Aluminate Liquor Research Articles

Ultrasonic-induced crystallization for efficient extraction of hazardous sodium oxalate with ultra-low alkali loss in alumina industry: From laboratory-scale to continuous pilot-scale

Since sodium oxalate (Na2C2O4) in Bayer liquor seriously threatens the sustainable development of the alumina (Al2O3) industry, efficient extraction of Na2C2O4 and reduction of alkali loss have received widespread attention. A new process for extracting Na2C2O4 from mother aluminate liquor by ultrasonic-induced crystallization (UIC) is established at laboratory scale. Due to the controlled sound field and cavitation effect, compared with conventional crystallization (CC) process, the UIC process increases the Na2C2O4 extraction rate from 61 % to 70 %, and reduces the alkali loss rate from 41 % to 19 %. Numerical simulation and sonochemiluminescence confirm that the cavitation effect is mainly concentrated near the axis and at the tip of the titanium alloy horn, and the average life of the cavitation bubble is maintained at 0.9 ms. Density functional theory (DFT) calculations, crystal structure observations and simulations show that the UIC process successfully promotes the development of Na2C2O4 from long strips to lamellar forms, maintaining the safety of Al2O3 production. Additionally, UIC process operates stably on continuous pilot-scale (CPSC) system, with the Na2C2O4 extraction rate and TOC emission rate remaining at around 50 % and 85 % respectively. The UIC method for extracting Na2C2O4 is expected to generate annual profits of $ 267.3 million for China, while also providing support for the innovation and application of ultra-low alkali loss in Al2O3 industry.

Improving decomposition efficiency of aluminate liquor through preparation and introduction of active seed during the decomposition process

The aim is to determine the optimal parameters for the preparation and dosing of active seeding (finely dispersed aluminium hydroxide) to control the decomposition of aluminate liquor in the Bayer process. Laboratory tests were carried out on a temperature-controlled rotating water bath (Intronics, Australia). The granulometric analysis of the obtained aluminium hydroxide was carried out using the VideoTest image analysis system and a Carl Zeiss Axioskop-40 microscope (Germany) supplemented with Image Analysis software. Finely dispersed aluminium hydroxide (active seed) was obtained by mixing an alkaline aluminate solution and recycled water in various ratios. The filling order of solutions was determined – first, recycled water, followed by cooled alkaline aluminate solution. Optimal conditions for the preparation of active seeding were established: the solution was held for 48–72 hours at 50°C at an aluminate solution to recycle water ratio of 60% and 40%, respectively. The dosing of the obtained active seeding into the head decomposers was examined. It was demonstrated that using active seeding in continuous decomposition mode stabilises the particle-size distribution of the production-grade aluminium hydroxide. The presence of active seeding allowed the initial decomposition temperature to be reduced from 62°C to 58°C without altering the particle-size distribution of aluminium hydroxide. In addition, the study confirmed the positive effect of active seeding on increasing the degree of decomposition of the aluminate liquor up to 1.5%. Therefore, based on the research results, it was established that the use of the new method for preparing and dosing active seeding into the main decomposers leads to the intensification of the decomposition process in alumina production.

Calculation and experimental determination of equilibrium composition of liquors in certain instances of the Na2O – К2O – Al2O3 – H2O System

