Applicability of the Freundlich and Langmuir adsorption isotherms in the bleaching of rubber and melon seed oils

Abstract The applicability of Freundlich and Langmuir adsorption isotherms to guide bleaching of vegetable oils was examined using rubber [ Hevea brasiliensis (Willd. ex Adr. Juss) Muell. Arg.] and melon [ Colocynthis vulgaris (Schrad)] seed oils at temperatures of 30, 55 and 80 C. Fuller’s earth, activated charcoal and a mixture thereof (1:1 ratio) were used as the decolorizing agents (adsorbents). The degree of bleaching was monitored spectrophotometrically. Plots of log(x/m) versus log X e (for Freundlich) and ( X e /x/m) versus X e (for Langmuir) were made; where x is the amount of coloring matter removed per unit mass of the adsorbent, m, and X e is the equilibrium concentration of the coloring matter. The results obtained show good agreement with Freundlich and Langmuir isotherms, indicating that the adsorption of the coloring matter from the oils proceeds by monolayer formation on the surface of the adsorbent. The specific adsorption (x/m) and the Freundlich and Langmuir constants were found to increase with temperature for a given oil/bleaching agent ratio, showing the formation of more active sites on the adsorbent with a rise in temperature.