Effective Removal of Aqueous Lead (II) Ions Using Partially Esterified Lignin as a New Adsorbent

Fresh lignin (LGN) was isolated from the almond shell (AS) through its fractionation in choline chloride/oxalic acid deep eutectic solvent (DES) under microwave irradiation. The isolated LGN has then undergone an esterification reaction with the same DES to obtain partially esterified lignin (PELGN). The fact that PELGN was obtained was confirmed by FT-IR, TGA, and EDX analyses. The FT-IR, FESEM, EDX, TGA, and BET characterization techniques confirmed that the adopted adsorbent possesses suitable functionality, morphology, and architecture to be used as a promising adsorbent to adsorb Pb2+ ions from aqueous solutions. The higher regression coefficient (R2) was achieved when the adsorption kinetic data were fitted with pseudo-second-order and equilibrium data with the Langmuir isotherm. Under optimized conditions, the equilibrium adsorption capacity of the PELGN was found to be 113.64 mg/g with a 2.00 g/L adsorbent at a pH of 6.50 and an ambient temperature of 25 ± 2 °C. The adsorption was spontaneous at low temperatures, pH-dependent, and exothermic. Chemical interactions are the foremost adsorption driving forces, accompanied by surface Coulomb forces and intra-particle diffusion. The reusability of the adsorbent was investigated using (0.10 mol/L) HCl as an eluent. The adsorbent preserved its effectiveness for four successive rounds, which affirms its applicability on industrial scales.