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Extracting critical metals from industry slags: one more step towards a circular economy

19 February 2021 News

A EU-funded project has pioneered new technologies, and new combinations of existing ones, to recover chromium and other metals from steelmaking by-products with high efficiency.

 

Chromium,vanadium, molybdenum and niobium: these four metals are crucial for the European industry. But they are almost exclusively mined and produced outside Europe – especially in China, Brazil, South Africa, Russia, Kazakhstan and Turkey – making the EU highly dependent on import. 

On the other hand, Europe has large quantities of those metals trapped in industrial by-products such as slags from steel, stainless steel and ferrochrome production. These slags are used mainly as aggregates in the construction industry, with small fractions even being landfilled. 

For four years, the partners in the CHROMIC project have worked to unlock the potential of these resources, in the end taking important steps towards the development of new sustainable ways of metal recovery and a near-zero-waste recycling of the entire slag- material. 

New technologies and smart combinations of existing ones have been developed and tested and applied to the three crucial steps of the recovery process: pre-treatment, selective leaching and selective metal recovery. A comprehensive study was undertaken to characterize the initial materials in more detail, prior to the recovery investigations.

The project succeeded in extracting over 95 % of chromium and lower amounts of the other three elements, using alkaline roasting with conventional or microwave heating  and water leaching (where the metal present in the solid mixture is dissolved into water). Heap leaching resulted in lower metal recovery, but might still have potential as lower cost and impact alternative for specific streams. 

The resulting solution (leachate) was treated by a combination of methods to separate valuable elements from impurities in the solution. The entire process reaches at least 85 % overall efficiency in recovering chromium. 

Ultimately, from the results of the tests performed during the technology validation stage, it was possible to estimate that (at least) 25000 tonnes of chromium per year can be recovered in Europe through the CHROMIC process. Potentially, thanks to CHROMIC, in the future the steel slags can be considered as metal deposits. 

However, a key remaining challenge is the valorisation of the treated matrix. The overall assessment performed in CHROMIC showed that this is a crucial factor for the economic and environmental sustainability of the process. Further optimization of the treatment tested in CHROMIC is needed to fully prevent the toxic form of chromium – Cr(VI) – leaching from the treated residue. The CHROMIC processes were shown to have potential in particular for waste streams that are currently landfilled due to Cr leaching. 

Beside technology-focused activities, CHROMIC also included an assessment of the impact of these technologies on the economy and – in a broad sense – on society. Through participatory events such as workshops and focus groups, CHROMIC collected the views and expectations of European citizens about the occupational, environmental and health aspects of metal production and recovery. The insight collected through the participatory events is meant to support researchers, the metal industry, EU policy makers and regulators in taking future decisions and steering further research, with the aim of increasing citizen’s awareness and gaining societal trust, hence preparing a path for successful market application of the system process and technologies introduced by CHROMIC. 

In all, the CHROMIC project has contributed to set the way towards the realization of a circular economy for critical raw materials, which has the potential to bring significant economic and environmental benefit to the European society.



This project received funding from the European Union’s Horizon 2020 Research and Innovation program under Grant Agreement n° 730471

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