Thickening and rheological properties of slurries as functions of the oxidized nickel ore composition

Abstract

The thickening and rheological properties of ore slurries and pulps after autoclave sulfuric acid leaching are analyzed as a function of the phase composition of oxidized nickel ore. Experiments have been carried out with samples of ferrous, silicate and combined ores. The initial concentration of the ore slurries is ∼28%. Higher values of thickening properties (thickening rate of 1.3 m/day, thickened layer concentration of 54%) are exhibited by the ferrous ore slurry and the pulp after its leaching (thickening rate of 0.9 m/day, thickened layer concentration of 42%). The thickening rate of silicate ore slurry is 0.15–0.2 m/day, the thickened layer concentration is 40–45%. The thickening properties of the pulp after autoclave sulfuric acid leaching of silicate ore strongly depend on the consumption of sulfuric acid. The thickening properties of combined ore and pulps after its leaching deteriorate with increase in the content of silicon dioxide in the ore. In terms of the rheological properties, all slurries are pseudoplastic systems. Poorly thickening slurries are characterized by a high dynamic yield stress (up to 7 Pa) and apparent plastic and effective viscosities. The effective viscosity at the equivalent shear rate corresponding to the mixer rotation rate in laboratory autoclave reaches 34 × 10^–3 Pa s. Boundary values are determined in rheological constants with regard to the thickening properties. For instance, if the dynamic yield point is <1.0 Pa, the thickening rate increases from 0.2 to 1.3 m/day; if the yield point is >1.0 Pa, the thickening rate decreases from 0.075 m/day to zero. The thickening and rheological properties are found to depend on the particle size of solid phase and its surface properties.