Sodium Aluminate Solution Research Articles

Wet oxidative removal of low-valent sulfur by addition of H2O2 to Bayer fluid

ABSTRACT The presence of sulfur in sodium aluminate solution can disrupt the Bayer process in alumina production. H2O2 is used as an oxidant to convert low-valent sulfur (S2−) into high-valent sulfur (i.e. S2O3 2−, SO3 2−, and SO4 2−). This paper combines thermodynamic calculations and experimentation to propose the mechanism of the oxidation reaction between H2O2 and different valences of sulfur (i.e. S2O3 2−, SO3 2−, and SO4 2−) in sodium aluminate solution with the oxidation effect of S2− being the most obvious. By studying the oxidation effect of H2O2 dosage, oxidation time, and oxidation temperature on different valences of sulfur in sodium aluminate solution, it was found that the removal rate of S2− reached 91.85% with 9% H2O2 dosage, 260 °C oxidation temperature, and 60 min oxidation time. The experimental results were consistent with the thermodynamic calculations. Finally, the reaction between H2O2 and different valences of sulfur in sodium aluminate solution was described in detail, providing theoretical support for the desulfurisation of high-sulfur bauxite in the production of alumina through the Bayer process.

Study on Reaction Behavior and Phase Transformation Regularity of Montmorillonite in High-Calcium Sodium Aluminate Solution System

The diaspore is a typical representative of bauxite resources in China, which is the primary raw material for the Bayer process in alumina production, particularly in regions such as Shanxi, Guangxi, Guizhou, and Henan. Clarifying the phase transformations and reaction mechanisms of the silicon-containing minerals during the Bayer leaching process of diaspore is essential for improving the efficiency of alumina production. This article focuses on montmorillonite, which is one of the silicon-containing minerals of diaspore-type bauxite, investigating the reaction mechanisms and phase changes of montmorillonite under the high-calcium sodium aluminate solution system by using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Magic Angle Spinning Nuclear Magnetic Resonance (MAS–NMR) and Fourier Transform Infrared Spectroscopy (FTIR). The results show that montmorillonite dissolved and transformed into Na6(AlSiO4)6 (hydrated sodium aluminosilicate) under the high-calcium sodium aluminate solution system, and calcium oxide and sodium aluminate in the solution reacted to form (CaO)3Al2O3(H2O)6 (hydrated calcium aluminate). With the increase of reaction temperature, caustic alkali concentration (Nk), and reaction time, hydrated calcium aluminate and hydrated sodium aluminosilicate react and transform into Ca3Al2SiO4(OH)8 (hydrogarnet). Under the optimal reaction conditions of a 120 min reaction time, a temperature of 240 °C, an Nk of 240 g/L, and a CaO–to–SiO2 mass ratio (C/S) of 3.5:1, the montmorillonite reaction degree can reach a maximum of 93.71%.

Study on the Continuous Whole Process Preparation of Peptizable Pseudoboehmite by High Gravity Strengthening Reaction of CO2 and Heat Transfer.

The preparation of highly peptizable pseudoboehmite faces challenges such as slow reaction rate, prolonged aging times leading to poor peptization performance, and difficulty in achieving continuous production. In this study, a novel approach was proposed involving a high gravity reactor to enhance carbonation reaction control for pseudoboehmite nucleation, a high gravity steam heating process, and a continuous aging process in pipelines. By coupling these three processes, the continuous whole process production of highly peptizable pseudoboehmite under high gravity conditions was achieved. First, the effect of high gravity reactor enhancement on the reaction and the resulting solid phase was investigated. Second, the impact of aging temperature and time on the solid phase formed at different reaction end points was studied using high gravity and steam heating of the liquid phase. Furthermore, the influence of synthesis conditions on the peptization performance of pseudoboehmite was extensively examined. Finally, the nucleation and growth mechanisms of pseudoboehmite under high gravity conditions were analyzed. It was found that increasing high gravity factor, CO2 gas flow rate, and CO2 content accelerated carbonation reaction rate, promoting pseudoboehmite crystal nucleation. Increasing aging temperature and time facilitated the growth of pseudoboehmite nuclei and improved peptization performance. The high gravity device altered the gas-liquid phase contact state of traditional kettle-type equipment, reducing the reaction time and heating time from minutes to seconds, thus achieving the continuous whole process production of pseudoboehmite with a peptization index of 100% from sodium aluminate solution by kiln flue gas.

