Formation Of Bayerite Research Articles

Fabrication of new in‐situ ternary nano/microcomposite LDH/Ag2O/Bayerite in trimetallic NiAg/Al layered double hydroxides for CO2 capture material

AbstractWe reported new in‐situ ternary nano/microcomposite layered double hydroxides/Ag2O/bayerite in trimetallic NiAg/Al layered double hydroxides (LDH) via hydrothermal technique; and characterization by powder X‐ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT‐IR), field emission scanning electron microscopy (FE‐SEM), energy dispersive spectroscopy (EDS), and N2 adsorption‐desorption. The formation of bayerite and silver oxide species on the LDH nanosheet depended on the excess of Al3+ and Ag+ in the solution under alkaline and hydrothermal conditions. The nitrogen isotherm adsorption profile for all ternary composites exhibited uniformity with mesoporous and lamellar characteristics. The surface area of all the composites ranged from 81.17 to 150.23 m2. g−1, the Barret‐Joyner‐Halenda (BJH) pore volume from 0.22 to 0.27 cm3. g−1, and the average pore diameter ranged from 3.47 to 5.78 nm. All composites show a laminar plate‐like structure covered with elongated pieces. The particle size of the composites ranged from 54.86 to 115.96 nm, indicating the size changed from nano to microcomposite because of the different molar ratios of Ag and Ni in the solid. The ternary composite reveals CO2 capture activity with adsorption capacity ranging from 13.93 to 19.61 mmol g−1. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Al-Monohydrate (Boehmite) to Al-Trihydrate (Bayerite/Gibbsite) Transformation During High-Energy Milling

The specific focus of this study is on the boehmite–water interaction during attrition milling of a boehmite prepared by thermal dehydroxylation of gibbsite. Various characterization studies confirm the formation of a new phase, bayerite (an Al-trihydroxide polymorph) during milling of boehmite with water as the dispersant. Bayerite is a more stable (thermodynamically) phase than boehmite. By forming bayerite, the free energy of the interacting system (consisting of disordered metastable boehmite and water) gets reduced. Such a transformation is of relevance in the digestion of Al-monohydrates in the Bayer process of alumina production. Furthermore, the presence of water during attrition milling itself is essential for the transformation. Bayerite does not form during attrition milling of the same boehmite in ethyl alcohol media and subsequent soaking in water up to 36 hours. Therefore, bayerite formation does not depend solely on structural degradation.

Thermodynamic Modeling and Experimental Studies of Bayerite Precipitation from Aluminate Solution: Temperature and pH Effect

Bayerite is one of the phases of aluminum hydroxide which is precipitated by the carbonation of aluminate solutions obtained from sintered nepheline syenite leaching. In this study, the conditions for the bayerite formation were predicted by thermodynamic modeling of the carbonation process and the Bromley- Zemaitis model was used for this purpose. Carbonation experiments were carried out at pH 11 and the temperature range of 50- 90 °C based on the data obtained from thermodynamic modeling results. XRD analysis of products showed that bayerite was the predominant phase at all temperatures. SEM and LDS analysis indicated that the bayerite precipitates had uniform morphology and bimodal particle size distribution with mean particle size of 4.6 μm at 50 °C to 12.9 μm at 90 °C. It was found that the d50 increased slowly at the precipitation temperature ranging from 80 to 90 °C, from 12.6 to 12.9 μm and the effect of temperature was on the shape of particles. XRF analysis of the products indicated that the amount of Al2O3 and SiO2 in the bayerites decrease by increasing the temperature. According to the thermodynamic modeling data and experimental results, the temperature of 80 °C and pH 11 were determined as optimal conditions for bayerite precipitation.

