Fig. 2: Unveiling phase transformations.
From: Sustainable nickel enabled by hydrogen-based reduction
The complex Ni-hosting mineral structure in the original ore, reduction mechanisms and a visual snapshot of a solidified sample. a, Phase evolution during melting of the original ore in Ar and a lean H2 atmosphere (Ar–10% H2) for 2 min and 4 min, depicting the transformation of the complex original ore with various phases into simple Mg-silicate phases. The term ‘(Ni–Fe) alloy’ (shown in bright green), represents the metallic nodules, and ‘Iron-fcc’, shown in grey, denotes iron droplets entrapped in silicates that could not be mechanically recovered. b, Photograph of the original ore alongside the complex structure of lizardite that is present in it. Lizardite exhibits the capacity to host Ni2+/Fe2+ ions by replacing Mg2+ ions, highlighting the structural intricacies within the ore. c, Schematic hypothesis of the reduction mechanism. Precipitation of metals is initiated by the removal of free oxygen from the melt. Hydrogen species extract free oxygen, leaving behind two electrons. These electrons selectively react with Ni2+, inducing the precipitation of metallic Ni. The corresponding ionic reactions are also illustrated. d, Solidified sample and cross-section. Notably, metallic nodules are observable within the sample, alongside substantial porosities resulting from gas entrapments. Scale bars, 1 cm (b) and 5 mm (d).
