Phosphorus Removal from Aqueous Solutions Using La(III) Modified Sugarcane Bagasse-Derived Hydrochar: Insights into Adsorption Behaviors and Mechanisms

This study explores the potential of lanthanum-modified sugarcane bagasse-derived hydrochar (SBH-La) as an effective biosorbent for phosphorus elimination from aqueous solutions. The hydrochar was fabricated under optimal hydrothermal carbonization conditions (solid-to-liquid ratio of 1:15, 200°C, 4 h) using 0.3 M lanthanum(III) chloride as the modifying agent. To clarify the adsorption mechanisms, isotherm, kinetic, and thermodynamic experiments were conducted by varying the initial phosphorus concentrations (40–500 mg/L), adsorption time (0–24 h), and temperature (298, 303, 313, and 323 K). Comprehensive characterization was also performed on the raw sugarcane bagasse (SB) and SBH-La. The results revealed that the SBH-La exhibited a significantly higher maximum phosphorus adsorption capacity (82.82 mg/g) than SB and many conventional biosorbents. The adsorption behavior was well-described by the Langmuir isotherm and Pseudo-second-order kinetic models, indicating that chemisorption was the dominant removal pathway. Thermodynamic analysis confirmed that the phosphorus adsorption onto SBH-La was spontaneous, feasible, and endothermic. Characterization results validated the successful integration of La(III) into SB to form hydrochar and notable improvements in surface area, pore volume, and pore diameter of SBH-La compared to raw SB. These findings provide valuable insights into the adsorption mechanisms, enabling the design of viable treatment systems for phosphorus-contaminated wastewater.