RU2376242C1 - Method of treating zinc selenide wastes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of treating zinc selenide wastes involves oxidation of zinc selenide at atmospheric pressure in an ammonium peroxodisulphate solution with concentration ranging from 35 to 37% at temperature ranging from 70 to 90°C. Further, the obtained black selenium is purified using a sulphite-cyclic method.

EFFECT: invention enables use of zinc selenide without wastes and simplifies treatment of zinc selenide wastes, formed when preparing materials in semiconductor engineering.

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Description

The invention relates to inorganic chemistry and relates to the development of a method for processing zinc selenide waste generated in the manufacture of materials in a semiconductor technique.

State of the art

A known method of processing zinc selenide by its oxidation with oxygen, followed by condensation of the formed vapor of selenium dioxide (see ZhNH, t.5, issue 10, 1960; Inorganic materials, t.11, No. 6, 1975).

The disadvantage of this processing method is the complexity of the process and hardware design.

A known method of producing selenium dioxide, including oxidation with nitric acid, evaporation of the resulting solution with the release of selenium dioxide and purification of the latter by dissolving in sulfuric acid with a concentration of 70-95% and subsequent isolation of the target product from the solution by increasing the concentration of sulfuric acid to 99-100% (see A.S. SU No. 1142443, class СВВ 19/04, publ. 02.28.1985).

The disadvantage of this method is the low quality of the resulting product.

The closest in technical essence, the achieved positive effect and adopted by the authors for the prototype is a method for producing high-purity selenium dioxide by oxidation of zinc selenide at atmospheric pressure, followed by condensation of vapor of selenium dioxide. The oxidation of zinc selenide is carried out in two stages simultaneously by two oxygen flows, and in the first stage, the oxidation of zinc selenide is carried out by an oxygen stream at a temperature of at least 300 ° C, and in the second stage, the oxidation of volatile products formed in the first stage at a temperature of at least 600 ° C . The oxygen flows in the first and second stages are supplied in a ratio of 1: (3-4), respectively (see US Pat. RU No. 2270166, class C01B 19/00, publ. 02.20.2006). The oxidation must be carried out in a tube furnace at a temperature of 650-800 ° C using oxygen. In this case, the reaction proceeds according to the scheme:

To obtain selenium from selenium dioxide and selenic acid formed in the second stage of oxidation, it is necessary to carry out their reduction, for example, with sulfur dioxide, and then purify selenium by known methods, for example, sulfite-cyclic, which complicates the process. Obtaining selenium by this method in one step is impossible.

Thus, the disadvantage of the prototype is the technological complexity of the hardware design process, its multi-stage.

Disclosure of invention

The objective of the invention is to develop a method for processing waste zinc selenide with obtaining selenium in one stage and creating a closed waste-free process for zinc selenide.

The technical result that can be achieved using the present invention is to simplify the processing of zinc selenide waste with the release of selenium in one stage and the waste-free process of using zinc selenide.

The technical result is achieved using a method of processing zinc selenide waste, including oxidation of zinc selenide at atmospheric pressure, followed by purification of the obtained crude selenium by the sulfite-cyclic method, while the oxidation is carried out in a solution of ammonium peroxodisulfate at a concentration of 35-37% and a temperature of 70-90 ° C, which greatly simplifies the process, makes it one-stage and cyclically closed using zinc selenide.

Thus, the problem is solved due to the fact that in the method of processing waste zinc selenide according to the invention, the oxidation of zinc selenide is carried out in a solution of an oxidizing agent of ammonium peroxodisulfate at a temperature of 70-90 ° C. In this case, the reaction proceeds according to the scheme:

Studies have shown that further oxidation under these conditions almost does not pass, and the result is pure selenium.

The essential features, the totality of which is aimed at solving the problem associated with the purpose of the invention, are:

- oxidation of zinc selenide in a solution of ammonium peroxodisulfate with a concentration of 35-37%;

- oxidation at a temperature of 70-90 ° C.

Only the use of ammonium peroxodisulfate under these conditions makes it possible to obtain pure selenium. The use of other oxidizing agents, in particular hydrogen peroxide, perchlorate and potassium permanganate, does not allow to obtain pure selenium, because the oxidation reaction proceeds to the end with the formation of selenite and zinc selenate according to the scheme:

