Showing papers on "Gibbsite published in 1977"

Adsorption on hydrous oxides.III.Fulvic acid and humic acid on goethite,gibbsite and imogolite

Abstract: Adsorption isotherms were obtained for fulvic and humic acids on synthetic gibbsite and goethite and on a natural imogolite. The results were interpreted with the help of spectra of the adsorption complexes, and measurements of hydroxyl displaced. The mechanism of adsorption involved ligand exchange with the surface hydroxyl groups and hydrogen bonding. The hydroxyl groups displaced included singly coordinated species on the (100) face of goethite and on the edge faces of gibbsite. The doubly coordinated hydroxyl groups on the (001) face of gibbsite were not replaced, and this face adsorbed only un-ionized fulvic acid probably by a hydrogen bonding mechanism. Imogolite adsorbed most fulvic acid because of its high porosity. Only isolated places on its surface reacted with fulvic acid to form carboxylate groups.

Adsorption on hydrous oxides: ii. oxalate, benzoate and phosphate on gibbsite

Abstract: Summary Adsorption isotherms, the infrared spectra of adsorbed species, and the amount of hydroxyl released when oxalate is adsorbed, all indicate that adsorption of oxalate, benzoate and phosphate at low solution concentrations occurs only on A1(OH)(H2 O) sites exposed on edge faces of the platy gibbsite crystals studied. This is confirmed by the finding that the vibrations of surface hydroxyl groups on the principal plate faces are unaffected when excess oxalate is present, and further supported by the low affinity for oxalate of imogolite, a tubular mineral with a very large gibbsite-like surface, but with a very low concentration of edge sites. Infrared spectra indicate that oxalate is adsorbed in bidentate form. Near neutrality and at low solution concentrations, gibbsite adsorbs more oxalate than does goethite of comparable surface area.

Properties and Quantitative Estimation of Poorly Crystalline Components in Sesquioxidic Soil Clays

Abstract: Sesquioxidic soil clays from Oxisols in South Africa, Australia and Brazil, and two clays from Andosols in Japan and New Zealand, were investigated by selective dissolution techniques. Acid ammonium oxalate (pH 3) was found to be superior to currently popular alkaline reagents for extracting amorphous aluminosilicates and alumina from these clays. Boiling 0.5 N NaOH dissolved large amounts of finely-divided kaolinite and halloysite, while hot 5% Na2CO3 reaction was too slow (partial dissolution of synthetic amorphous aluminosilicates with one extraction) and insufficiently selective (gibbsite and kaolin of poor crystallinity dissolve to a variable extent). On the other hand, synthetic gels (molar SiO2/Al2O3 ranging from 0.91 to 2.55) dissolved completely after 2 hr shaking in the dark with 0.2 M acid ammonium oxalate (0.2 ml/mg). Specificity of oxalate for natural allophane was indicated by removal of similar quantities of silica and alumina using different clay:solution ratios. Oxalate extraction data indicated that allophane is absent in Oxisol clays. Allophane was determined quantitatively in volcanic-ash soil clays by allocating hydroxyl water content to oxalate-soluble silica plus alumina on the basis of an ignition weight loss-chemical composition function for synthetic amorphous alumino-silicates. Parameters of chemical reactivity and distribution of electric charges following various chemical pretreatments of allophane were found to correspond closely to those predicted on the basis of synthetic gel behaviour. Results for Oxisol clays suggested that the role of amorphous (oxalate-soluble) alumina in governing physicochemical properties is generally less than that of the poorly-crystalline, Al-substituted iron oxide component which is removed by deferration with citrate-dithionite-bicarbonate reagent.

Geology and geochemistry of bauxite deposits in the lower Amazon Basin

Abstract: Aluminous laterites north of the Amazon River have formed on poorly consolidated clayey terrestrial sediments of Pliocene or Plio-Pleistocene age. The essential processes affecting the major elements were leaching of the surficial portion of kaolinitic sedimentary rocks causing a reduction of nonquartz silica in the entire laterized zone, downward transport in solution of aluminum and iron, and concentration of aluminum and iron as hydroxides and hydrated oxides at the base of the laterized zone.Measurement of the vertical distribution of 20 elements through the laterized profile shows large variations in their concentrations. Leaching has predominated in the upper portion and strong enrichment of many elements is characteristic of the aluminum- and iron-rich lower parts of the zone. When compared with the subjacent material, Fe, V, P, Ga, and Mn are strongly enriched and Pb, Sr, and Ba are strongly depleted in the laterized zone. Enrichment of minor elements in the principal mineral phases is marked for Cr, Ga, K, P, Mg, and V (in iron oxides) and Ba, Pb, and Sr (in kaolin). None of the minor elements measured show a preference for gibbsite. The distribution of the elements in the laterized zone is not consistent with a geochemcial control related to their ionic potential.

