Showing papers on "Gibbsite published in 1993"

Boron Adsorption Mechanisms on Oxides, Clay Minerals, and Soils Inferred from Ionic Strength Effects

Abstract: Prediction of anion adsorption behavior is enhanced by understanding the adsorption mechanism. This study was conducted to evaluate ionic strength effects on B adsorption and to infer B adsorption mechanisms on various surfaces. Boron adsorption on the Fe oxide goethite, the Al oxide gibbsite, the clay minerals kaolinite and montmorillonite, and two arid-zone soils was investigated as a function of solution pH (3-11) and ionic strength of the background electrolyte (0.01-1.0 M NaCl). Boron adsorption on the oxides and kaolinite increased from pH 3 to 6, exhibited a peak at pH 6 to 8.5, and decreased from pH 8.5 to 11. For B adsorption on montmorillonite and the soils, the adsorption maximum was located near pH 9. Ionic strength dependence, measured as the increase of the B adsorption maximum in 1.0 M NaCl solutions compared with 0.01 M NaCl solutions increased in the order: goethite (3%) < kaolinite (15%) < gibbsite (-30%) < montmorillonite (109%) ~ montmorillonitic soil (116%) = kaolinitic soil (129%). Shifts in zero point of charge were observed on goethite, gibbsite, and kaolinite following B adsorption. Ionic strength effect results suggest an inner-sphere adsorption mechanism for goethite, gibbsite, and kaolinite and an outer-sphere adsorption mechanism for montmorillonite and the soils. These mechanisms are also indicated by zero point of charge determinations, microelectrophoresis measurements, or both. The constant capacitance model, containing an inner-sphere adsorption mechanism, was able to describe B adsorption on goethite, gibbsite, kaolinite, and kaolinitic soil. The model was unable to describe B adsorption on montmorillonite and montmorillonitic soil because the computer optimizations diverged. B is an important element in crop production. Boron deficiency is of concern in areas receiving plentiful rainfall while B toxicity may be a problem in arid areas (Keren and Bingham, 1985). Because the concentration range between plant deficiency and toxicity is narrow and plants respond only to the B activity in soil solution, understanding the mechanism of B adsorption on soil materials is necessary. Although organic matter plays an important role in B sorption, this study focused on soil minerals. Anion exchange with surface hydroxyl groups has been invoked as the mechanism of B adsorption on Al and Fe oxide minerals (Sims and Bingham, 1968; McPhail et al., 1972). This type of ligand exchange is a mechanism by which anions become specifically adsorbed onto oxide mineral surfaces. Specifically adsorbing anions form inner-sphere surface complexes. Inner-sphere surface complexes contain no water molecules between the adsorbate anion and the surface USDA-ARS, U.S. Salinity Lab., 4500 Glenwood Dr., Riverside, CA 92501. Contribution from the U.S. Salinity Lab. Received 17 July 1992. *Corresponding author. Published in Soil Sci. Soc. Am. J. 57:704-708 (1993). functional group (Sposito, 1984). The zero point of charge (ZPC) of variable-charge minerals is shifted to a more acid value following specific adsorption of anions. Boron adsorption lowered the ZPC of boehmite (Fricke and Leonhardt, 1950), pseudoboehmite (Alwitt, 1972), Al-hydroxide gel (Beyrouty et al., 1984), and magnetite (Blesa et al., 1984), indicating specific adsorption. No information on the effect of B adsorption on the ZPC of clay minerals is available. Previous research has indicated that B adsorption occurs on the edges of the clay minerals illite (Couch and Grim, 1968) and montmorillonite (Keren et al., 1981). Ligand exchange with reactive surface hydroxyl groups on the broken edges has been suggested as the mechanism of B adsorption on clay minerals (Keren and Talpaz, 1984). By studying the effects of ionic strength on ion adsorption, Hayes and Leckie (1987) were able to distinguish between innerand outer-sphere metal ion surface complexes, while Hayes et al. (1988) were able to distinguish between innerand outer-sphere anion surface complexes. Outer-sphere surface complexes contain at least one water molecule between the adsorbate anion and the surface functional group (Sposito, 1984). Studying Se adsorption, Hayes et al. (1988) suggested that SeOI" , showing strong ionic strength dependence in its adsorption behavior, was weakly bonded as an outer-sphere surface complex, while SeO!" , showing little ionic strength dependence in its adsorption behavior, was specifically adsorbed in a strong inner-sphere surface complex. These adsorption mechanisms were verified spectroscopically using extended x-ray absorption fine structure measurements (Hayes et al., 1987). The constant capacitance model is a chemical surface complexation model that uses a ligand exchange mechanism to describe specific anion adsorption (Stumm et al., 1980). The model explicitly defines inner-sphere surface complexes and chemical reactions and considers the charge on both the adsorbate and the adsorbent. The constant capacitance model has been used successfully to describe B adsorption on various Al and Fe oxides via ligand exchange with surface hydroxyl groups (Goldberg and Glaubig, 1985), clay minerals via ligand exchange with aluminol groups (Goldberg and Glaubig, 1986a), and soils (Goldberg and Glaubig, 1986b) as a function of solution pH. The objectives of our study were to: (i) investigate the ionic strength effects on B adsorption behavior by oxides, clay minerals, and soils; (ii) evaluate the nature of the adsorbed B surface complexes using the ionic strength data; and (iii) investigate the ability of

