Abstract
A solid reduction process is described whereby chromite is reduced with the help of calcium chloride to produce ferrochrome alloy powders with high metal recovery. The process involves segregation reduction of chromite using graphite as the reductant and calcium chloride as the segregation catalyst. Experiments were performed in the temperature range of 1200–1400 °C to evaluate the influences of various design parameters using both a thermogravimetric analyzer and an electric tube furnace with continuous off-gas analysis. The reduced products were characterized by scanning electron microscopy, X-ray powder diffraction, synchrotron X-ray absorption spectroscopy, and were subjected to wet chemical analysis. It was concluded that the addition of calcium chloride not only accelerated the carbothermic reduction of chromite but also promoted the formation and growth of individual ferrochrome alloy particles. The alloy formation within chromite particles was minimized, enabling the effective separation of ferrochrome alloy particles from the unwanted gangue without the need for fine grinding. Majority of the calcium chloride remained in a recoverable form, with a small percentage (<10 wt %) consumed by reacting with the siliceous gangue forming wadalite. Pure ferrochrome alloy powders were successfully produced with high metal recovery using elutriating separation.
Highlights
Ferrochromium, which is a critical alloy in the production of stainless steel and high-alloying ferritic steel [1], has been produced worldwide by carbothermic smelting reduction of chromite in submerged electric arc furnaces (SAF) for almost a century [2,3]
Among the various SAF smelting technologies, pre-reduction of chromite before SAF smelting generally results in a lower specific energy consumption (SEC), because significant amounts of energy that are required for both heating the feed material and for enabling the endothermic reduction reactions are supplied by burning fuels in the pre-reduction stage, which is generally carried out in rotary kilns [5]
A series of isothermal TG-DSC-MS tests was firstly performed at 1300 ◦ C using a mixture of chromite (75–105 μm), graphite (25–37 μm, 25 wt % of ore), and varying amount of CaCl2
Summary
Ferrochromium, which is a critical alloy in the production of stainless steel and high-alloying ferritic steel [1], has been produced worldwide by carbothermic smelting reduction of chromite in submerged electric arc furnaces (SAF) for almost a century [2,3]. More than 90% of the high carbon ferrochrome produced, with a typical composition range of 60–70 wt % Cr, 6–8 wt % C and
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