Alumina Extraction Research Articles

High-Efficiency Desulfurization of High-Sulfur Bauxite Calcined in a Conveyor Bed: Kinetics, Process, and Application

The reaction process, mechanism, and kinetics of the desulfurization of high-sulfur bauxite during calcination were investigated using thermal analysis–infrared analysis. A conveyor-bed calcination system was used to study the variations in the physical phase, desulfurization rate, and alumina dissipation rate of high-sulfur bauxite in the range of 500 °C–650 °C. The results show that sclerite monohydrate, kaolinite, rhodochrosite, pyrite, and dolomite mainly decompose during the calcination of high-sulfur bauxite, generating H2O(g), CO2, and SO2 as gaseous products. The decomposition of sclerite monohydrate and kaolinite and the dehydroxylation reactions of rhodochrosite and pyrite occur at <650 °C, with inseparable temperature overlap. High-sulfur bauxite desulfurization follows a three-dimensional spherical diffusion mechanism, with an activation energy of 181.16 kJ/mol, controlled by the diffusion rate of O2 or SO2 through the solid product layer. High-sulfur bauxite was calcined at 600 °C–650 °C for around 3.5 s in a conveyor bed, resulting in a negative divalent sulfur content of <0.03 wt.%, desulfurization rate of >0.98, and relative dissolution rate of alumina of >99%, satisfying the requirements of aluminum extraction via the Bayer method. The desulfurization rate predictions of the kinetic model were consistent with the experimental data.

Hydrothermal preparation of lightweight calcium silicate powder from alumina-leaching residue of low-calcium sintering red mud

In order to realize the complete and high-value utilization of red mud, a hydrothermal process was proposed to prepare the lightweight calcium silicate powder from a sodium calcium silicate residue after alumina extraction. The synthesized products were characterized by XRD, XRF, SEM, EDS, and PSD, and the corresponding transition mechanism and physical properties were also studied. The main silicon- and aluminum-bearing phases in the clinker after the low-calcium sintering are Na2CaSiO4 and NaAlO2, and the former silicate keeps stable during the alumina leaching process under atmospheric pressure. In the hydrothermal process, Na2CaSiO4 in the alumina-leaching residue is converted into NaOH and Ca5Si6O16(OH)2·4H2O in the alkali solution, and the residual alumina is converted into Ca3Al2SiO8·4H2O which promotes the generation of Ca5Si6O16(OH)2·4H2O. Increasing the reaction temperature, duration and liquid-solid ratio of the hydrothermal process can facilitate the alkali removal efficiency in calcium silicate powder and decrease its bulk density, while the excessive hydrothermal temperature and duration reduce the alkali removal efficiency. The Na2O residue and bulk density of the calcium silicate powder are 0.42% and 0.30 g·cm−3 obtained at the optimal hydrothermal conditions. The flaky particles of Ca5Si6O16(OH)2·4H2O are aggregated into a porous cauliflower structure, which improves the absorption and insulation properties of calcium silicate powder.

Meta-bauxite deposit in the Tavşanlı Zone, NW Turkey: A new locality for gem-quality diaspore formation

