MXPA97002633A - Procedure for the recovery of the component parts of the salt from heavy different salts containing nitrates-nitra - Google Patents

Abstract

The present invention relates to a process for the selective recovery of the component parts of the salts from the aged salts containing nitrates-nitrites -hydroxides, which are produced during the heat treatment of the steel parts in the baths of salt, by dissolution of the salts aged in water, separation of the insoluble remnant and fractional crystallization of the alkali nitrate, characterized in that the aged salts are reduced to a grain size of 1 to 50 mm, which are dissolved in a solution containing nitric acid, hydrogen peroxide 40 to 90 ° C, after filtration of the insusluble remnant the potassium nitrate is precipitated by cooling the neutralized salt solution and concentrated to -10 ° C to + 20 ° C, sodium chloride is crystallized by subsequent concentration of the solution from 60 to 120 ° C and the sodium nitrate of the remaining solution is crystallized by addition of the nitric acid concent ra

Description

PROCEDURE FOR THE RECOVERY OF THE PARTIES COMPONENTS OF SALT FROM HARD AGED SALTS CONTAINING NITRITES-NITRATES DESCRIPTION OF THE INVENTION The invention relates to a process for the recovery of the component parts of the salts from aged salts containing nitrites-nitrates, which are produced during the heat treatment of steel parts in salt baths, by dissolution of salts aged in water, separation of the insoluble remnant and the fractional crystallization of the alkali nitrates. To increase the hardness or wear resistance of steel, heat treatment procedures have been carried out for a long time. For this, the technology of the salt bath is taken, where the work pieces are treated in the fusion of salts, where the foundry protection technique takes an important position. For the cooling of the construction parts, especially after the treatment in the coal baths, the salt baths containing nitrites-nitrates-hydroxides are used. The main components of these salt baths are nitrites, nitrates and hydroxides of the alkali metals sodium and potassium. In addition they still usually contain lower amounts in barium and chlorides and higher amounts in carbonates. In these salt fusions are oxidized those salts of cyanides fixed in the steel parts that are markedly increase the stability to the corrosion of steels. Due to the very appropriate cooling speed in these baths a high high resistance and a high hardness is achieved. As the melting salts are contaminated due to the bursting of the particles of scale of the surface REF: 24506 of the piece and consequently of the chemical reactions use the component parts of the salt bath, the baths must be in regular conditions without sludge and filled with fresh salt. This sludge consists of 50 to 99 percent of the salt component parts and must be used as aged salt in underground landfills. Up to now these aged salts are not worth to be economically recoverable, so that the acute concerns of the problem of aged salts are concentrated in the first line on the improvement of the capacity of the landfill and the particular decontamination of the parts. The aggregates of solutions for the partial recovery of component parts of salts from salts aged by hardening are for example described in the publication CAV 45 (1973), pages 69-75 and in the Chemie-Ing. -Technik 45 (1973), pages 1285 -1289. These procedures show a simultaneous treatment of aged salts containing nitrates and containing cyanide. For this purpose, in the fusion of salts, cyanide is decontaminated by reaction with nitrites and nitrates and the decomposition of nitrite and nitrate in excess is achieved by the addition of lean coal. In a final solution process, the barium carbonates can be separated from the other soluble salts. The decisive disadvantage of this process is that the decontamination of the cyanide in the fusion salts presents the danger of a reaction of the explosive type, especially when the cyanide content, as in some types of baths, increases above a threshold percentage. of 5. A promoter of the conduction of the reaction is therefore very difficult without great analytical performances. Consequently, toxic gases (Nox and CO) are present in this reaction, which must be burned catalytically. In the next step of the process, the precipitation of the barium carbonate, wastewater with high salt load is formed, to which no indication for recovery is made. The partial recovery of the component parts of the salts from the salts aged by hardening are published in DE-OS 24 00 318 and DE-OS 24 00 319. After the detoxification of cyanide, the melting is carried out at 450 to 550 ° C, the salt aged with hot water is treated by leaching. The remnant that is formed largely by barium carbonate is separated and a new preparation is carried out, eg. to barium chloride. The dissolved carbonate is converted to carbon dioxide by the addition of nitric acid and the amount of chloride is reduced by water evaporation of 10 to 15% by weight, where the sodium chloride can be obtained as crystallizate. The remaining solution is dried at 160 ° C and the mixture of salt from nitrate and nitrite as well as two percent sodium chloride and potassium should be directly used again in hardening. This process also has disadvantages, which have avoided a highly technical reaction. Thus NOx gases are released in large quantities by the addition of nitric acid, which must be incinerated