RU2492144C1 - Method of processing beryllium metal wastes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to processing beryllium-containing metal wastes. The method involves dissolving beryllium metal wastes in an alkaline solution in the presence of sodium nitrate or potassium nitrate. Nitric acid is added to the process in amount of 2.09-2.26 mol/mol beryllium. The nitric acid neutralises excess alkali and sodium beryllate or potassium beryllate to form sodium nitrate or potassium nitrate and crystalline beryllium hydroxide. A portion of sodium nitrate or potassium nitrate used to dissolve the following portion of wastes, and the rest of the sodium nitrate or potassium nitrate is used as a commercial-grade by-product.

EFFECT: invention reduces power consumption, cuts water consumption of the process and enables to obtain a commercial-grade by-product - sodium nitrate.

3 cl, 2 tbl, 2 ex, 2 dwg

Description

Known methods of processing waste metal beryllium to obtain hydroxide by dissolving in various environments: solutions of alkalis, acids, fluoride salts [S. S. Korovin, G.V. Zulina, A.M. Reznik, V.I. Bukin, V.F. Kornyushko. Rare and scattered elements. Chemistry and technology. M .: MISIS, 1996, p.126].

The disadvantage of these methods is the high fire and explosion hazard associated with the evolution of hydrogen:

$$Be+2NaOH=N{a}_{2}Be{\mathrm{<figure-callout\; id="2"\; label="O"\; filenames="00000010.png"\; state="\{\{state\}\}">O</figure-callout>}}_2+{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="00000010.png"\; state="\{\{state\}\}">N</figure-callout>}}_2\uparrow (\mathrm{one})$$

$$Be+2N{H}_{\mathrm{four}}\mathrm{<figure-callout\; id="2"\; label="H\; F"\; filenames="00000010.png"\; state="\{\{state\}\}">H\; </figure-callout>}{F}_{}{}_2={(N{H}_{\mathrm{four}})}_{2}Be{F}_{\mathrm{four}}+{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="00000010.png"\; state="\{\{state\}\}">H</figure-callout>}}_2\uparrow (2)$$

Known methods of electroerosive and electrochemical dissolution of metals. Electroerosive processing is based on the destruction of metal under the influence of an electric discharge passing through a dielectric medium, for example, water [Materials science and technology of metals / Comp. G.P. Fetisov, M.G. Karpman, V.M. Matyunin et al. M .: Higher School, 2000. S.598-599]. After the accumulation of the necessary charge, an electric breakdown of the liquid occurs between the cathode and the anode, resulting in the dispersion of the metal. Depending on the current strength and pulse frequency, either metal hydroxide or the powder of the metal itself can be obtained during metal processing. When metal is dispersed to produce hydroxide, hydrogen is released, which does not allow it to be recommended for implementation in industrial production.

The basis of electrochemical dissolution is the method of anodic dissolution of the metal. As the electrolyte, solutions of sodium or ammonium sulfates are used. [Report of VNIIHT, arch. No. 2107, 1984]. The disadvantage of this method is the significant release of ammonia during the electrolysis and subsequent boiling of the solution, high energy consumption, as well as low productivity of the process.

The closest is a method of processing metal beryllium waste, [RF patent No. 2315714, IPC C01F 3/00]. The method is based on the dissolution of beryllium waste in an alkaline solution with a concentration of 300 g / dm ³ at a temperature of 85-110 ° C in the presence of sodium or potassium nitrate, taken in an amount of 120-150% of the stoichiometrically necessary for the formation of gaseous ammonia, with a duration of 4 h (reaction 3).

$$\mathrm{four}Be+7NaOH+NaN{O}_3=N{H}_3\uparrow +\mathrm{four}N{a}_{2}Be{O}_2+H_{2}O\text{(3)}$$

The selection of beryllium hydroxide is carried out by hydrolysis of sodium beryllate when it is diluted to conc. 30 g / l NaOH and boiling:

$$N{a}_{2}Be{O}_2+2H_{2}O=2NaOH+Be{(OH)}_2\downarrow \text{(four)}$$

After separation of beryllium hydroxide by filtration, the mother liquor is evaporated in order to concentrate the alkali solution from 30 to ~ 300 g / l NaOH. During the evaporation, a part of the alkali is carbonized by reaction (5), as a result of which ~ 7% NaOH is lost in the form of soda, which is separated by filtration of the evaporated solution and removed from the technological process.

$$2NaOH+\mathrm{<figure-callout\; id="2"\; label="C\; O"\; filenames="00000010.png"\; state="\{\{state\}\}">C\; </figure-callout>}{O}_{}{}_2=NaC{O}_3+H_{2}O\text{(5)}$$

The concentrated alkali solution is again used in the process of dissolving the next batch of waste.

This method is selected as a prototype.

The advantage of this method is that instead of hydrogen, ammonia is released during the reaction (3). Moreover, its amount is 0.25 mol / mol of beryllium instead of 1 mol according to reaction (1). The disadvantages of this method include the high energy intensity of the process associated with the need for heating and evaporation of large volumes of solution, as well as significant watering of the process.

The proposed technical solution is aimed at reducing energy consumption, reducing the watering of the process and the implementation of the resulting commercial products - sodium nitrate.

