There is more than one way to make green steel

livemint.com:

greenhouse gas. As a consequence, steelmaking is reckoned responsible for about 9% of man-made greenhouse-gas emissions. A widespread aspiration is thus to introduce direct reduction by hydrogen alone.

The only by-product of such a reaction would be water (or rather, steam). Clever. But, thinks Tadeu Carneiro, not clever enough.

Mr Carneiro runs Boston Metal, a firm based not in Boston, but rather in Woburn, 17km to the north-west. Employing the insights of Donald Sadoway of the Massachusetts Institute of Technology, Boston Metal has created a way of separating iron from its ore by electrolysis. Instead of releasing CO2 or steam, its approach produces pure oxygen—which is not merely harmless, but actually valuable.

Electrolytic separation of metals from their oxides is not new. Aluminium is made this way. But the process uses carbon electrodes, and the oxygen liberated at the anode reacts with this carbon to generate CO2.

Boston Metal employs, instead, anodes made of chromium, iron and a secret mix of other metals in an alloy that does not react with oxygen. The other electrode, the cathode, is the liquid metal itself. Between these electrodes, as in any form of electrolysis, sits an electrolyte.

In this case it is a molten mixture of metal oxides, into which the iron ore is dissolved. Passing a current through the mixture both heats it, keeping it molten, and splits the iron oxide into its component elements. This arrangement has several advantages over direct reduction by hydrogen.

Direct reduction produces “sponge iron", a solid that must be melted before being used to make steel. Boston Metal’s process produces liquid iron directly. Sponge iron retains any impurities from the ore itself, meaning only high-grade ore