Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 81:688–693 (2006) DOI: 10.1002/jctb.1469 Characterization and bleaching properties of acid-leached montmorillonite Jadambaa Temuujin, 1∗ Mamoru Senna, 1 Tsedev Jadambaa, 2 Dashdendev Burmaa, 2 Shaarii Erdenechimeg 2 and Kenneth JD MacKenzie 3 1 Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Yokohama 223-8522, Japan 2 New Materials Center, Mongolian University of Science and Technology, Ulaanbaatar 46, Mongolia 3 New Zealand Institute for Industrial Research and Development, PO Box 31-3190, Lower Hutt, New Zealand Abstract: After being subjected to preliminary purification, montmorillonite clay was leached with varying concentrations of sulfuric acid (0.5–2 mol L −1 ) at 90 ◦ C for varying times (0.5–4 h). Acid leaching causes partial amorphization of the montmorillonite and increases its specific surface area by a factor of 3 (from 49.1 to 157 m 2 g −1 ). The bleaching efficiency for Mongolian mare’s milk oil, as judged by light absorbance measurements at 400 nm, was increased from 9.5% for the unleached clay to 93.8% for clay leached with 2 mol L −1 H 2 SO 4 for 4 h.  2006 Society of Chemical Industry Keywords: montmorillonite; acid leaching; mare’s milk oil; bleaching INTRODUCTION Traditionally, acid-leached clay, e.g. montmorillonite, has been used as an adsorbent, particularly for decolorization and deodorization of vegetable and animal oils. Leaching of the clay increases its spe- cific surface area and pore volume to improve its adsorption capacity for metallic impurities, phos- phatides, oxidation products and pigmentary sub- stances in oils. 1–3 The bleaching process involves several mechanisms, including physical or chemical adsorption, ion exchange, molecular trapping and chemical decomposition. 4 Acid leaching can bring about the transformation of montmorillonite to amor- phous silica. However, the production of a material for bleaching purposes does not necessarily require such complete disruption of the crystalline structure of the clay mineral. The final mineralogical and chemical composition of an acid-leached clay depends on many factors, including the composition of the starting clay, the acid concentration and the duration and temper- ature of the leaching process. The optimal leaching condition is correspondingly different for different clays. We have previously reported the acid-leaching behavior of a montmorillonite-containing clay from the Tuulant deposit in Mongolia. 5 This deposit contains more than 50 wt% of non-clay constituents which hinder the development of the high surface area desirable in an adsorbent (maximum 93.8m 2 g −1 after 12 h leaching). We have therefore adopted a wet purification process to remove the non-clay constituents from this mineral. The resulting clay was used, after acid activation, as a decolorizing agent for different types of oils including mare’s milk oil. The latter is used as an ingredient in Mongolian cosmetics because of its high content of polyunsaturated fatty acids which make it readily absorbed by human skin. 6 However, this oil can have an undesirable yellow color, rendering it unsuitable in its raw state for cosmetic applications. It is important to find a suitable and inexpensive adsorbent for decolorization of this unique type of oil. To the best of our knowledge, there are no previous reports in the literature on the bleaching behavior of mare’s milk oil. The aim of the present research is to characterize purified and acid-leached montmorillonite clay and investigate its suitability for the decolorization of mare’s milk oil for cosmetic purposes. EXPERIMENTAL The montmorillonite was supplied from the Tuulant deposit, Mongolia. It was purified by washing with water, passed through a 76 µm sieve, drying in air and then heating in an oven at 60 ◦ C for 24 h. The chemical composition of the purified clay (in wt%) was: SiO 2 (72.5), Al 2 O 3 (15.0), MgO (4.12), CaO (4.48), Fe 2 O 3 (2.92), K 2 O (0.75) and TiO 2 ∗ Correspondence to: Jadambaa Temuujin, Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Yokohama 223-8522, Japan E-mail: jtemuujin@yahoo.com Contract/grant sponsor: COE21 Contract/grant sponsor: Information Center for Particle Technology (Received 10 August 2005; revised version received 6 October 2005; accepted 20 October 2005) Published online 24 February 2006  2006 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2006/$30.00 688