Abstract

PAKTUNC, D.; THIBAULT, Y.; SOKHANVARAN, S.  and  YU, D.. Influences of alkali fluxes on direct reduction of chromite for ferrochrome production. J. S. Afr. Inst. Min. Metall. [online]. 2018, vol.118, n.12, pp.1305-1314. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2018/v118n12a9.

Prereduction and flux-aided direct reduction of chromite provide significant advantages in reducing energy consumption and greenhouse gas emissions during ferrochrome production. In this investigation, a comparative evaluation of the influences of several alkali fluxes was carried out based on experimental observations supplemented by advanced material characterization and thermodynamic predictions. Direct reduction of a chromite ore with alkali fluxes at 1300°C for 1 hour produced (Cr,Fe)₇C₃ type alloys with Cr/Fe mass ratios from 0.7 to 2.3. Among the alkali fluxes, reduction aided by NaOH resulted in a high degree (85%) of Cr metallization with the ferrochrome alloy being Cr4₂-46Fe₂4__2.8C₃. The formation of liquid slag, which facilitated Cr metallization, was limited by the formation of NaAlO₂ between 800 and 1300°C. This, in turn, restricted the collection and transport of the charged ionic Cr species (i.e. O^2-) to graphite particles. Under the conditions studied, ferrochrome particles were often small and largely unliberated, which would make the physical recovery of ferrochrome challenging. At 1400°C, the amount of liquid slag increased, enabling the growth of alloy particles. Direct reduction of chromite aided by NaOH is promising as an alternative technology to conventional flux-based smelting in electric arc furnaces.

Keywords : chromite; ferrochrome; direct reduction; prereduction; smelting; carbothermic reaction; alkali flux.

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