Direct sintering of chromite ore fines for ferrochrome production in submerge arc furnace

Abstract

Chromite ore is available in nature mainly in the form of Cr2O3.FeO which contains 40 - 52% Cr2O3 and 15- 20% FeO by weight. Global annual output of chromite ore is approximately 20 Mt, which has 20% lump ore and 80% fines (<8mm). These chromite fines have very high Cr content (>34 %). Agglomeration of these fines is needed before charging in SAF to produce ferrochrome alloy. At present, many ferro-chrome plants make pellets and briquettes from these fines. However, the high temperature curing in pelletization at 1300 oC involves operational problems (e.g. coagulation) and is very energy intensive process. Briquetting is a very slow process and involves with costly binder. To alleviate the above draw backs of pelletization and briquetting, direct sintering of chromite ore fines with suitable additives in presence of coke breeze ( like iron ore sintering) may be considered, which can yield the following advantages. a) Sintering of fines is possible just after mixing without any crushing/grinding/screening unlike pelletisation. b) It is a binder less process and produces semi-fused mass with a good cold strength as well as hot strength. c) Produced sinter is prefused and porous material which may be reduced faster in SAF. In view of the above, the present study aims at producing low-cost sinter of chromite ore fines with adequate handling and high-temperature strengths. Sintering was carried out in 10-12 kg scale in a pot sinter set up and the 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.