The valorization of agricultural waste peels as a low-cost biosorbent is a promising approach to water treatment. In this work, the improvement of the adsorption capacity of lemon peel to remove Ni (II) from aqueous effluents was explored using several chemical modifiers: HNO3, HCl, H3PO4, CaCl2, NH3 and NaOH. The surface pretreatment using NaOH was selected as the best option because of the improvement of the maximum adsorption capacity. The maximum adsorption capacity was of 36.74 mg g−1 according to the Langmuir model at optimum conditions (pH = 5, S/L = 5 g L−1, 25 °C). The pseudo-first order model of biosorption kinetics provides the best fit for experimental data. From thermodynamic studies, it was concluded that Ni (II) biosorption by modified lemon peel was endothermic and spontaneous. After five consecutives adsorption-desorption cycles using 0.1 M of HNO3 and H2SO4, a recovery of 90% of Ni (II) was obtained. Regarding characterization of the biosorbent, the surface morphology was studied by Scanning Electron Microscopy while the functional groups responsible for Ni (II) adsorption were evaluated by Fourier transform infrared spectroscop
