DE2353528A1 - Treating waste gases to remove nitrogen- and sulphur oxides - without the formation of nitric acid derivs - Google Patents

Abstract

The gases are washed with an aq. soln. contg. as catalyst metal ions which are effective for the redox reaction between SO2 and N oxides. The metal ion which may have several valencies is pref. present in the lower valency form. The aq. soln. contains in addition a reduction medium for the metal ion and to maintain the metal ion at the lower valency, and a complexing agent for the metal ion. Pref. Fe, Fe scrap, Fe ore and/or Fe salts are added to the soln.

Description

Method for treating exhaust gases = The invention relates to a Process for the treatment of exhaust gases, in which exhaust gases, the oxides of sulfur and Oxides of nitrogen (hereinafter referred to as SO or NOx), with an aqueous one Catalyst systems are treated to effectively reduce the SO and NOx levels to diminish.

The problem of air pollution from toxic gases released into the Exhaust gases obtained from various incineration plants are present, as in the Exhaust gases from power-generating boilers and ordinary boilers are becoming more and more serious. Nitrogen oxides and sulfuric anhydride present in exhaust gases are the Main causes of air pollution. To remove SO2 have already been various methods applied in practice. For example, there is one procedure for adsorption of S02 on activated carbon and a method for absorption in alkali to mention. However, it is well known in the art that these methods are hardly effective in removing N0.

A method has been proposed in which an exhaust gas with a Precious metal catalyst is treated to convert NOx into nitrogen. According to a Another method was NOx in a ferrous sulfate solution with the formation of (FeSO4) NO absorbed and NO separated therefrom. To carry out this procedure you must However, considerably large amounts of catalysts or absorbents are used and these procedures are therefore very expensive to carry out. You are therefore for the treatment of exhaust gases that are emitted in large quantities, such as exhaust gases from Incinerators, not suitable.

It is therefore the main object of the invention to provide an economical process for the treatment to make exhaust gases accessible, which is particularly effective for removing nitrogen oxides and sulfur oxides from exhaust gases.

The invention is also based on the object of providing a method for Treatment of waste gases to create, in which sælpitric acid derivatives, their reuse or removal leads to certain difficulties, not be formed at all.

It is also an object of the invention to provide an economical process for the treatment of exhaust gases, to make accessible in the case of what is present in the exhaust gas gaseous sulfuric anhydride used as a reducing agent for nitrogen oxides and the required amount of the agent for treating nitrogen oxides is decreased.

The invention thus provides a method for treating Exhaust gas characterized in that an exhaust gas containing NOx and S02 is brought into contact with an aqueous solution containing metal ions which as a catalyst for the oxidation reduction reaction between NO and S02 for reduction of NOx to nitrogen and conversion of S02 into sulfuric acid are effective.

It was found that there is a possibility that -O1 by SO2 is reduced - which, like NO, is present in an exhaust gas. More precisely, the change in free energy aG in the reaction of the reduction of NOx (the NO and NO2) with SO2 in an exhaust gas is negative at all times, as in table le 1 is shown, and all reactions shown in Table 1 are thermodynamic Respect to the right.

It is therefore believed that NOx by SO2 in the presence of a suitable Catalyst can likely be reduced to N2 and it becomes a process for treating NO1 with the help of this reduction reaction accessible if a suitable catalyst is used.

Table 1 aG (kcal / mol) 0 2980k 6000k 1000k 502 + 1 / 2NO2 7 503 + 1 / 4N2 -23.33 -18.66 -12.48 802 + N02 z 503 + NO -8.40 -6.81 -4.69 502 + NO = SO, + 1 / 2N2 -37.46 -29.72 -19.47 802 + 2NO = S07 + 2 ° -33.41 -19.44 -0.94 802 + N20 7 SO, + N2 -41.50 -40.00 -38.01 In order to achieve the objectives set out according to the invention, the above reaction is carried out in an aqueous system in the presence of a suitable catalyst.

In the process according to the invention are used as a catalyst to carry out metal ions are used in the reaction between SO2 and NOj in an aqueous system.

With regard to the redox potential, below which a lower valence of an atom is converted into a higher valence of the atom, it was found that that the metal ions to be used according to the invention have redox potentials; the in essential in the Middle between the redox potential at which NO is converted into N2 and the redox potential at which 502 is converted into S03, lies.

It is possible to have a combination of a metal ion, its redox potential comes pretty close to the redox potential at which NO is converted into N02, and to use another metal ion, whose redox potential corresponds to the redox potential comes close, at which SO2 is converted to SO.

