SE413196B - PROCEDURE FOR ELECTROCHEMICAL PREPARATION OF Sulfuric Acid Solution Used for Iron Betting - Google Patents

Description

'lO 50 55 40 7u14719-o difficult with increasing sulfuric acid content in the pickling solution used and it is prohibited by law to discharge sulfuric acid into the sewer containing pickling solutions. If one neutralizes the used pickling the solutions with lime increase the costs and difficulties, that is associated with this neutralization, in proportion to the acid content * i the pickling solution used. An additional disadvantage of neutralizing lime is that the neutralization reaction is heterogeneous, why there is no guarantee of complete neutralization of the acid even when using excess lime. In addition, the handling it, transport and storage of lime sludge cumbersome and causes high costs and in this treatment none appear to be of any use products, which could possibly be recycled.

The procedures known in industrial practice for reprocessing the used sulfuric acid-containing pickling solution consists in separation of the heptahydrate by vacuum crystallization. The acid concentration in the pickling solution used is increased by eliminating water, which in turn takes place by bonding crystal water and evaporating in a vacuum. Due to this, the solution can again be used for ning. A further spread of this process is prevented by the demand for heptahydrate, hence the bulk of the salt ends up on the slag warp, which means that the environmental problem finally not resolved by this procedure.

The insight into the above-mentioned problems has led to researchers over the last two decades has sought a technical solution which not only enables the recovery of the acid in the used the pickling solution but also enables the conversion of the ferrous sulphate to recyclable sulfuric acid. As a basis for such solutions can to use the electrochemical decomposition of ferrous sulphate in aqueous solution, which takes place according to the following reaction: Bfeßüq + H20 = H2SO4 + 0.5 02 In this reaction, iron precipitates from the solution at the cathode in an amount which is equivalent to the amount of sulfuric acid formed.

The realization of that indicated in the above reaction formula however, the electrochemical reaction is hindered by the iron only with poor efficiency can be separated cathodically from acidic solution. At increasing acid concentration, iron separation becomes less and less is finally completely formed, whereby hydrogen is evolved at the cathode instead for iron. s _ In this way, the end result is the decomposition of water. instead of electrochemical decomposition of ferrous sulphate. The hit- until the proposed solutions have therefore all had the purpose of 50 55 40 7414719-0 limit the decomposition of water. The cathodic hydrogen evolution can reduced, for example by using flowing mercury troder. In a flowing mercury cathode, iron can also be separated from acidic solution in the form of an amalgam. The iron is then separated after in a confined space anodic from the amalgam. Used one acid-free medium, the iron precipitates already at a solid cathode. Such a solution is described by F. Aigner and G. Jangg in Berg- und Hütten- - men's Mbnatsheften (1969, pp- 12-18) under the heading "Elektro- lytic refining of spent sulfuric acid solutions ".

Since the iron as described must be separated twice and the silver electrode can only be used in a horizontal position and half the device becomes relatively bulky and expensive. Mercury high prices increase the already significant investment costs and that is also known, that at all with mercury cathodes working procedures the cost of the final product is borne by the mercury losses. In the publication, the authors acknowledge that the economics of the procedure and the specific energy needs is stated with the limit values 12.5 - 15.5 kWh / kg Fe. similar objections can also be done against other procedures, which are based on the use of mercury cathode. This is also expressed i.a. in a public tion by A.T. Kuhn "A Review of the Role of Electrolysis in the Treatment of Iron Pickle Iiquor "(Iron and Steel, June 1971 pp. 175- 176). This publication also contains information, which in other views are valuable, namely information regarding technology position and a compilation of the most important sources for the various procedures and in addition there is a factual and valuable comparison of the different procedures with each other.

