Alumina Extraction Research Articles

Exploring dealkalization and Cr removal from red mud through freeze-thaw and acid washing: an experimental approach

Red mud (RM) is an industrial solid waste produced during the extraction of alumina from bauxite. The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization. This paper proposes a method for dealkalization and chromium (Cr) removal by repeated freeze and thaw to enhance the comprehensive utilization rate of RM. This study focused on the Bayer RM and investigated the effects of freeze-thaw (FT)-acid washing (AW) for dealkalization and Cr removal. The variables were the eluent concentration and FT cycles. The results showed that the synergistic action of FT-AW significantly improved the efficiency of dealkalization and Cr removal. After five FT cycles with 0.5 mol/L oxalic acid, the dealkalization and Cr removal rates reached 97.5% and 65.38%, respectively, 16.1% and 7.40% higher than those achieved at room temperature. The repeated FT disrupted the structure of the RM particles, leading to an increase in the pore space between the soil particles. This enables complete eluent contact and reaction with Cr and alkali, thereby enhancing the removal rate. The FT-AW process is suitable for practical engineering applications. It offers a novel method for RM dealkalization and Cr removal by using the FT alternation phenomena in seasonally frozen regions.

Formation of aluminum nitride in dross by contact-diffusion reaction during aluminum recycling

Secondary aluminum dross is a solid waste after aluminum extraction from the slag produced during aluminum recycling. It is classified as a hazardous waste due to the high content of active aluminum nitride (AlN). This work studied the thermodynamics and kinetics of AlN formation in aluminum dross. Aluminum tends to react with N2 to form AlN, when the partial pressure of nitrogen (N2) is much greater than that of oxygen (O2) (PN2≫PO2) in thermodynamics. Additionally, the reaction between aluminum and N2 is accelerated with the increasing temperature. Approximately 36.37% of aluminum was transformed into AlN at 700°C according to kinetic analysis. Aluminum recycling involves smelting, refining, and dross processing. The dross produced from these different processes has various compositions and hazardous properties. The formation mechanism of AlN from the three processes was revealed based on the thermodynamic and kinetic analyses. The reaction mechanisms in these processes were identified as surface contact reaction, internal and surface contact reaction, and rotational surface contact reaction between the aluminum melt and N2, respectively. X-ray diffraction (XRD) and electron probe microanalysis (EPMA) analyses were used to determine the phase and composition of the aluminum dross. The nitrogen content in the aluminum dross from smelting, refining, and dross processing was found to be 3.3%, 5.2%, and 9.6%, respectively. The monthly dross production were 276.3 tons, 22.7 tons, and 318.2 tons, respectively, according to statistics. It was calculated that the nitrogen generated in the three process was 9.12 tons, 1.18 tons, and 20.25 tons, respectively. Therefore, dross processing is the primary source of AlN. A rapid dross processing method with small-scale vertical stirring was proposed to shorten the reaction between the aluminum melt and N2, thereby reducing AlN formation. This work could provide guidance for reducing hazardous AlN in aluminum dross and optimizing the aluminum recycling process.

Characterization of Phosphogypsum Blended Red Mud as Geo-material

Red mud (RM) is a toxic material discarded after extraction of aluminum from the Bauxite and is disposed of in the form of slurry or as low-water content cake as stacking. Either form of disposal is a threat to the environment due to the alkaline nature of RM and also consumes vast tracts of land. Occasional failure of the dyke of the RM pond causes a slurry flooding over a large area, which creates geo-environmental problems. The highly alkaline nature of the RM restricts its bulk utilization, as the high pH value supports the leaching of the heavy metals. On the other hand, phosphogypsum (GYP) is an acidic (pH < 7) material produced from the phosphate industry, blending of which can reduce the alkalinity of the mixture. In the present study, an attempt has been made to use GYP blended RM as a resource geomaterial. The GYP is mixed with RM in 5%, 10%, and 15% on a dry basis to evaluate the chemical, physical, and mechanical properties of the newly developed resource material after 3, 7, and 28 days of curing period. The addition of 5% and 10% GYP lowered the maximum dry unit weight, however, 15% GYP increased the maximum dry unit weight upto 15.47 kN/m3. The 28-days strength of 5%, 10%, and 15% GYP blended RM was found as 433.57 kPa, 592.44 kPa, and 711.53 kPa, respectively, which further increased to 752.11 kPa, 1120.38 kPa, and 1371.80 kPa, respectively, after alkali activation.

