An Efficient Phosphorus Adsorbent Prepared from Calcium/Iron-Rich Storm Sewer Sludge: Performance and Mechanism

Calcium- and iron-rich sludge from urban storm sewer is an ideal source of phosphorus adsorbents. This study used urban storm sewer sludge to prepare phosphorus adsorbents via pyrolysis. Comparing adsorbents prepared under different conditions, the optimal material was produced at 800 °C in a nitrogen atmosphere and was named 800N. Analyses were conducted using scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller surface area analysis, and X-ray photoelectron spectroscopy. The results showed that 800N is rich in carbon, calcium, and iron. The adsorbent has a pore volume of 0.013 cm³/g and a specific surface area of 3.566 m²/g. Adsorption performance was most effective at a pH of 8, achieving an adsorption capacity (q_e) of 19.32 mg/g and a removal rate of 87.75%. Kinetic and thermodynamic studies revealed that the adsorption of phosphorus by the adsorbent conforms to the pseudo-second-order kinetic model and the Langmuir isotherm model. Based on the characterization results, it can be reasonably inferred that the primary mechanisms involved in phosphorus adsorption by the adsorbent are inner-sphere complexation, ligand exchange, and chemical precipitation. This study offers a novel solution for mitigating phosphorus pollution and promoting the resource utilization of urban storm sewer sludge.