Designing anionic lignin based dispersant for kaolin suspensions.

To generate effective dispersants for kaolin suspensions, it is important to study how the properties of dispersants affect their performance in suspensions. In this work, kraft lignin was modified via oxidation with nitric acid under varied conditions to produce oxidized lignin (OL) with different charge densities and molecular weights. The effects of anionic charge density and molecular weight of the lignin based products on the dispersion and sedimentation of kaolin particles were studied fundamentally. The adsorption of OLs on particles as well as the changes in the zeta potential, relative turbidity, hydrodynamic diameter and sedimentation of particles under static (non-stirring) and dynamic (stirring) conditions were systematically investigated. Dispersion studies suggested that both charge density and molecular weight had great impacts on the stability of kaolin particles. Sample OL8 with the charge density of −3.6 meq/g and molecular weight (Mw) of 30,243 g/mol was the most effective dispersant for kaolin suspension. The hydrophilicity of OLs were similar and thus did not affect the dispersion analysis. [ABSTRACT FROM AUTHOR]