Aluminate Ions Research Articles

Preparation of nanocrystalline aluminum hydroxide and alumina by thermal and vapor heat treatments of reaction products of terephthalic acid and aluminum hydroxide

We have studied the behavior of terephthalic acid (TPA) particles in sodium aluminate solutions. The results demonstrate that the addition of TPA to a solution at room temperature leads to appreciable TPA particle growth and the formation of amorphous aluminum hydroxide on the surface of the crystalline TPA floccules. With increasing initial aluminum concentration in solution, the interface displaces toward the central part of the floccules and an almost complete extraction of the dissolved aluminum is reached. The aluminate ion incorporation into the structure of TPA causes its conversion to an ionized form. In the resultant structure of amorphous aluminum hydroxide in TPA, the aluminum hydroxide crystallizes over time to form bayerite. Autoclaving in water vapor at 420°C produced boehmite ranging in crystallite size from 300 to 700 nm. Heat treatment in air for 2 h at 800°C leads to the formation of γ-Al2O3 in the form of spheres with a fiber length on the order of 300 nm and a thickness of 50–100 nm.

Effect of anodizing condition on corrosion resistance of Mg–Li–Y alloy

Effects of anodizing conditions on corrosion resistance of Mg–Li–Y alloy, which is most prominent super light alloy capable for easy deformation, were investigated with attention to the formation behavior and microstructure of anodic films. Barrier films or semi-barrier films were formed except at around 7 V and breakdown voltages similar to those associated with typical pure magnesium and AZ alloys. At the former voltages, thick porous type films were formed. The critical voltage of high current flow accompanied by breakdown was dependent on substrate composition; 45 V for Mg–Li–Y alloy, 60 V for 99.95% Mg and 120 V for AZ91D. When aluminate or phosphate ion was added in the electrolyte, the critical voltage of Mg–Li–Y alloy increased to 100 V. Lithium was highly enriched at the outer part of the film and yttrium was enriched in the middle to inner part when the film was barrier type. The ratio of barrier film thickness to anodizing voltage was as high as 4.25 nm/V compared to 1.9 nm/V of that associated with 99.95% Mg. When the film was porous type, the content of both lithium and yttrium decreased and distribution of both elements became uniform. Anodic films formed in sodium phosphate solution followed by sealing treatment in silicate exhibited sufficient corrosion resistance for practical usage.

Concentration variation of aluminate ions during the seeded precipitation process of gibbsite from sodium aluminate solution

The changes of aluminate ions in the Bayer seeded precipitation process were analyzed by the semi-quantitative FTIR analytical method and the ion structure of attached-liquid on the seed surface was determined using ATR-FTIR in order to investigate the gibbsite precipitation mechanism from sodium aluminate solution. The results show that the concentration of tetrahedral aluminate ions corresponding to the bands at 720 cm −1 and 880 cm −1 declines remarkably as the precipitation process proceeds, while the concentration of Al 2O(OH) 6 2− corresponding to the band at about 550 cm −1 increases slightly, suggesting that the gibbsite precipitation from sodium aluminate solution was mainly caused by the tetrahedral aluminate ions. The concentration of tetrahedral aluminate ions in the spent liquor declines with time, resulting in a reduction of the driving force of cluster formation of Al(OH) 4 −, which in turn leads to the reduction of the cluster size. Thus the clusters formed by Al(OH) 4 − could not get to the critical size to transform into Al(OH) 3 and consequently dissolve in the solution. So the rate of nucleation and growth is very slow in the late period of seeded precipitation and the content of Al(OH) 4 − in the attached-liquid on the aluminum trihydroxide surface remains constant.

