RU2622474C1 - Method of selective extraction of europium and yttrium from the waste products of phosphors - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes the dissolution of the original product, taken in the form of chlorides fusion cake, in distilled water. The solution is treated by 40% hydrofluoric acid. The resulting sludge is dried, calcined in muffle furnace at a temperature of 650-800°C and mixed with calcium metal shavings taken from 15-20% excess of stoichiometrically required amount. Next, the mixture is pressed and smelted to obtain yttrium metal and slag containing europium fluoride and calcium.

EFFECT: enables to selectively remove europium and yttrium almost completely from the product recycling phosphors, significantly reducing the duration of the process of separation up to 3-4 hours.

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Description

The invention relates to the metallurgy of rare metals, and in particular to the technology for processing waste phosphors based on zinc sulfide containing yttrium and europium, and can be used to separate these rare earth metals (REM) extracted from these wastes.

Spent phosphors are a promising raw material base for the extraction of rare-earth metals and their subsequent use in various industries: metallurgical, glass and ceramic, nuclear, electronic, radio-technical and textile. Considering the fact that rare-earth metals are extremely scarce and expensive materials, the solution of issues related to the creation of technology that allows the separation of rare-earth metals when extracting them from phosphor waste is quite relevant.

An object of the invention is the creation of a technology for the selective extraction of yttrium and europium from the waste products of phosphors.

Giredmet JSC has developed a technology for the processing of such waste by chlorination. As a result of this process, two products are formed: sublimates containing zinc, and a chloride melt in which rare-earth metals - europium and yttrium are concentrated.

Modern separation schemes used both in obtaining individual REMs from natural raw materials and in extracting them from waste are based on the use of liquid extraction and ion exchange.

A known method of extracting metallic yttrium and europium from phosphors covering the inner surface of glass tubes of fluorescent lamps (Rabah, M. A. Recyclables recovery of europium and yttrium metals and some salts from spent fluorescent lamps // Waste Manag. 2008. Vol. 28, No. 2 P. 318-325). The powder extracted from the used lamps contained REM oxides: yttrium — 1.65 wt.% And europium — 1.62 wt.% (The rest was calcium sulfate, calcium orthophosphate, and other impurities). Yttrium and europium were dissolved by autoclave leaching in a mixture of sulfuric and nitric acids for 4 hours at a temperature of about 125 ° C and a pressure of 5 MPa:

Y ₂ O ₃ + 3H ₂ SO ₄ = 2Y ₂ (SO ₄ ) ₃ + 3H ₂ O,

Eu ₂ O ₃ + 3H ₂ SO ₄ = 2Eu ₂ (SO ₄ ) ₃ + 3H ₂ O.

The solutions of REM sulfate salts obtained in this way were converted to thiocyanate salts at low temperature by adding an organic solvent with a thiocyanate salt. For the selective separation of Eu and Y from a solution of thiocyanate, trimethylbenzylammonium chloride was used, and then rare-earth metals were removed from this organic solvent using N-tributyl phosphate and nitric acid. As a result, the nitric salts of Eu and Y were obtained. They were separated from each other by dissolving yttrium nitrate in ethyl alcohol, in which europium nitrate did not dissolve.

Metallic europium and yttrium were obtained by thermal reduction using hydrogen gas at 850 and 1575 ° C, respectively:

Eu (NO ₃ ) ₃ + 3H ₂ = Eu + 3NO ₂ + 3H ₂ O,

Y (NO ₃ ) ₃ + 3H ₂ = Y + 3NO ₂ + 3H ₂ O.

An economic assessment showed that the proposed method seems suitable for industrial use.

However, this technology has several significant drawbacks: it requires significant time and labor costs, and most importantly - the use in large quantities of a number of aggressive acids and organic solvents that pose a significant environmental hazard.

Europium can be separated from other rare-earth metals by selective reduction to a divalent state:

Eu ³⁺ + e ^- = Eu ²⁺ .

In this case, the separation is facilitated due to significant differences in the properties of the compounds of divalent europium and other rare earth metals remaining in the trivalent form.

Known and widely used in industry for the production of rare-earth metals from natural raw materials, a method based on the reduction of europium by zinc dust from chloride solutions in the presence of sulfuric acid. The low solubility of EuSO ₄ , isomorphic barium sulfate and strontium, which can serve as “carriers” (Zelikman AN, Metallurgy of rare-earth metals, thorium, and uranium. M: Metallurgizdat, 1960. P. 145), is used.