Presently, one can definitely state a rising interest to potassium-bearing aluminium ores, which is due to a gradual depletion of conventional raw materials and the fact that the ores that are mined today are leaner and have a more complex composition. At the same time, soda-potassium products, potassium fertilizers, aluminium hydroxide, alumina and alumina materials are in high demand and sell at high prices. Today, the focus is on new deposits of urtite rock and nepheline ores, as well as those of ultrapotassium rischorrite and synnyrite rock. That’s why it is very important to have a basic understanding of the nature and properties of the technically important system Na2O – К2O – Al2O3 – H2O, which defines the performance of the key processes involved, as well as the output and quality of the final product. In this regard, studying phase equilibria in the above system, the information about which is lacking or inconsistent, can be pointed out as one of the current research priorities. Two methods were tested aimed at reducing the time necessary to reach equilibrium in the Na2O – K2O – Al2O3 – H2O system. One involves hydrolytic decomposition of aluminate liquors with aluminium hydroxide used as seed; the other involves a mathematical description of the curves characterizing the kinetics of gibbsite solubility in alkaline liquors with a given mole fraction of K2O. Similar laboratory equipment and materials were used in the experimental study regardless of the way equilibrium was reached and identified. Through experiments, it was established that the process of approaching equilibrium in predominantly potassium aluminate liquors has complex kinetics and mechanics impeding rapid identification of equilibrium composition of liquors. With regard to the technique that involves gibbsite dissolution in weak sodium-potassium liquors, the authors demonstrate how asymptotic approximation functions can be effectively used to determine maximum solubility of aluminium oxide. The results of experiments aimed at defining the equilibrium compositions of liquors at 60 oC in certain instances of the Na2O – К2O – Al2O3 – H2O system have a good and satisfactory correlation with the modelling data based on the additivity principle, which suggests that the modelling technique can effectively be applied to other temperatures and instances of the 4-component system in view. This research was funded by the Russian Science Foundation under the Agreement No. 18-19-00577-П dated April 28, 2021 on granting funds for basic scientific research and exploratory research.

Non-supercritical drying synthesis and characterization of monolithic alumina aerogel from secondary aluminum dross

In the present study, the pure and monolithic alumina aerogel is synthesized from secondary aluminum dross as a common waste of the aluminum smelting industry. The process includes the extraction of aluminum content of the waste as sodium aluminate liquor through a multi-stage hydrometallurgical treatment, gelation, removal of the salt by-product by washing, three-stage solvent exchange, aging, non-supercritical drying, and calcination. No chemical additives are used to strengthen the gel structure. It is worth mentioning that the drying step of the hydrogel, which has the main effect on the integrity of the aerogel, is performed at ambient pressure and a relatively low temperature (50 °C). The characterization of the obtained alumina aerogel revealed a density of 0.25 g/cm3, a total pore volume of 1.4 cm3/g, a specific surface area of 148.5 m2/g, and a purity of more than 97%.

Production and characterisation of sodium and potassium carbonate salts from carbonation alkaline aluminate liquor

ABSTRACT The polythermal crystallization method has been used to extract sodium and potassium carbonate salts as valuable by-products. The salt production was carried out using an alkaline carbonate solution from the Azarshar nepheline syenite pilot plant in Iran. The optimum conditions were obtained by comparison between the results of thermodynamic modelling and experiments. To better understand the properties of the carbonate salts, thermal analysis, chemical analysis, and X-ray diffraction methods were also utilised. The optimum density and temperature for sodium carbonate crystallization were found to be 1.50 g/cm3 and 115–120°C, respectively, and for hydrated potassium carbonate crystallization to be 1.68 g/cm3 and 130°C at the first stage, and 1.70 g/cm3 and 135°C at the second stage, respectively. The thermodynamic modelling showed good agreement with experimental data for the carbonate salts.

Prediction of component concentrations in sodium aluminate liquor using stochastic configuration networks

Online measuring of component concentrations in sodium aluminate liquor is essential and important to Bayer alumina production process. They are the basis of closed-loop control and optimization and affect the final product quality. There are three main components in sodium aluminate liquor, termed caustic hydroxide, alumina and sodium carbonate (their concentrations are represented by $$c_\mathrm{K}$$ , $$c_\mathrm{A}$$ and $$c_\mathrm{C}$$ , respectively). They are obtained off-line by titration analysis and suffered from larger time delays. To solve this problem, a hybrid model for $$c_\mathrm{K}$$ and $$c_\mathrm{A}$$ is proposed by combining a mechanism model and a stochastic configuration network (SCN) compensation model. An SCN-based model for $$c_\mathrm{C}$$ is also proposed using the estimated values of $$c_\mathrm{K}$$ and $$c_\mathrm{A}$$ from the hybrid model. A real-world application conducted in Henan Branch of China Aluminum Co. Ltd demonstrates the effectiveness of the proposed modelling techniques. Experimental results show that our proposed method performs favourably in terms of the prediction accuracy, compared against the regress model, BP neural networks, RBF neural networks and random vector functional link model.

