Dr Priscilla Freire, mechanical engineer, and Dr Bin Chen, technical director at TUNRA Bulk Solids, discuss the importance of materials testing in critical minerals projects.
With their importance for the global energy transition, critical minerals have seen a growing gain in popularity over the past couple of years. With significant investment from local and federal governments, Australia is leading the way not only in the exploration and production of critical minerals but also in providing consultancy for overseas miners.
As with every other type of bulk material, understanding the handleability of critical minerals is of utmost importance to ensure reliable operations. TUNRA Bulk Solids has seen an increase in projects involving not only critical minerals but also the so-called ‘strategic materials’ such as aluminium, copper, phosphorous and zinc.
Critical minerals and strategic materials
According to the Department of Industry, Science and Resources, critical minerals are the minerals essential to modern technologies, economies and national security for which Australia has a geological potential for resources, in demand from strategic international partners and vulnerable to supply chain disruptions.
On the other hand, strategic materials are important for the global transition to net zero and broader specific applications, for which Australia has geological potential for resources and in demand from strategic international partners, but their supply chain are not currently vulnerable enough to meet the criteria for the critical minerals list. This naturally means the list is somewhat ‘fluid’ and is bound to change according to supply and demand.
Knowledge transfer from ‘traditional’ commodities to critical minerals
In a recent article published by AusIMM, specialists from Sedgman discussed the question “Can existing expertise be leveraged to support critical minerals processing in Australia?”. Discussion points include the fact that Australia has historically placed significant focus on the ‘direct shipping ore’ (DSO) model for bulk exports, with in-country processing predominantly focussed on primary concentration (coal, base metals, bauxite) and gold. With the increase in demand for critical minerals combined with the fact that Australia holds significant reserves of critical minerals and strategic materials, incentives have recently been put in place to encourage downstream processing opportunities aimed at adding value to these resources, especially those related to electronics, renewable energy and electric vehicles.
According to the authors, the Australian mining and minerals processing industry possesses several of the skills and technical expertise and is well-placed to succeed in this space when it comes to mineral processing.
Similarly, Australia is a worldwide reference in the discipline of bulk materials handling in comparison to other prominent mining countries, and now it is time to leverage this extensive experience in more ‘traditional’ commodities to also grow capability in the critical minerals and strategic materials sector. Understanding the challenges posed by these commodities plays a key role in maintaining Australia’s technical leadership.
Handling challenges in critical minerals
Recent projects have involved, in some cases, rather comprehensive scopes with flow properties testing at their core; others were focused on specific challenges anticipated by the clients including dust issues or excessive moisture, potentially leading to concerns in transportation. Outside the testing space, TUNRA has also assisted clients with engineering and design aspects, including design review of existing handling equipment to ensure their adequacy when applied to ‘new’ materials. The experience gained in these projects has contributed to the development of TUNRA’s team in gaining a deeper understanding of the challenges posed by these materials.
Design constraints
TUNRA’s lab experts recently tested a sample of vanadium oxide, a material that plays a critical role in industrial applications and is growing in popularity in the energy transition due to its application in Vanadium flow batteries for energy storage. The material was tested at dry condition at the request of the client, and measurements taken with a direct shear tester resulted in low bulk strength and moderate friction against the liners tested. However, when looking at all the flow property results in conjunction, the conclusion was that, in order to promote mass flow in bins designed for this material under the tested conditions, very steep wall angles would be required, which would potentially make the design impractical to achieve the storage capacity. One potential solution is to adopt an expanded flow mode, though this approach would need to account for structural constraints – particularly the limited head height of the building housing the silo. Alternatively, a planar flow hopper would require a less steep hopper angle. TUNRA’s client, an Australian design house, is now investigating the use of bin inserts that would transform the conical flow profile into pseudo-planar flow and hence reducing the space requirements.
Materials requiring testing are not only being produced in Australia but also in other major mining countries.
A recent overseas project involved the testing of rare earths from a development that has been regarded in the industry as having a uniquely high reward from a metallurgical perspective given its high-quality material and relatively simple flowsheet to extract value. Once the materials handling testwork started, however, TUNRA’s experts soon noticed that the materials handling part of the process was proving to be much more complex and has the potential to introduce bottlenecks to the production.
Testing at the moisture of content of interest resulted in very steep flow functions with extremely high strength for low consolidation under instantaneous conditions, yielding critical opening dimensions larger than eight metres, which are naturally not practical for design.
The flow function is a measure of the material’s internal strength as a function of the consolidation pressure applied to it, and interpretation of the material strength coupled with wall friction measurements against the liner of interest result in the determination of the critical opening dimension for bins to prevent cohesive arching for given wall inclination angles and to promote mass flow. It is noteworthy that, for the design of storage systems, the flow functions under time consolidation should be used instead of the instantaneous condition, and, for highly adhesive materials such as this one, the material under consolidation is likely to exhibit even higher strength.
