A comparison of conventional and unconventional reductants through characterization and reactivity tests on solid state chromite reduction for application in the South Africa ferrochrome industry

Reductants form a significant portion of the production costs during ferroalloys processing. Consequently, the need arises to cut costs and drive profitability through raw materials optimization, viz, reductants. Unconventional reductants are expected to have a high reactivity and fixed carbon content, but their current availabilities are low. Innovation together with substitution has become a necessity to ensure sustainability and competitiveness of processing operations. The main objective of this research was to study and compare the reactivity of commonly used reductants and that of readily available, new sustainable carbon materials as potential reductants for the reduction of natural chromite at steady state. The selected reductants comprise of conventional Reductants A (Market Coke), B and B1 (Trial Market Cokes), C (Industrial Char) and unconventional Reductant D (Charcoal). This investigation was undertaken by initially characterizing the reductants with the use of advanced analytical techniques including proximate, ultimate, particle size distribution and petrography and then to determine the merits and demerits of each in typical ferrochrome processes. This was followed by reactivity tests in the solid state at temperatures ranging from 1100oC, 1200oC, 1300oC to 1400oC and over a 4 hour period. A thermo-gravimetric analysing (TGA) furnace was used with tests undertaken under inert atmosphere in order to determine the practical performance and application of each reductant. Data collected from a series of TGA furnace campaigns was utilised to determine the reactivity of the selected reductants. Analytical methods of chemical speciation, XRD and SEM-EDS were applied to confirm the extent of chromite reduction. The outcome of this research project indicated that the best reductants according to overall mass loss were D (122.03%), C (112.97%), A (91.61%), B (90.51%) and B1 (80.72%), consecutively in reducing order. Whilst the unconventional Reductant D was shown to be most reactive and having the highest mass loss at test temperatures 1100oC -1300oC, all conventional reductants performed better than the unconventional reductant at 1400oC. At this temperature, Reductant B had the highest mass loss of 51.5% followed by Reductants A (47.7%), B1 (44.1%), C (40.5%) and lastly D with 31.7%. Only Reductants D and C in most instances reached saturation within the test period (4 hours). Substantial reduction of Cr2O3 and FeO occurred (%DOR for FeO, 72.03% and Cr2O3, 67.96 %) as shown by the analysis of chemical phases present. This had the iron-chrome and chrome-iron phases dominating. It is hoped that the outcomes of this research will establish the relevancy of new unconventional reductants as benchmarked against the current reductant products used in ferrochrome processing. Finally, this study has developed a procedure for the ranking of reductant reactivity.
A research report submitted in partial fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and the Built Environment, of the University of the Witwatersrand, Johannesburg 2018
Chiwoko, Aaron (2018) A comparison of conventional and unconventional reductants through characterization and reactivity tests on solid state chromite reduction for application in the South African ferrochrome industry, University of the Witwatersrand, Johannesburg, https://hdl.handle.net/10539/27297