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Hafnium is widely used in space and nuclear industry applications because of its strategic material properties. The process of reduction of hafnium chloride generates around 5–10% unreacted hafnium chloride (HfCl4) residue, which needs to be recycled. The typical elemental composition of major impurities constitutes 3% aluminum, 0.5% chromium, 0.8% iron, and 0.17% silicon. In this work, the removal of aluminum oxide and silicon oxide was studied through alkali (sodium hydroxide) leaching. The optimization of the leaching process parameters was studied using Box-Behnken design (BBD) experiments through the response surface methodology. The impurities such as SiO2 and Al2O3 react with NaOH during the hydrometallurgical leaching process and form sodium aluminate and sodium silicate, respectively, which helps in the process. The leached samples were quantitatively analyzed by an ICP-OES analyzer. It is observed that ~ 85 wt.% SiO2 and ~ 66 wt.% Al2O3 were separated at optimal experimental conditions. The optimal conditions for the removal of impurities using 1 molarity of NaOH concentration, a solid-to-liquid ratio of 1:30 min, and 60 min leaching time are suggested by BBD. [ABSTRACT FROM AUTHOR]

The hydrothermal treatment of Moroccan coal fly ash (CFA) in a basic medium leads to the selective formation of Na-X zeolite. By fusion with sodium hydroxide in the presence of CFA, the particles are transformed into sodium silicate and sodium aluminate, from which hydrothermal reaction favourably results in the production of a pure Na-X zeolite. A good crystallinity of Na-X zeolite was attained at NaOH:fly ash ratio of 1.2. Their high surface area and pore characteristics make the Na-X zeolite useful for the removal of the model anionic dye RY145 from water. The adsorption efficiency of the synthesised Na-X zeolite was evaluated and compared to raw CFA. Dye adsorption is more significant at acid pH, suggesting that the zeolite surface is positively charged. Kinetic and isotherm models applied to fit the experimental data reveal that the adsorption process is physisorption. It results that zeolite X is an efficient adsorbent for the extraction of dyes. [ABSTRACT FROM AUTHOR]

The 13X zeolites were successfully synthesized from sodium silicate and sodium aluminate via hydrothermal treatment, and applied to the adsorption of carbon dioxide (CO2). The properties of the 13X zeolites were characterized and tested by powder X-ray diffraction (XRD), N2-physisorption measurements, CO2-temperature programmed desorption (CO2-TPD) and CO2 adsorption measurements. The results demonstrate that H2O/Na2O, Na2O/SiO2, and SiO2/Al2O3 molar ratios have an important influence on the adsorption performance of CO2 because of their different physicochemical properties. The pure 13X zeolite can be obtained with the optimal H2O/Na2O, Na2O/SiO2 and SiO2/Al2O3 molar ratios of 60, 4 and 3 in the preparation process, respectively. The 13X sample prepared with suitable synthesis conditions possesses the highest crystallinity, the maximum values of specific surface area (720.8 m2/g) and pore volume (0.458 cm3/g) and moderate strength of the interaction between 13X and CO2, thus presenting the highest adsorption capacity of CO2 (118.3 mg/g). [ABSTRACT FROM AUTHOR]

The diaspore is a typical representative of bauxite resources in China, which is the primary raw material for the Bayer process in alumina production, particularly in regions such as Shanxi, Guangxi, Guizhou, and Henan. Clarifying the phase transformations and reaction mechanisms of the silicon-containing minerals during the Bayer leaching process of diaspore is essential for improving the efficiency of alumina production. This article focuses on montmorillonite, which is one of the silicon-containing minerals of diaspore-type bauxite, investigating the reaction mechanisms and phase changes of montmorillonite under the high-calcium sodium aluminate solution system by using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Magic Angle Spinning Nuclear Magnetic Resonance (MAS–NMR) and Fourier Transform Infrared Spectroscopy (FTIR). The results show that montmorillonite dissolved and transformed into Na6(AlSiO4)6 (hydrated sodium aluminosilicate) under the high-calcium sodium aluminate solution system, and calcium oxide and sodium aluminate in the solution reacted to form (CaO)3Al2O3(H2O)6 (hydrated calcium aluminate). With the increase of reaction temperature, caustic alkali concentration (Nk), and reaction time, hydrated calcium aluminate and hydrated sodium aluminosilicate react and transform into Ca3Al2SiO4(OH)8 (hydrogarnet). Under the optimal reaction conditions of a 120 min reaction time, a temperature of 240 °C, an Nk of 240 g/L, and a CaO–to–SiO2 mass ratio (C/S) of 3.5:1, the montmorillonite reaction degree can reach a maximum of 93.71%. [ABSTRACT FROM AUTHOR]

Oxide ceramic layers of Ti 5 Al 16 O 34 were fabricated on commercially pure titanium grade 2 substrates by plasma electrolytic oxidation in aqueous electrolyte media at a fixed 10 g/L concentration of trisodium phosphate and 25 g/L sodium aluminate. Lowering the sodium aluminate concentration to 15 g/L and 20 g/L, β-TiAl 2 O 5 and Ti 2 Al 6 O 13 components were produced under similar PEO processing conditions. The composition and structure of the PEO coatings were studied using XPS, XRD, SEM, EDS, mechanical (hardness, adhesion, and tribology), electrochemical impedance spectroscopy, and potentiodynamic polarization tests. The layers possess a polycrystalline character with minor amorphous phases, while their thicknesses varied slightly between samples with similar treatment times. The PEO coatings consist of a compact inner layer with an enriched phosphorus content of about 5–10 wt% and a porous outer layer in which phosphorus is found in less than 1 wt%. Ti 5 Al 16 O 34 coatings showed better mechanical performance regarding microhardness and corrosion resistance compared to β-TiAl 2 O 5 and Ti 2 Al 6 O 13. At a longer applied PEO process duration of 10 min, Ti 5 Al 16 O 34 layer thickness, microhardness, and corrosion current densities of 40.2 μm, 9.37 GPa, and 2.8 nA/cm2 were measured. [Display omitted] [ABSTRACT FROM AUTHOR]

