Efficient and effective immobilization of thallium and organic dyes from wastewater by iron fabricated hydrochar derived from microalgae biomass

Co-pollution of toxic thallium (Tl) and dyes (crystal violet, CV) is common in industrial wastewater, and the coexistence of both significantly increases environmental risk. Meanwhile, large quantities of microalgae biomass generated from algal blooms are typically discarded. In this study, the magnetic microalga biomass hydrochar (MAHC) was fabricated using K2FeO4 to achieve simultaneous removal of Tl(Ⅲ) and CV from wastewater. Further, the MAHC140 exhibited high adsorption capacities of 326.9 mg/g for Tl(Ⅲ) and 446.6 mg/g for CV, respectively. Kinetic and isotherm analyses revealed that Tl(Ⅲ)immobilization followed a pseudo-second-order and Langmuir models, whereas CV adsorption matched pseudo-second-order and Freundlich models. Mechanistic characterization confirmed ion exchange and complexation as the dominant pathways for Tl(Ⅲ) removal, while π-π interactions and electrostatic attraction governed CV adsorption. MAHC140 retained over 67 % adsorption efficiency after five regeneration cycles, and the nutrient-containing liquid fraction promoted plant growth, suggesting potential for microalgae resource utilization and ecotoxicological risk reduction. This study provided novel pathways for waste reutilization and the removal and immobilization of inorganic-organic co-pollutions from wastewater.