The tectonic units of Sakarya Zone (Pontides) and Tavşanlı Zone (Anatolides) are exposed in the Mihalıççık area of central Anatolia. A Cretaceous accretionary complex that forms the İzmir-Ankara-Erzincan suture zone separates the units. Within this region, the Tavşanlı Zone is made up of a coherent series and tectonically overlying late Cretaceous mélange, which has undergone blueschist facies metamorphism. Coherent series consist of strongly retrogressed schists and conformably overlying platform-type thick marbles, known as the İnönü marbles.The İnönü marbles contain meta-bauxite lenses in the lower levels, which can be classified as karstic bauxites deposited in the karst holes within the original limestone. Considering the general stratigraphy of the Tavşanlı Zone, a middle Jurassic age can be envisaged for the bauxite formation. Geochemical data suggest that the bauxites were largely derived from redeposited argillic sediments, with minor and variable inputs from the weathering of intermediate to acidic rock. The mineral assemblage of the meta-bauxite consists of diaspore, chloritoid, muscovite, paragonite, Al-spinel (hercynite), magnetite, hematite and ilmenite. In addition, apatite, rutile, monazite, xenotime and zircon occur as accessory minerals. Limonite, goethite, akaganeite and kaolinite also formed during the latest stage of alteration. P-T conditions for the meta-bauxites are estimated as 20–27 kbar and 330–470 °C that are indicative of formation under high-P / low-T blueschist facies conditions.The meta-bauxites are cut by veins of diaspore, muscovite-paragonite, goethite, calcite and ankerite, and include gem-quality diaspore crystals up to 6 cm long. Textural evidence indicates that the diaspore formation is related to the extraction of aluminium from the meta-bauxite body and migration of Al-rich fluids into the shear zones during the last stage of the high-P metamorphism. During exhumation of the Tavşanlı Zone, these veins were brecciated by brittle deformation and the fractured minerals were cemented by granoblastic calcite and ankerite during the latest stage of the vein formation.

Sustainable process for valuable-metal recovery from circulating fluidized bed fly ash through nitric acid pressure leaching

Circulating fluidized bed fly ash ( CFBFA ) is receiving widespread attention due to its threat to the environment and its high content of alumina (30–50%), gallium (30–100 g/t), etc. In this research, nitric acid pressure leaching technology was proposed to selectively extract aluminum and gallium from CFBFA. The E-pH diagram of the Al–Fe–H 2 O system and experiments proved that the leachate ranged within pH −0.5 to 1, which was not favorable for the generation of Al(OH) 3 colloids. Moreover, Al entered the leachate as Al 3+ , and the divalent iron was initially oxidized by NO 3 − and then hydrolyzed to form hematite . The lg c Fe3+ at equilibrium of Fe 3+ hydrolysis had a certain relationship with pH. Thus, at high acidity with increased temperature, more Al entered the solution and more Fe entered the residue. Based on experiments, the optimum conditions were found to be as follows: leaching temperature of 220 °C, liquid-to-solid ratio of 4:1 mL/g, HNO 3 concentration of 340 g/L, and leaching duration of 2 h. The leaching rate of Al, Fe, and Ga were approximately 80%, 6%, and 78% respectively. The basic separation of aluminum and iron could be realized during leaching. In the evaporation, concentration and crystallization process of the leachate, aluminum nitrate precipitated out at room temperature when leachate density exceeded 1.38 g/cm 3 . A greater density of the leachate was concentrated, and crystallization benefited the formation of aluminum nitrate crystals with less crystal water. • A feasible process for recovering aluminum from solid waste (CFBFA) was developed. • The E-pH diagram of Al–Fe–H 2 O system at high temperature was analyzed. • Aluminum and iron were basically separated during the leaching process. • The leaching agent could be regenerated and the process was sustainable.

Processing of Low-Quality Gibbsite-Kaolinite Bauxites

The results of studies on the processing of gibbsite-kaolinite bauxite are presented. The developed technology includes preliminary chemical activation and thermal transformation during enrichment to obtain a concentrate suitable for processing by the Bayer method. As a result of the chemical activation of gibbsite-kaolinite bauxite in a solution of sodium bicarbonate, a change in the phase composition occurs, which made it possible to improve the results of gravity enrichment with the production of a coarse-grained gibbsite fraction. The transformation of bauxite in the temperature range of 900–1000 °C is explained by the decomposition reactions of siderite, gibbsite, kaolinite, calcite, dolomite and sodium ferro-sulfide oxide, as well as the formation of sodium aluminosilicate, hematite, quartz and the chemically stable phase of corundum. The optimum firing temperature of bauxite is 950 °C, after which, as a result of alkaline treatment during chemical enrichment, the extraction of SiO2 into solution was 74.9%. A silicon modulus of enriched bauxite 10.9 units was obtained. As a result of the autoclave leaching of gibbsite-kaolinite bauxite after a two-stage enrichment, the maximum extraction of alumina into solution was 87.4%. The yield of red mud during the processing of bauxite enriched and calcined at 950 °C was 37.62%. During the autoclave leaching of bauxite without enrichment, the yield of red mud was 71%.

