Biosorption potential assessment of modified pistachio shell waste for methylene blue: thermodynamics and kinetics study

Abstract

Batch scale studies were conducted to investigate biosorption potential of sodium hydroxide treated pistachio shell (PS) biomass for methylene blue (MB). Fourier transform infrared spectroscopy analysis confirmed interaction between acidic oxygen surface groups and MB nitrogen atoms. Scanning electron microscopy, wide angle X-ray diffraction (WXRD) technique, energy dispersive X-ray spectroscopy and N₂ adsorption/desorption isotherm studies were carried out to evaluate surface morphology, surface area and pore size of biomass. Optimum MB biosorption (92.12%) was observed at pH 5.63. A drastic decrease in biosorption from 21.6 to 2.75 mg/g was observed with increase in ionic salt (NaCl) concentration from 0.05 to 0.25 M. Contact time study showed increase in biosorption capacity from 5.75 to 23.07 mg/g with MB concentration (25–100 mg/L). Equilibration time ranged between 60 and 240 min. Biosorption was endothermic and physical process obeying pseudo second order kinetics model. Isotherm studies revealed applicability of Sips model. The MB recovery was 99.8% with 0.15 M oxalic acid (OA) within 15 min. Regeneration study confirmed almost constant recovery rate for four consecutive cycles.

Keywords:

• Pistachio shell
• Alkaline treatment
• Physisorption
• Desorption
• Regeneration

Acknowledgements

Authors would like to acknowledge Deanship of Scientific Research (RGP-VPP-052) at King Saud University, Riyadh.