Aluminum oxyhydroxides

Inorganic reactions in the soil interstitial waters also influence dissolved P concentrations. These reactions include the dissolution or precipitation of P-containing minerals or the adsorption and desorption of P onto and from mineral surfaces. As discussed above, the inorganic reactivity of phosphate is strongly dependent on pH. In alkaline systems, apatite solubility should limit groundwater phosphate whereas in acidic soils, aluminum phosphates should dominate. Adsorption of phosphate onto mineral surfaces, such as iron or aluminum oxyhydroxides and clays, is favored by low solution pH and may influence soil interstitial water concentrations. Phosphorus will be exchanged between organic materials, soil inter-... 

FIGURE 1.2. Formation of nanoparticles of metal oxide by reverse micelle method. A solution of inverse micelles is first formed by adding a long-chain alkylamine to a toluene solution. A small amount of water is trapped in the reverse micelle core. Mixing the reverse micelle solution with an aluminum alkoxy amine adduct results in hydrolysis of the aluminum alkoxide adduct and formation of nano-sized particles of aluminum oxyhydroxide after drying. These particles are shown in the SEM picture above. 

A variation of this method was used to control the surface properties of aluminum oxide particles, particularly the surface density of Lewis acid sites. Instead of using a long-chain amine surfactant, the solution of aluminum alkoxide precursor was mixed with a small amine to convert the alkoxide dimer (or oligomer in general) into monomeric alkoxide-amine adduct. Controlled hydrolysis of this adduct produces an aluminum oxyhydroxide in which the surface A1 ions are coordinated to amine... 

Rhodium and iridium nanoparhcles entrapped in aluminum oxyhydroxide nanofibers were shown by Park et al. to be suitable catalysts for the hydrogenation of arenes and ketones at room temperature, with hydrogen at ambient pressure [103]. Rhodium in aluminum oxyhydroxide [Rh/A10(0H)] and iridium in aluminum oxyhydroxide [Ir/A10(0H)], were simply prepared from readily available reagents such as RhCls and IrCls hydrates, 2-butanol and Al(O-sec-Bu) at 100°C. Substrates such as cyclopentanone, 2-heptanone, ethyl pyruvate, acetone and 2,6-dimethyl-4-heptanone were reduced to the corresponding alcohols either in n-hexane at room temperature (maximum TOF 99 h" for ethyl pyruvate) or in solventless conditions at 75 °C using 4 atm of H2 (maximum TOF 660h" for acetone, 330 for 2-heptanone). 

Silca, crystalline-quartz, 628 Chromyl chloride, 175 Fthylidene norbornene, 335 Methomyl, 443 Cobalt hydrocarbonyl, 182 Decaborane, 203 Benomyl, 67 Diborane, 211 Pentaborane, 555 Osmium tetroxide, 546 Cesium hydroxide, 131 Alumina trihydroxide, 38 Aluminum oxyhydroxide, 38 Vinyl toluene, 738 Nonylphenol, 541 2,4-Dinitrotoluene, 279 Trimethyl benzene, 712 Methylcyclohexanol, 465 Terphenyls, 656 Isooctyl alcohol, 409 Anisidine, 52... 

Alumina is a porous, high-surface-area form of aluminum oxide. The surface has more polar characteristics than silica gel does therefore, it has both acidic and basic characteristics, reflecting the nature of the metal. Alumina has a high melting point, slightly over 2000°C, which is also a desirable property for a support due to its thermal stability. Alumina is composed of aluminum trihydroxides, Al(OH)3 aluminum oxyhydroxides, AIO(OH) and aluminum oxide, Al203n(H20). 

