ITMI20091043A1 - PROCEDURE FOR RECOVERY OF ALKALINE SOLUTIONS - Google Patents

Description

OBJECT OF THE INVENTION

The present invention relates to a process for the treatment and recovery of alkaline solutions, in particular solutions based on caustic soda or caustic potash, used in the pickling reactions of aluminum.

STATE OF THE TECHNIQUE

The metalworking processes foresee some obligatory stages that are necessary in order to make the metal suitable for subsequent processing or subsequent surface treatments. A very important stage in the metal and metal alloy processing procedures is represented, for example, by chemical pickling, which, again by way of example, favors the adhesion and durability of glues and paints over time. In particular in the case of aluminum and its alloys, the pickling operations take place in an alkaline environment, mainly by means of caustic soda or caustic potash solutions. Furthermore, the same alkaline solutions of soda and / or caustic potash are widely used in the case of extrusion of aluminum profiles, which is a particular application of the technique known as extrusion, which is one of the foundations of the entire manufacturing industry. . In short, the extrusion process consists in compressing the metal to be processed by means of a shape called a matrix, in order to cause a deformation that leads it to assume the appearance and profiles according to the desired sizes and shapes. This deformation is impressed from the outside and, if the artifact in question must be hollow, also from the inside through the introduction of a core. This process therefore involves the compression of the starting materials, after heating that makes modeling easy, inside a cylinder or matrix, at the end of which there is a shaped hole, which gives the material the desired shape. The profile thus obtained after extrusion, undergoes further finishing processes and, possibly, painting, before being placed on the market. The extrusion of aluminum profiles therefore associates one of the basic techniques of industrial processing with one of the materials, aluminum, most universally widespread in the production of all kinds of products, from simple pots to very complicated components of jet engines. In any case, the extrusion of aluminum profiles constitutes the first step for the realization of numerous objects of daily use, from the already mentioned pots, to the jars, to the fixtures commonly used in apartments.

As described above, the metal extrusion process, in particular the aluminum extrusion process, involves the use of matrices capable of imparting the desired shape to the metal. Once the programmed extruded pieces have been obtained, the residue inside the channels of the extrusion dies remains in the shape of the die and must be eliminated before carrying out the next extrusion in the program.

Generally, the matrix is immersed in a bath, also called a pickling bath. The operating principle of this bath, in the case of aluminum, is based on the chemical reaction that takes place between metallic aluminum and NaOH (sodium hydroxide or caustic soda) or KOH (potassium hydroxide or caustic potash) in aqueous solution. In practice, soda or potash react with aluminum and form NaAIOz or KAI02 with the formation of gaseous hydrogen. In this way the aluminum accumulated in the matrix melts and the matrix is cleaned and is ready to be used again. As the 0 potash soda bath is used, the free potash 0 soda is consumed and its concentration decreases. When the concentration of soda or free potash reaches the minimum level below which the pickling bath is no longer able to perform its function, the bath is said to be exhausted or exhausted and must be replaced, with high costs and considerable disposal problems. .

At this point, in fact, the problem arises of disposing or recovering the bath or solution of soda or exhausted potash. The currently most used disposal and / or recovery systems can be schematized as follows.

1) Disposal after purification treatment, which involves high costs and in any case difficulties in disposing of the solution even after purification,

2) The exhausted bathroom is â € œcorrected 'and then used as a “flocculant” in purification plants. This system has no commercial value, in the sense that the â € œcorrectedâ € bathroom is sold without financial consideration, even paying for disposal. Also this method, in addition to not being profitable from an economic point of view, involves significant disposal problems.

3) Recovery of the exhausted bath according to two different systems:

3.1) dilution

3.2) transformation.

In the first case (3.1), the exhausted soda solution is diluted with water, in a ratio of about 1: 100. In this way there is the precipitation of AI (OH) 3 which is partially filtered and removed while the remaining solution can be reused, even if it contains dissolved quantities of AI (OH) 3 which can interfere, especially if the reuse is repeated. In this case, however, the soda or potash solution obtained from the aforementioned recovery process is very diluted and cannot be used as it is, but must be concentrated by evaporation, with considerable costs due to the energy consumption required. Alternatively, the diluted solution can be concentrated by means of a reverse osmosis process, but also in this case the costs are substantial, and the results are uncertain due to the presence of traces of aluminum, which are dangerous because they can cause the osmotic membranes to collapse.

