DE2456058A1 - PROCEDURE AND ARRANGEMENT FOR THE PROCESSING OF PICKLING SOLUTIONS, CONNECTED TO IRON PICKLING, IN A CIRCUIT OR IN Batches - Google Patents

Description

DR. STEPHAN G. BESZEDES PATENT ADVOCATE

806 DACHAU near MÖNCHEN

BOX 1168

AM HEIDEWEG 2

TELEPHONE: DACHAU 4371 Postal checking account Munich 1368 71 Bank account no.SO 637 at the district and city Sparkasse Dachau-Indersdorf

P 758

Description u η g

for patent application

LICENCIA OJALiLMANrOKAO? ERTEKESI TO * VALLALAO?

Budapest, Hungary

concerning

Procedure and arrangement for iron pickling associated processing of pickling end solutions carried out in a cycle or in batches

The. The invention relates to a method for in the circuit or Batch-wise electrochemical processing of final pickling solutions containing sulfuric acid (hereinafter also called final pickling called) as well as an arrangement for the implementation of this procedure

In the sulfuric acid removal Iron oxides or descaling of semi-finished products

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~ ² ~ 24560 & 8

relationship as semi-finished iron and steel industry, for example, sheets, strips, wires or profile bar forms. Iron sulfate, which can be removed from the final pickling solution by cooling the solution or by vacuum crystallization in the form of iron sulfate heptahydrate (PeSO ^. 7 HgO). Since the pickling speed decreases with the decrease in the sulfuric acid content of the pickling solution, the final pickling always contains unused or unused acid in an amount of at least 20 to 30 g sulfuric acid / l (even in the so-called "completely stripped" state). The concentration of the residual acid can, however, depending on the pickling procedure, reach the order of magnitude of 100 g / l and even exceed it. To increase the pickling rate, in practice the aim is generally to increase the acid concentration; this avoids the total depletion of the sulfuric acid, i.e. the so-called exhaustion of the bath. The performance or productivity of the pickling plant increases proportionally to the pickling speed.

However, there is a limit to this endeavor, namely by the fact that the increase in the acid content of the final pickling increases proportionally to the acid loss, i.e. the amount of acid added to the pickling but which is removed from this unused and thus the effort associated with the pickling. For the same reason, environmental protection problems arise to an increased extent, since the discharge of the acidic end solutions is strictly forbidden by the water law provisions. If the final pickling solution is neutralized with lime, as is often the case in practice , the effort and the difficulties of this measure also increase proportionally to the acid content of the final pickling. Another disadvantage of the treatment with lime is that the neutralization reaction is heterogeneous and therefore there is also at a Kalküberschuß not guarantee the complete neutralization of the acid. In addition, the hand

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handling, transport and storage of the lime sludge ' cumbersome and time-consuming; in the course of these operations there is no benefit (for example in the form of chemical recovery) a.

The process known in technical or industrial practice for working up 'sulfuric acids Final pickling consists in the separation of the iron sulfate heptahydrate by vacuum crystallization. The acid concentration of the final stain is determined by the dehydration caused by the Water of crystallization and vacuum evaporation occurs, increases; As a result, the 'solution can be used again for pickling will. The further spread of this process is due to the fact that the utilization of the iron sulfate heptahydrate runs into difficulties due to lack of demand and therefore most of the salt is dumped, that is Ultimately, the problem of environmental pollution. not being resolved is prevented.

Realizing these facts resulted in the last two. Decades the researchers more and more with the elaboration of technical solutions that not only recover the acidity of the final stain, but also enable the reconversion of iron sulphate into sulfuric acid. As the basis of such Solutions can be the electrochemical decomposition of iron sulfate in aqueous solution, which in the sense of the reaction equation

FeSO ₄ + H ₂ O> Fe + H ₂ SO ₄ + 0.5 O ₂

going on, serving. During this reaction, an amount of iron equivalent to the sulfuric acid formed is deposited on the cathode from the solution.