This study aimed to enhance the mechanical properties of calcium sulfoaluminate cement grouting materials (HCSA) by investigating the effects of ordinary Portland cement (OPC) content, the ratio of quicklime to gypsum, and the dosage of sodium aluminate on the compressive strength of the OPC-CSA composite system. The results indicate that as the OPC content increases, the compressive strength of the blended cement initially increases and then decreases, reaching a maximum at a 60% OPC replacement ratio within the experimental group. The addition of an appropriate amount of OPC to the CSA composite system effectively prevents the regression of compressive strength. With an increase in quicklime content, the compressive strength of the samples at various ages first increases and then decreases, with the optimal ratio of quicklime to gypsum found to be 2:8. Furthermore, sodium aluminate, used as an activator, when increased in dosage, leads to an initial increase followed by a decrease in the compressive strength of OPC-CSA samples, with an optimal incorporation rate of 0.75%, significantly enhancing the strength of the blended cement. In the orthogonal experiments, the dosage of sodium aluminate was identified as the most influential factor affecting the compressive strength of the composite grouting materials. [ABSTRACT FROM AUTHOR]

Zinc was focused on as an element causing hardening retardation due to delayed hydration of Ordinary Portland Cement (OPC), and its hardening inhibitory effect and the mechanism of hardening enhancement by sodium aluminate were analyzed by X-ray diffraction and scanning electron microscopy/energy dispersive X-ray spectroscopy. The addition of zinc hydroxide retarded hardening at more than 0.3 mass%, as previously reported, and zinc produced calcium zincate hydrates (qatranaite) and inhibited the hydration of tricalcium silicate (C3S), the main component of hydration of OPC. After the zinc had been fully consumed in qatranaite formation, C3S started normal hydration. The addition of sodium aluminate caused earlier re-hydration of C3S, which was inhibited by hydration, as the hydrates produced appeared to consume zincate anions. The rapid setting effect of sodium aluminate addition was also delayed by zinc hydroxide, but it was estimated that the addition of the same amount of zinc would ensure initial strength through early formation of hydrocalumite. In the longer term, strength was considered to be more enhanced by the onset of C3S hydration. [ABSTRACT FROM AUTHOR]

The physical properties, the phase diagram for the Na2O-Al2O3-H2O system, and the crystal structure of sodium aluminate were studied. In laboratory-scale experimentally simulation tests, the undesired sodium aluminate solution precipitation served as a sensor for the excursion during the makeup process and/or in the storage state. For example, the feedstock for the subsequent hydrous alumina oxide deposition on pigmentary titanium oxide could be avoided and even restored. On the basis of the guide from the "modified" phase diagram, the abnormal composition of sodium aluminate was mapped and regressed to the baseline of Na2O/Al2O3 with the mole ratio at 1.45, followed by the adjustment of water content through either water evaporation or water addition. The final required composition was recovered. [ABSTRACT FROM AUTHOR]

This paper presents the application of sodium aluminate, directly or after small adjustments in concentration and purity, in some other valuable intermediary products. Sodium aluminate is an intermediary product in Bayer technology applied by Alum SA Tulcea production of alumina and alumina products. Mainly, sodium aluminate is a carrier of aluminum hydroxide between important manufacturing stages in the Bayer process, bauxite processing, and aluminum hydroxide crystallization. After a short investigation of the uses of sodium aluminate, it was decided to choose and study the possibility of converting this secondary product into ecological material for the treatment of natural or industrial wastewater. Actually, on the market, products similar to sodium aluminate from Alum SA Tulcea provide treated waters with high purity and reasonable quality, excellent coagulation rates, rapid flotation, and sedimentation, and in addition, significant side effects, such as excellent removal of phosphorus and silica from treated water. Treatments do not require lime or hydroxide to control alkalinity, and chemical sludge remains at a minimum volume and mass. The test performed with sodium aluminate from Alum SA Tulcea was comparable with other tests with Al2(SO4)3 and FeCl3. The maximum removal yields of global organic load expressed by chemical oxygen demand (COD) and biochemical oxygen demand (BOD5), chromium (Cr VI), and total suspended solids (TSS) were: 83%COD, 71% BOD5, 99.7% Cr VI and 93% TSS.

Al (OH) 3 was introduced in the supersaturated sodium aluminate solution as the decomposition crystallization reaction seed. The influence of seed sizes on the apparent activation energy in the Arrhenius formula during the reaction process was investigated. The results demonstrated that the apparent activation energy decreases and the decomposition rate increases with the decrease of seed size. The morphology of the seed particles is assumed as ellipsoid. Based on this assumption, the apparent activation energy in the Arrhenius formula is modified [ABSTRACT FROM AUTHOR]

A series of ZSM-5 samples were synthesized by template-free hydrothermal synthesis without adding seed crystals. When synthesis parameters such as temperature, duration, and molar ratio of components being equal, various silicas (specifically, Silica-Fumed from Sigma-Aldrich; Rosil-175 from the Bashkir Soda Company (BSC), Russia; Silica from the Salavat Catalyst Plant (SCP), Russia; and Aerosil-300 from Evonik, Germany) and of aluminum (Al(NO3)3∙9H2O and NaAlO2) were varied. In the presence of sodium aluminate, highly crystalline ZSM-5 samples were synthesized, whereas the use of aluminum nitrate led to an amorphous product due to accelerating aluminosilicate condensation. The ZSM-5 crystals prepared from various SiO2 sources have different morphology, including the crystal size (ranging from 5.9 to 12.2 µm) and the aspect ratio (from 1.9 to 2.6). The ZSM-5 samples synthesized from available Russian-manufactured SiO2 sources (Rosil-175 (BSC) and Silica (SCP)) in the presence of sodium aluminate consisted of crystals with average sizes of 5.9 and 6.9 μm, respectively, and a narrow particle size distribution (cv < 20%). [ABSTRACT FROM AUTHOR]

