Mineralogical and physicochemical characterization of a natural bleaching earth containing sepiolite suitable for fast filtration and bioseparation

Abstract

AbstractA clay from the Mediterranean area classified as natural bleaching earth was comprehensively characterized and the quantitative phase content was determined. Morphology and surface characteristics were determined by environmental scanning electron microscopy (ESEM) and nitrogen adsorption. The BET surface area was >200 m2 g–1 and the average mesopore diameter was >10 nm. Thus the clay is suitable for bioseparation of larger proteins. X-ray diffraction (XRD), X-ray fluorescence (XRF), cation exchange capacity (CEC), layer charge measurement and simultaneous thermal analysis (STA) were used for mineralogical characterization. Determination of the phase content by Rietveld analysis was possible only after Sr2+ saturation, while Rietveld analysis of XRD patterns from Na+-saturated clay resulted in a strong overestimation of the amorphous content and masking of the sepiolite. The clay consists of sepiolite, dioctahedral smectite with high layer charge and low stack height, X-ray amorphous matter (probably mainly SiO2) and accessory feldspars.