Smelting method: there are many kinds of metals in tantalum niobium ore. The main steps of tantalum smelting are to decompose the concentrate, purify and separate tantalum and niobium to produce pure compounds of tantalum and niobium, and then to produce metals.
The ore can be decomposed by hydrofluoric acid, sodium hydroxide melting and chlorination. Solvent extraction (MIBK, TBP, SEC octanol, acetamide, etc.), fractional crystallization and ion exchange can be used for tantalum niobium separation.
Separation: firstly, tantalum and niobium are decomposed by hydrofluoric acid and sulfuric acid to form fluotantalic acid and fluoniobic acid in the leaching solution, and iron, manganese, titanium, tungsten, silicon and other associated elements are also dissolved in the leaching solution to form a strong acid solution with complex components. Tantalum niobium leaching solution is extracted by methyl isobutyl ketone and extracted into the organic phase at the same time. The trace impurities in the organic phase are washed by sulfuric acid solution. The pure organic phase washing solution containing tantalum niobium is combined with the raffinate solution, which contains trace tantalum niobium and impurity elements. It is a strong acid solution and can be comprehensively recovered. The pure organic phase containing tantalum and niobium is obtained by back extraction of niobium with dilute sulfuric acid solution. Niobium and a small amount of tantalum enter the aqueous phase, and then methyl isobutyl ketone is used to extract the tantalum in the aqueous phase to obtain a pure solution containing niobium. Pure tantalum containing organic phase can be obtained by water reverse extraction. The organic phase after back extraction of tantalum is returned to extraction and recycling. Potassium fluotantalate and potassium fluoniobate crystals are formed by the reaction of pure fluotantalate solution or pure fluoniobate solution with potassium fluoride or potassium chloride, respectively, and can also react with ammonium hydroxide to form tantalum hydroxide or niobium hydroxide precipitates. The hydroxides of tantalum or niobium are calcined at 900-1000 ℃ to form oxides of tantalum or niobium.
Tantalum production:
① Tantalum powder can be prepared by metal thermal reduction (sodium thermal reduction). Potassium fluotantalate was reduced by sodium metal in inert atmosphere: K2TaF7 + 5na - → TA + 5naf + 2kf. The reaction was carried out in a stainless steel tank. When the temperature was heated to 900 ℃, the reduction reaction was completed rapidly. The tantalum powder produced by this method has irregular particle shape and fine particle size, which is suitable for tantalum capacitors. Tantalum powder can also be prepared by molten salt electrolysis: tantalum pentoxide (Ta2O5) is dissolved in molten salt of potassium fluotantalate, potassium fluoride and potassium chloride mixture as electrolyte, and the purity of tantalum powder is 99.8-99.9% by electrolysis at 750 ℃.
② Tantalum can also be obtained by carbothermal reduction of Ta2O5. The reduction is generally carried out in two steps: first, the mixture of Ta2O5 and carbon with a certain ratio is made into tantalum carbide (TAC) in hydrogen atmosphere at 1800-2000 ℃, and then the mixture of TAC and Ta2O5 is made into tantalum metal by vacuum reduction according to a certain ratio. Tantalum can also be prepared by thermal decomposition or hydrogen reduction of tantalum chloride. Dense tantalum can be prepared by vacuum arc, electron beam, plasma beam melting or powder metallurgy. High purity tantalum single crystal is produced by the method of electron beam zone melting without crucible.