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effiCient mineral processing and Hydrometallurgical RecOvery of by-product Metals from low-grade metal contaIning seCondary raw materials

Periodic Reporting for period 2 - CHROMIC (effiCient mineral processing and Hydrometallurgical RecOvery of by-product Metals from low-grade metal contaIning seCondary raw materials)

Reporting period: 2018-05-01 to 2019-10-31

The CHROMIC project is developing new recovery processes for chromium, niobium, molybdenum and vanadium. These four metals are crucial for the European industry, but they are sourced mainly from outside Europe. Europe does have large stocks of industrial by-products, such as steel, stainless steel and ferrochrome slags, which contain significant amounts of these four elements that are currently not fully exploited. These slags are used mainly as aggregates in the construction industry, with small fractions of some slags even being landfilled. In these applications, the entrapped valuable elements are not used to their full value. The CHROMIC project aims to unlock the potential of these resources, by developing new sustainable ways of metal recovery, leading to a near zero-waste recycling of the entire slag materials. Smart combinations of existing methods and new technological innovations will be developed, tested and validated to extract valuable and critical raw materials from the slags in the most sustainable way. The candidate technologies cover the entire recovery process, from pre-treatment (size reduction, beneficiation) over selective leaching up to metal recovery.
CHROMIC is an inclusive project. Through participatory events, CHROMIC will collect the views and expectations of European citizens about the occupational, environmental and health aspects of metal production and recovery. This knowledge will help to prepare a path for successful market application of the technologies developed by the project.
The technology development was first done in separate dedicated work packages: mineral processing (WP2), selective leaching (WP3) and selective metal recovery (WP4). Frequent feedback loops and exchange of information between these work packages were implemented to ensure that the different steps in the overall process are matched.
The work started with a detailed characterization of the four model streams (carbon steel slags, LC and HC ferrochrome slags, stainless steel slags). This work revealed the need for a multi-analytical approach to gain insight in Cr distribution, and highlighted the importance of choosing an appropriate analytical technique for reliable Cr quantification (Horckmans et al., 2019).
Magnetic separation proved to be the best method for up-concentration, resulting in a pure metallic phase with potential for reuse, and enriched fractions for leaching. The use of microwave or electrodynamic pulse fragmentation to improve comminution efficiency proved unsuccessful due to the small particle size of the target minerals and metals.
For the leaching part, the best results were achieved with (conventional and microwave) roasting, reaching a selective Cr recovery > 95% with < 1% matrix dissolution. Feedback from the first iteration of the integrated (WP1) assessment showed that a change from KOH to NaOH in MW roasting is necessary to make the process economic. Heap leaching resulted in much lower recovery (21 %) but could be a low cost alternative to recover the easily leachable Cr.
Further investigations into the reusability of the matrix material are critical for the implementation of these new flow sheets. Initial tests show that washing is needed to remove excess soluble Cr(VI). Additional investigations into the use of the fine-grained residue for the production of building materials are scheduled for the next months.
Different metal recovery techniques were investigated for the separation of Cr from other elements of interest such as V and Mo. Layered double hydroxides with a very high selectivity for V over Cr were engineered to withstand the high pH values in the leachates. Recovery schemes based on nanofiltration and selective precipitation recover Cr almost completely in a very pure product (> 99% Cr hydroxide), but with a complicated procedure. Efficiency of the recovery could be improved by increasing the input Cr concentration.
Based on the unit process development, flow sheets were selected for the more detailed assessment (in WP1) and upscaling trials (in WP5). Preparatory optimization trials are ongoing. The economic feasibility and environmental impact of the developed flow sheets will be assessed in the second and third iteration of the integrated assessment.
In WP6, newsletters and podcasts are regularly prepared including the “Getting to Know” series specifically aimed at the general public. The project video is accessible on the project website, and was shown also at different events (e.g. G-STIC, PDAC). The project has been presented at different sector events in Europe, recently also at the EIT Raw Material Summit in Berlin. Two waves of focus groups, targeted at lay people and professional experts, respectively, were organized at four locations (Belgium, Germany, France, Italy). These focus groups have given valuable insights for the integrated assessment in WP1, and for the communication to the general public in WP6. A third wave of focus groups involving students and professionals is foreseen for 2020. CHROMIC is engaged in several clustering activities with other H2020 projects and the EIT Raw Materials, recently focusing mostly on the topics Sustainability Assessment and Societal acceptance.
The final goal of CHROMIC is to recover maximal value from secondary resources, in line with the requirements of the circular economy and with market demand. By turning valuable compounds which are left in the slag into metal, Europe’s raw materials supply source can be diversified. At the same time, fractions of primary materials are recovered that can be reused as input flows in production processes. This will improve the sustainability and reduce the environmental impact of the metal industry. Furthermore, in some cases a more efficient use of resources can free up land currently used for landfilling or intermediary stocks, alleviating the burden for future generations. To unlock the potential of slags as low grade metal resources, a radically new approach to metal recovery must be deployed. Crucial factor within this new value chain is the zero-waste approach, which captures not only the contained metals but also valorizes the residual matrix (often >95% of the bulk material). Such an approach requires the development of innovative, highly selective metal recovery technologies that fully capture the metal-value without impairing the properties of the residual matrix material for valorization.

At the moment, technical advances achieved by CHROMIC are:
•Tailored physical separation schemes based on magnetic separation to divide the input streams into metal concentrates on the one hand and metal-depleted residue matrix materials on the other hand. The resulting metallic fractions can be reintroduced into the metallurgical process
•The development of alkaline roasting processes using traditional and microwave heating to recover > 95% of Cr from the slags with high selectivity (< 1% matrix dissolution).
•The development of novel LDH-based sorbents for operation in highly alkaline environments
•The development of metal recovery schemes based on nanofiltration and selective precipitation able to recover Cr completely from solution in a high purity (> 99%) products

The know-how gained will increase the flexibility and broaden the range of suitable input streams for many minerals processing, metallurgical and recycling processes. Through replication, the potential impact can be multiplied.
CHROMIC overview figure