Hydrolysis Of Aluminum Research Articles

Aluminum speciation of coagulants with low concentration: Analysis by electrospray ionization mass spectrometry

Aluminum speciation of coagulants with low concentration was investigated in detail by electrospray ionization mass spectrometry (ESI-MS). In particular, comparison with 27Al nuclear magnetic resonance ( 27Al NMR) and Ferron colorimetric method for aluminum speciation of coagulants was discussed. The results indicated that various hydrolyzed aluminum species (monomeric, dimeric, trimeric and tetrameric aluminum species), which could not be identified by other methods, appeared in ESI-MS spectra. Thus, ESI-MS method was much better for hydrolyzed aluminum species in low concentration. In this paper, sample cone voltage was an important operating parameter during ESI-MS detection, and optimum voltage was 70 V. Too low (40 V) or high (150 V) sample cone voltage was not suitable for detecting all aluminum species. This study also evaluated the effects of coagulant concentration, aging, pH value and organic matter on aluminum species distribution. The results indicated that the distribution of hydrolyzed aluminum species at low concentration was largely dependent on the solution pH. At higher pH conditions, aging (8–12 h) may influence aluminum hydrolysis. Additionally, after adding salicylic acid into coagulant solutions, speciation and stability for both Al 13 species and aluminum–salicylate complexes varied significantly at different pH values.

Problems of designing fuel cell power plants for submarines

This article contains an analysis of the major problem related to the development of a power plant based on fuel cells for diesel-electric submarines – hydrogen storage/production. Various options of hydrogen storage/production have been studied. The analysis shows that hydrogen production based on hydrolysis of aluminium onboard the submarine seems to be promising. The article describes a block diagram of the developed plant for hydrogen production via hydrolysis of aluminium, and the test results of the full-scale prototype. The tests confirmed the possibility to create an efficient ship system for continuous hydrogen production based on hydrolysis of coarse-dispersed aluminium powder. As a result, hydrogen can be used in fuel cells of any type without purification, and the reaction product, that is boehmite, is commercially profitable.

Impact of Forming and Modification with Phosphoric Acid on the Acid Sites of HZSM-5

The individual and combined effect of phosphoric acid modification, the addition of an alumina-based binder, and steaming on the acid−base and catalytic properties of HZSM-5 have been investigated. Whereas all three processes reduce the concentration of Brønsted acid sites, the underlying mechanisms and the extent of the effects vary. Upon addition of an alumina-based binder or during steaming of the parent zeolite dealumination is the sole process occurring. Impregnation of HZSM-5 with phosphoric acid leads to hydrolysis of framework aluminum and to the condensation of Brønsted acid sites with POH groups. This latter process can be reversed in the presence of an aqueous phase. In the forming process, this leads to the reversible formation of phosphate anions and phosphoric acid and the redistribution of phosphate species between the zeolite and the alumina binder. This mobility is mitigated by introducing phosphate species to the (alumina) binder indicating that in aqueous phase equilibrium between phosphate ions and phosphoric acid the zeolite and the (alumina) binder exists. Whatever the first step of modification of the parent material is (doping with H3PO4 or addition of either alumina or phosphated alumina binder), steaming at elevated temperatures essentially reduces and equalizes the concentration of Brønsted acid sites. For all samples derived from one common parent zeolite, the rate of protolytic cracking of propane depends linearly on the concentration of strong Brønsted acid sites; that is, all modified materials have the same turnover frequency. This turnover frequency is notably higher than that of the parent material.