However, the realization of the electrochemical reaction represented by the above reaction equation is made by

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the fact that the iron from acidic solution can only be cathodically deposited with poor efficiency, prevented. With the increase in the acid concentration, the iron deposition becomes less and less and ultimately completely impossible. because at the cathode, instead of iron deposition, hydrogen is generated.

In this way, instead of the electrochemical decomposition of the iron sulfate by electrolysis, the electrochemical decomposition of water takes place in the end result. The known processes therefore all have the purpose of limiting the decomposition of water. The cathodic hydrogen evaporation can be limited, for example, by using a flowing mercury electrode. The iron can also be deposited from acidic solution in the form of an amalgam at this cathode. The iron is then anodically deposited from the amalgam in a separate room. If an acid-free medium is used, the iron is already deposited on a solid cathode. Such a procedure is of i ¹ . Aigner and G. Jangg in the Berg- und Hüttenmännische monthly notebooks 1969, pages 12 to 18 under the title "Electrolytic processing of used sulfuric acid pickling solutions". Since then the iron has to be deposited twice and the mercury electrode can only be operated in a horizontal arrangement and on one side, the corresponding device is disproportionately space-consuming and expensive. The high price of mercury drives up the already considerable investment costs and it is also known that in all processes using mercury cathodes, the production costs of the end product are burdened by substantial mercury losses. In the cited publication it is recognized by the authors themselves that the economic viability of the process can be questioned, and limit values of

509822/0926 " ⁵ "

12.5 "to 1315 kWh / kg Fe. Similar objections can also be raised against other methods based on the use of a mercury cathode. This also comes from the publication by AT Kuhn ¹¹ A Review of the Hole of Electrolysis in the Treatment of Iron Pickle Liquor "in Iron and Steel, June 19,71" pages 173 to 176. This publication also provides valuable information for an overview of the state of the art in other respects, namely in that the authoritative literature sources are compiled in it according to the effects on which the respective solutions are based and the various processes are compared with one another in an objective and judgmental manner.

The methods based on the use of permeability-selective or permselective membranes have also been investigated by many researchers. The essence of these processes is that the migration of the hydroxonium cations (H ^ O ⁺ ) to the cathode is prevented by means of a so-called ion exchange membrane placed between the anode and cathode spaces. The high electrical resistance of the membranes, their sensitivity to heat, acid and mechanical influences as well as their short service life and the associated high expenditure prevented the spread of the methods based on their application despite the promising laboratory results. In this regard, apart from the above-mentioned work by AT Kuhn, the publication "Treatment of Iron Containing Spent Sulfuric Acid by Electrolytic Dialysis" by the Japanese authors Tamurs and Ishio in Kogyo Kagaku Zseashi 59 (1966), 1 435 and the work "Separation of Iron Spent Sulfuric Acid by the Ion Exchange Resins "by the same authors along with co-authors (loc. Cit.) Attention;

Another possibility is to use the method based on bipolar active lead electrode

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to imagine. In this process, in the aqueous solution of the Iron sulphate with simultaneous cathodic iron deposition. Formed anodic lead sulfate and this in a separate Space cathodically reduced to lead, producing sulfuric acid. Prerequisite for using this procedure is, however, that the iron sulfate solution fed to the electrifying device is neutral. Therefore, the procedure for Processing of acidic final stains cannot be used immediately, but only after they have crystallized out beforehand and then redissolving the iron sulfate heptahydrate (J. Kerti: "Az active olomelectrod felhasznalasi lehetosege az elektrokesmiai iparban "(« 'Possibilities for application the active lead electrode in the electrochemical industry ") in MTA Kemiai Oszt. Közl. 2 £ [i956], 251 to 281, U.S. Patent 3,111,468 and British Patent 992

