The effect of viscosity on small-diameter hydrocyclones' performance in desliming process

Abstract

In recent years, the use of small diameter hydrocyclones, with internal diameters less than 75 mm, is growing in mineral processing for fine particle classification. These hydrocyclones are being used for recovery of kaolin and diatomaceous clay, for desliming of ores, water recovery and processing of old tailing deposits to respect environmental polices. Also, in the chemical and food-processing industries they are used for remission of particles from effluents, starch refinement and recovery of organic crystals. An important property of slurry flowing is its resistance to shear, or its viscosity. This property is present in many mineral processing systems, but its influence is rarely incorporated into models, analyses or optimisation processes. This work present a study carried out on slurry phosphate ore from the feed of a desliming circuit, 80% passing the 20 μm size. Tests were conducted adopting two different small-diameter hydrocyclones (25.4 and 50.8 mm internal diameters). The feed pressures ranged from 25÷65 psi. The slurry viscosity appeared naturally as 15.25% and 35% solid in weight, and the last one (35% w/w) was changed by a chemical reagent to low and intermediate viscosity. The usual measurements were made on feed slurry viscosity using a rheometer. Flow rates of the products, inlet feed pressures, solids contents and size distributions of the products were measured using a laser diffraction analyser. The flow rates were mass balanced by a computer program, and the water was split; d 50c and efficiency parameter. α (sharpness of separation), were calculated using Whiten equation. The results have shown that the slurry viscosity influenced the hydrocyclone performance: when the viscosity increases with the solid content, the d 50c increases too; when the viscosity is decreased by a dispersing agent, at high solid content, the d 50c decreases too (thus it is possible to work with slurry at high solid content and to get a d 50c as small as that for low solid content); viscosity had a negligible effect on efficiency parameter, α (sharpness of the separation), of the reduced partition curves as is observed for larger hydrocyclones; fish hook phenomenon was present in natural and dispersed slurries.