Modification of the rheological properties of concentrated slurries by control of mineral-solution interfacial chemistry

The rheological properties of a chalcopyrite slurry have been measured as a function of different chemical conditioning treatments. The magnitude of the yield stress (tau(B)) was reduced when either hydrochloric, nitric or sulfuric acid was used to decrease the pH. These results were consistent with an increase in repulsive electrostatic forces between particles. Surface analysis of the particles in the slurry revealed that reducing the pH removed an overlayer of insoluble calcium sulfate, This left the underlying heavily oxidised chalcopyrite surfaces covered with metal hydroxide species. For hydrochloric and nitric acids, the viscosity (eta(B)) of the slurry was also reduced with decreasing pH - behaviour which was attributed to changes in the surface chemistry of the particles with pH. However, for sulfuric acid, eta(B) increased with decreasing pH, It is proposed that precipitation of insoluble calcium sulfate increased the solid content of the slurry as the pH was reduced, resulting in a significant increase in viscosity. Addition of phosphates to the slurry also reduced tau(B) and eta(B) Adsorbed phosphate apparently produces an enhanced repulsive force between particles due to the presence of long-range electrostatic and, possibly, short-range steric interactions. Surface analysis showed that the phosphates dispersed insoluble calcium sulfate from the surface of the chalcopyrite particles. Additional phosphates adsorbed onto the chalcopyrite surfaces. The rheological parameters determined were used to calculate the energy required to pump the slurry through a pipeline. The calculations indicated that the use of either acids or phosphates permits the solid content of the slurry to be increased by over 10 wt.% for the same pumping energy input, (C) 2000 Published by Elsevier Science B.V, All rights reserved.