Effect of urea on the mullite crystallization

Due to its chemical, physical and mechanical properties, mullite has been used in equipments subjected to extreme mechanical strain and high temperatures. This paper reports the study of the effect of urea on the mullite crystallization, synthesized through the colloidal and polymeric sol–gel processes, using XRD and FT-IR. The colloidal precursors were obtained from silicic acid, water, aluminum nitrate nonahydrate (ANN) and urea. The polymeric precursors were obtained from TEOS, ethanol, ANN and urea. For both methods, urea was used in the molar ratio urea/Al 3+ equal to 0/1, 1/1 and 3/1. The urea addition in colloidal gels led to materials with higher concentrations of orthorhombic mullite, besides they crystallized mullite at lower temperatures (positive effect). However, a negative effect was observed when urea was added to polymeric gels. In addition, the amount of crystallized mullite increased with the urea content in the colloidal gels. The colloidal sample with the highest urea content proved to form mullite at a lower temperature. Moreover, this sample did not segregate the α-alumina phase. The positive effect of urea in the colloidal gels is related to its participation in the hydrolysis and condensation steps of aluminum and silicon, avoiding the extensive phase segregation of silica and alumina. The negative effect observed in the polymeric samples may have occurred due to a competition between the silanol, the ANN and urea by water molecules. The only water molecules that are present in the polymeric gel are those that are part of the ANN.

Hydrolysis and Speciation of Al Bound to Pectin and Plant Cell Wall Material and Its Reaction with the Dye Chrome Azurol S

Hydrolysis of aluminum (Al) in solution increases at pH >or= 4 and with an Al concentration. Pectin, an important anionic polysaccharide of plant cell walls, adsorbs Al, but this phenomenon is poorly understood. This study showed that Al(3+) hydrolysis results in binding of Al to pectin in excess of the stoichiometric equivalent, leading to oversaturation of the pectin with Al. However, the degree of pectin methyl-esterification did not affect the extent of Al hydrolysis. Binding of Al to purified cell wall material also resulted in Al hydrolysis in a pH- and soluble Al concentration-dependent manner, but the source of cell wall material had no effect at fixed pH. Staining of Al-treated pectin and cell wall material from wheat ( Triticum aestivum L.) and sunflower ( Helianthus annuus L.) with the Al-specific dye, chrome azurol S (CAS), resulted in the formation of a purple color, with the intensity related to the extent of Al hydrolysis.

Research of some physicochemical properties of basic aluminum sulfates

Properties of hydroxoaluminum sulfates produced by autoclave hydrolysis of aluminum containing sulfuric acid solutions in the absence and presence of ammonium sulfates.

Rapid synthesis of aluminium polycations by microwave assisted hydrolysis of aluminium via decomposition of urea and preparation of Al-pillared montmorillonite

The aim of this work is to provide a new efficient method of preparation of aluminium polycations/oligomers, and especially [AlO 4Al 12(OH) 24(H 2O) 12] 7+ (Al 13). The microwave assisted forced homogeneous hydrolysis of aluminium through breakdown of urea (M–Al–Urea) is studied and compared with aluminum hydrolyzed with OH − ions (C–Al–OH). M–Al–Urea solutions are characterized by UV–Visible (‘Ferron’ kinetic assay) and 27Al NMR spectroscopies. Al 13-sulphate precipitated from M–Al–Urea and C-Al-OH solutions are studied by XRD, TGA and SEM. Al-pillared montmorillonites are prepared with M–Al–Urea solutions as pillaring agent and characterized by XRD, BET, SEM-EDS, TGA and ATR techniques. The advantage of M–Al–Urea solutions as pillaring agent when compared to C–Al–OH is highlighted in the present study.

Density functional theory study of the aluminium(iii) hydrolysis in aqueous solution

Supermolecule density functional calculations were performed on the hydrolysis of aluminum(III) and prediction of pK(a) in aqueous solution. The optimization results showed that the most stable structures for the first, second and third hydrolysis products were hexacoordinate, hexacoordinate and pentacoordinate, respectively. The different coordination geometries could easily transform into each other due to the small energy gaps (within 2.5 kcal mol(-1)). The calculated value of 4.6 for the first hydrolysis constant agreed well with the experimental value of 5.0. The results from the different thermodynamic cycles have been compared, which revealed that the cycle involving the solvation of H(2)O and H(3)O(+) could reasonably predict the first hydrolysis constant, while the other cycle involving the solvation of H(+) acquired a fairly good correlation of the hydrolysis reaction free energies and the experimental pK(a).

