Preparation of tantalum

Preparation of tantalum

Smelting method: tantalum and niobium ore is often accompanied by a variety of metals. The main step of tantalum smelting is to decompose the concentrate, purify and separate tantalum and niobium, so as to produce pure compounds of tantalum and niobium, and finally to produce metals.

The ore can be decomposed by hydrofluoric acid, sodium hydroxide melting and chlorination. Tantalum and niobium can be separated by solvent extraction (MIBK, TBP, SEC octanol and acetamide), fractional crystallization and ion exchange.

Separation: firstly, the tantalum niobium concentrate is decomposed by hydrofluoric acid and sulfuric acid, and tantalum and niobium are dissolved in the leaching solution in the form of fluotantalic acid and fluoroniobic acid. At the same time, iron, manganese, titanium, tungsten, silicon and other associated elements are also dissolved in the leaching solution, forming a strong acid solution with complex composition. Tantalum and niobium are extracted by methyl isobutyl ketone from tantalum niobium leaching solution. The trace impurities in the organic phase are washed with sulfuric acid solution. The pure organic phase containing tantalum and niobium is obtained by combining the washing solution with the raffinate, which contains trace tantalum and niobium and impurity elements. It is a strong acid solution and can be comprehensively recovered. Pure organic phase containing tantalum and niobium was extracted by dilute sulfuric acid solution to obtain organic phase containing tantalum and niobium. Niobium and a small amount of tantalum enter the aqueous phase, and then the tantalum is extracted with methyl isobutyl ketone to obtain pure niobium solution. The pure aqueous tantalum containing organic phase was obtained. The organic phase after stripping tantalum is returned to extraction for recycling. Pure fluotantalic acid solution or pure fluoroniobic acid solution reacts with potassium fluoride or potassium chloride to form potassium fluotantalate (K ü TAF ₇) and potassium fluoride niobate (K Ψ NBF ₇), respectively. It can also react with ammonium hydroxide to form tantalum hydroxide or niobium hydroxide precipitation. Tantalum or niobium hydroxide is calcined at 900 ~ 1000 ℃ to form tantalum or niobium oxide.

Preparation of tantalum:

① Tantalum powder can be prepared by metal thermal reduction (sodium thermal reduction). Potassium fluotantalate was reduced by metal sodium in inert atmosphere: K2TaF7 + 5na - → TA + 5naf + 2kf. The reaction was carried out in stainless steel tank. When the temperature was heated to 900 ℃, the reduction reaction was completed rapidly. The tantalum powder prepared by this method has irregular shape and fine particle size, which is suitable for making tantalum capacitors. Tantalum powder can also be prepared by molten salt electrolysis: tantalum pentoxide (Ta2O5) can be dissolved in the molten salt of potassium fluotantalate, potassium fluoride and potassium chloride as electrolyte. Tantalum powder with purity of 99.8-99.9% can be obtained by electrolysis at 750 ℃.

② Tantalum can also be obtained by carbothermal reduction of Ta2O5. The reduction process is generally divided into two steps: first, the mixture of Ta2O5 and carbon is prepared into tantalum carbide (TAC) in hydrogen atmosphere at 1800 ~ 2000 ℃, and then the mixture of TAC and Ta2O5 is made into tantalum by vacuum reduction. 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 was prepared by crucible free electron beam zone melting.