The Natural Resources Research Institute (NRRI) has significantly enhanced its laboratory capabilities through an agreement with Swiss Tower Mills (STM) Minerals, introducing a state-of-the-art VRMmill™ pilot vertical stirred grinding mill technology at its Coleraine site. The 25-liter VRMmill™ (VRM25) is now fully operational, providing advanced grinding capabilities for a range of applications from ultrafine (P80 less than 5 µm) to coarse (F80 up to 800 µm) particle sizes.

The STM vertical stirred grinding mill is highly versatile, suitable for coarse, fine, and ultrafine grinding tasks. This flexibility facilitates innovative flowsheet design and process development, which is critical for optimizing mineral processing operations. NRRI highlights that processing coarse particles using this technology can assist Minnesota iron ore mining companies in adhering to stringent environmental, social, and governance (ESG) standards. This advancement is poised to support sustainable mining practices, enhancing the efficiency and environmental performance of the mining industry.

What sets NRRI's capabilities apart is the integration of the VRMmill™ technology with Weir Minerals’ High-Pressure Grinding Roll (HPGR). The HPGR is applied upstream in the comminution process, efficiently crushing larger rock particles into smaller sizes before they undergo further grinding in the VRMmill™. This combination is particularly innovative and effective for several reasons:

  1. Enhanced Energy Efficiency: The HPGR is known for its energy-efficient crushing capabilities, significantly reducing the energy required for subsequent grinding processes. This makes the overall comminution process more sustainable and cost-effective.
  2. Improved Grinding Performance: The VRMmill™ is highly versatile, capable of handling a wide range of particle sizes from coarse to ultrafine. When used downstream of the HPGR, it can further refine the pre-crushed material to the desired fineness with greater efficiency and precision.
  3. Innovative Flowsheet Design: The coupling of HPGR and vertical grinding technologies represents a forward-thinking approach in mineral processing. This combination is expected to form the core of future mineral processing flowsheets, offering improved performance, lower energy consumption, and reduced operational costs.
  4. Alignment with Decarbonization Goals: By utilizing these energy-efficient technologies, NRRI’s research supports the broader goal of decarbonizing the iron and steel industry. Reducing energy consumption directly contributes to lowering greenhouse gas emissions, which is crucial for meeting environmental, social, and governance (ESG) standards.

Industry experts recognize that the transformative mineral processing flowsheet of the future will likely incorporate these emerging technologies. By leveraging the synergistic effects of HPGR and VRMmill™, NRRI is at the forefront of developing innovative solutions that enhance efficiency and sustainability in the mining and mineral processing industries. This approach not only improves operational efficiency but also aligns with global efforts to reduce the environmental impact of industrial processes.


The commissioning team stands by the newly installed STM VRMmill™. Pictured (l. to r.) are Paul Mack (NRRI), Michael Moser (STM), Kyle Bartholomew (NRRI consultant, Metcom, Inc.), Fisher Wang (STM), Jeff Kinkel (NRRI) and Samantha Harbin (NRRI). Photo courtesy of NRRI.



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