Extraction of molybdenum, cobalt, and nickel from acidic leach solution of molybdenum leach residue of spent hydrodesulfurization catalyst

ABSTRACT After the extraction of molybdenum from the spent HDS catalyst, a residue containing aluminum, nickel, cobalt, and a small amount of molybdenum was obtained. The simultaneous recovery of nickel, cobalt, aluminum, and residual molybdenum from molybdenum leach residue can be achieved through hydrochloric acid leaching. In the work presented herein, the extraction of molybdenum, cobalt, and nickel from the acidic leach solution of molybdenum leach residue was investigated. Trioctyl tertiary amine can selectively extract cobalt and molybdenum from the acidic leach solution, the extraction of both cobalt and molybdenum reached more than 99% after two-stage countercurrent extraction. The combination of pure water and 25% ammonia water can be utilised for the separation and extraction of cobalt and molybdenum from the loaded cobalt-molybdenum organic phase. After the extraction of cobalt and molybdenum, a synergistic extraction system comprising decyl 4-picolinate and dinonylnaphthalene sulfonic acid can be employed for nickel extraction, achieving a nickel extraction exceeding 99.70% while maintaining aluminum extraction at only 0.32% after undergoing four-stage countercurrent extraction. The nickel stripping efficiency can reach 99.50% after four-stage countercurrent stripping, using a stripping agent of 2 mol/L H2SO4.

Evironmentally friendly comprehensive utilization of retired waste electrolytes of aluminum electrolysis by calcification leaching

Low energy consumption and environmentally friendly recycling methods can extract high-added value and high-demand elements from retired waste fluorinated aluminum electrolytes (RWE-Al), which is crucial for alleviating resource shortages and environmental hazards. This study aims to develop a method for recovering fluorine and aluminum from RWE-Al through calcium leaching transformation combined with acid leaching. Compared to the traditional high-temperature roasting transformation and high-concentration alkali-metal-salt leaching process, this new process only involves one step of low-temperature leaching, purification of fluorine, carbonization of excess calcium, and evaporation extraction of aluminum, avoiding the generation of high energy consumption and secondary hazardous waste (F-containing liquid/ residue). Fluorine and aluminum are effectively separated and purified with extraction rates exceeding 96%. The effects of leaching temperature, CaO addition coefficient, liquid–solid ratio, and leaching time on the leaching process were systematically studied. The effects of acid concentration, liquid–solid ratio, time, and temperature on the acid-leaching process were also investigated. In summary, the comprehensive utilization of RWE-Al by this new process has proved to be feasible.

The Use of Waste Materials Red Mud and Fly Ash as Road Embankment Fill

This study provides a comprehensive evaluation of red mud as a sustainable material for road base construction, particularly in combination with bottom ash. Red mud, a by-product of the Bayer process used in alumina extraction, is known for its high alkalinity and heavy metal content. For this reason, this waste material causes environmental challenges. Red mud sourced from the Eti Aluminum Factory in Seydişehir, Konya (Turkey), was stabilized with bottom ash. Then, these waste materials were tested through a number of experiments, such as in relation to their Atterberg limits, compaction characteristics, unconfined compressive strength (UCS), California bearing ratio (CBR), and microstructure through a scanning electron microscopy (SEM) analysis. The results highlight that the UCS of stabilized red mud samples significantly improved with the addition of bottom ash and longer curing periods. Specifically, the UCS values increased from 0.5 MPa to 2.5 MPa after 28 days of curing. Moreover, RM specimens stabilized with 25% bottom ash achieved a CBR value of 146.64% after 28 days, far exceeding Turkey’s road fill material requirement, which mandates a minimum unsoaked CBR value of 15%. These findings indicate that red mud stabilized with bottom ash not only meets but exceeds the structural requirements for road base materials. This approach provides a sustainable solution for the environmental management of red mud while contributing to infrastructure development. Through the recycling of these industrial by-products, this study presents a viable method to reduce waste and support economic and environmental sustainability in road construction projects.

