Source of Unimin kaolin rheological variation–Ca2+ concentration

The variations in rheological-pH behaviors between suspensions of low and high calcium (Ca) kaolin were evaluated via zeta potential, yield stress and sedimentation methods. Elemental analysis via x-ray fluorescence (XRF) showed that Riedel kaolin (0.028%) carries ∼18.0 times lesser Ca concentrations than Unimin kaolin where Riedel slurries displayed a maximum yield stress at ∼pH 2.0 when Riedel particles carried low negative zeta potential magnitudes while Unimin slurries exhibited a maximum yield stress at pH 8.6 when Unimin particles were highly negatively charged. With Ca2+ cations added to Riedel slurries at sufficiently high concentrations, Riedelʹs negative zeta potential magnitudes decreased especially along high pH, maximum yield stress peaks shifted to high pH and solids content obtained during consolidation increased by ∼14.0 weight percentages (wt%) at pH 8.0 to be similar to Unimin. These changes in Riedelʹs behaviors and the reasons for Uniminʹs behaviors is due to the adsorption of hydrolyzed Ca(OH)+ hydroxy complexes onto these particles, which reduced particle negativity and induced unlike charge attractions between these particles to improve consolidation and increase slurry network strengths, and the presence of hydrolyzed Ca(OH)2 precipitates, which increased yield stresses of these kaolin slurries at high pH. The hydrolysis-pH behaviors of Ca2+ cations varied via acid and base titration paths to correspondingly affect and cause the rheological-pH behaviors of Unimin slurries to be varied via acid and base titration paths. Overall, this study explains the effect of elemental variations between kaolin particles that affects the rheological-pH behaviors between the respective kaolin slurries.