News Center >> Now Location: Newmont Ahafo operation
Integration and optimization of blasting, crushing and grinding at the Newmont Ahafo operation
Metso Process Technology and Innovation (PTI) recently conducted a Process Integration and Optimisation (PIO) or Mine-to-Mill project at the Newmont Ahafo mine in Ghana. Plant trials over the end of the first quarter of 2010 showed a significant increase in mill throughput compared to the benchmark surveys on similar material conducted previously. This was achieved at a considerably lower amount of soft, Oxide feed and at a finer grind size.
Ahafo operates a number of open pits with the majority of ore coming from the Apensu and Awonsu working areas. A blend of both primary and oxide ore is fed to the mill to balance the head grade and recovery in the leach circuit. Ahafo operate a 54 x 75” gyratory crusher for primary ore and an MMD Sizer for oxide ore. This is followed by a SABC circuit comprising a 34 x 16.4ft, 13MW SAG mill in closed circuit with 2, MP800 pebble crushers. SAG milling is followed by a 24 x 39ft, 13MW ball mill in closed circuit with a cluster of 26 inch cyclones. After classification, the milling product is thickened and the overflow is fed to carbon-in-leach tanks. (quartz crusher)
SmartTag material tracking system
The Metso PIO methodology used at Ahafo has been applied successfully to a number of operations worldwide. A PIO project is normally comprised of a number of site visits spaced over a few months. The first site visit is to establish current operating practices, initiate rock characterization and collect measurements of blast fragmentation and mill performance during a series of plant trials or surveys. This is followed by modelling and simulation studies to determine how to best exploit hidden inefficiencies. These recommendations are then followed by further site visits to implement the changes, monitor the results and ensure the improvements are maintained over the time.
In a PIO project, it is important that the material being fed to the plant during the survey is the same material that has been characterized in the mine from the audited blast. PTI have developed a radio-frequency based material tracking system called, SmartTag™ (picture on the right), that allows parcels of ore to be followed from the mine, through the crusher, intermediate stockpiles or ROM pads and finally into the grinding mills. The tags are detected as they pass near antennae that are normally installed on conveyor belts. Being passive, the tags do not have a power source and therefore can last an indefinite period and reside in stockpiles for many years if necessary.
To monitor the effect of feed size and hardness on the grinding circuit, two full plant surveys were performed during the PIO project. One survey was conducted during the top bench of the test blast and the second survey when processing material from the bottom bench.
At the end of each survey, the SAG grinding mill was crash-stopped and the rock and ball loads were measured. The survey data was then used for mass balancing and model calibration.
Measured process improvements
Metallurgical hardness testwork on circuit feed samples were conducted by Newmont laboratories during both the benchmarking and validation phases of the project. The hardness results show that the ore processed during the validation trials was harder than the benchmarking period and therefore could not be attributing to the reported increase in mill throughput following the implementation of PTI’s recommendations.
A number of blast design options were modelled and then simulated to improve run-of-mine fragmentation for higher throughput. The blast patterns were designed to increase the amount of fines (e.g. % -13mm) generated in the blast as this cannot be created through conventional crushing. These fines are beneficial to both semi-autogenous and fully autogenous milling as they pass through the mill and onto the second stage, ball mill circuit. Consequently, issues around the ball mill need to be addressed as this becomes the circuit bottleneck. For the Ahafo project, the blast designs recommended by PTI aimed to increase the amount of fines from 18% to 24%. (railway track ballast production line)
As well as blast design changes, the performance of the primary crusher was reviewed before and after the PIO project implementation. It was recommended that Ahafo measure the actual closed-side-setting once a week during the maintenance shutdown and maintain it between 5 and 6 inches based on the operating power draw.
Additionally, it was suggested that Ahafo maintain a tighter pebble crusher gap setting and not target maximum SAG mill power but rather maintain a stable total load by running the mill at different speeds.
Completion of Metso PTI's Mine-to-Mill or PIO project at Ahafo has resulted in sustained improvements in drill and blasting practices and the process plant throughput. (ore processing)
The combination of Metso’s PIO methodology along with active engagement and cooperation of Newmont Ahafo personnel, an overall mill throughput increase was measured over a twelve month period. Ahafo is currently implementing additional PTI recommendations to develop standard operating practices for both SAG and ball mill circuits.