This study focuses on the synthesis of a monocarboaluminate (MCA)-based binder by treating marble waste (MW) powder with sodium aluminate (SA). The aim is to investigate the influence of various parameters, including the alumina modulus (MA) of SA, different contents of calcined clays with varying alumina levels, and curing temperatures, on the performance and phase composition of the resulting binder. The results demonstrate that the combination of SA and MW leads to the formation of an MCA-based binder, which exhibits a high compressive strength of up to 28 MPa after seven days of curing. Additional phases such as gibbsite, pirssonite, and gaylussite are observed, indicating the occurrence of a cationic exchange reaction between MW and SA, as confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The stability of the resulting binder is primarily influenced by the MA value, with higher values associated with greater stability. Regardless of the type of calcined clay used, incorporating calcined clay results in the formation of a calcium aluminate silicate hydrate (CSAH) phase alongside MCA, contributing to the improved stability of the hardened binder over time. Notably, calcined clay with a higher alumina content exhibits the highest strength at all curing ages. Furthermore, increasing the curing temperature up to 100 °C significantly enhances the early strength, which correlates with the formation of the kotoite phase at the expense of the MCA phase. [ABSTRACT FROM AUTHOR]

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Magnetite (Fe3O4) particles deposited with zeolite, which was made from sodium hydroxide (NaOH), sodium aluminate (NaAlO2) and sodium trisilicate (Na2O7Si3) using the hydrothermal process, were used in the adsorption of methylene blue (MB). A continuous stirred tank reactor (CSTR) system was used for the adsorption of MB using zeolite/Fe3O4. This study encircled the continuous reactor with a magnet to prevent the adsorbent from flowing to the output, thus producing clean water devoid of Fe3O4 particles. The performance of the adsorbent was assessed based on the effects of adsorbent mass, flow rate, pH and concentration. The adsorbent was able to remove approximately 90% of the 20 mg L−1 methylene blue from a 500 mL solution in 2 h, with a maximum adsorption capacity of 30.8528 mg g−1. This adsorption process also exhibited high removal efficiency even after 5 regeneration cycles and 55 h of operation, confirming the successful production of zeolite/Fe3O4 as an effective MB adsorbent. [ABSTRACT FROM AUTHOR]

Shotcrete technology has been widely used in tunnel engineering, road repair, underground engineering, and other scenarios due to its advantages of simple construction and fast progress. Liquid alkali-free accelerator is a necessary additive used in sprayed concrete, which can quickly set the concrete in a short period of time. Therefore, the development of alkali-free liquid accelerator is of great significance. The purpose of this research is to obtain low-cost and high-performance accelerator products and explore the influence of aluminum sulfate, hexafluorosilicic acid, and other raw materials on performance and stability. The main research results are as follows: (1) The accelerator product with low cost and high performance has been prepared. Its aluminum sulfate content is about 43%, hexafluorosilicic acid content is about 17%, sodium aluminate content is about 21%, the initial setting time is 1′ 15″, the final setting time is 2′ 05″, and the 1-day compressive strength is 9.5 MPa. (2) F ion plays a solubilizing role in the solution, and the appropriate ratio of aluminum sulfate and fluorine ion can greatly enhance the stability of accelerator solution. (3) Under the same cost condition, the influence of aluminum sulfate on the condensation performance is far greater than that of hexafluorosilicic acid and sodium metaaluminate. Subsequent research and development should focus on how to effectively increase the solubility of aluminum sulfate. [ABSTRACT FROM AUTHOR]

This study investigates the activation of New Zealand pumicite (pumice powder) using sodium aluminate (NaAlO₂) solution, both alone and in combination with 10 M KOH solution, at various weight ratios of 1, 3, and 5, to produce alkali-activated cement. Compressive strength tests and microstructural analyses were conducted to assess the effects of activator/precursor ratios, activator type, aging time, and curing temperature (65°C for 72 hours or room temperature). The internal porosity of the pumicite played a key role in aluminosilicate phase dissolution and mobility, resulting in similar compressive strengths across different ratios. NaAlO₂ alone achieved compressive strengths of 60 MPa and 67 MPa after 4 and 65 days, respectively, while the binary solutions showed reduced strength with increased aging. Room temperature curing required almost three times the aging period to match the 28-day compressive strengths achieved after curing at 65°C for 72 hours. Microstructural analyses revealed that NaAlO₂ solution adjusted the Si/Al ratio, forming high-Al and high-Si gels as well as zeolite-A, underscoring its benefits. This study demonstrates the potential of using locally sourced New Zealand pumicite as a precursor in alkali-activated cement, particularly in regions lacking traditional industrial by-products.

A novel and efficient procedure has been developed to synthesize furan‐2‐carboxylate derivatives through a one‐pot condensation of chloroacetate derivatives, 1,3‐diketones, and chloroform in the presence of magnetic sodium aluminate 40 wt. % (Aluminate NP‐40). The synthesized heterogeneous catalyst can be easily recovered from the reaction mixture by applying an external magnetic field. Magnetic aluminate NP catalysts provide a sustainable, environmentally friendly, and cost‐effective method for synthesizing furan‐2‐carboxylate derivatives. Additionally, the catalyst is stable and can be reused multiple times without losing its catalytic properties. High product yields in a short experimental time and easy workup are other advantages of the present method. All synthesized compounds were characterized by NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The anthropogenic carbon dioxide (CO2) fixation and various engineering strategies are gaining very significant attention because of the expansion of the net‐zero carbon environment in the atmosphere. Herein, we designed a sodium aluminate@γ‐alumina (NaAlO2@γ‐Al2O3) catalyst by a simple and facile precipitation and impregnation tactics. A series of different weight percentage NaAlO2@γ‐Al2O3 materials were successfully synthesized and well characterized by using advanced analytical and spectroscopic techniques such as TGA, XRD, FE‐SEM, TEM/HR‐TEM, FT‐IR, Raman, TPD, and XPS analysis. The NaAlO2@γ‐Al2O3 catalyst was employed as a competent catalyst for the CO2 fixation under atmospheric pressure reaction conditions. The catalytic activity results evidently revealed that the cycloaddition reaction successfully achieved 94% styrene oxide conversion and 93% selectivity, along with an 87% yield of the styrene carbonate at 120 °C for 6 h. Furthermore, we comprehensively examined the effect of different reaction parameters such as the effect of sodium aluminate amount, co‐catalyst amount, temperature, and time for CO2 fixation reaction. Additionally, different terminal and internal epoxides were tested under optimized reaction conditions and achieved moderate to excellent yield of the desired cyclic carbonate products. Interestingly, a plausible reaction mechanism was proposed for the styrene carbonate synthesis using NaAlO2@γ‐Al2O3 catalyst surface with the support of characterization and experimental results. Remarkably, the NaAlO2@γ‐Al2O3 catalyst could be easily recoverable and successfully recyclable up to six consecutive cycles without declining its initial catalytic activity along with stable structural and physicochemical properties. [ABSTRACT FROM AUTHOR]