In these metal ions, the redox potential fluctuates at which one lower valency of the atom is transferred to a higher valency level, depending on the metal ion concentration and the pH, in general It is possible, however, to limit it. the redox potential characteristic of a metal ion can only be recognized on the basis of the standard redox potential of this metal ion. Some Metals, however, show no reactivity, even if their standard redox potential between the redox potential, at which NO is converted into NO2, and the redox potential, at which 502 is transferred to SO.

As metal ions with a standard redox potential between the Redox potential, at which NO is converted into N2, and the redox potential, at which 502 is converted into 803, which is to accelerate the reaction are capable of being preventive ions of copper, iron, nickel, nangan, chromium and tin used. These metal sons can be used for sdch or in combination will.

The introduction of these metal ions into the treatment solution can thereby take place that water-soluble inorganic compounds of these metals, metallic Bulk or powder or water-soluble organic compounds of these metals, such as OxalXe and Citrate, can be dissolved in water or added to water.

When raw materials of these metal ions are in the form of a metal mass or a powder, the metal is gradually dissolved in water, whereby a low atomic valence ion is formed, and this ion reacts with NO.

Therefore, if a metal paste or a powder is used, it is the loss of metal is far less than in the case where the metal is in shape a connection is released.

Furthermore, the metallic form has activity for the reduction of an ion, which has increased valence as the reaction progresses.

For example, iron is reduced in the following way: The metal ion is added to an aqueous solution in an amount of at least 0.01 Molll. When the amount of the net all ion is 0.009 mol or less, the metal ion is easily oxidized to a higher valence level by the oxygen present in the exhaust gas to be treated and loses its activity for reducing NO1.

The upper limit of the amount of metal ion is the maximum amount dissolved this metaI1ios.

When a gas containing NO1 and 502 is introduced into an aqueous solution containing such a metal ion, the following reaction occurs: NO + H2 ° + 2X + 7 1 / 2§2 + 2QPI- 20E + 2M + (n + 1) 5O2 + 2H2O + 2Mt (fl + 1) = EzS04 + 2 <+ 20H + 2R + 2E20 + NO + QO, + 1120 L-- i --- 71 / 2g2 + EaS04 (1) As can be seen from the above reaction formulas, sulfuric acid is formed as the reaction continues, which leads to a reduction in the pH. If the pH is lowered, the reaction can hardly proceed to the right and hydrogen ions in the solution are reduced by the metal to nascent gaseous hydrogen, which in turn reduces SO2 to hydrogen sulfide. Such a reduction in the pH value is therefore not preferred.

As explained above, when the pH is reduced, the reaction does not proceed towards the right without the presence of metallic ions can be added.

However, when this measure is applied, the running cost increases. It is therefore necessary to adjust the pH to a range using suitable methods set of not less than 5.

Further, when the pH exceeds 9, the metal ion becomes in shape of a hydroxide precipitated and the amount of metal cone needed to accelerate the desired response is effective is decreased. Even with a pH of 8, the formation of a hydroxide is observed, however, as the amount of precipitated Hydroxide is not so large, it is possible to continue the reaction. As above indicated, the lowering of the pH makes it difficult for the reaction according to of the above reaction formula (1). runs to the right.

It is therefore necessary to adjust the pH. The setting the pH can be done in a very simple way. For example, if scrap iron is added to the treatment solution, which has a reduced pH value, it reacts with sulfuric acid to 3 form iron sulfate, whereby the pH value Rr increases.

According to the invention, it is also important to check the valence of the metal ion keep at a lower value that is effective for speeding up the desired Reduction reaction is to increase the lifespan of the catalytic converter extend and the treatment process is economically advantageous to design. For this purpose, stabilizers for metal ions are suitable Amounts of reducing agents and / or complexing agents used. The implementation of NOX and SO2 can be achieved by adding a suitable amount of such a stabilizer to be further improved.

Substances can be used as reducing agents, the reducing Show effectiveness in the form of an aqueous solution without causing hydrogen formation to lead. For example, sulfites, hyposulfites, thiosulfates and the like can be used can be used.

It is sufficient if these salts are added in an amount which is required to reduce the metal ion, which is dissolved in water by the Oxygen has been oxidized.

If the salt is added in a larger amount, it will through the Presence of a larger amount of the salt effective as reducing agent none Caused disadvantage because it prevents the metal ion from being fed in Oxygen present in exhaust gas is oxidized and therefore cannot react with NOx.

