Search Results (44)

The mineral-mapping capability of three spaceborne sensors with different spatial and spectral resolutions, the Environmental Mapping and Analysis Program (EnMap), Sentinel-2, and World View-3 (WV3), is assessed regarding bauxite mining wastes in Amphissa, Greece, with validation based on ground samples. We applied the well-established Linear Spectral Unmixing (LSU) and Spectral Angle Mapping (SAM) classification techniques utilizing endmembers of two established spectral libraries and incorporated ground data through geochemical and mineralogical analyses, X-ray fluorescence (XRF), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and X-ray Diffraction (XRD), to assess classification performance. The main lithologies in this area are bauxites and limestones; therefore, aluminum oxyhydroxides, calcite, and iron oxide minerals were the dominant phases as indicated by the XRF/XRD results. Almost all target minerals were mapped with the three sensors and both methods. The performance of EnMap is affected by its coarser spatial resolution despite its higher spectral resolution using these methods. Sentinel-2 is most effective for mapping iron-bearing minerals, particularly hematite, due to its higher spatial resolution and the presence of diagnostic iron oxide absorption features in the VNIR. World View 3 Shortwave Infrared (WV3-SWIR) performs better when mapping calcite, benefiting from its eight SWIR spectral bands and very high spatial resolution (3.7 m). Hematite and calcite yield the highest accuracy, especially with SAM, indicating 0.80 for Sentinel-2 (10 m) for hematite and 0.87 for WV3-SWIR (3.7 m) for calcite. AlOOH shows higher accuracy with SAM, ranging from 0.57 to 0.80 across the sensors, while LSU shows lower accuracy, ranging from 0.20 to 0.73 across the sensors. This study showcases each sensor’s ability to map minerals while also demonstrating that spectral coverage and the spatial and spectral resolution, as well as the characteristics of the selected endmembers, exert a critical influence on the accuracy of mineral mapping in mine waste. Full article

This article focuses on studying the phase transformation of bauxite iron minerals during electrolytic reduction processes in alkaline solutions (400 g/L Na₂O), with the aim of improving aluminum extraction in the subsequent Bayer process. The research employs electrolytic reduction to convert the refractory minerals in unmilled bauxite (alumogoethite (Fe,Al)OOH, alumohematite (Fe,Al)₂O₃, chamosite (Fe²⁺,Mg,Al,Fe³⁺)₆(Si,Al)₄O₁₀(OH,O)₈) into magnetite, elemental iron (Fe) and to minimize aluminum (Al) extraction during electrolysis. Preliminary thermodynamic research suggests that the presence of hematite (α-Fe₂O₃) and chamosite in boehmitic bauxite increases the iron concentration in the solution. Cyclic voltammetry revealed that, in the initial stage of electrolysis, overvoltage at the cathode decreases as metallic iron deposited and conductive magnetite form on the surface of the particles. After 60 min, the reduction efficiency begins to decrease. The proportion of the current used for magnetization and iron deposition on the cathode decreased from 89.5% after 30 min to 67.5% after 120 min. After 120 min of electrolytic reduction, the magnetization rate exceeded 65%; however, more than 60% of the Al was extracted simultaneously. Al extraction after electrolysis and subsequent Bayer leaching exceeded 91.5%. Studying the electrolysis product using SEM-EDS revealed the formation of a dense, iron-containing reaction product on the particles’ surface, preventing diffusion of the reaction products (sodium ferrite and sodium aluminate). Mössbauer spectroscopy of the high-pressure leaching product revealed that the primary iron-containing phases of bauxite residue are maghemite (γ-Fe₂O₃), formed during the hydrolysis of sodium ferrite. Full article