The same condition (absence of acid) is applied to the composition in the method according to Hungarian patent specification-156 806 the final stain. In this process, the anode compartment is separated from the cathode compartment by a diaphragm Sulphate ions in excess, based on the molar amount of sulfuric acid, which is preferably in the form of ammonium or an alkali sulfate are added, is present. The excess sulfate ions push the second dissociation stage the resulting sulfuric acid back in such a way that most of the protons of the sulfuric acid are in the form of HSO ^ anions is present, which due to their negative charge (resulting from their anionic character) are prevented by the To migrate through the diaphragm into the cathode compartment. The pickling solution is fed to this, but only then is possible when the solution is completely exhausted in terms of acid. If this precondition is not met, then as also pointed out in Hungarian patent specification 156 806, "the salt by known procedures (Crystallization or thermal decomposition) from the pickling

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Λ-

• solution removed and added to the catholyte. "

The invention is based on the object of a with diaphragms working method for the processing of pickling end solutions of iron pickling, through which in a simple manner without requiring a large amount of space and effort, as well as the other disadvantages of the prior art methods mentioned above the iron sulfate of the same is electrolytically decomposed to sulfuric acid and this can be isolated for reuse, without making the final pickling solution acid-free or exhausting its acid content or the iron sulfate heptahydrate crystallize out to have to, as well as to create an arrangement for the implementation of this procedure.

The investigation of the problems outlined above led to the finding that the electrochemical decomposition of the iron sulphate can advantageously be combined with the isolation of the acid and sulphate salt content of the final pickling solution if an ammonium sulphate, magnesium sulphate and / or alkali metal sulphate concentration of 0 is added to the final pickling solution , 5 to 1.0 mol / l is set, the acid content of the final pickling solution is exhausted to 100 g IL ^ SO ^ / l or a value below that, the final pickling solution in the cathode compartment of a cathode and The electrolyzer assembly having anode compartments is introduced and allowed to flow back through the cathode compartments of the electrolyzer cells of the electrolyzer assembly, the iron content of the solution being ^{exhausted to values of 7 to 15 g Fe +} Vl, then the solution is passed into the anode compartment of the electrolyzer assembly and through the Anode compartments of the E Electrolysis cells of the electrolysis arrangement are allowed to flow through in the same direction as the direction of flow maintained in the cathode compartments, the current density, based on the area of the diaphragms, being adjusted to 15 to 22 A / dm ² by voltage regulation and the working temperature

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The temperature of the electrolysis is set to 70 "to 90 ⁰ C by regulating the flow rate of the cooling water.

The subject of the invention is therefore a process for the recirculation or batch processing of final pickling solutions with a content of at most about 100 g sulfuric acid / l and at least 25 g iron ions / l by combining an electrolytic decomposition of the iron sulfate and an electrodialytic isolation of the Acid and sulphate salt components of the pickling solution in an electrolysis cell with anode and cathode compartments separated from one another by a diaphragm with addition of bisulfate-forming salts, the pickling solution being fed to the cathode compartment of an electrolysis cell, which process is characterized in that in the pickling solution by the Salt addition of ammonium sulphate, magnesium sulphate and / or alkali metal sulphate (■■ · ;. ■ filtration set from 0.5 to 1.0 mol / l and the final pickling solution to the cathode compartment of an electrol made up of cathode and anode compartments separated by diaphragms The electrolyzer assembly built up by the electrolyzer cells is supplied and allowed to flow through the cathode ^{spaces of the electrolyzer cells of the electrolyzer assembly, during which the iron content of the solution is exhausted by cathodic deposition to values of 7 to 15 g Pe ++} / 1, whereupon the solution is passed into the anode space of the electrolyzer assembly and flowing through the anode spaces of the electrolyzing cells of the electrolyzing arrangement in a direction identical to the direction of flow maintained in the cathode spaces, the current density, based on the area of the diaphragms, being at values of 15 to 22 A / dm and the working temperature of the electrolysis at values of 70 to 90 ⁰ C is kept.

By adhering to the above conditions, continuous working methods can be used in the stationary

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Equilibrium of the energy system one for the acid, the Iron sulfate and the bisulfate-forming additional salts are equally favorable gradual concentration distribution and as the consequence of which in the cycle is repetitive, beneficial transport processes and electrochemical ion exchange chain processes caused by the diaphragm. By realizing the electrochemical ion exchange do not need any requirements regarding the diaphragm the permeability selectivity.

