RU2493101C1 - Method of recycling wastes of metallic beryllium and special ceramics based on beryllium oxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to hydrometallurgy and can be used for recycling of wastes with obtaining compounds of beryllium and other metals of high purity. Purification of ammonium fluoroberyllate is performed in mode of AFB re-crystallisation by method of changing composition of microadmixtures. Change is achieved by introduction of small additions of reagent, which forms strong poorly-soluble complex compounds with elements-admixtures. In the process of evaporation said compounds are released together with primary AFB crystals. After further dissolution of crystals in conditions of increased content of fluorine in solution, admixtures remain in sediment, which is filtered. Secondary crystals of ammonium fluoroberyllate of high purity, initial material for obtaining metallic beryllium, are obtained from filtrate by evaporation.

EFFECT: increased efficiency of recycling.

4 ex, 4 tbl, 1 dwg

Description

The invention relates to hydrometallurgy and can be used for waste processing to obtain compounds of beryllium and other metals of high purity.

The absence in Russia of its own beryllium production and an increasing role in the development of such high-tech areas as telecommunications, electronics, aviation, rocket and space technology, nuclear power, etc. dictate the urgent need to involve beryllium-containing waste in the processing to produce high-quality secondary beryllium. In addition, the storage of toxic beryllium waste poses a serious environmental concern. Therefore, the processing of beryllium waste solves the problems of obtaining secondary beryllium and improving the sanitary and hygienic situation in the workplace.

Wastes of beryllium production depending on the type and content of beryllium are divided into several groups. A special group consists of waste contaminated with impurities generated during the processing of metal beryllium (chips, powders, paste for cleaning metal-ceramic and other industries, scrap products, etc.), as well as special ceramic waste based on beryllium oxide calcined at a temperature of 1100-1300 ° С . A distinctive feature of special ceramic wastes is that they dissolve only in a hot solution of ammonium bifluoride, which is also a solvent for metal beryllium waste, which makes it possible to utilize them in one processing chain to ultimately produce metallic beryllium.

As a rule, beryllium production wastes contain a significant amount of impurities (Table 1). The dissolution of waste in ammonium bifluoride followed by purification of the resulting solutions and the isolation of PBA crystals is the shortest way to obtain high-purity metallic beryllium.

A known method of processing beryllium-containing raw materials to obtain ammonium fluoroberylate (patent No. 2265576, C01F 3/00). The disadvantage of this method is the increased energy intensity of the process, which provides for the melting processes leading to increased toxicity in production plants.

There is also known a method of processing beryllium-containing raw materials to obtain ammonium fluoroberylate (patent No. 2310605 C01F 3/00) by exposure to an aqueous solution of ammonium bifluoride with preliminary activation in a planetary centrifugal mill.

The closest is a method of processing beryllium-containing raw materials to obtain crystals of ammonium fluoroberylate (Silina G.F., Zarembo Yu.I., Bertina L.E. Beryllium, chemical technology and metallurgy. M .: Gosatomizdat, 1960. P.77-78) , including a series of sequential operations:

- dissolution of beryllium hydroxide in ammonium fluoride and correction of the solution according to the molar ratio of NH ₄ F / BeF ₂ to 90% of theoretically necessary;

- purification of the FBA solution from aluminum with finely ground chalk;

- purification from manganese and chromium by the addition of lead dioxide;

- purification from copper, nickel and lead by precipitation with ammonium polysulfide;

- purification of silicon by the rapid introduction of ammonia;

- evaporation of the purified solution and the separation of the FBA crystals by centrifugation.

The specified method is characterized by a multi-stage cleaning process, as well as a large number of separation operations, which is associated with the need to use manual labor in hazardous conditions.

One of the simplest and most effective methods of processing waste to produce high purity compounds is the crystallization method, since most of the fluoride impurities contained in the initial solution have a low solubility. In this regard, the most attractive is the process of purification in the crystallization mode — recrystallization using the method of changing the composition of microimpurities, which is an effective means of controlling the values of the separation coefficients and deep cleaning of substances. The advantage of the method of cleaning solutions by crystallization - recrystallization (in contrast to precipitation methods) should include the fact that these operations are carried out in automatic mode.

