Flocculation of silica nanoparticles by natural, wood-based polyelectrolytes

Wood-based polyelectrolytes, produced from renewable and biodegradable sources, can be considered as more environmentally friendly flocculation agents for the wastewater treatment compared to the traditional synthetic flocculants. The aim of this study was to produce new natural-based polyelectrolytes (bio-PELs), water-soluble, cationic cellulose-based polymers derived from Eucalyptus bleached fibres (CDAC(f)) and to evaluate their effectiveness as flocculation agents by studying their interaction with model particles and the associated particle flocculation and accelerated sedimentation. Three different CDAC(f) with varying cationicity index/degree of substitution and molecular weight were synthesized by a two-step reaction. Firstly, by periodate oxidation of the surplus bleached fibres, the introduction of reactive aldehyde groups into the cellulose backbone can be achieved. This is followed by modification of the resulting polymers by introducing alkylammonium positively charged groups in the cellulosic chain, thus resulting in the formation of bio-derived, water-soluble, bio-PELs. The final products were characterized by several analytical techniques: FTIR-ATR, H-1 NMR, elemental analysis, dynamic light scattering, and electrophoretic light scattering. The CDAC(f) with the highest and the lowest degree of substitution (DS) of cationic groups were evaluated for their performance in solid/liquid separation of silica suspensions. The CDAC(f) with the highest cationicity performed better at lower dosages while higher bio-PEL dosages for the same apparent sedimentation efficiency were needed for the bio-PEL with lower charge density.