Aluminate Solution Research Articles

Enhanced Precipitation of Gibbsite from Sodium Aluminate Solution by Adding Agglomerated Active Al(OH)3 Seed

The addition of active seed for increasing the precipitation rate leads to the formation of fine Al(OH)3 particles that complicates separation of solid from the mother liquor. In this study, the enhanced precipitation of coarse Al(OH)3 from sodium aluminate solution using active agglomerated seed was investigated. Aluminum salt (Al2(SO4)3) were used for active agglomerated seed precipitation at the initial of the process. About 50% of precipitation rate was obtained when these agglomerates were used as a seed in the amount of 20 g L−1 at 25 °C within 10 h. The agglomerated active seed and precipitate samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). SEM images showed that agglomerates consist of flake-like particles that can be stick together by bayerite (β-Al(OH)3) acting as a binder. The precipitation temperature above 35 °C and the high concentration of free alkali (αk = 1.645Na2Ok/Al2O3 > 3) lead to the agglomerates refinement that can be associated with the bayerite dissolution.

Preparation of CaCO3/Al(OH)3 Composites via Heterogeneous Nucleation.

As one of the most widely used inorganic fine powder fillers, calcium carbonate is cheap. However, considering its poor light transmittance, it is not suitable to be added to resin matrix composites that require high light transmittance. Aluminum hydroxide has good light transmission and flame retardancy, but it is more expensive than calcium carbonate. CaCO3/Al(OH)3 composites with a core-shell structure that showed a trend toward the performance of aluminum hydroxide not only improved the surface properties of CaCO3, but also increased the added value of CaCO3. In the present paper, CaCO3/Al(OH)3 composites were successfully prepared in sodium aluminate solution via heterogeneous nucleation. Four types of calcium sources, including calcite-type precipitated calcium carbonate, vaterite-type precipitated calcium carbonate, ground calcium carbonate with two different particle sizes as the precursors and supersaturated sodium aluminate solution as the substrate, have been deeply investigated in terms of their influence on the preparation of CaCO3/Al(OH)3 composites. Results showed that the calcium carbonate precursor greatly affected the formation of CaCO3/Al(OH)3 composites. Both the precipitated calcium carbonate and the small particle ground calcium carbonate are likely to undergo anti-causticization and a complexation reaction with it to generate 3CaO·Al2O3·6H2O and 3CaO·Al2O3·CaCO3·11H2O, which go against the coating of calcium carbonate with aluminum hydroxide. Within the experimental range, the use of ground calcium carbonate with a particle size of 400-500 mesh is more suitable as a precursor for the preparation of core-shell CaCO3/Al(OH)3 composites.

DECOMPOSITION OF GIBBSITE FROM ALUMINATE SOLUTIONS IN LOW-INTENSITY ULTRASONIC FIELDS

The results of laboratory studies of the practical application of the reagentless method of strain-pulse regulation in the industrial method of obtaining gibbsite from aluminate solutions using the Bayer method are presented. During decomposition in regulatory regimes, the size and uniformity of crystals increases, and there is an increase in the rates of dissolution of the seed and crystallization of gibbsite. Quantitative characteristics of the degree of transformations are given and the parameters of gibbsite crystals obtained by the traditional method and in different modes of regulation are determined. The results of X-ray phase analysis and granulometric analysis of images obtained using a scanning electron microscope are described.

Tin Bronze Reinforced with Cu9Al4 Particles: Mechanochemical Synthesis and Consolidation by Sintering under Pressure