Organic montmorillonite (OMMT) was prepared from Na-montmorillonite (MMT) by Hexadecylamine (HDA) modification. The composite material has good smoothness, acidity, and salt resistance. OMMT was characterized using small-angle X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and a video optical contact angle measuring instrument. The results showed that the layer spacing was enlarged from 1.44 nm to 2.87 nm after the modification, and the hydrophobicity performance was greatly improved. The organic modification of MMT was successful. The surface morphology, roughness, and anticorrosion properties of the organic montmorillonite/epoxy (OMMT/EP) composite coating were investigated and compared with those of the epoxy (EP) coating. The OMMT/EP composite coating had a flatter surface than the EP coating. The roughness was reduced from 65.5 nm to 10.3 nm. The electrochemical impedance spectroscopy showed that the composite coating's thickness positively affected its anticorrosion performance, the corrosion current density (Icorr) decreased with the increase in thickness, and its maximum impedance was much larger than that of EP coating. The protection efficiency of the OMMT/EP composite coating was 77.90%, which is a significant improvement over the EP's 31.27%. In addition, the corrosion resistance of the composite coating gradually decreased with increasing immersion time, but the change was insignificant. [ABSTRACT FROM AUTHOR]

The present study explores a cost-effective method for using activated ground granulated blast furnace slag (GGBFS) and silica fume (SF) as cement substitutes. Instead of activating them with expensive alkali solutions, the present study employs industrial-grade powdered sodium aluminate (SA) and hydrated lime (HL) as activators, reducing expenses by about 94.5% compared to their corresponding analytical-grade counterparts. Herein, the exclusivity is depicted using less pure chemicals rather than relying on reagents with 99% purity. Two mixing techniques are compared: one involves directly introducing powdered SA and HL, while the other premixes SA with water before adding it to a dry powder mixture of GGBFS, SF, and HL. Microstructural analysis reveals that the initial strength results from various hydrate phases, including calcium–sodium–aluminate–silicate hydrate. The latter strength is attributed to the coexistence of calcium–silicate hydrate, calcium–aluminate–silicate hydrate, and sodium–aluminate–silicate hydrate, with contributions from calcite and hydrotalcite. The SF content significantly influenced the formation of these gel phases. Thermogravimetric analysis (TGA) reveals phase transitions and bound water related to hydration products. The optimal mix comprises 10% SF, 90% GGBFS, 9.26% HL, and 13.25% SA, with a water-to-solid ratio of 0.45. This approach yields a compressive strength of 35.1 MPa after 28 days and 41.33 MPa after 120 days, hence being suitable for structural construction. [ABSTRACT FROM AUTHOR]

This study aimed to enhance the mechanical properties of calcium sulfoaluminate cement grouting materials (HCSA) by investigating the effects of ordinary Portland cement (OPC) content, the ratio of quicklime to gypsum, and the dosage of sodium aluminate on the compressive strength of the OPC-CSA composite system. The results indicate that as the OPC content increases, the compressive strength of the blended cement initially increases and then decreases, reaching a maximum at a 60% OPC replacement ratio within the experimental group. The addition of an appropriate amount of OPC to the CSA composite system effectively prevents the regression of compressive strength. With an increase in quicklime content, the compressive strength of the samples at various ages first increases and then decreases, with the optimal ratio of quicklime to gypsum found to be 2:8. Furthermore, sodium aluminate, used as an activator, when increased in dosage, leads to an initial increase followed by a decrease in the compressive strength of OPC-CSA samples, with an optimal incorporation rate of 0.75%, significantly enhancing the strength of the blended cement. In the orthogonal experiments, the dosage of sodium aluminate was identified as the most influential factor affecting the compressive strength of the composite grouting materials.

This study proposes the utilization of kaolin as an alternate resource for alumina production due to the decreasing availability of bauxite ores in Nigeria. This project covers the procedures and operations required to produce a high surface area γ-alumina using kaolin, a refractory material. The kaolin used in this study was sourced from Ajebo in Ogun State, Nigeria. The mineral processing of kaolin was the initial step involving removing inherent impurities from the clay. Subsequently, calcination was performed to eliminate crystallised water and impurities and activate the kaolin's limited alumina content. This activation process facilitated the subsequent acid-leaching reactions. At 90oC, 5M HCl acid was used to leach meta-kaolin, which was then filtered. The filtrate was mixed with 5M NaOH at 900oC and was transformed into sodium aluminate. This reaction also facilitated the removal of magnesium and iron hydroxides. Subsequently, HCl was introduced to adjust the pH of the solution. The resulting aluminium hydroxide was then calcinated at temperatures of 700oC and 900oC for 2 hours each to produce γ-alumina. Ultimately, the calcined material was cooled to ambient temperature inside the furnace. The produced γ-alumina was further characterised using X-ray Fluorescence (XRF), Fourier Transform Infrared spectrometer (FTIR), and Scanning Electron Microscopy (SEM). [ABSTRACT FROM AUTHOR]