Boehmite Dissolution Model Based on Simulant Data

Several of the Hanford waste tanks contain significant quantities of boehmite. This boehmite will be dissolved through caustic leaching as part of the Hanford Tank Waste Treatment and Immobilization Plant (WTP) currently under construction. Therefore, it is important to fully understand the nature of this dissolution process so that caustic leaching can be effectively deployed on the Hanford tank wastes. This research determined the impact of aluminate ion on the dissolution kinetics of boehmite. In addition, other parameters that impact boehmite dissolution, such reaction temperature, were also assessed and used to develop a semiempirical model of the boehmite dissolution process. A shrinking core model was used to fit data from a series of boehmite dissolution tests with an additional term added to account for the approach to saturation. This revised model provided an adequate fit to the experimental data; however, a superior fit to the experimental data was obtained when a term was added to represent t...

Heat capacities of aqueous sodium hydroxide/aluminate mixtures and prediction of the solubility constant of boehmite up to 300 °C

A modified commercial (Setaram C80) calorimeter has been used to measure the isobaric volumetric heat capacities of concentrated alkaline sodium aluminate solutions at ionic strengths from 1 to 6 mol kg −1, with up to 40 mol.% substitution of hydroxide by aluminate, at temperatures from 50 to 300 °C and a pressure of 10 MPa. Apparent molar heat capacities for the mixtures, C pϕ , derived from these data were found to depend linearly on the aluminate substitution level, i.e., they followed Young’s rule. These quantities were used to estimate the apparent molar heat capacities of pure, hypothetical sodium aluminate solutions, C pϕ (‘NaAl(OH) 4’(aq)). Slopes of the Young’s rule plots were invariant with ionic strength at a given temperature but depended linearly on temperature. The heat capacities of ternary aqueous sodium hydroxide/aluminate mixtures could therefore be modelled using only two parameters in addition to those needed for the correlation of C pϕ (NaOH(aq)) reported previously from these laboratories. An assessment of the standard thermodynamic quantities for boehmite, gibbsite and the aluminate ion yielded a set of recommended values that, together with the present heat capacity data, accurately predicts the solubility of gibbsite and boehmite at temperatures up to 300 °C.

Combined effect of amino and carboxyl group in α-alanine on seeded precipitation of sodium aluminate solution

α-alanine was adopted as a new additive to elucidate the seeded precipitation mechanism of sodium aluminate solution. α-alanine has the inhibitory effect at the initial period of reaction, but the favorable effect in subsequent reaction. The combined effect of amino and carboxyl group in α-alanine was confirmed by investigating the effect of propionic acid, ethamine and the mixture of propionic acid and ethamine (mole ratio 1:1) on the precipitation of sodium aluminate solution, respectively. The inhibitory effect derives from the adsorption of amino or carboxyl group in α-alanine on the active surface sites of gibbsite, which was confirmed by the alleviating inhibitory effects of propionic acid, ethamine and α-alanine due to the double crystal seed mass. The semi-quantitative IR spectrum analysis of the relative concentrations of Al 2O(OH) 6 2– with the band at about 550 cm −1 and polynuclear aluminate ion with the bands at about 880 cm −1 and 635 cm −1, indicates that the dynamic balance among some aluminate species present in sodium aluminate solution is broken due to the addition of α-alanine, thus resulting in the change of the seeded precipitation ratio of sodium aluminate solution.

Study of the ethanolic tributylmethylammonium aluminosilicate solutions using 27Al NMR

Alkaline solutions containing both silicate and aluminate ions are of considerable research interest inter alia because of their involvement in the synthesis of zeolites. In the present work, we use 27Al NMR to characterize alkaline aqueous and ethanolic tributylmethylammonium aluminosilicate solutions with different Al/Si ratios. Tributylmethylammonium (TBMA) used as a cation template and no alkaline metals are used for preparation of aluminosilicate solutions. Aluminum-27 NMR spectra of TBMA aluminosilicate solutions indicate that considerable changes occurred by changing the Si/Al ratio. The distribution of aluminosilicate species was affected by the presence of the methanol and the method of mixing the silicate and aluminosilicate solutions. To understand the reaction between silicate and aluminate ions in this system, the evolutions of 27Al NMR spectra with time are investigated.

