The synthesis of oxide nanopowders through ultrasonic spray pyrolysis (USP) represents a sustainable method for producing high-purity, spherical particles tailored for advanced material applications. Recent developments in USP synthesis leverage the continuous transport of aerosols from an ultrasonic generator to a high-temperature furnace, with nanopowders collected efficiently using an electrostatic precipitator. This study explored the use of USP for titanium oxysulfate and aluminum nitrate solutions derived from the aluminum industry, focusing on resource recovery and waste reduction. Titanium oxysulfate was synthesized by leaching slag, generated during the reduction of red mud, with sulfuric acid under oxidizing, high-pressure conditions. After purification, the titanium oxysulfate solution was processed using USP in a hydrogen reduction atmosphere to yield spherical titanium dioxide (TiO2) nanopowders. The hydrogen atmosphere enabled precise control over the nanoparticles’ morphology and crystallinity, enhancing their suitability for use in applications such as photocatalysis, pigments, and advanced coatings. In parallel, both synthetic and laboratory solutions of aluminum nitrate [Al(NO3)3] were prepared. The laboratory solution was prepared by leaching aluminum hydroxide oxide (AlOOH) with hydrochloric acid to form aluminum chloride (AlCl3), followed by a conversion to aluminum nitrate through the addition of nitric acid. The resulting aluminum nitrate solution was subjected to USP, producing highly uniform, spherical alumina (Al2O3) nanopowders with a narrow size distribution. The resulting nanopowders, characterized by their controlled properties and potential applicability, represent an advancement in oxide powder synthesis and resource-efficient manufacturing techniques.

This study investigates the influence of specific surface area (SSA) and aluminum hydroxide particle size on sodium aluminate’s purification efficiency in the Bayer process. This research examines how variations in SSA affect the adsorption and incorporation of contaminants such as Cu, Fe, and Zn, as well as the optimal balance between effective purification and excessive Al2O3 loss. Different SSA values and purification durations are analyzed to optimize the purification process and determine conditions that maximize impurity removal while maintaining system stability. Additionally, solid residue characterization using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) provides insights into impurity incorporation mechanisms, including isomorphic replacement, surface adsorption, and co-crystallization. This study highlights key process parameters that influence impurity behavior and crystallization dynamics, offering valuable guidance for refining industrial purification strategies and improving aluminum hydroxide quality.

: This paper shows the preliminary results of an investigation into the possibility of using red mud slag (RMS) for phosphate sorption from aqueous solutions. The red mud slag was obtained from red mud treatment, specifically from carbothermal reduction at high temperatures. This process resulted in forming a metallic phase (iron) and slag enriched with other elements. The preliminary analysis of slag is performed to investigate its potential for use as a phosphate sorbent in wastewater treatment. The slag is divided into three categories. Two of them are obtained by sieving an original slag sample in the fine fraction and the coarse fraction (the slag residual after sieving). The third sample is the raw slag. After an experiment that included 24 h shaking of slag and phosphate solution, the results show potential for using red mud slag in phosphate sorption. It is an initial experiment that will be a starting point for further investigation of the sorption characteristics of red mud slag.

Using direct hydrogen reduction in a rotary kiln without smelting and the dissolving of solid residues under high pressure in an autoclave, this study investigates pyrometallurgical and hydrometallurgical techniques for decarbonizing and recovering precious metals from bauxite residue. The aim of this paper is to provide decarbonizing methods for removing iron from bauxite residue, a Bayer process by-product that cannot be disposed of in an environmentally responsible way. Hydrogen is being researched as a cleaner substitute for conventional carbon-based reductive melting, which produced large CO₂ emissions. A rotary kiln's hydrogen reduction process recovers 99.9% of the iron as iron, which can then be separated from the solid residue that contains other valuable metals using magnetic separation. In contrast to very stable oxides like titanium oxide, silica, and aluminum oxide, we found that hydrogen can reduce iron oxide from bauxite residues to metallic iron. Sulfuric acid leaching of titanium, iron, and aluminum is highly effective when done in an autoclave at high pressure.

