Novelty on deep reduction roasting through removal of lead and zinc impurities from iron ore afore ironmaking

Abstract

The novelty of deep reduction roasting is that iron (Fe) can be recovered to high degrees and a large proportion of zinc and lead impurities can be simultaneously removed. In this work, deep reduction roasting was performed at different temperatures, and phase changes were investigated during ironmaking. Haematite is the main Fe-bearing minerals in Xinjiang, China. It contains up to 91.35% iron and minor amounts of magnetite and iron silicate. The main form of zinc impurities is zinc oxide, and lead sulphide is present with low abundance. When the roasting temperature was 900 °C–1000 °C, the amount of coal reductant powder was 11%, the grade and recovery of Fe were 86% and 70% respectively. At 1050 °C–1200 °C, coal powder was added at C/O = 2.25 due to high coal powder consumption, and the magnetic separation concentrate products were obtained with an Fe grade of 86.34%–93.09% and Fe recovery rate of 75.06%–86.49%. In line with the requirement that the content of lead and zinc in iron concentrate powder products be less than 0.1%, the minimum contents of lead and zinc impurities in the magnetic separation concentrate were only 0.0084% and 0.048%, respectively. EPMA and EDS data revealed that after roasting, lead, zinc and sulphur impurities showed significant reductions and were absent from most microscopic areas. This study demonstrated that deep reduction roasting is suitable for removing lead and zinc impurities from iron ores before ironmaking.