6. Give examples of methods of processing molybdenum concentrates
Molybdenite - MoS2
Nitric acid concentrations above 20-25% when heated to actively oxidize the molybdenum. The advantage: the possibility of a more complete extraction of satellite molybdenum - rhenium. Both elements are removed by extraction with organic solutions.
After decomposition 27-30% HNO3 at 90 ° C acidic mother solutions contain 12-15 g / L Mo, and after decomposition with 54% acid 2, 5-3 g / l.
Mother solutions with a content of 1-3 g / L Mo supplied to extraction of molybdenum.
7. Describe modern technologies of processing of mineral raw materials containing gallium
Gallium is a soft, silvery-white metal, similar to aluminium. Gallium is a typical scattered element. It is found in the form of an isomorphous impurity (at concentrations of 0.04 to 0.001%) in many aluminum and iron minerals and in zinc blende. Bauxite: ores, in which aluminum is present as a component of minerals of the hydrated alumina (AI2O3xH2O) type, are the most important aluminum raw material.
Preparation of gallium concentrate from aluminate solutions
In order to isolate a gallium concentrate in the aluminum production process, it is necessary that gallium be separated from the bulk of the aluminum without necessitating any substantial changes in the bauxite processing technology. Hence, the methods used for the extraction of gallium depend on the methods of processing of the aluminum raw material.
The carbonation is a two-stage process. About 90% of the aluminum is precipitated in the first stage, while most of the gallium remains in the solution. In the second carbonation, the remaining aluminum is precipitated together with the gallium. The Ga2O3 concentration in the precipitates (the primary gallium concentrate) is several tenths of one percent.
The precipitates consist of sodium alumocarbonate Na2O*Al2O3*2C02*nH2O contaminated with gallium. In order to separate the bulk of the aluminum from the gallium, the precipitate is treated with lime water at 90°C (or at 140 in an autoclave) at a molar CaO:Al2O3 ratio of 4:1. As a result, 60 to 70% of the aluminum is precipitated as tricalcium aluminate while 85 to 90% of the gallium passes into solution from which it is precipitated (by carbonation) as a gallium concentrate containing 2 to 5% Ga2O3.The decomposition with lime water is roughly described by the equation:
The formation of sodium hydroxide ensures the retention of the galliumin the solution, provided that the precipitation of aluminum as calcium aluminate is not quantitative. Thus, the amount of CaO taken for the reaction must be smaller than the stoichiometric amount needed.
8. Show differences modern technology of processing of mineral raw materials containing molybdenum and tungsten.
Processing schemes production of tungsten concentrate are divided into two groups, depending on the method of decomposition: 1)Tungsten concentrate sintered with soda or treated with aqueous solution of soda in autoclaves. Wolframite concentrates sometimes decomposed with aqueous solution sodium hydroxide. 2)The concentrates decompose with acids.
In those cases for decomposition where used the alkali reagents, obtained solution of sodium tungstate, which, after their purification from the impurities produce the final product - ammonium paratungstate or tungstic acid.
When decomposition of concentrate with acid obtained precipitation of technical tungstic acid, which in the following operations was purified from impurities.
Molybdenum – containing ores are concentrated almost exclusively by flotation, which results in a fully satisfactory separation of molybdenite from the gangue and the accompanying minerals. Gravitational concentration has limited use. Magnetic concentration is occasionally used as an additional operation for the separation of iron.
Molybdenum concentrate are raw material for the production of ferromolybdenum and chemical compounds - molybdenum trioxide. Molybdenite decomposed using hydrometallurgical methods of oxidation, excluding oxidizing roasting. These include the oxidation of oxygen in alkaline and acid solutions, oxidation with sodium hypochlorite. Decomposition of nitric acid are already used in industrial practice.
When oxidative roasting of molybdenum concentrate occurs series of chemical reactions which can be divided into four groups:
1. Oxidation of molybdenite to form molybdenum trioxide
2. Interaction between the molybdenum trioxide and molybdenite
3. Oxidation of sulfide minerals accompanying elements (copper, iron) to form oxides and sulphates.
4. Interaction between molybdenum trioxide and oxides, carbonates, sulfates elements - impurities to form molybdates