Anionic Surfactant Impregnation in Solid Waste for Cu2+ Adsorption: Study of Kinetics, Equilibrium Isotherms, and Thermodynamic Parameters

Coconut shell powder (CP) and diatomite (Di) were modified with microemulsion (mu E), producing low-cost adsorbents for copper (II) removal from aqueous solutions. The mu E was prepared using as active phase an anionic surfactant sodium octanoate (SO), obtained from the saponification of octanoic acid. The effect of modification on the adsorption capacity of Cu+2 was evaluated taking into consideration the solution pH, equilibrium time, temperature, and initial concentration of metal in solution. The adsorbents were analyzed by characterization techniques of X-Ray Fluorescence, scanning electron microscope and Fourier Transform Infrared Spectroscopy. The obtained experimental data were analyzed using the equations of Langmuir, Freundlich, Temkin, and Dubinin Radushkevich models. The initial concentration of 50 mg Cu+2/L solution and 0.2 g of adsorbent materials modified with the mu E presented a Cu+2 removal efficiency of 86.81% and 96.3% for CP and Di, respectively. The kinetic models of pseudo first-order, pseudo second-order, Elovich, and intraparticle diffusion were used in this study to describe the adsorption rate. The presence of sodium octanoate functional (OS) group provided ion exchange sites suitable to Cu+2 adsorption. The stability of the OS impregnation using microemulsion was evaluated based on a desorption study.