On the preparation of concentrated gypsum slurry to reuse sulfate-process TiO2byproduct stream

The efficient use and transport of byproduct gypsum to be used as a secondary raw material implies its conditioning in a suitable physical form. Most frequently demands are to supply a concentrated suspension, which is sufficiently fluid and stable to be pumped and stored in tanks. The preparation of a fluid concentrated gypsum slurry is a demanding task, since particle anisotropy and surface interactions prevent the attainment of high solid loadings. In this paper we present the testing of different families of dispersants, and discuss the modifications of the surface interactions exerted by each, in terms of surface potential and macroscopic rheological properties. We show that by appropriately choosing the dispersing system it is possible to prepare pumpable concentrated slurries with a solid content approaching 80% by weight. Star-shaped polymers are shown to enable the preparation of highly concentrated suspensions, which exhibit good rheological properties and retain stability both under rest and at the highest shear rates, thus being adapted to be stored in tanks, and to be transferred by pumping. These dispersing agents do not induce electrostatic repulsion among the particles, ζ-potential being nearly zero. Steric repulsion is responsible for the dispersion, and even at the highest concentration the suspension does not show jamming and thickening.