Enhancing zinc circularity for the automotive industry

In my last blog I focused on the circularity of steel for the automotive industry. Today I want to discuss the circularity of zinc because this is also important for automotive steels.

Steel and zinc are synonymous

Steel is almost universally protected by zinc - in fact 50% of global zinc usage is for the protection of steel and of course steel is galvanised for almost all automotive Body in White applications. The ability of steelmakers to process zinc-coated scrap and recover zinc is of particular importance to the automotive supply chain to ensure the availability of affordable zinc for future generations.

Zinc extraction is a two stage process, an enrichment step (to a more economically viable content, ideally >50%) followed by extraction of pure zinc metal. The enrichment step is energy and carbon intensive, but the richer this material, the more economic and less energy and carbon intensive the extraction step.

Zinc and the Primary steel-making via BF / BOS route

As described in my previous blog, the blast furnace / basic oxygen steel-making (BF / BOS) route is limited to ~20% scrap because the process involves no active heating technology and the scrap cools down the molten steel. This means that the zinc concentration in the dust is <5% which is too low to be attractive to zinc producers, which makes it problematic to recycle. For this reason zinc-coated scrap is not processed via the BF / BOS route.

Zinc and the Electric arc furnace, EAF

Electric arc furnaces are a key technology for future steel-making whereby scrap can be re-melted and combined with pure sources of iron to make automotive products. Depending on the scrap charged, one ton of EAF melted steel scrap produces about 15–25 kg of dust, in which the content of zinc is 15–30%. The higher the zinc-coated scrap content, the greater the zinc-enrichment, but dilution with direct reduced iron (DRI) or other iron source to achieve steel cleanness targets clearly has a diluting effect on dust enrichment. So while EAF dusts are well suited to zinc recovery, the dust must first undergo enrichment before being processed to extract zinc metal.

Zinc circularity and the HIsarna process

Tata Steel has looked in detail at the asset requirements for a low carbon and circular automotive steel future and anticipates a future configuration with EAF, DRI and hydrogen technology, as do other steelmakers. But at Tata Steel we recognise the requirement for, and benefits of increasing the circularity of automotive steels. This is where HIsarna fits in.

The HIsarna unit will be used primarily to make iron but can be charged with up to 50% of zinc-coated scrap. The EAF furnace will be used primarily as a scrap melting unit in which up to 100% scrap can be charged, and the fraction of zinc-coated scrap can be varied without restriction because the collected dust will be charged and enriched in HIsarna. This configuration will give Tata Steel the capability of recycling large quantities of zinc-coated scrap and automotive pre- and post-consumer scrap in particular.

Processing zinc-containing dust using HIsarna permits enrichment up to >50% at which point it becomes attractive input material for zinc producers because the enrichment step can be entirely avoided, saving energy and CO2. Zinc can be extracted directly from the enriched dust.

A credible solution to enhanced automotive steel circularity 

Automotive steel scrap is inherently ‘clean’, low in residual elements and with HIsarna as a solution for processing of zinc-coated scrap, is will be possible process it back into automotive steels. By closing the product loop, automotive steel scrap will be available once again for the production of new automotive steel. So HIsarna has a role to play in preserving automotive scrap quality for future generations.

Today I have described how HIsarna is a key technology for improving the circularity of automotive steel scrap, enhancing the circularity of both zinc and steel. You can read more about HIsarna here. In my next blog I will explore how HIsarna can offer a solution to the production of low carbon steel.