Separate and simultaneous removal of doxycycline and oxytetracycline antibiotics by electro-generated adsorbents (EGAs)

In this paper, two Electro-Generated Adsorbents (EGAs) are presented as adsorbents of two antibiotics doxycycline hyclate (DCH) and oxytetracycline (OTC). The investigated adsorbents called EGANaCl and EGA NaNO3 were prepared by electrolysis in NaCl and NaNO3 electrolytes, respectively, using aluminum electrodes. The physical analyses showed that they were a mixture of AlO(OH) and three Al(OH)3 with bayerite as the main aluminum hydroxide. XRD, XPS and TGA studies ascertained the influence of NaCl and NaNO3 electrolytes towards the formation of bayerite and boehmite respectively in the alumina and, the possible EGA – antibiotic sorption through C 1 s peaks in the antibiotic laden EGAs. In view of industrial effluents and contaminated water bodies with a mixture of antibiotic compounds, the adsorption of OTC and DCH was studied from the three DCH – OTC mixtures (1:1, 1:0.5 and 0.5:1) despite from the respective aqueous solutions using batch methods. The compliance of three kinetic and five isotherm models was checked and discussed with respect to the sorption of antibiotic molecules.

The production of hydrogen as an alternative energy carrier from aluminium waste

BackgroundAluminium dross is a valuable resource that is often redirected to landfill as there are no real viable solutions for the utilisation of this industrial waste. A study has been conducted to provide a recycling process where the dross is reacted with an alkaline solution in order to generate hydrogen with bayerite and gibbsite products.MethodsSamples of aluminium dross were obtained from two sources: aluminium dross obtained from an aluminium recycling facility, recycled dross (RD) in Qatar and aluminous dross samples which were to be directed to landfill, landfill dross (LD), also in Qatar. Quantities of each sample were weighed in amounts that would contain equal amounts of aluminium reacting with an aqueous NaOH solution to generate hydrogen. The generated hydrogen has been analysed and compared with that reported in the literature.ResultsCertainly, the lower purity sample LD was treated at a lower standard than the recycled dross. The LD and RD samples generated 0.15 and 0.5 g/l Al, respectively, with the landfilled dross achieving a maximum flow rate of 0.8 l/min compared to an RD which generated hydrogen at 2 l/min.The results proved that both forms of aluminium dross possess the potential to provide an acceptable volume of hydrogen at relatively consistent flow rates. The RD sample provided higher flow rates, and the LD sample generated hydrogen at a lower but consistent flow rate for a longer period and at a volume rather close to that of the RD sample. XRD analysis of the resulting product also yielded promising results with the formation of bayerite and gibbsite, which would provide additional side products of market value; if this process will be conducted on a larger scale.ConclusionsThis study has shown very promising results, with both dross samples allowing for an acceptable production of hydrogen. It has shown that the utilisation of dross can be a potentially economically viable process for a product that provides clean, renewable energy and residual aluminous products of a real market value.

Phase transition of Al-hydroxides during the alkaline dissolution of aluminum and their effect on $$^{99} {\text{MoO}}_{4}^{2 - }$$ 99 MoO 4 2 - adsorption behavior

The metastable isotope 99mTc is one of the most useful radioisotopes, widely used for nuclear imaging, diagnosis, and therapy. 99mTc is derived from its mother isotope, 99Mo, by alkaline dissolution of neutron-irradiated UAlx targets with Al cladding. For the effective separation of 99Mo from the solution, the formation of Al-hydroxides should be avoided during the dissolution process because Al-hydroxides remove \(^{99} {\text{MoO}}_{4}^{2 - }\) ions by selectively adsorbing them from the solution. In this study, various conditions for the formation of Al-hydroxides were investigated from the alkaline digest of an Al6061 fake target. Controlled formation of two different phases of Al-hydroxides, gibbsite and bayerite, under different NaNO3/NaOH molar ratios in the dissolution solution was observed. In the solution of 4NaNO3·3NaOH, the gibbsite phase was more dominant than the bayerite phase. On the other hand, the bayerite phase was more favored in the 2NaNO3·1.5NaOH solution. The reaction time also affected the phase transition of the Al-hydroxides. With an increased reaction time, the formation of the bayerite was more promoted than the gibbsite. Additionally, the adsorption of \(^{99} {\text{MoO}}_{4}^{2 - }\) ions on both gibbsite and bayerite was characterized using ICP-AES. One gram of bayerite attracted up to 4.8 mg of Mo-ions, and this is significantly larger than the amount adsorbed on the gibbsite. This research focused on the optimal alkaline dissolution conditions to minimize the loss of \(^{99} {\text{MoO}}_{4}^{2 - }\) during the process. The formation of bayerite should be avoided by controlling the solution concentration, initial temperature, and reaction time.