X-ray diffraction analysis and optical and electron microscopy have been used to study the effect of mechanical activation conditions of the Cu–12% Sn mixture with different Cu9Al4 modifier contents on the structure and phase composition and morphology of formed composites. The mechanochemical intro-duction of 10 wt % of the modifying additive into the matrix of mechanically synthesized tin bronze mainly results in the formation of a ternary Al0.05Cu0.9Sn0.05 solid solution of aluminum and tin in copper. In the case of the 20 wt % modifying additive, the final product contains a Cu0.9Sn0.1 tin solid solution in copper and Cu9Al4 intermetallics. Studies of the mechanical and tribological characteristics of the material prepared by sintering under a pressure showed that the intensity of wear of the material based on the Cu–12 wt % Sn mechanochemically synthesized bronze is insignificant lower than that of commercial bronze alloy CuSn10P; the coefficient of friction (f) decreases by ~1.3 times and the range of its values is sufficiently wide,f = 0.7–0.9. The modification of the Cu–12 wt % Sn mechanically synthesized bronze with the Cu9Al4 inter-metallics allowed us to decrease the intensity of wear by 1.3 to 1.6 times and to substantially decrease the coef-ficient of friction (by 1.2 to 1.6 times). The stable value f = 0.5 is reached for the mechanically activatedCu‒12 wt % Sn + 20 wt % Cu9Al4 composition. The introduction of the intermetallics results in the increase in the microhardness of the alloys by 1.6 to 2 times (to Hμ = 2730 MPa) compared to those of CuSn10P and mechanically synthesized bronzes.

A Novel Spatio-Temporal Adaptive Prediction Modeling Strategy for Industrial Production Process

Evaporation is a key process for recycling resources and reducing environmental pollution in alumina production. Its outlet liquid material concentration is a significant production indicator for evaluating evaporation quality, and also an important basis for adjusting evaporation operation parameters. However, the quality detection of sodium aluminate solution lags behind, and the delayed production information affects the accuracy of optimization and control. Therefore, to achieve efficient and green production, a novel spatio-temporal prediction model based on mutual information is presented in this paper. First, data reconciliation is applied for preprocessing to obtain the high-quality process production information. Besides, the process mechanism model is constructed through utilizing process knowledge and balance principle. Taking into account the nonlinearity and time-varying characteristics, a spatio-temporal data-driven model with mutual information and moving window is established for mechanism error compensation. Finally, an evaporation industrial process is applied to illustrate the feasibility of the proposed prediction model, and more than 90% prediction error within the ±2% error range, which demonstrates that the proposed prediction model improves the prediction condition and performance effectively.

Study of Catalytic Properties of the HoxMg1-xAl2O4 Modified HZSM-5 Zeolite in Conversion of Methanol to C2-C4 Alkenes and p-Xylene

Selective conversion of methanol to C2-C4 alkenes and p-xylene is one of the appealing chemical routes. Currently, there are no effective catalysts for the co-production of C2-C4 alkenes and p-xylene from methanol. To date, modified medium-pore ZSM-5 zeolites are considered one of the excellent candidates for the development of selective catalysts for the conversion of methanol to lower alkenes and aromatic hydrocarbons. In this paper, nanosized (30-33nm) powders of HoхMg1-хAl2O4 spinel structure were obtained by the method of combustion of nitrate solutions of aluminium, magnesium, holmium, diethylmalonate and hydrazine monohydrate with the further calcination of nanopowders at 1000 °C. Obtained nanopowders used in the preparation of a solid-phase catalytic composition of HoхMg1-хAl2O4-HZSM-5. Various physico-chemical properties of the catalytic composition were investigated using X-ray diffraction (XRD), pyridine adsorption (BİO-RAD FTS 3000 MX) and low-temperature nitrogen adsorption (BET) techniques. The textural properties and acidity of the catalysts were altered by adjusting the nanopowder concentration (1.0-5.0 wt.%) in the catalytic composition. The conversion of methanol in the presence of the catalytic compositions was carried out in flow-type fixed-bed catalytic reactor at 400 °C, in the presence of nitrogen carrier gas with 1.0 h-1 flow rate. A correlation between the selectivity to C2-C4 alkenes and p-xylene with a ratio of Lewis (L) and Brønsted (B) acid sites and the volume of the catalyst pore, the amount of the modifier in the catalytic system has been established. As the amount of HoхMg1-хAl2O4 nanopowder increases, the ratio of B/L acid sites and the volume of the catalyst pore decrease, which play a significant role in the increase of the selectivity to C2-C4 alkenes and p-xylene. Maximum yield of C2-C4 alkenes (31.6%) and selectivity to p-xylene (80.5%) is achieved on a catalytic composition containing 5.0 wt.% HoxMg1-xAl2O4. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Effect of redox agents on the reaction behavior of pyrite in sodium aluminate solution at elevated temperatures

