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.

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.

<p>In this paper, the influence of process parameters on the morphological properties of fine precipitated hydrate was examined. The research was conducted with the aim of synthesizing fine precipitated aluminum hydroxide from the aluminate solution obtained by the Bayer process. Fine precipitated hydrates obtained in this way are mostly used in the non-metallurgical industry. The synthesized fine precipitated hydrate should comply with certain quality requirements such as granulometry (average particle diameter), purity, specific surface area, whiteness, etc. This paper shows the influence of certain technological parameters, namely the initial precipitation temperature, the amount and specific surface area of the seed, the influence of the NaOH/Al(OH)3 molar ratio on the characteristics of the synthesized fine precipitated hydrate in terms of the specific surface area, mean diameter and morphology of the obtained particles.</p>

It is known that the temperature of crystallization during the synthesis of zeolite is one of the most important process parameters. However, during the research work on the synthesis of zeolite 13X and the introduction of this material into regular industrial production, it was noticed that the heating rate of the starting reaction suspension can have an equally important influence. This influence can be so pronounced that a difference of just a few minutes in reaching the crystallization temperature can make a significant difference in product quality, affect the presence of other phases in the crystal, or even determine the direction of zeolite crystallization. Therefore, the aim of this work was to show the influence of the heating rate on the quality of the obtained 13X zeolite powders. The obtained samples were analysed in terms of crystallinity (by X-ray diffraction), chemical composition, granulometry and specific surface area (by Brunauer-Emmett-Teller analysis), and regarding water and CO2 adsorption capacities. Additionally, scanning electron microscopy analysis of the samples showed the morphological characteristics of different 13X zeolite powders. The analysis results of the obtained powders confirmed the influence of the heating rate and helped to define the optimal synthesis parameters i.e. the initial temperature and heating time, that resulted in stable product quality.

This paper presents research on hydrodynamics and mass transfer in a packed absorption column. Experimental data on dry column pressure drop, flooding point, and efficiency of absorption of CO2 in water is obtained on a lab-scale absorption column packed with Raschig rings. Auxiliary parts of equipment together with chemical analyses provide simple monitoring and collecting the data. All obtained data were used to test different mathematical models for a given problem, i.e. for determination of the dry column pressure drop, flooding point and the overall gas transfer unit height. For dry column pressure drop, models developed primarily for packed columns described the data the best, with the Billet model generating a 6.54 % mean error, followed by Mackowiak and Stichlmair models. In flooding point calculations, empirical models were tested and models of Lobo, Leva and Takahshi gave the best results. Mass transfer (absorption) experiments gave expected results, since absorption efficiency increased with the increase in the liquid/gas flow rate ratio, i.e. with approaching the flooding point. The Onda?s model was used to calculate partial mass transfer coefficients in liquid and gas phases based on which the height of the overall gas transfer unit was estimated and subsequently compared with the experimental data. Deviation of calculated and experimental results for the height of the overall gas transfer unit is in the expected range of 0-20 %, with mean value of 15.5 %. In conclusion, the available models for determination of the investigated hydrodynamics and mass transfer parameters in packed absorption columns gave adequate results in comparison to the experimental values.

The aim of this research was to determine the influence of the SiO2/Al2O3 molar ratio on the specific commercial properties of NaA zeolite subtypes as final market products (4A,4A-AG and 4A-MS) under the real production and process conditions. The value of the SiO2/Al2O3 molar ratio, so-called silicate module, was set as independently variable and the effect on the physical and chemical properties of each of the subtypes of NaA zeolites was examined. The paper investigates how the SiO2/Al2O3 molar ratio affects specific properties of NaA powders, namely the ion exchange capacity, oil adsorption capacity and water adsorption capacity. Some previous theoretical and experimental studies have shown that the molar ratio plays a crucial role in the formation of these very similar but for final application different subtypes of NaA zeolite. The experimental part of this work was performed and tested in real production conditions, which can be considered as an advantage in relevance to the obtained results. Various analytical and instrumental testing methods were used for the analysis of the obtained powders, including SEM, XRD and PSD analyses.

: As it is known, during regular conditions Bayer's process is used for production of alumina of a 99.0 % grade of purity. In order to obtain high-purity alumina which can then be used for special purposes, additional purification is performed in relation to the application of impurities, and, in the first hand removal of silica (Si) and calcium (Ca). One of the most effective ways of removing these compounds is the process of desilication. The method consists of treating an aluminate solution with lime that binds silica and calcium to tricalcium-aluminate (TCA) which is insoluble and therefore easily separated of the solution. The experimental research examined the impact of process parameters (temperature, time, concentration of added lime) on the efficacy of purifying aluminate solution from Si and Ca, which has a practical and theoretical contribution to aluminate solution research. Synthetic aluminate from non-metallurgic alumina and pure sodium-alkaline (NaOH) is used, in the caustic ratio in the range of 1.45-1.55. Classic volume analysis and analysis using optical emigration spectroscopy (ICP-OES) were used to determine the contents of aluminum and impurities. The experimental research found that short intervals are adverse because soluted compounds Ca(OH) 2 and tetra-calcium aluminum are formed. Also, during longer reaction time and higher temperatures there was an increase in the contents of Si and Ca in the aluminum, because some components from the limestone were dissolved. Small amounts of lime are adverse because there is an increase in calcium content in the solution since part of the lime dissolved, without interacting with the present impurities, while large quantities led to large aluminum loss due to the formation of TCA.

Polazeći od I i II zakona termodinamike, primjenjenog upovratnim procesima, a kod kojih je postignuta ravnoteža pritiskai temperature, u radu je izveden izraz za ukupni maksimalnizaprmenski rad zatvorenih sistema. Radi potpunije interpretacijeove problematike za dva karakteristična slučaja, dat je grafičkiprikaz u p-v dijagramu, gdje se na očigledan način zapaža da senajveći rad širenja sastoji iz izenropskog i izotermnog rada kao irada protiv pritiska okoline. Na bazi izvedenog izraza, koristećiodgovarajuće termodinamičke relacije, izveden je izraz zaspecifični maksimalni rad koji je pogodan za analizu. Dobijeni izrazje posmatran kao dvodimenzioni problem odnosno kao funkcijadvije promijenive: početni pritisak i početna temperatura kaoprimarni parametri. Primjenom matematičke analize dokazano jepostojanje minimuma posmatrane funkcije, i dato njeno grafičkopredstavljanje u prostornom koordinatnom sistemu. Detaljnommatematičkom analizom pokazano je da u opštem slučaju funkcijamaksimalnog rada geometrijski predstavlja jednu konkavnupovršinu u prostoru.Radi efikasnijeg rješavanja i analizepostavljenog problema, složena funkcija maksimalnog radaposmatrana je kao dvije funkcije sa jednom promjenljivomodnosno dvodimenzioni problem sveden je na dvajednodimenziona problema. Pokazano je da i kodjednodimenzionih problema takođe postoji tačka u kojoj jemaksimalni rad minimalan a različit od nule. Na kraj rada, date sumogućnosti primjene kompleksne problematike maksimalnograda a koje se odnose na eksergijsku analizu i optimizacijutermodinamičkih procesa, kao i smjernice za naredna istraživanjaproblema za slučaj ostalih gasova, poluidealnih gasova i Van derWaals – ovog gasa. Može se tvrditi, da postupak analizetermodinamičke funkcije maksimalnog rada, prikazanog u radu,nije uobičajen u literaturi.