The expression "batch work-up" is to be understood as meaning that the pickling solution from the The pickling plant can be removed and continuously regenerated via an intermediate tank.

This is because it is not, depending on the type of pickling plant always possible, the pickling plant continuously removes the used pickling solution and the product of the regeneration can also be continuously returned to the pickling plant and thereby create a closed cycle. In this case, the method of the invention is expedient carried out with the interposition of larger intermediate storage containers.

The decisive advantage of the method according to the invention consists in the fact that for its application a complete exhaustion of the acid content of the pickling solution or The iron sulfate heptali hydrate does not need to crystallize out is. This enables the regeneration of the final pickling solution to be carried out directly and in the circuit, even in Cases in which they contain up to about 100 g ILjSO (about 1 mol HgSO ^ / l) contains.

Appropriately, the volume speed of the im Circulation moving solution the current efficiency ', the' number

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of the electrolysis cells and the current intensity proportional, however, the difference in acid concentration between the solution leaving the electrolysis system and the solution entering it set inversely proportional and, in the event that the one in the last cathode compartment of the Electrolyzer cell series leaking solution measured pH is less than 1.8, the flow rate decreased, and if it is over 1.8, the flow rate increased ..

According to an expedient embodiment of the process according to the invention, the iron ions of the final pickling solution become Sheet iron cathodes are deposited and the cathode sheets, which have become thicker due to the deposition, are removed from time to time and replaced by new sheets.

The question of whether ammonium sulfate is used as a bisulfate-forming additive or another sulfate is used, has no effect on the efficiency, provided that only the molarity of the additional salts is the same in each case in the final pickling solution. Regarding the structure of the cathodically deposited iron, the type of the cation of the additional salt is of great importance.

If ammonium or magnesium sulfate or combinations of these two salts are used, then a smooth cathode coating with leaf respectively Plate structure preserved. So if a cathode product that can be processed into blocks is to be obtained, then the above-mentioned Additional salts used. In this case, the cathode sheets, the thickness of which was increased by the deposition, from time to time exchanged for new sheets (iron base sheets). The cathode sheets removed from the solution are refurbished by melting down, for example for alloys or castings

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When using sodium or potassium sulfate or, if necessary, a combination of these two salts, a coherent, not very shiny, but rather matt coating is obtained on the cathodes of the electrolyzing cells located at the beginning of the electrolyzing cell row. At the end of the row of electrolysis cells or, more precisely, from where the iron content in the cathode ^{compartment has dropped to a maximum of 25 g 3? E ++} / l and the molarity of the additional salt is greater than 1, the iron is deposited in powder form on the surface of the cathodes. In view of the significant demand, the production of iron powder is in itself of great practical importance, but especially in the present case, in which the extraction of iron powder is connected with the pickling process, the recovery of the final pickling and the solution of environmental protection problems.

According to a particularly advantageous embodiment of the process according to the invention, a sodium sulfate and / or potassium sulfate concentration of 0.5 to 1.0 mol / l is therefore used to combine the electrochemical work-up of sulfuric acid-containing final pickling solutions with the production of cathodic iron powder in the final pickling solution as an alkali metal sulfate concentration of 0.5 to 1.0 mol / l 0.5 to 1.0 mol / l are maintained and in the ^{catholytes or catholyte part containing at most 25 g]? E ++} / l aluminum, lead or graphite electrodes, from the surface of which the iron powder layer deposited on it is removed from time to time, submerged. In this way, the iron powder can easily be removed from the electrodes, which are occasionally lifted out of the solution, by being thrown off or by chipping or brushing. (If iron electrodes were used, the deposited particles would adhere more strongly to the sheet metal).

Should the total iron content of the final stain be in the form of Iron powder are obtained, then a pickling process

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Technique in which the iron content of the final pickling ^{does not exceed 25 g Fe +4} Vl and the acid content is less than 20 g / l. These conditions can be met in systems working with open pools.

