Aluminate Solution Research Articles

From dolomite waste to katoite-based binder: Synthesis, performance and characterization

Calcium aluminate cement, in which katoite (KT) is the main binder, has garnered significant attention for its resistivity against aggressive environments. Despite its impressive durability, the production of this cement is costly and generates a substantial CO2 emission. Therefore, the objective of this study was to develop an eco-friendly KT-based binder using exchange reaction between sodium aluminate (NaAlO2) solution and dolomite waste powder. The performance of KT-binder was evaluated by measuring compressive strength, drying shrinkage, bulk density, and porosity. The phase composition and microstructural changes were also investigated by XRD, TG/DTG, FT-IR, and SEM/EDS techniques. The resulting hardened materials exhibited 28-day compressive strengths ranging from 5 MPa to 50 MPa and contained primarily katoite Ca3Al2(OH)12, along with pirssonite Na2CO3·CaCO3·2H2O, thermonatrite Na2CO3·H2O, and aluminum hydroxide Al(OH)3 phases. EDS mapping indicated that only a small amount of Mg2+ was present in the katoite phase, suggesting that the alkalinity and atomic radius difference between Ca2+ and Mg2+ were the main factors. Altering the content of concrete waste (CoW) in the cementitious system within the range from 10 to 50 wt% leads to an improvement in compressive strength and a reduction in both pore volume and drying shrinkage of NaAlO2-DW mixture. Conversely, perlite waste (PW) shows an opposite trend despite its high amorphicity. The presence of highly water-soluble thermonatrite, which is a byproduct of the cationic exchange reaction, is responsible for the low water resistivity of the prepared binder. As a result, more research is needed to tackle this problem.

Liquid matrix SHS manufacturing and heat treatment of Al–Mg composites reinforced with fine titanium carbide

Aluminum matrix composites reinforced with ultra-fine refractory titanium carbide feature a unique combination of properties. They are promising structural materials. Self-propagating high-temperature synthesis (SHS) is an affordable and energy-saving composite making process. It involves the exothermic reaction between titanium and carbon (or their compounds) directly in the melt. We studied the properties of SHS composites based on the AMg2 and AMg6 commercially available alloys reinforced with 10 wt.%TiC. We investigated the macroand microstructure of the samples with XRD and EDS analysis. It was found that the β-phase is separated from α-solid solution of aluminum as early as the air cooling stage. We conducted experiments aimed at studying the effects of additional heating on the sample structure and properties and found the optimal temperature and time values. We also proposed a phenomenological model of the structural transformation sequence. We compared the physical, mechanical, and manufacturing properties and corrosion resistance of the original cold-hardened AMg2N and AMg6N alloys and the composites before and after heat treatment. It was found that additional heating reduces porosity and maintains electrical conductivity. It was also found that the compressive strength and relative strain of the composite based on the AMg2 alloy change insignificantly, while for the AMg6-based composite the reduction is more significant. Heat treatment increases the composite hardness while maintaining sufficient plastic deformation. It is confirmed by the measured values of the relative strain and the reduction ratio close to that of the original matrix alloys. It was also found that the composites retain high resistance to carbon dioxide and hydrogen sulfide corrosion.

INVESTIGATION OF THE PHOSPHATE IONS ADSORPTION FROM ALUMINATE SOLUTIONS BY Fe-AС NANOCOMPOSITE

The adsorption of phosphate ions from model solutions by a nanocomposite based on trivalent iron oxide-hydroxide and activated carbon (Fe-AС) was studied. Factors studied affecting the adsorption of phosphate ions: solution pH; adsorbent amount; initial concentration of phosphate ions in solution; contact duration. The efficiency of phosphate ion extraction increased with increasing adsorbent dosage (from 2.5 to 10 g/l) with an initial concentration of phosphate ions of 0.1 g/l. Adsorption is well described by the Langmuir and Frendlich isotherms. The results of the work showed that the Fe-AС nanocomposite has a good potential for adsorption of phosphate ions from aluminate solutions, which was confirmed by SEM/EDS analysis.

