This study describes, in detail, the chemical modification of sugarcane bagasse with phthalic anhydride to produce a carboxylate-functionalized sugarcane bagasse (SPA). The optimized modification conditions yielded SPA with a percent weight gain of 77.08% and an amount of carboxylic acid groups of 4.76 mmol/g. The SPA was characterized by PZC, FTIR, elemental analysis, TGA, and SEM-EDX. An SPA adsorbent was used to remove Co2+, Cu2+, and Ni2+ from aqueous solution in mono- and multicomponent systems in batch mode. The adsorption kinetics followed a pseudo-second-order model. The adsorption rate constants assumed the following order: k2,Co2+k2,Ni2+k2,Cu2+. Four mono- and multicomponent isotherm models were used to model the adsorption data. Monocomponent data were well described by the Langmuir model, whereas bicomponent data were well described by the modified extended Langmuir and P-Factor models. The maximum adsorption capacities (Qmax,mono) for the Langmuir model were 0.561, 0.935, and 0.932 mmol/g for Co2+, Cu2+, and Ni2+, respectively. Adsorption in bicomponent systems revealed that Cu2+ suppressed the adsorption of Co2+ and Ni2+, whereas Ni2+ suppressed the adsorption of Co2+. Desorption studies revealed that the SPA adsorbent could be fully desorbed with a 1mol/L HNO3 solution.