Chromite ore fines sintering for ferrochrome production

Abstract

Ferro-chrome alloy is produced from lump chromite ores in the submerged arc furnace (SAF). Majority of the lump ore is very lean (~30% Cr) in nature. Production of good quality ferro-chrome requires high-grade chromite ores; but these are fragile and tend to form fines during handling. Therefore agglomeration of these fines is needed before charging in SAF. Since the high-grade ores have higher softening point and low reducibility, a suitable ratio of Cr/Fe is to be maintained in the charge to get better productivity. To maintain the suitable ratio of Cr/Fe, low and high grade ore fines may be mixed and agglomerated as a pellet or briquettes or sinter. Consequently, many ferro-chrome plants make pellets of chromite ore fines. They replace, up to 50%, lump ore in the charge with those cured pellets. Curing at around 1300 0C is needed to make it suitable for transportation and high temperature use. However, the curing involves operational problems (e.g. coagulation) and energy consumption. Therefore to utilize these fines and maintaining suitable Fe/Cr ratio, mixing of fines and Pelletisation curing is one existing route. In this purpose briquetting may also be considered as an alternative agglomeration technique with the advantages of being a cold process and environment friendly. However, it is a very slow process and involves with costly binder and the products from it are green agglomerate with inferior high temperature properties. To alleviate the above draw backs, current study aims at producing sinter directly from the available chromite ore fines after granulation. Sintering was carried out in 10 kg scale in a pot sinter set up, which produces semi-fused mass with adequate cold-handling, high-temperature strengths. Characterization of produced sinter was done through shatter test, tumble test, abrasion test, phase identification through XRD, Optical microscope, EPMA and TG-DTA. Developed sinter was found to have >85% shatter index, >75% Tumbler index and ~5% abrasion index which are well acceptable for the use in the downstream process of SAF.