INVESTIGATION OF PYROAURITE-TYPE ANIONIC CLAY-DERIVED MIXED OXIDES WITH VARIOUS COMPOSITIONS

摘要

Pyroaurite, a natural mineral with the formula Mg6Fe2(OH)_(16)(CO3)·4H2O belongs to the large class of anionic clays and contains positively charged Mg(II) and Fe(III) layers alternating with layers containing carbonate ions and water molecules. Mesoporous pyroaurite-type anionic clays with different Mg/Fe molar ratios (1:3-5:2) have been successfully synthesized by coprecipitation method. The corresponding oxides were obtained by thermal treatment at 550°C and 900°C. The effect of samples' composition on the structural and textural characteristics of starting pyroaurite and corresponding oxides has been investigated. The crystallite size, the phase composition and BET surface area values were found to strongly depend on the Mg/Fe ratios. TEM micrographs revealed mat sheet-like morphology of the high Mg(II) content samples was preserved at 550°C, due to a special decomposition mechanism of pyroaurite.