The invention also relates to an arrangement for carrying out the method according to the invention, which is carried out by Cathode and anode compartments connected in series, staggered in steps and separated from one another by diaphragms 'having electrolysis cells, the diaphragms made of a base, acid and temperature resistant and advantageously consist of dense tissue and for conveying the solution from the cathode or anode compartment one electrolysis cell in the cathode or anode compartment of the next electrolysis cell in each electrolysis cell a level-regulating overflow is installed, is marked.

According to an advantageous embodiment of the arrangement according to the invention, this is designed so that in the individual Electrolyzing cells cathode and anode compartments alternately follow one another, these cathode and anode compartments each through a diaphragm are separated from each other and the cathode spaces below each other and the anode spaces through Holes in the wall of the electrolysis cell are connected to one another. This allows the catholyte and the anolyte to be independent flow from each other.

Advantageously, within the individual electrolysis cells, the cathodes and anodes are electrically connected in parallel to one another, but independently of one another, to the collecting busbar. In this way it is possible to raise any cathode independently of the other cathode from the liquid.

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For the production of iron powder in the manner already described .sind in the arrangement according to the invention at the beginning of the electrolysis cell row, sheet iron cathodes and at the end of the electrolysis cell row (more precisely: from the electrolysis cell in which the iron concentration is no more than 25 g / l) aluminum, lead or Graphite cathodes attached.

The chain of electrochemical ion exchange reactions and the mechanism of the gradual distribution of concentrations are explained in more detail on the basis of the following exemplary presentations in conjunction with the accompanying drawings.

The acid concentration of the pickling solution, which _{flows through the pickling basins P ^,, Pp ... P n} , decreases from basin to basin due to the pickling reaction and its iron concentration also increases from basin to basin as a result of the pickling reaction. The concentration of the bisulphate-forming additional salts (ammonium, magnesium and / or alkali sulphates) remains constant within the pool row. The final pickling agent is fed at constant speed to the cathode compartment of the electrolysis cell E ^, from where it flows through _{the cathode compartments of the cells Ep ... E n in sequence.} The iron is deposited on the cathode; this cathode process is accompanied by the evolution of hydrogen, depending on the acid concentration of the catholyte. The other part of the acid content of the final pickling agent migrates in the form of HSO ^, ~ ions through the diaphragm into the anode compartment. At the same time, the cations of the added sulfates migrate from the anode compartment through the diaphragm into the cathode compartment.As a result, the iron and acid concentration of the solution decreases as it flows through the cathode compartments of the electrolysis cells, from electrolysis cell to electrolysis cell, whereas the concentration of the bisulfate-forming additional salts of the electrolysis cell to elec-

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trolyzing cell increases. The process can essentially be summarized as follows: Through the ion transport, the acid content of the final pickling solution migrates through the diaphragm into the anode compartment (electrodialysis) and at the same time the iron sulfate in the catholyte is converted into ammonium sulfate and magnesium sulfate by the combined effect of the ion transport processes and the cathodic iron deposition and / or alkali metal sulfates exchanged. The solution which emerged from the cathode compartment of the last electrolysis cell (E), the so-called end catholyte, is practically acid-free (pH = 1.6 Ms 2.0), its residual iron concentration is 10 g Pe ⁺⁺ / 1 and the concentration an Sulphates is in the order of 1 ^ mol / l.

The end catholyte is pumped to the beginning of the Electrolyzing cell row reclaimed, while otherwise the transport and the direction of flow of the solution is achieved by the gradual sloping arrangement of the electrolysis cells each electrolysis cell has an overflow as an outlet opening. The pump delivers the solution (the EndkathQlyten) into the anode compartment of the electrolysis cell E ^, from where it passes through the anode compartments of the electrolysis cells Eg ... E continues to flow. The acidity increases from electrolysis cell to electrolysis cell and the concentration of the bisulphate-forming salts increases Electrolyzing cell to electrolyzing cell. The gradual increase in acid concentration is partly due to the anodic Enrichment of the acid ions and partly due to the ion transport already mentioned (the immigration of the HSO ^, "ions). The decrease in the salt concentration is explained by the fact that the cations of the salt are caused by the Move through the diaphragm into the cathode compartment.

