Coarse vertical stirred mill applications

Ballantyne, Foggiatto, Staples, Lane

Presented at the AusIMM Mill Operators Conference June 2021


Vertical stirred mills are more frequently being applied at coarser grinding duties as a replacement for ball milling. This trend is being driven by reductions in footprint and operating costs such as power and media consumption that counter the increased capital cost. Vertical stirred mills have been reported to use up to 40 percent less energy (decreasing to 20 percent for coarser applications P80>200μm) and 20 percent less media than equivalent ball mills.

However, this reduction is difficult to validate in operations as there is a tendency for these circuits to create a sharper product size distribution, and the evaluation techniques typically use P80figures.Although benefits are well established in regrind and tertiary duties, they have not been clearly proven in coarser applications following autogenous (AG) or semi-autogenous (SAG) mills and high-pressure grinding rolls (HPGR).

This paper brings together data from three operating sites to better evaluate the performance of vertical stirred mills in coarse duties. There are many applications where vertical stirred mills have been installed in coarse duties. Morenci conducted a long-term trial of a VertiMill™(VTM) in secondary duty following an HPGR closed with an 8mmwet screen. Boungou has recently commissioned a milling circuit with VTM following a SAG mill closed with a 6mmscalping screen.Tambomayo has an open circuit VTM following a single stage SAG circuit closed with hydrocyclones. Cannington has employed a VTM in closed circuit following a single stage AG mill circuit. Finally, Cadia, New Afton, Chino and Raglan have employed VTMsin a tertiary application to debottleneck the ball mills and stabilise the float feed by providing a dampening effect to process variability. The efficiencies of these plants are evaluated to better define when and where VTMs are best employed.


The authors would like to thank those who collected and published the data used in this analysis. Conversations with Martin Houde, Douglas Mazzinghy and Malcolm Powell were integral in the development of some of the ideas expressed in this paper. Finally, thanks to Ausenco for providing the impetus and opportunity to publish this paper.


G R Ballantyne1, B Foggiatto2, P Staples3and G Lane4

1.Director Technical Solutions, Ausenco, Brisbane. Email:This email address is being protected from spambots. You need JavaScript enabled to view it.

2.Senior Process Engineering Specialist, Ausenco, Vancouver.

3.VP and Global Practice Lead, Minerals and Metals, Ausenco, Vancouver.

4.Chief Technical Officer, Ausenco, Brisbane.


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