The composition of microimpurities is changed by introducing small amounts of specially selected reagents into the solution before crystallization, which form stable complex compounds with impurities. Complexation is one of the methods for the isolation of pure substances, especially inorganic ones.

The technical result of the invention is the processing of beryllium waste to obtain crystals of ammonium fluoroberylate of high purity and, ultimately, metallic beryllium

The technical result is achieved by the fact that beryllium waste is dissolved in ammonium bifluoride, then sodium in the form of soda in the amount of 0.003-0.008 mol / mol of beryllium is introduced as a complexing agent into the filtered solution to change the composition of microimpurities, then the solution is evaporated to obtain primary crystals containing impurities, which are dissolved in the condensate, precipitated impurities are separated, the filtrate is corrected by the molar ratio of fluorine to beryllium in the range of 4.5-5.0, then again evaporated to obtain a secondary x fluoroberyllates crystals of high purity ammonia.

Sodium forms with a number of impurities compounds of the cryolite type (Na ₃ AlF ₆ , Na ₃ FeF ₆ , Na ₃ CrF ₆ , Na ₃ MnF ₅ ), the solubility of which in the presence of sodium and fluorine ions decreases sharply. In particular, the solubility of aluminum cryolite (Na ₃ AlF ₆ ) in water is 2 · 10 ^-3 mol / L, and in a 0.1 M NaF solution it decreases to 5.6 · 10 ^-11 mol / L. In addition, sodium fluoride formed by the interaction of soda with ammonium fluoride significantly inhibits the solubility of fluorides of a number of other impurities (lead, magnesium, calcium). This method of reducing the solubility of the main limited impurities contained in the waste metal beryllium and beryllium oxide is the basis of the proposed method for producing high purity PBA crystals and, accordingly, secondary beryllium (Fig. 1). Table 1 shows the composition of the waste taken into processing.

Table 1 The composition of the waste taken for recycling Waste (origin) Mass fraction of elements,% Be Al Fe Si Mg Mn Cu Ni Cr Wood shavings (cermet wastes produced by Be) 94 0.5 2.6 2.2 0.02 0.02 0.02 0.04 0.11 Requirements for Be TU 95.103-82 ≥99.5 ≤0.04 ≤0.1 0 ≤0.02 ≤0.02 ≤0.03 ≤0.02 ≤0.04 ≤0.0 8 Beryllium oxide (waste from the production of special ceramics) 34.6 0.3 0.4 0.06 0.06 0.004 0.004 0.1 0.10 Requirements for BeO (grade N-4) BeO≥99.5 (Be≥35.82) ∑ impurity oxides (Mn, Ni, Fe, Ca, Si, Mg, Cu, Al, Zn, Cr, Na) ≤ 0.5

The waste composition (Table 1) is characterized by approximately the same set of impurity elements; therefore, the FBA solutions obtained after dissolving these wastes in ammonium bifluoride were combined to develop a technology for producing high-purity FBA crystals. The composition of the initial solution is given in table.2.

table 2 The composition of the initial solution Contents Be, g / l F / Be molar ratio The content of impurities in the solution, g / l Fe Al Cr Mn Mg Cu Ni Si 17.4 4,5 0.36 0.08 0,03 0.002 0.002 0.003 0.006 0.4

The resulting solution was processed by the prototype method and the proposed method. Examples of the method.