Ab Initio Molecular Dynamics Study of the Proton Transfer in Hydroxyl Ion-Induced Hydrolysis of Aluminum Monomers.

The hydrolysis process of Al(H2O)63+ induced by hydroxyl ions (OH-) is significant to aluminum solution chemistry. Previous investigations of hydrolysis reactions have primarily relied on static calculations in an implicit solvent environment. Herein, we employ ab initio molecular dynamics (AIMD) to investigate the evolution process of Al(H2O)63+ under various local alkaline conditions in an explicit solvent environment. Our work demonstrates the effect of solvent water in hydrolysis reactions. Specifically, the stepwise hydrolysis reaction induced by hydroxyl ions involves water wire compression and concerted proton transfers. Dehydration reactions occur when the number of hydroxyl ligands attached to the aluminum ion (Al3+) equals or exceeds three. Moreover, the Al(H2O)n(OH)3 species exhibit unique hydrolysis and dehydration reaction characteristics compared to other species. The geometrically stable aluminum monomers determined by AIMD are Al(H2O)5(OH)12+, Al(H2O)4(OH)2+, Al(H2O)1(OH)3, and Al(OH)4-. In addition, the topological analysis analyzes the interaction between Al3+ and coordinated H2O in different configurations, indicating the weakest interaction appearing in Al(H2O)n(OH)3 species.

Surface treatment of inorganic modifier for improving carbonation resistance of geopolymers

Geopolymer (GP) is a low-carbon binder with the potential to replace Portland cement in reinforced concrete, however, the risk of corrosion to reinforced steel bars due to its low carbonation resistance must be addressed. This study proposed the use of an inorganic surface modifier, sodium aluminate solution (AN), to improve the carbonation resistance of GP. The effects of AN surface treatment on carbonation depths were investigated for GP mortars using fly ash (FA), ground granulated blast furnace slag (BFS), or their blend as active fillers. Rational AN surface treatment conditions and microstructural changes of treated GPs were also discussed. The obtained results show that AN surface treatment can significantly reduce carbonation rates of FA/BFS blend-based GP, and largely delay the onset of neutralization of heat-cured GP through the reduction of cracks and the formation of Na-gmelinite and gismondine, which refine the surface layer of GP. The surface modification using 40 wt%-AN solution reduced carbonation rate coefficient by about 70% for the FA/BFS blend-based GP cured at 80 ℃, and by above 30% for that cured at 20℃. The larger the FA blending ratio or the smaller the liquid-active filler ratio, the greater the improvement in carbonation resistance of FA/BFS blend-based GPs, caused by the AN surface modification. For the ambient-cured GP, repeated surface treatment is preferred, while for the heat-cured GP, once treatment is enough, and seal curing after the AN surface treatment is recommended regardless of the curing method.

Characteristics of product layer and effects of sulfur-bearing ions on pyrite leaching in sodium aluminate solutions

During the utilization of high-sulfur bauxite by the Bayer process, the pyrite will react with sodium aluminate solution and generate various sulfur-bearing ions, however, the effect of these ions on pyrite leaching is seldom studied. This work clarifies the reaction mechanism of pyrite in various sulfur-bearing sodium aluminate solutions by characterizing electrochemistry and the product layers. The results show that the sulfur leaching efficiency are 48.0, 56.2, 23.1, 90.6 and 58.3 % in sulfur-free, S2-, S2O32-, SO32- and SO42--bearing sodium aluminate solutions at 260 °C for 40 min, respectively. With the disproportionation of S2O32- and accumulation of products, a dense sulfur-rich layer formed on the surface of pyrite retards the diffusion of sulfur into solution. However, the presence of SO32- can catalyze the transformation of pyrite into hematite plates, forming a loose layer which accelerates the diffusion of S2- and S2O32- into solution. In the presence of S2- and SO42-, the formation of easily removed products from surface slightly promote the reaction between pyrite and sodium aluminate solution.

