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Minerals of the Alunite group are designated as AB3(SO4)2(OH)6 with A = Na, K, Pb, NH4, Ag or H3O and B = Al (alunite) or Fe+++ (jarosite). Synthesis studies of Na-K and Al-Fe substitutions produce a series of solid solutions for which natural counterparts have been found. Synthesis has been successful at temperatures ranging from 78°C. to 180°C. with pressures up to 6 atmospheres. At the lower temperatures, analyses show a univalent cation deficiency and an excess of +H2O, indicating the presence of H3O+. DTA curves of hydronium-bearing jarosites show three endothermic reactions at approximately 350°C., 400°C., and 800°C. The 350°C. eaction is broad and represents a loss of hydronium ion. Similar results have been noted for natural, low-temperature jarosites.
Synthesis of alunites and jarosites with variable K-Na ratios shows a marked preference for K+. The Na-K substitution produces little change on the a0 dimension, but a pronounced effect upon c0 is recorded. The opposite effect obtains upon substitution of Fe+++ for Al. The preference for Fe+++ in the structure is lowered with increased temperature and reduced acidity.
Currently the parameters controlling the incorporation of Ag and Te in the alunite structure are being investigated.
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