Alumina, aluminum hydroxide adsorption

Cho et al. reported that a-alumina is formed from aluminum hydroxide prepared by precipitation with potassium hydroxide. However, when alkaline hydroxide is used as the precipitation agent, alkali cations are incorporated into the product, and commercial gibbsite samples are always contaminated with a small amount of sodium ions. Therefore their starting material seems to be contaminated with potassium, and the presence of potassium ions in their precursor seems to play an important role in the nucleation of a-alumina. They also reported that hydroxyl ions, acetic acid, and pyridine added to the glycothermal reaction system affect the morphology of the a-alumina particles because of their preferential adsorption to a specific surface. ... 

No satisfactory method has been found for removing the 3-4% of A-fraction presumably remaining in the Pentasol non-precipitated B-traction. Bates, French and Rundle have suggested that this may be removed by repeated treatment with cotton. Attempts to apply this purification have not been successful. Various grades of cotton, cellulose pulp, charcoal, activated alumina, precipitated aluminum hydroxide, bentonite and fuller s earth have been tested, without any significant improvement in the purity of the B-fraction. It is possible that Bundle s cotton treatment may introduce traces of lipid material (fatty acids or sterols) which mask the iodine adsorption. 

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). 

Various hydrated aluminum hydroxides serve as starting material for TLC alumina. By a series of nonuniform thermal dehydration processes, a variety of aluminas are obtained, and the ones most suitable for TLC are the crystalline modifications of x-ALOs and y-ALO (Rossler, 1969 Snyder, 1975). The physicochemical properties or the exact nature of adsorption sites of alumina are not well understood. Snyder (1975) has suggested that exposed A1 atoms, strained Al-O bonds, and perhaps other cationic sites serve as adsorption sites, whereas, unlike silica, surface hydroxyl groups are probably not important. Acids are probably retained by interaction with basic sites such as surface oxide ions. Gasparic and Churacek (1978) report that every A1 atom is surrounded by six atoms of... 

A very large number of articles and patents have been issued on methods to precipitate or adsorb lithium from brines, but by far the most common is the suggested adsorption or co-precipitation of lithium on aluminum hydroxide or alumina. When aluminum chloride is added to a neutral or basic solution containing lithium most of the lithium joins the voluminous aluminum hydroxide gel-like precipitate. In a similar manner, hydrated aluminum hydroxide can adsorb lithium, and a wide range of mixtures with aluminum hydroxide (either in a solid phase or as a co-precipitate) can act in a similar manner. This method was first proposed by... 

The application of infrared photoacoustic spectroscopy to characterize silica and alumina samples is reported. High quality infrared photoacoustic spectra illuminate structural changes between different forms of silica and alumina, as well as permit adsorbate structure to be probed. Adsorption studies on aerosil suggest adsorbed species shield the electric fields due to particle-particle interactions and induce changes in the vibrational spectra of the adsorbates as well as in the bulk phonon band. It is shown that different forms of aluminum oxides and hydroxides could be distinguished by the infrared spectra. 

Asare [50-52] studied the adsorption of Cu(H), Ni(II), and Co(II) onto titania, hematite, alumina, and quartz in ammoniacal solutions and found that the conventional sigmoidal adsorption curve was replaced by an adsorption profile that increased initially with increased pH, declined in adsorption as the ammine complexes formed, and then increased at high pH as the hydroxide ligands replaced the ammonia ligands. This effect was also reported by Luo and Huang [53], who studied Cu(H) adsorption onto iron(III), aluminum(Hl), and tin(IV) oxides in ammonia solution for the pH range 5-9. 

Alumina is a commonly used term for aluminum oxides and hydroxides, which exist as at least five thermodynamically stable phases and many more meta-stable transition forms. Other chapters include discussions of the physical forms of these materials and their methods of production. With the exception of some alpha aluminas, all forms possess surface hydroxyls which can have a certain degree of activity in adsorption. The treatise by Wefers and Bell is considered to be a good review of aluminum oxide phase chemistry [10]. 

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