Method of producing arsenic acid

FIELD: chemistry.

SUBSTANCE: sludge from production of non-ferrous metals, containing arsenic, sodium, zinc and cadmium compounds, is dispersed in water with mass ratio solid:liquid = 1:(2.5-3). Small portions of nitric acid are added to the obtained suspension until attaining concentration of HNO₃ from 15 to 20 g/dm³. While stirring, the mixture is heated to temperature ranging from 70 to 90°C and held while stirring for 2 to 3 hours. The residue which contains arsenic compounds and elementary sulphur is filtered from the mother solution which contains sodium, zinc, iron and copper sulphates. The residue is washed and water is added until attaining mass ratio solid:liquid=(1-2):(1-3). Nitric acid is added to the obtained solution until attaining pH = 1.5-2 and hydrogen peroxide is added in stoichiometric quantity of 105 to 110%.

EFFECT: wider raw material base for producing arsenic acid, recycling wastes from production of non-ferrous metals using an environmentally safe method, obtaining two end products - sulphur and arsenic acid.

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The invention relates to the chemical industry, in particular the production of arsenic acid, which can be used for antiseptic compositions to protect the wood and articles of wood from decay and destruction.

A method of obtaining arsenic acid by oxidation of pure lower trialkylamine (trimethyl-, triethyl-, Tripropylamine) hydrogen peroxide, using an aqueous solution of hydrogen peroxide with a concentration of 15 to 32 wt.% at a certain molar ratio of trialkylamine and hydrogen peroxide (RF patent No. 2286948, MKI C01G 28/00, 2006).

The disadvantage of this method is the use as a source of arsenic-bearing reagent organic compounds requiring preliminary distillation treatment.

A method of obtaining arsenic acid by leaching the copper-arsenic sludge solution of hydrogen peroxide in the presence of elemental sulfur (RF patent No. 2053201, MKI C01G 28/00, 1996) (prototype). The optimal process parameters are a temperature of 60-70°C, the duration of 120-150 minutes, W:T=5:1-10:1, the concentration of hydrogen peroxide 5-10%, sulfur consumption is 0.2-0.25 g per 1 g of copper in the sludge.

The disadvantage of this method is the use as a starting slurry containing copper, selenium, Nike is ü. Conclusion these valuable components of the production cycle in the form of sulphides is impractical, and the additional extraction of these metals requires special technology, that will significantly complicate the process of obtaining arsenic acid.

Thus, the authors was to develop a method of obtaining arsenic acid using a more sophisticated source of raw materials.

The problem is solved in a method of producing arsenic acid, including leaching of arsenic sludge solution of hydrogen peroxide in the presence of sulphur, in which the arsenic sludge use sludge metal production non-ferrous metals with its preliminary processing of nitric acid concentration of 15-20 g/DM³at a temperature of 70-90°C. and a ratio of T:W=1:2,5÷3,0; then add water to the ratio of T:W=1÷2:1÷3, then add nitric acid to pH=1,5÷2 and hydrogen peroxide in the amount of 105-110% of stoichiometry.

Currently, the patent and scientific literature is unknown way of getting arsenic acid using as a source of raw sludge generated in the wastewater treatment process and waste gases of metallurgical production of non-ferrous metals, with its preliminary treatment with nitric acid and subsequent leaching Perek the sue of hydrogen.

Large quantities of arsenic-bearing sludge accumulated in the steel production non-ferrous metals and must be disposed of. The main component of these slurries is water-insoluble compound As₂S₃. Experimental studies conducted by the authors, has helped to solve the problem of disposal of these sludges by leaching hydrogen peroxide to produce in the quality of the final product arsenic acid. Peroxide oxidation of sulphide of arsenic (III) under the conditions developed by the authors of the proposed technical solutions, translates the anion S^-2in elemental sulfur, As a⁵⁺- arsenic acid (H₃AsO₄. The final filtered solution contains arsenic acid at concentrations of 15-20%. Evaporation of the resulting solution or recycling to the leaching allows you to receive technical arsenic acid concentration of 40-60%.