A distinctive feature in relation to the prototype of the claimed invention is the use of ammonium peroxodisulfate as an oxidizing agent, the use of which allows the process of obtaining selenium in one stage. The temperature and concentration of ammonium peroxodisulfate were selected empirically in accordance with the optimal duration of the process and the maximum yield of selenium per unit volume. At temperatures below 70 ° C, the reaction rate is negligible and the duration of oxidation is more than 7 hours in a volume of 1 liter. With increasing temperature, the rate of the oxidation reaction increases, and the oxidation process can be carried out in 4 hours in the same volume. However, at temperatures above 90 ° C, intense hydrolysis of ammonium peroxodisulfate with the release of hydrogen peroxide is observed, which leads to an increase in the consumption of reagents, pollution of selenium with impurities of selenite and selenate, and loss of selenium with mother liquors. The highest oxidation reaction rate is observed in a concentrated solution of ammonium peroxodisulfate with its maximum solubility in water (58 g in 100 g of water) (see V.A. Rabinovich, Z.Ya. Khavin "Brief chemical reference book", "Chemistry", Leningrad branch 1977, p. 54). Using a concentrated solution of ammonium peroxodisulfate allows you to get the maximum yield of selenium per unit volume of the reactor.

Thus, only the use of ammonium peroxodisulfate as an oxidizing agent at a reaction temperature of 70-90 ° C allows one to obtain selenium from zinc selenide waste in one stage. This is the novelty of the proposed method.

The essence of the method of processing waste zinc selenide is as follows.

A certain amount of water is poured into the container, for example 320 ml, and a certain amount of ammonium peroxodisulfate, for example 180 g, is added with stirring. A certain amount, for example 120 g, of zinc selenide is added to the resulting solution. The suspension is heated to 70-90 ° C and the reaction mass is maintained at this temperature and at atmospheric pressure for 4-7 hours, depending on the number of loaded components and the temperature of the oxidation process. The yield of selenium is 85-95%. Purification of draft selenium from impurities of unoxidized zinc selenide is carried out by the well-known sulfite-cyclic method (see Kudryavtsev A.A. Chemistry and technology of selenium and tellurium, M., 1968, p.233). Insoluble in sodium sulfite, zinc selenide is separated from the sodium selenosulfate solution and again sent for processing, thereby ensuring waste-free use of zinc selenide waste.

The implementation of the invention

Examples of specific performance of the method of processing waste zinc selenide.

Example. 1. In a glass container, such as a glass, pour 320 ml of water and dissolve 180 g of ammonium peroxodisulfate (concentration 36%) with stirring. After its dissolution, 120 g of ground zinc selenide are charged, the suspension is heated and the reaction mass is maintained at a temperature of 65 ° C. After 16 hours, only 20% of selenium is detected in the reaction mass, and after 32 hours, the amount of selenium formed is not more than 25%. Thus, at a temperature of 65 ° C, the reaction does not go through and, therefore, the oxidation of zinc selenide at this temperature is economically disadvantageous due to the low yield of selenium and the long duration of the process.

The indicated temperature is not optimal.

Example 2. The process is carried out analogously to example 1, but the reaction is carried out at a temperature of 70 ° C. The duration of oxidation is 7 hours. The yield of selenium is 53 g (85%). To purify rough selenium from impurities of unreacted zinc selenide, rough selenium is dissolved in a boiling solution of sodium sulfite. After filtration, the resulting sodium selenosulfate solution is cooled, and the selenium precipitated upon cooling is separated, washed from sodium sulfite and dried. The obtained selenium corresponds in quality to the grade ST-1 according to GOST 10298-79.

Example 3. The process is carried out analogously to example 1, but the reaction is carried out at a temperature of 90 ° C. The reaction goes to the end within 4 hours. The yield of selenium is 59 g (95%). According to method 2 and 3, the processing of zinc selenide waste allows to obtain selenium with a yield of 85% and 95%, respectively, while the reaction time at 70 ° C is 7 hours, and at 90 ° C - 4 hours.

Example 4. The process is carried out analogously to example 1, but the reaction is carried out at a temperature of 95 ° C. The duration of oxidation is 2 hours. The yield of selenium is 40 g (64%). The mother liquor contains selenites and selenates in significant quantities. At a reaction temperature above 90 ° C, the yield of selenium decreases due to the hydrolysis of ammonium peroxodisulfate and the formation of hydrogen peroxide, which, in turn, leads to the formation of selenites and selenates and their pollution of selenium formed.

Thus, the most optimal are examples 2 and 3, which allow to obtain selenium with a yield of 85-95%.

The proposed solution in comparison with the prototype and other well-known technical solutions has the following advantages:

- simplification of the processing of zinc selenide waste with the release of selenium in one stage;

- the use of ammonium peroxodisulfate as an oxidizing agent;

- non-waste process for zinc selenide.

Claims (1)

A method of processing zinc selenide waste, including oxidation of zinc selenide at atmospheric pressure, followed by purification of the obtained rough selenium by a sulfite-cyclic method, characterized in that the oxidation is carried out in a solution of ammonium peroxodisulfate with a concentration of 35-37% at a temperature of 70-90 ° C.