Conventional processes of essential oils extraction use large quantities of plant material which in turn generate a lot of residues. This study proposes re-using the by-products, that have generally remained unexploited, to remove heavy metals from aqueous solutions. This proposed method proceeds without physical or chemical modification of the adsorbent produced. An advantage of this biosorbent is its high adsorption capacities. Using residues from the hydrodistillation of Centaurea nicaeensis plant as a biosorbent for removing Cu and Zn ions was investigated through a comprehensive analysis of the kinetics, equilibrium and thermodynamic aspects to confirm the nature of adsorption mechanisms. To achieve the maximum retention, the process parameters were mathematically optimized using Response Surface Methodology. Under optimal conditions, the Removal (%) of metal ions could reach 82.12% for Zn and 92.02% for Cu. The best fit of experimental data was achieved with the pseudo-first order kinetic model. The obtained Langmuir monolayer adsorption capacities were 0.212 mmol g−1 for Zn and 0.386 mmol g−1 for Cu. Sips isotherm gave the best fit to equilibrium data. Taking specific surface area into account, the proposed biosorbent is nearly 30 times higher in the retention capacity of Cu and more than 10 times better in the retention capacity of Zn than that of the reference commercial biochar. According to thermodynamic study, the processes, driven by electrostatic interactions, were spontaneous, physical and endothermic. These results could make our biosorbent a potential alternative to commercial biochar in heavy metals removal. Image 1 • The residue from Hydrodistillation process could be used as an effective biosorbent. • Isotherms, Thermodynamic and kinetic tests for Zinc and Copper solutions were carried-out. • Adsorption was spontaneous, physical, endothermic and driven by electrostatic interactions. • The optimization of the adsorption process was achieved using Response Surface Methodology.. • Optimal Removal (%) of metal ions could reach 82.12% for Zn and 92.02% for Cu. [ABSTRACT FROM AUTHOR]