Preparation of high concentration polyaluminum chloride with high content of Alb or Alc

A novel membrane distillation concentration method was used to prepare high concentration polyaluminum chloride (PACl) with high content of Alb or Alc. 2.52 mol/L PACl1 with 88% Alb and 2.38 mol/L PACl2 with 61% Alc were successfully prepared. Three coagulants, AlCl3, PACl1 and PACl2 were investigated on their hydrolysis behavior and speciation under different conditions. The effects of pH and dilution ratio on Al species distribution were investigated by ferron assay. Experimental result showed that pH had a significant effect on Al species distribution for the three coagulants. Dilution ratio had little effects on Alb and Alc distribution in whole dilution process except the beginning for PACl1 and PACl2. The results indicated that transformation of Al depends largely on their original composition. AlCl3 was the most unstable coagulant among these three coagulants during hydrolysis process. PACl1 and PACl2 with significant amounts of highly charged and stable polynuclear aluminum hydrolysis products were less affected by the hydrolysis conditions and could maintain high speciation stability under various conditions.

Density Functional Studies of the Hydrolysis of Aluminum (Chloro)Hydroxide in Water with CPMD and COSMO

Car-Parrinello molecular dynamics (CPMD) and the static density functional method (DFT) with a conductor-like screening model (COSMO) were used to investigate the chemistry of aluminum (chloro)hydroxide in water. With these methods, the stability, reactivity, and acidic nature of the chosen chlorohydrate were able to be determined. Constrained molecular dynamics simulations were used to investigate the binding of chlorine in an aquatic environment. According to the results, aluminum preferred to be 5-fold-coordinated. In addition, the activation energy barriers for the dissociation of chlorine atoms from the original chlorohydrate structure were able to be determined. The actual values for the barriers were 14 +/- 3 and 40 +/- 5 kJ mol (-1). The results also revealed the acidity of the original cationic dimer. DFT with COSMO was used to determine free energy differences for the reactions detected in the molecular dynamic simulations. In conclusion, new results and insight into the aquatic chemistry of the aluminum (chloro)hydroxides are provided.

Coagulation characteristics of polyaluminum chlorides PAC-Al 30 on humic acid removal from water

Coagulants polyaluminum chlorides with a high Al 30 content (PAC-Al 30) were prepared in laboratory, and the aluminum hydrolysis ratios ( B = [OH −]/[Al 3+]) of PAC-Al 30 were 1.2, 1.8 and 2.4 respectively. Coagulation behaviors of PAC-Al 30 with different B values and conventional coagulant AlCl 3 were compared by jar test to remove humic acid (HA) from water. Floc growth, charge neutralization capacity, HA removal and residual aluminum concentration in the purified water were investigated. The influences of initial pH and coagulant dosage on coagulation behaviors were considered. The results show that coagulants PAC-Al 30 exhibit much stronger floc formation capacity, have broader effective dosage range and initial pH range, reach higher HA removal efficiency, and get lower residual aluminum concentration than AlCl 3 does. The coagulation/flocculation capacity of PAC-Al 30 increases with the B value. The HA removal reaches 98.5% at an initial pH of 7.0 and PAC-Al 30 ( B = 2.4) dosage of 0.16 mmol L −1 (total aluminum concentration, Al t) when the initial HA concentration is 10 mg L −1; the residual aluminum in the purified water is 0.066 mg L −1. Al 30 is verified as highly efficient coagulation/flocculation species for HA removal.

Effects of low temperature on coagulation of kaolinite suspensions

In this study, coagulation of kaolinite suspensions at low temperatures is compared with that at an ambient temperature of 22 °C, and the process is examined with regard to the coagulation rate (CR) and chemical aspects of coagulation. Experiments using a photometric dispersion analyzer (PDA) show that coagulation of kaolinite suspensions can be taken as a two-phase process. Low temperature greatly reduces the CR of the first phase but not that of the second one. On the other hand, results show that low temperature did not serve to impede the hydrolysis of aluminum [Al(III)] within 1 min of alum addition. The measurements of electrophoretic mobility (EM) indicate that destabilization of kaolinite particles by hydrolyzed Al species was not hindered by low temperature within 1 min of alum addition. Slow coagulation at low temperature is due to the lowered CR but not the altered chemistry aspect of Al(III). Furthermore, the change in settled turbidity after 20-min flocculation as a function of coagulant dosage was more severe in the cold because of the low CR. Elongating floc-growth time, as observed, was able to counterbalance the retarded CR at low temperature and improve turbidity removal efficiency.

