RU2259321C2 - Tantalum pentoxide preparation method - Google Patents

Abstract

FIELD: industrial inorganic synthesis.

SUBSTANCE: invention relates to the area of hydrochemical fluoride processing of tantalum stock into pure tantalum an niobium compounds. Potassium fluorotantalate is heated to 220-250°C 1-3 times with intermediate coolings to 70-80°C to achieve 85% of product with fineness -100+40 μm. Product is then subjected to ammonia treatment at ambient temperature followed by hydrochloric acid treatment. Ammonia and hydrochloric acid treatments are performed 2-4 times each.

EFFECT: achieved full decomposition of potassium fluorotantalate to form granulated precipitate, increased purity of tantalum pentoxide, moderated purity requirements for starting material and reagents, and reduced corrosion of equipment.

1 dwg, 1 tbl

Description

The method relates to the field of hydrochemical fluoride processing of tantalum raw materials into pure compounds of tantalum and niobium.

Currently, the main method for processing tantalum raw materials is hydrochemical, which consists in the decomposition of concentrates with hydrofluoric (or hydrofluoric and sulfuric) acid, extraction and separation of tantalum and niobium to obtain a solution of ammonium fluorotantalate, which is the starting material for obtaining pure potassium fluorotantalate (FTK) and tantalum pentoxide .

A known method (1) for the production of tantalum pentoxide by neutralizing a solution of ammonium fluorotantalate with a solution of ammonium hydroxide to a pH value of> 7.5, separating the precipitated precipitate by filtration, washing it with water, drying and calcining.

The disadvantages of the method are:

- the formation of neutralization of a solution of ammonium fluorotantalate is not tantalum hydroxide, but a mixture of basic fluorides, the composition is close to the formula (NH ₄ ) ₂ Ta (OH) ₅ F ₂ . The precipitate contains up to 10-12% fluorine. The removal of fluorine and the conversion of basic fluorides to pentoxide occurs during high-temperature treatment associated with the release of ammonium fluoride and hydrogen fluoride into the gas phase, which leads to severe corrosion of the equipment and contamination of the product;

- high sediment moisture, up to 85%, poor filterability and sludge slurry, which makes it impossible to completely remove the mother liquor containing a large amount of NH ₄ F by washing.

The known method (2), in which potassium fluorotantalate is obtained from a solution of ammonium fluorotantalate, which, when heated to 70-80 ° C, is treated with an ammonia solution at a ratio of T: W = 1: 8-1: 10 for 8-10 hours and then 5% HCl solution at a ratio of T: W = 1: 10-1: 15 for one hour.The product of the treatment of potassium fluorotantalate with solutions of ammonia and HCl was tantalum pentoxide, which was confirmed by chemical and x-ray diffraction methods of analysis. 1% "(quote). The authors do not provide other information. And since the method is of practical interest, an attempt was made to reproduce it under laboratory conditions.

It was established that the declared final result can only be obtained if very small potassium fluorotantalate with a particle size of less than 2 μm is used (precipitation from a cold solution with dry potassium chloride with stirring), and the product obtained after ammonia and acid treatments is calcined at temperatures above 900 ° C .

The following disadvantages were identified:

- high humidity (up to 25%) finely divided FTK, which reduces the degree of its purification from impurities;

- FTC treatment with ammonia solution at a temperature of 70-80 ° C for a long time does not make sense, since NH ₃ flies out of solution in less than 1 hour;

- after ammonia treatment, a gelatinous, poorly filtered precipitate with a moisture content of more than 70% is formed, close to the composition [K, NH ₄ ] ₂ Ta (OH) ₅ F ₂ ;

- after acid treatment, a poorly filtering precipitate forms, in dry form containing up to 3-4% fluorine and 1-1.5% potassium. The mother liquor contains up to 3 g / l of tantalum, which reduces the extraction of tantalum into pentoxide;

- calcination of the dry product is accompanied by strong gas evolution. The calcined product contains up to 2% potassium. He is not chemically active.

The objective of the invention is the creation of technology that eliminates the above disadvantages, which allows to increase the purity of tantalum pentoxide, reduce the requirements for cleanliness of the starting material, reagents, reduce the corrosive effect on equipment, based on the method that implements the following fundamental differences:

- FTK with a particle size in the range of -100 + 40 μm over 85% is used as the initial one. This is achieved by 1-3-fold heating of large-crystalline FTK to a temperature of 220-250 ° C with intermediate cooling to 70-80 ° C. As a result of multiple polymorphic transformations, the crystals self-grind to the required sizes.

Treatment with FTK with ammonia water leads to the formation of (NH ₄ ) KTa (OH) ₅ F ₂ while maintaining the size and shape of the original particles. The precipitate quickly (1-2 min) and completely, with the formation of a dense layer, settles. This allows us to further eliminate filtering during intermediate operations. Ammonia treatment is carried out at room temperature, which reduces the consumption of ammonia water by 2-2.5 times;

- after the first ammonia treatment, water washing of the precipitate is carried out, which eliminates the loss of tantalum during acid treatment.

