Influence of Silica on the Lime-Free Roasting of Chromium-Containing Slag

Abstract

The evolution of silica during the lime-free roasting and their roles were investigated using chromium-containing slag with high content of ferric oxide and silica. The siliceous salt phases were analyzed by means of X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy. The reaction rule involved with silicon-containing compounds in the roasting process was also discussed. The results showed that both oxidation of Cr2O3 and leaching of Na2CrO4 were influenced by the siliceous salts. It suggested that roasting temperature and the amount of alkali act as important factors for the phase transformation of silicon. NaFe(SiO3)2 was formed in the temperature which is best for the production of Na2CrO4, while excess amount of alkali could decompose acmite into NaFeO2 and Na2SiO3. It was observed that a large amount of insoluble NaFe(SiO3)2 took shape during the lime-free roasting when the temperature was above 1273 K (1000 °C). The extracting rate of chromium from chromium-containing slag roasted at 1373 K (1100 °C) was only 29.99 pct and almost no silicon was leached out.