As an alternative to dilution, the spent soda or potash solution can undergo a chemical transformation (3.2) by adding carbon dioxide (C02). In this case, the chemical reactions involved involve the transformation of the residual soda (NaOH) or potash (KOH) into sodium carbonate (Na2C03) or potassium carbonate (K2C03) with the formation of water, as well as the transformation of NaAI02o KAI02 (which is formed by reaction between soda or potash and aluminum) in sodium carbonate (Na2C03) or potassium carbonate (K2C03) and aluminum hydroxide (AI (OH) 3) which precipitates and can be filtered and removed. In this way a final solution rich in sodium carbonate or potassium carbonate is obtained, which can be integrated with soda or potash, and used again in the treatment of the matrices by pickling. The limit of this method is represented by the fact that, over time, sodium carbonate or potassium carbonate accumulates in the solution, until further use is impossible. At this point, the problem of disposal arises again and is it is necessary to use a new solution of soda or potash, with high costs and considerable inconvenience. This transformation process therefore allows to reuse the same suitably treated solution for a limited number of times and in any case poses the problem of its disposal, as well as the need to provide new solutions for the treatment of the matrices.

AIMS OF THE INVENTION

The purpose of the present invention is to provide a process for the recovery of baths or exhausted alkaline solutions deriving from aluminum pickling reactions, in particular from the treatment of extrusion matrices used in aluminum extrusion, which allows the recovery of the solutions with consequent reuse of the same.

Another object of the present invention is to provide a process for the recovery of exhausted alkaline baths or solutions deriving from aluminum pickling reactions, in particular from the treatment of extrusion matrices used in aluminum extrusion, which does not provide for the correction, integration or substantial concentration of the recovered solution.

Always the aim of the invention is to provide a process for the recovery of baths or exhausted alkaline solutions coming from aluminum pickling reactions, in particular from the treatment of extrusion matrices used in aluminum extrusion, which is economically advantageous and which entails a significant economic advantage over the entire extrusion process.

The aim of the present invention is also to provide a process for the recovery of exhausted alkaline baths or solutions deriving from aluminum pickling reactions, in particular from the treatment of extrusion matrices used in aluminum extrusion, which it is simple, does not require the use of particular reagents and can be carried out in parallel with any extrusion process.

The object of the present invention is also the use of the aforesaid process, for the recovery of exhausted alkaline baths or solutions deriving from aluminum pickling reactions, in particular from the treatment of extrusion matrices used in aluminum extrusion.

DESCRIPTION

These and other objects and related advantages which will be better highlighted by the following description, are achieved by a process for the recovery of baths or exhausted alkaline solutions, in particular solutions of spent caustic soda (NaOH) or caustic potash (KOH) coming from alkaline pickling / degreasing of aluminum and / or its alloys products. These operations are found, for example, in the following sectors;

1) removal treatment of aluminum and its alloys from extrusion matrices

2) alkaline degreasing / pickling preliminary to the anodic oxidation of aluminum and its alloys

3) lightening and alkaline chemical milling of aluminum and its alloys in general and in the aeronautical and military sectors in particular

4} alkaline degreasing / pickling of aluminum strip or sheet pre-painting or pre-anodic oxidation, or an end in itself

The process includes a first phase of:

a) treatment of the bath or solution of soda or exhausted potash with carbon dioxide (C02), obtaining a first precipitate and a first solution,

b) treatment of said first solution with oxides and / or hydroxides of divalent metals, obtaining a second precipitate and a second solution.

According to the present invention, said second solution thus obtained is directly used in the processes referred to in points 1, 2,3,4 above, without needing to be concentrated, corrected or modified in any way.

More particularly, said phase a), when carried out on exhausted solutions of soda or potash from the aforementioned treatments, involves the following chemical reactions:

2NaOH C02- â – ºNa2C03 Î — 20 or

2KOH C02- â – ºKsCOa H20

2NaAI02 <+> C02H20 -â – ºNaaCOs 2AI (OH) 3 or

2KAI02 + C02 + H20 - â – º K2C032AI (OH) 3

where said first precipitate is represented by 2AI (OH) 3, while said first solution comprises Na2C030 K2CO3. Said first precipitate is advantageously removed by filtration, while the resulting solution, rich in sodium carbonate or potassium, is subjected directly to said step b). In particular, according to the invention, when said oxides and / or hydroxides of divalent metals are selected as CaO and / or Ca (OH) 2, said step b), it provides for the following chemical reactions:

Na20O3 + Ca (OH) 2-â – ºCaC032NaOH or

K2C03Ca (OH) 2- <â – º> CaC03 + 2KOH

Na2C03CaO H20 - -â – ºCaC03 + 2NaOH or

K2C03 + CaO H20 - <â – º> CaCOs 2KOH

Calcium carbonate (CaC03) is obtained in the form of a precipitate (called second precipitate), which is removed by filtration, while the resulting solution (called second solution) is reused as it is because it is rich in soda or potash.