Precipitation of Al(OH) 3 crystals from supersaturated sodium aluminate solution irradiated with ultrasonic sound

The influence of ultrasonic irradiation on precipitation of Al(OH) 3 crystals from supersaturated aluminate solution has been investigated under batch condition of isothermal crystallization. The results indicated that, the precipitation rate was greatly increased by ultrasonic irradiation. Compared with general process, the time of precipitation ratio from 0% to 45% was reduced about 15 h under the irradiation of 20 kHz, and also 33 kHz. The effect of ultrasound on the precipitation process varies with ultrasound frequency. Irradiation of 33 kHz ultrasound shortens the induction period and increases the second nucleation, while 20 kHz enhance agglomeration and growth of Al(OH) 3 which result in the increasing of the average diameter of final product by around 5 μm. Raman spectra and UV-absorbance analysis indicated that ultrasound is beneficial to the formation of sodium–aluminate ion pair, which will increase the decomposition rate of supersaturated aluminate solution.

Improved precipitation of gibbsite from sodium aluminate solution by adding methanol

A new method is explored to improve the precipitation of gibbsite from sodium aluminate solution by adding methanol to the pregnant liquor. The stability of sodium aluminate solution decreases in the presence of methanol, leading to faster crystallisation than the normal seeded precipitation process. The effects of methanol amount, caustic concentration, reaction time and temperature, stirring and feeding mode are systematically investigated. Considering possible industrial application, the optimum conditions are 1:1 volume ratio of methanol to sodium aluminate solution, ~ 170 g/L Na 2O and 1.55:1 caustic to aluminate ratio at 60 °C. The feeding mode and feeding rate have no significant effect on the final yield when moderately stirred. Under these conditions, 70% precipitation can be reached within 24 h, which is about 20% higher than the Bayer seeded precipitation practice of at least 56 h. Characterization of the crystals using XRD, SEM, and PSD shows a typical gibbsite phase composed of super-thin sheets with an average diameter of ~ 90 µm. IR and Raman spectra analyses suggest that added methanol captures water molecules from the aluminate ion hydration sphere thus catalyzing the crystallisation process.

Evaluation of optimal dose and mixing regime for alum treatment of Matthiesen Creek inflow to Jameson Lake, Washington

Churchill, J.J., M.W. Beutel and P.S. Burgoon. 2009. Evaluation of optimal dose and mixing regime for alum treatment of Matthiesen Creek inflow to Jameson Lake, Washington. Lake Reserv. Manage. 25:102–110. An innovative method of reducing external phosphorus (P) loading to lakes uses engineered systems to treat lake inflows with aluminum sulfate (alum). In this study we used a series of jar tests to examine the optimal alum dose and mixing regime to remove P from Matthiesen Creek, an important external source of P to Jameson Lake. Matthiesen Creek is a good candidate for alum treatment because the creek runs year round, and the majority of P in the spring-feed creek is in the form of bioavailable dissolved P that can be efficiently captured in alum floc. The mixing regimes in this study mimicked a range of possible treatment scenarios that relied on natural turbulence in the creek or conventional mechanical mixing, and presumed the discharge of alum floc either directly to the lake or to an on-shore settling basin. Jar tests showed that an alum dose of 5 mg-Al/L was sufficient to decrease P from around 0.13 mg-P/L to below 0.02 mg-P/L for most mixing regimes. For all mixing regimes, doses of up to 20 mg-Al/L did not depress pH below the recommended minimum pH of 6. Flash mixing prior to low-intensity mixing did not enhance P removal over low-intensity mixing alone, but flash mixing alone resulted in lower levels of P removal from creek water. Jar testing with a mixture of alum-treated creek water and lake water showed that lake waters tended to inhibit P uptake by alum floc. This, combined with the fact that high pH favors the formation of the aluminate ion which could exhibit chronic toxicity to aquatic biota, suggests that discharge of alum solids directly to the lake should be avoided. We recommend an engineered inflow treatment system on Matthiesen Creek that maintains an alum dose of 5–10 mg-Al/L under moderate mixing conditions (Gt of 1,000–3,000) with alum floc collected in an on-shore settling basin.

