Influences of alkali fluxes on direct reduction of chromite for ferrochrome production

摘要

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 Cr_(4.2-4.6)Fe_(2.4-2.8)C_3. The formation of liquid slag, which facilitated Cr metallization, was limited by the formation of NaAlO_ 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.