As the main sulfide mineral in diasporic bauxite, pyrite readily reacts with sodium aluminate solution in Bayer digestion at elevated temperatures, adversely affecting the utilization of high-sulfur bauxite for alumina production by the Bayer process. For better understanding of the reaction mechanism during Bayer digestion, this paper focuses on the impacts of oxidant and reductant on the reaction extents of pyrite at elevated temperatures. The extents of reaction between pyrite and sodium aluminate solution are 57.9, 38.3 and 99.0 % at 260 °C for 40 min with no, oxidant and reductant addition, respectively. In the presence of oxidant, a dense layer formed on the surface of unreacted pyrite retarding the reaction with sodium aluminate solution, which follows the Kröger and Ziegler diffusion control model at 240–260 °C. However, the presence of reductant favors the decomposition of pyrite due to the formation of hematite and then transformation to magnetite, and the development of “chemical etching channel”. Finally, the above results were experimentally verified by digesting high-sulfur diasporic bauxite at 260 °C for 60 min, in which the inhibition of pyrite reaction with oxidant addition is affected by the organic content of the bauxite. These results may facilitate the development of a technique for directly treating the high-sulfur diasporic bauxite for alumina production with the Bayer process bypassing desulfurization pretreatment.

Electron-Beam Welding Cu and Al6082T6 Aluminum Alloys with Circular Beam Oscillations

In this study, we present the results from electron-beam welding operations applied on copper and Al6082T6 aluminum alloys. The influence of beam-scanning geometries on the structure and mechanical properties of the welded joint is studied. The experiments were conducted using a circle oscillation mode with an oscillation radius of 0.1 mm and 0.2 mm. The beam deflection was set to 0.4 mm with respect to the side of the aluminum alloy, and the beam power was set at 2700 W. The phase composition of the obtained welded joints was studied by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used for the investigation of the microstructure of the joints. The chemical composition was investigated by using energy-dispersive X-ray spectroscopy (EDX). The mechanical properties were studied by micro-hardness investigations. The fusion zone of the weld seam contains three phases—an aluminum matrix, an ordered solid solution of copper and aluminum in the form of CuAl2, and pure copper. Electron beam-scanning geometries have significant influences on the structure of the weld. Increasing the beam oscillation’s radius leads to a decrease in intermetallic phases and improves homogeneity. The measured microhardness values in the fusion zone are much higher than the ones measured in the base metals due to the formation of intermetallic phases. The microhardness of the weld joint formed using an oscillation radius of 0.2 mm was much lower compared to the one formed using an oscillation radius of 0.1 mm.

Effect of annealing on the structure and phase composition of Cu-Al composite produced by conventional and accumulative HPT

The paper presents the first results of the investigation of the effect of annealing on the evolution of microstructure and phase composition of a Cu-Al composite obtained by accumulative high pressure torsion (HPT). Cu-Al composites produced under 6 GPa in 10 revolutions at room temperature with conventional and accumulative HPT were annealed at 450°C for 15 min. Electron microscopy and energy dispersive spectrometry analysis showed that annealing enhances the solid-state reaction. In the sample after conventional HPT and post-deformation annealing, grayer contrast layers containing intermetallic compounds were formed at the copper-aluminum interface. The contrast on the microstructure images of the sample after accumulative HPT and post-deformation annealing is more uniform than after conventional HPT and annealing. In the sample, a more intense phase transformation occurred. This led to a noticeable increase in the volume fraction of the intermetallic compounds up to 5 – 6 times. X-ray diffraction analysis indicates that in the annealed sample after accumulative HPT, alongside with initial copper, there is also a solid solution of aluminum in copper, which differs from copper with a crystal lattice parameter. Post-deformation annealing led to the formation of different quantity of intermetallic compounds in the studied samples.