Effects of Ni2+ on aluminum hydroxide scale formation and transformation on a simulated drinking water distribution system

Observations of aluminum containing sediments/scales formed within the distribution pipes have been reported for several decades. In this study, the effect of Ni2+ on the formation and transformation processes of aluminum hydroxide sediment in a simulated drinking water distribution system were investigated using X-ray diffraction spectrum (XRD), Fourier transform infrared spectrum (FT-IR), scanning electron microscope (SEM), and thermodynamic calculation methods. It was determined that the existence of Ni2+ had notable effects on the formation of bayerite. In the system without Ni2+ addition, there was no X-ray diffraction signal observed after 400d of aging. The presence of Ni2+, however, even when present in small amounts (Ni/Al=1:100) the formation of bayerite would occur in as little as 3d at pH 8.5. As the molar ratio of Ni/Al increase from 1:100 to 1:10, the amount of bayerite formed on the pipeline increased further; meanwhile, the specific area of the pipe scale decreased from 160 to 122m2g−1. In the system with Ni/Al molar ratio at 1:3, the diffraction spectrum strength of bayerite became weaker, and disappeared when Ni/Al molar ratios increased above 1:1. At these highs Ni/Al molar ratios, Ni5Al4O11⋅18H2O was determined to be the major component of the pipe scale. Further study indicated that the presence of Ni2+ promoted the formation of bayerite and Ni5Al4O11⋅18H2O under basic conditions. At lower pH (6.5) however, the existence of Ni2+ had little effect on the formation of bayerite and Ni5Al4O11⋅18H2O, rather the adsorption of amorphous Al(OH)3 for Ni2+ promoted the formation of crystal Ni(OH)2.

Forensic Investigation of Distressed Pavement Supported on a Base Course Containing Recycled Concrete Aggregate

The pressure for pavement and geotechnical engineers to incorporate sustainability into engineering projects has led to a rise in the use of recycled concrete aggregate (RCA) as fill and in pavement sublayers. Although the use of RCA has many economical, environmental, and engineering advantages, an oversight in quality control can lead to the use of contaminated RCA in the unbound layers. This can lead to premature deterioration that is costly to repair but, more important, can slow down the market acceptance of RCA. The authors forensically investigated an asphalt concrete pavement supported on a base course containing RCA and that had experienced a significant number of eruptions. Significant amounts of a white substance were found within the base course below each eruption. Sampling and testing showed the primary constituent of the substance to be bayerite, an unstable form of gibbsite, which could form when aluminum metal corroded in an alkaline environment. The adjacent ground topography would have encouraged drainage through the pavement site and thereby rendered the base course moisture susceptible to high alkalinity, because RCA in an aqueous solution has a high pH. Exposing aluminum metal to alkali in the laboratory to duplicate the field reaction confirmed the formation of bayerite. Moreover, exposing aluminum powder to an alkaline environment in a Geonor H-200 apparatus attained a maximum swell pressure of 430 kPa. When the pavement was numerically subjected to this swell pressure, the calculated deflections were found to be consistent with the observed pavement deflections and thus corroborated the hypothesized cause of distress. Suggestions are offered to avoid this type of distress.

