Describe and give examples of methods of decomposition of rare metal materials.
The rare metal place high demands on their frequency. They are not melted directly from ore concentrates, and is reduced by different methods of pre-produced and purified compounds.
In the production technology of rare metals can be separated following main steps:
Decomposition (opening) of ore concentrates and industrial waste containing rare metals using pyrometallurgical (oxidation or reduction roasting, chlorination, fusing or sintering with the reagents, sublimation, etc.) or hydrometallurgical processes (decomposition solutions of acids, alkalis, autoclave processes, etc.)
Obtaining of pure compounds
Obtaininf of technical-grade metal or its alloys
Refining of metals
Obtaining of ingots and blanks of metal or alloy thereof with a simultaneous fine control of the structure
The first stage of production is usually different types of enrichment materials. The next step is the production of decomposition of the concentrate obtained by calcining the enrichment, processing gases (chlorine, sulfur dioxide and others), processing liquid solvents (acid and alkaline). The final stage is to obtain a pure metal or alloy by electrolysis of solutions and melts, cementation, thermal dissociation.
Example. The decomposition tungsten concentrates with sodium hydroxide solution
The action of sodium hydroxide on tungsten reaction occurs with the formation of exchange decomposition of sodium tungstate and hydroxide iron and manganese:
MeWO4+2NaOH = Na2WO4+Me(OH)2
Full decomposition (98-99%) is achieved by treatment of micronized concentrate with 40-45% sodium hydroxide solution at temperatures of 110 -120° C. The required excess alkaline 50% and higher. The decomposition is carried out in steel hermetically sealed reactor equipped with agitator.
Passing the solution through the air accelerates the oxidation of iron hydroxide and manganese hydroxide.
Use of the process of decomposition of sodium hydroxide solution is limited, as it should be used only for opening of high-grade tungsten concentrates (65% - 70% WO3) with little impurity content of silica. In the treatment of low-grade concentrates produced highly polluted solutions, and it is difficult filtered precipitation. Scheelite concentrates not decomposed with sodium hydroxide.
5. Give examples of methods of processing tungsten concentrates
Methods of processing of tungsten concentrates:
Sintering with Na2CO3 – common method of decomposition of scheelite and wolframite.
Wolframite (FeWO4)+(MnWO4)
at T = 800 – 900 °C, ΔG° = - 260 kJ/mol
Scheelite (CaWO4)
t = 850 °C
2. Decomposition of tungsten concentrates with sodium hydroxide
25 - 40 % NaOH at t = 110 – 120 °C
3. Leaching of soda sinters
Reagent: H2O at t = 80 – 90 °C with intensive stirring
Recovery of W from sinter to solution is 98 - 99 %; C (Na2WO4) = 150 - 200 g/L