catalytically. A return to the addition of acid by the addition of barium nitrate to the solution then again requires an additional process step. Especially correspond the purifications of the salts obtained not to the demands of the raw materials for the preparation of hardened salts and are strongly dependent on the composition of the added aged salts, which present strong variations. Also the nitrate-nitrite salt obtained can not be directly added due to the variable composition, until the concentration of the remaining chloride does not correspond to the technical demands. By the addition of regenerators these have become in the past years the composition of aged salts presented at lower contents of cyanides and carbonates and larger portions of chlorides. These modified conditions in the framework can not be given in the described procedure without the additional steps of the procedure. The process for the separation of alkali chlorides is known per se, but these processes can not be carried out directly for the return gain of alkali nitrates from salts aged by hardening, since here very different compositions of products must be available. of departure and other conditions of the procedure have to be taken into account. It was then the duty of the present invention to provide a method for the selective recovery of the component parts of the salts from aged salts containing nitrites-nitrates-hydroxides, which can be present in the heat treatment of the parts of steel in the salt baths, by dissolution of the salts aged in water, separation of the insoluble remnant and fractional crystallization of the alkali nitrate, which is easy to carry out and leads to high yields of directly revalued salts. This duty is solved according to the present invention, in that the solid aged salts are reduced to a grain size of 1 to 50 mm in a solution containing nitric acid, hydrogen perhydroxide between 40 to 90 ° C, the potassium nitrate after filtration of the insoluble remnant by cooling the neutralized saline solution, concentrated from -10 to +20 ° C of the potassium nitrate, sodium chloride is crystallized by new concentration of the solution between 60 to 120 ° C and from the remaining solution, sodium nitrate is recrystallized by the addition of nitric acid. Advantageously, after dissolving the salts aged by the addition of carbonate and alkali, the barium optionally present in a slightly alkaline medium, such as barium carbonate, is precipitated and separated. Preferably the aged salts are reduced to a grain size of 5 to 10 mm. It has been found that after a reduction of the solid hardening-containing salts containing nitrites-nitrates-hydroxides to a size of 1 mm to 50 mm, preferably 5 mm to 10 mm, to a lye in a presentation containing nitric acid, hydrogen peroxide, the component parts of the salts are completely dissolved. Likewise, nitrite ions are immediately oxidized to nitrates as well as carbonates and hydroxides are neutralized under the formation of nitrate salts. Due to the presence of hydrogen peroxide with the container, NOx gas is not released when the nitrite salts appear in the form of coarse grains at the contact of the nitric acid container contrary to what was expected. This is due to the relatively small reaction surface and the immediate subsequent reaction of NOx gases obtained in the solution with hydrogen peroxide is explained. By this combination of reactants in the solution it is further established with certainty, that eventually a salt containing falsely characterized cyanide can be detoxified without inconvenience by reaction with nitrite and hydrogen peroxide. The promotion of the procedure can proceed by controlling the pH value and measuring the redox potential. Another advantage is the heat of reaction released in the oxidation and neutralization, which equals the endothermic dissolution process. As a result, a dissolution temperature of 50 ° C to 80 ° C is established, which makes it possible to achieve a very high salt concentration. Thus, between 100 kg to 200 kg of aged salt containing nitrate can be dissolved in a vessel from 50 kg of nitric acid and 50 kg of a hydrogen peroxide solution. By addition of potassium carbonate, barium carbonate present is possibly precipitated as barium carbonate and can thus be separated with other insoluble impurities by filtration. Finally, individual salt types can only be recovered by selective crystallization from the salt solution. That is why it is reached by the sought crystallization in the sequence, potassium nitrate, sodium chloride and finally sodium nitrate, where the salts have been recovered almost completely in high purity. The procedure parameter is also controlled by the ionoselective electrodes. Potassium nitrate can be crystallized by cooling the solution at a temperature between -10 ° C and + 20 ° C in a pure form, since the solubility of the sodium salts are essentially less strongly influenced by temperature and they they are in solution. From a solution with for example 30% by weight of potassium nitrate, 30% by weight of sodium nitrate and 5% of sodium chloride, 66% of the dissolved potassium nitrate can be recrystallized by cooling the solution to 0 °. C. By simply washing with a potassium nitrate solution, the crystals are released from the solution that fixes them. Thus a potassium nitrate is obtained according to the choice of the optimum crystallization temperature for the composition of the solution with a purity of over 96%.