In general, good results are obtained # when using these Salse be sugesetzt in an amount of at least 1 mole per mole of the metal ion.

Complexing agents to be used according to the invention are, for example, organic ones Acids such as citric acid, oxalic acid, tartaric acid and the like and their alkali metal salts to be mentioned, as well as ammonium salts, such as ammonium sulfate.

It is desirable that the complexing agent be one complex Ion that has a stability constant of at least 2. Any of the above listed complex-forming agent leads to a complex-xen ion with a stability constant of at least 2. Examples of combinations of metal ions as Catalyst and complexing agents and stability constants of the complex ions, which are formed from these combinations are listed in Table 2.

Table 2 Stability constants of complex ions of catalyst complexing Medium (metal ion) citric oxalic ammonium acid sulfate iron (Fe ++) 15.5- 18.5 4.0 copper (Cu ++) 12.0 8.9 2.3 manganese (Mn ++) 8.0 4.1 2.3 nickel (Ni ++) 9.0 8,5 2,3 These complexing agents react with metals to form more stable Complex ions. These complex ions are replaced by those present in the treatment solution oxidizing ions are not oxidized and become stable in the lower valence level held.

This way the reactivity of the metal can be opposite N ° x can be increased and therefore the effectiveness of the response will be improved.

Since the amount of the ion in the lower valence level also is greater when the supplied amounts of NO and 502 are constant, the reaction can be carried out with the aid of the catalyst for a long period of time.

The complex-bound metal ion is converted into a complex, in which the valence of the metal ion is increased by reacting with EJO. This The complex of the metal ion in the higher valence level becomes the oxidation of SO2 is used and thereby, the valence of the metal ion to the original lower Significance level reduced. Since the oxidation of 502 does not progresses until the conversion of S02 to S03 has reached 100%, the metal ion accumulates in the higher valence level gradually increases in the treatment solution; the However, the degree of accumulation is reduced by adding the complexing agent It is sufficient if the complexing agent is added in an amount which is sufficient to convert the metal ion into a complex. Good results can therefore can be achieved when the complexing agent in a larger amount than the equivalent amount is added to the metal ion. Since there is no particular disadvantage the removal of NO is caused even if the metal ion is precipitated to some extent it is sufficient to add the complexing agent in an amount of at least 0.7 up to 0.8 equivalents, based on the metal ion, to be added.

As explained above, according to the invention, the rate of Removal of NO can be greatly improved if a complexing agent specified above Agent is added, and the life of the catalyst can be extended, when the treatment is carried out in a continuous process.

The invention will hereinafter be described in more detail by way of examples explained.

Example 1 Under the conditions listed in Table 3 below was a combustion gas with the help of 60 ml of an aqueous solution of a copper, Nickel, iron or manganese salt treated.

The combustion gas was introduced into the aqueous solution. The one with it The results obtained are shown in Table 3.

T a b e l l e 3 Ver Catalyst (Mol / l) Tempera- To treat- Feed- NO reduction precipitation seeks the deformation rate no. Handling solution Gas * rate d. (%) Gas (1 / min) 1 CuSO4 (0.5), Fe-Gra- room temperature 1 0.2 77 - 88 not benalia (0.25) observed 2 FeSO4 (0.5) 60 ° C 2 0.2 60 - 80 observed 3 NiSO4 (0.05 room temperature 1 0.2 30 - 35 not observed 4 NiSO4 (0.5) room temperature 2 0.2 35 - 40 not observed 5 CuSO4 (0.5) room temperature 2 0.2 65 - 80 not observed 6 Fe granules (0.5) room temperature 1 0.2 60 - 70 observed 7 Mn (NO3) 2 (0.05) 60 ° C 2 0.2 30-40 observed 8 MnSO4 (0.5) 60 ° C 2 0.2 30-40 observed 9 CrSO4 (0.4) room temperature 1 0.2 30 - 40 not observed 10 SnSO4 (0.2) room temperature 1 0.2 40-50 observed 11 Sn granules (0.2) room temperature 1 0.2 40-60 observed * 1: 450 ppm NO, 2200 ppm SO2, 3.0 volume percent O2, 96.7 volume percent N2; 2: 500 ppm NO, 1500 ppm SO2, 3.0 percent by volume O2, 12.5 percent by volume CO2, 84.3 percent by volume N2.

Sulphates were used in most of the foregoing experiments. This is because the reaction product in the above treatment was a sulfate and therefore the metal ion was used in a form that corresponds to the reaction product corresponded.

The invention is explained below with reference to the drawings.