Many researchers have also investigated the use of perm- selective membrane-dependent procedures. These essentially consist of that the migration of the hydroxonium cation (H5O +) to the cathode is prevented by means of a, so-called arranged between the anode and cathode spaces, so-called jonbytar- membrane. The membrane's high electrical resistance, its heat sensitivity and sensitivity to acids and mechanical impact as well as its short lifespan and high price, however, make a more general one application of the procedure despite the fact that the laboratory results are high promising. In view of this, in addition to the above-cited the bait of A.T. Kuhn following works a special mention, namely- gen “Treatment of Iron Containing Spent Sulfuric Acid by Electrolytic Dialysis "by the Japanese writers Tamurs and Ishio (Kogyo Kagaku Zseashi 69, 1455 (1966)) and Separation of Iron Spent Sulfuric Acid by the Iron Exchange Resins "by the same author. '10 50 55 40 ' 7414719-0 L » A further possibility is the procedure, which is based on reversal of bipolar, active lead electrodes. In this procedure, in the aqueous solution ferrous sulphate during simultaneous cathodic separation of iron and anodic separation of lead, the latter in separated space is cathodically reduced to lead, whereby sulfuric acid is formed.

A prerequisite for the application of this procedure is, however that the ferrous sulphate solution fed into the electrolyzer is neutral ral. Therefore, the procedure cannot be applied immediately to reprocessing acidic, used pickling solutions without first having to tallize the heptahydrate and redissolve it (J. Kerti: Az active non-electrostatic precipitators for electrochemical applications (possible possibilities to use the active lead electrode in electrochemical induction tri) MTA Kêmiai Oszt. Közl. 25, 251-281 (4966), U.S. Pat. the patent specification 5 'M1 468 and the British patent specification 992 5811-).

The same condition, namely that the solution is free of acid, also applies to the proceedings under the Hungarian patent law '156 806 (4967). In the process described in this patent specification present in the anoderm, which is separated from the cathode by a diaphragm. room, sulphate ions in excess in relation to the amount of sulfuric acid, which sulphate ions have been added in the form of ammonium or alkali metal sulphates barrel. The sulfate ions present in excess repel sulfur. the second stage of dissociation of the acid so that most of the sulfur the protons of the acid are in the form of Sqfanions, which as a result of the negative charge resulting from the anion formation is prevented from to travel through the diaphragm into the cathode chamber. In the latter the pickling solution is fed, which, however, is possible only if is completely depleted of acid. If the latter is not the case the salt, as stated in the patent, must be removed from the solution in a known manner (crystallization or thermal decomposition) and set to the catholyte. e In examining the problems discussed above, it has been to the realization that electrochemical decomposition of ferrous sulphate on an advantageous manner can be associated with the isolation of sulphate and acid in the used pickling solution, if in the pickling solution, by addition of a salt sets up an ammonium, magnesium or alkali metal sulphate concentration of 0, 5 '|, 0 mol / liter,' exhausts pickling solution the acid content of 100 g of H2SO4 / liter or to a lower value, feeds the pickling solution into the cathode chamber of an electrolyzer constructed of cells containing by means of diaphragms separated from each other anode and cathode compartments, allowing the pickling solution to flow through the anode space, whereby the iron content of the solution is depleted to a value of 45 50 55 40 s 7414719-0 7-15 g Fe ++ / liter and then the solution passes through the anode compartment in the electrolysis device in the same flow direction as the one in which the cathode space is flowed through and maintains through voltage variation a current density through the diaphragm of 15-22 amperes / dm2 and through The cooling rate of the cooling water maintains a working temperature. temperature in the electrolysis at 70-90 ° C. By complying with these conditions, During continuous operation of the regeneration system, the stationary equilibrium of the system to provide one for the acid, the ferrous sulphate and the bisulfate-forming additives are equally favorable, gradually concentration distribution and, as a result, a cyclical scratching, favorable transport processes and electrochemical ions switch-chain flow through the diaphragm. By realizing the diaphragm For electrochemical ion exchange, it need not be required to be permselektiv. ' According to the invention, it is thus intended to work up pickling solvents. containing not more than 100 g of HQSO4 per liter and not less than 25 g iron ions, which reprocessing is carried out in cycles or batchwise and in connection with the pickling of iron and by a combination of electrolytic decomposition of ferrous sulphate and electrodialytic insulation the acid and sulphate components of the sulfuric acid content used give the pickling solution. According to the invention, the pickling solution is by adding salts an ammonium, magnesium or alkali metal sulphate concentration of 0.5-4.0 mol / liter and the solution is fed in the cathode space of an electrolyzer constructed of cells containing by means of diaphragms separated from each other anode and cathode spaces, wherein the solution is allowed to flow through said cathode space while of the iron antenna 11111 7-45 g FeH / liter, then the solution is led into the anode space of the device and through it in the same direction as the current maintained through the cathode space, the current density on the diaphragm is maintained at 15-22 amperes / dmz and the working temperature of the electrolysis temperature at 70-90 ° C.

