To navigate the complex landscape of mining rare earth elements, it’s important to have the right information at each stage of project development, ensuring financial feasibility and environmental best practice. Engineering firm MET63 leverages its wealth of industry knowledge and years of expertise in flowsheet development and project execution to provide their clients with customised and detailed project solutions, ensuring project success.
Seen as pivotal in the development and manufacture of smartphones, electric vehicles, wind turbines and aerospace components – among much else – rare earth elements (REEs) can be considered “the real MVP” of metallurgy, indispensable in our technology-driven world.
But, as with all mining procedures, the process of extracting REEs could have detrimental repercussions on the environment if not given proper due diligence in the early phases of project development. Reaching the point of being able to successfully mine a sustainable and viable resource of this kind requires a stringent validation process that needs to be overseen at the various project stages by experts in minerals and hydrometallurgical processing.
Determining the Right Mineralogy
Process engineering group MET63 prides itself on an extensive track record in minerals and hydrometallurgical processing, having been involved in due diligence studies and process reviews, flowsheet development, test work and financial evaluations across several REE projects in sub-Saharan Africa. The MET63 team includes experienced project managers and metallurgical specialists dedicated to delivering the highest-quality project outcomes.
Having adopted a forward-thinking approach to project development and execution (based on the latest minerals and hydrometallurgical processing technologies) MET63 believes that the first port of call with any REE development project is to undertake a pre-concept study phase.
According to one of MET63’s senior process engineers, the pre-concept stage is critical when it comes to understanding the science and viability of the resource.
“It is at this point that the mineralogy of the site is evaluated to determine the composition of the feed material, concentration of targeted REE’s and the presence or absence of Naturally Occurring Radioactive Materials (NORMs). During the pre-concept phase, we determine what beneficiation techniques should be evaluated during flowsheet development, depending on the composition of the mineral deposit and the outcomes of the scoping level leach tests,” says the process engineer.
It is usually at this early stage of project development that representative samples are analysed and tested to determine the amenability of the feed material to leaching. This gives the team insight, not only into the level of metals of interest present, but also the level of impurities.
If NORMs are present, this could hinder further project development due to the challenges posed by radioactive elements, which complicates downstream processing and results in radioactive waste. However, there are ways of managing NORMs effectively, though these usually come with a higher price tag and need to be carefully considered in the scope of the overall viability of the project.
Gathering Data to Determine Project Viability
Each stage of project development delivers a new level of data which, in turn, helps MET63 more accurately estimate the final capital outlay and related operational expenditure required to see the project through to fruition.
Ultimately, the more confidence MET63 can offer a client regarding a project’s viability, the further down the line of project study levels they are able to proceed, moving from pre-concept development to concept-level flowsheet development, pre-feasibility, feasibility and, ultimately, to bankable feasibility studies and execution.
“As we proceed down a predetermined pathway of study levels, we’re fine-tuning what starts off as a very high-level estimate of viability, to a more accurate determination of a project’s potential success,” notes the process engineer.
Refining the REE Ores
Once the sample has been evaluated and a conceptual flowsheet selected, the project can move on to the more detailed project development stages, which include more focused test work and piloting. This aims to confirm the selected flowsheet for refining the targeted REE metals from the feed material.
Minerals Processing
The refining process usually starts with a sequence of minerals processing methods that increase the concentration of REEs while decreasing the presence of gangue (waste) materials. Based on their collective experience, the MET63 team determines the sequencing of these processes.
Comminution
An act of crushing and grinding the ores to reduce their size for further processing, comminution always takes place at the outset, according to a MET63 mineral processing consultant.
During this phase, the goal is to reduce the size of the solid material while keeping it as coarse as possible to identify any waste material that can be removed prior to subsequent processing – the first stage of preconcentration.
Pre-concentration
“Pre-concentration is crucial, as it significantly reduces the environmental footprint and cost of a project by minimising the volume of material that requires intensive hydrometallurgical processing,” explains the consultant.
She adds that the team usually takes a staged approach to pre-concentration, with ore mineralogy and project budget strongly dictating which options should be considered. Usually, the first stage of pre-concentration is physical separation.
Physical Separation
The first physical separation step would be considered for the largest top size to reject waste material. Coarse pre-advanced optical and radiometric sorting techniques or, alternatively, dense medium separation (DMS), is considered.
“Depending on the liberation size of the value-bearing minerals, further gravity preconcentration steps could be evaluated at a finer particle size, which typically involves spiral, multi-gravity-separation (MGS), Falcon or Knelson concentrators,” says the processing consultant.
Other options include utilising the magnetic properties of certain rare-earth-bearing minerals for the removal of magnetic gangue minerals that might be present (magnetic separation).
Chemical Separation
If the project budget allows, the team may also opt to employ chemical separation methods to further concentrate the material. Flotation, for example, is a chemical separation process whereby chemical-based collectors are used to enhance the hydrophobicity of REE minerals in a slurry.
This allows the minerals to attach to air bubbles and float to the surface of a flotation slurry for collection, thereby separating them from the gangue materials which are usually depressed and sink to the bottom of the flotation cell.
Hydrometallurgy: The Core of REE Processing
Once the ore is in concentrated form, the final stage of processing, extractive hydrometallurgy, can get under way. Hydrometallurgy involves using aqueous chemistry to recover target metals from their ores or concentrates, as well as to further purify REEs and remove impurities.
Hydrometallurgical processing is critical for obtaining high-purity REEs required in high-tech applications. Depending on the desired outcome, hydrometallurgical processes can include a sequence of refining techniques, including:
- Calcination: Heating the REE ore or concentrate to alter its chemical properties, making it more amenable to leaching.
- Digestion: Leaching the calcined ore with acid or alkali solutions to dissolve the REEs into solution.
- Purification: Employing various chemical processes, like solvent extraction and ion exchange, to purify the REE solutions and remove impurities.
- Refining: Employing additional purification steps to achieve the desired purity levels. This includes splitting the REEs into individual elements or specific groups, depending on their designated application.
To determine the sequence of processing methods necessary for each project, the team at MET63 carefully considers the requirements and needs of the client – combined with MET63’s intimate knowledge and expertise of the industry – to develop a tailored plan for the process going forward.
The Impact of Flowsheet Development
While one cannot ignore how impactful the final stages of REE processing and refining can be for the success of a project, the process engineer notes that the real impact of a successful REE project lies in early flowsheet development and process reviews.
“In hydrometallurgy, the reagents used for the dissolution of the rare earth elements can dictate the rest of the purification process and which units of operations are included. These can have a significant impact on initial capital outlays as well as the associated operating costs. And, because these can often make or break a project, they need to be properly assessed as early on in the project as possible,” the consultant concludes.
Flowsheet development can offer more than a simple outline of capital and operating expenditure. Flowsheets can also detail opportunities to explore reagent recycling and waste management techniques, especially if the waste is radioactive.