Reactions of soluble phosphate with acid soils: the interpretation of adsorption‐desorption isotherms

Abstract: Summary Adsorption-desorption and isotopic-exchange isotherms for acids soils of known clay mineralogy indicated that when all the surfaœ P accessible to the solution was considered, the bonding energy for phosphate decreased exponentially with site coverage. The soils differed markedly in the quantities of surface P held at sites of very high bonding energy, defined as those in equilibrium with a solution concentration < 1 μM; the values ranging from 9 μmol g−1 in a soil with 40 per cent gibbsite in the clay fraction, to 1 μmol g−1 in a soil with only 1 per cent gibbsite and no interlayered material. The reversibility of current P adsorption on soil surfaces depended on the immediate history of the soil sample. Complete reversibility occurred when soil, previously enriched with soluble P and stored for 4 to 5 months at constant temperature, was suspended in solutions of constant pH and ionic strength. It is suggested that irreversibility occurs due to incomplete attainment of equilibrium during the adsorption phase, a condition predisposed by high initial P concentrations (>1mM), and the use of soils that are naturally in dis-equilibrium because of recent fertilizer additions or severe depletion of P by plant uptake.

The micromorphology of gibbsite forms in soils

Abstract: Summary Using optical and scanning electron microscopy various forms of gibbsite are described in some tropical soils. In a lateritic soil from Zaire gibbsite occurs on argillans, in randomly oriented crystal sheets, as nodular aggregates infilling vughs and on ped faces. The mineral also surrounds quartz grains and kaolinite pseudomorphs after biotite. In other soils gibbsite occurs as silt-size particles disseminated through the matrix, as large nodular aggregates, and as anatomizing sheets associated with crystal chambers. It is clear from these observations that alumina must be a mobile constituent and was probably translocated through the soil in solution.

Basicity of Exchangeable Aluminum, Formation of Gibbsite, and Composition of the Exchange Acidity in the Presence of Exchangers1

Abstract: Montmorillonite, vermiculite, and a sulfonic resin were treated with different concentrations of Al(OH)BCl₃₋B with the basicity B ranging from 0 to 2.2. The Al exchanged by vermiculite and the resin was always the nonbasic Al³⁺, independent of B and the amounts of Al(OH)BCl₃₋B added. The Al exchanged by montmorillonite was Al³⁺ when exchanged from Al(OH)BCa₀.₅B-montmorillonite containing 32 mmoles Al/100 meq CEC and became basic when large amounts of Al(OH)BCl₃₋B had been added before the exchange reaction. In contrast to vermiculite and the resin, the montmorillonite adsorbed preferentially relatively large OH-Al polymers and, therefore, accumulated much more Al in the interlayers than vermiculite and resin which excluded large OH-Al polymers because of their smaller d spacings and/or high charge densities. When more OH-Al accumulated in the interlayers of montmorillonite, the Al was adsorbed less strongly, and relatively large amounts of basic Al became exchangeable. It was shown also that an Al³⁺-saturated vermiculite is much more unstable than an Al³⁺-montmorillonite. These results are employed to discuss the widely-observed formation of gibbsite when smectite reacts with basic Al. Finally, the exchange acidity from an Al-saturated exchanger was shown to consist of both Al³⁺ and H⁺. The protons come from (i) the hydrolysis of exchanged Al³⁺ which, in turn, can be readsorbed as OH-Al; (ii) from the hydrolysis of adsorbed Al; and (iii) by the exchange of H⁺ from permanent charges. The latter portion mechanism provides an amount of exchangeable acidity that, if it exists, is relatively small.

Characteristics of Silica Sorption and Solubility as Parameters to Evaluate the Surface Properties of Tropical Soils: II. The Index of Silica Saturation1

Abstract: Silica sorption by some Alfisols and Ultisols from southern Nigeria was studied. The percentage of silica lost from a solution brought into contact with a soil is called the index of silica reactivity (ISR). For reference samples, the scale of ISR follows the order kaolinite < < goethite < gibbsite. For soils where Iron oxides are the only sorbing phases, ISR is ruled by the part of the total specific surface area due to these oxides. More generally, however, ISR is sensitive to both the nature and the magnitude of the surface area so that soils rich in gibbsite exhibit higher ISR than the soils devoid of this mineral. To become useful as a comparative index, ISR should be amended so as to also take into account the specific reactivity of the different minerals with respect to soluble silica.

Formation of clay minerals in andosoils under temperate climate

Abstract: The principal methods for studying clay minerals in andosoils differ especially by the succession of the pretreatments, i.e. differential dissolution of amorphous mineral cements before (first method) or after (second method) the dispersion and recovery of granulometric fractions. The first method permits a rapid total quantitative estimation of amorphous components and an accurate identification of crystallized clay minerals by means of X-ray diffraction. The second method only proves the presence of allophane and imogolite. The two methods were applied in two different laboratories on the same soils from the Massif Central. The comparison of the results emphasizes the profit of using the two methods, especially if hypotheses on the mechanisms of clay genesis are to be proposed. These results, if placed in the context of a more comprehensive study, suggest the exist- ence of two principal phases of clay genesis, strongly connected to the evolution of organic matter in andosoils, as follows: (i) an early, prepedologic phase during which halloysites and smectites would form ; (ii) a late phase giving rise especially to some kaolinite and gibbsite.