An investigation of goethite-seeded Al(OH)3precipitation usingin situX-ray diffraction and Rietveld-based quantitative phase analysis

Anin situX-ray diffraction investigation of goethite-seeded Al(OH)3precipitation from synthetic Bayer liquor at 343 K has been performed. The presence of iron oxides and oxyhydroxides in the Bayer process has implications for alumina reversion, which causes significant process losses through unwanted gibbsite precipitation, and is also relevant for the nucleation and growth of scale on mild steel process equipment. The gibbsite, bayerite and nordstrandite polymorphs of Al(OH)3precipitated from the liquor; gibbsite appeared to precipitate first, with subsequent formation of bayerite and nordstrandite. A Rietveld-based approach to quantitative phase analysis was implemented for the determination of absolute phase abundances as a function of time, from which kinetic information for the formation of the Al(OH)3phases was determined.

Carbonate-Induced Structural Perturbation of Al Hydroxides

AbstractThe chemistry of Al transformation has been well documented, though little is known about the mechanisms of structural perturbation of Al precipitates by carbonates at a molecular level. The purpose of the present study was to investigate the structural perturbation of Al precipitates formed under the influence of carbonates. Initial carbonate/Al molar ratios (MRs) used were 0, 0.1, and 0.5 after aging for 32 days, then the samples were analyzed by X-ray absorption near edge structure spectroscopy (XANES), X-ray diffraction (XRD), Fourier-transform infrared absorption spectroscopy (FTIR), and chemical analysis. The XRD data were in accord with the FTIR results, which revealed that as the carbonate/Al MR was increased from 0 to 0.1, carbonate preferentially retarded the formation of gibbsite and had relatively little effect on the formation of bayerite. As the carbonate/Al MR was increased to 0.5, however, the crystallization of both gibbsite and bayerite was completely inhibited. The impact of carbonate on the nature of Al precipitates was also evident in the increase of adsorbed water and inorganic C contents with increasing carbonate/Al MR. The Al K- and L- edge XANES data provide the first evidence illustrating the change in the coordination number of Al from 6-fold to mixed 6- and 4-fold coordination in the structural network of short-range ordered (SRO) Al precipitates formed under the increasing perturbation of carbonate. The fluorescence yield spectra of the O K-edge show that the intensity of the peak at 534.5 eV assigned to σ* transitions of Al-O and O-H bonding decreased with increasing carbonate/Al MR. The XANES data, along with the evidence from XRD, FTIR, and chemical analysis showed clearly that carbonate caused the alteration of the coordination nature of the Al-O bonding through perturbation of the atomic bonding and structural configuration of Al hydroxides by complexation with Al in the SRO network of Al precipitates. The surface reactivity of an Al-O bond is related to its covalency and coordination geometry. The present findings were, therefore, of fundamental significance in understanding the low-temperature geochemistry of Al and its impacts on the transformation, transport, and fate of nutrients and pollutants in the ecosystem.

From mesoporous alumina to Pt/Al 2O 3 catalyst: A comparative study of the aluminas synthesis in aqueous medium, physicochemical properties and stability

In the present paper are compared the physicochemical properties and stability of mesoporous aluminas synthesized following five routes in which water is the solvent. TEM shows that high pHs lead to heterogeneous materials because of the initial formation of bayerite, which is converted to η-alumina upon calcination and may reappear upon contacting the calcined oxide with water. The most promising procedures use neutral organic additives at moderate pH; materials are homogeneous, with specific surface areas of 350 ± 20 m 2 g −1. The similarity of results obtained for the different routes, whatever the organic additive, suggests that the formation of the precipitated phase occurs not around micelles, but through the formation and sticking of boehmite nanoparticles, mediated by the organic agent present in a molecular form or as aggregates. The different ways to overcome the limits imposed by this mechanism are discussed. The alumina prepared with the addition of glucose is checked to be suitable as support for a Pt/Al 2O 3 catalyst prepared by impregnation with a basic solution.

