Mineralogical and Physico-Chemical Characterizations of Ferruginous Beidellite-Rich Clay from Agadir Basin (Morocco)

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 14098To link to this article :Abstract-The mechanism of formation of detrital, beidellite-rich clay occurring in the Agadir basin (Morocco) is well documented, but its detailed characterization is incomplete which limits its application. The aim of the present study was to provide further details of the mineralogical and physico-chemical characteristics of this clay. Bulk raw clay and its Na + -saturated, <2 mm fraction were characterized using chemical, structural, and thermal techniques. Measurements of induced streaming potential (e.g. particle charge) and of specific surface area and porous volume are reported. The raw clay contained carbonate and quartz as associated minerals along with phyllosilicates (<2 mm particle size). X-ray diffraction and scanning electron microscopy analyses showed that the <2 mm fraction was dominated by a dioctahedral smectite. Because dehydroxylation of this mineral occurred at 510ºC, and because it re-expanded in ethylene glycol after Li + -saturation followed by heating at 240ºC for 24 h, the mineral was shown to be a beidellite rather than montmorillonite. This assertion was further supported by 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectra showing predominantly negative charges in the tetrahedral sheets due to notable Al-for-Si substitutions. The chemical composition of the <2 mm fraction showed an Fe 2 O 3 content which was~7.52 wt.% greater than those of other beidellite occurrences but not so much that it would be identified as a nontronite. The absence of stretching and bending absorption bands corresponding to characteristic (Fe 2 OH) units in mid-infrared spectra and their corresponding fundamental overtones or combination bands in near-infrared spectra supported this notion. The structural formula of the beidellite in the present study was determined to be (Si 7.51 Al 0.49 )(Al 2.99 Fe 0.68 Mg 0.33 ) (Ca 0.03 Na 0.54 Mg 0.11 )O 20 (OH) 4 , having dioctahedral ferruginous characteristics with almost 60% of the negative charge found in tetrahedral sheets. The cation exchange capacity determined from the structural formula was~108 meq/100 g. The specific surface area and total pore volume were~82.2 m 2 /g and 0.136 cm 3 /g, respectively. Interestingly, a detrital rather than a hydrothermal-alteration origin, as reported for other beidellite occurrences, explains its natural abundance and emphasizes the great interest in it.

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

“…The OH-Cr solution was prepared from 0.1 M chromium nitrate solution by the addition of 0.2 M NaOH (OH/Cr=2) at 60 °C and hydrolyzed for 1 day [14]. The OH-Cr solutions contained mainly trimeric species, Cr 3 (OH) 4 5+ , followed by tetra-, Cr 4 species [15]. OH-Cr-beidellite was obtained by slowly adding hydrolyzed OH-Cr-solution to beidellite (HB) water suspension (2% w/w).…”

“…The main structural characteristic in beidellite is that Al 3+ replaces part of the Si IV in the tetrahedral sheet. This isomorphic substitution results in negative charges on the layer, which are balanced by cations such as Na + , Ca 2+ , K + , Mg 2+ situated in the interlayer position [1][2][3][4][5][6].…”

Surfactant-modifications of Na+-beidellite for the preparation of TiO2-Bd supported photocatalysts: I-organobeidellite precursor for nanocomposites

“…Organomodified Bd were prepared starting from ‹ 2 μm Na + -exchanged Bd fine fraction (Na + -Bd), isolated according to the procedure described elsewhere (Rhouta et al, 2008;Bouna et al, 2012), from the raw clay (Bd) sampled from the region of western high Atlas basin of Agadir (Morocco). The raw clay and corresponding purified Na + -exchanged clay fraction were previously characterized in details (Bouna et al, 2012).…”

“…The raw clay and corresponding purified Na + -exchanged clay fraction were previously characterized in details (Bouna et al, 2012). The Na + -exchanged Bd is composed of 93% of Bd, and 7% of kaolinite (Kaol).…”

“…More recently, mineralogical, physico-chemical, textural and structural properties of an abundant Bd -rich clay deposit from Agadir basin (Morocco) were reported (Bouna et al, 2012). Bd is different from Mt in that it is an end member of dioctahedral Al-Sm with an average layer charge of 0.6 to 0.7 pretty completely created by the substitution of Si 4+ by Al 3+ in the tetrahedral positions (Nadeau et al, 1985).…”