Studies of the sintering method of ash and slag waste for the production of alumina from self-disintegrating sinters

The goal of this research is to select the optimal composition of the sintering charge of ash and slag waste for maximum extraction of alumina and obtaining self-disintegrating sinters of a given chemical composition. Experiments have shown that sintering of ash and slag waste using two-component charges makes it possible to extract alumina from sinters by no more than 60 %. The highest sintering rates were made using three-component charges. So, when sintering ash and slag waste from Almaty TPP-2 on a three-component charge of the composition CaO:SiO2 = 2; Na2O:(Al2O3+Fe2O3) = 1 at a duration of 60 min and a temperature of 1200 °C, alumina extraction was 83.68 %, under the same conditions, alumina extraction of 87.07 % was obtained during sintering of ash and slag waste from the Eurasian Energy Corporation, and alumina extraction was 90.2 % during sintering of ash and slag waste obtained after preliminary chemical activation.As a result of the conducted research on sintering of ash and slag waste in a three–component charge system, a self-disintegrating sinter of the following chemical composition was obtained, %: Na2O – 0.07; CaO – 26.88; SiO2 – 2.06; Fe2O3 – 5.01; Al2O3– 5.059.

Selective dealumination of large pore Zeolite Beta for effective Brønsted acid site utilization

Tuning of Al sites through spatial and geometric distribution is a novel pursuit for deterministic catalytic performance. To design an efficient Zeolite Beta for phenol alkylation with optimal physicochemical attributes, we conducted a systematic study with a series of dicarboxylic acids to selectively extract the framework and/or non-framework Aluminium. Herein, the post-synthetic treatment resulted in dealuminated catalysts of silicon-to-aluminum ratio ∼15–53. Extensive Al and Si NMR studies glean the selective extraction of aluminum from the zeolitic framework along with recomposition in T sites. The potency study alludes to the convoluted role of pH, chelating ability, and/or site accessibility for complexation. The differentiated Al extraction results in the emergence of unique super-strong acid sites. The novelty of our approach was established using phenol alkylation with cyclohexanol wherein we observed the highest conversion and desired CC alkylated product formation for the malonic acid-treated Zeolite Beta.

Highly selective extraction of aluminum from chloride and sulfate solutions using a mixture of alkoxycarboxylic acid and tributyl phosphate

Four different solvent extraction systems are compared for aluminum (Al) separation in the presence of alkali metals, alkaline-earth metals, and transition metals. The octoxyacetic acid (OOA acid) is utilized as an Al extraction reagent for the first time, exhibiting high selectivity for Al. The impacts of the concentration of extractants, the equilibrium pH of the aqueous phase, and the concentration of phase modifier were studied systemically. The results indicate that the Al extraction efficiency using OOA/TBP (tributyl phosphate) system could reach 98.9 ± 0.63 % via a single-step solvent extraction process while maintaining negligible extraction for the other metal ions at the pH value of ∼ 4.2. Meanwhile, the separation factors (β) of Al over magnesium, calcium, manganese, cobalt and nickel reach the maximum values (βAl/Mg = 285157, βAl/Ca = 18275, βAl/Mn = 19271, βAl/Co = 10814, βAl/Ni = 5969). Slope analysis and infrared spectroscopic characterization confirm that the extraction of Al by the OOA/TBP system follows the cation exchange mechanism. The OOA/TBP solvent extraction system is promising for the efficient separation of Al, with potential applications in a wide range of practical scenarios.