According to the present invention, it is therefore possible to carry out a process for the recovery of the exhausted alkaline solutions, in particular of soda or potash, used for pickling reactions of aluminum, in particular in the treatment and cleaning of extrusion matrices used in the ™ aluminum extrusion, as well as for the other operations referred to in points 2,3,4.

This process has considerable advantages with respect to the processes according to the known art.

In fact, it is possible to completely reuse the initial soda or potash solution without the need to carry out additional operations and treatments, resulting in time savings and also significant economic savings.

Another advantage is represented by the fact that it is not necessary to dispose of the exhausted solution, with consequent cost savings and advantages also from the point of view of the general management of the industrial process.

A further advantage is represented by the fact that, by operating according to the process object of the present invention, all AI (OH) 3 which is formed during phase a) of said process is removed by filtration or in any case by separation, since it is a matter of ¬ a precipitate (first precipitate). Since the solution does not undergo dilutions, there is no risk that a part of said Al hydroxide can redissolve or remain directly in solution and therefore remain, even only partially, present in said first solution.

The starting exhausted solution can advantageously undergo an optional dilution with water up to a ratio of 1: 1. This dilution can be advantageous because it helps in avoiding the precipitation of Na2C03 or KC03 in crystallized form during the reaction referred to in the above step a). If this dilution is carried out, the solution resulting from step b), and therefore the final solution, will be subjected to an optional concentration step c), which will take place, for example, by evaporation, until the concentration of soda or potash is reached. desired for reuse of the solution.

This optional evaporation step, and relative previous optional dilution step, does not involve the drawbacks due to the dilution when carried out according to the methods described above and commonly used according to the known art.

In fact, while in the dilution processes according to the known technique a dilution is carried out in a ratio of about 1: 100, according to the present invention the dilution ratio does not exceed 1: 1 and, consequently, also the possible concentration phase of the final solution , it is very simple, fast and with practically no additional costs.

A further advantage is represented by the fact that, even if said optional step of dilution of the starting solution and said optional step of concentration of the final solution (or said second solution) is carried out, since any dilution carried out is ! 1: 1 ratio, also in this case all the aluminum hydroxide (AI (OH) 3) will remain in the form of a precipitate, and can thus be completely removed. In other words, even if a dilution as indicated above is to be carried out, there will be the problem relating to a part of dissolved Al hydroxide, which instead occurs using known techniques. In fact, the dilution is such as to guarantee in any case that all formed AI (OH) 3 is removed in the form of a precipitated solid.

What has been described above will be more clearly indicated with the aid of the following practical embodiment examples, given only as an indication and not limitative of the present invention.

EXAMPLE 1

Procedure for the recovery of an exhausted NaOH bath

Starting solution

Exhausted pickling bath for aluminum extrusion matrices.

Solution content.

NaOH free 15-30%

Al (in the form of NaA! 02) 3-15%

Carbonaceous and oily residues from drawing

* The process allows to carry out the separation of aluminum in the form of pure hydroxide and allows its reuse as a secondary raw material. It also allows you to completely recover the free and combined NaOH.

* The process includes an optional pre-filtration phase, followed by a neutralization phase of the exhausted solution according to the following reaction scheme;

2NaOH C02- - â € ”â – ºNa2C03 H20

2NaAI02C02 + H20> Na2C03 + 2AI (OH) 3

<â–> Where for every 1Kg of NaOH it is necessary to add 0.55 Kg of C02 and for every 1Kg of Al it is necessary to add 0.81 Kg of CO ?.

<â–> The AI (OH) 3 filtration step (which precipitates completely) can advantageously be carried out by means of a belt filter, a rotary drum, a centrifuge or filter bags. The pure hydroxide obtained in this way is advantageously used as a secondary raw material because it is free from other contaminants.