Preparation of Near-Spherical α-Al2O3 Particles by Enhanced Precipitation of Gibbsite from Sodium Aluminate Solution Using Highly Dispersed Al2O3 as Seeds.

The near-spherical α-Al2O3 particles (∼200 nm) were prepared for the first time through the precipitation of gibbsite from a supersaturated sodium aluminate solution, with the addition of an acidic solution containing highly dispersed nanosized Al2O3 seeds. The near-spherical α-Al2O3 were achieved by employing seeds at 1100 °C, with the initial nucleation temperature being only 900 °C, due to the highly homogeneous dispersion of the seeds into gibbsite formation by in situ growth that can effectively enhance the role of the seeds in the phase transition. Moreover, the precipitation rate of sodium aluminate solution was significantly accelerated by 17-fold. This acceleration was due to the slightly acidic solution breaking the stability of sodium aluminate solution through a neutralization reaction on the seed surface, leading to the rapid formation of gibbsite nuclei on the seed surface. Our findings provide a feasible approach for the fabrication of well-dispersed α-Al2O3 particles and make the industrial production of well-dispersed α-Al2O3 from sodium aluminate solution a commercial reality.

Effect of sulfur on synergistic corrosion behavior of Q235 and 16Mn steel in sodium aluminate solution

In this study, the corrosion electrochemistry and corrosion behavior of two steels were studied under the simulated alumina production conditions. The corrosion rate of 16Mn steel is greater than that of Q235 steel. The effect of S2− concentration on corrosion rate was significantly higher than that of S2O32−. The synergistic corrosion rates of Q235 and 16Mn steels increase at first and then decrease with the sulfur content, and the peak value appears when the concentration of S2− and S2O32− is 4 g/L and 3 g/L respectively. There are two main types of corrosion products: one is surface octahedral grain, which is composed of Fe2O3, Fe3O4 and Al2O3.The other is the interlayer corrosion between the surface layer and the matrix, which is composed of FeS, FeS2 and NaFeO2.The formation mechanism of the corrosion and corrosion mechanism were obtained by analyzing the phenomenon of ion competitive adsorption. Further validation and analysis of ion competition adsorption phenomenon were conducted using first-principles calculations based on density functional theory (DFT). The formation of corrosion products on the steel surface was investigated at an ion level, and the adsorption energies of OH− and S2− at the top site of Fe(110) surface were calculated. It was found that S2− is more likely to be adsorbed on the Fe(110) surface compared to OH−. The corrosion mechanism of steel is discussed preliminarily.

Resolving intermediates during the growth of aluminum deuteroxide (Hydroxide) polymorphs in high chemical potential solutions

Aluminum hydroxide polymorphs are of widespread importance yet their kinetics of nucleation and growth remain beyond the reach of current models. Here we attempt to unveil the reaction processes underlying the polymorphs formation at high chemical potential. We examine their formation in-situ from supersaturated alkaline sodium aluminate solutions using deuteration and time-resolved neutron pair distribution function analyses, which indicate the formation of individual Al(OD)3 layers as an intermediate particle phase. These layers ultimately stack to form gibbsite- or bayerite-like layered heterostructures. Ex-situ characterization of the recovered precipitates using 27Al magic angle spinning nuclear magnetic resonance spectroscopy, Raman, X-ray diffraction, and scanning electron microscopy, suggests the presence of additional intermediate states, an amorphous compound bearing both tetrahededrally- and penta-coordinated Al3+. These observations reveal the complex pathways to form Al(OD)3 monolayers via either transient pentacoordinate species or amorphous-to-ordered transitions. The subsequent crystallization of admixed gibbsite/bayerite is followed by an Al(OD)3 monolayer attachment process.

