In the present work the influence of the addition of some dispersing agents employed for maximizing the solid loading of calcium carbonate suspensions has been investigated. Three commercial deflocculants were used: trisodium orthophosphate, sodium tripolyphosphate and sodium polyphosphate, Calcium carbonate aqueous suspensions were prepared at various solid volume fractions (0.270 to 0.382). Rheological tests were carried out at 25°C by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. All the suspensions prepared without deflocculant show a rheological behavior of the shearthinning type; good correlations between relative viscosity and shear rate data were found by applying the Quemada model. The application of rheological techniques permitted to evaluate the efficiency of the dispersing agents employed. The sodium polyphosphate proved to be the most effective for the calcium carbonate slurries studied; the highest efficiency of polyphosphate can be explained on the basis of its oligomeric nature.