Effects of Na2CO3/Na2SO4 on catalytic gasification reactivity and mineral structure of coal gangue

In this work, CO2 catalytic gasification was applied to the utilization of coal gangue (CG). The differences between Na2CO3 and Na2SO4 catalysts on the effects of the catalytic and activation reaction were evaluated comprehensively. Gasification reactivity and aluminum extraction yield were improved in the presence of both alkali metal salts and increased with increasing temperature at 800–1000 °C. The minerals species in Na2SO4 loaded ash (SCA) varied a lot from 800 °C to 850 °C, and the extraction yield can reach the peak (91.39%) at 850 °C. The aluminum ions solution obtained from SCA was purer than that from Na2CO3 loaded ash (CCA), this was owing to that SCA has more compact Si–O bond than CCA. What's more, according to the DFT results, Na2SO4 had a stronger ability to lengthen the Al–O bond and activate the aluminum in minerals. Besides these, it was found that the sodium in SCA was more favorable for accelerating gasification in theory. This research will contribute to the realization of high-value utilization of CG and Na2SO4.

Highly-efficient and sequential recovery of rare earth elements, alumina and silica from coal fly ash via a novel recyclable ZnO sinter method

A novel sinter method using ZnO as the activator instead of the conventional Na2CO3/CaCO3, (NH4)2SO4, and K2S2O7 was developed to achieve efficient sequential extraction of rare earth elements (REEs), alumina (Al), and silica (Si) from coal fly ash (CFA). Up to 93.3% Si, 87.1% REEs (70.7% Ce, 82.5% La, 83.2% Gd, 87.1% Nd, 62.3% Dy, and 81.7% Y), and 92.9% Al were extracted from CFA, respectively. Moreover, 93.1% of the ZnO activator was efficiently recycled, and the yield of red mud was only 14.9%. X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) results showed that the speciation transformation of Al/Si during CFA/ZnO roasting was as follows: mullite, quartz, amorphous Al2O3, and SiO2 → Zn0.75Al1.5Si1.5O6, kyanite and willemite → gahnite and quartz/cristobalite solid solutions. The change in the REEs occurrence mode hinted at the migration of most REEs in aluminosilicates forms with Si during roasting, and disassociation with Si into the acid-soluble form after alkali leaching. These results indicate that the coupling of Al-Si-REE in CF was broken by this ZnO sinter method, promoting the sequential and efficient extraction of REEs, Al, and Si from CFA. This study provides a green and efficient strategy for element recovery from CFA, substantially reducing residues and favoring REEs concentration.

Research on the Dealkalization Treatment of Bauxite Residue and Deep Extraction of Alumina.

Bauxite residue is the bulk solid waste generated by the alumina industry, and the environmental treatment of bauxite residue has always been a focus of attention. In this study, in the high calcium system, the bauxite residue was intensively digestion by the calcification-carbonation method, and the mole ratio of solution, the mass ratio of CaO/SiO2 of the digestion process were changed, so that the high-efficiency dealkalization of bauxite residue was realized and the aluminum oxide in bauxite residue was deeply extracted. The experimental results showed that the calcification process could achieve the recovery of 17.83% alumina at 260°C, reaction duration of 60min, liquid-solid ratio = 5:1, the mass ratio of CaO/SiO2 = 3.5, and 200g/L NaOH solution. The whole process can recover 49.61% of alumina from bauxite residue, and 94.4% of alkali in bauxite residue can be removed.

