Evidence for a new mechanism of Fe2O 3 decomposition in lightweight aggregate formation
2012
Wei, Yu-Ling | Yang, Jing-Chiang | Ko, Kuan-Wei
Hematite (Fe2O3) chemical reduction into FeO and Fe3O4 by releasing O2 at high temperatures is considered one of the generally accepted mechanisms for processing waste minerals and clay into lightweight aggregate construction materials. In many case studies, this mechanism has not been strictly confirmed. To verify whether hematite can effectively release O2 at 1,000–1,260°C, a material containing hematite, simulating waste sediments from a Taiwanese reservoir, was shaped into pellets and fired into lightweight aggregates at high temperatures for 20Â min and studied with various techniques. As revealed by the X-ray absorption near-edge structure technique, almost all the hematite remained as Fe(III) in the pellets when fired at 1,000–1,260°C, implying a negligible release of O2 leading to the creation of pores. This finding shows that the generally accepted mechanism for lightweight aggregate formation associated with hematite decomposition into FeO, Fe3O4, and O2 is invalid. Furthermore, Fe(III)-containing composites were formed in the fired pellets. Although firing at 1,000°C can trigger the decomposition of the components K2CO3, Na2CO3, and CaCO3 with a release of CO2, the sintering reaction was seemingly too weak to encapsulate the gases effectively. For pellets fired at 1,050–1,150°C, pores grew in size because the sintering reaction sufficed to generate a glassy phase that could better encapsulate gases.
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