Also important to note is that the flow functions are specific to the exact sample tested, under the conditions tested (i.e. moisture content, consolidation pressures, particle size distribution) and may vary greatly for materials of the same ‘type’. In other words, a different Rare Earth Elements ROM Ore might behave very differently from the example described herein.
Another recent project involved testing of Lithium Carbonate originated in South America. Flow properties testing resulted in some challenging handling conditions due to the very fine nature of the filter cake coupled with high moisture content. Moderate to large critical arching dimensions were calculated to overcome cohesive arching during mass flow discharge. With respect to hopper half angle, for this material, only a limited design window exists in which true mass-flow may be developed, which is heavily dependent upon the type of finish of the liners tested.
Moisture-related challenges
Another challenge with fine concentrates being produced for export is the potential risk for liquefaction. Concentrates such as copper and nickel are known to have caused serious accidents in seaborne transport over the years, leading to the development of standards and testing methods to determine the transportable moisture limit (TML) of bulk cargoes. The TML is the moisture considered the limit for safe shipping, and the International Maritime Solid Bulk Cargoes (IMSBC) clearly identifies which bulk materials are susceptible to liquefaction and must therefore be shipped with a TML certificate.
According to the Bulk Carrier Casualty Report 2013-2022, while safety has overall improved in comparison to the previous decade, significant loss of lives was still experienced associated with cargo liquefaction. The report also lists the most recent major loss of life incident associated with liquefaction: in 2019, the Nur Allya ship (Indonesia) sank near Buru Island, causing the death of all 27 crew onboard. The vessel was carrying a cargo of nickel ore. In addition to this accident, another three ships also carrying nickel ore were also affected, as well as a bauxite ship.
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TUNRA regularly contributes to the testing of several materials for shipping purposes including bauxite/alumina, concentrates (copper, zinc, magnetite) and coal. However, some new operations involving critical minerals are also using TML testing as an indication of material stability and behaviour with changes in moisture for purposes other than shipping. Recent projects have involved lithium tailings from a few different producers to aid in the investigation of dry stacking operations or to investigate potential for liquefaction in truck transport. Although not the intended use of the standardised TML testing methods, modified versions or customised test rigs are sometimes applied to these projects with the aim of replicating, as close as feasible, the vibration conditions experienced during truck or train transport which provide some insight into the possibility of transporting such materials via the intended means.
On the opposite side of the moisture spectrum, materials being handled at very low moistures are sometimes at risk of dust issues. Conducting a Dust Extinction Moisture (DEM) test is often the starting point in understanding the material’s propensity to dustiness, and, depending on the application, the dust lift-off potential can also be assessed using a wind tunnel. A recent project involved a series of wind tunnel tests to evaluate the dustiness potential of a sand material composed of Delithiated Beta Spodumene (DBS), a by-product of the lithium production chain, mixed with sand for use in road construction. The aim was to investigate the dustiness potential of this material when stockpiled under different compaction conditions, moistures and how effective would the use of an inorganic surface spray could be to reduce the dust potential.
Working with engineering firms
Projects involving critical minerals have expanded beyond materials testing. Working with renowned engineering houses in Australia and overseas, TUNRA has also contributed to the design of materials handling facilities for these materials. One of such projects involved testing and Discrete Element Method (DEM) calibration and simulations for a client who was re-purposing a transfer chute originally designed to handle iron ore which was now being assessed to handle spodumene. TUNRA had done a third-party design verification for the transfer when handling iron ore and then was approached by the engineering company working on this project to also test the spodumene and conduct a design check to assess whether the existing geometry would be appropriate for a material with very different handling characteristics. The analysis involved verifying the geometry for blockages, material build-up and residual material after flow, impact and abrasive wear on ceramic liner and central loading onto the belt.
Other engineering projects in the lithium chain comprised a design review of an existing acid roast feed bin to assess its suitability to handle two types of spodumene. After conducting flow properties testing on both bulk materials, TUNRA’s experts analysed the geometry of the existing bin, as provided by the client, and concluded that the bin’s opening was larger than the determined critical opening dimension, such that cohesive arching was not expected to form. However, testing on the existing wall liner material produced steeper angles than those of the bin’s current hopper, suggesting that mass flow was unlikely in the given configuration. Evaluating alternative liners revealed potential solutions to reduce wall friction and achieve mass flow without modifying the hopper geometry. Considerations were also made with regard to using a fluidiser to enhance flow inside the bin.
Final remarks
Working with our clients in the critical minerals space has allowed TUNRA experts to gain insight into some of the handling challenges that might be present in the production chain. As with traditional bulk commodities, a deep understanding of the material flow properties and the complex interactions between the bulk material, moisture and the surfaces it interacts with is key for the design of efficient storage and handling facilities as well as to define transportation and disposal options.