A New Synthesis of Hollandite. A Possibility for Immobilization of Nuclear Waste

Abstract

Na-buserite exchanges readily its Na⁺ for other ions. When Ba²⁺ is incorporated, dehydration to Ba-birnessite occurs. Subsequent heating at temperatures of ca. 500-800 °C in air in a furnace leads within hours to a structural rearrangement and to nucleation of hollandite. The latter is a tectomanganate with Ba²⁺ ions sitting in a tight fit in tunnels. The content of these tunnels is not exchangeable. The new way of synthesis is a topotactical reaction and leads to less finely divided products than previous preparation methods starting from MnO₄^- solutions. The new synthesis is also much easier than previously used hydrothermal methods. The product of analytical composition BaMn₂^III Mn₆^IV O₁₆ provides a means for immobilization of waste ions of appropriate size (≈ 1.4 Å) and is thermally stable up to 800 °C.