Comparative analysis of red mud reduction techniques was performed using both carbothermal and hydrogen-based reduction methods, combining thermochemical modeling and experimental validation. The reduction process is mostly important because of the high contamination risk assessment of soil with disposed red mud. Therefore, the minimization of red mud during the reduction process can be a novel strategy for the production of metallic iron and solid residue for hydrometallurgical treatment. Different strategies of hydrogen and carbon reduction in static and dynamic conditions were studied between 700 °C and 1700 °C. The separation of solid residue and formed iron was analyzed using magnetic separation. The main aim was to study the advantages and disadvantages of using decarbonizing technologies for the treatment of red mud, aiming to develop an environmentally friendly process. Thermochemical analysis of the reduction offered new data about mass losses during our process through the evaporation, thermal decomposition, and formation of metallic carbide.

This study explores both pyrometallurgical and hydrometallurgical methods for decarbonizing and recovering valuable metals from bauxite residue, with hydrogen plasma reduction and direct acid leaching as the primary approaches. The goal is to offer innovative techniques for extracting metals from bauxite residue, a by-product of the Bayer process, which cannot be disposed of in an environmentally sustainable manner. Additionally, reducing the volume of bauxite residue through combined treatments is a key objective. In contrast to traditional carbon-based reductive melting, which generated significant CO2 emissions, hydrogen is now being investigated as a cleaner alternative. Through hydrogen plasma reduction, approximately 99.9% of iron is recovered as crude metallic iron, which can be easily separated from the slag containing other valuable metals. Thermochemical analysis was used to predict slag formation and chemical analysis of slag during hydrogen reduction. To further recover metals like aluminum and titanium, the slag is subjected to sulfuric acid leaching under high-pressure of oxygen in an autoclave avoiding silica gel formation. The results demonstrated a leaching efficiency of 93.21% for aluminum and 84.56% for titanium, using 5 mol/L sulfuric acid at 150 °C, with almost complete iron recovery. Assisted ultrasound leaching of slag with sulphuric acid under atmospheric pressure leads to 54% leaching efficiency of titanium.

<p>Zeolite 13X is one of the best adsorbents among zeolites and one of the most commercially available zeolites.&nbsp; This paper investigates the influence of several process parameters on the properties of 13X zeolite, including crystallization temperature, crystallization duration and Si/Al molar ratio in the starting reaction mixture. The quality of the obtained powders was examined in detail through a series of analytical and instrumental methods, presented in the paper. Water and CO₂ adsorption capacities were determined as key quality parameters of 13X zeolite, and additional characterization was performed by determining material granulometry, specific surface area (BET analysis), crystallinity (X-ray diffraction method) as well and SEM analysis. The obtained results indicate a clear dependence between the examined process parameters of the system and the characteristics of the synthesized materials, thus enabling the selection of optimal conditions for the synthesis of 13X zeolite.</p>

This study presents a comparative analysis of titanium leaching from tionite (a byproduct of the titanium dioxide production process) and carbothermally reduced red mud (derived from aluminum residues). Tionites from the sulfate process and red mud residue are known for their environmental impacts due to their metal content and acidic/basic nature. This study explored leaching as a method to recover titanium and other metals under high-pressure and high-temperature conditions using sulfuric acid. Experiments were conducted in an autoclave with different parameter changes, like varying oxygen pressure, temperature, and reaction time to optimize metal extraction. The leaching efficiency of titanium was found to be higher in the carbothermal-reduced slag compared to tionite due to the altered mineral phases in the reduced material. XRD and SEM-EDS analyses confirmed the differing leaching behaviors, with titanium compounds in tionite showing greater resistance to dissolution. These findings highlight the importance of thermal pre-treatment for optimizing metal recovery from industrial residues. The main aim of this study is to contribute to the development of sustainable waste management solutions for tionites and red mud, emphasizing the potential of hydrometallurgical methods for metal recovery. The results are expected to inform future research and industrial applications, advancing the recovery of valuable metals while reducing the environmental footprint of titanium and aluminum residue disposal.

