The reversible extraction of the hexamminecobalt(III) cation by kanemite (NaHSi2O5·3H2O): enhanced extraction in the presence of a cationic surfactant

Abstract

Kanemite, NaHSi₂O₅·3H₂O, has been found to extract the metal complex cation, hexamminecobalt(m){[Co(NH₃)₆]^3±} directly from aqueous solution at ambient temperature. The enhancement of the extraction by the quaternary ammonium salt, hexadecyltrimethylammonium chloride, is related to the ability of the quaternary ammonium salt to decrease the effective interlayer charge at the layer edges, thus permitting greater diffusion of the complex cation. The extraction is reversible since the cobalt complex cation can be quantitatively released back into the aqueous phase by treating the loaded kanemite with HC1. Kanemite may be used at least three times in a cycle of extraction and elution plus regeneration using sodium hydroxide. Using MAS NMR, it has been shown that the Q³ silicon sites are associated with the exchange sites in kanemite and also with the strong hydrogen-bonding interactions that dominate the structure of kanemite. It has also been shown that only one of the two types of sodium present in kanemite was exchangeable.