In alumina production, the evaporation as the key process uses recyclable resources and reduces environmental pollution. In fact, the quality of export product with offline and delayed, results in low precision of process control and high energy consumption. To ensure green and efficient production, in this paper, a new prediction method integrating process knowledge and data-driven spatial-temporal adaptive model is put forward. First, to preprocessed production data for ensuring modeling accuracy, data reconciliation technology is adopted. Then, based on material and heat transfer mechanism, for equipment and industrial process, the mechanism models are established. Furthermore, with time difference and moving window model, an error compensation method is utilized in terms of double locally weighted kernel PLS for estimation error in hypothesis-based mechanism modeling. Finally, the data-driven spatial-temporal adaptive model and the process knowledge-based mechanism model are integrated. To illustrate the model feasibility, an industrial sodium aluminate solution evaporation is used. It demonstrates that, for the developed model, the prediction accuracy can reach more than 90% within the ± 2% error range, and effectively estimate the actual product quality and ensure the prediction effect. • A new concentration prediction method integrating knowledge and data-driven spatial-temporal adaptive model is proposed. • Mechanism modelling based on data reconciliation and process analysis is achieved to estimate concentration. • A TD-MW-DLWKPLS model considering both sample similarity and variable correlation is adopted for error compensation. • The performances of the developed method are validated on evaporation industrial application. [ABSTRACT FROM AUTHOR]

To improve the corrosion resistance of TiNi alloy fabricated by laser powder bed fusion (LPBF), a porous oxidation layer was synthesized by micro-arc oxidation in a sodium aluminate and sodium silicate electrolyte. The influences of the applied voltage and the processing time on the morphology of oxidation layer were investigated, and the corrosion behavior of the oxidation layer in artificial saliva was evaluated and compared with that of the as-fabricated LPBF alloy. The results indicate that, as increasing the applied voltage and the processing time, the oxidation layer becomes uniform and integrated. The optimum parameters are with an applied voltage of 450 V and processing time of 40 min. The oxidation layer primarily contains α-Al2O3 and consists of two layers, i.e., a thin, compact and uniform inner layer and a porous outer layer. The formation of stable α-Al2O3 phase in the coating and its almost non-porous dense structure reduce the channels for corrosion ions to penetrate into the substrate through coating, thereby improving the corrosion resistance of TiNi alloy. [ABSTRACT FROM AUTHOR]

The ultra-high lime aluminum method (UHLA) is a method that can effectively adsorb chloride ions in a solution. Calcium oxide (CaO) and sodium aluminate (NaAlO2) were mixed and added to the sodium chloride solution. After the reaction lasted for some time, the content of chloride ions in the solution was significantly reduced. Through the experiment of chloride ion adsorption, it was found that when the mass ratio of calcium oxide to sodium aluminate was m(NaAlO2):m(CaO) = 1:2.5, the reaction temperature was 25°C, and the stirring time was 60 min, the adsorption effect on chloride ion was the best. The adsorption rate can reach 93.3% in a 100 mg/L sodium chloride solution. With the increased sodium chloride concentration, the time required to reach adsorption equilibrium becomes longer. In a 2,000 mg/L sodium chloride solution, this method's unit adsorption mass of chloride ion can reach 63.5 mg/g. Through SEM and XRD analysis, calcium oxide and sodium aluminate react in solution to form Ca4Al2(OH)14 with a layered structure. The OH- between the layers can exchange with external chloride ions. After Ca4Al2(OH)14 adsorbs chloride ions, the product is Friedel's salt (Ca4Al2Cl2(OH)12) with the same layered structure. [ABSTRACT FROM AUTHOR]

The influence of process parameters in the three-stage purification of aluminate solution from the Bayer process and aluminum hydroxide was considered in this paper. One of the ways of purification is treating the aluminate solution in order to reduce the concentrations in the starting raw material (solution) and then treating the aluminum hydroxide at a certain temperature and time in order to obtain an alumina precursor of adequate quality. The purification process itself is divided into three phases. The first phase involves the treatment of sodium aluminate with lime in order to primarily remove Ca2+ and (SiO3)2− impurities. Phase II aims to remove impurities of Zn2+, Fe2+, and Cu2+ by treatment with controlled precipitation using specially prepared crystallization centers. In Phase III, Na+ is removed by the process of hydrothermal washing of Al2O3 ∙ 3H2O. In this work, parameters such as temperature (T), reaction time (t), and concentration of lime (c) were studied in order to remove the mentioned impurities and obtain the purest possible product that would be an adequate precursor for special types of alumina. [ABSTRACT FROM AUTHOR]

We developed a salt-assisted surface charge driven synthesis method of large pore alumina by introducing NaCl to sodium aluminate and aluminum chloride reaction system at room temperature. The adjustment of the dosages of NaCl would allow us to tailor the specific surface area, pore size, pore volume and surface acidity of the assembled alumina coiled plates. [Display omitted] Porous alumina has been widely used as catalytic support for industrial processes. Under carbon emission constraints, developing a low-carbon porous aluminum oxide synthesis method is a long-standing challenge for low-carbon technology. Herein, we report a method involving the only use of elements of the aluminum-containing reactants (e.g. sodium aluminate and aluminum chloride), sodium chloride was introduced as the coagulation electrolyte to adjust the precipitation process. Noticeably, the adjustment of the dosages of NaCl would allow us to tailor the textural properties and surface acidity with a volcanic-type change of the assembled alumina coiled plates. As a result, porous alumina with a specific surface area of 412 m2/g, large pore volume of 1.96 cm3/g, and concentrated pore size distribution at 30 nm was obtained. The function of salt on boehmite colloidal nanoparticles was proven by colloid model calculation, dynamic light scattering, and scanning/transmission electron microscopy. Afterward, the synthesized alumina was loaded with PtSn to prepare catalysts for the propane dehydrogenation reaction. The obtained catalysts were active but showed different deactivation behavior that was related to the coke resistance capability of the support. We figure out the correlation between pore structure and the activity of the PtSn catalysts associated with the maximum conversion of 53 % and minimum deactivation constant occurring at the pore diameter around 30 nm of the porous alumina. This work offers new insight into the synthesis of porous alumina. [ABSTRACT FROM AUTHOR]