Effects of low temperature on aluminum(III) hydrolysis: Theoretical and experimental studies

In this study, the effects of low temperature on aluminum(III) (Al) hydrolysis were examined both theoretically and experimentally by constructing a solubility diagram for amorphous aluminum hydroxide (Al(OH)3(am)) and a distribution diagram of hydrolyzed Al species. First, thermodynamic data of Al species at 4 degrees C were calculated from that at 25 degrees C. A well confirmed polymeric Al species, AlO4Al12(OH)24(7+)(Al13), was involved in building the diagrams and, correspondingly, the non-linear simultaneous equations with 13 degrees were resolved. Secondly, polarized Zeeman atomic absorption spectrophotometry (AAS), 27Al nuclear magnetic resonance (NMR) spectroscopy, and ferron-based spectrophotometry were applied for constructing the practical diagrams. The results show that a decrease of temperature from 25 to 4 degrees C caused the Al(OH)3(am) boundary on the solubility diagram to shift toward the alkaline side by about 1.0 pH unit and the minimum solubility of Al(OH)3(am) to reduce by 1.0 log unit. The distribution diagram indicates that the monomeric Al, Al13, and solid-phase Al(OH)3 were alternately the predominant species with the increase of pH value during Al hydrolysis. At 25 degrees C, Al13 was the dominant species in a pH range of 4.0 to 4.5, whereas at 4 degrees C, All3 was the leading species in a pH range spaced from 4.5 to 6.3. The predominant species changed from the monomeric Al to the solid-phase Al(OH)3 over the range of 1.8 pH units at 4 degrees C in comparison with the range of 0.5 pH unit at 25 degrees C.

Enhanced coagulation for high alkalinity and micro-polluted water: The third way through coagulant optimization

Conventional coagulation is not an effective treatment option to remove natural organic matter (NOM) in water with high alkalinity/pH. For this type of water, enhanced coagulation is currently proposed as one of the available treatment options and is implemented by acidifying the raw water and applying increased doses of hydrolyzing coagulants. Both of these methods have some disadvantages such as increasing the corrosive tendency of water and increasing cost of treatment. In this paper, an improved version of enhanced coagulation through coagulant optimization to treat this kind of water is demonstrated. A novel coagulant, a composite polyaluminum chloride (HPAC), was developed with both the advantages of polyaluminum chloride (PACl) and the additive coagulant aids: PACl contains significant amounts of highly charged and stable polynuclear aluminum hydrolysis products, which is less affected by the pH of the raw water than traditional coagulants (alum and ferric salts); the additives can enhance both the charge neutralization and bridging abilities of PACl. HPAC exhibited 30% more efficiency than alum and ferric salts in dissolved organic carbon (DOC) removal and was very effective in turbidity removal. This result was confirmed by pilot-scale testing, where particles and organic matter were removed synergistically with HPAC as coagulant by sequential water treatment steps including pre-ozonation, coagulation, flotation and sand filtration.

Synthesis and properties of thermostable γ-alumina prepared by hydrolysis of phosphide aluminum

A thermostable phosphor-containing γ-alumina was prepared by hydrolysis of phosphide aluminum and the properties were investigated. The phase structure and thermal stability were studied by X-ray diffraction and transmission electron microscopy. The results showed that the alumina crystal was nano-particle and had high α-phase transformation temperature and prominent thermal stability. After calcined at 1473 K for 3 h, the surface area of the alumina was 71 m2/g and the main phase was transition alumina. The results of infrared spectroscopy and X-ray photoelectron spectroscopy suggested that a few phosphors dispersed highly in the bulk of γ-alumina after calcinations at 773 K. Thus, the thermal stability of γ-alumina was promoted greatly. The increase of calcination temperature resulted in the phosphor migrating from the bulk of alumina to the surface. In addition, various intensities of Lewis acid centers were observed on the surface of the γ-alumina.

