= Direct reduced iron
<Direct reduced iron> is metallic <iron> produced by removing chemically bound <oxygen> from <iron ore> without melting the iron. Its porous structure gives rise to the name sponge iron. Gas-based processes can use <hydrogen> and <carbon monoxide> as reducing agents; the product can subsequently be melted during <steelmaking>.<Direct Reduced Iron by Midrex Technologies>[Process developer, solid-state oxygen removal and steelmaking feed]{ref}
For the idealized hydrogen reaction $\mathrm{Fe_2O_3+3H_2\to2Fe+3H_2O}$, the removed oxygen leaves in water. This reaction changes the direct chemical product relative to a carbon-based reduction, but the full environmental comparison also depends on how the <hydrogen>, process <heat> and electricity are supplied. Solid-state reduction and final steel melting remain distinct operations.
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