Shear-dependent behaviour of calcium carbonate aqueous suspensions

The rheological behaviour of calcium carbonate aqueous suspensions has been studied. The mixes were prepared at various solid volume fractions (0.316 to 0.426). The tests were carried out at 25°C by using the coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P. Flow curves were determined by varying the shear rate from 0 to 1000 s-1 at constant shear acceleration. All systems show shearthinning flow behaviour. The experimental data of shear stress and shear rate were treated with rheological models of the both τ=f(γ̇) and τ=f(γ̇,Φ) type. In particular, as for the application of the τ=f(γ̇) models the Herschel-Bulkley one seemed to be the most effective for application to calcite suspensions; as regards the fitting of experimental data with the τ=f(γ̇,Φ) models, the Quemada equation was taken into consideration. Good correlations of the rheological parameters with pigment concentration were found.