A reaction sequence analogous to that in Eq. 4.40 can also be developed for the specific adsorption of bivalent metal cations (e.g., Cu2+, Mn2 or Pb2+) by metal oxyhydroxides.21 In this application the abstract scenario in the first row of Table 4.3 is realized with A = =Al-OH, B = M2+, C = =Al-OH - - M2+, D = = Al-OM+, and E = H where M is the metal complexed by an OH group on the surface of an aluminum oxyhydroxide. Analysis of pressure-pulse relaxation kinetics data leads to a calculation of the second-order rate coefficient kf, under the assumption that the first step in the sequence in Eq. 4.40 is rate determining. Like k(l, the rate coefficient for the dissolution of a metal-containing solid (Section 3.1 cf. Fig. 3.4), measured values of k, correlate positively in a log log plot with kw,. , the rate coefficient for water exchange on the metal... 

Most of the ion exchange reactions that occur in soils involve three or more principal ions. For example, in soils at pH < 4, the trio H+, Ca2+, Al3+ might be considered, and, in soils at pH > 7, the set Na+, Mg2+, Ca2 is important.1 Multicomponent cation exchange is the norm for reactions on humic substances13 and the same is true for anion exchange on metal oxides (e.g., CE, NOJ, and SO4 on iron or aluminum oxyhydroxides).14... 

AIH02 aluminum oxyhydroxide (beta)) 14457-84-2 25 00 3.4400 1 432 BaC2H6N203S2 barium thiocyanate trihydrate 68016-36-4 25.00 2 2860 1... 

Grantham M. C., Dove P. M., and DiChristina T. J. (1997) Microbially catalyzed dissolution of iron and aluminum oxyhydroxide mineral surface coatings. Geochim. Cosmochim. Acta 61, 4467—4477. 

Iron and aluminum oxyhydroxides and hydroxysulfates with sorbed metals that form in ARD and in surface waters affected by ARD. 

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),... 

One can speculate that other soil aluminum oxyhydroxide phases, diaspore, bayerite, and nordstrandite also exhibit low surface free energies, similar to those for gibbsite and boehmite. More calorimetric studies are needed to quantify these relations. 

Laberty and Navrotsky (1998) determined the enthalpies of formation of a number of iron oxide and oxyhydroxide polymorphs. Data are listed in Table 2 which also compares the enthalpy relations among aluminum, iron, and manganese. It is evident that the Fe oxyhydroxide phases are much less stable relative to the anhydrous ferric phase (hematite) than are the aluminum oxyhydroxides relative to corundum. This is consistent with the much more frequent observation of hematite than of corundum in the field. It is also evident that the iron phases are as rich in polymorphism as the aluminum phases. It is clear that the enthalpy differences for both anhydrous (AI2O3, Fe203, Mn02) and hydrous (AlOOH, FeOOH, MnOOH) polymorphs are small, setting the stage for nanoscale stability crossovers. 

In our weathering example (Table 7,2) kaolinite, rather than the aluminum oxyhydroxides, was the chief weathering product of the feldspars. This reflects the fact that the silica present in soil moisture and natural waters, generally, is high enough to stabilize kaolinite relative to the aluminum oxyhydroxides. This observation is better understood if we write the kaolinite dissolution reaction ... 

The aluminum oxyhydroxides, kaolinite, and halloysite dissolve to form cationic aluminum species at low pH and the anionic species (Al(OH)4) at high pH. The same amphoteric behavior is also true of the Fe(III) oxyhydroxides, although the latter are much less soluble, in general, under oxidizing conditions. We next compute the solubilities of the ferric oxyhydroxides as a function of pH. The approach is identical to that described above for the Al-oxyhydroxides. 

TABLE 12.7 Solubility products of some secondary aluminum oxyhydroxides and sulfate minerals observed resulting from the interaction of acid mine waters with geological materials... 

Soil solution phosphate concentrations are maintained at low levels as a result of absorption of phosphorus by various soil constituents, particularly ferric iron and aluminum oxyhydroxides. Sorption is considered the most important process controlling terrestrial phosphorus bioavailability. Plants have different physiological strategies for obtaining phosphorus despite low soil solution concentrations. 

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