Thermal Analysis and X-Ray Diffraction of Roasting of Egyptian Molybdenite

Molybdenite is the main ore mineral for the molybdenum industry and the production of molybdenum. The industrial processing of molybdenite is based on its oxidized roasting to technical grade molybdenum oxide, followed by its purification by distillation or its ammonia leaching.The present work reports a thermal analysis study of the oxidized roasting of Egyptian molybdenite, using a derivatograph. The reaction products were identified microscopically and by using a Siemens Crystalloflex diffractometer.The DTA curves of the roasting of molybdenite show that its oxidation begins at 360–370°C, as indicated by the small exothermic peak at such temperatures. This is followed immediately by a large, wide exothermic peak with maximum at 510–520°C, representing the intensive oxidation of molybdenite. The medium endothermic peak at 795–800°C reflects the melting and sublimation of molybdenum oxide. The vigourous vaporization of molybdenum oxide and its boiling are associated with the large, sharp endothermic peak at 1150°C. This is accompanied by a large loss in mass (TG).The study includes calculation of the thermodynamic constants and the kinetics of the reaction of oxidation of molybdenite.The oxidized roasting of molybdenite results in the production of molybdenum oxide, which is the essential starting material of the molybdenum industry. The molybdenum oxide produced has the molybdite structure and crystallizes in the orthorhombic system in the form of elongated, thin, light-green crystals.This revised version was published online in November 2005 with corrections to the Cover Date.     

Flame Emission Spectromethic Method POH Determinanoh of Rhehium in Molybdenite Flue Dust

Abstract

Optimum conditions for the determination of rhenium by flame emission speetronetry vere ascertained. The mart mim signal emanates from a region immediately above the tip of the inner cone of fuel-rich oxygen-acetylene flame. The sample was introduced as a solution in cyclohexanone by a sprayer-burner. Emission intensity at 3460 Å vas measured. In molybdenite flue dust, after normal dissolution steps, rhenium(VTl) vas extracted from 1.8–3.6 N H₂SO₄ vita cyclohexanone and the organic phase, vas. sprayed directly into the flame. Detection limit is 2.5 μg/al.     

分子吸收分光光度法测定辉钼矿中钼的不确定度评定

对分子吸收分光光度法测定辉钼矿中钼元素的不确定度进行了评定,分析了不确定度的来源,包括工作曲线拟合、标准溶液配制、样品重复测定、分析仪器、样品称量、样品溶液定容等引入的不确定度。计算了钼含量测定结果的合成标准不确定度和扩展不确定度。当辉钼矿中钼含量为0.108 1%时,扩展不确定度为0.002 1%(k=2)。     

Electrical properties of molybdenite single crystals

Molybdenite crystals used in the present work were grown by direct vapour transport or sublimation method. The electrical resistivities and I-V characteristics were measured at different temperatures in the symmetry plane. The room temperature resistance of a specimen annealed for different periods has also been measured. These results are described and discussed.