Example 1. The processing of beryllium waste by the method prototype. A small excess of fluorine (molar ratio F / Be = 4.2-4.5) is added to the FBA initial solution obtained after dissolving the waste in ammonium bifluoride. Excess fluorine is necessary to ensure complete dissolution of the waste. Then, the solution is neutralized with stirring with ammonia to pH = 8-8.5 to precipitate impurities of iron, aluminum, silicon. The suspension thus obtained is filtered off: the insoluble precipitate and the precipitated hydroxides of the impurities are discarded, and the solution is purified from the impurities of heavy metals by adding a 12% solution of sodium dimethyldithiocarbamate (DMDCN) to a slight excess. The presence of excess is determined by the qualitative reaction with a solution of copper sulfate. Carbamates of impurities (Cu, Ni, etc.) are adsorbed on activated carbon, which is added in an amount of 1 g / l of solution. After 20 minutes stirring, the precipitate of carbamates of impurities is separated, the solution is heated to 80-85 ° C and purified from lead and chromium and manganese. The amount of lead dioxide necessary for the oxidation of impurities is determined by the content of these impurities in the initial solution (~ 1 g / l). After an hour exposure at the indicated temperature, the pulp is cooled to ~ 50 ° C and then filtered. The solution purified from impurities is subjected to evaporation in order to isolate PBA crystals. The degree of evaporation is approximately ~ 90%. The mother liquor is returned to the waste dissolving operation. The resulting crystals are dried to constant weight at a temperature of 100-120 ° C and then analyzed for the content of beryllium and impurities.

Example 2. The proposed method.

A small excess of fluorine (molar ratio F / Be = 4.2-4.5) is added to the FBA initial solution obtained after dissolving the waste in ammonium bifluoride. Then, with stirring, the solution is neutralized with ammonia to a pH value of 8-8.5 to precipitate impurities of iron, aluminum, silicon, and stirred for 30 minutes. and add a 12% solution of the complexing agent - sodium dimethyldithiocarbamate (DMDCN) to a slight excess to precipitate heavy metal carbamates. The presence of excess is determined by the qualitative reaction with a solution of copper sulfate. Carbamates of impurities (Cu, Ni, etc.) are adsorbed on activated carbon, which is added in an amount of 1 g / l of solution. After filtering off the insoluble precipitate and impurities (hydroxides and carbamates) released during the purification process, anhydrous carbonate soda (GOST 5100-73) in the amount of 0.003 mol / mol Be is introduced into the filtered solution to change the composition of microimpurities as a complexing agent. Then the solution is evaporated by ~ 90%. The resulting crystal pulp is filtered: the mother liquor is returned to the waste dissolving operation, and the separated (primary) crystals containing impurities are dissolved in the condensate, the solution is adjusted by the F / Be molar ratio to ~ 5.0 and the solution is again evaporated by ~ 90%. An excess of fluorine contributes to an increase in the yield of beryllium due to the “salting-out” action of NH ₄ F. The dried crystals are analyzed for the content of beryllium and impurities.

Examples 3 and 4 are carried out analogously to example 2 with the difference that soda is added to the solution before evaporation in the amount of 0.005 and 0.008 mol / mol of beryllium, respectively. The experimental results are shown in table.3.

Table 3 No. of Example Additive soda, mol / mol Be We analyze. crystals The chemical composition of crystals The output of Be in crystals,% Sod. Be,% wt. The content of impurities,% to beryllium Fe Al Mn Cr Cu Ni Si one 0 primary 7.36 0,03 0.015 0.009 0,03 0.01 <0.01 0.006 98.1 2 0.003 primary 7.1 0.05 0.02 0.013 0.04 0.01 0.01 0.008 - secondary 3 0.005 primary 7.40 0.02 0.008 0.007 0.015 0.01 <0.01 0.005 98.4 secondary 7.0 0.06 0,03 0.015 0.04 0.01 0.01 0.009 - four 0.008 primary secondary 7.42 0.01 0.003 0.003 0.008 0.01 <0.01 0.004 98.4 FBA Crystal Requirements 7.0 0.06 0,03 0.012 0,035 0.01 0.01 No. of Example Additive soda, mol / mol Be Analyze the crystal. Chemical Composition of FBA Crystals The output of Be in crist.,% Sod. Be,% wt. Mass fraction,% to Be Amount at meshes,% to Be Fe Al Mn Cr Cu Ni Si one 0 primary 7.36 0,03 0.015 0.009 0,03 0.01 <0.01 0.006 0.11 98.1 2 0.003 primary 7.10 0.05 0.02 0.013 0.04 0.01 0.01 0.008 0.151 - secondary 7.40 0.02 0.008 0.007 0.015 0.01 <0.01 0.005 0,075 98.4 3 0.005 primary 7.0 0.06 0,03 0.015 0.04 0.01 0.01 0.009 0.174 - secondary 7.43 0.01 0.003 0.003 0.008 0.01 <0.01 0.004 0,048 98.4 four 0.008 primary 7.0 0.06 0,03 0.012 0,035 0.01 0.01 0.009 0.166 - secondary 7.3 0.01 0.003 0.003 0.008 0.01 <0.01 0.004 0,048 96.9 FBA Crystal Requirements - ≤0.04 ≤0.015 ≤0.01 ≤0.03 - <0.01 - - -