FIG. 1 denotes a graphic representation which shows the relationship between the NOx reduction rate and the SO2 concentration at the outlet of an exhaust gas treatment device and the duration of treatment.

Figure 2 shows a curve showing the spectrophotometric absorption of the exhaust gas before entering the exhaust gas treatment device and after exiting made clear from this device.

Figure 3 is a graph showing the relationship between the NOx reduction rate and the treatment time in an example and comparative example.

Figure 4 is a graph showing the relationship between the NOx reduction rate and the treatment time in another example and comparative example shows.

Figures 5 and 6 show flow diagrams, the apparatus systems for Represent the regeneration of the used treatment liquid.

The change in the rate of NO reduction over time, which in Experiment 1 was observed is shown in FIG.

The graph in Figure 2 illustrates the percentage Absorbance at each wavelength measured using a spectrophotometer and was obtained in the measurement of a treated gas obtained by treatment of a gas containing 1% NQ according to Experiment 1 was obtained. From the in figure 2; it can be seen that NO was substantially selectively reduced to N2 and 802 in sulfuric anhydride, was converted by the analysis of the gas composition »according to the Treatment was found to be the concentration of gaseous sulfurous anhydride at the exit of the reaction tube compared to the original concentration by one The amount decreased almost equal to the amount decreased during the treatment NO was (450 ppm).

As can be seen from the results shown in FIG the rate of reduction of NOX suddenly decreased when the supply of SO2 was interrupted. It is therefore easy to understand that according to the invention actually SO present in an exhaust gas is used as an agent for reducing NOx and that therefore the removal of SO takes place simultaneously with the removal of NOx can.

Example 2 A combustion gas was produced in the same manner as in Example 1 treated using 60 ml of an aqueous solution containing the metal salt catalyst contained a reducing agent.

The results are shown in Table 4. The gases to be treated 1 and 2 were the same as in Example 1.

T a b e l l e 4 Ver Catalyst (Mol / l) Tempera- To treat- Feed- NO reduction precipitation seeks solution for the rate of deformation no. Handling solution Gas * rate d. (%) Gas (1 / min) 1 CuSO4 (0.05), room temperature 1 0.2 70 - 80 observed Na2SO3 (0.25) 2 CuSO4 (0.05), Na2SO3 (0.5) 60 ° C 2 0.2 60 - 95 observed 3 CuSO4 (0.05), Na2SO3 (0.5) 60 ° C 1 0.2 60 - 80 observed 4 FeSO4 (0.5), Na2SO3 (0.5) 60 ° C 1 0.2 40 - 50 observed 5 FeSO4 (0.5), Na2SO3 (0.5) room temperature 1 0.2 70 - 80 observed 6 NiSO4 (0.5), Na2SO3 (0.5) 60 ° C 2 0.2 50 - 60 observed 7 MnSO4 (0.5) Na2SO3 (0.5) 60 ° C 2 0.2 60 - 70 observed As from the in table As can be seen in the results shown in FIG. 4, the rate of NO reduction can be increased by adding a reducing agent can be improved. Because some reducing agents at high Temperatures are decomposed, is preferred when using such reducing agents, the reaction at a temperature below the decomposition points of these reducing agents perform.

Example 3 A combustion gas was obtained with the aid of 60 ml of an aqueous Solution of metal ions as a catalyst treated in the same way as in Example 1. To check the influence of the metal ion concentration on the rate of NG reduction, the metal ion concentration was varied in the manner shown in Table 5. The results are shown in Table 5. As the gas 1 to be treated, it became the same Gas used as gas 1 in example 1.