The influence of process parameters on the morphological characteristics of fine precipitated hydrate

<p>In this paper, the influence of process parameters on the morphological properties of fine precipitated hydrate was examined. The research was conducted with the aim of synthesizing fine precipitated aluminum hydroxide from the aluminate solution obtained by the Bayer process. Fine precipitated hydrates obtained in this way are mostly used in the non-metallurgical industry. The synthesized fine precipitated hydrate should comply with certain quality requirements such as granulometry (average particle diameter), purity, specific surface area, whiteness, etc. This paper shows the influence of certain technological parameters, namely the initial precipitation temperature, the amount and specific surface area of the seed, the influence of the NaOH/Al(OH)3 molar ratio on the characteristics of the synthesized fine precipitated hydrate in terms of the specific surface area, mean diameter and morphology of the obtained particles.</p>

Adsorption of Phosphate Ions from Aluminate Solutions on an Fe–AC Nanocomposite

Adsorption of Phosphate Ions from Aluminate Solutions on an Fe–AC Nanocomposite

Effect of temperature on N-A-S-(H) and zeolite composition, solubility, and structure

This paper investigates the effect of temperature on the composition, solubility, and structure of sodium aluminosilicate hydrate (N-A-S-(H)) and zeolite synthesized using sodium silicate and sodium aluminate solutions across a range of bulk aqueous Si/Al ratios at different temperatures. It was found that temperature had minimal effect on the composition for both N-A-S-(H) and zeolite species. A decrease in N-A-S-(H) and zeolite solubility with increasing temperature was observed and attributed to the temperature-dependent pH. As expected, the solubility of N-A-S-(H) was higher than that of its crystalline counterpart. Estimation of thermodynamic properties also revealed that for both the N-A-S-(H) and zeolite phases, the Van't Hoff expression yielded similar enthalpy and Gibbs free energy of formation data as a three-parameter Gibbs free energy model that includes a heat capacity term. An additional benefit of the Van't Hoff approach is that it obviates the need for estimating the heat capacity from reference reactions.

TECHNOLOGICAL FEATURES OF MANUFACTURING ALLOY AK7h STRENGTHENED WITH ZIRCONIUM INTRODUCED WITH ZIRCONIUM TETRAFLUORIDE

The paper considers the important features of the technology of strengthening AK7ch aluminum alloy with zirconium introduced with its tetrafluoride. The choice of a complex flux containing zirconium tetrafluoride in its composition is justified. It is indicated that in order to recover zirconium from its tetrafluoride in the aluminum melt, it is first of all necessary to ensure the formation of sodium or potassium fluorozirconate in the strengthening mixture. The mechanism of recovery of zirconium from tetrafluoride is presented. Technological recommendations for obtaining AK7ch alloy are given. It has been established that the complex flux intended to the alloy, which is modified, must be injected into liquid aluminum before the introduction of other alloying elements, namely silicon and magnesium. The maximum appropriate temperature for injecting zirconium into the aluminum melt from the complex flux is indicated. The maximum amount of zirconium that was recovered is 0.4%. The microstructure and mechanical properties of an alloy strengthened by zirconium from its tetrafluoride, which was injected into the alloy in the amount from 0.8 to 1.2%, were studied. As a result of the modification of aluminum alloy AK7ch with zirconium, the grains of silicon solution in aluminum (α-phase) are grind. No other structural changes are observed. The value of tensile strength and relative elongation of the alloy increases by 1.3 and 1.7 times, respectively.