Formation mechanism of aluminum hydroxide polymorphs

Abstract: Substantial studies have been carried out to investigate the mechanism of the formation of Al(OH)3 polymorphs. The influence of the nature of Al precipitation products on the formation of Al(OH)3 polymorphs still remains obscure. In this study, X-ray diffraction, infrared and thermal analyses, and electron microscopic observations of the Al precipitates formed at the initial pH 8.2 and at a citric acid/Al molar ratio of 0.01 and aged for 3 hr to 60 days revealed that the transformation from the initially formed noncrystalline materials to pseudoboehmite occurred through the formation of intermediate materials with various degrees of ordering and sizes of particles that apparently had a wide range of solubility. By increasing the pH of the suspension of precipitation products of Al to 10.0 after 3 hr and 3, 11, 31, and 60 days or longer, the crystalline precipitation products were hayerite, nordstrandite and bayerite, nordstrandite and pseudoboehmite, pseudoboehmite and gibbsite, and pseudoboehmite, respectively. This work shows evidence that, as the nature of the starting Al precipitates changed, the rate of their dissolution apparently changed, and various Al(OH)3 polymorphs consequently formed. Therefore, the data substantiate the hypothesis that the mechanism of the formation of an Al(OH)3 polymorph is determined by the rate of its nucleation, which is, in turn, influenced by the rate of dissolution of the noncrystalline or poorly ordered Al-oxides initially formed.

Kinetics and mass transfer of pseudomorphic replacement: Application to replacement of parent minerals and kaolinite by Al, Fe, and Mn oxides during weathering

Abstract: Parent rock minerals are universally replaced by kaolinite and oxides of Al and Fe (and, occasionally, Mn) during lateritic weathering. The kaolinite is itself also replaced by the oxides. The replacement is pseudomorphic and globally involves enormous volumes of parent rock. For each parent mineral in a weathering profile, the replacement horizon is systematically overlain by one in which the parent mineral exhibits dissolution voids. This spatial association of textures forms through two coupled local reactions, a congruent dissolution above and a pseudomorphic replacement below. The dissolution of a grain is driven by H[sup +]s supplied from above, and it releases aqueous Al and/or Fe. In turn, this Al (or Fe) travels a short distance downward and drives the replacement of another grain by gibbsite (or hematite). Any silicate grain that becomes pseudomorphically replaced by gibbsite or hematite requires import of Al or Fe, unless the porosity of the replacing aggregate is very high. Combining the condition for pseudomorphic recplacement (that the replacing mineral grows about as fast as the replaced mineral dissolves) with reaction rate expressions leads to predicting windows in local water chemistry within which pseudomorphic replacement is possible but outside of which it is not. The modelmore » predicts replacement rates, and correctly accounts for the systematic occurrence of a horizon of partially replaced grains followed upward in the weathering profile by a horizon where grains exhibit dissolution voids but no more replacement. 41 refs., 5 figs., 1 tab.« less

