Green steel next stop for Canadian researchers

Researchers at the University of Toronto in Canada have developed a new way of recycling steel to support decarbonisation of the industry. 

The innovative method is said to be easy to implement and relies on an oxysulphide electrolyte for electro-refining. Professor Gisele Azimi explains this is an alternative way of removing copper and carbon impurities from molten steel. The process also generates liquid iron and sulphur as by-products.  

Removing impurities

‘Our study is the first reported instance of electrochemically removing copper from steel and reducing impurities to below alloy level,’ Azimi says. She notes that only 25% of steel produced currently comes from recycled material.

‘The main problem with secondary steel production is that the scrap being recycled may be contaminated with other elements, including copper,’ Azimi points out. ‘The concentration of copper adds up as you add more scrap metals to be recycled, and when it goes above 0.1 weight percentage (wt) in the final steel product, it will be detrimental to the properties of steel.’

Crucially, traditional electric arc furnaces cannot remove copper from molten steel scrap.

Electromotive force

To reduce copper content in iron to below 0.1 wt, the team developed an electrochemical cell capable of withstanding temperatures up to 1 600°C. Within the cell, electricity flows between the cathode and anode through a unique oxysulphide electrolyte derived from steelmaking slag.

‘We use contaminated iron with copper impurity as the anode,’ Azimi explains. ‘Applying voltage forces the copper to react with the electrolyte. This process removes copper from the iron, simultaneously producing new iron at the other end of the cell.’

High-grade products

The Toronto research means steel can be recycled into high-grade products such as galvanised cold rolled coil used in the automotive sector or steel sheets for deep drawing as used in the transport sector. Typically, steel is recycled into lower value products, such as rebar used in the construction industry.

Azimi’s lab collaborated with Tenova Goodfellow, a global supplier of advanced technologies, products and services for metal and mining industries. Looking forward, her team wants to fine tune the electro-refining process to remove other contaminants such as tin from the steel.