Chlorination of Alumina Obtained from Nepheline Concentrate Processing and Comparative Assessment of the Complete Aluminum Production Cycle

Abstract—Extended tests of alumina fluid chlorination are performed. The implementation of the chlorine technology is possible when using alumina, which has a high reactivity with chlorine. The improved nepheline technology for obtaining such an oxide is proposed: non-desilicated aluminate liquors undergo carbonization followed by separation of aluminum hydroxide with sodium hydroaluminosilicate and its calcination at 600–800°C. The proposed upgrade, compared to the existing method, is less energy intensive. Two-stage desilication is eliminated, and more favorable conditions are created for the low-temperature digestion of sintered material, reducing the secondary losses of alumina and alkali. The technological parameters of charge chlorination, both powdered and pelleted, are worked out on a scaled-up installation in fluidized bed conditions. The operational and capital cost of a complete aluminum production cycle based on the chlorine technology are evaluated in comparison with the conventional alumina production according to the Bayer process and subsequent electrolysis of cryolite-alumina melts. The comparative cost analysis has shown the advantages of the chlorine technology at the stage of aluminum chloride electrolysis (up to 30%) and the presence of additional costs at the stage of obtaining the intermediate product for chlorination. The chlorine method of aluminum production in modern conditions has the prospects of development not as a mass technology, but as an effective process for obtaining high-purity aluminum (HPA) in small workshops.

Recovery of Fine Aluminum Hydroxide with High Whiteness Index from Low Quality Bauxite Using Caustic Roasting and Water Leaching

A bauxite of low quality containing 6.75% reactive silica and 37.4% Al2O3 as gibbsite was roasted with additives including NaOH (caustic/total alumina molar ratio of 2-4:1) and CaO (CaO/total SiO2 molar ratio of 0.5-3:1) at 300-1000 ℃, producing calcines containing sodium aluminate (Na2O.Al2O3), silicates and hematite. Optimum conditions included roasting at 350-400 ℃ with CaO added at a CaO/total SiO2 molar ratio of 1:1 for 2-3 h. Dissolving the calcine in water at 90 ℃ produced a sodium aluminate liquor from which aluminum hydroxide (Al2O3.3H2O - alumina trihydrate or ATH) was precipitated. The addition of CaO reduced the silica extraction to <15% at optimum conditions, whereas the total organic carbon(TOC) was ~200 mg/L as carbon in all cases. Losses of alumina and caustic were experienced, as different phases of Al-Ca-Si or Na-Ca-Al-Si minerals were formed during roasting and/or leaching. The extracted alumina in the leached solution were precipitated at 60 ℃ for 20 h to produce a fine aluminum hydroxide having D50 of 1.9-2.8 μm with a whiteness index of 96.8-97.5, better than commercially available products. (Received May 11, 2017; Accepted September 29, 2017)

Removal of carbonate and oxalate pollutants in the Bayer process using thermal and chemical techniques

In the Bayer process, diasporic bauxite is dissolved in a caustic soda solution in the presence of lime at high temperature. During this process, concentration of carbonate and oxalate gradually increases causing problems in the alumina refining process. In this work, removal efficiency of the carbonate and oxalate pollutants from sodium aluminate solution has been increased using thermal and chemical techniques. The pollution of sodium aluminate solution has been reduced by heating the bauxite and removing the carbonate and oxalate by applying a chemical method. Bauxite heating leads to the organic compounds and carbonates in magnesite and calcite minerals exit as CO2, preventing addition of these substances into the sodium aluminate solution. In the method of chemical removal of the carbonate and oxalate soluble in sodium aluminate liquor, barium aluminate with structures of Ba2Al2O5, Ba2Al4(OH)16 and BaAl2O4, calcium aluminate (Ca3Al2(OH)12) and sodium phosphate (Na3PO4)–lime were separately used. As a result, these substances were sedimented as carbonate or barium oxalate, calcium and apatite. The results also showed that soda was retrieved as sodium aluminate or sodium hydroxide. Investigating the effect of temperature, time, concentration of caustic soda, Al2O3 and sodium carbonate revealed that using Ba2Al4(OH)16 and the heating methods are the most efficient technique to remove the carbonate and oxalate, respectively.