A clean two-stage Bayer process for achieving near-zero waste discharge from high-iron gibbsitic bauxite

The current Bayer process focused on alumina extraction without considering the comprehensive utilization of other valuable components, such as iron, and the resulting red mud caused severe ecological and environmental safety risks. This work proposed a clean two-stage Bayer digestion technology to obtain iron-rich red mud with low Na2O content from high-iron gibbsitic bauxite processing. The effects of digestion conditions on alumina extraction rate and iron enrichment degree in red mud were studied systematically. The ICP, XRD, SEM, and TEM were used to investigate the chemical compositions, phase structures and microstructures of bauxite and red mud. Results show that approximately 83% Al2O3 was extracted, and about 43% SiO2 was separated simultaneously in gibbsitic bauxite in the first stage, whereas undigested aluminum-bearing minerals mainly originated from substituted aluminum in goethite. Hydrogen was produced by the reaction of glycerol with sodium aluminate solution in the second stage, which promoting the reaction of Al-goethite with titanium-bearing minerals to form Fe(Ⅱ) and Ti(Ⅳ)-substituted hematite. The increase in reductants amount, caustic alkali concentration, reaction temperature, and time favored Al-goethite transformation in digestion. The total Al2O3 recovery and the Fe2O3 in red mud could reach more than 99% and 86%, respectively. Moreover, the content of Al2O3, SiO2, and Na2O in red mud satisfied the iron ore concentrate standard of GB/T 36704-2018, which was attributed to avoiding the generation of desilication products (DSP) in red mud. The 93% silicon could be removed from the liquid phase by two separations of the digested slurry. This work will facilitate the large-scale reduction of red mud discharge through further the value-added use of novel red mud technology in collaboration with steel and aluminum, achieving the green and sustainable development of the alumina industry.

Mechanical and corrosion-resistant coatings prepared on AZ63 Mg alloy by plasma electrolytic oxidation

Using the plasma electrolytic oxidation (PEO) process conducted in galvanostatic mode at a constant current density of 0.2 A/cm2 in aqueous aluminate, silicate, and phosphate electrolytic solutions, we successfully produced magnesium oxide coatings (up to 182 μm) on AZ63 alloy. Structural, chemical composition, and morphological evaluations of the coatings were investigated by XRD, XPS, and SEM. The results indicated that mixed-crystalline magnesium oxide grown on pure AZ63 alloy forms porous 8–30 μm PEO layers with increased hardness and improved corrosion resistance. At the same time, values of 26.9 GPa and 2.0 μA/cm2 yield noticeable performance characteristics.

New strategies for the removal of template from the ion and molecularly imprinted polymers: Application to the fast and on-site Cr(VI) detection with a smartphone

The extraction of templates from MIPs is not an easy task as well known, because of the high affinity between monomers and templates. Herein, a new strategy for the immediate removal of the template was developed. Two polymers were prepared, one for hexavalent chromium (Cr(VI)) and the other for rutin molecule, to overcome the extraction problem for ions and molecularly imprinted polymers. A diphenylcarbazide solution was used for removing Cr(VI), allowing an immediate extraction of this ion from the polymer. For rutin molecule, the aluminum solution allowed fast removal. Since these removal strategies imply extracting with coloration development, these elution solutions could be used simultaneously for the extraction and detection of the analyte. Indeed, an analytical reading kit has been 3D-printed for the Cr(VI) smartphone detection. In this tool, a column containing the ionic imprinted polymer (IIP) was used as sorbent and diphenylcarbazide solution for eluting and detecting Cr(VI). The developed sensor exhibited a detection limit of 0.006 µg mL-1. The proposed procedure was applied successfully for Cr(VI) determination in tap and river waters showing satisfactory recoveries. These extraction methods pave the way for the application of other ligands for the gentle, fast and on-site removal of different templates.

Passivation and pH-Induced Precipitation during Anodic Polarization of Steel in Aluminate Electrolytes as a Precondition for Plasma Electrolytic Oxidation