Effects of Methanol on the Seeded Precipitation of Al(OH)3 from Potassium Aluminate Solution

AbstractThe effects of methanol on the seeded precipitation of Al(OH)3 from potassium aluminate solution are investigated. The solubility of Al(OH)3 decreases in the presence of methanol, leading to a faster crystallization and a higher precipitation ratio than the normal seeded precipitation process. Under the optional precipitation conditions of temperature 323.15 K, K2O concentration 170 g L−1, and addition of an equal volume of methanol to potassium aluminate solution, the precipitation ratio can exceed 85% within 7 h. Characterization of the Al(OH)3 products using X‐ray diffraction, scanning electron microscopy, and particle size distribution shows a typical gibbsite crystal phase composed of sheet‐like agglomerates with an average particle size of 74 µm. An interaction model between methanol molecules and Al(OH)3 crystal face is established and calculated by using the molecular dynamics method, which indicates the morphology transition mechanism of the Al(OH)3 crystal. The result indicates that methanol molecules would hinder the growth of the (002) crystal face, so that the (002) crystal face is eventually retained and becomes the main crystal face for the Al(OH)3 product. Infrared radiation and Raman spectra analyses suggest that the added methanol captures water molecules from the aluminate ion hydration sphere and thus catalyzes the crystallization process.

Improving Corrosion and Photocatalytic Properties of Composite Oxide Layer Fabricated by Plasma Electrolytic Oxidation with NaAlO2.

The present work dealt with the development of a protective and functional oxide layer via one-step plasma electrolytic oxidation (PEO) on pure titanium by employing highly concentrated aluminate solution in a short processing time. A compositional analysis showed that Al2TiO5 active compound was formed successfully by means of Al2O3 incorporation when TiO2 was spontaneously developed with the aid of plasma swarms. The electrochemical performance showed the protective and functional capabilities of the layer, which was attributed to the respective amounts of Al2O3 and Al2TiO5. Such capabilities were achieved in a short processing time, thus reducing the total production cost.

Virtualization of a tube digester in alumina production

In this work, we develop a digital twin of a tube digester and a software application automatically calculating the aluminate solution quality based on mass balance equations with the purpose of improving the quality of hydro-chemical process management at the Rusal Achinsk JSC alumina plant. A mimic diagram of the nepheline sinter leaching process was visualized using the Wonderware InTouch software package. Quick scripts were created to display the process animation. The input parameters include the solution temperature, the consumption of sinter and recycled solution, as well as the chemical composition of raw materials. The air temperature, vibrations and equipment malfunction were used as the main disturbing effects. Output parameters consisted of sludge and aluminate solution yields, power consumed by the drive and the silicon ratio of the resulting solution. Based on the mass balance of sinter and recycled solution, calculated using industrial laboratory data, an algorithm for modelling variations in the digestion process and a software application for calculating the quality of aluminate solution were developed using the InTouch built-in capabilities of scripting in its own programming language. A digital twin of a tube digester was developed on the basis of an operating unit utilized at the Rusal Achinsk JSC. It was shown that the developed software application predicts the quality of the finished product (aluminate solution) using a simple balance model under variations in both the composition of raw materials (cake and recycling solution) and the rate of fed raw materials, as well as present the results of calculations performed using a mimic diagram of the process. Thus, the developed interface can be used to simulate various technological operations performed in a tube digestor, including solution drainage, sludge discharge and variations in the inlet flows. At the same time, it becomes possible both to observe current changes in process parameters and archive plots, as well as to select the optimal composition of raw materials to obtain an aluminate solution of higher quality.

