Hydrous Aluminum Research Articles

Adsorption of selenium on hydrous alumina

AbstractAdsorption of selenite (SeO) and selenate (SeO) on hydrous alumina (γ‐Al2O3) was studied using batch equilibrium experiments. pH, the single most significant parameter, affected both speciations of selenium (Se) and of surface hydroxo groups on alumina that, in turn, determined the extent of adsorption of the oxyanions. Adsorption of both anions could be described satisfactorily by the Triple Layer Model (TLM). In the presence of SO, Se (VI) adsorption decreased significantly. Fixed bed adsorbers of alumina with an empty bed contact time (EBCT) of 2 minutes or longer provided excellent removal of Se(IV) from dilute aqueous solutions in the pH range of 5 to 8 for a long period. Spent alumina beds were successfully regenerated with 0.25 percent NaOH solution followed by rinsing with deionized water and 0.05 M HCl. While two percent of alumina was lost per cycle on an average, the loss in adsorption capacity of regenerated alumina was insignificant.

FTIR Study on interfacial interactions between hydrated aluminium and polar groups in ethylene copolymers

AbstractBy means of reflection‐absorption infrared spectroscopy, interfacial interactions were studied between hydrated aluminium and two ethylene copolymers, poly(ethylene‐c‐butyl acrylate) (EBA) and poly(ethylene‐c‐acrylic acid) (EAA). The hydrated aluminium surfaces were obtained by immersion in boiling water, which produces a pseudo‐boehmite film consisting of aluminium oxyhydroxide. This films of the polymers were prepared on the substrates by solution casting. Owing to the relatively large surface area of the substrates after hydration, it was possible to obtain spectra only representing polymer interacting with the surface. For EBA, the carbonyl absorbance of the bulk at 1735 cm−1 was displaced to 1698 cm−1 at the interface, owing to an interaction with the hydroxy groups on the hydrated surface. For EAA, on the other hand, a carboxylate was observed at the interface with the hydrated surface. The carboxylate formation and the large displacement of the carbonyl in the case of EBA indicate that strong bonds are formed at the interface. This is also supported by the results of the adhesive strength for EBA, where the locus of failure was changed from adhesive to cohesive.

Phase composition analysis of hydrous aluminium oxides by thermal analysis and infrared spectrometry

A general method for determination of the phase composition of hydrous aluminium oxides by thermal analysis and infrared spectrometry, and determination of the transformation temperature of mixtures of Al(OH) 3 and AlOOH into α-Al 2O 3 are described.

Effect of montmorillonite on phosphate sorption by hydrous Al-oxides

Phosphate sorption by two hydrous oxides of aluminium was studied, as a function of pH and phosphate concentration, in the presence and absence of different amounts of montmorillonite. The clay had no effect on P sorption when the sorption values were independent of the amount of sorbent. When P sorption was dependent on the mass of sorbent, the clay was effective in eliminating such dependence. The results are explained in terms of the adsorption capacity of the clay in reducing the amounts of Al-hydrolysis species that are normally present in hydrous oxide suspensions, and are known to possess high affinities for phosphate in solution.

Sorption of dissolved organic carbon by hydrous aluminum and iron oxides occurring at the confluence of Deer Creek with the Snake River, Summit County, Colorado

Organic solute sorption by hydrous iron and aluminum oxides was studied in an acidic, metal-enriched stream (the Snake River) at its confluence with a pristine stream (Deer Creek). From 1979 to 1986, typically 40% of the dissolved organic carbon (DOC) was removed from solution by sorption onto aluminum and iron oxides, which precipitate as the two streamwaters mix. Upstream DOC concentrations, which increase during snowmelt, were identified as the most significant variables in a multiple regression for determining the DOC concentration below the confluence, and the extent of Al and Fe precipitation was much less significant

YTTRIUM ALUMINATE CERAMIC FIBERS VIA PRE-CERAMIC POLYMER AND SOL-GEL ROUTES

ABSTRACT Yttrium aluminum garnet (YAG - Y3Al5O12) fibers have been prepared by dry spinning solutions of yttrium and aluminum carboxylate polymers (precursor route) and by dry spinning aqueous oxide sols (sol-gel route). Fibers from aqueous diphasic gels are prepared by mixing a colloidal alumina sol containing 50-nm hydrous alumina with a colloidal yttria sol containing 10-nm yttrium oxide, using polyvinylpyrrolidone as a spinning aid. Fibers by the precursor route are made from spinnable THF solutions of yttrium isobutyrate and aluminum isobutyrate or from aqueous solutions of polymeric aluminum formate and yttrium acetate. The isobutyrate materials decompose between 200-400°C to an amorphous residue. Crystallization occurs abruptly between 875°C and 900°C, forming the YAG phase directly. The formate-acetate also decomposes to amorphous residues, which form YAG at 900°C. In the diphasic gel, YAG forms gradually between 1000 and 1200°C, with intermediate products YAP (YalO3 perovskite) and/or YAM (Y4Al2O...

