|Spoluautoři DENG Peng, LI Xuefeng, MA Hongwen|
Aluminothermic reduction of magnesia under vacuum condition has been proved to be an effective way to extract magnesium from dolomite and magnesite. This thermal reduction process involves solid, liquid and vapour phases and the briquette preparation condition has a great influence on the extent of the reactions. In this paper, the effects of briquetting pressure, ranging from 10 MPa to 250 MPa, on the vacuum thermal reduction of magnesia by aluminium at 1200 oC were investigated. The variations of the reduction ratio of magnesia, the phase constitution as well as morphology of the briquette residues, with the changes in the briquetting pressure, were studied via X-ray diffraction analysis, scanning electron microscopy and energy dispersive spectrometry. It was revealed that the reduction ratio of magnesia increases with the increase in the briquetting pressure. The briquette residues show a whitish core and the grayish outer shell. The core part mainly contains the spinel phase and unreacted aluminium phase, which does not change with the briquetting pressure. The phases presented in the outer shell of the briquette residues vary greatly with the briquetting pressure varies. At lower pressure such as 10 MPa and 50 MPa, the major phases are spinel, the MAO (magnesium aluminium oxide) and unreacted magnesia and aluminium, while at high pressure 100MPa to 250 MPa, the major phases are alpha-alumina, MAO and unreacted aluminium.