A comparative study of the catalytic performance of nickel supported on a hibonite-type La-hexaaluminate synthesized from aluminum saline slags in the dry reforming of methane

In this work, a hibonite-type Ni/La-hexaaluminate (Ni/LHA) synthesized from an industrial waste is used and compared as catalyst in the dry reforming of methane (DRM) at 973 K. The structure, catalytic behavior, and stability during a run time of at least 50 h of three Ni-catalysts obtained from two commercial supports and two preparation methods were used for comparison. An aluminum solution (9.40 g/L) obtained from an aluminum saline slag waste by acid extraction was used to synthesize the hexaaluminate by mixing with a stoichiometric amount of lanthanum nitrate and methanol/Peg400/PegMn400 under hydrothermal conditions at 493 K for 16 h. The Ni/LHA catalyst (10 wt% NiO) was obtained by impregnation of the synthesized support, calcined previously at 1473 K for 2 h. The resulting solids were characterized by several techniques as: X-ray diffraction (XRD), N2 adsorption at 77 K, temperature-programmed reduction (TPR), scanning electron microscopy (SEM) and transmission electron microscopy (HR-TEM). In order to compare the catalytic behavior and properties of the Ni/LHA catalyst, three Ni catalysts obtained from two commercial supports (γ-Al2O3 and SiO2) and two preparation methods (wet impregnation (I) and precipitation-deposition (PD)) were synthesized. Analysis of the TPR patterns for the catalysts allowed the type of metal support interaction and NiO species to be determined, with a weak interaction with the support being observed in Ni/LHA and Ni–I/SiO2. The NiO species observed, with crystallite sizes between 9.7 and 40.4 nm, confirm the X-ray structural analyses. The Ni/LHA catalyst was found to be active and very stable in the DRM reaction after 50 h. The catalytic behavior was evaluated from the CO2 and CH4 conversions, as well as the H2/CO selectivity, with values of 99% over almost all the time range evaluated. The behavior of this catalyst is comparable to that of Ni–I/Al2O3 and Ni-PD/SiO2. The results found indicating that the strong interaction of nickel with the support favors the stability of the catalysts in the DRM reaction.

Effect of calcium on electrical resistance and phase composition of Al – 1.5 % Mn alloy

The authors used experimental and modelling techniques to look at the specific electrical resistance and phase composition of low-alloy Al – Ca – Mn alloys after they had been subjected to various annealing regimes. The study focused on four alloys in the form of ingots and cold-rolled sheets containing 1.5% Mn and up to 1% Ca. Templates cut out of ingots and sheets were annealed in a muffle furnace using multi-stage modes in the temperature range of 300 to 600 oC. They were soaked for 3 hours at each stage of the process and air cooled after each stage. It was found that, in the as-cast state, all manganese in all four alloys makes a part of the aluminium solution (Al), whereas calcium is comprised in the (Al) + Al4Ca eutectic, which agrees with the Sheil-Gulliver non-equilibrium solidification simulation. Annealing of cold-rolled sheets for 3 hours at 600 oC results in an equilibrium phase composition and a uniform structure – i. e. globular submicron particles evenly distributed throughout the aluminium matrix. In their initial state, when almost all Mn is comprised in (Al), the ingots and coldrolled sheets of all the studied alloys have little to no difference between each other in terms of specific electrical resistance. On the other hand, Ca helps to significantly lower the specific resistance (by 6 μΩ·mm) compared with the base alloy after cold-rolled sheets have been annealed at 350–400 oC. It may be attributed to a higher rate of aluminium solution breakdown, which is associated with a dropping concentration of Mn in (Al) and Al10CaMn2 particles forming in line with the Al – Ca – Mn phase diagram.This research was funded under Grant of the Russian Science Foundation N 20-19-00746.

