Impact of Molecular Weight of Oxidized Lignin on its Coagulation Performance in Aluminum Oxide Suspension
Year: 2023
Journal: Waste and Biomass Valorization, Volume 14, 2023-07-01
Authors: Gao, Weijue; Beery, Steven R.; Kong, Fangong; Fatehi, Pedram
Keywords: Lignin; Adsorption; Aluminium oxide; Coagulation; Impact of salt
In this work, hardwood kraft lignin was oxidized with nitric acid to produce oxidized lignin (OL) with three different molecular weights of OL1 = 2600 g/mol, OL2 = 35,000 g/mol, and OL3 = 64,000 g/mol but with similar charge densities of − 1.8 to − 2.1 meq/g. Then, the coagulation efficiency of the lignin derivatives in aluminum oxide suspensions was studied fundamentally. The adsorption studies depicted that all three OLs had similar adsorption at a low dosage (< 2 mg/g). At higher dosage, because of its smaller size, OL1 adsorbed relatively more on the surface of the particles. Regardless of the molecular weight of OL, the highest reduction in relative turbidity did not occur at neutral zeta potential suggesting a patching mechanism of coagulation for particles. Generally, the coagulation happened at a low dosage of 0.4 mg/g, while the charge reversal and re-stabilization of particles dominated at a higher OL dosage. The coagulation studies revealed a similar coagulation affinity of lignin derivatives for the particles, which is ascribed to their similar charge densities. Also, the coagulation studies in a saline system depicted that the presence of salt improved the adsorption of OL on aluminum oxide particles due to the improvement in the hydrophobic-hydrophobic interactions between OL and particles.