Template formation of aluminum–magnesium hydroxide nano-branches on linear poly(ethylene imine)

Linear poly(ethylene imine) (PEI) can self-assemble into fibrous aggregates composed of a crystalline core and a brush-like shell of ethylene imine (EI) segments, and thus can be used as “templates” to prepare a range of inorganic materials. To further illustrate the feasibility of this technique, an investigation of low-temperature formation of nanostructured aluminum–magnesium hydroxide (AMH) on linear PEI “templates” is described, and the corresponding reaction mechanism suggested tentatively. AMH nano-branches were formed after hydrolysis of aluminium and magnesium lactates on PEI, indicating the site-selective deposition process of AMH on surfaces of PEI. The technique reported in this paper could be potentially used to fabricate other nanostructured complex metal oxides.

Microstructure control of porous alumina film using aqueous sol containing poly(ethylene glycol)

To fabricate a porous and thick alumina film with large surface area on a substrate by a dip-coating technique, we prepared an aqueous sol containing poly(ethylene glycol) (PEG). The sol was prepared by hydrolysis of aluminum (III) isopropoxide with large amount of water and following peptization to colloidal particle from precipitate. The films were coated on the glass substrate by the dip-coating and then calcined at 500 °C. The maximum thickness of the film prepared by one-run dip-coating was ca. 1,000 nm. The film was an aggregate of alumina particles with a diameter of 30–50 nm and pores were interstices between the particles. The porosity of alumina film can be controlled in the range of 40–59% by changing PEG concentration in the dip-coating solution.

Aluminum speciation and thermal evolution of aluminas resulting from modified Yoldas sols

Aluminas resulting from sols prepared via a modified Yoldas procedure were studied with differential thermal analysis (DTA), differential thermal gravimetrie (DTG), 27Al nuclear magnetic resonance ( 27Al MAS NMR) and X-ray diffraction (XRD) concerning their thermal properties, aluminum speciation and phase content. Hydrolysis of aluminum- sec-butoxide in aluminum nitrate solutions allowed to prepare stable sols with varying NO 3 - / Al molar ratios, solids contents and pH values. Resulting sols contained different aluminum species including also Al 13 polycations. Sol preparation conditions also determined aluminum speciation in solid products obtained after thermal treatments of gels obtained from these sols. Al 13 polycations and AlO 5 species were found to play an important role for thermally induced transformation from amorphous products via eta-Al 2O 3 to alpha-Al 2O 3. Intermediately formed eta-Al 2O 3 promotes the phase transformation to alpha-Al 2O 3.

Effect of initial pH on the removal of humic substances from wastewater by electrocoagulation

This investigation deals with the effect of initial pH batch removal of synthetically prepared wastewater having high concentration of humic substances by electrocoagulation method using plate electrodes. The effects of initial pH on an electrocoagulation system may be twofold. These are distribution of aluminum hydrolysis product, transformation of humic substance related to the initial pH and finally the effects of the gel layer especially in high humic substance concentrations and high initial pH formed on the anode surface. It has been observed that initial humic substance concentration and initial pH are highly effective on the removal rate and efficiency. For example, in the range of 200–500 mg L −1, decrese in the removal efficiency was observed due to gel layer formation on the surface of the anode surface. This gel formation especially starts at an initial concentration of 120 mg L −1; thickness and effect of the layer increase as concentration increases. In order to prevent this gel formation, initial pH of the wastewater was adjusted to 5.0 and high removal efficiencies were observed. Thus, the system should be operated at low pH values (i.e. 5.0) at high concentrations.

Preparation and Characterization of Alumina Nanoparticles from Alkoxides and Na (AOT) Surfactant

Nanosized α-aluminum oxides have been prepared by hydrolysis of aluminum alkoxides using a sol-gel procedure. The Na(AOT) as a surface active agent was added into the alumina precursor solution to investigate the influence on size and morphology of alumina particles. The product phase was mainly boehmite with mean particle size of 20~30 nm. The crystal phases and morphology of the alumina nanoparticles were analyzed by X-ray diffractometry and by transmission electron microscopy, respectively. The TEM observations revealed that α-Al2O3 with about 80 nm spherical and hexagonal shapes was formed after calcination at 1200oC. The TG/DSC analyses were also done to determine the phase changes of alumina precursors from room temperature to 1200oC.