Hydrogen reduction of oxidized nickel concentrates

Thermal gravimetric analysis was used to investigate the weight change of Ni/Cu/Co calcines upon heating in an inert as well as hydrogen atmosphere. The two calcines investigated contained approximately 50 wt pct combined of hematite and magnetite in addition to sulfides of Ni, Cu, Co, and Fe. Mass spectrometry was used to analyze the gas species evolved during heating and reduction. The calcine samples are 100 pct less than 100 mum with hematite/magnetite rims around a central sulfide core. When heating the calcines at 10 degreesC/min in hydrogen, reduction starts at around 400 degreesC and is nearly complete at about 700 degreesC with all the reducible oxygen removed. Isothermal reduction tests show that at temperatures from 650 degreesC to 800 degreesC, half the oxygen is removed in less than 4 min. The TGA results combined with microscopic analysis show that the reduction followed a uniform internal reduction model. The reduced calcines will quickly get re-oxidized if they are allowed to contact air while they remain hot.