Molybdenite can be decomposed by nitric acid and is more easily decomposed by aqua regia to form sulfuric acid and molybdic acid; it is insoluble in hydrochloric acid. The oxidized minerals of molybdenum are soluble in nitric acid and hydrochloric acid. The sulfide minerals and oxidized minerals of molybdenum can also be decomposed by alkaline fluxes such as sodium hydroxide, sodium peroxide and sodium carbonate-potassium nitrate. It can also be decomposed by calcium oxide or zinc oxide sintering.
Molybdenum ore is oxidized by nitric acid to molybdenum oxide, which crystallizes upon evaporation, but is re-dissolved in excess acid to form molybdic acid. When the sample is decomposed, sulfuric acid should be added at the end and evaporated to a thick smoke to completely dissolve the molybdenum oxide. Such decomposition of the sample separable silicon, lead, tungsten, niobium and tantalum. However, if the residue contains a large amount of lead iron or tungstic acid, a small amount of molybdenum will be carried. Copper , iron and barium ions enter the solution.
(2) Alkali melting method
Commonly used fluxes are: sodium hydroxide, potassium hydroxide, sodium peroxide, sodium hydroxide-sodium peroxide and sodium carbonate-sodium peroxide. After the sol is leached with water, molybdenum forms molybdate into the solution, while interfering elements such as iron, copper and bismuth remain in the residue.
MoS 2 +9Na 2 O 2 +6H 2 Oâ†’Na 2 MoO 4 +2Na 2 SO 4 +12NaOH
MoO 3 +2Na 2 O 2 +H 2 Oâ†’Na 2 MoO 4 +2NaOH+O 2 â†‘
Silicic acid and lead are respectively converted into sodium silicate and lead salt into the solution, and excess sulfuric acid can be added and heated to evaporate to remove the smoke and precipitate.
(3) Sintering method
Using 2:1 sodium carbonate-zinc oxide as sintering agent, sintering at 700 Â° for 1 to 1.5 hours, the sinter is extracted with water to make molybdenum with sodium molybdate and tungsten, vanadium , arsenic and chromium into the solution, lead, antimony , Elements such as manganese , iron and copper remain as carbonate or hydroxide in the precipitate, and most of the silicon is in the state of zinc silicate remaining in the precipitate.
Calcium oxide ( magnesium )-potassium permanganate is used as a sintering agent. After water leaching, molybdenum is left in the precipitate with calcium molybdate (magnesium) and elements such as iron, lead and manganese, and removed by filtration. Solubilized molybdate only 0.05 to 0.2 mg, for measuring primary molybdenum concentrate rhenium.
(4) Treatment of molybdenum concentrate samples before analysis
When the molybdenum concentrate contains flotation oil and coal , it is difficult to directly decompose the sample with acid. Therefore, the molybdenum concentrate should be calcined at 300 Â° in advance (molybdenum and arsenic are not volatilized below 300 Â°). 5 g of molybdenum concentrate was weighed and placed in a porcelain crucible of known weight, dried at 105 to 110 Â° for 30 minutes, then calcined at 300 Â° for 1 hour, and weighed. The weight lost is the amount of water and flotation oil. The calcination temperature should be gradually increased to 300Â° to prevent the sample from collapsing when a large amount of volatile flotation oil escapes. After the sample is roasted, it is thoroughly ground and then stored in a weighing bottle for use.
Second, the separation method of molybdenum ore
Separation of molybdenum can be carried out by sedimentation, extraction and ion exchange.
(1) Precipitation method
Hydrogen sulfide is introduced into the acidic solution, and the molybdenum gradually forms molybdenum sulfide and is separated from iron, aluminum , chromium, nickel , cobalt , zinc, manganese and alkaline earth elements. Since hydrogen sulfide can reduce hexavalent molybdenum, the molybdenum cannot be completely precipitated. The solution needs to be boiled to drive off the hydrogen sulfide, the ammonium persulfate is added to oxidize the molybdenum, and then the hydrogen sulfide is precipitated once. Lead, lead, cadmium and antimony form a sulfide precipitate together with molybdenum. When the sulfide precipitate is treated with a sodium hydroxide-sodium sulfide solution, the molybdenum sulfide is dissolved and separated from lead, copper, cadmium and tellurium. In the presence of tungsten or vanadium, hydrogen sulfide is introduced into a formic acid solution or an acidic solution containing tartaric acid to precipitate molybdenum into molybdenum sulfide and separate from tungsten; hydrogen sulfide is introduced into an ammoniacal solution containing tartaric acid to make molybdenum The molybdenum sulfide precipitates and separates from the vanadium.
Can be made with ammonium hydroxide Fe (â…¢), titanium, niobium, tantalum, bismuth, tin, germanium, and rare earth metals molybdenum separation, in a large amount of iron (â…¢) exists, antimony, vanadium, arsenic and phosphorus are also simultaneously be precipitated . If there is a considerable amount of lead and calcium present, lead with molybdate and calcium molybdate remain in the precipitate. When separating by precipitation with ammonia water, the acidic solution containing molybdenum should be slowly poured into the ammonia water instead of adding ammonia water to the solution. Instead of ammonium hydroxide, sodium molybdenum can be used to separate molybdenum from iron (III), titanium, zirconium , hafnium , tantalum and niobium.
Certain organic agents, such as alpha-benzoin, can be separated from iron, titanium, zirconium, hafnium, and tantalum by precipitation of molybdenum in a dilute acid solution. Antimony, bismuth, tungsten, chromium (VI) and vanadium (V) are precipitated together with molybdenum. If chromium (VI) and vanadium (V) are reduced to a low price in advance, they are not precipitated. The copper-iron reagent can also precipitate molybdenum in an acidic solution to separate it from aluminum, chromium, nickel, cobalt, manganese (II), zinc, cerium and alkaline earth metals.
It is melted with sodium carbonate, extracted with water, and filtered, and the molybdenum is separated from elements such as vanadium, niobium and calcium. The use of sulfuric acid to heat the smoke causes the lead to precipitate as a lead sulfate and separate from the molybdenum.
(two) extraction method
In dilute hydrochloric acid solution, molybdenum (VI) can be extracted by diethyl ether and separated from copper, manganese, nickel, cobalt, chromium and aluminum. The molybdenum (VI) can then be back extracted with water. A milligram of molybdenum (VI) can be extracted with 1:1 acetopropane-trichloromethane in a 6N sulfuric acid solution, and some of the iron is simultaneously extracted.
Further, molybdenum 8-hydroxyquinoline can be extracted by chloroform in an acidic medium having a pH of 1.55. The Î±-benzoin molybdenum was extracted with chloroform in 2M hydrochloric acid. The molybdenum thiocyanate can be extracted with a solvent of diethyl ether, diisopropyl ether, isoamyl ether, ethyl acetate and butyl acetate.
(3) Ion exchange method
After the molybdenum (VI) and a large amount of Fe(III) solution of 0.5 M hydrochloric acid pass through the cation exchange resin, the molybdenum (VI) can be eluted with a 0.04 M ammonium thiocyanate solution. After the calcium (VI) and hydrazine sodium hydroxide solution is passed through the anion exchange resin, the molybdenum (VI) can be rinsed with a 1 M potassium oxalate solution, and then rinsed with 7N hydrochloric acid.
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