Effect of urea on decomposition of sodium aluminate solution

Aluminium hydroxide particles were synthesized from sodium aluminate liquor by urea decomposition method at elevated temperatures in presence and absence of seed. Different parameters such as alumina to caustic (A:C) ratio, temperature, time period of precipitation, urea concentration, etc. were studied. Characterisations of the products were also carried out using X-ray diffraction, scanning electron microscopy, TG-DTA, etc. In general, higher precipitation ratios were observed with the addition of urea in sodium aluminate solution. Temperature was found to have a significant role in precipitating aluminium hydroxide with higher yield enhancement ratio compared to that obtained at lower temperatures. Higher precipitation ratios were also obtained with urea at elevated temperatures under available supersaturation. In the presence of urea, the precipitation ratios on yield enhancement front were observed to increase with decrease in A:C ratio. It has been observed that the liquor concentration reached below the equilibrium solubility limit after 30h of precipitation when 460mmol/L urea is added. The synthesized aluminium hydroxide particles showed gibbsitic nature and globular morphology, with agglomerates of mostly hexagonal platelets, as revealed through XRD and SEM studies, respectively. Calcination of the product at 1000°C results in weight loss similar to that observed with gibbsite. Endothermic peaks at 325°C and 550°C revealed through DTA study indicated boehmite and chi-alumina transformations, respectively. The possible mechanism of urea decomposition method is also discussed.

Pre-desilication and digestion of gibbsitic bauxite with lime in sodium aluminate liquor

The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different temperatures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, hematite, kaolin, quartz, and minor boehmite. Lime increases the desilication efficiency of the bauxite during the pre-desilication process by promoting the conversion of sodalite and cancrinite to hydrogarnet. Desilication reactions during the digestion process promoted by lime result in the loss of Al2O3 entering the red mud, but the amount of aluminogoethite-to-hematite conversion promoted by lime leads to the increase of aluminogoethitic Al2O3 entering the digested liquor. The alumina digestion rate at 245°C is higher than that at 145°C due to the more pronounced conversion of aluminogoethite to hematite. The soda consumption during the digestion process decreases due to lime addition, especially at higher temperatures.

Growth Mechanisms and Kinetics of Gibbsite Crystallization: Experimental and Quantum Chemical Study

We present experimental and molecular modeling studies, which examine the influence of crystal growth modifiers (CGMs) on the crystallization mechanism and kinetics of gibbsite crystallization in supersaturated sodium aluminate solutions. Seeded, pure caustic sodium aluminate synthetic liquors and real industrial Bayer liquor containing significant amounts of organic and inorganic impurities, in the absence and presence of a CGM containing oleate ions, were investigated. Our results show massive growth of colloidal sized protrusions on the seed particle surfaces on addition of the CGM in the pure synthetic caustic aluminate liquors. Although the activation energies for both secondary nucleation and growth were found to be increased, the overall crystallization rate was surprisingly also increased by addition of CGM. This behavior is attributed to the increased pre-exponential factor possibly arising from higher probability of effective collisions due to more effective species orientation facilitating the crystallization process. The crystallization rate was significantly slower in the industrial Bayer liquor, most likely due to the presence of impurities; nevertheless, a greater degree of surface protrusions on crystal growth was noted on addition of the CGM. In conjunction with the experimental results, we use semiempirical quantum-chemical calculations to examine the underlying processes that result in the enhanced growth due to the presence of the CGM. Our quantum-chemical modeling results suggest that the increased crystallization rate may be due to a mechanism by which Al(III)-containing dimers are produced due to intervention by the oleate ion.

An in situ synchrotron X-ray diffraction investigation of lepidocrocite and ferrihydrite-seeded Al(OH) 3 crystallisation from supersaturated sodium aluminate liquor

Lepidocrocite and ferrihydrite-seeded Al(OH) 3 crystallisation from supersaturated sodium aluminate liquor at 70 °C was investigated using in situ synchrotron X-ray diffraction. The presence of iron oxides and oxyhydroxides in the Bayer process has implications for the nucleation and growth of scale on process equipment, and a greater understanding of the effect they have on Al(OH) 3 crystallisation may allow for development of methods for Al(OH) 3 scale prevention. The early stages of both crystallisation reactions were characterised by nucleation of gibbsite on the seed material. This was followed by a rapid increase in gibbsite concentration, which coincided with the appearance of the bayerite and nordstrandite polymorphs of Al(OH) 3. The lepidocrocite-seeded reaction then proceeded via a mechanism similar to that which has been observed previously for goethite, hematite and magnetite-seeded Al(OH) 3 crystallisation. Different behaviour was observed in the ferrihydrite-seeded experiment, with nucleation as well as growth occurring during the period of rapid increase in gibbsite concentration, followed by a period of diffusion controlled growth.