Low Temperature Synthesis and Characterization of Zirconia Doped Alumina Nanopowder by Hydrothermal Process

Al2O3-ZrO2 composite precursor powder containing 5–20 wt% ZrO2 was prepared by hydrothermal method at a reaction temperature of 190°C and pressure 4 kgf/cm2. X-ray diffraction (XRD) of as-synthesized powder confirms the formation of bayerite and boehmite. The phases present in the powders calcined at 500°C and 800°C are α-Al2O3 and t-ZrO2. The Frontier Transform Infrared (FTIR) studies revealed the formation of α-Al2O3 in corroboration with X-ray studies. The transmission electron microscopy (TEM) analysis of the calcined powders at 800°C revealed the average particle size of alumina platelets is 60–70 nm in diameter and 10–15 nm in thickness whereas zirconia is observed as clusters of size 10–20 nm. Energy Dispersive Spectroscopy (EDAX) confirms the presence of alumina and zirconia particles.

Synthesis of aluminum oxides from the products of the rapid thermal decomposition of hydrargillite in a centrifugal flash reactor: III. Properties of aluminum hydroxides and oxides obtained via the mild rehydration of the products of the centrifugal thermal activation of hydrargillite

The interaction between the amorphous product of the centrifugal thermal activation of hydrargillite (CTA HG) and aqueous electrolytes (pH 5–11) under mild conditions (15–35°C, atmospheric pressure) has been investigated by a variety of physicochemical methods. This interaction causes material morphologic and phase changes in CTA HG, and the product composition is governed by the pH of the electrolyte and by the hydration temperature and time. The product that forms in a basic medium or water in <24 h contains up to 50% pseudoboehmite. Raising the pH or temperature or extending the hydration time results in the formation of bayerite as the major phase (∼80%). An X-ray amorphous hydroxide forms in acid media. The heat treatment of this hydroxide at 550°C yields aluminum oxides differing from alumina prepared via hydroxide reprecipitation. Products with new, unusual properties can thus be obtained.

Influence of Precursor Preparation via Ammonolysis Route on Alumina-Zirconia Nanostructure.

Al2O3-ZrO2 composite precursor was synthesized by introducing ammonia into a liquid mixture of ZrO2 sol and Al(NO3)3 aqueous solution. Precipitation of bayerite suggested a degradation in the dispersion of ZrO2 nanoparticles in the Al2O3 matrix during heat treatment. In order to avoid the formation of bayerite, it was preferred to produce a precipitation with a diluted NH3 water solution with NH3+N2 gas by controlling the hydration temperature and the NH3-adding methods. After suitable calcination and hot pressing, we successfully synthesized a uniform Al2O3-ZrO2 microstructure in which tetragonal zirconia particles of 30nm were finely dispersed within the alumina grains.

Mechanisms of Reaction of Hydratable Aluminas

The reactivities of four hydratable aluminas were investigated. Rates of heat liberation during hydration from 15° to 55°C were determined by isothermal calorimetry. Rates of heat evolution show two peaks. An initial mixing peak is due to wetting and initial dissolution reactions. A second, main heat peak is associated with the hydration step. The hydration product was bayerite in all cases. Although the specific surface areas for the aluminas studied were as high as about 260 m2/g, they did not react completely. The origin of incomplete reaction is related to the microstructure of the hydratable alumina grains. The particles are approximately 10 μm in size. High surface areas are not the result of small particle size, but are the result of high internal surface areas. The Bayerite formation appears to block the porosity in the grains, thereby inhibiting further reaction.

Formation of bayerite, gibbsite and boehmite particles by laser ablation

Aluminium hydroxides were prepared by the laser ablation method, a nanosecond pulsed laser being employed to irradiate an Al rod immersed in H2O solvent. Through the course of aging, bayerite, gibbsite and boehmite particles were formed simultaneously. These crystals exhibited three different morphologies. Their shapes were triangular (bayerite), rectangular (gibbsite) and fibrous (boehmite). The dimensions averaged several hundred nanometers. The measurements of the UV-vis absorption can serve as a tool to identify whether or not the crystalline particles had been obtained, in addition to the TEM images. A dissolution–recrystallization process was observed in the development of aluminous materials. The progression of formation from bulk Al to nano-aluminium hydroxides is discussed. Both basic and acidic conditions showed an influence on the growth of particles. The boehmite products can be generated solely by increasing the solution temperature.