The acidity of the endanolyte is given by the following relationship:

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«Reg". «Η»!. * ¹ · ⁷⁵

where C _re g. ^the acid concentration of the final anolyte in g / 1, Cv j the acid concentration of the final stain in g / 1,

is the iron concentration in the final pickling in g / 1 and ^{the iron concentration} ' ^l: ' ^ra ' ^t ' ^{ion in the} final catholyte in g / l.

The factor 1.75 is the ratio of the equivalent weights of Acid to iron.

The bisulphate salt content of the endanolyte is necessarily exactly as high as the bisulphate content of the final stain, since in the steady state, the amount of additional salt entering the electrolysis unit in the unit of time is exactly the same is as high as the amount of salt emerging from this in the unit of time. According to the mechanism described, the bisulfate-forming salt mediates the electrochemical ion exchange, but the salt acts on the electrode processes does not participate.

Compliance with the above-mentioned process parameters is necessary because otherwise the concentration gradation explained does not come about or cannot be maintained within the cycle and as a result, the electrochemical decomposition of the associated with the separation of the iron sulfate from the residual acid Iron sulfate is impracticable by the mechanism described. When the concentration of the bisulfate forming salt in the final pickling solution is less than 0.5 mol / l, then is the amount of salt used to catalyze the electrochemical

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Ion exchange chain insufficient. On the other hand is the Concentration of the bisulfate-forming salt is greater than 1.0 mol / l, then the pickling rate and the water solubility of iron sulphate ". If the residual acid content of the final pickling solution is significantly higher than 100 g / l, then the current efficiency is significantly reduced and the specific energy requirement during regeneration increased considerably. If a diaphragm was not used. then the anolyte and catholyte were separated by the evolution of gas mix together quickly and thwart the electrochemical ion exchange described. If wanted If the iron content of the solution were to be completely depleted, then the efficiency of the electrolysis would be reduced and so would it there would be a risk of the catholyte becoming alkaline. If the final catholyte would contain more than 15 g iron ions / l, then the 2-valent iron ions would be anodically oxidized to 3-valent ones, which also reduces the efficiency and in addition, an increase in pickling losses would result. If the flow direction in the cathode and anode compartment is not identical, then the ion exchange mechanism described gets completely confused and neither the electrodialytic separation the residual acid or the electrochemical decomposition of the iron sulphate can be carried out with satisfactory efficiency be performed. When the current density is less than

15 A / dm, the arrangement is not sufficiently efficient or productive and, moreover, the diffusion taking place through the diaphragms could not be sufficiently overcompensated by the ion transport, which would also lead to a decrease in the efficiency. In the event of a load with a current density of more than 22 A / dm, the structure of the coating on the cathode is unsatisfactory and operational malfunctions occur. The transfer rate of the ions participating in the current transport depends on the temperature. In the given system, the ion exchange mechanism described

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mus of best transport numbers at temperatures above 7O ⁰ C achieved. At temperatures above 9O ⁰ C foaming is increased to an undesirable extent, which also leads to operational difficulties. The continuous mode of operation during regeneration is necessary because setting the steady-state concentration distribution takes several hours and during this time the cycle cannot be maintained with sufficient efficiency. Interrupting the electrolysis is always associated with significant loss of time and loss of production.

The iron concentration of the final pickling can be chosen as desired with regard to the regeneration. However, since the pickling speed is reduced with an iron content of more than 90 g Fe * ⁺ / 1 in the final pickling solution, it is not advisable to exceed this limit, if only because the higher the iron concentration, there is also the risk of deposition of Iron sulfate heptahydrate becomes larger.

The flow rate of the solution will meet the requirements calculated according to the concentration gradation, for example, according to the following relationship regulated:

_v _ 1.85. Ύ. η. I.

ioo. (c _res -

In this equation, V is the overall flow velocity System in l / hour, Y the current efficiency in percent, η the number of electrolysis cells connected in series and I is the strength of the electrolysis current in amperes. The remaining symbols have the same meaning as above.

