Project Status: Complete
Project Participants: CSIRO, University of Queensland
Project Leader: Marko Hilden (University of Queensland)
The main aim of this project was to dry process the ore to near ball mill product size and to accurately determine the energy required to achieve this. A three-pass High Pressure Grinding Roll (HPGR) flowsheet was expected to be more energy efficient than current Autogenous Grinding/Semi-Autogenous Grinding/ball mill circuits and was tested at pilot-scale on several ore types. The flowsheets were compared on direct and embodied energy consumption and on an economic basis (capital, consumables, maintenance) against current circuits.
Test work was carried out on three samples using the 0.75 metre diameter and 1.0 metre diameter Köppern HPGR units at AMMTEC in Perth. This choice allowed a feed size of around 32 millimetres top size which is comparable to the feed size used in industrial HPGRs and therefore a more meaningful scale than the smaller scale HPGR usually used for HPGR experimental work. The product from the HPGR grinding after three passes was then milled using a laboratory mill to determine its grindability to a size of 150 microns. Energy measurements were made at each sizereduction step.
The results show that there is a limit to the number of times that an ore can be crushed efficiently by HPGRs in series. Following a reasonably large size reduction ratio on the first pass and second passes, a drop in grinding efficiency is experienced on the third HPGR pass – indicating a limit of two HPGR passes for efficient grinding of hard ores.