Laterization of the ultramafic-Gabbro Association at North Cape, Northernmost New Zealand

Abstract: Laterites occur at North Cape, above an ultramafic-mafic plutonic association, the Kerr Pluton, composed predominantly of seperntinites by layered gabbros. Laterite profiles average 32 m over gabbros, but only 6 m over serpentinites. Iron pan, formed from a layer of near-surface residual boulders, is abundant over sepentinite-derived laterites. Pain d'epice facies-is more common over gabbros. Initial decomposition of serpentinites yields hisingerite which later crystallizes to smectite + chlorite. At the top of the profile limonite, goethite and minor smectite occur. Gabbros initially decompose to form kaolinite, halloysite, smectites and pyrophyllite which are susbsequently replaced by limonite-goethite, kaolinite and gibbsite. During laterite formation, elements are released from tlte serpentinites in the following general order: MgO, CaO, TiO2, SiO2, Fe2O2, Al2O3, NiO, MnO. Gahbros hehave similarly except that iron is always enriched relative to alumina in the soils. It is believed that under ...

Process for producing alumina catalyst carriers

Abstract: Alumina catalyst carriers are produced by bonding pre-fired gibbsite with microcrystalline boehmite. Superior strength of the product is achieved by use of gibbsite fired to an L.O.I. at 1000° C of 8% or less, or preferably less than 4%.

Structural Defects and Thermal Reaction in Gibbsite

Abstract: Samples of gibbsite have been broadly classified into well- crystalline and poorly crystalline by X-ray diffraction and differential thermal analysis methods. The study of solid state thermal reactions of both well- and poorly crystalline materials shows that the degree of crystallinity affects the course of reaction. Various types of crystal structures produced in the process of transformation of both types of gibbsite are discussed.

Desiccation of soils derived from volcanic ash

Abstract: Five volcanic-ash-derived soils from the island of Hawaii were studied to determine the relation of changing moisture content to engineering behavior. Two soils weathered on the leeward side of the island under relatively dry conditions; the other three developed on the windward side under high mean annual rainfalls. The dry soils show little change on desiccation whereas the desiccation of the wet soils is accompanied by an irreversible hardening that causes drastic changes in the index properties. Engineering behavior of the dry soils is similar to that of a sandy silt. The wet soils behave as plastic clays but, when they are dried out, their engineering characteristics change to those of a sand. Mercury porosimetry tests reveal that, in wet soils, volume changes between field mositure content and the oven-dry state are about 150 percent. The dry soils exhibit very small volumetric shrinkage. Drying tests under controlled relative humidity provide data on drying rates and critical moisture contents. The mineralogy of the soils was studied by using X-ray diffraction and fluorescence, differential thermal, and thermogravimetric analyses. The predominant minerals are gibbsite, iron oxides, and allophane. Mineralogical studies indicate that irreversible hardening is accompanied by an increase in gibbsite content. Mercury porosimetry results and mineralogical analysis indicate that a major portion of the shrinkage is due to contraction of the intermediate-size pores and that the extent of shrinkage is a function of allophane content. /Author/

The substitutional incorporation of Fe(III) and Cr(III) ions within gibbsite by homogeneous precipitation

Abstract: Fe(III) and Cr(III) have been incorporated in gibbsite (∼ 1%) by oxidation of a Fe(III)-triethanolamine complex with Cl2 and reduction of K2CrO4 with hydrazine at an appropriate rate, during the precipitation of gibbsite from an alkaline aluminate solution. The products show characteristic single ion ESR spectra.

DETERMINATION OF ALLOPHANE AND AMORPHOUS INORGANIC MATTER IN CLAY FRACTION OF SOILS : II. Soil Clay Fractions

Abstract: The quantitative determination of allophane and amorphous inorganic matter in the clay fractions of volcanic ash soils was examined by means of five methods. An outline of the results is as follows: An alternate dissolution with 8 N HCl for 30 min and warmed 0.5 n NaOH for 5 min according to the method of Segalen (8) was suited for the purpose. The coexistence of gibbsite did not strongly influence the determination of allophane and amorphous matter, but goethite and hematite in soils behaved just as amorphous matter in this method. A method based on the weight loss with heating at 200°C, which is newly proposed in this study, was statistically analyzed in the clay fractions of soils and the allophane-halloysite mixture samples, compared with the result of the method by means of the alternate dissolution with HCI and NaOH. It was clarified that the method based on the weight loss with heating at 200°C could be applied to a determination of allophane and amorphous matter, i.e., a high linearcorrel...

A Study of Thermal Reactions of Gibbsite by Electrical Conductivity Measurements

Abstract: Gibbsite samples, both natural and synthetic, have been classified into well- and poorly crystalline types by X-ray diffraction method. Electrical conductivity of both well- and poorly crystaline materials shows a number of structural transformations of the gibbsite when it is heated up to 580°C. It is shown that crystallinity of the parent substance has a marked influence on the course of thermal reaction of gibbsite. Experimental results of the investigation are discussed.