced corrosion resistance of Ti(N,O) cathodic arc evaporation-coated 304L stainless steel using oxide nano-layers deposited by atomic layer deposition (ALD). In this study, we deposited Al2O3, ZrO2, and HfO2 nanolayers of two different thicknesses by ALD onto Ti(N,O)-coated 304L stainless steel surfaces. XRD, EDS, SEM, surface profilometry, and voltammetry investigations of the anticorrosion properties of the coated samples are reported. The amorphous oxide nanolayers homogeneously deposited on the sample surfaces exhibited lower roughness after corrosion attack compared to the Ti(N,O)-coated stainless steel. The best corrosion resistance was obtained for the thickest oxide layers. All samples coated with thicker oxide nanolayers augmented the corrosion resistance of the Ti(N,O)-coated stainless steel in a saline, acidic, and oxidising environment (0.9% NaCl + 6% H2O2, pH = 4), which is of interest for building corrosion-resistant housings for advanced oxidation systems such as cavitation and plasma-related electrochemical dielectric barrier discharge for breaking down persistent organic pollutants in water

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

Rare earth elements (REEs) are essential raw materials in a variety of industries including clean energy technologies such as electric vehicles and wind turbines. This places an ever-increasing demand on global rare earth element production. Coal fly ash (CFA) possesses appreciable levels of REEs. CFA, a waste by-product of coal combustion, is therefore a readily available source of REEs that does not require mining. CFA valorisation to zeolites has been achieved via various synthesis pathways. This study aimed to evaluate one such pathway by monitoring how REEs partition during CFA processing by the wet, magnetic separation process and zeolitisation. South African CFA was subjected to wet, magnetic separation and subsequent zeolitisation of the nonmagnetic fraction (NMF); solid products were characterised by XRD, SEM, XRF and LA-ICP-MS. The wet, magnetic separation process resulted in the partitioning of a specific set of transition metals (such as Fe, Mn, Cr, V, Ni, Zn, Cu, Co and Mo) into the magnetic fraction (MF) of CFA, while REEs partitioned into the NMF with a total REE content of 530.2 ppm; thus, the matrix elements of CFA were extracted with ease. Zeolitisation resulted in a solid zeolite product (hydroxysodalite) with a total REE content of 537.6 ppm. The process of zeolitisation also resulted in the selective enrichment of Ce (259.1 ppm) into the solid zeolite product (hydroxysodalite), while other REEs were largely partitioned into the liquid phase. CFA valorisation by wet, magnetic separation and zeolitisation therefore allowed for the partitioning of REEs into various extraction products while recovering the matrix elements of CFA such as Fe, Si and Al. The findings of this study highlight the geopolitical importance of REEs in terms of the development of alternative processes for REE recovery from waste and alternative sources, which may potentially give countries that employ and develop the technology a key advantage in the production of REEs for the global market

Adsorption of lead ion from aqueous solution unto cellulose nanocrystal from cassava peel

Acid hydrolysis was used for the synthesis of cellulose nanocrystal (CNC) from cassava peel (CP). The process was carried out at 450C for 45 min using 64% concentrated sulphuric acid, Pb2+ was removed from aqueous solution using the synthesized CNC adsorbent. Cassava peel cellulose nanocrystal (CPCNC) was characterised using FT-IR and X-Ray diffraction techniques. The different operational factors were examined to enhance the conditions for optimum adsorption of Pb2+. The equilibrium adsorption figures fitted well into both the Freundlich and Langmuir isotherm models, indicating that adsorption was due to the formation of a monolayer adsorption unto a homogenous surface and showed a good relationship between the Pb2+ and the CPCNC. The separation factor, RL, which is a dimensionless constant ranged between 0.02 and 0.248 and indicated that the adsorption was feasible and favourable. The optimum adsorption capacity was 6.4 mg Pb2+/g CNC at 25oC and pH 6. This study revealed that this novel nanomaterial has an unlimited prospect for effective removal of lead ion from aqueous solution

Preparation and Characterisation of Cellulose Nanocrystal from Sugarcane Peels by XRD, SEM and CP/MAS 13C NMR

Sugarcane peels are agro-waste resources discarded before taking the sugarcane juice. In the present study, cellulose nanocrystal was isolated from sugarcane peel by sulphuric acid hydrolysis. Two pretreatments, alkaline treatment and bleaching with acidified sodium chlorite, were applied. Sulphuric acid hydrolysis was performed at 450C for 45 min using 64% concentrated sulphuric acid. The resulting cellulose nanocrystal (CNC) of the sugarcane peel was characterised by studying the surface morphology using scanning electron microscope (SEM). X-ray diffraction (XRD) was studied to identify the crystalline nature of the CNC. CP/MAS 13C solid- state NMR was used to evaluate the purity and molecular structure of the CNC. The SEM image of the nanocrystal showed that the bundles of fibre were separated into individual CNC, with the size decreasing to a nanosize indicating an effective removal of the amorphous region. XRD diffraction pattern showed that the CNC possessed the cellulose crystalline configuration with crystallinity index of 99.2% and crystallite particle size dimension of 5.56 nm. The NMR spectra of the CNC revealed that all the signals have six carbon atoms of cellulose and the disappearance of several signals also indicated the disruption of the amorphous region. The results revealed effective synthesis of CNC from sugarcane peel, suggesting the leaching of the amorphous domain, apparent crystallinity and purity of the CNC. The cellulose nanocrystal prepared is considered to be a potent material for various industrial applications

Isolation and characterisation of cellulose nanocrystals obtained from sugarcane peel by SEM, XRD and CP/MAS 13NMR

Sugarcane peels are agricultural waste materials discarded before taking the sugarcane juice. In the present study cellulose nanocrystal was isolated from sugarcane peel by sulphuric acid hydrolysis. Two pretreatments; alkaline treatment and bleaching with acidified sodium chlorite were applied. Sulphuric acid hydrolysis was performed at 450C for 45 mins using 64% concentration sulphuric acid. The resulting cellulose nanocrystal (CNC) of the sugarcane peel was characterised by studying the surface morphology using scanning electron microscope (SEM), SEM-EDX was used to identify the elemental composition of the sample. X-ray diffraction (XRD) was studied to identify the crystallinity nature of the CNC. CP/MAS 13C solid- state NMR was used to evaluate the purity and molecular structure of the CNC. The SEM image of the nanocrystal showed that the fibre bundles were separated into individual CNC; with the size decreasing to a nanosize indicating an effective removal of the amorphous region. EDX showed the presence of 0.93 wt% of elemental sulphur impurity with the major components (carbon and oxygen). XRD diffraction pattern showed that the CNC retained the cellulose crystalline structure with crystallinity index of 99.22% and crystallite particle size dimension of 5.56 nm. The NMR spectra of the CNC revealed that all the signals were attributed to six carbon atoms of the glucose unit and the disappearance of several signals also indicated the disruption of the amorphous region. The results revealed effective synthesis of CNC from sugarcane peel, suggesting the leaching of the amorphous domain, apparent crystallinity and purity of the CNC. The cellulose nanocrystal obtained is considered to be a potential material for various industrial applications