Isothermic, Kinetic and Thermodynamic Studies of Chromium (VI) Ions Adsorption on Composite Adsorbent of Chitosan- Eggshell Activated Carbon

The removal of heavy metals such as chromium (VI) ions from wastewater is indispensable for the accomplishment of safeguarding the environment and human health. Hence, the adsorption properties of Cr (VI) ions on synthesized, characterized composite adsorbent of chitosan–eggshell activated carbon are investigated in this study. Excellent agreements were achieved between the predicted optimum values of yield and DDA of the extracted chitosan from the St. Peter’s fish scales, the predicted optimum values of the yield and surface area of eggshell activated carbon and their corresponding experimental values, with % error < 5. For the first time, exhaustive isothermic, kinetic and thermodynamic studies were carried out wherein thirteen 2–parameter (p), two 3–p isotherms and 9 kinetic models were employed with 3 kinetic models to establish the phenomenon of Cr (VI) ions adsorption. The 2–p Langmuir isotherm, which indicates monolayer coverage on the synthesized composite adsorbent and with maximum adsorption capacity of 4.0717 mg/g, and the pseudo second–order kinetic model are the most suitable for correlating the adsorption equilibrium and kinetic data of Cr (VI) ions adsorption respectively, based on the highest regression coefficient, R2 and lowest values of error functions. The adsorption of Cr (VI) ions on the composite adsorbent was film-diffusion controlled and chemisorbed. The thermodynamic studies reveal that Cr (VI) ions adsorption is spontaneous and exergonic since ΔG0 values are negative, endothermic since ΔH 0 = +1.7293 J/mol, and ΔS 0 = +63.7684 J/(mol K) indicating feasibility of the adsorption process with high affinity of adsorbate on adsorbent.