Synthesis, modification, and characterization of new biochar adsorbents for some organic species and low-level radioactive liquid waste treatment

Three types of agricultural waste; date palm fronds (date fronde iacebam- DFI), water hyacinth (Eichhornia crassipes, SFP) and banana pseudostems (MSFV) were used to synthesize low-cost, high-efficiency biochar adsorbents via physical (by pyrolysis under a high-purity N₂ atmosphere with the temperature increased to 600 or 800 °C) and chemical (H₃PO₄, NaOH, ZnCl₂) activation processes. Biochar materials were characterized using FTIR, SEM, BET–DFT and CHNS analyses and tested for the removal of cationic radionuclides (¹³⁷Cs, Co(II), ⁸⁵Sr, Ce(III)), anionic ⁷⁵Se, and organic pollutants (methylene blue, phenol and Rhodamine B) from aqueous solutions under batch conditions (initial concentration = 100 mg L⁻¹, dosage = 2.1 g L⁻¹, T = 25 °C, contact time = 2 h, pH ≈ 6.5). FTIR confirmed the presence of hydroxyl, aliphatic, and aromatic groups. SEM revealed highly porous, irregular morphologies, while BET results showed that NaOH-activated biochar (SFPNa8) exhibited the highest porosity. CHNS analysis indicated that N₂-activated biochar (MSFVN8) had the highest carbon content (51.33%), whereas NaOH-activated samples (MSFVNa8 and SFPNa8) contained higher oxygen and hydrogen levels. The NaOH-activated biochar (SFPNa8) exhibited the highest removal efficiency for ⁷⁵Se (66.73%) and ⁸⁵Sr (66.73%), while H₃PO₄-activated biochar (DFIA8) achieved 99.96% MB removal. Physically activated biochar (MSFVN8) showed exceptional affinity for Co(II) (84.98%). The results demonstrate that these low-cost, porous biochar materials are promising for treating complex waste streams containing radioactive and organic contaminants.