Characterization of high purity hydrothermal magnesite deposits for refractory manufacturing

Abstract

Mineralogical, microstructural, and firing characteristics of dead burned magnesia produced from hydrothermal magnesite deposits of eastern Iran have been evaluated. The ore bodies are highly pure crystalline magnesite with only trace amounts of impurities such as quartz, calcite, and dolomite. Ratio of CaO/SiO₂ in the bulk ore is variable. It was shown that the composition of dead burned magnesite from these deposits, calcined at different temperatures and durations, is predictable from phase equilibria. Textures of the calcined magnesite were studied by SEM; results show that the principal impurities produced during calcination are forsterite (F₂S), monticellite (CMS), merwinite (C₃MS₂), dicalcium and tricalcium silicates (C₂S, C₃S) and that these are located primarily at triple junctions of the periclase crystals. The size of periclase crystals increased with temperature and duration of calcination and the amount of periclase-periclase grain contacts was reduced by increasing the concentration of impurities in the starting ore EPMA analyses revealed that CaO and FeO contents in periclase increase steadly with an increase in the CaO/SiO₂ ratio and FeO content of the bulk ore, respectively. Moreover, it was found that limited solid solution exists between impurities. This study demonstrates that high quality dead-burned magnesia refractories with low CaO, SiO₂ and FeO contents can be produced from the studiedmagneiste deposits.