Influence of texture and composition on the properties of Mg-clays for adsorption applications

MUSSO, TELMA BELÉN; PETTINARI, GISELA; ROCA JALIL, M.E.; BASCHINI, MIRIA; GALÁN, ANA BELÉN; SANCHEZ, MICAELA; MAGGIO, ANDREA; RODRIGUEZ-AMEIJIDE, VANINA; VILLA, LUIS; PEREZ-ABAD, ALEJANDRO; POZO, MANUEL

Conferencia; International Conference of European Clay Groups Association; 2023

Samples of clayey materials consisting of magnesian clay minerals from lithofacies of theMiocene Intermediate Unit of the Madrid Basin have been studied. Taking into account theircomposition and texture, the aim is to evaluate their possibilities for their application asadsorbent clays. In the compositional characterization, XRD, FTIR, DTA-TGA, NMR andelemental chemical analysis were used. The textural study was carried out by opticalmicroscopy (petrography) and electron microscopy (SEM, TEM). The properties analyzed wereBET specific surface area and porous system, cation exchange capacity (CEC) and grain-sizedistribution. Clays with a predominance of fibrous (sepiolite, palygorskite) or lamellar(bleaching clays, bentonite) clay minerals were differentiated. Thus, they have been groupedinto four mineralogical assemblages, according to their clay mineralogy, depending on whetherfibrous minerals (sepiolite or palygorskite) or lamellar minerals (saponite or kerolite-magnesiansmectite) predominate. Petrographically, varied textures have been observed ranging fromgranular to massive and laminated microfacies, where evidence of recrystallization is common,with several generations of the same clay mineral being observed, especially in the case ofsepiolite.The results indicate that smectite do not control the highest BET specific surface area values,since the samples with values above 250 m2/g correspond to the samples richest in sepiolite andto the most kerolitic sample, where the smectite content barely exceeds 20%. On the other hand,with respect to cation exchange capacity, it has been observed that, in addition to thepercentage, the type of smectite and its texture play an important role. Thus, the cation exchangecapacity is especially relevant in the bentonite sample, which is the richest in smectite of mostlysaponite composition; however, the samples rich in stevensite of the bleaching clays do notexceed the cation exchange capacity of samples with a much lower smectite content. It hasbeen observed that in general, as the volume of mesopores increases, the specific surface areaincreases, but the cation exchange capacity decreases. This is especially true in samples withseveral recrystallization stages as those of sepiolites.From the point of view of textural properties (specific surface area BET, porous system), allsamples are mesoporous (2-50 nm), but with differences in pore sizes within this wide range.The grain size distributions vary from bimodal to polymodal, with the bleaching clays havingthe highest median values (76-128 µm) with low contents (