The Bayer process is used to extract alumina from bauxite, resulting in the formation of a highly alkaline solid residue known as bauxite residue (BR). However, such residue contains insufficient iron (<35% Fe) and complex impurity composition for use in blast furnace ironmaking. This study investigates the potential for enhancing the extraction of aluminium (Al) and increasing the concentration of Fe in residue by electrolytical reduction in suspension of BR in a spent Bayer process solution. A maximal current efficiency of 43.7% was obtained during the electroreduction of the coarse fraction of BR. The magnetite-containing residue obtained was further used as an aid in the high-pressure Bayer process leaching of gibbsitic bauxite. Adding the reduced BR increased the Al extraction rate by up to 7.2%. The kinetics of bauxite leaching at 120–160 °C and time interval 0–40 min in the presence of reduced BR were investigated using a shrinking core model (SCM). The results showed that the leaching kinetics of Al correlate well with the intraparticle SCM equation, indicating that the reaction velocity is regulated by the diffusion of the OH⁻ or Al(OH)₄⁻ through the product layer. The apparent activation energy of the process at 140–160 °C was found to be 32.2 kJ/mol. Al in the solid residue is closely associated with Fe, i.e., it is enclosed in a solid matrix of iron minerals. Full article

With the rapid increase in global lithium demand, the exploration of newly discovered lithium in the bauxite of the Wenshan area in southeastern Yunnan has become increasingly important. However, the current research on clay-type lithium in the Wenshan area has primarily focused on local exploration, and large-scale predictive metallogenic studies remain limited. To address this, this study utilized multi-source remote sensing data from ZY1-02D and ASTER, combined with ALOS 12.5 m DEM and Sentinel-2 imagery, to carry out remote sensing mineral identification, structural interpretation, and prospectivity mapping for clay-type lithium in the Wenshan area. This study indicates that clay-type lithium in the Wenshan area is controlled by NW, EW, and NE linear structures and are mainly distributed in the region from north of the Wenshan–Malipo fault to south of the Guangnan–Funing fault. High-value areas of iron-rich silicates and iron–magnesium minerals revealed by ASTER data indicate lithium enrichment, while montmorillonite and cookeite identification by ZY1-02D have strong indicative significance for lithium. Field verification samples show the highest Li₂O content reaching 11,150 μg/g, with six samples meeting the comprehensive utilization criteria for lithium in bauxite (Li₂O ≥ 500 μg/g) and also showing an enrichment of rare earth elements (REEs) and gallium (Ga). By integrating stratigraphic, structural, mineral identification, geochemical characteristics, and field verification data, ten mineral exploration target areas were delineated. This study validates the effectiveness of remote sensing technology in the exploration of clay-type lithium and provides an applicable workflow for similar environments worldwide. Full article

With the continuous exploitation of bauxite mineral resources, Guangxi bauxite faces many difficulties in alumina production due to its characteristics of high silicon content, high iron content, and a low Al-Si ratio. In view of this, this study is closely related to the key link of bauxite pre-desiliconization and strives to break free from the status quo to improve the aluminum/silicon ratio and help optimize the subsequent alumina-refining process. In the work presented in this paper, the unique mineralogy of Guangxi bauxite was comprehensively considered, covering its complex mineral composition and fine distribution characteristics. The barium hydroxide pre-desilication technology was first used for in-depth experimental exploration, and the silicon removal efficiency under different working conditions was systematically compared. The system compared the silicon removal effect and the associated aluminum loss under different working conditions. The results of this study will lay a solid foundation for the rational and efficient development of bauxite in Guangxi, which is expected to reduce the cost of alumina production, improve the economic benefits for the Guangxi aluminum industry, simultaneously strengthen the efficiency of resource recycling, accelerate the sustainable development of the industry, and provide a useful reference example for subsequent similar studies. Full article

Iron-rich bauxite residue (red mud) is a hazardous alkaline solid waste produced during the production of alumina from high-iron bauxite, which poses severe environmental challenges due to its massive stockpiling and limited utilization. In this study, metallic iron was recovered from high-iron red mud using the smelting reduction process. Thermodynamic analysis results show that an increase in temperature and sodium oxide content, along with an appropriate mass ratio of Al₂O₃ to SiO₂ (A/S) and mass ratio of CaO to SiO₂ (C/S), contribute to the enhancement of the liquid phase mass fraction of the slag. During the smelting reduction process of high-iron red mud, iron recoveries for low-alkali high-iron red mud and high-alkali high-iron red mud under optimal conditions were 98.14% and 98.36%, respectively. The metal obtained through reduction meets the industrial standard for steel-making pig iron, which is also confirmed in the pilot-scale experiment. The smelting reduction process of high-iron red mud can be divided into two stages, where the reaction is predominantly governed by interfacial chemical reaction and diffusion control, respectively. The apparent activation energy of high-alkali high-iron red mud is lower than that observed for low-alkali high-iron red mud. The reduced slag can be used as a roadside stone material or cement clinker. This proposed method represents a sustainable process for the comprehensive utilization of high-iron red mud, which also promotes the minimization of red mud. Full article

