Impact of physicochemical properties of lignin-based polymers on their flocculation and adsorption performance

Abstract

Industrial and municipal effluents contain colloidal charged particles, dissolved salts, heavy metals and other impurities, which may represent varied health risks and must be removed before discharge into the environment. Coagulation and flocculation techniques are highly efficient for the treatment of hydrophobic pollutants and suspended particles. Natural based polymers have been recognized as green chemicals for wastewater treatment system, which are environmentally attractive and financially feasible. In this research, lignin, the second most abundant aromatic polymer was polymerized with cationic, anionic and non-ionic monomers to synthesize lignin-based macromolecule with desired characteristics (i.e., charge density, molecular weight, hydrodynamic radius). The successful polymerization reaction was assessed using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectrophotometry, gel permeation chromatography (GPC) and elemental analyses. The interaction of lignin-based derivatives with different suspended particles and their adsorption/flocculation performance in various waste solutions was comprehensively assessed. Moreover, a strong correlation between the molecular conformation of lignin-derivatives and their flocculation behavior was observed, in which the polymer with more extended configuration (larger hydrodynamic radius and radius of gyration) revealed the greater bridging affinity. It was also shown that the conformational changes of lignin macromolecules had a remarkable effect on its molecular weight and subsequently the flocculation performance and floc properties (e.g., size, shape and strength) when they are used in suspension systems.... The findings of the present research prove the possibilities for use of the lignin macromolecule as flocculant or adsorbent in various wastewater system and provides more insights into how the structural changes of lignin-based derivatives would notably alter their performance in aqueous solution and suspension systems. The results shed light on the extending lignin applications via engineering the characteristics of lignin macromolecules.