Recovery and precipitation:

2EuCl ₃ + 2H ₂ SO ₄ + Zn = 2EuSO ₄ ↓ + ZnCl ₂ + 4HCl

carried out at a pH of 2-4 and a temperature of 0-5 ° C, which contributes to an increase in the solubility of sulfates of unreduced rare earth metals and their better separation. From concentrates with a high europium content (3-5% of the total REM), EuSO ₄ can be precipitated without a carrier. From sediment passes from 75 to 95% europium. The filtrate and wastes are returned to secondary recovery. At a low europium content in the starting material (<0.25%), EuSO _{4 is} deposited on a support, the best of which is SrSO ₄ ; in this case, up to 95% of europium is precipitated (Mikhaylichenko A.I., Mikhlin E.B., Patrikeev Yu.B. Rare-earth metals. M: Metallurgy, 1987. P. 127-128).

Pure europium oxide from rich concentrates is also obtained by precipitation of hydroxides. The concentrates are dissolved in hydrochloric acid, and then restore europium chloride with zinc by the reaction:

2EuCl ₃ + Zn = 2EuCl ₂ + ZnCl ₂

and ammonia solution is added to the mixture to pH 11-12. All trivalent rare-earth metals are precipitated in the form of R (OH) ₃ (where R is rare-earth metals), while the solution remains Eu (OH) ₂ hydroxide and complex zinc ammonia. The filtered solution was treated with a small amount of HNO ₃ to oxidize europium and precipitate it as Eu (OH) ₃ . The precipitate was washed with NH ₄ OH, dissolved in HNO ₃ and europium hydroxide was precipitated again. The processes of dissolution and precipitation of hydroxide are repeated until zinc is completely removed. In the last stage, europium oxalate is precipitated, calcined and europium oxide of the desired purity is obtained. Operations with solutions are carried out in a protective atmosphere of nitrogen, carbon dioxide, argon (Mikhaylichenko A.I., Mikhlin E.B., Patrikeev Yu.B. Rare-earth metals. P. 129).

The technology described above allows the processing of REM concentrates with the release of europium oxide into an independent product. However, a large number of deposition of europium hydroxide, repeated to obtain pure oxide, leads to a low degree of extraction of the target product, makes the process time-consuming and difficult to automate.

A known method for the selective reduction of europium, including the dissolution of its mixtures with yttrium contained in the waste of phosphors extracted from red fluorescent lamps. In this case, the europium valence changes under the influence of ultraviolet radiation. As the starting material, either artificial mixtures of europium and yttrium salts, imitating industrial compositions, or solid particles of real red phosphor wastes were used. After the salts or wastes were dissolved in 0.5 M hydrochloric acid, (NH ₄ ) ₂ SO _{4 was} added to the resulting REM chloride solution, and 1 M NaOH was added dropwise. Then, 20 vol% of the absorbent, isopropanol, was introduced. The resulting solution was irradiated with ultraviolet light using an 11 W low-pressure mercury lamp. Restored to the divalent state, europium was precipitated in the form of sulfate. In this way, 95% europium in the form of sulphate with a purity of 98.5% was extracted from artificial mixtures of Eu and Y, and 96% of europium in the form of EuSO _{4 with a} purity of 96% was extracted from industrial powders of 50% europium (Van den Bogaert B., Havaux D., Binnemans K. , Van Gerven, T. Photochemical recycling of europium from Eu / Y mixtures in red lamp phosphor waste streams // Green Chemistry. 2015. Vol. 17, No. 4. P. 2180-2187). The method adopted for the prototype.

The disadvantages of the method include:

- the duration of the process (in the case of real waste, only the irradiation stage lasts 50 hours);

- low yield and insufficient purity of the final products.

The technical result of the invention is to increase the degree of extraction and separation of yttrium and europium from waste products of phosphors.

The technical result is achieved by the fact that in the method for the selective extraction of yttrium and europium from the waste products of phosphors, including dissolving the product followed by precipitation of insoluble salts, according to the invention it is dissolved in distilled water, the solution is treated with 40% hydrofluoric (hydrofluoric) acid before precipitation of the multicomponent fluoride, the resulting precipitate is dried, calcined in a muffle furnace at a temperature of 650-800 ° C and mixed with shavings of calcium metal, taken with a 15-20% excess m of the stoichiometrically required quantity, the resulting mixture is compressed and melted in an arc furnace with a nonconsumable electrode in an argon atmosphere at a pressure to obtain a yttrium metal and slag containing calcium fluoride and europium.

