Industrial Preparation of Molybdenum Metal

Molybdenum is recovered primarily from its sulfide ore, molybdenite, MoS2. It also is produced, although to a much lesser extent, from the tungsten ore wulfenite, which yields lead molybdate, PbMoO4. The first phase of the recovery process generally involves concentration of the ore, because ore coming from the mine is very lean and usually contains less than one percent molybdenum.

Industrial Preparation

Molybdenum Metal

High-purity molybdenum metal powder is prepared by reducing either pure molybdenum trioxide or ammonium dimolybdate with pure hydrogen at 600°C but not higher in order to prevent sintering and caking. Dense molybdenum metal is obtained either by powder metallurgy (e.g., Plansee AG in Austria) or by melting and casting (e.g., H.C. Starck and formerly CSM).

Powder metallurgy of molybdenum consists of the hot isostatic pressing of molybdenum metal powder at 100 to 300 MPa and then heating the compact preforms by the Coolidge method or by indirect heating using tungsten heating elements, while in the melting techniques, presintered electrodes are melted by vacuum-arc remelting (VAR) or electronbeam melting (EBM).

Ferromolybdenum

Ferromolybdenum can be prepared in the laboratory by reacting a molybdenite with ferromaganese to yield ferromolybdenum and MnS2. However, on a commercial scale, ferromolybdenum is either produced from molybdenum trioxide by carbothermic reduction performed inside a submerged-arc furnace or by aluminothermic or silicothermic reduction.

In the carbothermic reduction process, molybdenum trioxide is mixed with iron oxides, iron scrap, fluorspar (CaF2), and lime (CaO) as fluxes and charcoal as reductant. Because of the high temperatures in the furnace (1800°C), the raw materials are briquetted to minimize loss of the volatile molybdenum trioxide by sublimation that occurs above 1200°C. The specific energy consumption is 4.5 kWh/kg of FeMo. But the most efficient commercial process consists of the metallothermic reduction of molybdenum trioxide with aluminum or silicon.

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