PROCESSING OF THE VANADATE FRACTION IN AJINAUR TITANIUM-MAGNETIC CONCENTRATES

The conditions for purification and waste-free utilization of the vanadate fraction of processing Ajinaur titanomagnetite concentrates in Azerbaijan by the carbonization method, including desiliconization, extraction of aluminum, regeneration of sodium carbonate and production of vanadium pentoxide, have been determined. It was found that TABAC (three alkylbenzylammonium chloride) is an effective extractant for extracting vanadium from carbonate – vanadate solutions without destroying carbonate ions. A technological scheme for processing carbonate-alkaline vanadate solutions to obtain vanadium pentoxide of reactive purity 99.7% corresponding in the quality to the analytical grade, -Al2O3 and soda regeneration has been drawn up

Study on the Cathodic Behavior of Impurities in the Process of Aluminum Extraction by Soluble Anode Electrolysis

The preparation of coarse Al–Si alloys by carbon-based electrothermal reduction is a viable means of recycling scrap aluminum on an industrial scale to allow the high-value utilization of this resource. However, the presence of impurities on the cathode can have significant effects on the product purity. The present study explored the behavior of impurity elements on the cathode and the reasons for the decreased purity of aluminum deposited at the cathode with increases in electrolysis time. X-ray diffraction, scanning electron microscopy and inductively coupled plasma-atomic emission spectroscopy were used to study the compositions of the molten salt electrolyte and of the cathode product, as well as the phases and element distribution on the working electrode. With increasing cell voltage, the elements added as impurities were found to precipitate in the order of Fe > Al > Si > Mn > Ti > Mg > Ca. Increasing the concentration of these elements in the molten salt electrolyte was determined to increase the cell voltage, with Mg and Ca having the greatest effect.

Conversion of Harmful Fly Ash Residue to Zeolites: Innovative Processes Focusing on Maximum Activation, Extraction, and Utilization of Aluminosilicate.

Reuse of the solid residue from coal fly ash alumina extraction (FAAE) by acid leaching is problematic. Conversion of this solid residue into aluminum-rich zeolite (13X) and silicon-rich zeolite (ZSM-5) was investigated in this research. The FAAE residue was activated by alkali roasting with Na2CO3 powder (110% mass fraction) at 890 °C for 60 min. Silicon and aluminum were mainly present as two mineral phases, Na2SiO3 and NaAlSiO4, respectively, in the product obtained after roasting. The roasted product was dissolved in water (liquid/solid ratio of 2) after 20 min at 100 °C. The water-leaching liquor was investigated for total conversion to aluminosilicate zeolites without external aluminum or silicon addition. Hydrothermal synthesis of aluminum-rich zeolite 13X was successful after fine tuning of the conditions, although the filtrate had an unusually high SiO2/Al2O3 molar ratio. Production of 13X consumed a large amount of aluminum, which increased the Si/Al ratio to a level suitable for synthesis of ZSM-5. The synthesis of ZSM-5 from the mother liquor of 13X was proved feasible. The FAAE residue was transformed into high-value zeolite products by nearly 100%. Additionally, the tail liquid of this process, mainly containing Na2CO3, was completely recycled. This process could be used to realize high-efficiency and high-value utilization of similar aluminosilicate solid wastes.

Spinel Ferrite Transformation for an Efficient Fe Removal from Circulating Fluidized Bed Fly Ash by Carbothermal Reduction at a Low Temperature.