Ultisols of “lowland Dipterocarp forest” in East Kalimantan, Indonesia

Abstract: Thirty five Typic Paleudults and Typic Hapludults under a Lowland Dipterocarp Forest were characterized for clay minerals, free oxides, cation exchange capacity, and exchangeable bases. Kaolinite was predominant in the soil clays followed by quartz, vermiculite and gibbsite and an accessory amount of illite, partially-interlayered-vermiculite (PIV) and goethite in most soils. Goethite formation appeared to take place concomitantly with the weathering of illite into PIV. Lepidocrocite was found only in the soils of the middle to lower slopes. The magnitude of lepidocrocite formation under hydromorphic conditions was associated with the exchangeable Al level. Cristobalite and hematite were found only in the “red” soils, which may have been subjected to some thermal influences associated with coal combustion. The levels of Fed, Ald, and Alo of the soils were, as a whole, positively correlated with the clay content, respectively. Goethite was considered to be a possible source of crystalline Fe oxide...

Temperature effects on boron adsorption by reference minerals and soils

Abstract: Information on the effect of temperature on B adsorption by soils and soil minerals is scant. These data are needed to understand B availability. Boron adsorption on goethite, gibbsite, kaolinite, montmorillonite, calcite, and two arid zone soils was investigated as a function of solution pH (3–12) and reaction temperature (10, 25, and 40|MoC) after 2 h of reaction time. Boron adsorption on all materials increased from pH 3 to 7, exhibited a peak at pH 7.5 to 10, and decreased from pH 10.5 to 12. Temperature dependence measured as the increase of the B adsorption maximum at 10|MoC compared with 40|MoC on reference minerals increased in the order: calcite (3|X%)

Aluminium solubility in rainwater and molten snow

Abstract: Large variations of aluminium solubilities are found in marine and rural precipitations. The results of seven field experiments are used to produce a model of the solubilization of aluminium independent of the sampling site. Large variations of solubility appear, and the pH seems to be a major factor explaining this solubility changes. Thermodynamic calculations at T=278K suggest that, at higher pHs (>5), equilibrium with gibbsite (αAl(OH)3) or a trivalent alkaline insoluble form acts as a limiting of aluminium solubility and at lower pHs (<5), Al could be in equilibrium with a hydroxysulfate salt Al(OH)1.5(SO4)0.75.

Routine identification of aluminium hydroxide polymorphs with the laser Raman microprobe

Abstract: The laser Raman microprobe spectrum of gibbsite displays four intense v (OH)- stretching bands at ~3365, 3435, 3525 and 3618 cm-1, bayerite shows three near 3425, 3545 and 3564 cm-1, nordstrandite has three near 3492, 3566 and 3623 cm-1, and doyleite one broad band centred at -3545 cm-1 with sometimes a prominent shoulder near 3615 cm-1. The four polymorphs also possess distinctly different Raman signatures of medium to strong bands in the region 100–1200 cm-1. These differences provide a non-destructive routine determinative procedure by direct microsampling of untreated crystals, fragments, and microcrystalline powders. Sample preparation is minimal. Excessive noise and non-quenchable fluorescence are the principle limitations of the technique.

Morphological and phase changes of transition aluminas during their rehydration

Abstract: Transition aluminas (TA), obtained by fast (0.5–1 s) calcination of gibbsite in the temperature range 375–600°C, were rehydrated at 20, 70 and 90°C. The rehydration process was investigated using transmission electron microscopy. X-ray, and thermogravimetric-differential thermal analysis. During rehydration, the TAs react yielding aluminium hydroxides: pseudoboehmite, boehmite, and bayerite. The phase-composition changes are accompanied by changes in particle morphology. Using transmission electron microscopy, six stages of rehydration were found, with characteristic morphological changes occurring. The changes are responsible for connecting the particles into stable grains during the process of obtaining catalyst carriers or adsorbents from TA.

