Redox-Mediated Phosphorus Adsorption on Manganese Oxysulfide in Aqueous Solutions

Although phosphorus is essential for living organisms, its release into the environment requires strict control due to pollution concerns. This study investigated the potential of phosphorus removal from water by manganese oxysulfide (MnO_xS_y) synthesized using a one-pot chemical precipitation method. Phosphorus adsorption capacity obtained as 42.1 mg/g (initial phosphorus concentration, 105.0 mg/L; pH 4.95; adsorbent dosage, 1 g/L). The adsorption mechanism included phosphorus speciation, MnO_xS_y protonation, electrostatic attraction, and redox adsorption. Phosphorus was removed by chemisorption as indicated by pseudo-second order kinetics (R², 0.9963-0.9999) forming monolayer coverage on MnO_xS_y (Langmuir, R² 0.9775). Negative ΔH° and ΔG° values revealed that the adsorption was exothermic and spontaneous, confirming energetic favorability at ambient temperature. The phosphorus removal efficiencies in real liquid digestate (86.7% ± 0.7%), simulated nutrient-rich wastewater (87.9% ± 0.1%), and only phosphorus added solution (93.1% ± 1.8%) were also comparable. These results indicated that MnO_xS_y is a promising adsorbent for the treatment of phosphorus from aqueous environment.