Study of the uptake of inorganic ions and organic acids at theα-alumina-electrolyte interface in a colloidal system by radiochemical techniques and microelectrophoresis

Abstract

The interactions of the alumina-electrolyte in the presence of inorganic ions (copper, selenium) and/or organic acids (benzoic acid, glutamic acid, phenol) have been studied. The acid-based properties ofα-alumina have been determined in NaCl media (pzc=8.5±0.3). Three types of hydroxy groups with different acidity constants have been found. The adsorption of copper and selenium have been described by the formation of the surface complexes: (=Al1−OH, CuCl) and (=Al1, SeO3)−. The interaction of copper with the surface oxygen atoms is strong and so is the interaction of selenium with the surface aluminium atoms, which involves a shift of the iep of alumina. For the three organic acids studied (HX), the adsorption equilibrium is:=Ali−OH+HX⇆(=Ali, X)+H2O. The interaction of the X− group and the aluminium atoms is strong following the order: glutamic acid > benzoic acid > phenol. The uptake of selenium is uninfluenced by the presence of organic acids with carboxylic, amino-acidic and phenolic groups. The uptake of copper is highly increased by the presence of organic acids but it is not influenced by the presence of the phenolic groups. Both of these behaviours can be extrapolated to inorganic ions of the same chemical structure.