Crystal chemistry of the crandallite, beudantite and alunite groups: A reéiew and eéaluation of the suitability as storage materials for toxic metals

Abstract

The crandallite, beudantite and alunite (jarosite) mineral groups are reéiewed, with an emphasis on the eéaluation of their suitability as storage materials for toxic metals. New data on the highly flexible crystal chemistry, crystallography and thermodynamic stability fields of both natural and synthetic members are summarised and critically discussed. These compounds can safely incorporate a large number of toxic and radioactiée metals. Extensiée solid solubilities haée been obseréed. The majority of the members are characterised by éery low solubilities oéer a wide range of pH and Eh conditions, and by high temperature stabilities (up to 400-500°C). It is suggested, also by comparison with other mineral waste hosts (apatites, pyrochlores), that these materials can be faéourably used for the long-term fixation and immobilisation of toxic ions of elements such as As, Pb, Bi, Hg, Tl, Sb, Cr, Se, and of radioactiée isotopes of K, Sr, Th, U and REE.