Effect of grain size on the synthesis of active alumina from gibbsite by flash calcination and rehydration

Abstract: Two series of alumina have been prepared by flash calcination (FCAL) and subsequent rehydration of “coarse” (> 50 μm) and “fine” grain size gibbsite (< 50 μm). The initial grain size of the gibbsite was found to determine the degree of amorphization, water content, rehydration ability, composition and pore structure of FCAL products. Active alumina materials having pore structure parameters similar to those of commercial alumina adsorbents and catalyst supports were obtained by FCAL and subsequent rehydration of fine grain size gibbsite.

Influence of geogenesis and pedogenesis on clay mineral distribution in northern vietam soils

Abstract: This is a study of a sequence of five soils developed in the Red River valley of Vietnam along a transect extending from the foothills to old terraces. Most of these soils are chemically depleted, having, in particular, a very low CEC. The mineralogical study shows that the <2-μm fraction is made up of a mixture of vermiculite, illite, kaolinite, quartz, and iron oxyhydroxides. Other minerals, such as pyrophyllite in the foothills and chlorite and gibbsite in the old terraces, are present in small quantities. The major mineralogical differences among these soils lie in the relative abundance of quartz in the <2-μm fraction, the vermiculite/illite ratio, and the degree of the intergrade character of vermiculites, which is variable not only within each profile but also from one region to another. The amount of quartz generally increases toward the foothills, indicating the greater weathering of foothill materials relative to old terraces, which have been less weathered during geogenesis. The vermiculite/ illite ratio, which also increases toward the foothills, indicates an increasing transformation of 2:1 minerals. The effects of pedogenesis are characterized by the difference in vermiculite/illite ratios between the surface and 1-m-deep horizon. Nevertheless, the intensity of pedogenesis cannot be evaluated in profiles developed on highly weathered sediments because illite of the parent material has been completely transformed into vermiculite during a preweathering stage. Alternate wet and dry conditions apparently lead to an increase in illite content by the collapse of vermiculite sheets in surface horizons. The creation of a plow pan in these hydromorphic conditions may have favored the dissolution of clay by ferrolysis and the lateral leaching of fine clay particles out of the profile, increasing quartz content in the <2-μm fraction of the plow pan.

Effect of dry mixed grinding of talc, kaolinite and gibbsite on preparation of cordierite ceramics

Abstract: The effect of dry mixed grinding of tale, kaolinite and gibbsite using a planetary ball mill on the preparation of cordierite ceramics was investigated by XRD, TG-DTA, SEM, TEM-EDX, EPMA, density and specific surface-area measurements. The structures of talc, kaolinite and gibbsite are easily transformed from crystalline state to amorphous state by grinding within 240 min. This behavior leads to homogeneity in the micro-scale composition of the mixture as well as the aggregation of obtained fine particles. The amount of α-cordierite formed in the sintered body is increased with increase in grinding time for the mixture. In addition, α-cordierite phase in the sintered body obtained from the ground mixture is crystallized at a relatively lower sintering temperature than that of the unground mixture.

Aluminum hydroxide with low coagulated particle content and narrow particle size distribution and its production

Abstract: PURPOSE:To obtain aluminum hydroxide widely usable as various fillers and to provide a production method to directly obtain aluminum hydroxide in a process of precipitation from sodium aluminate solution CONSTITUTION:Aluminum hydroxide having 6-16mum average secondary particle diameter based on weight, containing =30mum diameter, /g BET specific surface area and =5g/l of powdered gibbsite having >=10 MF value and 3-10mum average particle diameter is added

Weathering patterns in representative soils of Guanxi Province, south-east China, as indicated by detailed clay mineralogy

