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

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 degrees C. The reduction reactions occurred in a non-topochemical mode at low temperatures between 350 degrees C and 600 degrees C with its rate controlled by the solid-gas chemical reactions. The reduction rate increased with the increase in temperature from 350 degrees C up to 1100 degrees C. Between 600 degrees C and 1200 degrees 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 degrees C which substantially reduced the sample porosity, the reduction rate decreased. Above 1200 degrees C, the reduction rate increased again due to the increased diffusion of the reducing gas through the molten sample at higher temperatures. (C) 2013 Elsevier Ltd. All rights reserved.