The rheology of concentrated aqueous suspensions of calcium carbonate

The rheological behaviour of concentrated aqueous suspensions of calcium carbonate dispersed with a surfactant, comprising a 1:1 mole ratio mixture of lauric acid and a polyethoxy-nonylphenol with an ethylene oxide chain length of nine units, is shown to be pseudoplastic (shear-thinning). This behaviour is shown to be consistent with the adsorption characteristics of this surfactant system, the sedimentation behaviour, the variation of electrophoretic mobility with surfactant concentration and the particle potential energy of interaction curves. Equivalent determinations were made on suspensions of calcium carbonate without dispersant, dispersed with the non-ionic component alone and dispersed with a polymeric anionic surfactant. The rheological behaviour of the first two systems was also pseudoplastic and the last system showed shear thinning followed by shear thickening behaviour as the shear rate was increased. A possible mechanism is suggested for this reversal of behaviour upon increasing the shear rate