<â–> The soda regeneration phase takes place by reacting the solution containing Na2C03 with CaO or with Ca (GH) 2, according to the following reactions:

Na2C03Ca (OH) 2â € ”- â – º CaC03 + 2NaOH

Na2C03 + CaO H20 - - <â–> â † ’CaC03 + 2NaOH

â € ¢ For example, the starting concentration in Na2C03 is between 5 and 25%, while the quantity of CaO used for each Kg of Na2C03 is 0.528 Kg. The reaction temperature is between 40 and 100 ° C and the reaction time can vary between 10 minutes and 3 hours. The caustic soda solution thus regenerated will have a concentration between about 2.5% and 15%. The final solution, if necessary, can be concentrated up to the desired value (between 5 and 30%) for example by means of a steam or hot water concentrator in heat pump or multi-stage evaporators.

â € ¢ The soda solution thus recovered can be stored for example in iron, PVC, PP, fiberglass, SS silos. The titer of the solution can be checked for example by acidimetric titration. At the controls, the following residues are highlighted: Al 10-1000 ppm, Ca 10-300 ppm,

EXAMPLE 2

Procedure for the recovery of an exhausted KOH bath

Starting solution

Exhausted pickling bath for aluminum extrusion matrices.

Solution content.

KOH free 15-30%

Al (in the form of KAi02) 3-15%

Carbonaceous and oily residues from drawing

<â–> the process allows to carry out the separation of aluminum in the form of pure hydroxide and allows it to be reused as a secondary raw material. It also allows you to completely recover the free and combined KOH.

<â–> the procedure includes an optional prefiltration step, followed by a neutralization step of the exhausted solution according to the following reaction scheme:

2KOH C02- - â – º K2C03 + H20

2KAI02C02H20 - - â – º K2C032AI (OH) 3

<»> Where for every 1Kg of KOH it is necessary to add 0.39 Kg of C02 and for every 1 Kg of Al it is necessary to add 0.81 Kg of C02.

<â–> The filtration phase of AI (OH) 3 (which precipitates completely) can advantageously be carried out by means of a belt filter, a rotary drum, a press, a centrifuge or filter bags. The pure hydroxide obtained in this way is advantageously used as a secondary raw material because it is free from other contaminants.

<â–> The regeneration phase of potash takes place by reacting the solution containing K2C03 with CaO or with Ca (OH) 2, according to the following reactions:

K2C03Ca (OH) 2- - â € ”â – ºCaCOs 2KOH

K2C03CaO H20 â € ”- â €” â – ºCaC03 + 2KOH

* For example, the starting concentration in K2C03 is between 5 and 25%, while the quantity of CaO used for each Kg of K2CO3 is 0.40 Kg. The reaction temperature is between 40 and 100 ° C and the reaction time can vary between 10 minutes and 3 hours. The caustic potash solution thus regenerated will have a concentration between 2.5% and about 15%.

â– The final solution, if necessary, can be concentrated up to the desired value (between 5 and 30%) for example by means of a steam or hot water concentrator in heat pump 0 multi-stage evaporators.

â– The potash solution thus recovered can be stored for example in iron, PVC, PP, fiberglass, SS silos. The titer of the solution can be checked for example by acidimetric titration. At the controls, the following residues are highlighted; At 10-1000 ppm, Ca 10-300 ppm.

EXAMPLE 3

Procedure for the recovery of an exhausted NaOH bath - Specific Case

ANALYSIS OF THE EXHAUSTED SOLUTION

<â–> NaOH releases 15.5%

<â–> NaAI0215.18% (A! = 5%)

<â–> d = 1, 28

Note: The combined free NaOH content is therefore equal to 23%

PROCESS SEQUENCE:

1) PREPARATION OF THE â € œAâ € SOLUTION

2) CARBONATION AND PRECIPITATION REACTION AI (OH) 3

3) FILTRATION OF THE PRECIPITATE (MUD}

4) NaOH REGENERATION REACTION

5) RECONCENTRATION OF THE NaOH SOLUTION

1) PREPARATION OF THE â € œAâ € SOLUTION

* 1 Kg exhausted solution

<â–> 1 Kg H20 net

2) REACTION OF CARBONATION AND PRECIPITATION AKOHÌ?