By concentrating the solution in the next step, preferably in a vacuum crystallizer, at a temperature of 60 ° C and 120 ° C the water that comes from the nitric acid is evaporated with the solution of nitrogen peroxide and the sodium chloride crystallizes at a concentration of around 3% by weight. By adding a concentrated nitric acid, the sodium nitrate is separated in the last step. As both salts of nitrates can behave surprisingly differently, it happens that, sodium nitrate recovers with a very high purity of over 98%, by washing it is allowed to increase even a far purity of over 99%. To reduce the concentration of sodium nitrate in the solution from 5 to 15% by weight, a concentration of nitric acid between 10 and 30% by weight is used, where the highest concentrations of nitric acid exert a strong decrease in the concentration of sodium nitrate. By heating the salt with fixed nitric acid, the still small part of chloride in the salt can completely react to the gaseous hydrogen chloride, which after the neutralization reaches the highest purity demand in a sodium nitrate solution containing slightly hydroxides .

The figure shows a driving scheme of the method according to the present invention, in which the implementation of the described steps is established.

After the reduction of the aged salts, it proceeds to the leaching in a container that contains nitric acid and hydrogen peroxide. Barium carbonate and other insoluble solids are separated. The individual salts in the sequence, potassium nitrate, sodium chloride and sodium nitrate are separated from the solution by selective crystallization. The solution of the remaining nitric acid is again led by a leaching of other aged salts.