Hydrothermal chemical modification of red mud for efficient adsorption of methylene blue

ABSTRACT Red mud (RM) is the industrial solid waste produced after alumina extraction from bauxite, and most RM is directly discharged to the landfill yards without any treatment. In this study, modified red mud (MRM) was synthesized by a hydrothermal chemical modification method as an efficient adsorbent for methylene blue (MB) removal. The prepared MRM was characterized by X-ray fluorescence spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope, and Fourier transform infrared spectrometer. The effects of reaction time, initial MB concentrations, MRM dosage, temperature, and system pH were investigated in the MB batch adsorption experiments. The results showed that the modification method increased the specific surface area of RM material from 16.72 to 414.47 m2/g. The maximum adsorption capacity of MRM for MB was 280.18 mg/g under the conditions of initial MB concentration of 1000 mg/L, reaction time of 300 min, temperature of 25 ℃, and natural pH of 6.06. Meanwhile, the adsorption kinetics and equilibrium isotherms were demonstrated to fit well with the pseudo-second-order kinetic model and Temkin isotherm, respectively. This study provides a new method for the valorization of RM and demonstrates that MRM can be used as a low cost and environmentally friendly potential adsorbent for the removal of MB from wastewater.

Preparation of calcium aluminate and spinel by hydrolysis and calcination from secondary aluminum dross

AbstractThe direct extraction of alumina from secondary aluminum dross (SAD), which is a dangerous solid waste, is difficult. Moreover, this process easily produces a large amount of solid waste residue, which is not easily utilized. In this paper, a new green process was developed to prepare calcium aluminate and Mg‐Al spinel from SAD by hydrolysis–calcification roasting. The effects of calcium oxide (CaO) content, sintering temperature, and holding time on the properties of calcium aluminate were investigated by single‐factor experiments. The phase transformation mechanism of calcium aluminate was studied by thermodynamic analysis, X‐ray diffraction analysis, X‐ray fluorescence spectroscopy, and scanning electron microscopy. Under the optimal conditions (Ca/Al molar ratio of 0.8, sintering temperature of 1300°C, and holding time of 2 h), the main calcium aluminate phases are CaAl2O4 and Ca2Al2SiO7, the soluble alumina content of the calcium aluminate sample is 49.71 wt.%, and the main phases of the acid‐insoluble residue are Mg‐Al spinel and a very small amount of CaTiO3. The Ca/Al ratio is the key factor affecting the calcium aluminate phase—with increasing Ca/Al ratio, the calcium aluminate phase is transformed from CaAl4O7 to CaAl2O4 and eventually to Ca12Al14O33, and the Si‐containing phase changes from Ca2Al2SiO7 to CaSiO4.

Influence of silica on the crystallization of sodium hydroaluminate

To extract aluminium from highly concentrated aluminate solutions of alumina-containing raw materials, decomposition is performed through the crystallization of sodium hydroaluminate. This paper presents the results of a study on the stability of aluminate solutions. To calculate the probable yield of Al2O3 in the solid phase, it is necessary to determine the crystallization rate of sodium hydroaluminate according to the composition of the initial solutions and the conditions of the process. The influences of SiO2 content on the decomposition of aluminate solutions with Na2Ok concentrations of 540 g/dm3 and 590 g/dm3 with and without inoculum were studied. In addition, the influence of silica on the appearance of precipitating crystals of sodium hydroaluminate was considered. A sharp increase in the stability of the aluminate solutions at rest in the presence of silica was observed. Different crystallization conditions for sodium hydroaluminate have been investigated. Silica slows the crystallization process of sodium hydroaluminate, affecting both the nucleation and crystal growth rates. The effect of SiO₂ on the rate of decomposition is similar to the reduction in the degree of supersaturation.

Hydrochemical Method for the Production of Alumina from Nepheline Using Effective Calcium Reagents

The use of alumina-containing nepheline raw materials as an alternative source of alumina is relevant in the context of the limited bauxite reserves in Kazakhstan. Nepheline processing can result in products such as alumina, sodium and potassium salts, silicate products and rare metals. In terms of economic value, alumina is the most important. This article considers an advanced technology for nepheline processing for the extraction of alumina that is first purified from potassium. The application of calcium sulphate and calcium oxide as additives to the nepheline raw materials is studied. The optimal conditions for two-stage leaching with calcium additives in the form of calcium sulphate and calcium hydroxide are determined.

