Influence of Inorganic and Organic Ligands on the Formation of Aluminum Hydroxides and Oxyhydroxides

Abstract

Abstract--Hydroxide and oxyhydroxide products of aluminum were formed at room temperature at an initial AI concentration of 2 x 10 -3 M, pH 8.2, and at varying concentrations of organic and inorganic ligands commonly found in nature. The effectiveness of the ligands in promoting the formation of noncrystalline products over crystalline AI(OH)3 polymorphs was found to be in the following order: phthalate ~ succinate < glutamate < aspartate < oxalate < silicate -~ fluoride < phosphate < salicylate malate < tannate < citrate < tartrate. The lowest ligand/A1 molar ratio at which the production oral hydroxides or oxyhydroxides was inhibited ranged from 0.02 to 15. Above critical ligand/A1 ratios, crystalline products were inhibited and ligands coprecipitated with noncrystalline products which remained unchanged for at least 5 months. Polydentate and large ligands generally were more inhibitive than those with fewer functional groups or of smaller size.The perturbing ligands promoted and stabilized the formation of pseudoboehmite over crystalline AI(OH)3 polymorphs in the following sequence: chloride < sulfate < phthalate ~ succinate < glutamate < silicate < aspartate < phosphate < salicylate ~ malate < tannate < citrate < tartrate. The optimal range of the ligand/A1 molar ratios for the formation ofpseudoboehmite varied, for example, from 0.005-0.015 for tartrate to 600-1000 for chloride. Pseudoboehmite was not formed in the presence of fluoride.

Amorphous Aluminum Hydroxide Formed at the Earliest Weathering Stages of K-Feldspar

“…It is well known that amorphous aluminum hydroxide transforms into crystalline materials such as gibbsite, bayerite, nordstrandite or boehmite by prolonged aging, depending strongly on pH, temperature and concentration of organic and inorganic ligands present in solution (Barnhisel and Rich 1965;Hsu 1966Hsu , 1989Taylor 1987;Violante and Huang 1985, 1992. Gibbsite, bayerite and nordstrandite have a similar structure composed of basic sheets of close packed hydroxyls with A1 in octahedral co- ordination with different stacked sequences (Taylor 1987).…”

Experimental Study on the Formation of Zeolites from Obsidian by Interaction with NaOH and KOH Solutions at 150 and 200 °C

“…Such fibrous boehmite is well known as "pseudoboehmite", whose disordered structure is caused by random intercalation of water molecules into the octahedral layers (Tettenhorst and Hofmann 1980). Similar material can be easily produced by aging of amorphous Al-hydroxide prepared by neutralization of acidic solution containing A1 ions (Souza-Santos et al 1953;Violante and Huang 1985;Violante et al 1993).…”

Effect of removal of free oxides on changes in dispersibility and charge characteristics of soils

“…This order generally corresponded to the results obtained by Kato (1977). According to Violante and Huang (1985), the capability of organic acids to solubilize A1 oxides was controlled by their chelating power for A1, or stability constants. It was demonstrated that stability constants of A1 complexes decreased in the following order: citrate>oxalate>tartrate>>acetate (Martell and Calvin 1956;Earl et al 1979).…”