Display omitted •Biomass waste-derived biochar with a novel nanoflake self-assembly is presented.•Both heavy metals and organic pollutants can be treated efficiently by the biochar.•A synergistically physical/chemical adsorption behaviors is elucidated.•Biochar has a potential application for treating cross contamination in industry. With the presence of emerging organic pollutants (EOPs) in aqueous systems, the heavy metals (HMs)-transfer mechanism has been given considerable attention again. Here, a facile molten-salt method is used to successfully convert banana waste into nanoflake-assembled biochar (BC350) for the first time. It is a type of macro-mesoporous biochar with a pore size composed of ~ 3.8 nm and ~ 50 nm, and its maximum adsorption capacities are 459 mg g−1 for Pb2+ and 148 mg g−1 for tetracycline (TC), which outperforms the reported adsorbents ranging from several times to dozens of times. The pore-filling effect, electrostatic interaction, coordination affinities and π-π stacking as synergistically physical/chemical adsorption behaviors of BC350 on Pb2+/TC that has been comprehensively elucidated relying on adsorption kinetics and isotherms, and key effect parameter investigation. The competitive adsorption effect becomes insignificantly in the adsorption efficiency of BC350 on Pb2+/TC cross contamination at a control condition. Moreover, BC350 also exhibits outstanding adsorption efficiency (>95%) on Pb2+/TC in five industrial wastewater samples. This study contributes to a plausible mechanism in biochar adsorption removal of metal/organics cross contamination and its potential application explored in industrial wastewater treatment.