Oxidation of Kraft Lignin with Hydrogen Peroxide and its Application as a Dispersant for Kaolin Suspensions

Lignin is an underutilized byproduct of pulping and cellulosic ethanol production plants. However, if utilized efficiently, it can facilitate the development of sustainable processes. In this work, oxidized kraft lignin (OKL) was prepared via treating kraft lignin (KL) with hydrogen peroxide, an environmentally friendly and industrially attractive oxidizing agent, under alkaline conditions. The oxidized kraft lignin with a carboxylate group content of 1.53 mequiv/g was obtained under the optimal oxidation conditions of 80 degrees C, 2 h treatment, at a 0.77 molar ratio of NaOH/H2O2, and 2.85 molar ratio of H2O2/lignin, which was then employed as an anionic dispersant for kaolin suspensions. The zeta potential, particle size, and specific surface area as well as the relative turbidity and flocculation index of the kaolin suspension were affected by the pH of the suspension. By increasing the dosage of OKL to 40 mg/L, the relative turbidity of the suspension was increased to 1.18 at pH 5 and the kaolin concentration of 4 g/L, which made its performance superior to that of commercially produced lignosulfonate.