From the analysis of the data in Table 3 it follows that the PBA crystals obtained from solutions without the addition of soda (example!) Correspond to the presented values, but the impurity content in them is practically at the limit of technical requirements. With the introduction of soda (examples 2-4), hardly soluble cryolites of the main impurities are formed, which are quantitatively concentrated in the primary crystals. After dissolution of the primary crystals, due to the high molar ratio of fluorine to beryllium, these impurities remain in the precipitate, which makes it possible to obtain cleaner solutions before crystallization II and, accordingly, more pure secondary PBA crystals.

The optimum should be recognized as the addition of soda in an amount of 0.005 mol / mol Be, because this ensures the production of PBA crystals of high purity with high extraction of beryllium into crystals.

The introduction of soda in an amount of 0.003 mol / mol Be, apparently, does not provide a sufficiently complete complexation of impurities, as a result of which the quality of II PBA crystals is slightly lower than when adding soda in an amount of 0.005 mol / mol Be.

The addition of soda in an amount of 0.008 mol / mol of beryllium provides high-quality crystals, however, the extraction of beryllium in crystals is reduced due to the formation (with an excess of sodium) of sodium beryllate, which is characterized by a lower content of beryllium.

Table 4 shows the data on the influence of the molar ratio of fluorine to beryllium in solution (M.O.) on the quality of secondary PBA crystals and the extraction of beryllium in the process of their preparation.

Table 4 M.O. F / be FBA secondary crystal quality Soder. Be in mother r-re, g / l Ex. Be in crystals,% Be,% wt. Mass fraction,% to beryllium Fe Al Mn Cr Cu Ni Si 4,5 7.40 0.01 0.003 0.003 0.008 0.01 0.01 0.004 5,4 98.1 5,0 7.42 0.01 0.003 0.003 0.008 0.01 0.01 0.004 3.3 98.4 5.5 7.0 0.008 0.003 0.003 0.007 0.01 0.01 0.003 2.1 98.8

An increase in the molar ratio of fluorine to beryllium in the solution before isolation of the secondary crystals (Table 4) contributes to a decrease in the beryllium content in the mother liquors and, accordingly, to an increase in the extraction of beryllium into PBA crystals. However, with an increase in the F / Be molar ratio above 5.0, a decrease in the beryllium content in PBA crystals is observed due to the simultaneous precipitation of crystals of ammonium fluoride, which will complicate the subsequent process of obtaining beryllium fluoride. At a molar ratio F / Be below 4.5, the extraction of beryllium into crystals decreases due to a decrease in the “salting out” effect that ammonium fluoride exerts during the crystallization of PBA.

The molar ratio F / Be = 4.5–5.0 should be considered optimal, since this ensures the production of PBA crystals of high purity with a high degree of extraction of beryllium into finished products.

Claims (1)

A method of processing waste metal beryllium and special ceramics based on beryllium oxide, including dissolving the waste in ammonium bifluoride, purifying the solution from impurities, filtering, subsequent crystallization of ammonium fluoroberylate, characterized in that sodium is introduced into the filtered solution as a complexing agent in the form of a complexing agent as soda in an amount of 0.003-0.008 mol / mol of beryllium, then the solution is evaporated to obtain primary crystals containing impurities that are dissolved in the condensate, from the precipitated impurities are separated, the filtrate is adjusted by the molar ratio of fluorine to beryllium in the range of 4.5–5.0, and then evaporated again to obtain secondary crystals of high-purity ammonium fluoryl beryllate.

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