Innovator in vertical stirred milling to sponsor CEEC

With social license to operate being one of the key challenges facing the mining industry, environmental, social and governance (ESG) performance measures have moved from a ‘nice to have’ to a ‘need to have’ for miners and investors alike. Increasingly, leading miners are taking up alternative comminution and processing options to reduce their energy footprint and move towards decarbonisation.

Swiss Tower Mills Minerals AG (STM), a company that has successfully translated the vertical stirred milling technology of industrial minerals to hard rock minerals processing, is the latest sponsor to support the work of the not-for-profit Coalition for Eco-Efficient Comminution (CEEC).

Ralf Hesemann, STM Managing Director, said supporting CEEC’s work was a natural fit for the company.

“The uptake of new technology in the mining industry is traditionally a slow process. Tapping into a trusted independent body that communicates the latest technical findings on efficient comminution practices is a win-win for both of us. I look forward to our collaboration,” he said.

Swiss-based STM developed the Vertical Regrind Mill (VRM) and released it to the minerals market in 2012. More than 60 of the stirred media grinding mills have been sold to mines across the Americas, Europe, Africa, Asia and Australia. For fine and ultra-fine grinding applications it is marketed under the name HIGmill, through the company’s partner Metso:Outotec. For coarse regrind applications, STM offers the VRM mill directly to customers in the minerals market.

Since the grinding principle of multi-compartment grinding offers substantial energy savings, a new stirred mill has been developed for coarse grinding applications up to 6 mm feed size, the Vertical Power Mill (VPM). Mill sizes range from 700 to 12,500 kW with high flow rates, and potential energy savings of up to 40%. Due to its small footprint, STM is marketing the VPM as a viable ball mill replacement in HPGR circuits or for capacity increase in existing plants.

The energy savings are achieved through uniquely designed rotors and stator rings in a vertical arrangement that enable high power intensities, even with relatively low tip speeds. This results in higher energy efficiency, a smaller footprint and the potential for increased recoveries. Power intensities of 200-300 kW/m³ are typical, and operational tip speeds range between 6-12 m/s, depending on application and mill size.

CEEC Director Chris Rule said it was encouraging to see energy efficient, stirred media mills being installed by industry as a step towards more sustainable mining practices, in line with ESG considerations and net zero emissions commitments.

The 2020 CEEC Medal winning paper (Operations) - Reducing Energy and Water Consumption Through Alternative Comminution Circuits – states that “reductions in the order of 35% of energy consumption relative to Bond” have been demonstrated by different stirred mill technologies, with actual savings varying “depending on feed size to the stirred mill”.

One of the first HIGmills be commissioned, in 2015, was a 700 kW mill for a copper concentrate regrind application at the Kevitsa mine in Finland. Several papers have been published on the energy efficiency and metallurgical performance of this mill, including an Outotec paper presented at Comminution Capetown 2016, and A Review of Published Full-Scale Stirred Mill Results by Michael Larson, Molycop, USA, presented at the SAG 2019 Conference.

The technology will also be installed at the ground-breaking Iron Bridge Magnetite Project in Western Australia. The joint venture between Fortescue Metals Group and Formosa Steel IB Pty Ltd is the world’s first large scale plant without horizontal milling. The flowsheet consists of a 2-stage HPGR circuit feeding 10 advanced HIGmill grinding mills in total.

Elsewhere in Australia, 17 HIGmills are already in operation across various gold, iron, copper and molybdenum facilities, according to the STM website.

Rule said stirred mill grinding technology had been well proven for decades in industrial mineral applications such as in the opacifiers, fillers, ceramics, paint and pharmaceutical industries.

“We commend STM for translating this technology to mineral processing, offering miners an energy-efficient, low footprint alternative to high-intensity ball milling,” he said. “Having STM on board as a CEEC sponsor means greater opportunities for us to learn about and share alternative comminution approaches. This support from our valued sponsors over the past 10 years is what enables CEEC to help keep industry aware of demonstrated advances that help mining leaders tackle the challenges of reducing the energy consumption, emissions and overall footprint of their operations.”

Hesemann said declining ore quality meant that energy efficient comminution was becoming a more critical stage for realising profit.

“We’re proud of the part our technology plays in lowering the footprint of mineral processing, while at the same time decreasing CAPEX and OPEX and improving the bottom line,” he said. “Being a CEEC sponsor will enable us to more widely share any advances in this field, as well as learning from the global network of industry experts that CEEC brings together through its events and online resources.”