Because the sludge from production of non-ferrous metals (copper, zinc, lead and others) contain not only the sulphide of arsenic (3+), but the sulphides of sodium, zinc and other metals required pre-treatment of sludge to prevent emissions of hydrogen sulfide and contamination of the final product. The sulphides of other metals contained in the sludge, insoluble in water. In this regard, the authors were experimentally determined the trading conditions pre-treatment of sludge for subsequent leaching. Considering the fact that the processing of non-oxidizing acids leads to the release into the atmosphere of hydrogen sulfide, the authors propose the pre-treatment of sludge with a weak solution of nitric acid, which ensures the transfer of insoluble sulfides to soluble sulfates. While trivalent arsenic enters the water-insoluble oxide of arsenic As₂O₃. In addition to the impurities of sulfides of metals sludge metal production also contain excess sulfur in the composition of the polysulfide arsenic As₂S₃·nS. The ratio of S:As in such slurries is about 1.5 times higher than theoretical. It must be emphasized that the most complete translation of insoluble compounds of the metals contained in the sludge, as well as the optimal conditions of oxidation As³⁺can only be achieved when carrying out the process in the proposed range of values of the operating parameters. So, raspolirovyvayut in water slurry at a mass ratio less than 1:2.5, the heated slurry to a temperature less than 70°C., adding nitric acid to a concentration of less than 15 g/DM³do not provide a full translation of insoluble compounds of the metals contained in the sludge, soluble sulfates, the resulting suspension contains residual amounts of sulphides of sodium, zinc and other metals which contaminate the final product. If u is laviani in water slurry at a ratio greater than 1:3, heating the suspension to a temperature of over 90°C, adding nitric acid to a concentration of more than 20 g/DM³leads to the release into the atmosphere of hydrogen sulfide, to the excessive volume of secondary effluent and the additional consumption of thermal energy.

The process when the pH value is more than 2 and with an excess of hydrogen peroxide is less than 5% of the stoichiometry observed contamination arsenic acid arsenic acid and, as a consequence, the decrease of the yield of the target product. The process when the pH value is less than 1.5 leads to the appearance in the final product of the residual nitric acid, which requires additional cleaning. The process of adding hydrogen peroxide in the amount of more than 10% from stoichiometry causes the formation of sulphurous anhydride, thereby violating the environment in the process.

The proposed method can be implemented as follows.

Sludge metal production non-ferrous metals, containing 14.6% of As; 0,8% Na; 0,9% Zn; 0,4% Cd, Rasulova in water at a mass ratio of T:W=1:(2,5÷3), in suspension in small portions poured nitric acid to a concentration of HNO₃15-20 g/DM³, is heated under stirring up to 70-90°C and maintained under stirring for 2-3 h, while maintaining the original volume by adding water. Then on the suction-filter residue is separated from the mother liquor, with the holding sulfates of sodium, zinc, iron, copper and other metals, and optionally washed with water. The washed sludge again Rasulova in water (T:W=1:2,5÷3), acidified with nitric acid to a pH of 1.5 to 2, a thin stream poured hydrogen peroxide in the amount of 105-110% of stoichiometry, keeping the temperature not above 60°C or termination of the supply of hydrogen peroxide, or by cooling the reaction mixture to 55°C.

After adding the required amount of hydrogen peroxide suspension is stirred for 1-2 h, and then filtered to separate the resulting solution of arsenic acid from sulfur. The solution containing 14-15% arsenic acid, sent to concentration by evaporation to obtain the desired concentration (usually 40-60%).

The precipitate on the filter (elemental sulfur) is washed with water, controlling in the washed precipitate the arsenic content, the presence of which the precipitate was washed with additional 3-5% hydrogen peroxide solution. The filtrate is sent to raspulpovka sludge in the beginning of the process. The precipitate of sulphur is dried at a temperature not exceeding 80°C, analyzed, packaged and sent to the warehouse for further implementation or use.

The proposed method is illustrated by the following examples.