Depending on the desired purity of the final product, the ammonia-hydrochloric acid treatment cycle is repeated (2-4 cycles).

The sequence and parameters of operations are indicated on technological scheme 1 (see the end of the description).

The proposed technology has the following advantages:

1. High extraction of tantalum in pentoxide due to its low content in ammonia and acid filtrates (at level 3 0.01 g / l).

2. The ability to carry out all the operations of decomposition of FTK in one reactor without overloading the sludge through the use of decantation to separate solutions.

3. High degree of decomposition of FTK after 2 cycles. The content of tantalum pentoxide dried at 120 ° C is:

fluoride  0.5% potassium  0.006%

After 3 cycles

fluoride  0.12% potassium  0.002%

After 4 cycles

fluoride  <0.1% potassium <0.002%

Further repetition of the cycles of the determined result does not give.

4. After two or more cycles, the dry precipitate has the composition Ta ₂ O ₅ · 3H ₂ O. A temperature of 500 ° C is sufficient to transfer it to tantalum pentoxide.

5. The low fluorine content in the sediment reduces the corrosion of drying and calcining equipment.

6. At the FTK decomposition operations, it is allowed to use household drinking or artesian water and reagents of the technical grade without mechanical pollution. And only at the last acid treatment is it necessary to use distilled water and hydrochloric acid of the brand "ChDA", "ChP".

7. The repetition of acid treatments of hydroxide leads to the effective purification of tantalum from impurities.

Example 1:

1. Crystalline FTK weighing 100 g with a particle size of -100 + 40 μm 85% is heated to a temperature of 220 ° C and then cooled to 70 ° C, re-heated to a temperature of 220 ° C and cooled to room temperature.

2. 100 g of FTK obtained as described in claim 1 are loaded with stirring in 600 ml of a 10% aqueous solution of ammonia, the pulp is stirred for at least 2 hours, settled for 15-25 minutes. The settled solution (about 78% taken for processing) is removed by decantation. 400 ml of water are added to the thickened pulp, stirred for 0.5 hours, the pulp is left to stand for 15-25 minutes and the solution is removed by decantation (100% of the volume of added water).

3. 600 ml of 5% hydrochloric acid are added to the thickened pulp obtained as described in claim 2, the pulp is stirred for at least 0.5 hours and settled for 1.5-2 hours, the solution is removed by decantation (100% by volume added acid).

4. To the thickened pulp obtained as described in paragraph 3, add 600 ml of a 3-4% ammonia solution, the pulp is stirred for at least 0.5 hours, and sedimented for 15-25 minutes. The solution is removed by decantation.

5. 600 ml of 3% hydrochloric acid are added to the thickened pulp obtained as described in claim 4, the pulp is stirred for 0.5 hours and filtered.

6. The filtered precipitate obtained as described in claim 5 is washed on the filter twice with 50 ml of water and dried at a temperature of 120 ° C. The content in the precipitate of fluorine <0.1%, potassium 0.009% in terms of Ta ₂ O ₅ . The impurity content is shown in table 1.

LIMITS OF PARAMETERS, JUSTIFICATION.

1. The size of the FTK - 100 + 40 microns more than 85%. With a decrease in the fraction of this fraction, the sedimentation of the tantalum pentoxide precipitate worsens. With the enlargement of the FTC, its incomplete decomposition.

2. The temperature ranges of heating and cooling of the PTC are explained by the beginning and end of the direct and reverse polymorphic transformations. Beyond these points, the temperature does not matter.

3. Volumes of reagents, their concentration during the processing of FTK were found experimentally. At the same time, an increase in the concentration of the reagent and its volume of the degree of decomposition of the FTC does not increase at this stage, their decrease leads to a decrease in the degree of decomposition.

LITERATURE:

1. A.N. Zelikman, G.A. Meerson "Metallurgy of rare metals". - "Metallurgy"; 1973, p. 203.

2. P. S. Kindyakov, K. M. Rubaylova "Processing of tantalum concentrate by the silicofluoride method." Collection of scientific works of Giredmet, t.1 - "Metallurgizdat"; 1959, pp. 672-673.

Claims (1)

A method of producing tantalum pentoxide, including treating potassium fluorotantalate with sequentially a solution of ammonia and hydrochloric acid, characterized in that for the complete decomposition of potassium fluorotantalate with the formation of a granular precipitate, increasing the purity of tantalum pentoxide, reducing the purity requirements for the starting material and reagents, reducing the corrosion effect on equipment potassium fluorotantalate is preheated in the range of 220 ÷ 250 ° C 1 ÷ 3 times with intermediate cooling to 70 ÷ 80 ° C until a particle size of -100 + 40 μm bol e 85% ammonia treatment is carried out at room temperature, and the cycles of ammonia and hydrochloric acid treatments performed 2 ÷ 4 times.