A New Method of Producing High Purity 4A-Molecular Sieve from High Modulus Sodium Silicate Liquor Purified by Carbonization

A new technology for producing high purity 4A-molecular sieve was developed with high modulus sodium silicate liquor and sodium aluminate liquor extracted from coal fly ash as starting materials. The sodium silicate liquor extract was purified by precipitating ferrous, titanium, and other impurities by carbon dioxide injection. Concentration of carbon dioxide in the extract was maintained at 48%, and the pH value of the extract controlled in the range of 11 and 11.2. After that, the purified sodium silicate liquor was mixed with sodium aluminate liquor in the ratios of SiO2/Al2O3=2.0, Na2O/SiO2=1.6 and H2O/Na2O=60. The mixture was then heated to 90°C and kept for 2 h. A high purity 4A-molecular sieve product was obtained after washing and drying the crystals obtained from the reaction mixture. The molecular sieve product has a purity of 99% and aperture of 0.4nm. Its calcium absorption capacity is about 290mg/g. The product was also characterized by SEM, BET, XRD and IR analysis.

Additive action on boehmite precipitation in sodium aluminate solution

Precipitation of boehmite (Al(2)O(3)·H(2)O) instead of gibbsite (Al(2)O(3)·3H(2)O) from sodium aluminate liquor can be an energy saving option for alumina production. Gibbsite is stable at precipitation temperature lower than 90 °C. Thus when boehmite is precipitated below 90 °C it is always accompanied with a gibbsite phase. However, the addition of certain organic additives favours precipitation of a monophase product i.e. boehmite at a temperature lower than 90 °C. At a temperature as low as 60 °C additives like tartaric acid, xylose and glucose could favour the precipitation of single phase boehmite precipitation. The role of the additive is proposed to be complete inhibition of gibbsite formation and facilitation of boehmite nucleation through different extent of complex formation by multidentate ligands.

Desilication of sodium aluminate solution by Friedel's salt (FS: 3CaO·A1 2O 3·CaCl 2·10H 2O)

Controlling silica level in Bayer liquor is critical in order to prevent scaling or alumina quality issues. The conventional method of removing silicates from aluminate solutions requires the introduction of calcium oxide or calcium hydroxide. In this work, Friedel's salt (FS: 3CaO·A1 2O 3·CaCl 2·10H 2O) is proved for the first time to remove up to 95% silica from sodium aluminate solution. FS is a mineral anion exchanger belonging to the layered double hydroxides (LDHs) which was prepared by adding calcium chloride to sodium aluminate over the temperature range of 50–90 °C. It was characterized by XRD, SEM, Particle Size Analyzer and TG-DSC. FS prepared at 50 °C has a relatively high desilication capacity, better than calcium oxide. Experimental parameters affecting the desilication process, such as temperature, sodium aluminate liquor composition, initial silica concentration (4–10 g/L) and FS dosage were investigated in detail and a comparison of desilication between FS and CaO was carried out. The desilication products (DSP) were mainly calcium aluminium silicates, identified by XRD to be Chabazite and Wadalite and the final chloride concentration in the sodium aluminate solution after anion exchange with FS was ∼ 0.015 g/L. The rate of desilication by FS was first order with a rate constant 2.582 × 10 6 min − 1 . The apparent activation energy was estimated to be 57.7 kJ mol − 1 over the temperature range of 80–110 °C.