Example 1. In the reactor of stainless steel 12X18H10T with a capacity of 1 m³fitted with mechanical stirrer, jacketed for steam heating and water cooling,valve bottom drain, the boot hatch and exit for exhaust ventilation, pour 0.5 m³water, through the loading hatch of the reactor when operating the mixer portions of 3-5 kg load 200 kg of sludge gas purification copper production composition containing 14.6% of arsenic. Then from the measuring device nitric acid in a thin stream serves nitric acid density of 1.35 to 1.37 g/cm to obtain a concentration of 15 g/DM³. The suspension is heated under stirring, maintaining a temperature of 70°With the steam in the jacket of the reactor. Mixing lead for 3 hours, maintaining a constant volume by adding water. Then the suspension through the valve bottom drain serves on the suction filter of stainless steel, filled with a layer of Dacron, two layers of filter paper and a bag of Dacron, and wring out under vacuum up to a maximum separation of the mother liquor. The filter cake was washed with 100 DM³water, prambody added to the stock solution. The mixture of mother liquor and located direct on the wastewater treatment plant.

In the same, pre-washed reactor pour 400 DM³water load when operating the mixer washed the precipitate with suction filter. In suspensio serves nitric acid for acidification her to pH=1,5. Then measure hydrogen peroxide in a thin stream serves 36%hydrogen peroxide in the amount of 88 DM³(105% from stoichiometry), uridicheski controlling the temperature of the suspension and preventing its increase of more than 70°C, stopping the flow of hydrogen peroxide when overheated to spontaneous or forced its cooling. After that, the suspension is heated at 70°C for 2 h and served on a suction filter, wring out. The precipitate is washed with 50 DM³water. The mother liquor is directed to the process of evaporation to the desired concentration.

The precipitate of sulfur after additional washing is dried at a temperature not exceeding 80°C and kept in stock for use or sale.

Example 2. In the reactor of stainless steel 12X18H10T with a capacity of 1 m³fitted with mechanical stirrer, jacketed for steam heating and water cooling, the lower discharge valve, a loading opening and an exit for exhaust ventilation, pour 0.5 m³water, through the loading hatch of the reactor when operating the mixer portions of 3-5 kg load 200 kg of sludge gas purification copper production composition containing 14.6% of arsenic. Then from the measuring device nitric acid in a thin stream serves nitric acid density of 1.35 to 1.37 g/cm³to obtain a concentration of 20 g/DM³. The suspension is heated under stirring, maintaining a temperature of 90°With the steam in the jacket of the reactor. Mixing lead for 2.5 h, maintaining a constant volume by adding water. Then the suspension through the valve bottom drain serves on the suction filter of stainless steel, filled layer is of asana, two layers of filter paper and a bag of Dacron, and wring out under vacuum up to a maximum separation of the mother liquor. The filter cake was washed with 100 DM³water, prambody added to the stock solution. The mixture of mother liquor and located direct on the wastewater treatment plant.

In the same, pre-washed reactor poured 500 DM³water load when operating the mixer washed the precipitate with suction filter. In suspensio serves nitric acid for acidification her to pH=2. Then measure hydrogen peroxide in a thin stream serves 36%hydrogen peroxide in the amount of 93 DM³(110% from stoichiometry), periodically controlling the temperature of the suspension and preventing its increase of more than 70°C, stopping the flow of hydrogen peroxide when overheated to spontaneous or forced its cooling. After that, the suspension is heated at 70°C for 2 h and served on a suction filter, wring out. The precipitate was washed with 60 DM³water. The mother liquor is directed to the process of evaporation to the desired concentration.

The precipitate of sulfur after additional washing is dried at a temperature not exceeding 80°C and kept in stock for use or sale.

Thus, the authors propose a method of obtaining technical arsenic acid from metallurgical wastes of non-ferrous metals, allow the Commissioner to dispose of waste in an environmentally safe manner with the receipt of two commercial products: sulphur and arsenic acid, which can be used to obtain the antiseptic compositions of the type CCA (chromated, dry or-copper-arsenate) to protect the wood and articles of wood from decay and destruction of bacteria, fungi, insects.

The method of obtaining arsenic acid, including leaching of arsenic sludge solution of hydrogen peroxide in the presence of sulfur, characterized in that as arsenic sludge use sludge metal production non-ferrous metals with its preliminary processing of nitric acid concentration of 15-20 g/DM³at a temperature of 70-90°C. and a ratio of T:W=1:(2,5÷3,0); then add water to the ratio of T:W=(1÷2):(1÷3), then add nitric acid to a pH of 1.5÷2 and hydrogen peroxide in the amount of 105-110% of stoichiometry.