1. The smelting method of high purity tantalum
Tantalum-niobium ore is often accompanied by a variety of metals. The main steps of high purity tantalum smelting are to decompose the concentrate, purify and separate tantalum and niobium to produce pure compounds of tantalum and niobium, and finally produce the metal. Decomposition of ore can adopt hydrofluoric acid decomposition method, sodium hydroxide melting method and chlorination method.

The separation of tantalum and niobium can use solvent extraction method [commonly used extractants are methyl isobutyl ketone (MIBK), tributyl phosphate (TBP), sec-octanol and acetamide, etc.], fractional crystallization and ion exchange methods.

Separation: First, use hydrofluoric acid and sulfuric acid to decompose the tantalum and niobium of the tantalum-niobite concentrate to form fluorotantalic acid and fluoroniobium acid dissolved in the leachate. At the same time, iron, manganese, titanium, tungsten, silicon and other associated elements are also dissolved In the leaching solution, a strong acidic solution with a very complex composition is formed. The tantalum-niobium leachate is extracted with methyl isobutyl ketone and the tantalum-niobium is simultaneously extracted into the organic phase, and the trace impurities in the organic phase are washed with sulfuric acid solution to obtain a pure organic phase washing solution containing tantalum-niobium and the raffinate combined, which contains The trace amounts of tantalum, niobium and impurity elements are strong acid solutions and can be recovered comprehensively. The pure organic phase containing tantalum and niobium is stripped with dilute sulfuric acid solution to obtain an organic phase containing high purity tantalum. Niobium and a small amount of tantalum enter the aqueous phase, and then the high purity tantalum is extracted with methyl isobutyl ketone to obtain a pure niobium-containing solution. The pure tantalum-containing organic phase is back-extracted with water to obtain a pure tantalum-containing solution. The organic phase after stripping tantalum is returned to the extraction cycle. Pure fluorotantalic acid solution or pure fluoroniobate solution reacts with potassium fluoride or potassium chloride to generate potassium fluorotantalate (K2TaF7) and potassium fluoroniobate (K2NbF7) crystals, and can also react with ammonium hydroxide to generate hydrogen Tantalum oxide or niobium hydroxide precipitates. The hydroxide of tantalum or niobium is calcined at 900~1000℃ to produce high purity tantalum or niobium oxide.

Preparation of high purity tantalum
① Metal high purity tantalum powder can be prepared by metal thermal reduction (sodium thermal reduction) method. Reduce potassium fluorotantalate with metallic sodium under an inert atmosphere: K2TaF7+5Na─→Ta+5NaF+2KF. The reaction is carried out in a stainless steel tank. When the temperature is heated to 900°C, the reduction reaction is completed quickly. The tantalum powder prepared by this method has irregular grain shape and fine grain size, which is suitable for making tantalum capacitors. Metal tantalum powder can also be prepared by molten salt electrolysis: use the molten salt of potassium fluorotantalate, potassium fluoride and potassium chloride as the electrolyte to dissolve tantalum pentoxide (Ta2O5) in it, and electrolyze it at 750°C to obtain Tantalum powder with a purity of 99.8% to 99.9%.
② The high purity tantalum of metal can also be obtained by reducing Ta2O5 by carbothermal. The reduction is generally carried out in two steps: first, a mixture of Ta2O5 and carbon in a certain proportion is made into tantalum carbide (TaC) in a hydrogen atmosphere at 1800～2000℃, and then TaC and Ta2O5 are made into a mixture vacuum according to a certain proportion. Reduced to metal tantalum. Tantalum metal can also be obtained by thermal decomposition or hydrogen reduction of tantalum chloride. The dense metal tantalum can be prepared by vacuum arc, electron beam, plasma beam smelting or powder metallurgy. The high-purity tantalum single crystal is prepared by the crucible-free electron beam zone melting method.