Utilization of NaCl for phillipsite synthesis from fly ash by hydrothermal treatment with microwave heating

The coal fly ash was treated hydrothermally with the mixture of NaOH aqueous solution and NaCl aqueous solution at 373 K, using the microwave heating and the conventional heating in order to clarify influences of the NaCl concentration in the hydrothermal solution on the growth rate and the crystalline phase of synthesized zeolites. As a result, it was found that phillipsite crystallinity of product powder increases with the additive NaCl concentration in the hydrothermal solution when the concentration of NaOH is so low as not to generate the zeolite from fly ash. On the other hand, in case that NaOH concentration is relatively high, the addition of NaCl to the hydrothermal solution using the conventional heating hardly affects phillipsite crystallinity of product powder; however, the generation of hydroxysodalite is enhanced by the microwave heating. Moreover, it was revealed that the necessary treatment time to complete the crystallization of phillipsite increases with increasing concentration of NaCl in the hydrothermal solution. This is because the substitution of NaCl for NaOH reduces the dissolution rate of aluminate and silicate ions from fly ash and the generation rate of the precursor aluminosilicate gel. However, this delay of the completion of the crystallization can be shortened by the microwave heating method. These experimental results concluded that the utilization of NaCl for the hydrothermal solution is effective in phillipsite synthesis from fly ash only when the NaOH concentration is relatively low in the hydrothermal solution and especially, when the microwave heating is used.

Participation of Aluminum Hydride in the Anodic Dissolution of Aluminum in Alkaline Solutions

The mechanism of anodic alkaline dissolution of aluminum was investigated through the analysis of cyclic voltammetry (CV) and potential step experiments. Attention was focused on the role of aluminum hydride as a reaction intermediate, as suggested by the recent detection of formation during open-circuit dissolution. Potential step experiments at pH 11.75 revealed that the potential at the metal–surface film interface was close to the Nernst potential of oxidation. This finding suggested a reaction mechanism in which an interfacial layer is formed continuously by reaction of cathodically formed H with Al, and is then oxidized to the dissolution product, aluminate ions. However, potential step experiments at pH 11 did not indicate the presence of interfacial ; instead, the metal–film interface was close to the equilibrium potential of Al oxidation. Analysis of the CV indicated an abrupt transition in dissolution behavior between the two pH values, from a relatively rapid dissolution controlled by diffusion and film conduction in highly alkaline solutions, to a slow dissolution at a lower pH controlled by a highly resistive surface film. The formation of interfacial occurs readily at the higher pH, but is suppressed as the pH approaches neutrality.

Surface Processes Accompanying Corrosion-Induced Hydrogen Absorption into Aluminum

The role of hydrogen-containing species in the alkaline dissolution of aluminum was studied by secondary ion mass spectrometry (SIMS). Large number densities of submicron particles nucleated and then disappeared during dissolution, at intervals of approximately 3 min. The particles were composed of aluminum hydride, with an aluminum hydroxide surface layer. When particles first appeared, the aluminate ion concentration near the surface was at the solubility of Al(OH)3, and the potential was close to the Nernst potential for oxidation of AlH3 to Al(OH)3. The observed formation of AlH3 indicates that the dissolving Al surface was poised near this equilibrium potential, i. e. that a hydride species serves as an intermediate in the dissolution process.

Spectra of sodium aluminate solutions

The UV spectra of sodium aluminate solutions were obtained in the sodium oxide concentration range from 59 to 409 g/L and the caustic ratio range from 1.5 to 4.0 to reveal the structure characteristics of them, It is found that a new peak appears at about 370 nm besides peaks at about 220 and 266 nm in all solutions. The new peak is strongly favored by high hydroxide concentration and high caustic ratio. And it only appears when the solutions are prepared by dissolving sodium hydroxide and aluminum hydroxide. In addition, the IR and Raman spectra of sodium aluminate solutions with high alkali concentration and high caustic ratio were measured, and the UV spectra of aqueous solutions of Al(H 2O) 3+ 6 and AlF 3- 6 were measured as well. According to the crystal field theory in coordination chemistry as well as the above spectra characteristics, this new peak at about 370 nm is determined as the evidence of a new species of aluminate ion with a coordination number of 6.