T a b e l l e 5 Ver Catalyst, Concentra- Tempera- To treat- Feed- NO reduction precipitation search in treatment of the loading change rate No. Solution solution gas * rate d. (%) (Mol / l) gas (1 / min) 1 CuSO4 (0.01) Room temperature 1 0.2 30 - 40 not observed 2 CuSO4 (0.05) "1 0.2 65 - 80 not observed 3 CuSO4 (0.1) "1 0.2 70 - 80 not observed 4 CuSO4 (0.5)" 1 0.2 70 - 80 not observed 5 CuSO4 (1.0) "1 0.2 70 - 80 not observed 6 Fe granules (0.01) "1 0.2 60-70 observed 7 Fe granules (0.05)" 1 0.2 60-70 observed 8 Fe granules (0.1) "1 0.2 60 - 70 observed 9 Fe granules (0.5)" 1 0.2 60 - 70 observed 10 Fe granules (1.0) "1 0.2 60 - 70 observed 11 NiSO4 (0.01) "1 0.2 10 - 20 not observed 12 NiSO4 (0.05)" 1 0.2 30 - 35 not observed 13 NiSO4 (0.1) "1 0.2 35 - 40 not observed 14 NiSO4 (0.5)" 1 0.2 35 - 40 not observed 15 NiSO4 (1.0) "1 0.2 40 not observed 16 MnSO4 (0.01)" 1 0.2 15 - 20 observed 17 MnSO4 (0.05) "1 0.2 30 - 40 observed 18 MnSO4 (0.1)" 1 0.2 30-40 observed 19 MnSO4 (0.5) "1 0.2 30-40 observed 20 MnSO4 (1.0)" 1 0.2 30-40 observed As from the results obtained in Example 3 As can be seen, the tendency of the metal ions used as the catalyst became observed that the reactivity in the order copper ions, metallic iron, Iron ions, nickel ions and manganese ions are reduced. In terms of the crowd of the catalyst, the tendency was observed that at a lower concentration of the metal ion, the life of the catalytically active aqueous solution is short, which is probably due to the fact that the metal ion is through the oxygen, which is present in the gas to be treated, to an ion of a higher one Valence level is oxidized. When copper was used as a metal ion, and a Gas containing 500 ppm NO and 2200 ppm SO2 passed through at a rate of 200 cm3 / min 200 cm3 of an aqueous solution with a concentration of 0.01 mol / l was passed, the life of the treatment solution was 4 hours (the total amount of reduced NO was 0.6 mol). However, when a treatment solution having a concentration of 0.5 Mol / L was used in the same amount, became the life of the treatment solution extended to 16 hours (the total amount of reduced NO was 2.1 moles).

In particular, in the case of a metal such as iron, the metal becomes first converted into an ion of the lowest valency level and then the valency level gradually increased. An ion in a low valence level therefore takes directly participate in the reaction with NO and, as a result, the life of the treatment solution compared with a treatment solution that contains iron only in ionic form Contains shape.

Example 4 A hard glass reaction tube with an inside diameter of 30 mm and a length of 150 mm was treated with 150 mm of a treatment solution charged composition given below.

A combustion gas that contains 500 ppm NO, 1500 ppm SO2, 3.0 percent by volume Q2 and 12.5 percent by volume of C02 and the remaining proportion N2, was in a Rate of 200 ml per minute with this Treatment solution in contact brought about the results given below were obtained.

Treatment solution: 0.5 mol / 1 FeSO4.7H2O, 0.5 mol / l Fe (mild steel), 1.0 Molil sodium citrate Contact temperature: 60 ° C NO reduction rate: 80 - 100% Die Results of this example are illustrated more specifically in Figure 3 in which the Curve 4 shows the results obtained by treating both NO and SO2 containing gas were obtained, and curve 3 shows the results of the comparative experiment shows in which a gas free of SO2 was treated. As shown in Figure 3 As can be seen from the results shown, the NO reduction rate is excellent low when SO2 does not coexist with NO.

Comparative Example 1 The treatment was carried out under the same conditions as in the example, with the modification that the composition of the treatment solution and the contact temperature was changed in the manner described below.

Treatment liquid: 0.1 Molil Fe (powder) Contact temperature: 55 ° C, N reduction, rate: 60 - 72 ffi (formation of precipitation) In comparison with the results obtained in Example 4, in this comparative example, in which no complexing agent was used, the NO reduction rate is lower example 5 The treatment was carried out under the same conditions as in Example 4, with the modification that the composition of the treatment solution is in the following was modified in the manner indicated.

Treatment liquid: 0.05 mol / l copper sulfate, 0.1 mol / l oxalic acid Contact temperature: 60% NO reduction rate: 83-90% Example 6 The treatment was carried out under the same conditions as in Example 4, with the modification that the composition of the treatment solution and the contact temperature ir R @ below have been modified in the manner specified.

Treatment liquid: 0.05 Molll CuSO4, 0.10 Molil Na2S03, 0.50 Molil ammonium sulfate Contact temperature: 25 ° C NO reduction rate: 80 - 90% Example 7 The treatment was carried out under the same conditions as in Example 4, with the modification that the composition of the treatment solution in the following was modified in the manner indicated.

Treatment liquid: 0.1 mole NiSO4, 0.5 mole ammonium sulfate Contact temperature: 60 ° C NO reduction rate: 60 - 75 k.

