Molybdenum Production
Molybdenum Production
The main feedstock for Molybdenum extraction consists of standard Molybdenum concentrates, which contain 47-50 % Mo, 28-32 % S, 1-9 % SiO2 as well as other impurities. After ore mining, grinding and floatation, the obtained concentrate is undertaken to oxidizing roasting at 570-600°C in multiple-bedded furnace or in fluidized-bed kiln. The roasting process converts MoS2 concentrate into roasted molybdenite concentrate, (also known as Technical Molybdenum Oxide) by the chemical reactions at temperatures between 500 and 650°C: The cinder in the furnaces contains contaminated MoO3. Pure molybdic oxide MoO3 is necessary for further molybdenum metal manufacture. For this reason the roasted molybdenite concentrate produced worldwide is further processed into a number of chemical products. Upgrading is performed either
1. by sublimation to produce pure (MoO3) or
2. by wet chemical processes to produce a wider range of pure molybdenum chemicals (mainly molybdic oxides and molybdates).
The latter involves the oxide leaching by ammonium dissolving the Molibdenium trioxide, followed by removal of impurities (Cu, Fe) by precipitation and filtration and/or solvent extraction. The resulting ammonium molybdate solution is then converted to any one of a number of molybdate products by crystallisation or acid precipitation and roasting at 450-500°C. The result of processing Molibdenium trioxide with less than 0.05 % impurities.
Molybdenum metal is produced by hydrogen reduction of pure molybdic in tube-type furnace, which is a two-step powder metallurgical process, first at 550-700°C and then at 900-1000°C. The first step results obtaining relatively small rods with cross-section 2-9 sm2 and length 450-600 mm. Molybdenum powder is pressed in steel die set under 200-300 MN/m2. Then, after preliminary sintering at 1000-1200°C the high-temperature sintering at 2200-2400°C follows. Metal forming, which consists of forging, drawing and rolling, is the next operation. The bigger rods 0-200 kg) is produced by hydrostatic (isostatic) pressing in elastic bags. Rods of 500-2000 kg are produced by arc melting in furnace with cooled copper crucible and sintered rods as consumable electrodes.