Structure and reactivity of sodium aluminate complexes in alkaline solutions

The underlying mechanism by which tetrahedrally-coordinated aluminate solution species react to precipitate octahedrally-coordinated Al3+ in gibbsite is unknown. Sodium aluminate solutions provide the opportunity to investigate the role of ion speciation and local structure in the reaction, as the solution metastability can be controlled by varying ratio of excess NaOD to Al3+. Here, capitalizing on this tunable precipitation behavior, aluminate speciation was investigated through a combination of Raman, infrared, and NMR spectroscopies, together with geometrical fitting of neutron and X-ray radial distribution functions. These techniques reveal a mixture of monomeric Al(OD)4− and dimeric Al2O(OD)62− in all compositions, but solutions avoiding precipitation for extended timescales (i.e. months to years) show an increased dimeric Al2O(OD)62− population formed at the expense of the Al(OD)4− monomer. Conversion between these species, as well the potential for further oligomerization and formation of larger pre-nucleation species is driven by the hydrogen/deuterium bonding (H/D-bonding) and proton/deuteron transfer reactions. Changes within the local environment around the aluminate anions, including solvation and the presence of solvent-shared ion pairs or contact ion pairs, will consequently govern the reactivity of these aluminate species to either promote or inhibit precipitation.

Synthesis and Acidity Study of Na-ZSM-5 Zeolite

Zeolites are a special class of structured aluminosilicates with a developed inner surface and a large number of micropores, which allows them to be used as sorbents, membrane materials, and catalysts. Zeolite ZSM-5 is an aluminosilicate formed by parallel channels with a diameter of 5.3–5.6Å interconnected by sinusoidal channels with a diameter of 5.1–5.5Å. At the same time, the presence of aluminum atoms in the zeolite crystal lattice makes it possible to carry out dehydrogenation, esterification, isomerization, and aromatization reactions, and the presence of microchannels significantly increases the number of collisions of reacting compounds, which leads to a significant increase in the rate of chemical transformations in such systems. The synthesis of ZSM-5 zeolite using structure-directing agents has been known since the late 70s of the last centuries, while the high cost of structure-directing agents used and the long duration of hydrothermal synthesis and the need for subsequent post-synthetic procedures lead to a high cost of the resulting zeolite. One of the possible ways to reduce the cost of the synthesis of ZSM-5 zeolite is the direct use of ZSM-5 zeolite as a structure-forming agent, while the synthesis conditions play a decisive role in the structure of the resulting zeolite. The article presents the results of a study of the synthesis of ZSM-5 zeolite and a study of its acidic properties using locally produced reagents. Zeolite was prepared using pre-milled silica gel, sodium hydroxide, and sodium aluminate. The pre-weighed silica gel sample was filled with sodium hydroxide solution and stirred at 70 ℃ to form a colloidal solution, after which the pre-prepared sodium aluminate solution was added, and hydrothermal synthesis was carried out at 180 ℃ for 24 hours. During the synthesis, the Si/Al ratio was varied in the range from 7.5 to 2000, while the resulting acidity ranged from 0.002 to 0.265 mmol(NH3)/g(ZSM-5). It was found that the synthesis of ZSM-5 using pre-prepared reagent solutions is superior to the method using direct dissolution of solid reagents in an autoclave. An increase in the Si/Al ratio from 7.5 to 100 leads to a corresponding increase in surface acidity from 0.066 mmol(NH3)/g(ZSM-5) to 0.265 mmol(NH3)/g(ZSM-5). A further increase in the Si/Al ratio to 2000 leads to a decrease in surface acidity to 0.002–0.005 mmol(NH3)/g(ZSM-5). A reliable and simple method for the synthesis of ZSM-5 zeolite has been developed, providing a zeolite yield of up to 97%.

Preparation and characterisation of seed for simultaneous removal of sulphur and iron from sodium aluminate solution

ABSTRACT This research focuses on the preparation and characterisation of a seed used to remove sulphur and iron simultaneously from sodium aluminate solution. Avrami equation could describe the crystallisation process of sulphur and iron, and their apparent activation energy was calculated. It was found that the Avrami index n of sulphur and iron were between 1.5 and 2, and the crystals grow in one-dimensional acicular and two-dimensional lamellar structures with fine particle size. SEM images displayed that the prepared seed had obvious step morphology, and the growth mechanism was confirmed to be a multilayer spiral growth model. XRD analysis demonstrated that the main components of this seed were Fe2O3, FeS2, NaFeS2·2H2O, Fe(OH)3 and NaFeO2. In the experiment, these components could play the dual role of induced crystallisation and reactive crystallisation, and promote the effective removal of sulphur and iron with little effect on the loss of aluminium.

