Mine-to-mill optimisation: effect of feed size on mill throughput

Over the past 15 years, mine-to-mill studies have focused attention on the impact blast fragmentation has on concentrator throughput. Blasting provides the first opportunity for comminution – or size reduction. It is also a cheaper and more efficient process, compared to both crushing and grinding.

One of the most valuable aspects of blasting is the generation of very fine particles (e.g., smaller than 12mm) that will pass through the primary mills and onto the secondary ball mill circuits, alleviating a common bottleneck.

Modifying blasting practices to achieve a more suitable mill feed size – which varies according to the crushing/grinding circuit – can achieve up to a 30% increase in throughput. Following an initial benchmarking of an operation’s practices, SRK can advise on how value-added blasting will deliver improvements in both mill capacity and overall consistency of performance. SRK employs modelling tools to simulate the effect of upstream changes in blasting and crushing on grinding circuit tonnage.

To demonstrate the expected improvements, extended plant trials of higher-energy blasted feed are arranged so the benefits can be monitored directly.

If drill and blast costs need to be increased to improve the quality of fragmentation, these costs are far outweighed by the reduction in mill operating costs – typically 7 to 10 times any increase in mine costs.

At the same time, the concentrator must be prepared to take advantage of the much improved, higher quality feed material. A review of the current crushing and grinding practices is undertaken, with the assistance of simulation tools, to make it clear where the benefits can be obtained. Therefore, a well-managed mine-to-mill project must consider both sides: how well the mine (supplier) delivers a consistent quality feed and how well the mill (customer) is working to maximise the benefit.

For operations that have undertaken such an exercise in finer, improved fragmentation (for the mill’s benefit), the mine rarely is willing to return to the old ways of cost-minimised blasting. The reason is that the mine also benefits greatly from more consistent fragmentation with less oversize material to deal with.

The overall productivity improvement when easier-to-handle material is passed from the mine to the mill is appreciated by all involved; especially those looking at the bottom line … and who isn’t these days?

Adrian Dance: adance@srk.com

Haul truck bed showing fine content from modified blasting practices
 


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