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 t he yield stress (tau(B)) was reduced when either hydrochloric, nitric or su lfuric acid was used to decrease the pH. These results were consistent with an increase in repulsive electrostatic forces between particles. Surface a nalysis of the particles in the slurry revealed that reducing the pH remove d an overlayer of insoluble calcium sulfate, This left the underlying heavi ly oxidised chalcopyrite surfaces covered with metal hydroxide species. For hydrochloric and nitric acids, the viscosity (eta(B)) of the slurry was al so reduced with decreasing pH - behaviour which was attributed to changes i n the surface chemistry of the particles with pH. However, for sulfuric aci d, eta(B) increased with decreasing pH, It is proposed that precipitation o f insoluble calcium sulfate increased the solid content of the slurry as th e pH was reduced, resulting in a significant increase in viscosity. Additio n of phosphates to the slurry also reduced tau(B) and eta(B) Adsorbed phosp hate apparently produces an enhanced repulsive force between particles due to the presence of long-range electrostatic and, possibly, short-range ster ic interactions. Surface analysis showed that the phosphates dispersed inso luble calcium sulfate from the surface of the chalcopyrite particles. Addit ional phosphates adsorbed onto the chalcopyrite surfaces. The rheological p arameters determined were used to calculate the energy required to pump the slurry through a pipeline. The calculations indicated that the use of eith er acids or phosphates permits the solid content of the slurry to be increa sed by over 10 wt.% for the same pumping energy input, (C) 2000 Published b y Elsevier Science B.V, All rights reserved.