Eco-friendly removal of heavy metals using Moroccan calcite-quartz clay: Adsorption performance and mechanistic insights

Abstract

The treatment of water polluted by harmful metals such as zinc and copper is a major challenge due to its consequences for the environment and health. This study examines the potential of a calcite-quartz clay from western Morocco as an abundant, inexpensive, and effective adsorbent for their removal. The adsorption mechanisms were elucidated using kinetic and isothermal modeling, supported by an in-depth physicochemical and structural characterization of the adsorbent, including X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, thermal analysis, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and textural characterization by specific surface area measurement. The kinetics, which follow the pseudo-second order model, are both rapid and efficient. For Zn2+ (10 mg/L, pH= 6.5), equilibrium is reached in 120 minutes, with a maximum capacity of 61.22 mg/g and a removal rate of 99.46%. Cu2+ (pH=5.6) shows comparable behavior, with stabilization at 150 minutes, a capacity of 59.40 mg/g and an efficiency of 91.46%. Analysis of the isotherms shows that the adsorption of Cu2+ by the clay under study follows the Langmuir model, whereas the adsorption of Zn2+ exhibits behavior consistent with adsorption at multiple sites, in accordance with the Freundlich model. SEM-EDX and FTIR analyses confirmed the adsorption of the metals studied at the clay interface. These results highlight the validity and importance of the calcite-quartz clay analyzed for the treatment of effluents loaded with copper and zinc, offering a favorable alternative to traditional methods.