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The factor 1.83 expresses the amount of 100% efficiency sulfuric acid generated by 1 ampere hour.

Furthermore, the invention is not based on the following as limiting examples explained in more detail.

example 1

Pickling of steel pipes to be galvanized in open tanks with the electrochemical method Combined sulfuric acid regeneration

It was pickled in 4 open tanks connected in series with regard to the flow in sulfuric acid solution at 70 ^{0 O.} In the steady-state equilibrium of the circular process, the following concentrations were established in the individual basins:

pool
•No. H ₂ SO ₄
in
g / l Fe ⁺⁺
in
g / l 1 262.5 30th 2 195.0 50 3 127.5 70 4th 60.0 90

The ammonium sulfate concentration in all 4 tanks was 80 g / l.

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The final pickling solution which emerged from the fourth basin was continuously to the cathode compartment of the row of electrolyzing cells fed. The solution flowed through the cathode compartment, its iron content being attached to that in the liquid Farewell to iron sheets .. While the solution flowed through the cathode compartment, its pH value rose to 1.8 and its iron content rose decreased to 12 g / l. The ammonium sulfate content rose 165 s / l · The anode compartment was through a (made of stretched polypropylene fabric existing) diaphragm separated from the cathode compartment. The electrolysis cells were made of textile bakelite moldings manufactured using silicone rubber as a seal. Semi-hard ones containing 1% silver were used as anodes Lead plates used. The end catholyte was returned to the beginning of the row of electrolysis cells by means of a pump and fed there to the anode compartment, from where it successively opens the anode compartments of the successive electrolysis cells flowed through. The acid content of the solution rose to 294 · g / l and the ammonium sulfate content fell to 80 g / l · Es was electrolysed with a current density of 18 A / dm, the temperature in the electrolysis vessels being controlled the flow rate of the cooling water was kept at about 85 ° 0. The endanolyte was replaced by To remove the sulfate loss that occurred, sulfuric acid was added until its acid concentration was 330 g / l. Thereafter the regenerated acid was returned to the first pickling tank and the cycle was closed. In the In electrolysis and in the basins, the loss of water from evaporation and that caused by drainage were determined Replaces ammonium sulphate loss. The electrochemical regeneration achieved a current efficiency of 64% and the specific energy requirement, based on 1 kg of cathode iron recovered, was 6.1 kWh. The cathode sheets were changed daily. The cathode sheets removed from the solution and thickened into blocks by the deposition were melted down.

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Example 2

Electrochemical processing of the during manufacture The final pickling from iron bars is combined with the production of iron powder

It was pickled in discontinuous operation guide in independently operating open basin at 80 ⁰ C. The final pickling agent contained 80 g of acid / 1, 80 g of Fe ⁺⁺ ions / 1 and 90 g of sodium sulfate / 1. The final catholyte contained 12 g iron / l and 174 g sodium sulfate / l. The endanolyte contained 199 g sulfuric acid / l and 90 g sodium sulfate / l.

The electrolyzing arrangement consisted of 16 electrolyzing cell units connected in series. The steady-state concentrations established in the cathode compartment of the 1-1 cell were as follows: 16 g sulfuric acid / 1, 24 g Fe ⁺⁺ ions / 1 and 148 g Na ^ O ^ / l. In the first 10 electrolysis vessels, iron sheets were suspended as cathodes and treated in the manner described in Example 1. Cathode plates made of soft lead were hung in the remaining electrolysis vessels. These lead plates were taken out of the liquid once in each work shift and allowed to pass through a roller gap which slightly bent the lead. ' The cathodes were always removed from the solution under current. Since there were several cathodes working in each electrolyzer cell, removing 1 cathode plate did not cause a current interruption. The degree of current effect was tezog-en 60 # on block iron and 60 # on iron powder

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based on 66%. The energy requirement for Bloekeisen was 7.0 kWh / kg and for iron powder 6.4 kWh / kg.

