RU2294982C1 - Method of recovery of the spent solutions of the hydrochloric acid - Google Patents

Abstract

FIELD: chemical industry; metallurgy industry; other industries; methods of recovery of the spent solutions of the hydrochloric acid.

SUBSTANCE: the invention is pertaining to the methods of recovery of the spent solutions of the hydrochloric acid from the spent pickling solutions (SPS) containing the non-used hydrochloric acid and the salts of iron and may be used in the galvanic productions, in the metallurgy and other industries. The method includes the azeotropic distillation, before which they admix the distillation residue gained at the distillation of the flashed waters with the spent hydrochloric acid. The vapors liberated during the azeotropic distillation of the mixture are used for preheating up of the spent hydrochloric acid. The produced condensate is corrected according to the contents of the acid and is sent back into the process bosh. The part of the residue of the process of the azeotropic distillation is directed into the tank supplied with the refrigerator. For withdrawal of the chlorides of iron and other metals which have transferred into the hydrochloric acid at the pickling by chilling of the solution and the crystallization of the part of the dissolved salts of iron. The vapors gained at the flashing waters distillation are used for heating, and the produced condensate also is sent back into the production cycle for realization of the flashing operations. The technical result of the invention consists in creation of the closed cycles for the technological solutions - for the hydrochloric acid and for the flashing waters.

EFFECT: the invention ensures creation of the closed cycles for the technological solutions - for the hydrochloric acid and for the flashing waters.

1 ex, 1 dwg

Description

The invention relates to methods for the recovery of hydrochloric acid from spent pickling solutions (OTP) containing unused hydrochloric acid and iron salts, and can be used in galvanic industries, in the metallurgical, chemical and other industries.

A known method of regeneration of spent solutions of hydrochloric acid containing iron ions (USSR AS No. 1351176, class C 23 G 1/36, C 23 F 1/46, published 04/14/94, bull. No. 7). According to this method, a solution is sprayed in hot products of fuel combustion, oxide dust is separated, and then an aqueous solution of hydrochloric acid is obtained. In this case, the preparation of an aqueous hydrochloric acid solution is carried out by absorption of hydrogen chloride by wastewater and an additional increase in the concentration of regenerated hydrochloric acid by repeated evaporation and heat treatment, in which the decomposition of hydrogen chloride occurs. The degree of regeneration of spent hydrochloric acid increases to 20.8%.

The disadvantages of this method include the use of high temperatures during acid regeneration, which requires special measures to protect the environment and working personnel. In addition, this method is used to process solutions with a low concentration of hydrochloric acid and iron chlorides (total chloride content ~ 10 g / l).

Of the known technical solutions, the closest to the claimed technical essence is the application No. 424 078 FRG, MKI C 01 B 7/07, C 01 F 7/50 (decl. 28.11.92, published 1.08.94), which proposes a method and installation for the purification and concentration of diluted contaminated hydrochloric acid, which allows to obtain pure concentrated hydrochloric acid and at the same time suitable for use high-purity aluminum salts. The method consists in azeotropic distillation of contaminated hydrochloric acid by vacuum distillation methods. For azeotropic displacement, high-boiling components, for example, CaCl ₂ or AlCl ₃ , are added to hydrochloric acid, as a result of which HCl polluting acids (hydrofluoric, sulfuric, and nitric) are precipitated in the form of aluminum salts, with AlF ₃ precipitated first, separated by vacuum microfiltration, and then sulfur precipitated - and nitric salts of aluminum, which are dried to dryness by evaporation.

The disadvantage of this method is that it is applicable to solutions of hydrochloric acid contaminated with other acids and not containing iron ions. In addition, the proposed method uses vacuum distillation, which significantly complicates the technological scheme and requires the use of complex, expensive and corrosion-resistant equipment, and also do not regenerate the wash water, with which up to 15% of acid is lost.

The problem solved by the proposed method is improving the process of regeneration of hydrochloric acid and wash water after the etching process, increasing the degree of regeneration of the processing solutions.

The technical result from the use of the proposed method is to create closed cycles for technological solutions: hydrochloric acid and wash water.

This result is achieved by the fact that in the method of regeneration of spent hydrochloric acid solutions, including azeotropic distillation, before the azeotropic distillation, the bottom residue obtained by washing water distillation is mixed with spent hydrochloric acid, the vapors released during the azeotropic distillation of the mixture are used to preheat the spent hydrochloric acid, the resulting condensate is adjusted for the acid content and returned to the process bath, part of the bottom residue of the azeotropic process distillations are removed to a container equipped with a refrigerator to remove iron chlorides and other metals converted to hydrochloric acid by etching by cooling the solution and crystallizing part of the dissolved iron salts, the vapors obtained from the distillation of the washings are used for heating, and the condensate also returns into the technological cycle for washing operations.

The method is as follows.

Wash water after the etching process, containing 0.2-0.3 M hydrochloric acid, is subjected to distillation in a distiller of any known type with a number of plates of at least 8. Hydrochloric acid has the property of forming an azeotropic mixture at a concentration of 6.3 M acid with a boiling point of 108 , 6 ° C, which is higher than the boiling point of both pure water (100 ° C) and pure hydrochloric acid (-84.8 ° C). A characteristic feature of solutions giving such azeotropic mixtures is that when distilled, their composition always tends to the composition of the azeotrope. This means that during the distillation of pre-azeotropic mixtures, water will mainly pass into the vapor phase, and acid will accumulate in the cube. During distillation of the azeotropic mixtures, hydrochloric acid will pass into the vapor phase, respectively, and an azeotropic mixture will accumulate in the cube.