Characterization of Mg-Saponites Synthesized from Gels Containing Amounts of Na+, K+, Rb+, Ca2+, Ba2+, or Ce4+ Equivalent to The CEC of the Saponite

AbstractSaponites were hydrothermally grown in the presence of amounts of NH4+, Na+, K+, Rb+, Ca2+, Ba2+, and Ce4+ equivalent with the CEC of the saponite (155 meq/100 g), with or without F−, at a temperature of 200°C for 72 hr. XRD and CEC data revealed the formation of a two-water-layer saponite with mainly Mg2+ as interlayer cation. Dehydration occurred between 25° and 450°C and dehydroxylation occurred in two steps between 450° and 790°C and between 790° and 890°C. The relatively small length of the b-axis between 9.151 and 9.180 Å is explained by considerable octahedral Al substitution (between 0.28 and 0.70 per three sites) and minor tetrahedral Al substitution (between 0.28 and 0.58 per four sites). Under the synthesis conditions applied in this study, less than 13% of the interlayer sites are occupied by Na+, K+, and Rb+; between 13.3% and 21% by Ca2+ and Ba2+; while NH4+ gives the highest value at 34%. The remaining sites are mainly filled by Mg2+. Ce4+ is not found in the saponite structure due to the formation of cerianite, CeO2. The presence of F− had little influence on the saponite composition. The formation of Mg-saponites is explained by a model in which an increased bayerite formation resulting in a higher octahedral Al3+ substitution and more Mg2+ in solution. Mg2+ is preferentially incorporated compared with the other interlayer cations due to its smallest ionic radius in combination with its 2 + charge.

Kinetics of the dehydration process of aluminium hydrate formed in the kaolin-aluminium powder system

The activation energy of the dehydration process of amorphous aluminium hydrate obtained by aluminium powder hydration ranges from 87 to 100 kJ mol −1. Different values of activation energy are the consequence of the degree of order in the metastable structure of amorphous aluminium hydrate. The resistance to the dehydration process increases when the structure is changing to a bayerite formation. The differences in the structure of the amorphous hydrate occur as a result of the variable conditions of hydrate formation.

Thermal Behavior of Alumina—Silica Xerogels During Calcination

Xerogels of 3Al2O3·2SiO2 mullite were prepared by hydrolyzing Al(NO3)3·9H2O and Si(OC2H5)4 solutions with pH values of 8.3, 9.4, 10.1, and 10.4; the xerogels were composed of a combination of singlephase and diphasic materials. A strong alkaline solution enhanced bayerite formation in the gels. Mullite from the diphasic xerogels was produced by reacting θ‐Al2O3 with amorphous SiO2, whereas mullite from the single‐phase xerogels was transformed from Al‐Si spinel. For the single‐phase xerogel, the DTA curve closely resembled the kaolinite‐to‐ mullite reaction. For the diphasic xerogels, the Al3+ ‐containing solution gelled to pseudoboehmite, which transformed to bayerite in solution. The bayerite then decomposed to η‐Al2O3 and to θ‐Al2O3 sequentially on heating.

Réhydratation d'oxydes d'aluminium amorphes. Application à l'étude de l'équilibre boehmite-bayérite

Prolonged grinding of aluminum hydroxides leads to the formation of amorphous aluminium oxide which presents a large specific area (200 m2/g) and a high reactivity. We have studied the rehydration of this oxide in contact with water or water vapour. At 25 °C, dissolution of the oxide is followed by bayerite precipitation. This allows calculation of the apparent solubility product and the free energy of formation of bayerite : — 1158.1 kJ/mole. The temperature of the boehmite/bayerite equilibrium is around 102 °C. Rehydration experiments in water vapour demonstrate the influence of water activity on the temperature of boehmite/bayerite equilibrium. They allow the calculation of the Gibbs free energy of formation of boehmite (— 917.1 kJ/mole) and the entropy of bayerite (68 J/K.mole). Boehmite can sometimes be co-precipitated with bayerite, probably in small pores of the solid where water molecules are tightly bound to the mineral surface.