Red mud is a by-product of alumina production, which is largely stored in landfills that can endanger the environment. Red mud, or bauxite residue, is a mixture of inorganic compounds of iron, aluminum, sodium, titanium, calcium and silicon mostly, as well as a large number of rare earth elements in small quantities. Although certain methods of using red mud already exist, none of them have been widely implemented on a large scale. This paper proposes a combination of two methods for the utilization of red mud, first by carbothermic reduction and then, by leaching under high pressure in an autoclave in order to extract useful components from it with a focus on titanium. In the first part of the work, the red mud was reduced with carbon at 1600 °C in an electric arc furnace, with the aim of removing as much iron as possible using magnetic separation. After separation, the slag is leached in an autoclave at different parameters in order to obtain the highest possible yield of titanium, aiming for the formation of titanium oxysulfate and avoiding silica gel formation. A maximal leaching efficiency of titanium of 95% was reached at 150 °C using 5 mol/L sulfuric acid with 9 bar oxygen in 2 h. We found that high-pressure conditions enabled avoiding the formation of silica gel during leaching of the slag using 5 mol/L sulfuric acid, which is a big problem at atmospheric pressure. Previously silica gel formation was prevented using the dry digestion process with 12 mol/L sulfuric acid under atmospheric pressure.

Submicron and nanosized powders have gained significant attention in recent decades due to their broad applicability in various fields. This work focuses on ultrasonic spray pyrolysis, an efficient and flexible method that employs an aerosol process to synthesize titanium-based nanoparticles by transforming titanium oxy-sulfate. Various parameters are monitored to better optimize the process and obtain better results. Taking that into account, the influence of temperature on the transformation of titanium oxy-sulfate was monitored between 700 and 1000 °C. In addition to the temperature, the concentration of the starting solution was also changed, and the flow of hydrogen and argon was studied. The obtained titanium-based powders had spherical morphology with different particle sizes, from nanometer to submicron, depending on the influence of reaction parameters. The control of the oxygen content during synthesis is significant in determining the structure of the final powder.

Abstract Red mud, a voluminous industrial waste produced during the Bayer process in the alumina industry, has numerous application possibilities across various fields. Its potential uses are diverse, ranging from the construction industry and metallurgy to environmental protection and agriculture. There are three main aspects of red mud utilization. First, it can be analyzed from the point of view of resource utilization, where it could be applied as raw material mostly in the construction industry. Second, it could be a useful source of valuable components, such as rare earths and metals, especially iron. Third, red mud could have different environmental applications, in wastewater treatment, soil remediation, etc.The paper summarizes current data on red mud utilization methods and aims to emphasize the potential for red mud utilization in various fields.

Red mud, byproduct of the aluminum industry, poses a significant environmental problem due to its chemical composition and the large quantities generated. This study explores the potential for its valorization through a multi-step process that includes reduction, leaching with acid solution, purification, and ultrasonic spray pyrolysis (USP). In the first step, red mud undergoes carbothermal reduction, during which metal oxides are transformed into metal phase and slag. In the second step, the slag is subjected to leaching under various conditions, including changes in pressure, temperature, and acid concentration, which allows the recovery of titanium in the form of titanium oxysulfate and other metals. Finally, after purifying the solution using precipitation or solvent extraction, ultrasonic spray pyrolysis is used to synthesize titanium dioxide (TiO₂) nanopowders from titanium oxysulfate (TiOSO₄). This integrated approach not only reduces waste but also produces high-value materials with broad industrial applications.

Bauxite residue, also known as red mud (RM) is waste produced during alumina production in Bayer process. It is posing a significant threat to the enivorment due to its high alklalinity, fine particle size and complex structure various compounds. This study presents a sustainable, approach to its utilization, with focus on the recovery of valuable metals such as titanium. Different decarbonizing technologies were used presented in this work: hydrogen reduction without smelting in rotary kiln, high pressure leaching in an autoclave, ultrasonic spray pirolysis and aluminothermic reduction. Firstly red mud was subjected to hydrogen reduction in order to selectively remove iron, which can be used and transfered in the steel industry. Separation of Iron and solid residue was done using magnetic property of iron and magnetite, Solid residue is further processed in acid leaching with high pressure of oxygen in an autoclave. Leaching process optimizes various process parameters to extract titanium in the form of titanium oxy sulfate as well as iron and aluminium. Additionally, aluminum and iron solutions were also obtained by this process. The remaining solid residue, primarily composed of calcium sulphate and silica, was evaluated for potential use as an adsorbent in wastewater treatment. This innovative process demonstrates an efficient method of bauxite residue utilization with near zero waste concept, offering a promising solution to both environmental and industrial challenges. The planned improvement of proposed research strategy can be reached using solvent extraction and remelting process.