Humic substances and trace metals associated with Fe and Al oxides deposited in an acidic mountain stream

Hydrous iron and aluminum oxides are deposited on the streambed in the confluence of the Snake River and Deer Creek, two streams in the Colorado Rocky Mountains. The Snake River is acidic and has high concentrations of dissolved Fe and Al. These metals precipitate at the confluence with the pristine, neutral pH, Deer Creek because of the greater pH (4.5–6.0) in the confluence. The composition of the deposited oxides changes consistently with distance downstream, with the most upstream oxide samples having the greatest Fe and organic carbon content. Fulvic acid accounts for most of the organic content of the oxides. Results indicate that streambed oxides in the confluence are not saturated with respect to their capacity to sorb dissolved humic substances from streamwater. The contents of several trace metals (Mn, Zn, Cu, Pb, Ni and Co) also decrease with distance downstream and are correlated with both the Fe and organic carbon contents. Strong metal-binding sites associated with the sorbed fulvic acid are more than sufficient to account for the trace metal content of the oxides. Complexation of trace metals by sorbed fulvic acid may explain the observed downstream decrease in trace metal content.

The occurrence of thiosulfates and other unstable sulfur species as natural weathering products of old smelting slags

Orthorhombic barium thiosulfate monohydrate, triclinic barium thiosulfate fluoride, triclinic barium sulfite and monoclinic hydrated barium aluminium trisulfide hydroxide have been isolated and identified as natural weathering products in old smelting mill slags. None of them have been found in nature before, but two of them are known as laboratory products. They represent a stepwise sequence in sulfur oxidation numbers and are potential intermediates in the familiar but little-understood oxidation of sulfides to sulfates and thus throw light on the mechanism of the natural oxidation of sulfide ores. The nature of these phases and co-existing species suggests formation between about Eh -0.45 v at pH 11 and Eh -0.6 v at pH 13.[▭

Coagulation of submicron colloids in water treatment by incorporation into aluminum hydroxide floc

In a series of laboratory experiments it was observed that the rate and stoichiometry of aluminum hydroxide precipitation depended on pH and Al dose, and on HCO{sub 3}{sup {minus}}, SO{sub 4}{sup 2{minus}}, and natural organic matter concentrations. Incorporation of hydrous aluminum oxide colloids into the precipitate followed either of two paths. At pH 7.5 a loose floc formed; colloid removal involved subsequent aggregation of the colloids with the floc. At pH 6.5, the precipitate coated the seed particle surface; removal involved rapid self-coagulation of the colloids. Removal was {ge} 99.9% at both pH's. At pH 5.5, colloid removals were insignificant. Results suggest that heterogeneous nucleation and growth of precipitate at pH 6.5 gives destabilized particles and smaller, compact floc. The homogeneous pathway involving precipitation and subsequent particle aggregation was less efficient. The heterogeneous pathway had a lower precipitate OH/Al ratio and a lower electrophoretic mobility.

Surface characterization of coated powders: Al2O3SiO2‐coated TiO2

AbstractThe aim of this study has been to find experimental strategies to characterize surface of coated powders. We have studied hydrous alumina + silica‐coated TiO2 pigments using different XPS methods, isoelectric points (ieps) and x‐ray fluorescence (XRF). We tested especially the applicability of a simple XPS analysis method introduced by Tourgaard et al.Coated TiO2 powders were analysed qualitatively with ieps, XPS surface concentrations, XPS depth profiling, and Ti 2p photoemission peak‐to‐background ratio D, The ratio D together with surface concentrations, was found to characterize well the quality of the coating. Differences in surface layers were affirmed also by ieps and XPS profiling.The asymptotic value of D for uncoated, uncontaminated TiO2 powder, interpolated from qualitative results, was ∼25 eV. This is within 25% of the predicted universal constant (25.2 eV) for transition metals and alloys.Coating layer thicknesses were calculated from XRF and XPS data, the latter assuming an exponential attenuation model with superficial carbon. Based on the value of D, Ti 2p photoelectron mean path lengths (R) also were calculated from the experimental equation by Tougaard. We found good correlation between the results from conventional XPS layer calculations and the Tougaard equation. The methods are independent of each other. Together, they seemed to give more reliable information on the non‐ideal powder surfaces studied than either of the methods alone.