Selective electrochemical reactions of an alumina hydrate crystallization inhibitor

Selective reactions of catechol have been studied in regard to its inhibition properties towards alumina hydrate crystallization. Electrochemical reactions of the inhibitor leading to products without inhibition behaviour have been obtained using different conditions. First, a pure sodium hydroxide solution (1.0 M NaOH) was used to electrochemically react the catechol. The inhibitor reactions were then carried out in both saturated and supersaturated sodium aluminate solutions (NaAl(OH)4). Electrocatalytic hydrogenation (ECH) of the aromatic ring over rhodium-based catalysts leads to the saturated non-inhibiting molecule, 1,2-cyclohexanediol. Temperature shows no significant influence on the ECH process within the temperature range where the alumina hydrate crystallization is normally carried out. The presence of aluminate ions in solution has, however, a detrimental effect on the current efficiency. Electro-oxidation of the catechol produces muconic acid by cleavage of the carbon-carbon bound. It also produces other oxidation products and, eventually, may lead to total mineralization of catechol into carbonate, which is a less inhibiting molecule. A detrimental effect of the presence of aluminate on the electro-oxidation is also observed. Electrochemical techniques are proposed as new pathways for organic control in caustic medium.

Aluminium-27 NMR Investigation of the 2-Hydroxyethyl(trimethyl)ammonium Aluminosilicate Solution

Abstract Alkaline solutions containing both silicate and aluminate ions are of considerable research interest inter alia because of their involvement in the synthesis of zeolites. 27Al NMR spectra of alkaline aluminosilicate solutions generally show a maximum of five broad bands. In the present work, we use 27Al NMR to characterize aluminosilicate solutions with different Al/Si ratios using 2-hydroxyethyl(trimethyl)ammonium as a cation template, no alkaline metals are used for preparation of aluminosilicate solutions. To understand the reaction between silicate and aluminate ions in this system, the evolutions of 27Al NMR spectra with time are investigated.

Evidence for formation of metallo-siloxane bonds by comparison of dip-coated and electrodeposited silane films

It has been amply demonstrated that thin films of organofunctional silanes deposited by dipping or spraying on metals, such as aluminum, can provide protection against various forms of corrosion. In this paper we show that denser films with higher pore resistance and better corrosion protection performance can be obtained if the silane film is produced by electrodeposition rather than by dipping. In such a process the silane reacts with the metal oxide in a different way, and in the case of aluminum, aluminate ions seem to be incorporated into the silane film. The resulting films can protect aluminum alloys against uniform and pitting forms of corrosion in a salt solution for more than 1000 h, which is comparable to the standard chromate-based treatments. This paper discusses the protection mechanism in some detail. An important aspect of this work is that the use of XPS and TOFSIMS to analyze electrodeposited silane films provided direct evidence for the presence of O2Al(O–Si–O) and OAl(O–Si–O)2 groups at the silane–aluminum oxide interface. Such bonds have been suggested, but they have largely remained elusive over the years.

Interaction of Np(V), (VI), and (VII) with Aluminosilicates in Alkaline Medium

The behavior of Np in higher oxidation states in alkaline solution containing silicate and aluminate ions was studied. In formation of a crystalline aluminosilicate in a solution, Np(V), (VI), and (VII) are not incorporated into its crystal structure but hamper formation of the solid phase. The possibility of sorption of Np on various aluminosilicates is primarily governed by its oxidation state. Np(V) and Np(VII) are not sorbed from strong alkali. Np(VI) is retained by aluminosilicate materials to various extents depending on the surface characteristics and surface area of these materials. On heating, the degree of Np(VI) sorption decreases, which suggests the physical nature of the process.

