Preparation of chitosan-EDTA bifunctionally modified magnetic walnut shell biochar and study on its copper ion (Cu( <scp>ii</scp> )) adsorption performance

), enables rapid magnetic separation within seconds, and retains 91.13% of its initial adsorption capacity after five adsorption-desorption cycles. By integrating the combined advantages of EDTA (high selectivity), chitosan (abundant complexation sites), and magnetic biochar (easy separation), this study fills the gaps in existing literature and provides an efficient, sustainable, and engineering-applicable solution for heavy metal pollution control and high-value utilization of agricultural waste.