A 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.

The main physico-chemical properties of a new smectitic clay containing large amounts of amorphous material are reviewed and potential industrial applications of this type of clay are discussed. Due to a 34% amorphous material content (natural silica gel), the investigated clay has very high porosity and can be used as it is or in acid-impregnated form for oil bleaching or phosphate reduction in edible oil. In the field of biodiesel purification, the new clay can be used to remove, in particular, mono-, diglycerides and glycerol. The natural silica-smectite mixture is also suitable as a carrier for liquid ingredients, for example in animal feeds, and might serve as a partial or complete substitute for synthetic precipitated silicas. In the field of bioseparation processes, the clay can be used as an adsorbent for protein separation by means of cation exchange. Due to the suppressed swelling (compared with smectite alone), it can be packed in columns which can be regenerated.