Algal biochar for inorganic pollutant removal via adsorption process: synthesis, solution chemistry, and mechanistic insights

With growing concern over water pollution from inorganic contaminants, sustainable and cost-effective treatment strategies have become an urgent research priority. Among the available approaches, algae-derived biochar has emerged as a promising adsorbent because of its renewable feedstock, high adsorption capacity, and environmental benefits. Although most previous reviews have focused on lignocellulosic biochars or broad pollutant categories, the specific role of algae-based biochars in removing inorganic contaminants remains underexplored. This review summarizes the recent progress in algae-derived biochar, with an emphasis on synthesis strategies, adsorption performance, mechanisms, and reusability. Preparation methods, such as hydrothermal carbonization and pyrolysis, are discussed, along with modification approaches including acid activation and metal oxide incorporation. The analysis addresses four aspects: (i) adsorption behavior under varying pH, ionic strength, and competing ions; (ii) adsorption isotherms, kinetics, and diffusion processes; (iii) mechanistic pathways such as ion exchange, electrostatic attraction, complexation, precipitation, and redox reactions; and (iv) desorption properties and reusability. By combining the performance, safety, and economic perspectives, algae-derived biochar holds great promise as a sustainable solution for wastewater treatment. Overall, these findings underscore the potential of algae-derived biochar as a sustainable adsorbent, highlighting the need for further optimization to bridge laboratory success with real-world wastewater treatment applications.