Alumina (Al2O3) extraction from circulating fluidized bed (CFB) fly ash (CFBFA) is one of the most important pathways for value-added utilization. However, in CFBFA, impurity iron (Fe) normally coexists, resulting in complicated separation processes, low Al2O3 extraction efficiency, and substandard Al2O3-based products. How to remove Fe impurity effectively from CFBFA has become an important issue. For an effective Fe removal from CFBFA, spinel ferrite transformation by carbothermal reduction at a low temperature was discussed in the paper. The effects of the reduction temperature and reduction time on the removal efficiency of Fe and the recovery of aluminum (Al) as well as the removal of other metals were systematically investigated, and the transformation mechanisms of Fe-containing phases were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and a scanning electron microscope–energy dispersive spectrometer. The results showed that Fe in CFBFA was present in the form of weakly magnetic α-Fe2O3, leading to a Fe removal of about 17.1% after magnetic separation; however, the recovery efficiency of Al reached 97.4%. Weakly magnetic hematite (α-Fe2O3) could be converted to strongly magnetic spinel-type ferrite (MFe2O4) after carbothermal reduction at 700 °C for 60 min, and the Fe removal efficiency could reach 62.8% after magnetic separation; however, the recovery of Al was 81.2%, which was decreased compared to the recovery of Al under the condition without carbothermal reduction treatment. However, the carbothermal reduction–magnetic separation process did not have a major effect on the existing form and leaching behavior of Al, Li, and Ga. Simultaneously, it could be observed that some transition metal elements such as Mn, Cr, and so forth could be enriched in spinel-type MFe2O4 and removed after magnetic separation, which also provided a way for transition metal enrichment and extraction of transition metals from other tailings.

Effect of the medium composition on the extraction of chromium, aluminium and iron hydroxides from wastewater by electroflotation

The process of electroflotation is used for treatment of wastewaters carrying heavy and non-ferrous metals in the form of poorly soluble compounds if the concentrations of contaminants are too high to be handled by adsorption process. The problem of raising the efficiency of electroflotation process is currently of relevance. This paper examines how the composition of the medium, i.e. the nature of the electrolyte, surfactants and hardness salts, can influence the extraction of iron, aluminum and chromium hydroxides from aqueous solutions by electroflotation. It was found that the electrolyte (NaCl, Na2SO4) nature has no significant effect on the process. The hydroxide extraction performance can be impacted by the presence of calcium ions regardless of the electrolyte nature. It happens due to the adsorption of Ca2+ on the hydroxide surface, which makes it more hydrophilic. The degree of dispersed phase extraction can be increased due to the introduction of surfactants: didecyldimethylammonium chloride, sodium dodecyl sulfate and a mixture of primary oxyethylated synthetic alcohols. Sodium dodecyl sulfate, which is an anionic surfactant, proved to deliver the best result. The high process efficiency in terms of dispersed phase extraction is due to the hydrophobization of the particle surface by adsorbed sodium dodecyl sulfate and the stabilization of gas bubbles. The particle sizes of iron and chromium hydroxides vary in the range of 0.04 to 4 microns. At the same time, most of the aluminum hydroxide particles are bigger than 10 microns, which can be attributed to the high polymerization ability of aluminum ions and subsequent particle coagulation. The efficiency of electroflotation extraction of chromium, aluminum and iron hydroxides in the presence of calcium ions using anionic surfactant is at least 90%. Additional filtration is recommended to ensure the treated wastewater is in compliance with applicable standard.

Simultaneous and clean separation of titanium, iron, and alumina from coal fly ash in one spot: Electrolysis-hydrolysis method

Large amounts of heavy-metal-containing coal fly ash can cause serious environmental hazards. The separation and extraction of titanium, iron, and alumina from coal fly ash can provide economic and environmental benefits. This work presents an electrolysis-hydrolysis method to alter the precipitation order of iron and alumina by changing the ion charge sequence to extract iron and alumina in an orderly manner while recovering the waste heat to polymerize the precipitated titanium. The separation and extraction of titanium, iron, and alumina in one spot can shorten the process and make full use of the electric energy. Under optimal conditions, the efficiencies of iron, titanium, and alumina were 97.6%, 93.1% and 88.5%, respectively. The iron product had a composition of 95.8% Fe2O3, 0.5% Al2O3, 0.3% CaO, 0.1% SO3, and 0.4% TiO2. The alumina product had a composition of 88.7% Al2O3, 0.1% Fe2O3, 0.2% CaO, 9.1% SO3 and 0.2% TiO2. The titanium product had a composition of 63.78% TiO2, 3.11% Al2O3, 8.15% Fe2O3, 0.28% CaO, 4.12% SiO2, and 9.6% SO3. Moreover, in the entire electrolysis process, no expensive membranes or chemical additives were required, avoiding the limitations of membranes and high costs. Fe, Al(OH)3, Ti(OH)4, O2, and H2 were generated during the electrolysis-hydrolysis process; therefore, no harmful substances were produced. Thus, this study proposes an alternative electrolysis-hydrolysis process for the simultaneous separation and extraction of titanium, alumina, and iron from coal fly ash leachate in one spot.