Insufflation of CO2 according to the following reactions

2NaOH C02â € ”Na2C03 + H20

2NaA! 02+ C02 + 3H20 â † ’Na2CC> 3 2AI (OH) 3j (precipitate)

<â–> The reaction required, as per stoichiometry, a total of 126.5 grams C02 <â–> Reaction temperature 20 ° C

<â–> C02 pressure: 1, 5 bar

3) FILTRATION OF THE PRECIPITATE (MUD)

<â–> After filtration they measured themselves

Quantity of the sludge Î'Î ™ (ΟΗ) 2 (r.s. = 100%) obtained; 144,4 gr Quality of the sludge obtained; AI (OH) 38.5%

â– The filtered solution was then analyzed and found to contain exclusively:

Na2C03 286.47gr (13.56% against a theoretical of 15.2,%): yield 94%

Al (<10 ppm)

H20 difference at 2000g

NaOH REGENERATION REACTION

n Expected reaction

Na2C03Ca (OH) 2- + 2NaOH CaC034 (precipitated as sludge)

n Reaction conditions

<â–> Quantity of hydrated lime required: 212.8 gr

<â–> Reaction temperature: 80 ° ~ 90 ° C

â € ¢ Reaction time: 60â € ™

a Reaction results:

<â–> Amount of sludge (CaC03) obtained: 287.5 g (R.S. 100%)

<â–> Quality of sludge: (CaC0399.3%)

<â–> The solution reported in volume with distilled, filtered H20 was analyzed and found to contain:

NaOH 204.7 g (concentration 10.325%, against a theoretical 10.81%) yield 95% Al lower than 0.5%

H20 difference to 2000 gr

5) RECONCENTRATION OF THE NaOH SOLUTION

B Reaction conditions:

â € ¢ Concentration by evaporation

â € ¢ Temperature 100 ° C

â € ¢% evaporated 50%

n Result of the reaction

â € ¢ NaOH 201.5 g (20.15%) against theoretical of 20.4%) yield 97.7%

â € ¢ At less than 1%

â € ¢ Ca less than 1%

<â € ¢> Na2C03 residual: 1, 9%

â € ¢ H20 difference to 1000 gr

A) PRACTICAL RESULTS OF THE PROCESS:

n Quantity of reagents used;

- CG2 126.5 gr

- Ca (OH) 2 212.8 gr

a Quantity of sludge obtained

- From reaction 2 (Al (OH) 3): 144.4 gr

- From reaction 4 (CaCQ3): 287.5 gr

a Amount of regenerated NaOH

20.4% (with a yield of 88.6%)

n Regenerated NaOH quality

- Al, Calcium lower 1%

- Na2C03 residual 1.9%

to Final Yield

- Initial total NaOH; 23%

- NaOH after regeneration:: 20.15%

- Final yield: 88%

EXAMPLE 4

Procedure for the recovery of an exhausted KOH bath - Specific Case

ANALYSIS OF THE EXHAUSTED SOLUTION

<â–> KOH frees 15.5%

<â–> KAI0218.5% (Al = 5%)

-d = 1.28

Note ; The combined free KOH content is therefore equal to 32.2% PROCESS SEQUENCE:

1) PREPARATION OF THE â € œAâ € SOLUTION

2) REACTION OF CARBONATION AND PRECIPITATION AI (OH) a3) FILTRATION OF THE PRECIPITATE (MUD}

4) KOH REGENERATION REACTION

5) RECONCENTRATION OF THE KOH SOLUTION

1) PREPARATION OF THE SOLUTION â € œA

â € ¢ 1 Kg exhausted solution

â € ¢ 1 Kg H20 net

2) CARBON REACTION AND PRECIPITATION AKOHh Insufflation of CO2 according to the following reactions

2KOH C02â € ”K2C03 + H20

2KAI02C02 + 3H20 â † ’K2C03 + 2AI (OH) 31 (precipitate)

<â–> The reaction required, as per stoichiometry, a total of 84 grams C02â € ¢ Reaction temperature 20 ° C

<â–> C02 pressure: 1.5 bar

3) FILTRATION OF THE PRECIPITATE (MUD}

<â–> After filtration they measured themselves

Quantity of the sludge AI (OH) 3 (r.s, = 100%) obtained: 144.4 gr

Quality of the sludge obtained: AI (OH) 38.5%

* The filtered solution was then analyzed and found to contain only K2C03358gr {17.9% against a theoretical of 19.04%: yield 94%)

Al (<10 ppm)

H20 difference at 2000g

4) KOH REGENERATION REACTION

a Predicted reaction

K2CO3 Ca (OH) 2â € "2KOH CaC03i {precipitated as mud)

a Reaction conditions

<â–> Quantity of hydrated lime required: 200 gr

â € ¢ Reaction temperature: 80 ° ~ 90 ° C

<â–> Reaction time: 60 '

n Reaction results:

