Lecture 3 Modern technology in the processing of

Lecture 3. Modern technology in the processing of molybdenum and tungsten containing rare-metal raw materials. Yerbolat Sailaukhanuly, Ph. D

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Mo, molybdenum, 1778 • The name is from Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead • The metal was first isolated in 1781 by Peter Jacob Hjelm • The free element, which is a silvery metal with a gray cast, has the sixth-highest melting point of any element. • It readily forms hard, stable carbides in alloys, and for this reason most of world production of the element (about 80%) is in making many types of steel alloys, including high strength alloys and superalloys. 3

W, tungsten or wolfram, 1781 • The word tungsten means “heavy stone” in Swedish. • Pure tungsten metal was first isolated by two Spanish chemists, the de Elhujar brothers in 1783. • Tungsten is a greyish-white lustrous metal, which is a solid at room temperature. • Tungsten has the highest melting point and lowest vapor pressure of all metals, and at temperatures over 1650°C has the highest tensile strength. • It has excellent corrosion resistance and is attacked only slightly by most mineral acids. • Its important ores include wolframite and scheelite. 4

Mo and W minerals W Mo Wolframite, (Fe, Mn)WO 4 Wulfenite Pb. Mo. O 4 Scheelite, Ca. WO 4 Powellite Ca. Mo. O 4 Molybdenite Mo. S 2 5

Properties of Mo and W Mo W Atomic number 42 74 Standard atomic weight (±) (Ar) 99. 95 183. 84 Melting point 2896 K (2623 °C) 3695 K (3422 °C) Density 10. 28 g/cm 3 19. 25 g/cm 3 6

Production of WO 3 W ores are enriched receiving standard concentrates containing 55 – 65 % WO 3 Highly degree if enrichment are reached by following methods: 1 Gravitation 2 Flotation 3 Magnetic and electrostatic separation 7

Methods of processing of tungsten concentrates 1 Sintering with Na 2 CO 3 Wolframite at t = 800 – 900 °C, ΔG° = - 260 k. J/mol Scheelite t = 850 °C 2 Decomposition of tungsten concentrates with sodium hydroxide 25 - 40 % Na. OH at t = 110 – 120 °C 8

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2 Leaching of soda sinters Reagent: H 2 O at t = 80 – 90 °C with intensive stirring Recovery of W from sinter to solution is 98 - 99 %; C (Na 2 WO 4) = 150 - 200 g/L 10

Processing solution of sodium tungstate C (Na 2 WO 4) = 150 - 200 g/L Cleaning from element impurities (Si, P, As, F, Mo) Deposition of Ca. WO 4 Decomposition of Ca. WO 4 to H 2 WO 4 (WO 3*H 20) Dissolution of H 2 WO 4 in ammonia – (NH 4)2 WO 4 Calcination of (NH 4)2 WO 4 to WO 3 11

Cleaning from impurities 1. Si Hydrolytical decomposition of Na 2 Si. O 3 to H 2 Si. O 3 at p. H 8 – 9 2. P and As. 3. F ions. Mg. Cl 2 + F = Mg. F 2 4. Mo ≥ 0. 1 % (0. 1 -0. 2 g/L) 12

Obtaining of H 2 WO 4 Na 2 WO 4 + Ca. Cl 2 = 2 Na. Cl + Ca. WO 4 at 80 - 90 °C Ca. WO 4 + HCl = Ca. Cl 2 + H 2 WO 4 at 90 °C C (HCl) = 90 – 100 g/L Cleaning of H 2 WO 4 and obtaining WO 3 Evaporation WO 3 99. 95 % for W production; WO 3 99. 99 % for alloys 13

Production of Mo. O 3 Oxidation calcination of Mo concentrate The main reactions 365 – 500 °C 550 – 600 °C Side reactions 550 – 600 °C 14

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