The essence of the method is as follows.

The product of the processing of phosphor wastes by chlorination — a chloride melt containing europium and yttrium, is dissolved in distilled water, then 40% hydrofluoric acid is added to the resulting solution to precipitate multicomponent fluoride:

RCl ₃ + 3HF + nH ₂ O = RF ₃ ⋅nH ₂ O ↓ + 3HCl,

where R is yttrium, europium, n is the number of crystallization water molecules; the precipitate obtained is dried, calcined in a muffle furnace at a temperature of 650-800 ° C and reduced with metallic calcium, taken with a 15-20% excess of the stoichiometrically necessary amount, in an arc furnace with a non-consumable electrode in an argon atmosphere under excess pressure (0.1 -0.2 kgf / cm ² ). When heated in an arc furnace, yttrium is reduced by calcium to metal:

2YF ₃ + 3Ca = 2Y + 3CaF ₂ ,

and europium - to a divalent state, forming the compound EuF ₂ :

2EuF ₃ + Ca = 2EuF ₂ + CaF ₂ ,

and completely goes into slag.

Justification of the declared modes

The claimed temperature range for the operation of calcining the precipitated multicomponent fluoride is 650-800 ° C. At annealing temperature below 650 ° C, incomplete decomposition of crystalline hydrates of multicomponent fluoride (RF ₃ ⋅nH ₂ O) is possible, which, upon subsequent reduction, will lead to a decrease in the yield. If it exceeds 800 ° C, the interaction of fluorides with oxygen will become possible, which will also adversely affect the quality and yield.

The claimed excess of metallic calcium during the reduction of multicomponent fluoride - 15-20% of the stoichiometrically necessary amount - ensures the completeness of the selective reduction of Y and Eu. Reducing the excess of reducing agent will lead to the fact that part of the yttrium will not be restored and together with europium will go to slag, and the increase will lead to unproductive consumption of calcium.

An example of the method

As an example, data from a production experiment are given. The starting material is the product of the processing of phosphor waste, which is a multicomponent chloride with a mass ratio of europium and yttrium of 1:10. A 315 g sample was dissolved in hot distilled water. Then, 220 ml of a 40% solution of hydrofluoric acid was introduced into the resulting solution, and multicomponent fluoride was precipitated. The precipitate was scattered on baking sheets with a layer of ~ 2 cm and dried under heat-emitting lamps at a temperature of ~ 100 ° C for 2-3 hours, then calcined in a muffle furnace at a temperature of 650-800 ° C for one hour. Calcined fluoride weighing 230 g was mixed with a chip of calcium metal weighing 114 g (with a 20% excess of the stoichiometrically necessary amount). The mixture was compressed and melted in an arc furnace with a nonconsumable electrode in an argon atmosphere at a pressure of 0.1-0.2 kgf / cm ^2. The melting time is about 10 minutes. In this case, yttrium was reduced to a metal, and europium was reduced to a divalent state and, in the form of EuF _2, completely converted to slag.

As a result of the recovery, 140 g of yttrium and 191 g of slag were obtained. The analysis of the products showed that europium (residual content of 0.01 wt.%) Is practically absent in the metal phase, and yttrium (residual content of 0.01 wt.%) In slag.

Thus, the claimed method allows almost completely selectively extracted from the concentrate - a product of the processing of waste phosphors, europium and yttrium. This significantly reduces the duration of the separation process (from 50 hours of the prototype) to 3-4 hours.

Claims (1)

A method for the selective extraction of yttrium and europium from products of processing phosphor wastes, including dissolving the starting material followed by precipitation of insoluble salts, characterized in that the starting product, which is a chloride melt containing yttrium and europium, is dissolved in distilled water, the precipitation is carried out by processing a 40% solution hydrofluoric acid before precipitation of multicomponent fluoride, the resulting precipitate is dried, calcined in a muffle furnace at a temperature of 650-800 ° C and mixed with shavings of metallic calcium, taken with a 15-20% excess of the stoichiometrically necessary amount, the resulting mixture is pressed and melted in an arc furnace with a non-consumable electrode in an argon atmosphere under excessive pressure to obtain metallic yttrium and slag containing europium and calcium fluorides.