Processing of nickel laterite ores is complicated by their non-Newtonian rheological properties. These properties have been reported to range from shear-thinning to shear-thickening and from thixotropic to rheopectic. Rheological studies on materials from the Ramu Deposit in Papua New Guinea support findings that laterite suspensions exhibit reversible rheopectic time dependent properties. Results showed that apparent viscosity and degree of rheopexy were lowered by adding a dispersing agent (sodium hexemetaphosphate) and by lowering the pH from 6.5 (close to i.e.p. for goethite) to 3.0. Since both of these would increase the electrostatic repulsion and dispersion, it is proposed that the rheopectic response is due to shear induced (secondary minimum) coagulation. In practice, these results can be exploited to improve material handling during processing and increase the maximum solid content for pressure acid leaching.
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