Effect of oleic acid on gibbsite precipitation from seeded sodium aluminate liquors

Effect of oleic acid on precipitation ratio, agglomeration and morphology of gibbsite was investigated at selected conditions. The results of titrimetric analysis suggest that oleic acid inhibit gibbsite precipitation from seeded sodium aluminate liquors, and the inhibitory effect is stronger at 65 °C than that at 75 °C. The variations of particle size distribution (PSD) indicate that the agglomeration of gibbsite is significantly enhanced when the concentrations of oleic acid are in a low range (0.01 g/L–0.05 g/L). However, relatively higher concentrations of oleic acid (> 0.1 g/L) suppress agglomeration. The morphology of gibbsite was examined with scanning electron microscope (SEM). It shows that low concentrations of oleic acid in the sodium aluminate liquors lead to the formation of compact gibbsite particles, while high concentrations of oleic acid favor the growth of smooth texture of gibbsite surfaces, that is, the growth habit of gibbsite crystal changes under the influence of oleic acid.

Thermal decomposition behaviour of polyacrylamidomethyltrimethyl ammonium chloride in red mud separation process

In order to provide references for selecting highly efficient red mud flocculants, the behaviour of polyacrylamidomethyltrimethyl ammonium chloride (PATAC) in red mud separation process was investigated. PATAC was employed as a flocculant for red mud separation from the caustic aluminate liquor at 95 °C. The used red mud was generated from Chinese diaspore bauxite in Bayer process of alumina production. And the changes of PATAC before or after being treated in caustic solution at 95 °C were studied by thermogravimetry (TG) and Fourier transform infrared (FTIR) spectral analysis. The results show that PATAC fails in effectively flocculating red mud and PATAC is readily converted to a quaternary ammonium hydroxide (PATAH) in caustic solution. PATAH can be decomposed to a new polymer (HPATAH) even at 95 °C. Furthermore, there is an intramolecular hydrogen bond formed in the HPATAH polymer chain with two functional groups of -CH2-OH and -CONH2. Therefore, the poor flocculation property of PATAC for red mud separation can be attributed to the thermal decomposition of PATAC in the caustic red mud slurry at 95 °C and the formation of intramolecular hydrogen bond in the polymer chain of HPATAH during the thermal decomposition, which causes the absorbable functional groups of PATAC to decrease greatly.

Effect of tetracarbon additives on gibbsite precipitation from seeded sodium aluminate liquor

Effects of tetracarbon additives, 1-butanol, 1,4-dioxane and tetrahydrofurane on gibbsite precipitation from caustic seeded sodium aluminate liquor were investigated. The additive was charged into supersaturated seeded sodium aluminate liquor, then the precipitation ratio of aluminate liquor in 10 h was evaluated and compared, and the particle size distribution of product was measured. The Mulliken atomic charge of oxygen in the additive molecule was calculated with DMol3 program. The results show that 1-butanol has little effect on gibbsite crystallization, while the precipitation ratios under the effect of 1,4-dioxane and tetrahydrofurane are 1.7% and 3.6% higher than that of the blank, respectively. The agglomeration efficiency of the product is also enhanced obviously by the addition of 1,4-dioxane and tetrahydrofurane. The precipitation ratio is inversely proportional to Mulliken atomic charge of oxygen atom, which implies that functional group in the additive molecule is involved in the gibbsite precipitation process more fundamentally than carbon chain.

Precipitation of boehmite in sodium aluminate liquor

Gibbsite is generally precipitated from sodium aluminate liquor in the presence of huge quantity of gibbsite seed at a temperature between 60 and 70 °C. This gibbsite is then calcined to produce alumina. Boehmite is a stable phase at higher temperature (> 100 °C) and formation of boehmite below 100 °C in supersaturated sodium aluminate liquor is unusual. In the present study an attempt has been made to produce boehmite under atmospheric pressure conditions. Effect of various parameters such as temperature, alumina/caustic (Al 2O 3/Na 2O) ratio, seed size, amount of seed, organic additives, precipitation time, etc., on boehmite formation has been investigated. At higher temperature and low alumina/caustic ratio, boehmite is found to be precipitated under atmospheric pressure by adding boehmite seed. The optimum quantity of seed required for precipitation has been found to be 300 g L − 1 . Reduction in precipitation temperature could be achieved by using different organic additives. Tartaric acid has been found to be highly effective in reducing the temperature of boehmite precipitation to 50 °C. Increase in precipitation time increased boehmite production.