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UBC Theses and Dissertations
Chromium stabilization in ferrochromium slag for its utilization as aggregate material Tasnim, Tahmeed Bin
Ferrochromium slag is a byproduct of ferrochromium production via the smelting of chromite ores. Every year 12-16 million tonnes of ferrochromium slag are produced, a majority of which is dumped in landfills. The mechanical properties of this slag make it a potential material to be used as an inexpensive construction material, the utilization of which can reduce the use of natural resources. Despite its potential use, ferrochromium slag is treated as a waste due to environmental and health concerns regarding the leaching of its heavy metal content, the most concerning of which is carcinogenic chromium (VI). Research has shown that the spinel phase in ferrochromium slag stabilizes chromium by trapping it in the spinel structure and preventing its leaching to the environment. This study investigates the effect of heat treatment and composition change on spinel formation in ferrochromium slag and subsequently on the stabilization of chromium. Slag samples of the MgO-Al₂O₃-SiO₂-CaO-FeO-Cr₂O₃ system were synthesized at 1650°C for 10 h in a vertical tube furnace. Samples were heat treated after synthesis by holding them at 1400, 1475, 1550°C for 12 h before quenching. Leaching tests on heat treated slag samples reveal that samples held at 1400°C have the lowest chromium leachability. With a holding temperature of 1400°C, slag samples were prepared with variations in Al₂O₃ content in the range of 0-20%. Higher Cr leaching is observed from samples as the Al₂O₃ content increases. Similar heat-treated samples were prepared with constant Al₂O₃ content and basicity (CaO/SiO₂) varying from 0.3 to 0.7. An increase in basicity increases the amount of Cr released from the samples during leaching experiments.
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