Acid activation and bleaching capacity of bentonites from the Troodos ophiolite, Cyprus

摘要

Acid activation with HCl and H_2SO_4 of a bentonite from the Troodos ophiolite complex, Cyprus, resulted in a 2.2-fold increase of the surface area of the raw materials. The activated materials have been rendered suitable for decolourization of crude maize oil and sunflower oil through removal of β-carotene. Activation increased microporosity and changed hysteresis of adsorption isotherms from H4-type to H3-type, suggesting aggregates of plate-like particles, which form slit-shaped pores. The coloring agents are not intercalated in interlayer sites, but are adsorbed in active centres present in crystal edges. Bleaching capacity is linearly related with BET specific surface area. STS diagrams combined with bleaching experiments are useful for evaluation of acid activated bentonites. The activated Cyprus bentonite cannot remove even small amounts of β-carotene selectively from sunflower oil, when other coloring agents are present.