Techno-economic assessment of solar photovoltaic electrification and calcium looping technology as decarbonisation pathways of alumina industry

Aluminium industry stands out as a significant source of CO2 emissions, due partially to the high energy demand of the alumina extraction stage. Accordingly, this study explores the implementation of direct resistive heating of mid-temperature processes in alumina production as an alternative to decrease CO2 emissions. Additionally, two different strategies are evaluated to decarbonize alumina industry: the generation of renewable electricity through solar photovoltaic panels and the integration of a CO2 capture plant based on calcium looping technology. This work comprehends the modelling and sizing of these plants and the assessment of their economic performance through the calculation of their Net Present Value and their respective payback periods. The integration of both strategies into an alumina refinery model reveals that electrification of low and mid-temperature processes yields a 15 % reduction in CO2 direct emissions, whereas calcium looping demonstrates the potential to capture 97 % of emissions with a 7 % energy penalty. Also, economic assessments indicate substantial potential for improvement through in-site electricity generation via solar photovoltaic panels, exhibiting a payback time of 4.5 years. Conversely, the feasibility of a calcium-looping plant is hindered by high capital expenses, necessitating a longer payback period of 19–24 years. Sensitivity analyses underscore the suitability of in-site renewable electricity generation, whereas carbon emission taxes emerge as crucial in incentivizing carbon-neutral processes, with thresholds around 95–125 €/tonne of CO2. Despite potential deviations from real industrial settings, this study provides evidence for environmentally friendly strategies in alumina production that demonstrate limited adverse effects on economic performance.

A STATE OF ART AND PROSPECTS OF RED MUD MANAGEMENT

The basic data on the global volumes and composition of red mud, which is a highly alkaline waste of the aluminum industry, namely the Bayer process – technology for the extraction and purification of alumina (aluminum oxide) from bauxite are presented. The analysis of the current state of red mud management allows to distinguish the following main directions: physical-mechanical, physical-chemical, biological and combined methods of handling it, which are used in agriculture (chemical land reclamation (increasing soil pH), use as fertilizers); building materials industry (cement, construction mortar, expanded clay, fireclay, bricks, building blocks, ceramic tiles, concrete alkali-acid-resistant products, refractories); road construction (soil strengthening for the lower layers of the road surface, asphalt); production of other materials (sorbents, catalysts, flocculants, pigments, caustic soda, filler for polymer composites); ferrous and non-ferrous metallurgy. Currently, the most common methods of red mud utilization are its direct use, use in the construction materials industry, as well as pyrometallurgical technologies, as a result of which iron or its alloys are obtained, as well as slag, from which alumina, titanium, rare earth metals can be extracted or which is processed into various building materials. The most expedient method of red mud disposal is either direct use of red mud with minimal changes in its properties, or complex processing with maximum yield of target components and minimization of new waste generation. At the same time, one of the promising ways of red mud management can be its biological processing with the help of plants and microbes, which will help reduce the dangerous man-made load from red mud in the territory adjacent to bauxite processing plants. Bibl. 113, Fig. 2.

Extraction of Alumina from Kaolin found in Gem Mining Sites of Sri Lanka

Extraction of Alumina from Kaolin found in Gem Mining Sites of Sri Lanka

Mechanism study of synergistic aluminum extraction and purification by ammonium for high-value conversion of secondary aluminum dross

Secondary aluminum dross (SAD) constitutes a significant volume of hazardous solid waste with huge productions. Balancing extraction efficiency and purity within the current resourcing recovery process proves challenging and impedes high-value conversion. Consequently, the NH4HSO4-H2SO4 system was employed in this study to convert SAD into high-purity alumina nanoparticles, and the effect of ammonium was investigated. The results indicated that the leaching rate reached 85.98 % under the optimum conditions (170 °C, [Htot]=12 mol/L, 16/1,6 h); the interaction of NH4+ and H+ with the oxygen atoms on the surface of Al2O3 was demonstrated to enhance the reactivity of the aluminum atoms by DFT calculations. The incorporation of NH4+ also facilitated the separation of aluminum by leveraging the temperature-dependent solubility characteristic of NH4Al(SO4)2. Molecular dynamics simulation revealed that NH4+ inhibits the diffusion rate of Al3+, thereby regulating the doping impurities such as Mg and Ca, and improving the purity of Al2O3 (95.29–99.64 %). Additionally, Nanoscale regulation was executed through the conversion of the NH4AlO(OH)HCO3 precursor and control. The sintering and agglomeration problems brought about by pyrolysis in atmospheres such as H2O and SO3 were avoided. This research provides reference for the high-value utilization of aluminum-containing solid waste.