Cost-efficient removal of organics from Bayer liquor by tricalcium aluminate hexahydrate: Insights into the organic micelle and multilayer adsorption

The existence state and effective removal of organics from Bayer liquor have troubled the alumina industry for six decades. This study delved into the aggregation behavior and micellization of organics in Bayer liquor. Tricalcium aluminate hexahydrate (3CaO·Al2O3·6H2O, TCA) was then employed as a cost-effective adsorbent to remove organics by regulating the aggregation behavior of organics. Sodium dodecylsulfate (SDS), acting as a research object of organics, aggregated into inhomogeneous and large micelles (>3080.00 nm) with an extremely low critical micelle concentration (CMC) of 0.14 mmol·L−1 in the sodium aluminate solution (CNa2O = 2.42 mol·L−1, αK = 3.0, I ≥ 4.84 mol·L−1) at 298 K. Decreasing temperature facilitated the formation of these large micelles and the micellar size reached 2.20 μm in length. The solvated Ca2+ (Ca(OH)+) of TCA, acting as counterions with a content exceeding 11.97 wt%, initially induced the formation of micelles and then enlarged their size. Furthermore, these large micelles exhibited a preferential aggregation at the active concave of TCA. As a result, the interaction among inhomogeneous micelles, solvated Ca2+ (Ca(OH)+), and special active concave collectively contributed to the maximum organic carbon adsorption capacity of 32.46 mg·g−1 (equivalent to 64.92 mg·g−1 of SDS) at 298 K. These results open up new perspectives for understanding the existence state of the anionic organics in sodium aluminate solutions, as well as a cost-effective and eco-friendly approach to removing organics from Bayer liquor.

A short process for organics removal from sodium aluminate solution by regulating electrical double layer of tricalcium aluminate hexahydrate

A short process for organics removal from sodium aluminate solution by regulating electrical double layer of tricalcium aluminate hexahydrate

A single-step crystallization process to remove potassium from sodium aluminate solution

The high concentration of potassium in sodium aluminate solution seriously threatens the seed precipitation process and reduces the quality of alumina products, but the separation of potassium is quite difficult due to the similar chemical properties between potassium and sodium ions. In this work, a novel single-step double salt crystallization (SDSC) process with low energy consumption was proposed to remove potassium from the concentrated sodium aluminate solution using sodium sulfate, and the corresponding removal performance, kinetics and mechanism were studied. The potassium concentration decreases with the increase of additive dosage and reaction temperature, while the high caustic alkali concentration hinders the potassium removal. At 70 °C, the SDSC process exhibits a rapid crystallization and reaches an equilibrium within 60 min because of the low activation energy and weak bonding of 3 K2SO4·Na2SO4·9H2O. Under the optimum conditions, the potassium removal efficiency can achieve 85.68 %, and the potassium concentration is reduced from 120 g∙L−1 to 24.54 g⋅L−1. Finally, a cyclic utilization pathway was obtained to economically and effectively remove potassium from the sodium aluminate solution.

Investigation of the behavior and mechanism for defluoridation by modified mayenite (Ca12Al14O33) in sodium aluminate solution

Removal of fluorine in sodium aluminate solution facilitates the purity of aluminum products and reduces the corrosiveness of equipment. Hence, a modified synthetic method was used to prepare mayenite (Ca12Al14O33) adsorbent with the enhanced fluorine adsorption capacity in sodium aluminate solution. The adsorption process conformed to a pseudo-second-order kinetic model (R2 = 0.99) and Langmuir adsorption isotherm (R2 = 0.98) indicating that the adsorption of fluorine by Ca12Al14O33 is chemisorption. According to X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT − IR), X-ray fluorescence (XRF), and X-ray photoelectron (XPS) analysis, the mechanism of fluorine adsorption by Ca12Al14O33 was the ligand exchange with − OH and the formation of F − Al bond. Therefore, Ca12Al14O33 could be used as a potential adsorbent for fluorine in sodium aluminate solution.

