Aluminum hydroxides/oxyhydroxides

Aluminum oxide (alumina or AI2O3) occurs in various crystallographic modifications. Completely anhydrous aluminum oxide is a-Al203 (corrundum), which is the most stable. It has a structure of hexagonal closest packing of oxide ion, with Al ion occupying two-thirds of the octahedral sites, a-Alumina is prepared by heat treatment above ca. 1470 K of aluminum hydroxides, oxyhydroxides, or alumina hydrates, which are obtained by neutralization of solution of aluminum salts or hydrolysis of aluminum alkoxides. Heat treatments at lower temperatures form various kinds of transi-... 

Hsu PH (1989) Aluminum hydroxides and oxyhydroxides. In Dixon JB, Weed SB (ed) Minerals in soil environments, 2nd edn, pp 331-378 Inskeep WP, McDermott TR, Fendorf S (2002) Arsenic (V)/(III) cycling in soils and natural waters chemical and microbiological processes. In Frankenberger WT Jr (ed) Environmental chemistry of arsenic. Marcel Dekker, New York, pp 183-215... 

The acid generated through sulfide oxidation reacts with the nonsulfide gangue minerals within the mine wastes. The most significant pH-buffering reactions in mine settings are the dissolution of carbonate minerals, aluminum hydroxide and ferric oxyhydroxide minerals, and aluminosilicate minerals. 

Aluminum adjuvants in human vaccines are either aluminum hydroxyphosphate (commonly referred to as aluminum phosphate) or aluminum oxyhydroxide (aluminum hydroxide). Aluminum-based vaccines are prepared by adsorption of antigen to commercial aluminum hydroxide or aluminum phosphate gels or by mixing antigen with alum (potassium aluminum sulfate),... 

Violante, A., and Huang, P. M. (1985). Influence of inorganic and organic hgands on the formation of aluminum hydroxides and oxyhydroxides. Clays Clay Miner. 33, 181-192. 

McBride, M. B. (1982). Cu-+-adsorption characteristics of aluminum hydroxide and oxyhydroxides. Clays Clay Miner. 30, 21-28. 

He has contributed to research on the interface between soil chemistry and mineralogy and soil biology. His special areas of research include the formation mechanisms of aluminum hydroxides and oxyhydroxides, the surface chemistry and reactivities of short-range-ordered precipitation products of Al and Fe, the influence of biomolecules on the sorption and desorption of nutrients and xenobiotics on and from variable charge minerals and soils, the factors that influence the sorption and residual activity of enzymes on phyllosilicates, variable charge minerals, organomineral complexes, and soils and the chemistry of arsenic in soil environments. 

Solubilities of Aluminum Hydroxides and Oxyhydroxides in Alkaline Solutions... 

In this paper, the procedures are summarized by which the solubilities of gibbsite, boehmite, and diapore in alkaline solution are evaluated and used to compute thermodynamic properties of boehmite and the aluminate ion. Published data are then used in conjunction with the derived properties of the aluminate ion given in this paper to calculate preliminary thermodynamic properties for bayerite, and the Gibbs free energy of formation of nordstrandite at 25°C. Aluminum hydroxide and oxyhydroxide, and corundum... 

Uncertanties are = 2c when based upon a statistical evaluation. Note that the uncertainties in AH298. AG298 and log K298 of the aluminum hydroxides and oxyhydroxides with respect to corundum and liquid water are between 2 and 5 times smaller than those of the corresponding properties with respect to the elements. 

Table IV summarizes log Kj4 values for aluminum hydroxides and oxyhydroxides, and corundum between 0 and 350 C. They were calculated using the modified H.K.F. equation of state (70) together with the data given in Tables I and II. These values are suitable for incorporation into distribution of species codes such as EQ3 (67), provided that A1(0H)4 (or AIO2) is made a basis species. Calculation of dissolution constants for other aluminosilicates can be made using the Gibbs free energy data for Al(OH)4 or AIO2 Provided in Table II.

Table IV. Log for Aluminum Hydroxides and Oxyhydroxides, and Corundum taken along the Water Saturation Surface...

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). 

Table 3.1 Crystal data of aluminum hydroxides and oxyhydroxides...

The chemistry of the precipitation of aluminum hydroxides and oxides is very complex (40). When the solubility is exceeded, gelatinous precipitates, which are found to be amorphous by X-ray diffraction, usually form initially. Al MAS NMR shows the predominance of octahedraUy coordinated Al ions in these amorphous hydroxides, as are present in the crystalline trihydroxides and oxyhydroxides. However, in the amorphous materials some pentacoordinated and tetracoordinated Al ions are also found (15). As discussed above, there are many different crystalline hydroxides or oxyhydroxides, and which of them will be formed depends on the conditions (4f). Primary factors are temperature and pH, as well as aging time however, the nature of the anions present and the possible presence of organic components (42,43) also play a role. At low temperature in an excess of water, the hydroxides are preferentially formed, specifically bayerite at pH values between 5.8 and 9 or gibbsite for pH values smaller than 5.8 or larger than 9. 

Aluminum is another abundant metal that is obtained from the ore bauxite, a mix of the minerals boehmite (aluminum oxyhydroxide) and gibbsite (aluminum hydroxide). The production of aluminum is very expensive because the bauxite must be heated with the compound cryolite to make a molten solution in which the aluminum is concentrated by an electric current. Aluminum is used in products such as cans, foil, windows, vehicles, and household items and mixed with other metals in alloys. 

The aluminum hydroxide (gibbsite, y-Al(OH)3) and oxyhydroxide (boehmite, y-AlOOH diaspore a-AlOOH) minerals in bauxite ore are selectively extracted from the insoluble components (mostly quartz, clay minerals, and iron and tita-... 

The results of development work on processes indicate that the two main methods of preventing the duplex microstructure from forming appear to be fast-firing, or increasing the amount of / "-alumina at low temperatures. Based on these results, Duncan et al. [21] and Zyl et al. [22] have described production processes starting from aluminum oxyhydroxides or aluminum hydroxides as precursors for the synthesis of the solid electrolyte "-alumina. Duncan et al. described an alumina precursor which substitutes in part or wholly for a-alumina in an established slurry solution spray-drying process. As a precursor, hydrothermal boehmite, Cera hydrate, has been used. A calcination step is important at the begirming of the process. Boehmite was used both in the as-received condition and after calcination. The effect of the calcination temperature on the fired properties of /S"-alumina can be seen in Table 21.5. 

This technique is based on the in situ formation of coagulant as the sacrificial anode (usually aluminum or iron) corrodes due to an applied current (figure 7). Aluminum and iron materials are usually used as anodes, the dissolution of which produces hydroxides, oxyhydroxides and polymeric hydroxides. In EC, settling is the most common option, while flotation may be achieved by H2 (electroflotation) or assisted by air injection. 

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