Smelting method: Ta-Nb ore is often accompanied by many metals. The main steps of Ta smelting are decomposing concentrate, purifying and separating Ta and Nb to produce purified compounds of Ta and Nb, and finally producing metal.
Hydrofluoric acid decomposition method, sodium hydroxide melting method and chlorination method can be used for ore decomposition. Tantalum and niobium can be separated by solvent extraction (commonly used extractants are methyl isobutyl ketone (MIBK), tributyl phosphate (TBP), sec-octanol and acetamide), step-by-step crystallization and ion exchange.
Separation: First, tantalum-niobium iron concentrate is decomposed with hydrofluoric acid and sulfuric acid to form tantalum and niobium fluoride-tantalum acid and niobium fluoride-niobic acid in the leaching solution. At the same time, iron, manganese, titanium, tungsten, silicon and other associated elements are also dissolved in the leaching solution, forming a very complex strong acidic solution. Tantalum-niobium leaching solution was extracted with methyl isobutyl ketone and extracted into organic phase at the same time. Trace impurities in organic phase were washed with sulfuric acid solution. Pure organic phase wash solution containing tantalum-niobium and residual solution were merged, which contained trace tantalum-niobium and impurity elements. It was a strong acidic solution and could be recovered comprehensively. The pure organic phase containing tantalum and niobium was extracted back from niobium by dilute sulfuric acid solution to obtain the organic phase containing tantalum. Niobium and a small amount of tantalum enter the aqueous solution and then extract tantalum with methyl isobutyl ketone to obtain pure solution containing niobium. Pure tantalum-containing organic phase can be extracted by water back-extraction to obtain pure tantalum-containing solution. After stripping tantalum, the organic phase is returned to extraction for recycling. Pure tantalum fluoride acid solution or pure fluoroniobic acid solution reacts with potassium fluoride or potassium chloride to form potassium tantalum fluoride (KTaF) and potassium niobate (KNbF) crystals, respectively. It can also react with ammonium hydroxide to form tantalum hydroxide or niobium hydroxide precipitation. The hydroxides of tantalum or niobium are calcined to form tantalum or niobium oxides at 900-1000 ~C.
Ta production:
Metal tantalum powder can be prepared by metal thermal reduction (sodium thermal reduction). Reduction of potassium tantalum fluoride by sodium in inert atmosphere: K2TaF7+5Na-Ta+5NaF+2KF. The reaction is carried out in stainless steel tank. When the temperature is heated to 900 C, the reduction reaction is completed rapidly. Tantalum powder prepared by this method has irregular grain shape and fine grain size. It is suitable for making tantalum capacitors. Tantalum powder can also be prepared by molten salt electrolysis: Ta2O5 is dissolved in molten salt of potassium tantalum fluoride, potassium fluoride and potassium chloride mixture as electrolyte, and the purity of Ta2O5 is 99.8-99.9% by electrolysis at 750 C.
(2) Tantalum can also be obtained by carbothermal reduction of Ta2O5. Reduction is usually carried out in two steps: TaC is prepared from a mixture of Ta2O5 and carbon in a hydrogen atmosphere at 1800-2000 C, and then TaC and Ta2O5 are reduced to tantalum in a vacuum at a certain ratio. Metal tantalum can also be prepared by thermal decomposition or hydrogen reduction of chloride of tantalum. Dense tantalum can be prepared by vacuum arc, electron beam, plasma beam melting or powder metallurgy. High purity tantalum single crystals are prepared by crucible-free electron beam zone melting.