Abstract
Currently, lignin of black liquor is incinerated to generate energy in pulp mills; but it has potential to be valorized through different modification methods. In this work, kraft lignin (KL) was polymerized with 2-[(methacryloyloxy) ethyl] trimethylammonium chloride (DMC) to produce cationic water soluble polymers. After producing five polymers with different molecular weights and charge densities, their flocculation efficiency in kaolin suspensions was investigated. The adsorption, zeta potential and flocculation results confirmed that the polymer with the highest charge density and molecular weight (KLD5) was a more effective flocculant than other polymers. The structure and size of flocs formed from the interaction of kaolin with KLD were determined by a focused beam reflectance measurement (FBRM). The sedimentation studies, conducted under gravitational (by vertical scan analyzer) and centrifugal force (by Lumisizer analytical centrifuge), revealed that KLD5 was very effective in flocculating kaolin particles.
Highlights
Lignin of black liquor is incinerated to generate energy in pulp mills; but it has potential to be valorized through different modification methods
The results indicated that varied DMC amounts were responsible for different nitrogen contents, charge densities, and molecular weights of KLD polymers, which were closely related to their flocculation performance
The efficiency of KLD5 was higher than other KLDs in flocculating kaolin particles due to its higher adsorption as well as its charge density and molecular weight
Summary
Lignin of black liquor is incinerated to generate energy in pulp mills; but it has potential to be valorized through different modification methods. Since most naturally occurring colloids are predominantly negatively charged, the addition of cationic polymers is an effective alternative to isolate suspended particles from wastewater effluents[3,4] Synthetic organic polymers, such as cationic polyacrylamide (PAM) and poly diallyldimethylammonium chloride (PDADMAC), have been extensively applied as flocculants in wastewater treatment of mineral processing and papermaking operations[5,6,7,8,9]. These polymers were reported to form large and strong flocs with acceptable settling performance, which affords their effective removal[10]. As it is unclear how lignin-based polymers would agglomerate particles, the second purpose of this paper was to investigate how the charge density and molecular weight of lignin-DMC polymers impact the formation and settling of agglomerated flocs
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