Amorphous aluminum hydroxide

Commercial production of bayerite is relatively small and employs CO2 neutralization of caustic aluminate Hquor obtained from either Bayer or sinter processes. The product obtained is about 90% crystalline bayerite having small amounts of gibbsite, pseudoboehmite, and amorphous aluminum hydroxides. 

Amorphous adsorbents, 1 587-589 for gas separation, 1 631 properties and applications, l 587t Amorphous aluminum hydroxide, 23 76 Amorphous carbohydrates, material science of, 11 530-536 Amorphous carbon, 4 735 Amorphous cellulose, 5 372-373 Amorphous films, in OLEDs, 22 215 Amorphous germanium (a-Ge), 22 128 Amorphous glassy polymers, localized deformation mechanisms in, 20 350-351... 

Fig. 5.2.1 Transformation of the solid phase from amorphous aluminum hydroxide to spheroidal cubic particles of basic aluminum sulfate with aging time under the standard conditions [Al3 ] = 1.0 mol dm-3, IS042 ]/[A13+] = 2/3, [NaOHJ/[AI3+ = 1.8. temperature = 100°C. (From Ref. 1.)...

Anderson, M.A., Ferguson, J.F. and Gavis, J. (1976) Arsenate adsorption on amorphous aluminum hydroxide. Journal of Colloid and Interface Science, 54, 391-99. 

Amorphous hydroxide Al(0H)3.nH20 Amorphous aluminum hydroxide... 

Deep and geothermal wells are inherently hot and are well served by aluminum phosphate formulations (see Chapter 11). The dynamic temperature in these wells is 250 °F (121°C) or higher, and the static temperature is >350 °F (235°C). For these wells, berlinite-based CBPC works well with its maximum solubility at 244 °F (118°C) of alumina and phosphoric acid solution. As we have seen in Chapter 11, this reaction takes place at 302 °F (150°C) that is in the range of the temperatures of deep and geothermal wells [7]. Even at these temperatures, the solubility of aluminum oxide is too low, but addition of a small amount of microcrystalhne or amorphous aluminum hydroxide aids in increasing the soluble ions in the solution. With its large surface area, alumina provides the necessary solubility at the given downhole temperamre. 

Correlations between concentrations of dissolved metals (iron and/or aluminum) and of either DOM or organic acids in infiltrating waters suggest that DOM, or some component of DOM, facilitates metal solubilization and translocation in soils (14). The role of DOM in metal mobilization is also supported by the occurrence of organically complexed metals in soil solutions (3, 15, 16). Precipitation and transformations of soil minerals can be inhibited by DOM, which tends to stabilize metastable phases [such as amorphous aluminum hydroxide and pseudoboehmite (17), ferrihydrite (18), and octacal-cium phosphate (19)] and to prevent formation of more crystalline phases. 

The pH at equilibrium with the aluminum sulfate salts on the other hand, is near neutral. For alunite in equilibrium with amorphous aluminum hydroxide, the reaction is... 

ELECTRON SPIN RESONANCE SPECTROSCOPY Electron spin resonance (ESR) is a technique that can also be used on aqueous samples and has been used to study the adsorption of copper, manganese, and chromium on aluminum oxides and hydroxides. Copper(II) was found to adsorb specifically on amorphous alumina and microcrystalline gibbsite forming at least one Cu-O-Al bond (McBride, 1982 McBride et al., 1984). Manganese(II) adsorbed on amorphous aluminum hydroxide was present as a hydrated outer-sphere surface complex (Micera et al., 1986). Electron spin resonance combined with electron spin-echo experiments revealed that chromium(III) was adsorbed as an outer-sphere surface complex on hydrous alumina that gradually converted to an inner-sphere surface complex over 14 days of reaction time (Karthein et al., 1991). 

Scholtz, E.C. et al., Point of zero charge of amorphous aluminum hydroxide as a function of adsorbed carbonate, J. Pharm. Sci., 74, 478, 1985. 

Groundwater at MW-86 is at the second geochemical phase when calcite in the aquifer is depleted. The fluid pH of the groundwater is reduced to about 4.5 and is buffered by amorphous aluminum hydroxide or kaolinite. 

Sorption of As(III) to Fe(III) oxyhydroxides has been widely observed (101,105-107,109). At high pH values, As(III) can be sorbed to a greater extent than As(V). Sorption of As(III) on clays and amorphous aluminum hydroxide has been reported (102). However, removal of As(III) by coagulation with alum is generally poor (110,111). Adsorption experiments conducted with hydrous aluminum oxide under conditions comparable to water treatment with coagulants (pH 6, 120 pM total Al) showed 99% removal of As(V) but only 3% removal of As(lll) at initial arsenic concentrations of 10 and 100 pg/L (112). 

FIGURE 2.77 H MAS NMR spectra measured at a spinning rate of 35 kHz and a magnetic field of 14.09 T for amorphous aluminum hydroxide (1) initial and (2) dried at 90°C for 90 min. (Redrawn from J. Colloid Interface Sci., 261, Isobe, T., Watanabe, T., d Espinose de la Caillerie, J.B., Legrand, A.P., Massiot, D., Solid-state H and Al NMR studies of amorphous aluminum hydroxides, 320-324, 2003, Copyright 2003, with permission from Elsevier.)... 

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