The following examples serve to more closely illustrate the process of the present invention: i. 100 kg of a mixture of aged salt containing nitrates is reduced to a grain size of 10 mm. 10 kg of the aged salt are prepared in partial quantities of each. For this the aged salt was placed under leaching in a 55 ° C container, which contained 2.7 kg of 65% nitric acid as well as 4 kg of hydrogen peroxide solution. With the help of the polymeric flocculation agents it was possible to isolate the insoluble impurities from the solution. By adding 0.1 kg of potassium carbonate and adjusting the pH value by addition of the potassium hydroxide to 9, the barium was precipitated as carbonate. The solution neutralized with nitric acid to pH 7 was cooled to -5 ° C and the crystallized potassium nitrate was then removed. By evaporation of 4.1 I of water respectively, the sodium chloride was crystallized at a temperature of 105 ° C. To the concentrated solution was added the aforesaid amount of nitric acid and therefore the crystallized sodium nitrate was separated at 10 ° C as well as The bound chloride is released by heating to 100 ° C. The nitric acid solution reacted with the previously used amount of hydrogen peroxide of hydrogen and was brought back to the leaching of the next charge. The mass balance of the preparation gave the following results: 2. Compound Part in the salt quantity of the unit of the aged product product KNO3 24.5% 57.5% 99.0% KNO2 30.2% 0.0 kg - 2. 100 kg of an aged salt containing nitrate, poor in nitrite, is reduced to a grain size of 10 mm. 10 kg of the aged salt are prepared in partial quantities of each. For this, the aged salt was placed under bleach in a 65 ° C container, which contained 15.1 kg of 65% nitric acid as well as 1.7 kg of 50% hydrogen peroxide solution. With the help of the polymeric flocculation agents it was possible to isolate the insoluble impurities from the solution. By adding 3 g of potassium carbonate and adjusting the pH value to about 9 by addition of potassium hydroxide, the barium was precipitated as carbonate. Then, the solution neutralized with nitric acid to pH 7 was cooled to 10 ° C and the crystallized potassium nitrate was separated. By evaporation of 3.4 I of water respectively, the sodium chloride was crystallized at a temperature of 90 ° C. To the concentrated solution was added the aforementioned amount of nitric acid at 30 ° C and therefore the crystallized sodium nitrate is isolated by heating at 100 ° C of the bound chloride. The nitric acid solution reacted with the previously used amount of hydrogen peroxide and was brought back to leaching. The mass balance of the preparation gave the following results: 3. 100 kg of an aged salt containing nitrate, rich in potassium, is reduced to a grain size of 10 mm. 10 kg of the aged salt are prepared in partial quantities of each. For this the aged salt was placed under bleach in a 65 ° C container, which contained 2.8 kg of 65% nitric acid as well as 5.2 kg of 50% hydrogen peroxide solution. With the help of the polymeric flocculation agents it was possible to isolate the insoluble impurities from the solution. By adding 0.08 kg of potassium carbonate and adjusting the pH value to about 9 by the addition of potassium hydroxide, the barium was precipitated as carbonate. Then, the solution neutralized with nitric acid to pH 7 was cooled to -10 ° C and the crystallized potassium nitrate was separated. By evaporation of 3.4 I of water respectively, the sodium chloride was crystallized at a temperature of 105 ° C. To the concentrated solution was added the aforesaid amount of nitric acid and therefore the crystallized sodium nitrate was removed at a temperature of 10 ° C. C. By heating to 100 ° C the fixed chloride was finally released. The nitric acid solution reacted with the previously used amount of hydrogen peroxide and was brought back to leaching. The mass balance of the preparation gave the following results: 4. 100 kg of an aged salt containing nitrate, rich in sodium, is reduced to a grain size of 10 mm. 10 kg of the aged salt are prepared in partial quantities of each. For this the aged salt was placed under bleach in a 50 ° C container, which contained 6.8 kg of 65% nitric acid as well as 0.05 kg of 50% hydrogen peroxide solution. With the help of the polymeric flocculation agents it was possible to isolate the insoluble impurities from the solution. By adding 0.03 kg of potassium carbonate and adjusting the pH value to about 9 by the addition of potassium hydroxide, the barium was precipitated as carbonate. Then, the solution neutralized with nitric acid to pH 7 was cooled to 15 ° C and the crystallized potassium nitrate was separated. By evaporation of 2.4 I of water respectively, the sodium chloride was crystallized at a temperature of 100 ° C. To the concentrated solution was added the aforesaid amount of nitric acid and therefore the crystallized sodium nitrate is isolated by heating at 5 ° C. C of the fixed chloride. The nitric acid solution reacted with the previously used amount of hydrogen peroxide and was brought back to leaching. The mass balance of the preparation gave the following results: . 100 kg of a mixture of aged salt containing nitrate is reduced from Example 1 different from the parameters found. The salt was reduced to a grain size of 0.5 mm and in a container partial quantities of 10 kg at 65 ° C were treated by leaching, which contained 2.7 kg of 65% nitric acid as well as 4 kg of hydrogen peroxide solution. 50% Also, some nitrous gas (NOx) was released. With the help of the polymeric flocculation agents it was possible to isolate the insoluble impurities from the solution. By adding 1 kg of potassium carbonate and adjusting the pH value to about 9 by the addition of potassium hydroxide, the barium was precipitated as carbonate. Then, the solution neutralized with nitric acid to pH 7 was cooled to 30 ° C and the crystallized potassium nitrate was separated. By evaporation of 4.1 I of water respectively, the sodium chloride was crystallized at a temperature of 50 ° C. To the concentrated solution was added the aforementioned amount of nitric acid and therefore the crystallized sodium nitrate is isolated by heating at 0 °. C. The nitric acid solution reacted with the previously used amount of hydrogen peroxide and was brought back to leaching. The mass balance of the preparation gave the following results: This example shows that when the parameters according to the present invention are removed, the recovered salts are more impure and when nitrogenous oxides are dissolved in the aged salts. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (3)

1. CLAIMS 1. Procedure for the selective recovery of the component parts of the salts from the aged salts containing nitrates-nitrites -hydroxides, which are produced during the heat treatment of the steel parts in the salt baths, by dissolution of the salts aged in water, separation of the insoluble remnant and fractional crystallization of the alkali nitrate, characterized in that the aged salts are reduced to a grain size of 1 to 50 mm, which are dissolved in a solution containing nitric acid, peroxide hydrogen at 40 ° C to 90 ° C, after filtration of the insoluble remnant the potassium nitrate is precipitated by cooling the neutralized salt solution and concentrated to -10 ° C to + 20 ° C, sodium chloride is crystallized by subsequent concentration of the solution at 60 to 120 ° C and the sodium nitrate of the remaining solution is crystallized by the addition of the concentrated nitric acid.
2. 2. Method according to claim 1, characterized in that by addition of carbonate and alkali in the alkaline medium after the dissolution of the aged salts, the barium is precipitated as barium carbonate and separated.
3. 3. Process according to claims 1 and 2, characterized in that the solid aged salts are reduced to a grain size of 5 to 10 mm.