Kinetics and Thermodynamics of Cd(II) Ions Sorption on Mixed Sorbents Prepared from Olive Stone and Date Pit from Aqueous Solution

Problem statement: The aim of this study is to remove Cd(II) ions from aqueous solutions by adsorption. Mixed sorbent prepared from olive stone and date pit, an agricultural solid by-product was used as adsorbent. Approach: The adsorption experiments of Cd(II) onto the mixture of olive stone and date pit were conducted at different parameters such as, percent of olive stone and date pit in the mixture, temperature, initial solution pH and initial Cd(II) concentration. Adsorption isotherms were obtained at different percent of olive stone and date pit in the mixture. Results: This adsorption data was fitted with the Langmuir. Kinetic studies revealed that the initial uptake was rapid and equilibrium was established in 20 min for all the studied metals and that the data followed the pseudo-second order reaction. The thermodynamic of Cadmium sorption on the mixed sorbent follows the Langmuir model and the sorption capacity for cadmium increases when we add a small amount of olive stone at date pits (90% of date pits in mixture and 10% of olive stone) and a small amount of date pits at olive stone (90% of olive stone and 10% of date pits in mixture. In addition, the thermodynamic parameters, standard free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°) of the adsorption process were calculated. The sorption of Cd(II) onto the mixture of olive stones and dates pit is spontaneous and presents an endothermic nature. The characteristics of the mixture were determined by the analysis of infra red spectral analysis. Conclusion: The results show that the mixture sorbent from olive stone and date pit is an alternative low-cost adsorbent for removing Cd(II).