Abstract
Nowadays, there is an increased interest in the High-Pressure Grinding Rolls (HPGR) technology in the mining industry due to its lower energy consumption than a conventional grinding circuit. Despite the benefits, the high quantity of material required to size the HPGR makes it difficult for new mines to consider this technology. The piston press test has been used in The University of British Columbia to predict the behaviour of the HPGR. It is possible to predict the energy requirements and size reduction utilizing a small amount of material to size the HPGR. However, a throughput prediction model is still missing.
The HPGR throughput depends on several operational parameters, such as the rolls speed and the operating gap. However, the operating gap results from the equilibrium in between the force applied by the HPGR floating roll and the resistance to compression from the material. The resistance from the compression of the material depends on several material properties, such as the moisture content, the fines content, the particle size distribution (PSD), and particle breakage resistance.
The PSD of the bulk material plays an important role in how the particle bed will pack. Fuller and Thompson determined a specific PSD shape that can achieve the highest packed density called Fuller Curve. When a compressive force is applied to a particle bed, the contact points between particles will affect how the energy is propagated and dispersed. As particles break, the PSD also changes, affecting the packing of the particle bed, and thus, the applied energy distribution.
This study investigates the differences of compressing three different sample PSDs obtained from the same copper ore, which was crushed to passing 12.5 mm. The first PSD corresponds to the natural distribution resulting from the crusher. The second is built artificially to recreate the Fuller curve. The third corresponds to a truncated feed, built from removing the fines (-300 µm) from the natural feed. The test is performed utilizing a piston-and-die press test (PPT) apparatus with an 86 mm diameter die. Three pressures of 140, 190, and 240 MPa are applied to 240 ml of sample from each PSDs.
Entirely different behaviours can be expected while compressing different PSDs of the same material. Differences in the specific energy consumption, grinding efficiency and final compacted densities are some of the differences that can be observed. The change of these responses significantly affects the throughput of the HPGR. Future work is required to quantify these responses and correlate them with the behaviour during the HPGR compression.