The technical result is achieved due to the fact that in the method of processing metal beryllium waste, including dissolving it in an alkaline solution in the presence of sodium or potassium nitrate, followed by the isolation of crystalline beryllium hydroxide, nitric acid in an amount of 2.09-2.26 mol is additionally introduced into the process / mole of beryllium, which neutralizes the excess alkali and sodium or potassium beryllate with the formation of sodium or potassium nitrate and crystalline beryllium hydroxide, and part of the sodium or potassium nitrate is used To dissolve the next batch of waste, and the remaining sodium or potassium nitrate realized as commercial products simultaneously obtained.

$$NaOH+HN{O}_3=NaN{O}_3+H_{2}O\text{(6)}$$

$$N{a}_{2}BeO+HN{O}_3=Be{(OH)}_2\downarrow +2NaN{O}_3\text{(7)}$$

Sodium or potassium nitrate is not added directly at each loading of beryllium waste for dissolution, but is introduced as a circulating product obtained in subsequent operations of the technological cycle;

After separating the beryllium hydroxide by filtration, the solution was evaporated to give sodium nitrate salt. A portion of the obtained NaNO ₃ in an amount of 105-115% of the stoichiometrically necessary by reaction (3), which corresponds to 0.26-0.29 mol / mol Be, is sent to the "head" of the process to dissolve the next batch of waste, the rest of the sodium nitrate can be implemented as a by-product. Sodium nitrate is widely used in the metallurgical industry as a component of the charge of quenching baths in the processing of cutting tools, in the manufacture of glass and agriculture (nitrogen fertilizer).

Example 1. Prototype

Waste with a beryllium content of 95% and a mass of beryllium of 100 g was used as the starting material. The experiment was carried out in an airtight apparatus. A weighed portion of waste weighing 105.3 g was placed in the apparatus, a saturated sodium nitrate solution was poured, then an alkali solution (conc. NaOH 300 g / l) was added. The excess reagents were taken at the rate of 150% of stoichiometry by reaction (3). The waste was dissolved at a temperature of 85-110 ° C for 4 hours. After the waste was dissolved, the sodium beryllate solution was diluted to 80 g / L NaOH (to maintain the stability of the filter material) and insoluble impurities were filtered off. Then, the sodium beryllate solution was hydrolyzed (reaction 4). In order to ensure maximum isolation of beryllium in the form of hydroxide, the Na ₂ BeO ₂ solution was diluted to 30 g / L NaOH and hydrolysis was carried out for 1 hour at the boiling point of the solution. After cooling the suspension, beryllium hydroxide was filtered off. The resulting mother liquor was evaporated to obtain a solution of NaOH conc. 300 g / l, which was then used in the next waste dissolution cycle.

Example 2. The proposed method

The experiment on dissolving the above wastes (100 g beryllium, 105.3 mass%) was carried out under similar conditions: in an airtight apparatus at a temperature of 85-110 ° C for 4 hours, the alkali and sodium nitrate consumption was taken at a rate of 110% of stoichiometry according to reaction (3). After dissolving the waste, the sodium beryllate solution was diluted to 80 g / L NaOH and insoluble impurities were filtered off. Then, the obtained filtrate was neutralized with nitric acid in an amount of 2.16 mol / mol Be to a pH of ~ 7 (reactions 6 and 7). In this case, beryllium hydroxide precipitated, which was filtered off. The filtrate, which is a sodium nitrate solution, was evaporated to obtain a saturated sodium nitrate solution, which was used in the next cycle of dissolving beryllium waste and isolating commodity crystals of sodium nitrate.

Fig. 1 and 2 show the basic technological schemes of beryllium waste processing. The results of the experiments in equilibrium mode of operation of the prototype and the proposed method are shown in tables 1 and 2.

A comparison of the data given in table 1, allows us to conclude that the extraction of beryllium into hydroxide is sufficiently high both in the prototype and in the proposed method. However, the consumption of NaOH and NaNOs in the second case is much less. The introduction of relatively cheap nitric acid provides a significant reduction in energy consumption in the case of work on the proposed method (table 2), because eliminates the need for significant dilution of solutions during hydrolysis of sodium beryllate (prototype). In addition, this reduces the amount of condensate formed during the evaporation process (~ 3 times), and it becomes possible to get additional profit due to the sale of the products obtained along the way - sodium nitrate salt. The optimal in the proposed method should be considered the consumption of NaOH, NaNO ₃ and HNO _3, respectively, 1.93, 0.27 and 2.17 mol / mol of beryllium, since this achieves a high extraction of beryllium at a lower consumption of reagents. Deviation in the direction of reducing the consumption of reagents leads to incomplete dissolution of the waste and, consequently, to the loss of extraction of beryllium in hydroxide. The increase in the consumption of reagents is unjustified, because it does not increase the cure of beryllium.

Claims (3)

1. A method of processing metal beryllium waste, including dissolving it in an alkaline solution in the presence of sodium or potassium nitrate, followed by the isolation of crystalline beryllium hydroxide, characterized in that after dissolving the waste, nitric acid is additionally introduced into the process in an amount of 2.09-2.26 mol / mole of beryllium, which neutralizes the excess alkali and sodium or potassium beryllate with the formation of sodium or potassium nitrate and crystalline beryllium hydroxide, and part of the sodium or potassium nitrate is used for p stvoreniya following waste portions, and the remaining sodium or potassium nitrate realized as commercial products simultaneously obtained. 2. The method according to claim 1, characterized in that the amount of sodium or potassium nitrate returned to dissolve the beryllium waste is 0.26-0.29 mol / mol of beryllium, and the amount of sodium or potassium nitrate sold as a by-product is 1.83-1.98 mol / mol of beryllium. 3. The method according to claim 1, characterized in that for the dissolution of waste alkali consumption is 1.84-2.01 mol / mol of beryllium.

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