An efficient carcinogenic metal biosorbent was prepared by immobilizing the microalgae Auxenochlorella protothecoides (AP) within a sugarcane bagasse (SB) lignocellulosic matrix. The characterization of AP-SB as a proposed biosorbent was performed by various spectroscopic methods, including Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), and Thermogravimetric analysis (TGA/DTA). The immobilization technique enhanced the biosorption of nickel by 32.25\% at equilibrium compared with that of free Auxenochlorella protothecoides. The maximum metal biosorption capacities of free and immobilized A. protothecoides were calculated to be 42.08 and 62.1 mg/g, respectively. The removal efficiency of nickel ions was evaluated with a Box-Behnken factorial design using three parameters: pH solution, contact time, and biosorbent concentration. A maximum metal removal rate of 97.96\% was obtained using the RSM-DF platform with the following optimal conditions: pH 5.06, biosorbent concentration of 1.6 g/L, and contact time of 53.33 min. The experimental equilibrium adsorption isotherms for the nickel bioprocess were analysed using sixteen models with two, three, and four parameters. An evaluation of the goodness of fit of various nonlinear regression isotherms indicated that the Fritz-Schlueuronder (IV) model was the most suitable model to describe the equilibrium curves; this model was selected based on the values of four error functions: the coefficient of determination (R2), the hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), and the average relative error (ARE). The thermodynamic factors and kinetics analysis demonstrated that the bioprocess was exothermic, favourable, and spontaneous at 298-318 K. Finally, the biosorption of nickel ions on SB-AP was explained by four proposed mechanisms based on the network structure of cellulose, lignin, N-acetyl-b-D-glucosamine, and b-D-glucosamine units. (c) 2023 Published by Elsevier B.V. on behalf of SAAB.