Distilling the wash water after the etching process with a sufficient number of plates allows water to be obtained as condensate, and to accumulate hydrochloric acid in a cube of the distillation column with a concentration equal to the HCl content in the etching bath. This still solution is mixed with the spent hydrochloric acid coming from the pickling bath and sent for regeneration by a single distillation method, while the azeotropic mixture is immediately poured into the cube. If the solution feed rates for distillation are equal to the speed of distillation, the acid content in the resulting condensate is almost the same as in the solution supplied for regeneration.

Chlorides of iron and (or) other metals as they are distilled, will accumulate in the cube, where their crystallization is possible upon reaching the saturation state. For their withdrawal, continuously or periodically, part of the bottoms is sent to a special container equipped with a refrigerator. With a decrease in temperature from the boiling point to a temperature of + 20 ° С, the solubility of iron chlorides decreases approximately by half. After separation of the precipitated crystals of iron chloride, the solution is again returned to the cube of the distillation unit.

The water vapor distilled from the distiller is used to preheat the washing water entering the distiller and, after the final condensation, is sent for washing operations. After azeotropic distillation, vapors of regenerated acid are used in the same way to preheat spent hydrochloric acid and, after final cooling, are sent to a container where the hydrochloric acid is adjusted in composition, since part of the acid is spent on the metal etching process itself with the formation of the corresponding chlorides.

An example implementation of the method.

The method is carried out in accordance with the scheme shown in the drawing, where 1 is a container for preparing the etching solution, 2 is an etching bath, 3 is a collection of spent solution, 4 is a pre-heater for acid, 5 is a distiller for hydrochloric acid, 6 is a condenser, 7 - rinse bath, 8 - rinse water collection, 9 - pre-heater for rinse water, 10 - distiller for rinse water, 11 - condenser, 12 - apparatus for removing metal chlorides.

Wash water after the etching process, containing 0.2-0.3 M hydrochloric acid, from the wash bath 7 is sent to a collector 8, from where it is passed through a pre-heater 9 and distilled in a distiller 10 of any known type with a number of plates of at least 8. Salt acid has the property of forming an azeotropic mixture at an acid concentration of 6.3 M with a boiling point of 108.6 ° C, which is higher than the boiling point of both pure water (100 ° C) and pure hydrochloric acid (-84.8 ° C). Therefore, during distillation in the cube, acid accumulates, the composition of which tends to the composition of the azeotrope, and water will predominantly pass into the vapor phase.

Hydrochloric acid, containing unused etching acid and ferric chloride, comes from pickling bath 2 to collector 3, into which acid is supplied from distillation cube 10. From collector 3, the solution through preheater 4 enters distillation cube 5, where hydrochloric acid is poured acid with a concentration of 6.3 M, which corresponds to an azeotropic mixture of water - hydrochloric acid.

The concentration of hydrochloric acid solutions for steel etching usually does not exceed 3-4 mol / dm ³ ; therefore, when they are added to the azeotropic mixture located in the cube of distiller 5 and the same amount of solution is taken as was supplied to the cube, the acidity of the condensate obtained will be correspond to the acidity of the solution supplied for regeneration. The vapors distilled from the distiller 5 are sent to the preheater 4 to heat the solution entering the distiller and then to the condenser 6, from where the regenerated acid enters the tank 1, where the hydrochloric acid is adjusted in composition, as part of the acid is spent on the metal etching process itself with the formation of corresponding chlorides.

Chlorides of iron and (or) other metals as the distillation will accumulate in the cube of the distiller 5, where it may be precipitated upon reaching the saturation state. To withdraw them continuously or periodically, part of the bottoms from the distiller 5 is sent to a special apparatus 12, equipped with a refrigerator. When the solution is cooled from the boiling point to a temperature of + 20 ° С, the solubility of iron chlorides decreases approximately by half, and excess salts precipitate. After separation of the precipitate of crystals of iron chloride, the solution is again returned to the cube of the distillation unit.

Thus, the proposed method allows to reduce the amount of waste, to create closed cycles both for pickling solutions and washing water, while the degree of regeneration of hydrochloric acid increases to 70%.

Claims (1)

A method of regenerating spent etching solutions of hydrochloric acid, including azeotropic distillation, characterized in that before the azeotropic distillation, the bottom residue obtained by washing water distillation is mixed with spent hydrochloric acid, the vapors released during the azeotropic distillation of the mixture are used to preheat the spent hydrochloric acid , the condensate obtained is adjusted for acid content and returned to the process bath, part of the bottom residue of the azeotropic distillation process It is removed to a container equipped with a refrigerator to remove iron chlorides and other metals converted to hydrochloric acid by etching, by cooling the solution and crystallizing part of the dissolved iron salts, the vapors obtained by the distillation of washing water are used for heating, and the condensate obtained is returned to the process cycle for flushing operations.