A novel biosorbent (‥Manna_COOH…) was synthesized via dual reaction stages of direct carbonylation of hydroxyl groups of richly cellulosic manna root powder and subsequent esterification of the resultant anhydride analogue into an ester of high carboxyl content. Both the biosorbent precursor and the 2,3-dihydroxybutanedioic acid sustain complementary features that ensured their efficient complexation. The biosorbent depicted a carboxyl content of 412.36 m.eq -COOH/100 g sample and was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The study further evaluated the cobalt ion adsorption capacity of the synthesized ‥Manna_COOH… under the effect of some process variable via batch mode. The Freundlich and pseudo-second-order models emerged as the best fit for the equilibrium and kinetic data, respectively. The rich oxygen-based surface functional groups entrenched on the ‥Manna_COOH… sequel to its functionalization played a major role in making it a promising biosorbent for aqueous Co (II) uptake.