Example 8 A gas containing 500 ppm NO, 1500 ppm SO2, 3.0 percent by volume O2 and 12.5 percent by volume CO, and the remaining portion contained N2, was in one Rate-of 200 ml per minute brought into contact with a treatment solution, the Contained scrap iron and ferrous sulfate. The experiment was carried out with or without the addition of Sodium citrate performed as a complexing agent. The change in the NO reduction rate in the course of time is shown in Figure 4, in which curve 5 shows the results obtained in the experiment in which the complexing agent of the treatment solution was added. Curve 6 shows the results obtained in the experiment without the addition of a complexing agent to the treatment solution. As from the in Figure 4 shows the results shown, the NO reduction rate during can be kept at a high value for a long time when the treatment solution is on complexing agent is added than in the case of a complexing agent free treatment solution.

By adding a complexing agent to the treatment solution the catalytic life of this treatment solution can be extended.

The regeneration of the used treatment solution is as follows with reference to FIGS. 5 and 6.

Figure 5 illustrates an embodiment in which the consumed Treatment solution is regenerated by passing through an iron packed layer is directed. An exhaust gas is introduced into a reaction column 12 through a vent 11 and nitrogen oxides are reduced in this reaction column 12. That from the The gas coming from the reaction column is heated with the aid of a sewage burner 17 and through a chimney 18 discharged into the atmosphere 19. The circulated Treatment solution does not contain any deposits in the first stage; with advancing However, the reaction results in the formation of deposits.

The deposits are removed with the aid of a separator 13 and the treatment solution is introduced into a column 15 with the aid of a pump 14, which is loaded with iron. The filled column 15 becomes water from a tank 16 fed. While the treatment solution is passed through the filled column 15 part of the iron in the treatment solution dissolves and forms ferrous ions (Fe + 2). The treatment solution, which will thus contain the freshly formed Fe + 2 introduced again into the reaction column 12 with the aid of a pump 14 'and for reduction used by NOx.

Figure 6 illustrates another embodiment of the regeneration a treatment solution in which the ferric ion formed in the treatment solution (Be + 3) is reduced to Fe + 2 with the aid of an electrolytic cell 23. An exhaust becomes Introduced from a vent 11 into a reaction column 12, in which the gas with a Treatment solution is brought into contact and treated as in that in Figure 5 'shown embodiment. The gas is then discharged through a chimney 18. The treatment liquid coming from the reaction column 12 is fed into the electrolytic cell 23 initiated in which Fe + 3 is converted into Fe + 2. The treatment solution, which contains the iron ions reduced in this way, is again with the aid of a pump 14 in the Reaction column 12 introduced and used to reduce NOx.

Claims (8)

P A T E N T A AN S P R tt-.C H E 1. Process for removing toxic substances from exhaust gases by Treatment of exhaust gases that contain sulfur dioxide and oxides of the stick, toff-s, with an aqueous solution containing metal catalysts, thereby g e k e n n z e i c h n -e t, - 'that the treatment of the exhaust gases with the help of an aqueous solution performs the -a as a catalyst for the redox reaction, between sulfur dioxide and nitrogen oxides contains active metal ion. 2. The method according to claim 1, characterized in -g e k e n n'z e i e h -n e t that one .the treatment of the exhaust gases is carried out with the aid of an aqueous solution, the one ion of a metal, which can be present in several valency levels, contains in the lower valence level. 3. The method according to claim 2, characterized in that g e k e n n z e i c h -n e t that the aqueous treatment solution also a reducing agent in a Amount added, -the reduction of the metal ion and for transferring and holding the Metal ions in the lower valence level is capable. 4. The method according to claims 1 to 3, characterized in that g e k e n n -z e i c h n e t that one, the aqueous treatment solution, a complexing agent in adds to an amount that is too much to convert the metal ion into one Transfer complex. 5. The method according to claims 1 to 4, characterized in that g e k e n n -z e i c N e t that one of the aqueous treatment solution, iron, scrap iron, iron ores and / or adding iron salts. 6. The method according to claims 1 to 4, characterized in that g e k e n n -z e i c It does not mean that at least one metal ion is used in the aqueous treatment solution which adds ions of iron, copper, nickel and manganese. 7. The method according to claims 1 to 6, characterized in that g e k e n n -z e i c n e t that at least one of the compounds citric acid, Oxalic acid, tartaric acid, their alkali metal salts or ammonium sulfate are added. 8. The method according to claims 2 to 7, characterized in that g e k e n n -z e i c It should be noted that the reducing agent used is at least one sulfite, hyposulfite and / or Thiosulfate used. L e r s e i t e