TGA kinetic study on the hydrogen reduction of an iron nickel oxide

•We examine the kinetics for the hydrogen reduction of an iron nickel oxide.•Chemical reactions control the reduction rate below 600 °C.•Gas diffusion through the sample control the reduction rate between 600 and 1200 °C.•Decrease in sample porosity reduces the reduction rate above 1200 °C.•Reduction rate increases with the increase of PH2 with the reaction order of 1.44.

Reduction of a mixed iron nickel oxide by hydrogen to produce ferronickel alloy was investigated by thermo-gravimetric analysis (TGA). The iron nickel oxide, which contains 50 wt% Fe and 10 wt% Ni mainly in the form of hematite (Fe2O3) and nickel ferrite (NiFe2O4), is a residue produced from the water leaching of a selectively sulfation roasted nickel calcine. Continuous heating tests with a fixed heating rate as well as isothermal tests were performed. Results indicate that the reduction of the mixed oxide began above 350 °C. The reduction reactions occurred in a non-topochemical mode at low temperatures between 350 °C and 600 °C with its rate controlled by the solid–gas chemical reactions. The reduction rate increased with the increase in temperature from 350 °C up to 1100 °C. Between 600 °C and 1200 °C, the rate controlling step was the diffusion of reducing gas through the pores of the sample bed with an apparent activation energy of 34.1 kJ/mol. Due to the melting of the silicate material at 1200 °C which substantially reduced the sample porosity, the reduction rate decreased. Above 1200 °C, the reduction rate increased again due to the increased diffusion of the reducing gas through the molten sample at higher temperatures.