Over a billion tons of high-sulfur bauxite has not been utilized effectively currently in China, because the pyrite existing in the bauxite poses a range of hazards during the Bayer process. A novel idea was proposed to remove sulfur by the silicon-containing minerals in bauxite reacting with sulfur species in sodium aluminate solution to form sulfur-bearing desilication products (SDSP) for discharge with the red mud in the Bayer process. This study investigated the reaction behavior between kaolinite and different sulfur-containing ions under the simulated Bayer process conditions, elucidating the desulfurization rate variation and formation mechanism of SDSPs. The thermodynamic calculations suggest that the reaction between kaolinite and sulfur-bearing sodium aluminate solution to form SDSPs can occur spontaneously. The experimental results demonstrated that various SDSPs can be produced through the reaction of kaolinite and sulfur-containing ions in sodium aluminate solution during the simulated Bayer process, resulting in various desulfurization efficiencies, while the desulfurization process will not result in additional alkali consumption. Increasing the kaolinite dosage, extending the reaction time, and elevating the reaction temperature all contribute positively to enhancing desulfurization efficiency. Kaolinite reacted with  S 2 O 3 2 −  in sodium aluminate solution to generate Na8Al6Si6O24S2O3·2H2O, achieving a desulfurization rate exceeding 90% under optimized conditions. Under the simulated Bayer digestion process conditions at elevated temperature, the desulfurization rates of kaolinite ranked in ascending order as  S 2 −  <  SO 3 2 −    <  SO 4 2 −  <  S 2 O 3 2 − . Kaolinite reacted with  SO 4 2 −  and  S 2 O 3 2 −  to form cancrinite type SDSPs, and a superior desulfurization rate can be achieved. This work can provide a theoretical foundation and technological support for the efficient utilization of high-sulfur bauxite by the Bayer process. [ABSTRACT FROM AUTHOR]

Mordenite's excellent physical and chemical qualities set it apart from other zeolites with similar applications in industry. Mordenite is frequently produced through hydrothermal processing with TEA+ cations. The best template agent is TEA+ cations, despite the fact that they may lead to a variety of problems, such as the release of toxicity, the high cost of production, the contamination of wastewater, and environmental damage. So, it's important to develop a mordenite synthesis technique that doesn't need an organic template or a cheap template. The mordenite-type zeolites were prepared using sand from the western part of Iraq (Ar-Rutbah). Silica was extracted from Iraqi sand as a silica source and sodium aluminate as a source of alumina Al by using the SOL-GEL method through the hydrothermal technique at temperatures ranging from 23 to 27 °C over a period of 7 days. Analyses such as XRD, BET surface area AFM, FT-IR, and FE-SEM were performed on the sample. The average particle size was 31.9 nm, and the BET surface area was 202.487. XRF detected the ratio of silica to alumina (Si/Al = 4.55), and the exchange of sodium ions for hydrogen ions through ionic exchange is 100%. The micrograph clearly reveals a tiny portion of the crystal band with a flaky habit, while FE-SEM images of synthesized H-MOR show that plates form the majority of the crystals. [ABSTRACT FROM AUTHOR]

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For the study, to effectively promote the activity of waste brick powders for recycling, they were being treated by microwave radiation, calcination, and chemical-activation. Specimens of neat paste were prepared with a 7 ∶3 mass ratio of cement and waste brick powder and 3 d, 7 d, 14 d and 28 d compressive strength of the specimens was tested. Their crystal phase composition and micro-structure were observed by XRD and SEM. The results showed that the amorphization of Al2O3was promoted in the waste brick powder by microwave radiation and the compressive strength of the neat paste of cement and waste brick powder was increased in 3-28 d and increased with the increase of the time of microwave radiation. The increase of the activity of waste brick powder was not influenced significantly by quenching after microwave radiation. At the temperature between 600 ℃ and 800 ℃, the activity of waste brick powder was on the increase with the increase of the temperature of calcination. The activity of waste brick powder quenched immediately after calcination at high temperature was better than that activated by microwave radiation. The activation by HMTA and sodium aluminate led to the development of a large amount of AFm in the neat paste of cement-waste brick powder at the age of 28 d while the C-A-S-H and AFt developed during the activation by polyaluminium chloride (PAC) had smaller size and were stable, and the micro-structure of the hardened paste was more dense. [ABSTRACT FROM AUTHOR]

The alkaline slag produced during alkali recovery might cause harm to the furnace's refractory components. The seat-drop technique and static dry pan method are used to explore the cladding features and corrosion characteristics of alkaline slag on the surface of magnesia-alumina spinel refractory in this paper. SEM-EDS and XRD are used to study the microstructure, fundamental changes, and compound composition of the molten cladding and interfacial layers, as well as the trends of slag column alterations. Factsage 7.2 software is used to model the interaction between the molten slag and the refractory. The results demonstrate that the wettability process of the slag column is impeded in a reducing environment. Combine with the results of the thermodynamic simulate, it is found that the formation and transformation of a large number of high melting point compounds in a reducing atmosphere is the decisive reason for the inhibition of wettability. Temperature increases promote the production of high melting points substances such as magnesium silicate and sodium metal aluminate, which alters the micro-morphology of the materials and improves slag resistance and permeability resistance of refractories. [ABSTRACT FROM AUTHOR]

Due to its thermodynamic stability, silica sand is traditionally used during the metal casting process in foundries. The sand-casting process involves a wide range of organic and inorganic binders. Due to ease in mold making process and less adverse environmental impact, sodium silicate has emerged as the most popular binder. Sand castings exposed to elevated temperatures lose the binding property and can no longer be used in the foundries. Present work reports the formation of cristobalite, a polymorph of quartz in sodium silicate bonded sand exposed to temperature of 1000 °C. It was believed that sodium silicate is responsible for the conversion of silica sand into cristobalite, leading to the loss of binding property. To avoid cristobalite formation, further, the binder was replaced with sodium aluminate. The mineralogical characterization of such sand also showed the presence of cristobalite under the same experimental conditions. It was suspected that apart from sodium, other cations could also be responsible for cristobalite formation. To support this hypothesis, the sand was mixed with a solution of different cations, namely NaCl, KCl, KOH, CaCl2, Al2(SO4)3 and FeCl3 were calcined at two different temperatures. It was found that the conversion of silica sand to cristobalite takes place at a temperature of 1000 °C in the presence of monovalent cation sodium. In the presence of all other cations, the transformations occur at a temperature of 1250 °C. These conversions were supported using XRD, SEM-EDS and FTIR analyses. Reclamation of such sand is not possible due to its inertness. [ABSTRACT FROM AUTHOR]