Online Detection of Component Concentration in Synthetic Sodium Aluminate Solution Using Orthogonal Regression and BP Neural Network

Online Detection of Component Concentration in Synthetic Sodium Aluminate Solution Using Orthogonal Regression and BP Neural Network

Conversion of secondary aluminum dross into hierarchical carbonate-intercalated Mg-Al layered double hydroxide for efficient CO2 capture

This paper explores the preparation of hierarchical Mg-Al layered double hydroxide (LDH) from secondary aluminum dross waste for the first time. The aluminum content of the waste was initially extracted in the form of a sodium aluminate solution using a multistep wet chemical process. CO3-intercalated Mg-Al LDH was then prepared at pH values of 9 and 11 by adding magnesium chloride to a mixed solution of sodium aluminate and sodium carbonate. The X-ray diffraction (XRD) analysis revealed that a pure LDH structure could be formed at pH 11. The quantification of the XRD data revealed that the synthesized LDH had an interlayer spacing of 3.1 Å. The microstructural porosity was 0.76 cm3/g, and the specific surface area was 134 m2/g. The field emission scanning electron microscopy (FESEM) analysis revealed a hierarchical layered structure composed of flake-like particles in the microstructure. The elemental mapping of the synthesized LDH showed a proper distribution of Mg, Al, C, and O. The synthesized Mg-Al-CO3 LDH was then used for a study on CO2 capture. The CO2 capture experiments demonstrated that the amount of CO2 adsorption is influenced by temperature, gas pressure, adsorbent mass, and exposure duration. Investigating the effects of time and temperature revealed that a CO2 adsorption of 0.94 mmol/g can be achieved at a temperature of 25 °C during a 90-minute exposure period. Varying the gas pressure from 1 to 2.5 bar, while maintaining a constant temperature of 25 °C and an adsorbent mass of 1.5 g, resulted in an increase in CO2 adsorption from 1.7 to 2.3 mmol/g. Reusability tests showed that the LDH could maintain a satisfactory adsorption value of 0.84 mmol/g after 5 cycles, indicating its potential for repeated use.

Seeded Precipitation of the Coarse Sodium Fluoride with High Purity for Efficient Removal of Fluoride Ion from Sodium Aluminate Solutions

Seeded Precipitation of the Coarse Sodium Fluoride with High Purity for Efficient Removal of Fluoride Ion from Sodium Aluminate Solutions

Preparation and Corrosion Resistance of OMMT/EP Composite Coatings in Sulfur-Containing Sodium Aluminate Solution

Organic montmorillonite (OMMT) was prepared from Na-montmorillonite (MMT) by Hexadecylamine (HDA) modification. The composite material has good smoothness, acidity, and salt resistance. OMMT was characterized using small-angle X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and a video optical contact angle measuring instrument. The results showed that the layer spacing was enlarged from 1.44 nm to 2.87 nm after the modification, and the hydrophobicity performance was greatly improved. The organic modification of MMT was successful. The surface morphology, roughness, and anticorrosion properties of the organic montmorillonite/epoxy (OMMT/EP) composite coating were investigated and compared with those of the epoxy (EP) coating. The OMMT/EP composite coating had a flatter surface than the EP coating. The roughness was reduced from 65.5 nm to 10.3 nm. The electrochemical impedance spectroscopy showed that the composite coating’s thickness positively affected its anticorrosion performance, the corrosion current density (Icorr) decreased with the increase in thickness, and its maximum impedance was much larger than that of EP coating. The protection efficiency of the OMMT/EP composite coating was 77.90%, which is a significant improvement over the EP’s 31.27%. In addition, the corrosion resistance of the composite coating gradually decreased with increasing immersion time, but the change was insignificant.

Effect of inorganic anions on precipitation of desilication products based on low-temperature Bayer process

The effect of inorganic anion impurities in sodium aluminate solution on the composition, structure and micro-morphology of desilication products (DSPs) based on the low-temperature Bayer process was systematically investigated via XRD, FT-IR, SEM and PSD methods. The sodalites with chloride-type, carbonate-type and nosean-type precipitate in the presence of chloride, sulfate and carbonate in solution, and the aluminate ions in DSPs are partly replaced by the incorporation of anion impurities. The binding capability of sulfate to the DSPs cage is stronger than aluminate, chloride and carbonate. The particle size, agglomeration degree and thickness of the circular lamellar structure of DSPs are increased by rising the concentration of anion impurities. The anions enhance the dissolution of the zeolite framework and the formation of tetradentate rings in sodalite, which promotes the transformation of zeolite to sodalite.