Kinetic Analysis of Aluminum Extraction from Ethiopian Kaolinite Using Hydrochloric Acid

The aim of this study was kinetic investigations of aluminum extraction from Ethiopian kaolinite with hydrochloric acid. The effects of extraction parameters, namely, solid-to-liquid ratio (0.05, 0.075, 0.100, and 0.125 g·mL−1), acid concentrations (2, 3, 4, and 5 M), reaction temperature (50, 60, 70, and 80°C), and time (20, 40, 60, 80, 100, 120, 140, 160, and 180 min), on yield of aluminum were investigated. The results revealed that the extraction yield of aluminum increased with increase of acid concentration, reaction temperature, and time and declined with increase of solid-to-liquid ratio. The kinetic analysis of aluminum extraction was evaluated using pseudohomogeneous, nucleation growth (Avrami), and shrinking core models. The results showed that kinetics of aluminum extraction were controlled by surface chemical reaction. The experimental results were well fitted by the shrinking core model of surface chemical reaction with first-order rate. The activation energy and the preexponential factor were 25.40 kJ·mol−1 and 0.949 cm·min−1, respectively. The leached solution samples were crystallized using evaporation and concentrated hydrochloric acid pouring. The volume ratios of concentrated hydrochloric acid to the samples were from 0.30 to 0.90 (v/v). The crystallization efficiency of aluminum chloride hexahydrate crystals increased with volume of hydrochloric acid and crystallization time. The crystallization yield of aluminum chloride hexahydrate crystals reached 90%. This study’s results clearly revealed that Ethiopian kaolinite could be a promising raw material to produce aluminum chloride hexahydrate, which could be used for water treatment application.

Extraction of valuable metals from acidic wastewater and blast furnace slag by a collaborative utilization process

AbstractTwo typical wastes, acidic wastewater and titanium‐bearing blast furnace slag, are generated in the smelting process of vanadium‐titanium magnetite. Generally, the acidic wastewater is neutralized by lime or limestone and titanium‐bearing blast furnace slag is directly stacked in the tailings pond, which not only pollutes the ecological environment but also causes the waste of metal resources. In this study, a collaborative utilization process for efficient extraction of titanium, iron, magnesium, and aluminum from acidic wastewater and low titanium‐bearing blast furnace (LTBBF) slag was proposed. At the leaching temperature of 80°C, the leaching time of 50 min, and the liquid–solid ratio of 9:1, 99.26% Ti, 99.47% Mg, and 99.45% Al could be extracted from LTBBF slag by acidic wastewater. Leaching residue mainly composed of Ca and Si could be used as silicon fertilizer. The Ti in the leaching solution could be separated by adding Na3PO4. The precipitation efficiency of Ti reached 98.53% under the molar ratio of Na3PO4 to TiO2 of 1.4, reaction temperature of 85°C, and reaction time of 40 min. The titanium phosphate ((TiO)2P2O7) was obtained by calcination of the precipitate at 900°C for 3 h. Adding oxalic acid to the filtrate above, the precipitation efficiency of Fe, Mg, and Mn reached 96.47%, 99.21%, and 99.45%, respectively, under the optimal conditions, while the precipitation efficiency of Al was only .38%. By adjusting the pH of the filtrate to 6.5, 99.83% Al could be precipitated as Al(OH)3, and the final solution was evaporated to obtain Na2SO4 products. The method proposed realizes the harmless treatment of acidic wastewater and LTBBF slag and recovers the metal resources in both of them.

Cleaning Disposal of High-Iron Bauxite Residue Using Hydrothermal Hydrogen Reduction.