Red mud from bauxite processing is among the large-tonnage technogenic waste that poses a significant ecological threat. At the same time, red mud serves as a raw material source for expanding the resource base for obtaining iron, rare metals, and rare earth elements. Numerous studies on their utilization have shown that only through comprehensive processing, combining pyrometallurgical and hydrometallurgical methods, is it possible to maximize the extraction of all the useful components. This work addresses the first stage of a comprehensive technology for processing red mud through reduction smelting, separating iron in the form of pig iron, and producing slag. Studies were conducted on the reductive smelting of red mud using waste slurry from alumina production as the calcium-containing material, taken in proportions calculated to obtain a fluid slag with a hydraulic modulus of 0.55–0.8. The permissible mixing range of red mud with waste slurry was determined to be in the ratio of 0.56–1.2. In cases where the charge was prepared in violation of the required hydraulic modulus value, pig iron was not obtained during smelting. When the hydraulic modulus requirement was met, the temperature of the reductive smelting process was 1350–1400 °C. The total amount of recovered iron obtained as pig iron and fine fractions amounted to 99.5% of the original content. The low iron content (0.23–0.31%) in the non-magnetic slag fraction allows for the production of high-quality titanium oxide and rare earth element concentrates in the subsequent stages of the comprehensive hydrometallurgical processing of red mud, involving acid leaching. Based on the results of a phase analysis of the slag, pig iron, and melt, the reactions of the reductive smelting process were established, and their thermodynamic likelihood was determined. In fluid slags, the content of the sodium aluminosilicate phase is twice as high as that in slag with a higher hydraulic modulus. The reductive smelting of 100% red mud with the addition of calcium oxide, calculated to achieve a hydraulic module of 0.55 at a temperature of 1350–1400 °C, produced pig iron and slag with high alkali and iron contents. Full article

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. Full article

The use of reduction leaching in the production of alumina from bauxite by the Bayer process in order to decrease the amount of waste (bauxite residue) by adding elemental iron or aluminum, as well as Fe²⁺ salts and organic compounds in the stage of high-pressure leaching, requires the purchase of relatively expensive reagents in large quantities. The aim of this study was to investigate the possibility of the use of electrolytically reduced bauxite residue (BR) as a substitute for these reagents. Reduced BR was obtained from Al-goethite containing BR using a bulk cathode in alkaline suspension. The degree of deoxidation of Fe³⁺ compounds was 55% after 2 h of electrolysis with a current yield of more than 73%. The addition of reduced BR according to the shrinking core model leads to a change in the limiting stage of the high-pressure boehmitic bauxite leaching from a surface chemical reaction to internal diffusion. The activation energy decreased from 32.9 to 17.2 kJ/mol by adding reduced red mud. It was also shown that the addition of reduced BR increased the rate of thickening of the slurry after leaching by a factor of 1.5 and decreased the Na₂O losses by 15% without the addition of lime. The solid residue was examined by means of X-ray diffraction analysis and scanning electron microscopy to confirm the presence of magnetite and elemental iron. A preliminary techno-economic analysis was carried out to assess the applicability of the proposed process. Full article

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. Full article

The suitability of microsilica as a raw material for the production of ceramic mullite–silicate proppants was assessed. The chemical and mineralogical compositions of the initial materials were studied. The mineral composition of bauxite is mainly represented by gibbsite Al(OH)₃ and, to a lesser extent, kaolinite Al₄[Si₄O₁₀](OH)₈, with impurities of hematite and quartz. It is established that, in order to obtain mullite–silicate proppants, compositions containing 10–20% microsilica are optimal. The sintering of these compositions occurs at 1350–1380 °C. A lightweight ceramic proppant was obtained with a bulk density of 1.21–1.41 g/cm³, breaking ratio at 51.7 MPa of 19.1–20.3%, and sphericity and roundness of 0.7–0.9, and the optimal roasting temperature was determined as 1370–1380 °C. Full article

