RU2394769C2 - Method of producing highly pure arsenic - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in electronic industry, in optical and semiconductor engineering, glass manufacturing and in chemical industry as a catalyst additive. Trialkylarsenites of general formula (RO)₃As, where R = CH₃, C₂H₅, are reduced using hydrazine from the "pure" or "highly pure" category with molar ratio of esters to hydrazine equal to 1:3-1:3.2 and temperature (70-100)°C or hydrazine hydrate from the "pure" or "highly pure" category with molar ratio of esters to hydrazine hydrate equal to 1:3-1:6 and temperature (130-150)°C. Precipitate of amorphous arsenic is filtered off, washed and dried.

EFFECT: invention enables to obtain arsenic with purity of up to 99,99 wt %, with output of up to 97% of the theoretical value, simplifies the technology and widens the raw material base for producing pure arsenic.

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Description

The invention relates to the chemical technology of inorganic substances, and more specifically to a method for producing pure elemental arsenic.

It is known that to obtain the various compounds of high purity arsenic used in high technologies (microelectronics, optoelectronics, etc.) as the starting materials used arsenic trioxide AS ₂ O _3, elemental arsenic and arsenic trichloride AsCl _3/1 /. The first two of them are extracted from ores, and arsenic trichloride by known methods is obtained either by hydrochlorination of “white arsenic” As ₂ O _{3 with} concentrated hydrochloric acid, or by chlorination of elemental arsenic. In industry, arsenic trichloride is preferred as a precursor to high-purity arsenic and its other compounds. This compound is a liquid substance with a relatively low boiling point and can be cleaned of interfering impurities much more efficiently in comparison with solids by methods of distillation, absorption, etc. The separation coefficients of it from impurities, for example, during rectification, are incomparably higher than those for sublimation sublimation of solids / 2 / (arsenic oxide, arsenic, etc.). In addition, liquid-phase processes are more technologically advanced from the point of view of chemical engineering than processes with solids.

However, moisture sensitivity and increased corrosive activity of arsenic trichloride in relation to structural materials from which this substance is purified from microimpurities (distillation columns from fused silica are used at the final stages of purification) limit the scaling of technological plants and increase the cost of the resulting products.

Recently, processes are being developed that use other precursors. One of these precursors may be arsenous acid trialkyl esters As (OR) ₃ (trialkylarsenites), especially lower esters, which are also liquid substances with low boiling points, but not as aggressive.

The scientific literature widely covers the issues of obtaining arsenic As ₄ / 1-2, 3, 4 / and methods for its purification to the qualification “osch” / 4, 5-8, 9-10,11-12 /.

One of the main methods for obtaining arsenic qualification “OPC” is the chloride method / 10, 17-19 /, which consists in the thermal reduction of arsenic trichloride of high purity with hydrogen:

with subsequent re-sublimation of precipitated amorphous arsenic to transfer to a crystalline state. This method gives commercial crystalline arsenic of high purity, which is further used to obtain semiconductor products.

There is a method based on the reduction of arsenic trioxide / 1-2, 20-21 / activated carbon or hydrogen, according to the equation:

A method based on the reduction of pure arsenic oxide with gaseous ammonia at a temperature of 500 ÷ 1000 ° C is described in / 25-27 /. Both of these recovery methods are low-tech.

The authors of works / 13-16, 22-24 / widely described the hydride method for producing arsenic, based on the thermal decomposition of previously purified arsine AsH ₃ . Arsine is a gas with a very low condensation temperature and has very toxic properties. Known difficulties with the purification of arsine (low-temperature distillation and adsorption), as well as the problem with its storage and transportation, limit the use of the hydride method for producing arsenic to processes of applying thin films of arsenic to products.

All of the above methods for producing arsenic involve bringing the product to the qualification “osch” by repeated sublimation, melt distillation, or zone and parazone purification.

The main methods for purifying elemental arsenic to the qualification “osch” are described in the works: / 5 / - repeated sublimation, / 11 / - distillation from the melt, / 12 / - zone and parazon cleaning.

The disadvantages of all the above methods for producing arsenic are high energy intensity, cumbersome hardware design and a low degree of extraction of arsenic (78-90)%.