Preparation of Monodispersed Hydrous Aluminum Oxide Powders

Hydrolysis of aluminum secondary-butoxide was studied in various solvents. Mixtures of n-octanol and organic solvents affected the properties of the final products. Gel was formed when hydrophobic solvents were added, whereas sol was formed in case of hydrophilic solvents. The mixed solvent of n-octanol and acetonitrile was found to be optimum in the preparation of monodispersed spherical powders. In addition, the influences of water, acetonitrile, dispersant, hydrolysis temperature and aging time on the preparations of monodispersed aluminum oxide particles were investigated.

The Chemistry of Iron, Aluminum, and Dissolved Organic Material in Three Acidic, Metal‐Enriched, Mountain Streams, as Controlled by Watershed and in‐Stream Processes

Several studies were conducted in three acidic, metal‐enriched, mountain streams, and the results are discussed together in this paper to provide a synthesis of watershed and in‐stream processes controlling Fe, Al, and DOC (dissolved organic carbon) concentrations. One of the streams, the Snake River, is naturally acidic; the other two, Peru Creek and St. Kevin Gulch, receive acid mine drainage. Analysis of stream water chemistry data for the acidic headwaters of the Snake River shows that some trace metal solutes (Al, Mn, Zn) are correlated with major ions, indicating that watershed processes control their concentrations. Once in the stream, biogeochemical processes can control transport if they occur over time scales comparable to those for hydrologic transport. Examples of the following in‐stream reactions are presented: (1) photoreduction and dissolution of hydrous iron oxides in response to an experimental decrease in stream pH, (2) precipitation of Al at three stream confluences, and (3) sorption of dissolved organic material by hydrous iron and aluminum oxides in a stream confluence. The extent of these reactions is evaluated using conservative tracers and a transport model that includes storage in the substream zone.

Effects of residues of triple superphosphate on the quantity-intensity relationships of fresh phosphate in some soils from Brazil and Colombia

Isotopic exchange of phosphate was investigated in soils which had received 0–176 kg P ha−1 as triple superphosphate in the field. The soils were kaolinitic oxisols from near Manaus, Brazil, and Pescador, Colombia, and an allophanic andept with much organic matter from Popayan, Colombia. When fresh phosphate was added to these soils in the laboratory the residues of triple superphosphate decreased the intensity of phosphate in the liquid phase that was associated with a specific quantity of exchangeable phosphate. However, residues of triple superphosphate increased phosphate taken up by maize at Manaus. Residues did not cause this effect in soils from Colombia in which the major minerals were halloysite and imogolite. The cause of the anomalous results in kaolinitic soils may be that in the field, during long contact between soil and phosphate, the latter penetrated into the mineral crystal so that, although it maintained adequate concentration for crops, exchange of the residues was slower in the laboratory than exchange of the fresh phosphate that was added for the measurements. In the andept the effect may have been caused by strong sorption of fertilizer phosphate onto hydrous oxides of aluminium released from organic matter by lime. The results indicated that although short term exchange data may be useful to differentiate phosphate sorption characteristics in untreated soils they may not, at least in some soils, represent long term behaviour of phosphate residues in relation to phosphate taken up by crops.

Dissolution of Sparingly Soluble Inorganic Compound to Aqueous Suspension with Ion Exchange Resin (Part 4)

Dissolution behavior of synthetic ettringite in an aqueous suspension containing a strongly acidic ion exchange resin, hydrogen-form (H-R) was investigated by monitoring the variations in pH and specific conductivity and by analyzing the fraction of dissolved ions using ion chromatography. The results obtained are summerized as follows;(1) Initial cation exchange reaction between ettringite and H-R in aqueous media produces a hydrous alumina gel incorporated with small amounts of calcium and sulfate ions (Eq. 1).Al2Ca6(OH)12(SO4)3+6(H-R)→3CaSO4(aq)+3(Ca-R2)+6H2O+2Al(OH)3 (1)(2) In the final stage, the released H2SO4 produced by the subsequent ion exchange reaction between CaSO4 (aq) and H-R reacts with the gel to be dissolved accompaning with the complete dissolution of the ettringite.

