Optimisation de l'adsorption simultanée du Fe(II) et du Mn(II) en solution aqueuse par des biosorbants de peaux d'orange activées à l'acide phosphorique

Water pollution by trace metal elements is a major environmental concern linked to the growth of industrial, mining and agricultural activities. This study aims to valorizeorange peels, an abundant and low-cost agro-industrial by-product in Ngaoundéré (Cameroon), as a biosorbent for the simultaneous removal of Fe(II) and Mn(II) from aqueous solution. Biosorbents were obtained by chemical activation of orange peels with concentrated phosphoric acid (85%). Characterization revealed a specific surface area of 73.25 m²/g and a porosity of 19.52 mg/g, a marked improvement over the untreated material. A two-level fractional screening design identified the Mn(II)/Fe(II) molar ratio, adsorbent mass and pH as the most influential factors. Optimization using a central composite design then determined the optimal conditions for simultaneous adsorption: pH 7.71, adsorbent mass 0.29 g and molar ratio 0.34, yielding adsorbed quantities of 699.99 µmol/g for Fe(II) and 232.81 µmol/g for Mn(II). The kinetic study showed that the pseudo-second-order model best described the process (R² > 0.99) for both ions, while equilibrium isotherm modelling revealed a better fit with the Freundlich model (R² of 98.37% and 98.80% for Mn(II) and Fe(II) respectively), reflecting adsorption onto an energetically heterogeneous surface. These results confirm the potential of activated orange peels as an efficient, economical and eco-friendly biosorbent for treating water polluted by iron and manganese.