Although vertical mills have long been part of full-flowsheet provider FLS’s comminution portfolio, the company continues to advance this technology to enhance metal recovery and support its sustainability objectives.

According to Peter Wulff, Global Product Line Manager for Vertical Regrind Mills at FLS, vertical media mills, in which material is broken down through attrition rather than impact, are playing an increasingly important role as ore grades continue to decline worldwide.

“As miners seek ways to maintain or improve recoveries from deposits whose ore grades are in decline, vertical grinding mills offer the advantages of internal classification and energy savings in one compact footprint,” says Wulff.

“The vertical orientation of the grinding chamber means that the basic laws of physics work in our favour to minimise overgrinding as finer particles can be discharged from the mill quickly, while coarser particles are held inside the grinding media charge until further reduced in size. This allows finer grinding while consuming less energy than traditional horizontal ball mills for the same duty.”

Vertical mills are proven for their economical energy consumption compared to horizontal mills, achieving as much as 25 to 30% energy saving, leading to a lower carbon footprint. With certain deposits like copper, iron, and lead-zinc bearing ores, this increases the profitability of recovery in the downstream flotation process.

FLS’s tower mill, branded the FTM, with its central agitator screw being the only moving component in contact with the slurry and steel media, reduces energy and media consumption in hard ore applications while also minimising water use in secondary and tertiary grinding due to the high concentration of solids in the feed. The robust design of components and proven wear materials provide higher operational availability, enhanced by intelligent operations management software to maximise circuit performance.

The company’s other vertical grinding technology is the VXPmill which uses ceramic media rotated by a variable speed disc assembly allowing it to be customised to specific grinding duties. This vertical ceramic media stirred mill is for finer grinding applications and is easily capable of achieving product sizes below 20 micron. The system uses a modular impeller with removable discs and spacers to adjust the number of discs in operation to suit the target product size while avoiding excess energy consumption.

The vertical footprint of FLS’s vertical grinding mills brings the advantage of occupying a relatively small footprint in a process plant.

“Having a reduced footprint in comparison to horizontal mills of the same capacity can support customers’ plant space optimisation, while also requiring less costly civil engineering infrastructure for its base,” says Wulff. “This lends the technology to easier retrofitting into an existing plant, especially where there are space constraints.”

Enhancing the cost effectiveness of these mills for customers is the lower capital expenditure permitted by components being factory tested and pre-assembled for rapid on-site erection – which results in significantly shorter lead times for installation and commissioning. He highlights how these factors, combined with energy efficiency and high uptime, contribute to the lowest total cost of ownership.

A recent indication of the popularity of this technology was an order from a customer in India for 18 of FLS’s FTM-5000 vertical tower mills – reported to be the largest order yet for FLS and the wider industry. The mills will serve what is set to become one of the world’s most efficient iron ore beneficiation plants.

Also significant is that the vertical grinding mills will be the largest of their type ever built and are employed in two separate grinding stages. The first stage of FTM tower mills receives the screened product of FLS’s largest built HPGRs, featuring 3m diameter rolls with a 2m width, in a typical tertiary grinding application. The second stage of FTM5000 receives the magnetic portion of the previous stage to further upgrade the iron content.