Closest to the invention are works / 28, 29, 30 /. The possibility of obtaining arsenic of an increased degree of purity by electrolysis of trimethylarsenite or triethylarsenite in an aqueous solution of potassium or sodium hydroxide using a platinum anode and a cathode made of nickel or stainless steel 12X18H9T is shown in / 28 /. To exclude the presence of heavy metal impurities in the released arsenic, purified arsenites are used. 25 ml of a 3N aqueous solution of KOH, 50 ml of bidistilled water and, with cooling, 9.8 g of (CH ₃ O) ₃ As were loaded into the cathode chamber of the electrolyzer. 30 ml of a 3N aqueous KOH solution were washed down into the anode chamber. The electrolysis was carried out at a current of 3A (current density of 0.068 A / cm ² ) and a temperature of 15-20 ° C for 4.5 hours. At the end of the electrolysis, arsenic (3.2 g) was separated from the contents of the cathode chamber on a glass filter. The precipitate was washed with double distillate to a pH of 6-7, and then dried in a vacuum desiccator over potassium hydroxide. The arsenic yield for the substance was 73.5%, and for the current, 26.2%. The resulting arsenic contained metal impurities: Fe, Zn, Cu at a level of 1-2 · 10 ^-3 %; Mo, Ca at the level of 1-5 · 10 ^-4 %; Al, Pb, Na, Li, Sn <1-5 · 10 ^-4 %; Co, Ni, V <1-5 · 10 ^-5 %; Mn - 4 · 10 ^-6 %. Arsenic of this composition can be cleaned to a level that meets the requirements of the "osch" by vacuum sublimation / 5 /.

The disadvantage of this method is the low yield of ~ 74%.

The authors of / 29 / set out a method for producing arsenic by thermal decomposition of highly pure trialkyl arsenites of the general formula (RO) ₃ As, where R = CH ₃ ; C ₂ H ₅ ; C ₃ H ₇ ; C ₄ H ₉ ; C ₅ H ₁₁ in a hydrogen medium in the temperature range 673 ÷ 1500K.

The quality of pure arsenic is determined by the carbon content in the target product. A comparative distribution of the main carbon-containing products in the temperature range 673–1500 K shows that, in an inert medium, the decomposition of As (OR) ₃ occurs predominantly with the formation of solid (~ 60% Stv at T = 673 ° C) and with increasing temperature the content of Stv carbon increases. The solid carbon content decreases upon reduction in a hydrogen medium in the temperature range (673 ÷ 973) K. With increasing temperature, the content of Stv in the product increases. An increase in the number of carbon atoms in the radical also leads to an increase in the content of Cb in arsenic. The optimal condition for thermal decomposition is the ratio of H ₂ : As (OR) ₃ = 10 · n in the temperature range (673 ÷ 973) K (n is the number of carbon atoms in the radical).

The thermal decomposition of trialkyl arsenites (RO) ₃ As (where R = from CH ₃ ; to C ₄ H ₉ ) was studied on a quartz apparatus at temperatures (700–1000) K. The installation was similar to that in the process of hydrogen reduction of arsenic trichloride. It was shown that the process should be carried out in a hydrogen stream at a molar ratio of H ₂ : As (OR) ₃ ≥ (4.0 ÷ 4.5) in a narrow optimal temperature range (830 ÷ 870) K. Under these conditions, arsenic is obtained with a yield of about 95% and a carbon content of 10 ^-2 % wt.

The disadvantage of this method is the use of high temperatures, complex instrumentation (quartz) and a high content of carbon impurities in the target product.

According to published data, arsenic esters in non-aqueous solvents are reduced in an electrochemical cell with the formation of thin films of arsenic on the electrode surface / 30 /.

The aim of this invention is to expand the raw material base and simplify the process of obtaining pure arsenic. This goal is achieved by the interaction of trialkylarsenites (RO) ₃ As (where R = CH ₃ ; C ₂ H ₅ ) of the qualification “osch” with hydrazine and (or) hydrazine hydrate of the qualification “h” or “osch”, produced by the industry.

The recovery process is described by the following equations (1) and (2):

A distinctive feature of the proposed method is the use of hydrazine or hydrazine hydrate as a reducing agent.

The process is conducted in the liquid phase at moderately low temperatures, atmospheric pressure and a molar ratio of trialkylarsenites to hydrazine of 1: 3 ÷ 1: 3.2 and, or, 1: 3 ÷ 1: 6 of trialkylarsenites to hydrazine hydrate. The use of less than 3 moles of hydrazine does not guarantee the completeness of the process, and the use of a reducing agent in amounts of more than 3.2 moles leads to an unjustified overspending of raw materials and the complication of some technological operations. When hydrazine hydrate is used as a reducing agent, the ratio of trialkyl arsenite-hydrazine hydrate varies from 1: 3 to 1: 6. It is better to use a reagent ratio of 1: 6.

The use of a very effective reducing agent determines the rapid course of reactions and a high percentage of yield of the target product; during the process, only one solid product is formed - amorphous As, which can be easily isolated from the reaction mass by simple filtration. Translation of the obtained samples of amorphous arsenic into crystalline form and packing of these samples is carried out by re-sublimation in the same way as when hydrogen arsenic trichloride is reduced by hydrogen.

