Utilization of low-grade banded hematite jasper ores: recovery of iron values and production of ferrosilicon

Abstract

A novel approach for the complete utilization of a low-grade banded hematite jasper ore assaying ~ 47% Fe has been taken in order to address the issue of rapid consumption of high-grade iron ores and the rising concerns of waste disposal. The process includes the enrichment of Fe through reduction roasting followed by magnetic separation, and smelting of the non-magnetic fraction to produce ferrosilicon alloy. The optimum values of iron grade of ~ 66% Fe and recovery of ~ 72% as determined by the Taguchi-based statistical design of experiments have been achieved at a temperature of 900 °C, time of 90 min, coal-to-feed ratio of 0.15, coal of size − 3.35 + 1 mm and ore of size − 1 mm. The ore and the roasted products have been subjected to characterization techniques such as optical microscopy and X-ray diffraction that reveal the phase transformation under different conditions. Further, the smelting of the silica-rich non-magnetic part in a laboratory-scale electric arc furnace has resulted in a ferrosilicon alloy with ~ 20% Si as indicated by scanning electron microscopic studies. This innovative approach of recovering the maximum iron values using reduction roasting and exploiting the non-magnetic reject as a silica source for ferrosilicon production has the potential to reduce industry’s reliance on high-grade iron as well as silica resources.