Depending on the ore quality, a washing process can be conducted with the bauxite, which basically consists of scrubbing the ore and screening in order to increase the available alumina grade, i.e., the alumina extractable using the Bayer Process, and reduce the impurity content. Tailings are usually disposed of in a tailings dam in the form of a slurry, which is a mixture of solid particles and liquid, consisting mainly of ultra-fine kaolinite, making the dewatering operation challenging. To reduce the environmental impact, mining companies are studying alternative methods to dewater the tailings, and different dewatering methods are available worldwide. The use of new technologies to dewater the tailings has contributed to facing the challenges of achieving sustainable development with their disposal. The decanter centrifuges are already an option for operations for the Canadian oil sands, gold ore in Peru, and nickel in New Caledonia; they are also being tested for iron ore in Brazil. In the present work, bauxite dewatering using the decanter centrifuge was evaluated to understand more about the behavior of these materials and to investigate the effects of various process parameters on the solid recovery and solid content of the flows, using three different kinds of equipment. The results indicated that decanter centrifuges can be used to achieve a high concentration of solids in the cake, with values ranging from 60% to 80% solids per weight and a great clarification in the liquid phase (centrate) from 0 to 6% solids per weight, values which mean the solid phase is suitable for reutilization in the processing circuit. Additionally, the present work provides a better understanding of how different solid contents feed can affect the behavior of the equipment. Full article

In times of increasing demand for resources, processing various waste materials is becoming more economically and ecologically viable. Red mud is a waste material that originates from the bauxite process, also known as the Bayer process. Red mud, due to its high alkalinity and heavy metal content, is often stored in landfills, which can lead to accidents such as those in Brazil or Hungary, especially if the storage takes place above ground. Red mud contains not only iron and aluminum residues but also other economically valuable metals such as manganese, titanium, cadmium, or cobalt. Currently, only 4 million tons of the annual production of 150 million tons are utilized in various industries, which is a relatively small amount. Typically, only the iron content is further processed, leaving other potential resources untapped. Chitin has a high binding capacity for various trivalent and divalent metal ions, making it a suitable material for separating red mud into its components. It has been demonstrated that chitin can effectively remove aluminum, barium, cadmium, cobalt, copper, manganese, iron, nickel, lead, strontium, and various lanthanides from a red mud-like sludge. The elements bound to chitin can be easily removed using wet chemistry. Biologically compatible substances are predominantly used in this process, with few exceptions. The removal of elements from red sludge or other mining wastewater using chitin is a viable alternative to traditional mining methods. Full article

Titanium oxide is a major component of bauxite residue (BR) with a high value, but it is often an unwanted element in common BR reuse options such as cement or iron production. Conventional carbothermic reduction smelting of BR produces a slag still containing a large amount of Ti. This study investigates an aluminothermic process for producing an FeTi alloy by combining BR, ilmenite ore, and fluxes. Based on thermodynamic calculations and batch experiments, the amounts of aluminum (reductant) and fluxes were investigated to achieve the optimum alloy production in parallel with a slag that could be further valorized in the cement industry. The mineralogical and chemical analysis of the metallic and slag phase agreed with the thermodynamic calculations. The results obtained by this study can lead to the development of a new process for the complete valorization of BR, paving the way for scaling up aluminothermic processes for producing ferroalloys from all iron-rich residues. Full article

Hydrogen is increasingly being recognized as a crucial element in reducing carbon emissions in the metallurgical industry. Its use in the steel sector is gaining momentum through various initiatives at high TRL levels. Moreover, hydrogen shows promise in other metal production processes as well. One application involves utilizing hydrogen for effective selective reduction copper from copper slags with a low amount of iron being reduced. Hydrogen can also be employed in the pre-reduction of manganese ore, leading to the carbon-free production of manganese metal through aluminothermic reactions. Additionally, hydrogen can be used in the processing of bauxite residue, where iron is partially or completely reduced to separate an iron-rich fraction, allowing for alumina recovery via leaching. Full article