The problem that sulfur causes in alumina production using the Bayer process can be eliminated by adding sodium nitrate, and, while the reaction mechanism is not perfect, this paper studies the reaction mechanism of sodium nitrate and different valence sulfurs in a sodium aluminate solution by combining thermodynamic calculations and experiments. Through thermodynamic analysis, it is deduced that sodium nitrate undergoes oxidation reactions with low valence sulfur (S2−, S2O32−, and SO32−) of different valence states in a sodium aluminate solution, while the oxidation effect of S2− is the most obvious. By studying the influence of the sodium nitrate dosage, oxidation time, and oxidation temperature on the different valence sulfurs in a sodium aluminate solution, it is concluded that S2− removal reaches 67.74% under the conditions of 3% sodium nitrate dosage, 260°Coxidation temperature, and 60-min oxidation time. However, the oxidation effect on S2O32− and SO32− is not obvious. The experimental results are consistent with the thermodynamic calculation results. Finally, the reaction mechanism of sodium nitrate with different valence sulfurs in a sodium aluminate solution is described in detail, which provides theoretical support for the desulfurization of high-sulfur bauxite in the production of alumina using the Bayer process. [ABSTRACT FROM AUTHOR]

[Display omitted] • A modified synthesis of mayenite with enhanced adsorption capacity of fluorine. • The maximum adsorption capacity of mayenite for fluorine reached 36.86 mg/g. • Fluorine desorption yield of fluorine-loaded mayenite reached 83.28%. • Ligand exchange of fluorine with − OH and the formation of F − Al bond. Removal of fluorine in sodium aluminate solution facilitates the purity of aluminum products and reduces the corrosiveness of equipment. Hence, a modified synthetic method was used to prepare mayenite (Ca 12 Al 14 O 33) adsorbent with the enhanced fluorine adsorption capacity in sodium aluminate solution. The adsorption process conformed to a pseudo-second-order kinetic model (R2 = 0.99) and Langmuir adsorption isotherm (R2 = 0.98) indicating that the adsorption of fluorine by Ca 12 Al 14 O 33 is chemisorption. According to X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT − IR), X-ray fluorescence (XRF), and X-ray photoelectron (XPS) analysis, the mechanism of fluorine adsorption by Ca 12 Al 14 O 33 was the ligand exchange with − OH and the formation of F − Al bond. Therefore, Ca 12 Al 14 O 33 could be used as a potential adsorbent for fluorine in sodium aluminate solution. [ABSTRACT FROM AUTHOR]

d6r units were proved to be crucial for the synthesis of SSZ-16 zeolite with AFX topology, and FAU zeolite owning plenty of d6r units was chosen as the essential raw material for constructing AFX frameworks. In this work, SSZ-16 zeolite was directly synthesized using colloidal silica and sodium aluminate as the raw materials in short crystallization time of 5 h. The corresponding crystallization process were carefully investigated by various characterizations, demonstrating that the key to this success was the formation of d6r units built up by a large amount of s4r units which were formed with the assistance of the appropriate organic structure directing agent (OSDA) and seeds in the synthetic media. Interestingly, the products of C-SSZ-16 zeolites presented spherical shapes consisted of relatively small particles with size range from 30 to 50 nm. Moreover, after ion-exchanged with Cu ions, the Cu-C-SSZ-16 products showed excellent performance in the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) and better hydrothermal stability than conventional Cu-SSZ-16-con samples due to slightly higher Si/Al ratio of the Cu-C-SSZ-16. Therefore, remarkable catalytic performance and the use of low-cost raw materials as well as short period of synthesis time make AFX zeolites as potential applicants in NH 3 -SCR field, from an industrial viewpoint. [Display omitted] • SSZ-16 zeolite was synthesized directly using colloidal silica and sodium aluminate as raw materials. • Plenty of d6r units were built up by a large amount of s4r units with the assistance of the OSDA and seeds. • The Cu-based SSZ-16 product shows excellent activity and high hydrothermal stability in the NH 3 -SCR reaction. [ABSTRACT FROM AUTHOR]

The one-part geopolymer binder was synthesis from the mixing of aluminosilicate material with solid alkali activators. The properties of one-part geopolymers vary according to the type and amount of solid alkali activators used. This paper presents the effect of various sodium metasilicate-to-sodium aluminate (NaAlO2/Na2SiO3) ratios on fly ash-based one-part geopolymer. The NaAlO2/Na2SiO3 ratios were set at 1.0 to 3.0. Setting time of fresh one-part geopolymer was examined through Vicat needle apparatus. Mechanical and microstructural properties of developed specimens were analysed after 28 days of curing in ambient condition. The study concluded that an increase in NaAlO2 content delayed the setting time of one-part geopolymer paste. The highest compressive strength was achieved at the NaAlO2/Na2SiO3 ratio of 2.5, which was 33.65 MPa. The microstructural analysis revealed a homogeneous structure at the optimum ratio. While the sodium aluminium silicate hydrate (N-A-S-H) and anorthite phases were detected from the XRD analysis.

Aluminum alloys, along with positive properties - low density, high specific strength, electrical conductivity, ductility, viscosity and others, have disadvantages: low hardness, modulus of elasticity, wear resistance and high chemical activity in many inorganic acids. The method of microarc oxidation (MАO) can eliminate these shortcomings. The transformation of the surface layers of the workpiece into high-temperature oxides of aluminum will strengthen the surface and increase its protective properties. The properties of MАO coatings depend on many factors, one of which is the composition of the electrolyte. According to the literature, the most widely used alkaline-silicate electrolytes, which have shown the greatest efficiency in MАO of aluminum alloys. The data available in the literature on the use of multicomponent electrolytes containing sodium aluminate NaAlO2 and sodium hexametaphosphate Na6P6O18 do not allow to elucidate their role in the formation of MАO coatings. Studies of the use of hexametaphosphate to alkaline silicate electrolyte have shown that Na6P6O18 promotes the formation of a thicker coating. The rate of thickness formation in the absence of hexametaphosphate is 0.5 ,7 0.7 μm / min, and at a hexametaphosphate content of 10 g / l - 0.9 ÷ 1.1 μm / min. As for the effect on the phase composition, the effect was not detected. It was studied that the addition of aluminate-silicate electrolytes of sodium aluminate in the amount of up to 13 g / l does not have a significant effect on the thickness of the coating, but affects the phase composition of the coating.

