Grinding of magnetite using a waterjet driven cavitation cell

Abstract

This paper presents the results of an experimental study investigating the effect of stand-off distance, inlet pressure, exposure time and feed particle size on grinding of magnetite using waterjet technology. A unique experimental set-up consisting of a conventional abrasive cutting head coupled with a cavitation chamber was employed for this purpose. The results of grinding tests were evaluated based on Rosin-Rammler parameters of the products and specific energy consumption (SEC) values for generation of particles below 25μm. A three-level experimental design for two independent variables with three center points was used to examine the effects of inlet pressure (69MPa, 138MPa and 207MPa) and anvil stand-off distance (3mm, 50mm, 97mm) using a feed material below 600μm particle size. The results showed that the anvil stand-off distance and pressure intensity are important factors for size reduction of magnetite particles. However, the effect of inlet pressure on size parameter was found higher than the stand-off distance. SEC values were found very similar for all pressure intensities tested at 3 and 50mm anvil stand-off distance. The largest size parameter and highest SEC value were obtained using 69MPa inlet pressure and 97mm anvil stand-off distance. Stepwise closed circuit grinding tests were also performed operating the experimental set-up at 3mm anvil stand-off distance and 138MPa pressure. The size parameter of the ground products and the SEC values were found very similar after 50s of waterjet exposure time. The feed material used in aforementioned tests was wet screened to produce mono-size fractions using a √2 sieve series. The fractions were subjected to waterjet grinding at 3mm anvil stand-off distance and 138MPa inlet pressure. The largest size parameter and SEC value was obtained when the coarsest fraction (600–425μm) was used as feed material in these tests. The 600–425μm mono-size fraction has also been subjected to waterjet grinding to determine the prevailing size reduction mechanism using 3mm stand-off distance at different pressure values. Most of the particles detected in the SEM image of the lowest inlet pressure product (69MPa) were identified as coarse and blocky particles with sharp edges. It was found that the number of blocky particles diminished by increasing inlet pressure indicating the impact breakage conditions. It was found that the destructive breakage conditions have become prominent by increasing pressure.