Lead ion adsorption on functionalized sugarcane bagasse prepared by concerted oxidation and deprotonation.

Targeting the removal of Pb2+ in wastewater, sugarcane bagasse was treated with nitric acid and an alkaline solution to prepare adsorbents. On a typical adsorbent, the adsorption isotherms agreed well with the Langmuir expression, and the maximum adsorption capacity reached 200.3 mg/g. In the presence of 150 ppm Ca2+, a common cation in natural water, the Pb2+ adsorption capacity slightly declined. In contrast, Mg2+ obviously prohibited the adsorption for Pb2+. The spent adsorbent could be regenerated at least five times through elution with an EDTA solution. EDS and XPS results demonstrated that nitric acid functioned as an oxidant instead of nitrification agent in the treatment of bagasse. The adsorption process was consistent with quasi-second-order kinetics. Based on thermodynamic studies, the changes in enthalpy and Gibbs free energy were calculated to be - 33.3 and ca. - 18 kJ/mol, indicating that the adsorption process was exothermic and spontaneous. The equilibrium Pb2+ adsorption amounts were proportional to the numbers of carboxylate groups on different adsorbents. The binding energies of Pd 4f5/2 and Pd 4f7/2 XPS spectra of Pb2+ adsorbed were 0.6-0.7 eV lower than those of free Pb(NO3)2, indicating the transfer of electrons during adsorption. The conversion of hydroxymethyl groups in sugarcane bagasse into carboxylate groups, as well as the chelation between Pb2+ ions and carboxylate groups, was validated in this work, which is beneficial for the treatment of wastewater polluted by lead ions.