Two Parameter Isotherm Models of Colour Pigments Removal from Cottonseed Oil onto Biopolymer Prepared from Oyster Shell Waste

The effectiveness of chitosan prepared from oyster shell powder and its application in removing colour pigments and other impurities from cottonseed oil was carried out in this study. The bleaching was carried out at various adsorbent dosages (1.0 to 3.0 g). The bleaching adsorbents, (oyster shell powder, OSP and chitosan prepared from oyster shell powder COSP) were characterized using XRay Fluorescence (XRF) for the elemental composition, XRay Diffraction (XRD) for mineral composition and crystallinity, Scanning Electron Microscopy (SEM) for the surface morphology, and Fourier Transform Infrared (FT-IR) was used to investigate the presence of functional groups in the samples. The results showed that there was alteration in the concentration (wt %) and distribution of different compositional elements. The XRD analysis revealed the amorphous and crystalline characters in OSP while it suggested pure crystalline character in COSP and entirely composed of aragonite (2θ value of 29.2). The differences observed in surface morphology of the samples revealed some changes that occurred during the preparation of COSP and the absence and shifting of absorption bands in COSP indicated changes in the structure of the samples. The bleaching process was tested with four different isotherms (Langmuir, Freundlich, Temkin and Dubinin – Radushkevich (D-R). The adsorption process followed Freundlich isotherm (R2 is 0.891 in COSP and 0.929 in ROSP). The free mean energy of the process revealed that the adsorption occurred via chemisorption in both OSP and COSP (9.132 and 18.9 EkJ/mol respectively). The result also revealed that OSP improved the colour of cottonseed oil (% bleaching efficiencies at 1.0 and 1.5 g were 81.20 and 76.18 respectively) better than COSP (% bleaching efficiencies at 1.0 and 1.5 g were 66.7 and 70.63 respectively).