Claims

509822/0926

Claims (8)

- 22 claims Process for the recycle or batch processing of final pickling solutions with a content of at most about 100 g sulfuric acid / l and at least 25 g iron ions / l through a combination of electrolytic decomposition of the iron sulphate and electrodialytic isolation of the acid and sulphate salt components of the final pickling solution in an electrolysis cell with anode and cathode compartments separated by a diaphragm with addition of bisulfate-forming salts, the final pickling solution being fed to the cathode compartment of an electrolysis cell, characterized in that an ammonium sulfate, magnesium sulfate and / or alkali metal sulfate concentration is added to the final pickling solution by adding salt of 0.5 to 1.0 mol / l and the final pickling solution is fed to the cathode compartment of an electrolyzing arrangement made up of electrolyzing cells having cathode and anode compartments separated from one another by diaphragms, and through the cathode compartment oden rooms of the electrolysis cells of the electrolysis arrangement can flow through, during which the iron content of the solution is ^{exhausted by cathodic deposition to values of 7 to:} 15 g I "e ⁺⁺ / 1, whereupon the solution is passed into the anode compartment of the electrolysis arrangement and through the anode spaces of the Electrolyzing cells of the electrolyzing arrangement are allowed to flow through in a direction identical to the direction of flow maintained in the cathode compartments, the current density, based on the area of the diaphragms, being set to values of 15 to 22 A / dm and the working temperature of the electrolysis at values of 70 to 90 ⁰ G keeps. - 23 -509822/0926 2.) Method according to claim 1, characterized in that • That the volume speed of the solution moving in the circuit, the current efficiency, the number of Electrolysis cells and the current proportional, but that between the solution leaving the electrolysis system and the solution entering it existing acid concentration difference adjusts inversely proportional and, in the event that the in the The pH value measured by the solution emerging from the last cathode compartment of the row of electrolysis cells is lower than 1.8, the flow rate is decreased, and if it is over 1.8, the flow rate elevated. 3.) Method according to claim 1 or 2, characterized in that that one separates the iron ions of the pickling solution on sheet iron cathodes and that through the Deposition, cathode sheets that have become thicker are removed from time to time and replaced with new sheets. 4.) Process according to claim 1 or 2, characterized in that for the combination of the electrochemical work-up of sulfuric acid-containing pickling solutions with the production of cathodic iron powder in the pickling solution as alkali metal sulfate concentration of 0.5 to 1.0 mol / l a sodium sulfate - and / or potassium sulfate concentration of 0.5 to 1.0 mol / l and in the ^{catholyte or catholyte part containing at most 25 g Fe ++} / 1 aluminum, lead or graphite electrodes, from the surface of which you can see the iron powder layer deposited on it from time to time ^ removed, dives. 5098 2 2/0926 5 ·) Arrangement for carrying out the method according to claim 1 to 4, characterized by arranged in rows, staggered and arranged through Electrolysis cells having cathode and anode compartments separated from one another by diaphragms (E ^ - ^ n ^ »where ä-ie diaphragms made from a caustic, Acid and temperature-resistant and advantageously dense tissue and for further transport the solution from the cathode or anode compartment of one electrolysis cell in the cathode or respectively Anode compartment of the next electrolysis cell in each electrolysis cell a level-regulating space Overflow is built in. 6.) Arrangement according to claim 5, characterized in that that in the individual electrolysis cells cathode and anode spaces alternately follow one another, these The cathode and anode spaces are separated from each other by a diaphragm and the cathode spaces are separated from each other and the anode spaces with one another through bores in the wall of the electrolysis cell w are connected. 7.) Arrangement according to claim 5 or 6, characterized in that that within the individual electrolysis cells the cathodes and anodes are electrical, seen are connected to the busbar parallel to one another but independently of one another. 8.) Arrangement according to claim 5Ms 7 »characterized in that that sheet iron cathodes at the beginning of the electrolyzing cell row and at the end of the electrolyzing cell row Aluminum, lead or graphite cathodes are attached 509822/092 6