The hydrothermal hydrogen reduction process for treating high-iron bauxite residue (red mud) was investigated, and the optimum conditions of alumina extraction as well as the enrichment of iron minerals were verified by experiments. Results show that the surface magnetization of Al-goethite under the function of hydrogen reduction accelerates its conversion to hematite and/or magnetite. This conversion releases the substituted Al in goethite as well as the undigested gibbsite/boehmite and further enriches the iron content in residue. After hydrothermal hydrogen reduction with H2/Red mud ratio of 0.085mol/20g at 270°C for 60min, the alumina relative recovery ratio reaches 95.40% and the grade of iron (total iron in the form of iron element) in the residue can be enriched to 55.85%. Further, co-processing of the obtained iron-rich residue in the steel industry can achieve a significant reduction of red mud discharge.

Comparison and evaluation of alumino-silicate samples as a dual source of alumina and potash values

ABSTRACT The current study evaluates mica, sericite, diaspore, and feldspar to extract aluminum and potassium values. Mechanical and thermal activation followed by HCl leaching is systematically investigated. Milling improved the surface area of mica, diaspore, and sericite (40-50 m2/g), whereas feldspar (32 m2/g) showed a limited response. Mica and sericite yielded 75-80% aluminum extraction, and diaspore yielded 70% potassium extraction after 8 h milling. The low alumina content in the feldspar and hard phase in the diaspore is responsible for the inadequate size reduction with limited aluminum dissolution (40-45%). The thermal activation energy of the NaOH baking for diaspore was 400 kJ/mol, mica (282 kJ/mol), and sericite (330 kJ/mol). The aluminum extraction was 72-80%, and potassium extraction was 55-84% at varying SiO2/Al2O3 ratios. The techno-economic assessment showed that alkali thermal treatment (8.1-12.6 kWh/kg Al2O3) consumed less energy than the milling treatment (28.9-37.9 kWh/kg Al2O3). Additionally, the specific HCl consumption is minimal in mica (1.85 kg), followed by diaspore (2.51 kg), sericite (5.47 kg), and feldspar (6.39 kg).

Optimal Factor Evaluation for the Extraction of Alumina from Clays by Sulfuric Acid Leaching Process Using Box–Behnken Design Methodology

Optimal Factor Evaluation for the Extraction of Alumina from Clays by Sulfuric Acid Leaching Process Using Box–Behnken Design Methodology

Thermo-kinetic modelling of the acidic leaching of anorthosite: Key learnings toward the conception of a sustainable industrial process

• Specific ion Interaction Theory model can suitably describe the electrolyte solution. • Geochemical simulation gives conditions for Al 3+ extraction & SiO 2 (am) precipitation. • Gudvangen anorthosite dissolution proves to proceed in chemical reaction regime. • Kinetic model helps refining process parameters (incl. particle size distribution). • The counter-current configuration can outperform the batch performance. The world is facing critical technological and environmental challenges in the production of basic materials in high demand, such as aluminium and silica, whose processes were developed long ago. New production routes, involving using alternative resources and innovative technological solutions, are needed to secure access to these base materials at a lower cost to the environment, in terms of waste and carbon footprint. The European project AlSiCal is currently investigatingan environmentally friendly multi-step process for producing alumina and silica from anorthosite, an abundant feldspar mineral. The present paper focuses on the modelling strategy of the dissolution of anorthosite in concentrated hydrochloric acid, which is the first step of the AlSiCal process. The objectives of this study are (i) to give a reliable first-level prediction of the product speciation in the aqueous and solid phases, (ii) to provide the sensitivity of the process to key operating variables, and finally, (iii) to evaluate the performance of both batch and continuous leaching processes. The proposed methodology is based on the coupling of geochemical equilibrium simulations and particle reaction models, using different computational tools and relevant literature data. This makes it possible to select the favourable operation window and process configuration for the quantitative extraction of aluminium in solution and the production of amorphous silica with an acceptable purity for large-market applications.