Rheological properties of calcium-carbonate concentrated suspensions

The present work deals with the flow behaviour sf concentrated suspensions prepared with a calcium carbonate powder; moreover, the influence of the ad dition of some dispersing agents employed for maximising the solid loading of the suspension has been investigated. Two commercial deflocculants were used: a sodium polyphosphate and a sodium polyacrylate. Calcium carbonate a queous suspensions were prepared at various solid volume fractions (0.31 to 0.53). Rheological tests were carried out at 25+/-0.1 degrees C by using t he rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M 5-osc., measuring device MV1P with serrated surfaces. The tests were perfor med under both continuous and oscillatory now conditions. All the suspensio ns prepared without deflocculant show a rheological behaviour of the sheart hinning type; good correlations between relative viscosity and shear rate d ata were found by applying the Quemada model. The application of rheologica l techniques permitted to evaluate the efficiency of the dispersing agents employed. The sodium polyacrylate proved to be more effective than the sodi um polyphosphate for the calcium carbonate slurries investigated; the highe r efficiency of polyacrylate can be explained based on its polymeric nature .