Multiple trade-off studies have shown that grinding circuits with high pressure grinding rolls (HPGR) can be more energy efficient than the circuits with semi-autogenous (SAG) mills. However, such studies are difficult to conduct because the current practice of sizing and selecting the HPGR requires large samples for pilot-scale testing that are expensive and difficult to obtain. There is therefore a need for a small scale test procedure that can reliably predict the energy requirements of the HPGR for a given ore-body.
Three methodologies involving piston press tests were developed recently at the Norman B. Keevil (NBK) Institute of Mining:
- The “Direct Calibration Methodology” calibrates piston press test results to pilot-scale HPGR results on a representative composite sample from a deposit. Piston press tests can then be used to determine the energy-size reduction relationship for a range ore types within the deposit.
- Similarly, the “Database-Calibrated Methodology” calibrates piston press tests against a database of pilot-scale HPGR and piston press tests. The database includes results from pilot scale HPGR tests on 15 different ores for which piston press testing was also conducted.
- The “Simulation Methodology” involves piston press testing on five narrow size classes of particles at three energy levels from a mineral deposit. The results are used to define the energy-breakage relationship that can be used for circuit simulation.
All three test methods are valuable tools for predicting the energy-size reduction relationship for the HPGR. The ability to conduct simple piston press tests requiring less than 10kg of sample greatly assists assessment of the HPGR for early stage projects.Read Article
A method for determining the minimum practical energy for comminution was developed and is presented in this paper. An objective of the method was to determine experimentally the energy-breakage relationship for a wide size range in order to evaluate the energy performance of both crushing and grinding processes using one energy benchmarking value.
Single-particle compression breakage, referred to in the field of comminution as one of the more efficient forms of mechanical comminution, was the basis for a test regimen to characterize the energy-breakage properties of ores. Existing models for impact breakage were found to be valid for single-particle compression breakage when used in a modified form. A key parameter of the adopted model, the threshold energy, was also investigated for three ore types and a range of particle sizes.
The energy performance of comminution processes at a Canadian mining operation was determined by comparing the determined minimum practical energy, using the new method, with actual site specific energy requirements. In order to evaluate the energy performance of different crushing and grinding technologies, the proposed energy benchmarking method was used to compare the energy performance of alternative comminution flowsheets.Read Article
A cave-to-mill study being conducted at the New Afton block caving operation demonstrated the potential for sensor-based ore sorting equipment to reject waste and improve the grade of feed to the mill. The lack of selectivity and potential for dilution entry associated with the block cave mining method results in many caving operations having to mine and process material that is below cut-off grade at certain stages of production. Online monitoring and bulk-sorting systems hold the potential to alleviate this problem and improve the productivity of caving operations while reducing energy and water requirements for each tonne of concentrate produced.
As part of the cave-to-mill study, the suitability of a range of sensors, such as X-Ray Fluorescence and induction type sensors, to sort mine production from the New Afton mine was investigated. Results showed that discrimination of ore and waste can potentially be carried out by implementing surficial sensors into the material handling system. The study also showed that a combination of sensor outputs could be used to identify a certain ore type so that pre-emptive changes can be made in the mill to improve beneficiation performance. Overall, outcomes of the study on implementing sensor systems to block cave mines are considered to be of significant relevance to a number of existing and future caving operations.Read Article
Over the last 10 years the benefits of optimizing both blast designs and operation of crushing and grinding processes, also known as drill-to-mill optimization, have been shown at a number of mining operations. Significant improvements in production and revenue potential are typically associated with the successful implementation of drill-to-mill strategies. Less information is available on the impact of energy intensity with respect to all fuels used.
To address the technical challenges of implementing drill-to-mill strategies, an energy study was carried out for a Canadian open-pit copper mine. In addition to quantifying improvements in energy intensity and impact on carbon footprint, the associated cost benefits due to increased production are also presented.
For many existing and future operations, the implementation of carbon taxes in their respective jurisdictions and increased energy unit costs have provided more economic incentive to reduce the energy intensity of mining processes. For this reason it is of interest to determine the impact of modifying blast designs on the overall energy intensity of an operation.Read Article