Smelting method: Tantalum-niobium ore is often accompanied by a variety of metals. The main steps of tantalum smelting are to decompose the concentrate, purify and separate Tantalum and niobium to prepare pure compounds of Tantalum and niobium, and finally to prepare metals.
hydrofluoric acid decomposition, sodium hydroxide melting and chlorination can be used for ore decomposition. Tantalum and niobium can be separated by solvent extraction (commonly used extractant is methyl isobutyl copper (MIBK), tributyl phosphate (TBP), sec-octanol and acetamide, etc.), fractional crystallization and ion exchange.
separation: firstly, tantalum and niobium are decomposed by hydrofluoric acid and sulfuric acid into fluotantric acid and fluoniobic acid, which are dissolved in the leaching solution, while accompanying elements such as iron, manganese, titanium, tungsten and silicon are also dissolved in the leaching solution to form a strong acidic solution with complex components. Tantalum and niobium leaching solution is extracted into the organic phase by methyl isobutyl ketone, and trace impurities in the organic phase are washed by sulfuric acid solution to obtain pure organic phase washing solution containing tantalum and niobium, which contains trace tantalum and niobium and impurity elements, and is a strongly acidic solution, which can be comprehensively recovered. The pure organic phase containing tantalum and niobium is back-extracted with dilute sulfuric acid solution to obtain the organic phase containing tantalum. Niobium and a small amount of tantalum enter the aqueous phase, and then the tantalum in it is extracted by methyl isobutyl ketone to obtain a pure niobium-containing solution. The pure organic phase containing tantalum is back-extracted with water to obtain the pure tantalum solution. The organic phase after stripping tantalum is returned to extraction for recycling. Pure fluotantalate solution or pure fluoniobate solution reacts with potassium fluoride or potassium chloride to generate potassium fluotantalate (K2TaF7) and potassium fluoroniobate (K2NbF7) crystals respectively, and can also react with ammonium hydroxide to generate tantalum hydroxide or niobium hydroxide precipitate. Tantalum or niobium hydroxide is calcined at 9 ~ 1℃ to generate tantalum or niobium oxide.
preparation of tantalum:
① metal 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, and the reduction reaction was quickly completed when the temperature was heated to 9℃. Tantalum powder prepared by this method has irregular particle 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) is dissolved in the molten salt of the mixture of potassium fluotantalate, potassium fluoride and potassium chloride as electrolyte, and tantalum powder with purity of 99.8 ~ 99.9% can be obtained by electrolysis at 75℃.
② metallic tantalum can also be obtained by carbothermic reduction of Ta2O5. The reduction is generally carried out in two steps: firstly, the mixture of Ta2O5 and carbon with a certain proportion is made into tantalum carbide (TaC) in hydrogen atmosphere at 18 ~ 2℃, and then the mixture of TaC and Ta2O5 with a certain proportion is made into tantalum metal by vacuum reduction. Metal tantalum can also be prepared by thermal decomposition or hydrogen reduction of tantalum chloride. Dense metallic tantalum can be prepared by vacuum arc, electron beam, plasma beam melting or powder metallurgy. High-purity tantalum single crystal is prepared by crucible-free electron beam zone melting.