The Lewis acid-base adducts of bismuth and aluminium trihalides — crystal structures of [Bi2X4][AlX4]2(X = Cl, Br)

AbstractThe reactions of BiCl3with AlCl3and of BiBr3with AlBr3yield [Bi2Cl4][AlCl4]21and [Bi2Br4][AlBr4]22in almost quantitative yield. The reactions were performed in closed, evacuated glass ampoules at temperatures of 240 °C and 200 °C, respectively. The colorless and yellow crystals are sensitive towards hydrolysis by moist air.1crystallizes in the monocline space groupP21/c(a= 7.7322(2) Å,b= 11.9565(3) Å,c= 10.3535(3) Å,β= 95.090(2)°,Z= 2),2crystallizes in the triclinic space groupP-1 (a= 7.693(2) Å,b= 7.706(2) Å,c= 9.739(2) Å,α= 104.19(2)°,β= 102.65(2)°,γ= 99.46(2)°,Z= 1). Both structures are made up of [Bi2X4] cations and [AlX4]–anions. The centrosymmetric cations consist of four membered Bi2X2rings with an additional halogen atom attached to each Bi atom in atransarrangement. The tetrahalogeno aluminate ions are almost regular tetrahedral. Although both compounds contain isomorphous ions, the structures of1and2are not isotypic. The different packing can be understood by abstracting both structures to simple AB2types.1adopts the PtHg2structure type with eightfold coordination of the cations whereas2adopts the MoSi2structure with tenfold coordination.

Effects of Sodium Hydroxide and a Chelating Agent on the Removal of Aluminum from Radioactive Sludge

:An essential step during the remediation of nuclear waste by the U.S. Department of Energy involves the separation of nonradioactive components such as aluminum from high-level waste sludges to minimize the ultimate volume to be stored in a nuclear waste repository. Plans for waste treatment at Hanford and the Savannah River Site include the use of 1 to 3m sodium hydroxide (NaOH) at an elevated temperature to leach the aluminum from the sludge. Triethanolamine (TEA) was added to caustic leaching solutions in an effort to improve the solubility of aluminum from authentic tank-waste sludge. High-level radioactive waste sludge with significant amounts of gibbsite and hard-to-dissolve boehmite phases was used in these tests. In concept, a chelating agent such as TEA can both improve the dissolution rate and increase the aluminum concentration in the liquid phase. However, TEA could also increase the solubility of other sludge components that are potentially problematic to downstream processing.Six tests were performed with leachate concentrations ranging from 0.1 to 3.0m NaOH, 0 to 3.0m TEA, and 0 to 2.9 m NaNO3. One test was performed using 3.0m NaOH at 80°C in order to simulate the baseline process, while the other tests were performed at 60°C. As expected, more aluminum entered the solution at 80 C than at 60°C when other test conditions were held constant. With caustic alone, equilibrium was achieved at both temperatures within 10 days. The addition of TEA significantly increased the concentration of aluminum in the leachate, and the aluminum concentration continued to increase even after 11 days of processing. The fraction of aluminum dissolved at 60°C increased from 35% using 3.0 in NaOH alone to 87% using a combination of 3.0 m NaOH and 3.0m TEA. The high-nitrate, low-hydroxide solutions did not significantly dissolve the aluminum because aluminate ion could not be produced. A small addition of TEA to these low-caustic solutions had no effect on aluminum removal.The use of TEA also increased the solubility of copper, nickel, and iron, which are only minor constituents. The TEA also had a significant effect on the solubility of the radionuclides 137Cs and 60Co. The significant presence of 137Cs in the leachates was expected with and without TEA. The high-nitrate leaches, which were the least effective of the leaching solutions, removed 69% of the 137Cs from the washed sludge, while a combination of 3.0m NaOH and 3.0m TEA removed 96%. Very little 60Co was removed from the sludge except with the use of the 3.0/h NaOH-3.0m TEA solution, which removed 53%. These results indicate that only TEA and 60Co need to be examined for potential chemical and radiological impacts, respectively, on downstream processes.