Acidic wastewater generated during sulfuric acid leaching of reduced tionite within the EUROTITAN process was treated using three low-cost adsorbents: fly ash, bentonite, and red mud slag. Tionite is a solid residue originating from the sulfate route of TiO2 production, whereas the investigated wastewater is a secondary acidic stream produced during hydrometallurgical treatment of reduced tionite. The initial wastewater was characterized by low pH and elevated concentrations of Fe, Al, Ti, B, Cu, Mn, Pb, Cr, and Li. Batch adsorption experiments were carried out by varying contact time from 4 to 24 h and adsorbent dosage from 5 to 15 g/L. The results showed distinct selectivity depending on adsorbent type and solution chemistry. Bentonite exhibited the most stable performance, achieving nearly complete removal of Pb, Cu, B, and Li, while Fe and Al were only partially removed and Ti removal remained limited. Fly ash showed high affinity toward Pb and Cu, but its performance was strongly affected by dosage and contact time. Red mud slag demonstrated excellent Pb removal, high Cu removal, and time- and dosage-dependent Ti removal, although partial dissolution of Fe- and Al-bearing phases occurred under strongly acidic conditions. Overall, the results confirm that industrial by-products and natural clay materials can contribute to partial purification of acidic metallurgical wastewater, while additional neutralization or polishing steps are required for complete treatment.

Abstract In this study, the possibility of using slag derived from hydrogen-plasma reduction of red mud (H2RMS) as a low-cost adsorbent for phosphate removal from aqueous solutions was investigated. Batch adsorption experiments were conducted to evaluate the effects of contact time, solution pH, sorbent dosage, and initial phosphate concentration under controlled laboratory conditions. Phosphate concentrations were determined spectrophotometrically using the ammonium molybdate method. These results demonstrated that phosphate adsorption onto H2RMS is strongly pH-dependent, with maximum removal efficiency achieved under acidic conditions (pH ≈ 2). Adsorption equilibrium was achieved after approximately 18 h of contact time. Increasing the sorbent dosage enhanced phosphate removal efficiency, although improvements became marginal beyond a dosage of 10 g/L. At optimal conditions, phosphate removal efficiency of approximately 90% was achieved. These findings indicate that H2RMS shows significant potential as an effective adsorbent for phosphate removal, offering a possible pathway for the valorization of metallurgical waste residues.

Fenton processes, in which hydrogen peroxide in the presence of divalent iron ions generates hydroxyl radicals (•OH), are widely used for the degradation of organic pollutants (phenols, antibiotics, dyes). In this review, red mud is analysed as a cheap source of iron ions in Fenton processes. Raw red mud can be used without additional modifications, but to increase the catalytic efficiency, its modification is required, which includes chemical reduction, carbothermal treatment or doping with metals. Particular attention is given to photo-Fenton and electro-Fenton processes, where red mud doped Cо, Sn or Cе, or in combination with reduced graphene oxide and biochar, allow the generation of not only hydroxyl radicals (•OH) but also singlet oxygen (1O2) and superoxide radicals (•O2–), achieving ≥99% pollutant removal. At the same time, the synthesised catalysts showed high stability and reusability. Based on a comparative analysis of more than 30 studies, it is concluded that red mud represents a cheap source of iron ions for heterogeneous Fenton processes, with significant potential for industrial application.Keywords: Fenton process, hydroxyl radicals, organic pollutants, red mud.

EURO-Titan project aims upscaling Ti-metal powder manufacturing from metallurgical residues, abundantly available in Europe. The demonstration of the overall process is planned at the Al-Doo Aluminium plant (Bosnia-Herzegovina) and at ORANO (France). For Ti extraction from red mud, reduction was applied at 1600 ?C in an electric arc furnace to remove most of the iron through magnetic separation. Then the slag is leached by sulfuric acid at variable pressure to obtain the highest yield of titanium oxysulfate. Highest Ti-leaching efficiency (95%) was reached at 150 ?C using 5 mol|L sulfuric acid at 9 bar oxygen in 2 h. For Ti-leaching by sulfuric acid from tionite, a byproduct of the titanium dioxide production through sulfate processing, gave lower leaching efficiency under high pressure in an autoclave, altered Ti-compounds resist to dissolution. Nanosized and submicron TiO2-powders were prepared from Ti oxysulfate, using ultrasonic spray pyrolysis and hydrogen reduction between 700 and 1350°C.

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.