Cationic kraft lignin-acrylamide copolymer as a flocculant for clay suspensions: (2) Charge density effect

Abstract

Abstract Kraft lignin valorization is achievable via making it soluble in water for treating wastewater effluents. In this paper, acrylamide (AM), (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) and kraft lignin (KL) were polymerized in an aqueous solution to produce a water-soluble lignin-based copolymer. Two cationic KAD polymers, with the same molecular weight, but different charge densities, were used as flocculants for simulated clay suspensions. The higher charge density copolymer (KAD1) had greater adsorption on kaolin (2.58 mg/g) and bentonite particles (1.83 mg/g) at 4 mg/g (based on clay) adsorption. Furthermore, KAD's higher charge density improved its performance in changing zeta potential and turbidity of the clay suspensions. At 4 mg/g copolymer dosage in clay suspensions, the particle size of kaolin was increased from 4.7 to 22.3 and 16.2 μm, and that of bentonite was increased from 6.1 to 31.9 and 19.8 μm for KAD1 and KAD2, respectively. In addition, the interfacial tension between water and kaolin and between water and bentonite dropped from 12.3 mN/m to 5.8 mN/m and from 9.5 mN/m to 5.2 mN/m when KAD1 was used, respectively. Moreover, KAD1 produced stronger flocs and showed high regrowth affinity at different shear rates.