Removal of cadmium from phosphate industrial wastewater using pozzolan: characterization, experimental and Monte Carlo/SAA simulations studies

The removal of cadmium for the treatment of contaminated wastewater was investigated using a natural local pozzolan clay excavated from the Laayoune region of Morocco. The adsorbent was characterized using different techniques, such as FTIR, SEM, BET, and XRD. Adsorption experiments were conducted under various operational parameters, where the results showed the following optimal conditions: temperature of 25 °C, pH value 6, and the adsorbent mass of 0.05 g for a 50 mg L⁻¹ initial cadmium concentration. It was found that under these optimal conditions, the high adsorption percentage was 95.4%. The adsorption process shows a strong correspondence with a pseudo-second-order kinetic model with an R² of 0.998. The experimental data closely matched the Langmuir isotherm model with R² and Q_m values of 0.989 and 166.67 mgg⁻¹, respectively. The obtained thermodynamic parameters (ΔG °, ΔH °, and ΔS °) showed a spontaneous and endothermic elimination process. The adsorption configurations of cadmium (II) ions onto the SiO₂ (111) surface, which is the major component of the investigated pozzolan, were explored using Monte Carlo simulation. The theoretical part aims to explain and facilitate the understanding of the adsorption mechanism through the calculated adsorption energy (kcal mol⁻¹) of the Cd²⁺ ion on the surface of SiO₂ (111) in gaseous and aqueous phases.