In this study, we propose a chemical pretreatment to improve the performance of a hemp-based material in felt form used as an adsorbent for removing the metals from aqueous mixtures of Cd, Co, Cu, Mn, Ni, and Zn. The felt was coated with a maltodextrin-1,2,3,4-butane tetracarboxylic polymer in order to provide ion-exchange properties to the material by introducing carboxylic groups. It was characterized by solid-state 13 C-NMR technique and by Energy-dispersive X-ray spectroscopy. This new adsorbent was then used in batch experiments and its performances were compared with those of non-modified hemp. Different controlling experimental conditions have been investigated. Modified hemp exhibited strong adsorption capacities due to a chemisorption mechanism (complexation, ion exchange): up to 25 mg/L (in reality, 150 mg of metals per L), all metals in the solution were removed. A modified hemp dosage of 1 g was able to remove 13.91 mg of metals in 100 mL of solution at a concentration of 25 mg/L for each metal, whereas non-modified hemp only removed 7.4 mg in the same experimental conditions. Adsorption of metals reached equilibrium in 60 min and the performances were pH-independent between 3 and 6, but dependent on the presence of NaCl, except for Cu.