â– Amount of sludge (CaC03) obtained: 270 g (R.S. 100%)

<â–> Quality of sludge: (CaC0399.3%)

â– The solution reported in volume with distilled, filtered H20 was analyzed and found to contain:

â € ¢ KOH 305.9 g (concentration 15.2%, against a theoretical one of 16.1%) yield 95% â € ¢ A! less than 0.5%

<â–> H30 difference at 2000 gr

5) RECONCENTRATION OF THE KOH SOLUTION

a Reaction conditions:

â € ¢ Concentration by evaporation

â € ¢ Temperature 100 ° C

â € ¢% evaporated 50%

n Result of the reaction

<â–> KOH 299 g (29.9% against theoretical 30.59%): yield 97.7%) * Al lower than 1%

â € ¢ Ca less than 1%

â € ¢ K2C03 residual: 1.9%

* H20 difference at 1000 gr

A) PRACTICAL RESULTS OF THE PROCESS:

a Quantity of reagents used:

- C0284 gr

- Ca (OH) 2200 gr

n Quantity of sludge obtained

- From reaction 2; AI (OH) 3: 144.4 gr

- From reaction 4; CaC03: 270 gr

<Q> Amount of KOH regenerated:

- 29.9% (with a yield of 92.8%)

n Regenerated KOH quality:

- Al, Calcium lower 1%,

- K2C03 residual 1.9%

to Final Yield

- Initial total KOH: 32.2%

- KOH after regeneration: 29.9%

- Final yield: 92.8%

Claims (14)

CLAIMS 1. Process for the recovery of baths or exhausted alkaline solutions, coming from aluminum pickling reactions, which includes a first phase of: a) treatment of said bath or exhausted alkaline solution with carbon dioxide (C02), obtaining a first precipitate and a first solution, and a second phase of b) treatment of said first solution with oxides and / or hydroxides of divalent metals, obtaining a second precipitate and a second solution. 2. Process according to claim 1, characterized in that said pickling reactions include reactions for the treatment of extrusion matrices used in aluminum extrusion. 3. Process according to claim 1, characterized in that said baths or exhausted alkaline solutions are baths or exhausted solutions of caustic soda (NaOH) or caustic potash (KOH). 4. Process according to claim 1, characterized in that said metal is aluminum. 5. Process according to claims 3 and 4, characterized in that said first precipitate is aluminum hydroxide (AI (OH) 3) and said first solution is a solution of sodium carbonate (Na2C03) or potassium carbonate (K2CO3 ). 6. Process according to claim 5, characterized in that said oxides and / or hydroxides of divalent metals are CaO and / or Ca (OH) 2. 7. Process according to claim 6, characterized in that said second precipitate is calcium carbonate CaC03 and said second solution is a solution of soda (NaOH) or potash (KOH). 8. Process according to the preceding claims, characterized in that said first and second phases take place according to the following chemical reactions: 2NaOH C02- Na2C03 + H20 or 2 KOH C02-> K20O3 + H20 2NaA! 02+ C02H20 - â € ”Na2C03 2A! {OH) s or 2KAI02C02H20 - â € "* K2C03 + 2AI (OH) 3 Na2C03 + Ca (OH) 2â € ”â €” CaC03 + 2NaOH or K2C03 + Ca (OH) 2- â – ºCaC03 + 2KOH Na2C03 + CaO H20 - â € ”-â – ºCaC03 + 2NaOH or K2C03 + CaO H20 - â € ”* CaC03 + 2KOH 9. Process according to the preceding claims, characterized in that said first and said second precipitate are removed by filtration, 10. Process according to the preceding claims, characterized in that it comprises an initial dilution step and an optional step c) for concentrating said second solution 11. Process according to claim 10, characterized in that said dilution step takes place with water with a ratio from 1: 0.5 to 1:10 12. Process according to the preceding claims, characterized in that said bath or exhausted alkaline solution is a solution of soda NaOH or potash KOH in concentrations in soda or free potash comprised between 15 and 30%, the concentration of said first carbonate solution sodium Na2C03 or potassium carbonate K2C03 is between 0.7 and 40%, the reaction temperature in said second phase b) is between 40 and 100 ° C and the reaction time is between 10 minutes and three hours, obtaining said second NaOH soda or potassium KOH solution at a concentration of between 0.7 and 30%. 13. Use of said second solution as per the preceding claims for aluminum pickling reactions. 14. Use of said second solution as per the preceding claims for the treatment of extrusion dies used in aluminum extrusion.