Evaluation of the Adsorption Performance of Geological Materials Based on Limestone and Green Shale from the Taza Region, Morocco: Application for Leachate Treatment

The present study aims, on the one hand, to examine and evaluate the potential of natural geological adsorbents elaborated from limestone and green shale for leachate treatment. In contrast, it highlights an innovative approach based on the separate evaluation of these two natural materials, which has not yet been explored in depth in the literature, with a view to offering a sustainable and economically accessible alternative to commercial adsorbents. To this end, the studied materials were prepared from rocks collected around the city of Taza, Morocco. The absorbent properties of the produced materials were evaluated for different types of pollutants contained in the leachate studied through structural analyses carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) before and after the adsorption process. In addition, kinetic and isotherm models were analyzed to evaluate the adsorption efficiency. Characterization before the adsorption process revealed that the prepared materials had a partially homogeneous surface with particles of irregular sizes and varied atomic compositions. The material prepared from limestone showed the highest performance, with reduction rates of 39%, 43%, and over 80% for COD, BOD, and heavy metals (Cr, Fe, Ni, Pb, and Zn), respectively. The results of the kinetic and isothermal models showed that the removal efficiency of COD was significantly related to the initial concentration and time of contact, with reduction rates of 40 % and 32 % for the materials prepared from limestone and green schist, respectively. Furthermore, the pseudo-second-order and Freundlich models well adjusted the kinetic and isothermal models. These results confirm the potential of these low-cost adsorbents for sustainable environmental applications, with limestone exhibiting superior performance.