Modern demands reshaping mineral process flowsheets, says Bjorn Nielsen

A 20-year-plus veteran of the mineral comminution business, Bjorn Nielsen is excited about what lies ahead for the industry and for Metso. “We are seeing more and more interest in new mineral processing technology and how it can be combined,” he said in the lead up to IMARC 2026, where he will present on energy and other benefits of innovative comminution circuits.

“HPGR [high pressure grinding roll] use continues to grow. We’re seeing renewed interest in AG milling and pebble milling to eliminate grinding media.

“And then the interest from the market in the Vertical Roller Mill is very, very significant at the moment.

“There’s a real pull from the market for a technology offering the energy, water and wear reduction benefits that VRM does.”

A heavyweight manufacturer and supplier of traditional comminution plant and mineral processing equipment, and a raft of newer technologies, Metso is working with a number of the world’s biggest miners on process flowsheet advances for an era pitting demands for higher ore throughput rates and recoveries from lower-grade materials directly against corporate ambitions to cut energy and water use, waste generation and other environmental impacts.

“There is a need in the mining industry for more sustainable mineral processing solutions,” say the authors of a paper that recently took out the Coalition for Eco-Efficient Comminution’s 2025 CEEC Medal. The four authors from Metso and Germany’s Loesche described the impact of dry VRM grinding in an integrated flowsheet with modern magnetic separation or coarse flotation components.

“The focus is on saving electrical energy, reducing water consumption and managing tailings in a sustainable manner,” they wrote. “Comminution [primarily grinding] has an energy share of more than 50% in standard mineral processing and approximately 2-3% of the worldwide energy consumption. Hence, energy saving in comminution has a big lever to reduce the energy consumption needed to process ores.”

Nielsen, vice president HPGR and Dry Grinding at Metso, says the company’s partnership with Loesche in VRM dry grinding, announced in February this year, has opened up new pathways for optimising beneficiation performance and supporting more sustainable, resource-efficient mineral processing.

“VRM technology has got a long history and was invented by Loesche almost 100 years ago,” he says. “Loesche has got more than 2400 operating references in cement and other industry applications such as blast furnace slag grinding.

“Palabora in South Africa put it to work on rock phosphate and there have been other applications there.

“The time was right for us commercially but on the customer side there’s obviously the continuing emphasis on energy, carbon and water and this really ticks all the boxes. We’ve seen 40%-plus improvements in energy efficiency in some cases.

“And we can operate with a coarse secondary crushed feed and grind down to the final grind size, so we’re substituting most of the [conventional] grinding and eliminating all that grinding media and mill lining wear associated with conventional grinding mills. Downstream processes also benefit from improved mineral liberation and steeper particle size distribution. Wear inside the [VRM] unit is very low: a fraction of the total wear mass per tonne compared to conventional grinding technologies.

“Dry comminution means we can optimise water addition to the downstream plant, assuming it's a wet beneficiation process, or otherwise integrate it seamlessly in a dry beneficiation process. Flow sheets with coarse particle flotation, magnetic separation or other coarse beneficiation technologies can be facilitated. We are talking about reducing or even eliminating water consumption if fully dry processes are feasible.

“There are a lot of dry magnetic separation technologies that are coming on through the market these days.

“We see a role in enabling that.

“It’s much more efficient than dry ball milling or any other technology for those applications.

“Clearly a dry feed is optimum for a roasting application and then another attractive application is across hematite and magnetite iron ore producing a pelletising feed.

“We do also have some interest in using the VRM on pebble circuits and pebble stockpile processing.

“We can deliver the product directly, for example, to a ball mill sump or cyclone feed hopper so we're essentially producing final product from the mill pebbles. That will relieve the SAG mill, but also the ball mill, from the hardest material in the process.”

The CEEC Medal-winning Metso Loesche paper on the benefits of combined VRM-coarse flotation early gangue rejection put a spotlight on industry-first development by Metso and Loesche of an integrated grit recirculation system and on important testwork at Metso Loesche’s Ore Grinding Plant (OGP) pilot facility in South Australia.

Advances in hydrodynamics and process chemistry are increasingly pushing new coarse particle flotation (CPF) technologies to the fore. Nielsen says energy and water efficiency benefits of early waste material classification are also gaining currency.

“There’s a lot of interest in that coarse gangue rejection stage,” he says.

“Conventional comminution circuits are not a great fit for certain-size material in part because classification at the target particles sizes is difficult. Targeting 300-500 microns is really too fine for screens at large scales and right up towards the coarse end of what’s feasible to achieve with a hydro-cyclone.

“With the vertical roller mill we can produce that size fraction fairly easily and we do that with grit extraction. Grit is the oversized particles from the classifier in the vertical roller mill. Instead of returning those oversized particles to the table we can extract them and send them to coarse particle flotation or magnetic cobbing or other coarse beneficiation technologies.

“CPF is really very interesting for us because we’re also taking the fines out of that material, so it's easier to handle and easier to process with CPF. And then there’s still the fine product from the vertical roller mill that would go directly to flotation stages and that can be combined with a CPF concentrate via regrinding as well.”

Nielsen will be available at Metso’s IMARC stand G21 with a flowsheet showing what that looks like.

“It’s potentially a big enabler of CPF,” he says.

While incumbent technologies, including horizontal mills, will continue to be mining’s comminution workhorses, Nielsen will explore how miners can draw on a broad portfolio of flowsheet solutions, including combinations of HPGRs and stirred mills, to help them balance capital cost, operating cost, reliability, availability and sustainability.

“I think the bottom line is that there are technologies and flow sheet arrangements available today that are cost effective in terms of total installed cost but also provide the availability, operating cost and sustainability benefits the industry is looking for.”