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.