Ligand exchange of oxyanions on synthetic hydrated oxides of iron and aluminum

The adsorption of oxyanions, P(V), As(V), Se(IV), Mo(VI), and Cr(VI), on the synthetic hydrated oxides of iron and aluminum was studied. The adsorption sequence of the oxyanions was in the order of As(V), Se(IV)>Mo(VI)>P(V)>Cr(VI) on the goethites, hydrons ferric oxide and hydrous aluminum oxide, and P(V)>Mo(Vl)> As(V)>Se(IV), Cr(VI) on the gibbsites. The amount of adsorption of the oxyanions on the hydrated oxides of iron and aluminum was larger in the amorphous hydrous oxides than in the crystalline ones. Ligand exchange took place between oxyanions and OH or OH2 coordinated on the hydrated oxides of iron and aluminum during the adsorption. The OH2 ligand exchange mainly occurred at pH 5.5 for the adsorption of As(V), Se(IV), and P(V) on the amorphous hydrated oxides of iron and aluminum.

Coagulation of Submicron Colloids by Supramicron Silica Particles

The coagulation of submicron colloids (hydrous aluminum oxide or chrysotile) by supramicron silica particles was studied in settling columns and fluid shear experiments. The purpose was to provide insight into the fate of submicron colloids in lakes. Values of α, the sticking factor, were near 0.01 for both particles.

The high dispersion of organic dye into a transparent alumina film and its applications to photochemical and non-photochemical hole burnings

The dyes active in PHB (photochemical hole burning) and NPHB (non-PHB) were embedded in matrices of transparent alumina film by the sol-gel process using hydrous alumina sol derived from aluminum chloride. The dyes doped were sodium resorufin, 5,8-dihydroxy-1,4-naphthoquinone (DNQ) and α,β,γ,δ-tetrakis(4-sulphophenyl) porphine (TPPS). The undesirable dye aggregation usually observed in aqueous solution is largely reduced in the film even at a concentration as high as 10 −2 M. Spectral shifts were observed in the absorption spectra of the films similarly to those in polar matrices. The spectrum of TPPS doped into the film corresponds to that in aqueous solution at pH 2.5. It seems thus that the protonation occurs for resorufin and TPPS in the films. Reflecting this fact, the spectrum of the DNQ film contains the band active in PHB while the spectra of the resorufin and TPPS films do not. The latter dyes reveal active bands on exposure to NH 3 gas because of deprotonation. The thermal durability of the hole profile was investigated by the temperature cycling method. Some discussion is given on the thermal durability in the alumina film compared to those in polystyrene (PS) and poly(methyl methacrylate) (PMMA).

Studies on the removal of some toxic metal ions from aqueous solutions and industrial waste. Part I (Removal of lead and cadmium by hydrous iron and aluminium oxide)

Abstract The adsorption of two metal ions Pb2+ and Cd2+ has been observed on hydrous aluminium and iron oxide which are prepared and characterized by well known methods. Hydrous ferric oxide exhibits bettwr sorption capacity for the metal ions. The uptake of lead is much higher than cadmiua and follows Langmuir model. Thermodynamic parameters of the process have been estimated by kinetic measurements which also provide mechanistic information.

Effect of aluminium alkoxides on the mechanical properties of calcium aluminate cements at high temperatures

Synopsis The effect of aluminium alkoxides, Al(OR)3, (where R is C2H5, C3H7 or C4H9), on the mechanical properties of calcium aluminate refractory cements at temperatures up to 1000°C was investigated. The magnitude of strength improvement obtained by adding alkoxides to the cement pastes depended on three factors: (1) the number of carbons in the alkoxides; (2) the phase of the transitional aluminium compounds sintered by in situ conversion of sol-gel particles of hydrous aluminium hydroxides over the temperature range 300 to 1000°C; and (3) the molecular mass and the amount of alcohol produced by hydrolysis of the alkoxides.

New preparation technique for a highly dispersed nickel—alumina catalyst and its application to liquid phase hydrogenation

A highly dispersed nickel-alumina catalyst has been prepared by the sol-gel process using hydrous alumina sol derived from an aluminum salt solution. The size of the nickel particles is controlled by the dimensions of the network of the homogeneous precursor alumina gel. This new catalyst shows higher selectivity in the liquid phase hydrogenation of 1,3 and 1,5-cyclooctadiene and methyl linolenate than either Raney nickel or impregnated nickel-alumina catalysts. However, it shows lower activity than Raney nickel. This may be due to the tendency of the nickel particles to be encapsulated within the alumina particles.