In situ neutron diffraction study of the reduction of New Zealand ironsands in dilute hydrogen mixtures
The reduction of New Zealand titanomagnetite ironsand in a dilute hydrogen-nitrogen gas mixture was studied in situ using neutron diffraction. Neutron diffraction allowed in situ observation of large samples during reduction at high temperatures. Australian hematite ore, studied as a comparison, reduced much more quickly than the pre-oxidised ironsand, which in turn reduced more quickly than raw ironsand. The ironsand was predominantly titanomagnetite with small amounts of titanohematite. The rate of wüstite formation increased and metallic iron was formed only after the reduction of titanohematite. Experimental results confirmed the expected reduction pathway for initial reduction of titanomagnetite ore was described well by a three-interface shrinking core model. The rate controlling step in the reduction reactions studied was the mass transport of water vapour in the bulk gas. At higher temperatures, slow removal of water vapour meant that the pH2O increased, thus preventing reduction of wüstite to metallic iron.