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Tantalum Smelting Method
Sep 26, 2017

Tantalum Ta, metallic element, mainly exists in tantalite, with niobium symbiosis. The hardness of tantalum is moderate. It is malleable and can be made thin thin foil. Its thermal expansion coefficient is small. Tantalum has excellent chemical properties and is highly resistant to corrosion. No reaction to hydrochloric acid, concentrated nitric acid and "wang shui" in cold and hot conditions. It can be used to make evaporation vessels, and also can be used as electrodes, rectifiers and electrolytic capacitors. A tissue that is used to make laminated or fine lines and repair damage. Although tantalum is resistant to corrosion, its corrosion resistance is due to the stable oxidation of tantalum (Ta2O5) protective film.

Tantalum also has excellent chemical properties, with extremely high corrosion resistance, no reaction to hydrochloric acid, concentrated nitric acid and "wang shui" in cold and hot conditions. But tantalum corroded in hot concentrated sulfuric acid, and under 150 ℃, tantalum is not concentrated sulfuric acid corrosion, only in the higher temperature will have a reaction, 1 year, in the 175 degrees of sulfuric acid corrosion of thickness is 0.0004 mm, the tantalum in 200 ℃ of sulfuric acid soaking for one year, the surface damage of only 0.006 mm. At 250 degrees, the corrosion rate increased, and the thickness of the corrosion was 0.116 mm per year. At 300 degrees, the rate of corrosion was accelerated, and the surface was corroded 1.368 mm. The corrosion rate of sulfuric acid (15% of SO3) is more serious than that of concentrated sulfuric acid. In this solution of 130 degrees, it is soaked for 1 year and the surface is corroded by the thickness of 15.6mm. Tantalum will also be phosphoric acid corrosion at high temperature, but the reaction occurred in 150 degrees of above commonly, in 85% of the 250 degrees of phosphoric acid, soak 1 year, surface corrosion of 20 mm, in addition, tantalum can quickly dissolved in hydrofluoric acid and mixed acid of nitric acid, can be dissolved in hydrofluoric acid. But tantalum is more afraid of a strong base, and in a caustic solution of about 40 percent of the concentration, tantalum is quickly dissolved, in the same concentration of potassium hydroxide solution, as long as 100 degrees is dissolved quickly. In addition to the above situation, general inorganic salt is generally not corrosive to tantalum under 150 degrees. It is proved that tantalum is not effective for alkali solution, chlorine gas, bromide, dilute sulfuric acid and many other agents at normal temperature, but only reacts under the action of hydrofluoric acid and hot concentrated sulfuric acid. Such situations are rare in metals.

But at high temperature, the oxide film of tantalum is destroyed, so it can react with a variety of substances, and the tantalum can react with fluorine at normal temperature. In 150 degrees, tantalum chloride are in inertia, the bromine iodine in 250 degrees, tantalum for dry chlorine corrosion resistant ability, still in the chlorine containing water vapor heated to 400 degrees, can still keep shining, in 500 began to corrode, above 300 degrees tantalum reaction with bromine, the iodine steam is both areas when the temperature reached before the red heat inertia. The hydrogen chloride reacts with the tantalum at 410 and produces the pentachloride, and the hydrogen bromide reacts at 375 degrees with the tantalum. When heated to 200 degrees or lower, S can function with Ta, carbon and hydrocarbons at 800-1100 degrees and tantalum.

Smelting method: tantalum niobium 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 make the pure compound of tantalum and niobium, and finally make the metal.

The decomposition of ore can be divided into hydrofluoric acid decomposition method, sodium hydroxide melting method and chlorination method. The separation of tantalum and niobium can be obtained by solvent extraction (commonly used extraction agent is methyl isobutyl ketone (MIBK), tributyl phosphate (TBP), zhongxin mellow and acetamide, etc., fractional crystallization method and ion exchange method.

Separation: first use of tantalum niobium ore concentrate hydrofluoric acid and sulfuric acid decomposition of tantalum and niobium tantalum niobium acid and fluorine in fluorine acid dissolved in leaching liquid, at the same time, iron, manganese, titanium, tungsten, silicon and other associated elements also dissolved in leaching liquid, form the strong acidic solution composition is very complicated. Tantalum niobium leach liquor with methyl isobutyl ketone extraction of tantalum niobium extraction into the organic phase at the same time, with the trace impurities in the sulfuric acid solution washing organic phase, get pure tantalum niobium containing organic phase lotion and extraction residue were merged, which contain traces of tantalum niobium and impurity elements, is a strong acid solution, the comprehensive recovery. The organic phase of pure tantalum niobium containing tantalum was obtained by using dilute sulfuric acid solution. Niobium and a small amount of tantalum are entered into the aqueous phase and then the tantalum is extracted with methyl isobutyl ketone and the pure niobium solution is obtained. A pure tantalum solution is obtained from pure tantalum containing organic phase water. The organic phase after extraction of tantalum was used in extraction cycle. Pure fluorine fluorine of tantalum acid solution or pure niobium acid solution with potassium fluoride or potassium chloride reaction respectively to generate potassium fluoride tantalum acid (K2TaF7) and fluoride potassium niobate (K2NbF7) crystallization, reaction with ammonium hydroxide can also generate hydroxide precipitation tantalum niobium oxide and hydrogen. Tantalum and niobium hydroxide under 900 ~ 1000 ℃ calcination of tantalum and niobium oxide.

Tantalum preparation:

The metal tantalum powder can be used in metal heat reduction (sodium thermal reduction). Under inert atmosphere with reduced metal sodium fluoride tantalum acid potassium: K2TaF7 + 5 na ─ and Ta + 5 + 2 kf naf. Reaction was carried out in stainless steel tank, when heated to a temperature of 900 ℃, reduction reaction quickly completed. Tantalum powder produced by this method is irregular in grain shape and fine grain size, suitable for making tantalum capacitor. Metal tantalum powder can also be by molten salt electrolysis legal system: with tantalum acid potassium fluoride, potassium fluoride and potassium chloride mixture of molten salt electrolyte the tantalum pentoxide (Ta2O5) dissolved, electrolysis under 750 ℃ and 99.8 ~ 99.9% purity tantalum powder can be obtained.

The metal tantalum can also be obtained by reducing Ta2O5 with carbon heat. Reduction generally divided into two steps: first, to a certain proportion of the mixture of Ta2O5 and carbon under 1800 ~ 2000 ℃ in hydrogen atmosphere made of tantalum carbide (TaC), and then make TaC and Ta2O5 according to certain proportion as mixture vacuum reduction into metal tantalum. The metal tantalum can also be used in the method of pyrolysis or hydrogen reduction tantalum chloride. The compact metal tantalum can be prepared by vacuum arc, electron beam, ion beam melting or powder metallurgy. The high purity tantalum single crystal is used in the melting process of the non-crucible electron beam region.

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