Abstract: SUMMARY The mineralogy of five soils situated on a south-west to north-east transect of Guanxi Province, south-east China was determined by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and chemical composition. One soil had formed on granite under tropical conditions, the others on sedimentary rocks under subtropical conditions. In all soils, kaolinite dominates the clay fractions, and is accompanied by vermiculite or chloritized vermiculite. In the saprolites of the granite-derived and sandstone-derived soils, the kaolinite has a morphology close to that of hydrated halloysite. The formamide and hydrazine/water tests suggested the presence of both poorly-crystalline (dehydrated halloysite) and well-ordered kaolinite. Gibbsite was identified in the saprolites of the granite-derived and sandstone-derived soils but not in the soils themselves. Gibbsite was also identified in the lowermost horizon of a soil derived from Pleistocene sediments. The upper horizon clay of a Rendzina soil formed on Permian limestone contains much more gibbsite and is much more weathered than the corresponding lower horizon clay. Only in the more humid, southernmost soil can the mineral composition be explained by present-day climatic conditions. In the soils from drier areas, the clay mineral composition reflects weathering that had taken place under moister, paleoclimatic conditions. Some of these paleoclimatic conditions had been conducive to lateritic weathering, as is indicated by the presence of goethite-containing pisolitic nodules in one of the soils and in its parent material. Two of the soils appear to be polymorphic, with one part of the soil having weathered more strongly than the other part.

Redox front geochemistry and weathering: theory with application to the Osamu Utsumi uranium mine, Poços de Caldas, Brazil

Abstract: Numerical calculations describing weathering of the Pocos de Caldas alkaline complex (Minas Gerais, Brazil) by infiltrating groundwater are carried out for time spans up to two million years in the absence of pyrite, and up to 500,000 years with pyrite present. Deposition of uranium resulting from infiltration of oxygenated, uranium bearing groundwater through the hydrothermally altered phonolitic host rock at the Osamu Utsumi uranium mine is also included in the latter calculation. The calculations are based on the quasi-stationary state approximation to mass conservation equations for pure advective transport. This approximation enables the prediction of solute concentrations, mineral abundances and porosity as functions of time and distance over geologic time spans. Mineral reactions are described by kinetic rate laws for both precipitation and dissolution. Homogeneous equilibrium is assumed to be maintained within the aqueous phase. No other constraints are imposed on the calculations other than the initial composition of the unaltered host rock and the composition of the inlet fluid, taken as rainwater modified by percolation through a soil zone. The results are in qualitative agreement with field observations at the Osamu Utsumi uranium mine. They predict a lateritic cover followed by a highly porous saprolitic zone, a zone of oxidized rock with pyrite replaced by iron-hydroxide, a sharp redox front at which uranium is deposited, and the reduced unweathered host rock. Uranium is deposited in a narrow zone located on the reduced side of the redox front in association with pyrite, in agreement with field observations. The calculations predict the formation of a broad dissolution front of primary kaolinite that penetrates deep into the host rock accompanied by the precipitation of secondary illite. Secondary kaolinite occurs in a saprolitic zone near the surface and in the vicinity of the redox front. Gibbsite forms a bi-modal distribution consisting of a maximum near the surface followed by a thin tongue extending downward into the weathered profile in agreement with field observations. The results are found to be insensitive to the kinetic rate constants used to describe mineral reactions.

Aluminium and mineral stability in soils from the As Pontes region

Abstract: Al fractions susceptible to be liberated from the solid phase, Al forms in soil so­ lutions and the saturation indexes for certain Al-minerals (gibbsite, microcristali­ ne gibbsite, kaolinite, alunite, jurbanite and basalunite) are studied in the A and B horizonts of soils derived from different parent materials representative of the studied area (granitic rocks, gneisses, schists, phyllites, quarzous sediments and metabasic rocks). The results show that the soils from granite, phyllite and gneiss had the highest levels of exchangeable, labile potential, maximun poten­ tial.Al in the solid phase and total Al in soil solution; the soils derived from me­ tabasic rocks showed high quantities of maximun potential Al and low levels of

Polyglycerols by bayer process

Abstract: PCT No. PCT/EP91/02251 Sec. 371 Date Jun. 7, 1993 Sec. 102(e) Date Jun. 7, 1993 PCT Filed Nov. 28, 1991 PCT Pub. No. WO92/10426 PCT Pub. Date Jun. 25, 1992.The invention concerns the production of aluminum trihydrate crystal by the Bayer process, by digesting ground bauxite, filtering off the red mud, cooling the filtrate, and crystallizing out the dissolved aluminum hydroxide as gibbsite. Before and/or during the crystallization, polyglycerines of the general formula H-(OCH2CHOH-CH2)n-OH, where n is an integer equal to or greater than 3, are added.