Synthesis and characterization of ecofriendly materials zeolite from waste glass and aluminum scraps using the hydrothermal technique

In this study, we reported a simple and easy process for zeolite synthesis using waste glass and aluminum scraps. The silica source was obtained from glass of the end-of-life fluorescent tubes and aluminum source was scraps collected from aluminum workshop in the region of Sfax, Tunisia. The zeolitic materials were prepared by hydrothermal treatment at 60 °C for 6 days using 10 g of glass powder mixed with 100 mL sodium aluminate solution prepared from aluminum scraps. In order to optimize the nature of the recovered zeolites, reaction time, particle size, aluminum concentration and liquid/solid ratio were monitored. The starting materials and the prepared zeolites were characterized by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Nuclear Magnetic Resonance (NMR) of 27Al and 29Si nuclei. The characterization techniques demonstrated that the recovered solid after 6 days of crystallization at 60 °C using different particle sizes (ø <63 µm, ø <125 µm, ø <325 µm) was zeolite Na-LTA contaminated with small quantity of Na-P1.

Multilayer adsorption improving the organic removal by foam flotation from sodium aluminate solutions

Effective enrichment of organics by foam flotation will notably contribute to the removal of organics from the Bayer liquor. The present study shows that the removal efficiency increased with increasing concentration of sodium laurate (SL) and sodium stearate (SS). Over 29% SS removal with a concentration ratio of 2.92 was obtained from the Bayer liquor. The surface pressure increased with increasing spreading concentration, while the mean molecular area decreased. From the remarkable difference in the π-A isotherms of SS on the surface of sodium aluminate solution and water, a minimum molecular area of 2.39 Å2 occurred in the sodium aluminate solution, which was notably lower than 24.6 Å2 in water. Adding sodium palmitate (SP) into SS increased the minimum molecular area, while the addition of sodium oleate (SO) raised the maximum surface pressure. From Langmuir-Blodgett films, the micellar size of SS and SL increased with increasing spreading concentration. Adding SP and SO into SS enlarged the micellar size owing to the synergistic interaction between organics. As a result, the complicated interfacial structure, multilayer adsorption of micelles at the air/solution interface, and precipitation of aluminum hydroxide synergistically promoted the removal efficiency of organics from the sodium aluminate soluion.

Rich microbubbles modifying the leaching mechanism of aluminum and aluminum nitride of secondary aluminum dross in sodium aluminate solution

An understanding of the mechanisms of reactive Al and AlN in a sodium aluminate solution contributes to the safe and effective utilization of secondary aluminum dross (SAD). This study demonstrates that the slurry temperature increased exponentially with an increase in the SAD dosage. Synergistic kinetic phenomena in the form of a large dosage and high temperature occurred initially in relatively stable microbubbles and later in the slurry. The leaching efficiencies of pure Al and AlN powders were greater than that of Al and AlN in SAD, respectively. Meanwhile, the leaching rate became higher for Al in SAD but lower for AlN in SAD compared to that of pure Al and AlN powder. The AlN particles in SAD were covered by Al(OH)3 precipitated from the saturated solution in the bubbles. As a result, the relatively stable microbubbles with a thick border accelerated the reaction of Al and AlN and produced a saturated solution thereby changing the leaching efficiency and leaching rate of AlN in SAD. The embedded Al and AlN grains in the SAD, relatively stable microbubbles, and the SAD particles covered by Al(OH)3, synergistically changed the leaching mechanism. These results provide further understanding of the reaction mechanism of rich bubbles and facilitate the optimization of the comprehensive utilization of SAD.