Optimization of Adsorption for the Removal of Cadmium from Aqueous Solution Using Turkish Coffee Grounds

In this study, the effectiveness of the use of spent Turkish coffee grounds as an adsorbent in the treatment of water polluted with cadmium (Cd) ions through adsorption was investigated. The change in adsorption efficiency (%) with independent variable parameters was planned using the Box-Behnken experimental design method, which is a subset of the response surface methodology (RSM), and the relationship was modeled mathematically. The optimum amount of adsorbent, initial Cd (II) concentration, and pH were found to be 3.63 g/L, 67.97 mg/L, and pH 8.87, respectively, when the desirability function method was applied. While the highest adsorption capacity under optimum conditions is 1.32 mg/g, Cd (II) removal efficiency is 96%. Batch adsorption test results demonstrated that Cd (II) adsorption occurred very rapidly and equilibrium was reached in a short period of 60 min. The adsorption of Cd (II) ions increased as pH increased. As the initial Cd (II) concentration increased (up to the initial concentration of 200 mg/L), the removal percentage and adsorption capacity also increased. The adsorption behavior of Cd (II) was investigated with the Langmuir and Freundlich models, and the experimental data were determined to be compatible with the Langmuir isotherm (R-2 = 0.9996). Furthermore, the pseudo-second-order model described the adsorption kinetics of Cd (II) ions on the coffee grounds in the best way. Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscope results and zeta potential showed that Cd (II) was bound to coffee by electrostatic forces and complexation reactions.