Decolorization of Rice Bran Oil Using Modified Kaolin

Measurements show that kaolin from Ranong, obtained from a major deposit in southern Thailand, can be modified to produce a material that is suitable for decolorizing rice bran oil. Its sorption properties were determined after various physical and chemical modifications of this kaolin. Physical modification was achieved by grinding via a planetary ball mill (300 rpm for 1 h), and this was followed by chemical treatment using sulfuric or oxalic acids. The optimum decolorization capacity (~80%) was achieved by using 2 M sulfuric acid. With oxalic acid, the best results were obtained with 0.7 M, but these were slightly lower than those obtained with 2 M sulfuric acid. Compared to the original kaolin sample, the specific surface area of the modified clay increased from ~13 to ~244 cm² g⁻¹, and the total pore volume from 0.06 to 0.43 cm³ g⁻¹. The pore size distribution curves show that most pores are in the mesoporous region with their diameters between 3.0–4.5 nm, and are suitable for adsorption of pigment molecules that are present in rice bran oil. Desorption and spectroscopic studies suggest that both electrostatic and chemical processes are involved in the interaction between pigments and active sites on the clay surface.