Micelles and structural variation of the solution synergistically changing the viscosity of sodium aluminate solutions

Complicated organic behavior in the sodium aluminate solution limits the economical alumina production and improvement in alumina quality by Bayer process. Sodium gluconate (SG) or sodium stearate (SS) in sodium aluminate solution containing sodium oxalate (SO) changed the interfacial occurrence of anionic organics. The single anionic organic compounds or mixed organics initially decreased and then raised the viscosity of the sodium aluminate solution, and further increasing total organic carbon (TOC) remarkably increased the viscosity of the industrial sodium aluminate solution. Correspondingly, increasing concentration of anionic organic compound raised initially and then reduced diffusion coefficient. The minimum viscosity of the solution nearly occurred at the critical micelle concentration (CMC) of the anionic organic compound. Anionic organics also increased the viscous flow activation energy of sodium aluminate solutions. The disordered structure of sodium aluminate solution reduced the viscosity and increased the diffusion coefficient at low concentrations of organics less than CMC. Further increasing the concentration of organic compound more than CMC, micelles then contributed to the ordered structure of the sodium aluminate solution, increasing viscosity and reducing the diffusion coefficient of the sodium aluminate solution. Therefore, a large amount of micelles and the different solution structures synergistically changed the viscosity and diffusion coefficient of the sodium aluminate solution.

Effect of zinc(II) and caustic content on the decomposition of sodium aluminate solutions and relevance to the Bayer process

The impact of zinc (Zn) on the seed decomposition process of sodium aluminate solution at different caustic concentrations was investigated. The results showed that as the concentration of Zn(II) in sodium aluminate solution increased from 0 to 1000 mg/L, the decomposition efficiency of the solution and average grain size of the resulting aluminum tri-hydroxide (ATH) changed little at a caustic concentration of 141 g/L. At caustic concentrations of 160 g/L and 177 g/L, the decomposition efficiency increased from 35.8% and 21.6% to 40.6% and 24.9%, respectively, while average grain size of the ATH crystal seeds increased from 14.2 and 9.25 μm to 17.9 and 15.9 μm, respectively. The XRD, FT-IR, and SEM analyses showed that zinc can enter the ATH seeds and interact with the α-ATH crystal planes. It may also form interactions with the AlO octahedral growth structure, thus promoting solution decomposition and influencing crystal growth. The research results will provide valuable references for improving the quality of alumina products.

A new prediction method for sodium aluminate solution evaporation integrating process knowledge and data-driven spatial-temporal adaptive model

In alumina production, the evaporation as the key process uses recyclable resources and reduces environmental pollution. In fact, the quality of export product with offline and delayed, results in low precision of process control and high energy consumption. To ensure green and efficient production, in this paper, a new prediction method integrating process knowledge and data-driven spatial-temporal adaptive model is put forward. First, to preprocessed production data for ensuring modeling accuracy, data reconciliation technology is adopted. Then, based on material and heat transfer mechanism, for equipment and industrial process, the mechanism models are established. Furthermore, with time difference and moving window model, an error compensation method is utilized in terms of double locally weighted kernel PLS for estimation error in hypothesis-based mechanism modeling. Finally, the data-driven spatial-temporal adaptive model and the process knowledge-based mechanism model are integrated. To illustrate the model feasibility, an industrial sodium aluminate solution evaporation is used. It demonstrates that, for the developed model, the prediction accuracy can reach more than 90% within the ±2% error range, and effectively estimate the actual product quality and ensure the prediction effect.

The Corrosion Behavior of 12Cr1MoV and 16Mn Alloy Steel in Sulfur-Containing Sodium Aluminate Solution

The Corrosion Behavior of 12Cr1MoV and 16Mn Alloy Steel in Sulfur-Containing Sodium Aluminate Solution

Progressive methods of alkaline refining and bleaching of cottonseed oil

The article presents data from a study of the refining process of cottonseed oil, which differs from other vegetable oils in its complex composition and the presence of gossypol, which requires the use of alkali solutions (NaOH) of high concentration and in excess quantities. The use of magnetized solutions of sodium aluminate with a concentration of 15 to 25% has been proposed as an alkaline agent. Studies have shown that with the action of this reagent, a decrease in the acid number and color index of both press oil and oils obtained by extraction is observed.