Calcium modified mesoporous silica from marble for the removal of cadmium, lead, chromium, iron, and manganese from Siwa Oasis groundwater

This study assessed the health risks of heavy metal contamination in groundwater in Siwa Oasis, Egypt's northwestern desert, and their potential decontamination using a marble-based nanoporous Ca-MCM-41 structure as an adsorbent. Fe, Cd, Cr, Pb, and Mn contents exceeded World Health Organization (WHO) guidelines with potential non-carcinogenic risks and carcinogenic risks based on the hazard index (HI) and Monte Carlo simulations. Ca-MCM-41 showed significant performances in the removal of most of these toxic ions with batch saturation uptake capacities of 239 mg/g Cd(II), 252 mg/g Fe(II), 308 mg/g Pb(II), 132 mg/g Cr(VI), and 154.7 mg/g Mn(II). The batch adsorption behavior display monolayer, homogenous, multi-ionic, nonparallel properties. The adsorption energies (< 8 kJ/mol) highlight the impact of the physical mechanisms and potential regeneration value. The column study using the structure as a fixed bed (3 cm thickness) reflected successful retention for 148.9 mg (Cd (II)), 161.5 mg (Fe (II)), 179.6 mg (Pb (II)), 103.2 mg (Cr (VI)), and 123.7 mg (Mn (II)). The realistic treatment of groundwater in Siwa Oasis demonstrates removal percentages of 84.2% (Cd (II)), 48.8% (Fe (II)), 84.8% (Pb (II)), 52.6% (Cr (VI)), and 52.6% (Mn (II)), considering the variation in the starting concentration and the competitive effect of other pollutants.