Structural changes of Cr-beidellite treated up to 1350 °C in oxygen or nitrogen atmospheres

Abstract

Beidellite clay mineral after intercalation of OH-Cr(III) species were thermally analyzed up to 1350 °C in oxygen and nitrogen atmospheres. OH-Cr-beidellite can be used as a pillared clay precursor for catalysis or as adsorbent applications. However, in this paper beidellite enriched in chromium were analyzed at different thermal treatments up to high temperature for evaluating structural changes for possible future ceramic applications. The structural changes were followed by thermal analysis and X-ray diffraction. The thermal treatment of OH-Cr-beidellite in oxygen and nitrogen atmospheres developed different mineralogical phases up to 1050 °C, but at higher temperatures, the same phases were developed in both atmosphere treatments. Eskolaite phase (Cr2O3) appeared in the sample after heating at 400 °C in oxygen atmosphere, whereas grimaldite (CrO-OH) in nitrogen atmosphere, maintaining the starting phases. At 1000 °C the raw clay minerals disappeared, as it is knew. At 1050 °C in nitrogen atmosphere, grimaldite was absent and eskolaite appeared. At 1350 °C in the samples calcined in both atmospheres, quartz, cristobalite and mullite as the main phases and in lower contents aluminum oxide and aluminum-chromium oxide [(Al,Cr)2O3] were present.

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“…Akpomie and Dawodu (2016) [ 67 ] reported changes in the peaks of montmorillonite treated with acid medium, indicating an alteration in the alumina content. Similarly, effects were observed in beidellite intercalated with chromium [ 63 ] and in clinoptilolite intercalated with cadmium [ 68 ].…”

“…Another component of smectites is beidellite [ 62 ]; this mineral was observed in both C-2 clay (55.0%) and C-3 clay (36.5%), with the corresponding XRD peaks. Santos et al (2018) [ 63 ] observed reflexions of beidellite at 2θ = 7.1 and 14.2°.…”

“…In addition, the XRD spectrum of C-3 clay showed diffraction peaks corresponding to beidellite (36.5%), Ca-montmorillonite (15.0%), and calcite (12%) [ 63 , 64 ]. Clinoptilolite (80%) was the main component of C-4 clay, whose XRD pattern contained diffraction peaks characteristic of this mineral [ 65 ].…”