Analysis of sodium polyacrylate as a rheological modifier for kaolin suspensions in seawater

This research aims to analyse the effect of sodium polyacrylate on the rheological behaviour of kaolin pulps in seawater by means of rheograms and dynamic oscillatory assays. Then, the rheological properties were associated with zeta potential and particle aggregation/dispersion phenomena. Seawater raised the rheological properties compared to distilled water, generating an evident non-Newtonian behaviour, characterised by the appearance of yield stress, followed by a shear-thinning behaviour. This occurred because the high concentration of electrolytes compresses the ionic cloud that surrounds the particles' surfaces, overcoming the electrostatic repulsions, but besides, the seawater counterions (like Mg and Na) contribute to forming cationic bridges between the anionic particles. The addition of sodium polyacrylate did not induce significant alterations on the zeta potential; however, this formed a steric stabilisation where chord length measurements showed a greater presence of fine particles and fewer kaolin aggregates. The yield stress significantly diminished after polymer addition, while the viscoelastic modules and complex viscosity indicate that sodium polyacrylate reduces the strength of the particle networks that make up the slurry, but in turn, the phase angle indicates increase in its solid-like character.