The reduction process with hydrazine (reaction 1) is carried out at a temperature of (70 ÷ 100) ° C in a stainless steel reactor at atmospheric pressure.

The recovery process with hydrazine hydrate (reaction 2) is carried out at a temperature of (130 ÷ 150) ° C in a sealed stainless steel reactor.

Keeping the process below 70 ° C in the first case and 130 ° C in the second does not guarantee complete conversion of the reagents, and raising the temperature above 100 ° C and 150 ° C is not advisable and only leads to a higher cost of the process.

Example 1

Obtaining amorphous arsenic from trimethylarsenite and hydrazine

To 38.4 g (1.2 mol) of hydrazine at 70 ° C, 67.2 g (0.4 mol) of trimethylarsenite are added. The process is conducted in an atmosphere of inert gas with constant stirring. After the reaction, the resulting suspension is incubated for 2 hours at a temperature not lower than 70 ° C. Then the obtained precipitate of amorphous arsenic is filtered off and washed with deionized water until neutral. The precipitate is dried to constant weight in a heated vacuum dryer. During the synthesis, 29.1 g of amorphous arsenic with a basic substance content of 99.9% were obtained. The yield of arsenic is 97%.

Example 2

Obtaining amorphous arsenic from trimethylarsenite at a temperature of 100 ° C is carried out analogously to example 1. The reaction time is somewhat reduced, but the intensity of heat dissipation increases.

Example 3

Obtaining amorphous arsenic from triethylarsenite and hydrazine

To 38.4 g (1.2 mol) of hydrazine at a temperature of 70 ° C, 84 g (0.4 mol) of triethylarsenite are added. The process is carried out as in example 1. In the process received 29.07 g of amorphous arsenic with a basic substance content of 99.95% wt. Yield 96.9% of theory.

Example 4

Obtaining amorphous arsenic from triethylarsenite at a temperature of 100 ° C is carried out analogously to example 3.

At the same time, the intensity of the process slightly increases, but this does not affect the course of the process.

Example 5

Obtaining amorphous arsenic with hydrazine hydrate

In a hermetically sealed reactor with a capacity of 180 cm ^3, 60.3 g (0.3 mol) of triethylarsenite (or 49.7 g - 0.3 mol of trimethylarsenite) are placed and 90.4 g of hydrazine hydrate (1.8 mol in terms of hydrazine) are added. The reactor is hermetically sealed and placed in an oil bath preheated to 130 ° C. The reactor was incubated for 2 hours at a temperature of 130 ° C. Cool and open. The obtained precipitate of amorphous arsenic is transferred to a filter with deionized water, washed until neutral, and dried under vacuum with heating. As a result of the synthesis, 20.4 g of amorphous arsenic (or 21.6 g) were obtained, which is 94.9% (or 95.7%) of theory. The content of the main substance in the obtained samples of amorphous arsenic is 99.99% wt.

Example 6

The recovery of trialkyl arsenites with hydrazine hydrate at a temperature of 150 ° C is carried out, as in example 5.

No visible changes during the process.

Example 7

The recovery of trialkyl arsenites with hydrazine hydrate at temperatures of 130 ° C-150 ° C and a molar ratio of 1: 3 is carried out, as in Example 5. At the same time, the process time is increased to 4–5 hours and the completeness of conversion of the reagents is not always achieved, which leads to a decrease in the yield of the target product, and consequently, to excessive consumption of raw materials and the cost of the process.

According to atomic emission analysis, the content of metal impurities in all obtained arsenic samples was at the level of (10 ^-4 ÷ 10 ^-5 )% wt.

The invention allows to simplify the process, in comparison with hydrogen reduction, by mitigating the reaction conditions and increasing the yield of arsenic using an effective reducing agent, and also allows to obtain a high-quality product with a high yield of up to 97%.

Finally, this method of trialkyl arsenite recovery can be used for technological and environmental purposes. Unused residues of these substances (vat after cleaning, their technological solutions, substandard masses, etc.) can be disposed of by the proposed method. In a small excess of the reducing agent (already of technical quality), arsenic from them is completely immobilized into a solid, less dangerous mass of elemental arsenic, and the remaining organic waste is sent for bio-treatment or incineration.

LITERATURE

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Claims (1)

A method of obtaining amorphous arsenic of the qualification “osch” by the reduction reaction of trialkylarsenites of the general formula (RO) ₃ As, where R-CH ₃ , C ₂ H ₅ , characterized in that hydrazine or hydrazine hydrate qualification “h” or “osch” is used as a reducing agent and the process is carried out at a temperature of 70-100 ° C or 130-150 ° C, respectively, and a molar ratio of esters to hydrazine of 1: 3 ÷ 1: 3,2 or to hydrazine hydrate 1: 3 ÷ 1: 6.