Separation of fluorine and aluminum from secondary aluminum dross by calcium-cured alkali roasting−water leaching

A combined strategy of calcium-cured alkali roasting and water leaching was devised to treat secondary aluminum dross. The effects of calcium oxide dosage, sodium hydroxide dosage, roasting temperature, and time on aluminum extraction behavior and fluorine curing behavior were studied. Under optimal experimental conditions: roasting temperature of 1000 °C, Al꞉NaOH mole ratio of 1꞉0.6, F꞉CaO mole ratio of 1꞉2.5, and roasting time of 2.0 h, fluorine and aluminum were separated, with 99.98% of the fluoride solidified and 52.97% of the aluminum extracted. The sodium aluminate products obtained by evaporation and crystallization from leaching solution met the industrial standards of China. The aqueous residue can be used as a raw material for quick-setting cement. Overall, this study provides an effective and environmentally friendly strategy for the treatment of secondary aluminum dross.

Leaching kinetics of waste pharmaceutical blister package aluminium in phosphoric acid media

This study investigated the process of treating secondary aluminium recovered from waste pharmaceutical blister packages (WPBs) using phosphoric acid solutions as a potential strategy for recycling this currently non-recycled waste material. The findings indicate that, when recycling via the hydrometallurgical process, the aluminium passivated during leaching can be effectively counteracted by employing moderately concentrated phosphoric acid solutions (1.0 M), elevated temperatures (60–80 °C) and specifically the addition of H2O2 (1.25–2.5 vol.%). Under these conditions, complete extraction of aluminium was achieved within four hours. The estimated activation energy (∼82 kJ/mol) indicates that the leaching reaction is primarily limited by the chemical reaction rate rather than film diffusion. An aluminium phosphate solution could be obtained by leaching WPBs in a way that is suitable for subsequent aluminium phosphate crystallisation. This approach could provide a promising pathway for valorising aluminium from the currently under-utilised waste fraction of pharmaceutical blister packages.

Aluminium Determination in Foodstuffs by ICP-MS: Influence of Microwave Digestion Parameters on the Recovery

Aluminium (Al) is the third most common element in the Earth’s crust and occurs naturally in drinking water and agricultural products, and humans are consequently exposed to the element from dietary sources. A tolerable weekly intake of 1 mg/kg has been established by the European Food Safety Authority (EFSA); however, no maximum levels for aluminium in foodstuffs have so far been established in the European Union (EU) legislation. Official food control requires validated methods for the determination of aluminium. Acid digestion assisted by microwaves is the main sample preparation technique used for the determination of aluminium, usually in combination with atomic spectrometry for quantification. In the present study, different parameters in the digestion step were investigated including test portion, digestion temperature, the reagent used and duration of the digestion to assess the aluminium extraction. The presented work is following up on an observation from a proficiency test (PT) on trace elements (including aluminium) in cocoa powder organised in 2020 by the European Union Reference Laboratory for metals and nitrogenous compounds in feed and food (EURL-MN), where the participant results for aluminium showed an unexpectedly large variation. In addition to the PT material, different certified reference materials were included in the present study, and the results highlighted that the temperature and reagent used are the most critical parameters to obtain a satisfactory sample digestion prior to aluminium determination. Based on the obtained results, it is recommended to digest food samples with a mix of ultrapure water and nitric acid for 25 min at a temperature of at least 240 °C with a mix of HNO3 and H2O to achieve satisfactory microwave-assisted digestion.