Potentiodynamic and potentiostatic polarization tests in the potential range between open circuit potential (OCP) − 0.1 V and OCP + 4 V were carried out in aluminate–phosphate electrolytes with an aluminate concentration of 0.2 mol/L and varying phosphates contents between 0 and 0.1 mol/L. The pH was adjusted between 11.5 and 12.0 due to phosphate and optional KOH addition. A high-strength, dual-phase steel, which is relevant for lightweight construction, served as the substrate material. The layer microstructure was investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy and Raman spectroscopy were used for element and phase analyses. We found that iron hydroxides or oxides are initially formed independently of the electrolyte composition at low potentials. At around 1 V vs. standard hydrogen electrode (SHE), the current density suddenly increases as a result of oxygen evolution, which causes a significant reduction in the pH value. Precipitation leads to the formation of porous layers with thicknesses of 10 µm to 20 µm. In the case of a pure aluminate solution, the layer mainly consists of amorphous alumina. When adding phosphate to the electrolyte, the layer additionally contains the hydrous phosphate evansite. At the highest phosphate content in the electrolyte, the highest P content and the most pronounced crack network were observed.

Inhibition of aluminum silicate scaling by phosphonate additives under geothermal stresses

The formation, precipitation, and deposition of so-called “aluminum silicate” in geothermal waters have been subjects of intense interest. Such scaling poses a severe threat to the smooth process of any water-supported industrial system that utilizes water that is high in both aluminum and silicate. The aim of our approach is the systematic study of the influence of phosphonate-based chemical additives on silica polycondensation chemistry in the presence of aluminum ions. The focus of this work is the prevention of “aluminum silicate” formation using a variety of well-known phosphonate additives. These are: 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), hydroxyethylidene-1,1-diphosphonic acid (HEDP), amino-tris(methylenephosphonic acid) (AMP), hexamethylenediamine-tetrakis(methylene-phosphonic acid) (HDTMP), diethylenetriamine-pentakis(methylene phosphonic acid) (DTPMP) and bishexamethylenetriamine-pentakis(methylenephosphonic acid) (BHMTPAMP). Inhibition experiments were carried out in solutions of silicate (150 ppm, expressed as SiO2) and aluminum (a variety of concentrations, as Al) at pH 7.0. The phosphonate additives used were found to act as stabilizing agents, most likely by complexing the Al3+ cations and, thus, preventing “aluminum silicate” formation. On the basis of a plethora of experimental data, a number of useful functional insights have been generated, which add to building a more complete and comprehensive picture of the mechanism of “aluminum silicate” formation and stabilization.

Nanotwin stability in alloyed copper under ambient and cryo-temperature dependent deformation states

Nanometer size grains, solid solution strengthening, low temperatures, and a high density of nanotwins can provide significant strengthening to a material. Nevertheless, under loading the microstructure may evolve altering the effect of grain size, twin density, etc. on this strengthening. In some cases, these effects can be coupled as in detwinning, which is a mechanism for cryogenic grain growth. In this work, a series of copper nanotwinned columnar grains are solid solution alloyed with aluminum and subject to ambient and cryogenic (−196 °C) environments during mechanical indentation, with the influence of alloying on the detwinning evolution studied. Under indentation, at a lower aluminum solute content (2 at.%), the columnar grains bent corresponding to a loss of twins. At a higher aluminum solute content (8 at.%), the grains shear and retain the nanotwins. Atomistic-scale simulations reveal an increase in the incoherent twin boundary velocity with decreasing temperature, but this boundary velocity is reduced with increasing alloy solute content. The coupling of solid solution strengthening and nanotwin stabilization is then used to explain the microstructural stability as a function of indentation at different temperature conditions.

