Synthesis of Hydrotalcite and its Anion Exchange Properties

Abstract

As one of effective usages of the wastes in an aluminum regeneration process, the syntheses of hydrotalcite (HT), which is a functional inorganic material having layered structure of complex hydroxide, were carried out by using aluminum dross and MgCl₂ waste solution as raw materials. Various physical properties such as crystal structure, surface texture and anion exchange properties were measured for the obtained products. The removal of chromic acid ion was investigated with various products.
CO₃^2- type HT can be obtained from the aluminum dross and MgCl₂ waste solution by a co-precipitation method. A slight amount of Ca, Na, Si, Fe etc. remains in the product as impurity components. The anion exchange order of HT is as follows; CO₃^2- > SO₄^2- > F^- > Cl^- > NO₃^- ≥ I^-. It is possible to remove chromic acid ion from an aqueous solution with various products by an anion exchange reaction. The Mg/Al complex oxide, which is obtained by calcination of the CO₃^2- type HT at 773 K, is superior to the original HT for the removal of chromic acid ion.