Study of the Adsorption of ${\mathrm{Ag}}^{+}$ by Zinc Chloride–Modified Peanut Shells: Adsorption Kinetics, Thermodynamics, and Isothermal Properties

In recent years, with the development of China’s industry, the pollution problem of heavy metal wastewater in the country has become increasingly serious. In this paper, peanut shells modified with zinc chloride were selected as an adsorbent for the adsorption of ${\mathrm{Ag}}^{+}$, and the optimal conditions for this adsorption were investigated. The results showed that the best adsorption effect was achieved at pH 4.0, an initial concentration of $250\mathrm{\mu g}/\mathrm{mL}$ of ${\mathrm{Ag}}^{+}$, a dosage of 0.10 g of peanut shell, a contact time of 40 min, and a temperature of 20°C. The prepared materials were also characterized by scanning electron microscopy and an X-ray diffraction analyzer. It was found that the skeleton did not change after the peanut shell treatment: the pores became larger; and the peanut shells had good adsorption capacity for ${\mathrm{Ag}}^{+}$ after being modified with zinc chloride. The kinetic, thermodynamic, and isothermal properties of the adsorption process were analyzed, showing that the adsorption conforms to the quasisecond-order kinetic equation and to the Freundlich adsorption isotherm. By this method, the heavy metal ${\mathrm{Ag}}^{+}$ in wastewater can be absorbed at low cost and with high efficiency, providing protection to the environment.