Mechanochemical modification of tin bronzes with intermetallide Cu9 Al4

The influence of the conditions of mechanical activation of a mixture of Cu–12 wt. % Sn with different content of the modifier Cu9 Al4 on the structural-phase composition and morphology of the formed composites was studied by the methods of X-ray diffraction analysis, optical and electron microscopy. With the mechanochemical introduction of 10 wt. % of the modifying additive into the matrix of mechanosynthesized tin bronze, the product mainly forms a ternary solid solution of aluminum and tin in copper, Al0.05Cu0.9Sn0.05. In the case of 20 wt. % of the modifying additive, the product contains a solid solution of tin in copper Cu0.9Sn0.1 and an intermetallic compound Cu9 Al4. Studies of the mechanical and tribotechnical characteristics of the material obtained by sintering under pressure showed that the intensity of wear of bronze of the mechanochemically synthesized powder Cu–12 wt. % Sn is slightly less than that of industrial bronze BrTPh10-1, the friction coefficient f decreases by a factor of 1.4, and the range of its values is quite wide f = 0.7–0.9. Modification of mechanically synthesized Cu–12 wt. % Sn bronze with the Cu9 Al4 intermetallic compound makes it possible to reduce wear by a factor of 1.4–1.8 and significantly reduces the friction coefficient (by a factor of 2). A stable value of f = 0.5 is achieved for the MA composition Cu–12 wt. % Sn + 20 wt. % Cu9 Al4. The introduction of an intermetallic compound increases the microhardness of the alloys by a factor of 1.6–2.0 (up to Hμ = 2730 MPa) relative to the bronze alloy BrTPh10-1and mechanically synthesized bronze.

The Influence of Production Technology on the Structure and Mechanical Properties of Niobium–Silicon–Aluminum Alloys

Cast Nb–14 at % Si–9 at % Al alloys fabricated by self-propagating high-temperature synthesis (SHS) and by SHS followed by electric arc remelting have been investigated. A structure consisting of a solid solution of silicon and aluminum in niobium (NbSS), a Nb3Al intermetallic compound, and a β-Nb5(Si,Al)3silicide formed in the alloy fabricated by SHS. Electric arc remelting suppressed the formation of the Nb3Alphase and resulted in the formation of a dispersed two-phase NbSS and β-Nb5(Si, Al)3 structure in the alloy.The increased volume fraction of NbSS and the dispersed structure formed after electric arc remelting in thealloy increase its fracture toughness to 14.8 ± 0.8 MPa m1/2 compared to 7.7 ± 0.8 MPa m1/2 for the SHSpreparedalloy.

Decision Support for Lake Restoration: A Case Study in Swedish Freshwater Bodies

A considerable number of lakes in Sweden have high phosphorus internal loading from the sediments which cause cyanobacterial blooms every summer. Due to potential risks with such blooms for human health, drinking water supply, and ecosystem services, measures need to be taken to control the phosphorus content. Measures to control the phosphorus input from the surrounding land has been in focus. However, the measures have not been sufficient. This is because phosphorus deposited at the bottom of the lakes for many years are finally starting to leak to the water phase when the decomposition of sediments leads to anoxic conditions. In order to determine effective and efficient lake restoration measures, methods for lake restoration decision support by a multi-criteria analysis and the application of a decision analysis are developed. The multi-criteria analysis includes the determination of costs, longevity, and efficacy of six common lake restoration measures to reduce internal phosphorous loads in two lakes selected as a case study. The results show that aluminum treatment combines a highest efficacy with a high-cost efficiency being thus the optimal identified measure. The method involves adding an aluminum solution to the lakes’ sediment, which binds phosphorus, preventing it to be released to the water column. The multi-criteria model is integrated to a decision analytical model. The decision analytical model is used to identify the monetary socio-economic and environmental boundaries for the implementation of the optimal lake restoration measure.

The effect of abrasive additives on the tribotechnical properties of lubricants for the wheel–rail system

The paper studies the polishing power of a tribochemically active abrasive material based on a solid solution of iron and aluminum oxides, as well as a solid solution of aluminum and iron oxides modified by zirconium oxide and yttrium oxide additives, and the tribotechnical properties of a lubricant doped with these abrasive materials. The modified Al2O3·Fe2O3·ZrO2·Y2O3 powders prove to have an essentially higher polishing power producing a considerably lower surface roughness than that of the unmodified Al2O3·Fe2O3 powder. By varying the content of the modifying oxides, one can change the tribochemical activity of the abrasive powder and select the best composition depending on the material to be polished. The addition of these abrasive powders is shown to have an essential effect on the tribotechnical properties of the lubricant for the wheel–rail contact. The laboratory testing of the lubricant compositions suggests their effective applicability to the wheel–rail contact.