SU653306A1 - Method of regeneration of used acid pickles - Google Patents

Description

The invention relates to the regeneration of acid etching solutions, acid eluates of cation-exchange filters, and any other concentrated solutions containing acids together with their salts.

The known method of regeneration of spent acid etching solutions by electrolysis in a diaphragm electrolyzer using an inert anode at a current density of 2.5-10 a / dm 2 and a temperature of 30-100 ° C 1.

The disadvantage of this method is the low degree of regeneration of the pickling solutions.

There is a method of regeneration of spent acid etching solutions by electrodialysis in an electrodialyzer separated by a cation-exchange membrane. In this vanodic space, the acid is regenerated, and metal cations penetrate through the membrane into the cathode chamber, where a certain amount of acid 2 must be introduced.

The disadvantage of this method is the impossibility of obtaining, after regeneration, etching solutions containing hydrochloric or

sulfuric or nitric acid with a concentration of 5-i2 ° / o while obtaining a powder-like metal.

The purpose of the present invention is to provide regeneration of solutions containing hydrochloric or sulfuric or nitric acid, to obtain an acid concentration of 5-22% and powder-like metals.

For this, the process is carried out in a three-chamber electrodialyzer with the cathode chamber filled with the regenerated solution, the anode chamber with acid, and the middle chamber with the produced catholyte at a current density of 20-50 a / dm until the residual metal content in the catholyte is 1.5-15 wt. %

The drawing shows a diagram illustrating the proposed method.

Claims (2)

The electrodialyzer I with an anionic and cationic membranes 2 and 3 is divided into three equal-volume chambers. Electrodes are placed in the outer chambers: the cathode 4 in the chamber formed by the anion-exchange membrane, and the anode 5 in the chamber formed by the cation-exchange membrane, the collection tank 6 for weakly concentrated solutions. The cathode chamber is filled with a solution to be regenerated, which is a highly concentrated acid-salt system. The middle chamber, which is enclosed between the anion exchange membrane and the cation resin membrane, is filled with a weakly concentrated solution (initially acidified water) of the same acid or salt as in the cathode chamber to provide electrical conductivity. The anode chamber, regardless of the nature of the solution being regenerated, is filled with sulfuric acid with a concentration of 600-800 g / l. When an electrodialyzer is connected to a direct current source, the following processes take place in each of the chambers: a) the decomposition of acids and their salts takes place in the cathode chamber; hydrogen cations, and then metal cations (except alkali and alkaline earth metals) are discharged at the cathode to form molecular hydrogen and pure metal, and negatively charged anions of acids and salts under the action of electric field forces pass through anion exchange membrane in the middle chamber. The decomposition reactions proceed according to the scheme: 2H4-2e H2t Me + e Me. As a result, the total concentration of catholyte decreases and, depending on the duration of the process, can reach any predetermined value; the catholyte produced is collected in collection tank 6; b) in the anode chamber, due to the fact that hydroxyl ions are discharged at the anode is much easier than sulfate ions, the main process is the decomposition of water with the formation of molecular oxygen and free hydrogen ions: 2NgO + 4e 021 + 4H By the action of electric field forces and by virtue of the law of electroneutrality of the solution, the resulting free hydrogen ions pass through the cation-exchange membrane from the anode chamber into the middle chamber. The use of an anode chamber is necessary to prevent direct contact of the anode with easily-depleted anions accumulating in the middle chamber. Sulfuric acid, which does not decompose at the anode, provides the electrical conductivity of the solution. In this case, the acid is not consumed and its quantity in the anolyte remains unchanged; c) hydrogen ions and anions formed by decomposition of the acid and their salts in the cathode chamber, as a result of the impermeability of the anion exchanger membrane for cations and the cation membrane for anions, are in the middle chamber. Acid formation and concentration are underway. When choosing the range of concentration of the obtained acid, we were guided by the fact that the proposed method allows; To study acid of any concentration, not more than 22 ° / oHD However, an acid concentration of less than 5% is rarely used. The acid most commonly used for etching is a concentration of 15-20%: The current density required to obtain a powder-like metal at the cathode depends on the concentration of the metal salt in the catholyte, which decreases during its production. In the proposed method, the current density range is 20-50 a / dm, the upper limit of the metal content in the catholyte does not exist. The more salt in the regeneration process can be left, the better. The lower limit, 1.5%, is due to the peculiarities of the process: an increase in energy consumption with deeper electrolyte production. Along with the main regeneration process, the transfer of water through the anion-exchange membrane from the cathode chamber into the middle chamber is also observed, due to the presence of hydration shells in the anions. As a result, as the process progresses, the volume of the catholyte decreases, and the volume of the solution in the middle chamber increases, which leads to some dilution of the regenerated acid and to a mismatch between the volume of the solution supplied for regeneration and the volume of the regenerated solution. Depending on the nature of the anions. (I.e., the nature of the regenerable acids), the water transfer is from 10 to 40% by volume. To eliminate the adverse effect of water transfer, the following sequence of operations is proposed for one regeneration cycle: 1. The average chamber is filled with initially acidified water before starting the process and, in all subsequent cycles, with a weakly concentrated solution from the collection tank. At the same time, the chamber is not completely filled, but in such a way that the difference between the volume of the solution in the cathode chamber and the volume of the solution in the middle chamber before the beginning of the process corresponds to the amount of water transfer. Therefore, the initial filling of the chamber is 60-70 vol. % 2. As the process progresses, the decrease in water from the cathode chamber is compensated for by the addition of a weakly concentrated solution from the a-collector bath, and the amount of additives to the end of the regeneration process corresponds to the amount of transfer. 3. The regeneration process is carried out until the solution in the cathode chamber is developed to such a concentration of metal salt that is acceptable by the quality requirements of the regenerated acid. 4. After the end of the process, the regenerated acid is removed from the middle chamber and used in production, and the developed (weakly concentrated) solution is removed from the chamber and collected in the storage tank. At the same time, the cathode is cleaned of the powdered metal released on it, followed by a new cycle regeneration. Thus, on each unit of the volume of the solution supplied for regeneration, a unit of the regenerated solution is formed with a permissible content of metal salt in the absence of its own discharge of wastewater from the installation. The proposed method provides a regeneration solution containing hydrochloric or sulfuric or nitric acid with a concentration of 5-22 wt. % and powdered metals. Claims The method of regeneration of spent acid etching solutions by electrodialysis, characterized in that, in order to ensure the regeneration of solutions containing hydrochloric or sulfuric, or nitric acid, to obtain an acid concentration of 5-22% and powdered metals, the process is carried out in a three-chamber electrodialysis apparatus with filling the cathode chamber with the regenerated solution, the anodic chamber with acid, the middle chamber with the produced catholyte at a current density of 20-50 a / dm to a residual metal content in the catholyte of 1.5-15 weight. 0/0. Sources of information taken into account in the examination 1. USSR author's certificate number 438729, cl. From 23 G 1/36, 1970. 2. US patent number 3481851, cl. 204-180, 1969. + L -, /