Fly ash-bottom ash of coal is a solid waste in many industries and electric power plants. One method to reduce that solid waste is by using it to produce artificial zeolite. The Filicium decipiens charcoal was added into artificial zeolite to increase its performance to adsorb water pollutants. The pumice stone is also used in this work as a source of silica. The manufacture of artificial zeolite was carried out by the hydrothermal method by optimizing the composition of sodium silicate from Lampung pumice silica, sodium aluminate from aluminum scrap, and charcoal of Filicium decipiens. From the characterization of the LCR meter, the optimum artificial zeolite obtains the conductivity value from 9.14×10-6 (S/cm) to 6.09×10-6 (S/cm), confirming that artificial zeolite is a semiconductor material. The highest conductivity of artificial zeolite will increase its performance as a catalyst and absorbent. The composition of the artificial zeolite after XRF characterization was aluminum, silica, phosphorus, potassium, calcium, titanium, vanadium, chromium, Mangan, and ferrite. From the XRD characterization result obtained, the dominant phase is Zeolite-A. SEM-EDX characterization results obtained a spherical and cylindrical microstructure of artificial. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation method was used to form ceramic coatings on pure Ti substrates, using various aqueous solutions of sodium aluminate (15 g/L and 20 g/L, with or without the addition of NaOH, 2 g/L). The PEO process was carried out at constant time and voltage (300 seconds, 200 V). The ceramic coatings obtained by PEO were investigated by SEM, EDS, XRD, and XPS. Their corrosion behavior has been evaluated as well. The study aimed to understand the role of NaOH in the development of the PEO process and to evaluate the results obtained by short treatments in potentiostatic regime. [ABSTRACT FROM AUTHOR]

In this study, a certain percentage of lignin in original bamboo kraft black liquor (BKBL) was separated, and the residual BKBL with low lignin content was expected to be fed into the alkali recovery boiler to reduce the heat transfer load of the alkali recovery boiler. With the decrease in lignin content, the rheological properties/volumetric isothermal expansivity (VIE) of BKBL change. When the lignin content was 70% remaining in the original BKBL, the viscosity of BKBL with low lignin content is close to that of the passivated BKBL at the same solids content, the dynamic viscoelasticity is superior, and the VIE decreases by 57.2%. When the amount of desilication agent is 1.5%, the viscosity of BKBL with low lignin content did not change much, and the VIE increased sharply and was 62.7% higher than that of the passivated BKBL. Therefore, the combination of partial lignin separation process and sodium aluminate desilication process can effectively improve the ability of alkali recovery boiler to deal with BKBL and reduce the influence of "silicon interference". [ABSTRACT FROM AUTHOR]

The addition of active seed for increasing the precipitation rate leads to the formation of fine Al(OH)3 particles that complicates separation of solid from the mother liquor. In this study, the enhanced precipitation of coarse Al(OH)3 from sodium aluminate solution using active agglomerated seed was investigated. Aluminum salt (Al2(SO4)3) were used for active agglomerated seed precipitation at the initial of the process. About 50% of precipitation rate was obtained when these agglomerates were used as a seed in the amount of 20 g L−1 at 25 °C within 10 h. The agglomerated active seed and precipitate samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). SEM images showed that agglomerates consist of flake-like particles that can be stick together by bayerite (β-Al(OH)3) acting as a binder. The precipitation temperature above 35 °C and the high concentration of free alkali (αk = 1.645Na2Ok/Al2O3 > 3) lead to the agglomerates refinement that can be associated with the bayerite dissolution. [ABSTRACT FROM AUTHOR]

Geopolymer bricks from lead glass sludge (LGS) and alumina flakes filling (AFF) waste were synthesized in the present work. AFF waste was chemically treated to prepare sodium aluminate (NaAlO2) powder. Silicate source (untreated LGS and thermally treated one at 600 °C (LGS600)) and sodium oxide (Na2O) concentration (as NaAlO2) were the compositional parameters, which affected the physical and mechanical properties (compressive strength, water absorption, and bulk density) of the prepared bricks. High organic matter content inside LGS caused a retardation effect on the geopolymerization process, resulting in the formation of hardened bricks with modest 90-day compressive strengths (2.13 to 4.4 MPa). Using LGS600 enhanced the mechanical properties of the fabricated bricks, achieving a maximum 90-day compressive strength of 22.35 MPa at 3 wt.% Na2O. Sodium aluminosilicate hydrate was the main activation product inside all samples, as confirmed by X-ray diffraction and thermal analyses. Acetic acid leaching test also proved that all LGS600-NaAlO2 mixtures represented Pb concentrations in leachates lower than the permissible level of characteristic leaching procedures, indicating the mitigation of environmental problems caused by these wastes. [ABSTRACT FROM AUTHOR]

Background. An urgent problem of natural gas purification is the creation of an adsorbent on a local raw material base, of which interest is attracted by zeolites created using template additives that provide their predetermined functional properties. Purpose: to study a two-stage approach to the synthesis of nanostructured crystalline type A zeolite with the inclusion of chitosan gel crosslinked with glutaraldehyde as a template in the process, solving the problem of removing the chitosan template from the structure of the resulting zeolite.. Methodology. The use of the hydrothermal method in the sol-gel process of synthesizing nanostructured crystalline zeolite type A. The use of SEM, EMF, X-ray diffraction, nitrogen porosimetry to determine the structural characteristics, the study of CO2 adsorption-desorption on the resulting nanozeolite. Originality. Nanostructured crystalline type A zeolite was synthesized by a two-stage method. Chitosan crosslinked with glutaraldehyde was used as a template. To remove the chitosan template from the aluminosilicate, the product was treated with hydrogen peroxide. Findings. Nanostructured crystalline type A zeolite was synthesized, its physicochemical characteristics were studied, incl. no pore shrinkage, crystallinity, CO2 adsorption. [ABSTRACT FROM AUTHOR]