By the expression, that the reprocessing is carried out batchwise is meant that the solution is taken batchwise from the pickling plant and via an intermediate coupled container is continuously subjected to regeneration. It is due to the construction of the pickling plant is not always possible continuously to withdraw the used pickling solution and return carry on the regeneration continuously and in this way achieve an end cycle. In such cases, the process according to the invention is carried out preferably during interconnection of a larger container.

The decisive advantage of the method according to the invention is states that for its application one does not need to be completely exhausted '10 '15 40 1414719-o 6 the pickling solution with respect to acid or crystallize hepta- the hydrate. This enables regeneration immediately in the cycle to and for solutions containing up to 100 g H2SO4 / liter, ie approximately 'In moles / liter.

The chain of electrochemical ion exchange reactions and the stepwise the mechanism of the concentration distribution is illustrated in the accompanying the drawing.

The acid concentration in the pickling solution, as in order through the pickling containers P1, P2 n, sinks through the pickling the reaction from container to container, the iron concentration the reaction also rises from the container due to the pickling reaction to containers. The bisulfate-forming additives (ammonium, magnesium or alkali metal sulphate) concentration remains within the the holder series constant.

The pickling solution used is fed at a constant speed in the cathode space of the electrolytic cell, from which it flows through the cathode the rooms in cells E2 ... One in the order mentioned. At the cathode differs the iron. This cathode process is accompanied depending on the cathode lyten acid concentration of hydrogen evolution. The remaining acid in the pickling solution used migrates in the form of IISOZr ions through diameters fraggnan into the anodrmlmmet. At the same time, the cations migrate out of the anode space from the added sulfates through the diaphragm into the cathode chamber. To as a result, the iron and acid concentration in the solution decreases, while this flows through the cathode space of the cells and the concentration becomes lïmdallägre from cell to cell. However, the bisulfate-forming ones increase the concentration of the additives from cell to cell. The process can essentially summarized as follows: Through ion transport the acid in the reaction solution through the diaphragm: Ln in the anode compartment (elec- trodialysis) and at the same time the ferrous sulphate in the catholyte is replaced by it combined effect of ion transport processes and cathodic iron separation ammonium, magnesium or alkali metal sulphate. The ur cathode- the room in the last cell (A) exiting solution, the so-called the final catalyst, is practically free of acid (pH = '|, 6-2.0), its residual iron concentration amounts to 10 g of FeH / liter and sulphate the concentration is about 1.5 mol / liter.

The final catalyst is transported by a pump back to the cell. the beginning of the series, while the transport and flow of the solution direction is otherwise achieved by the cells being arranged stepwise at an ever lower level, with each cell as an outlet having an drain. The pump pumps the solution (final catalyst) into the anode valve in cell 13.1, from which it flows on through the anodexum in the cells '15 wi 55 40 v 7414719-0 'E2 En. In this case, the acid content increases from cell to cell and the bisul- the concentration of barrel-forming salts decreases from cell to cell. The the gradual increase in the acid concentration depends on one side on it the anodic separation of the acid ions and on the other side of it the aforementioned ion transport (the immigration of HSOÃ ions). The reduction of the salt concentration is due to the fact that the cations of the salt migrate nom diaphragm in i katodrxzmmet.

The acid content of the final anolyte is shown by the following equation: Greg = Cbet + 1'75 (Femäx _ Fe; in> in which equation Greg means the acid concentration of the final anolyte in grams / liter, Chet means the acid concentration of the pickling solution used also in grams / liter, Feï 'means the pickling used the iron concentration of the solution and Femin means the iron of the concentration (both iron concentrations being given in grams / liter).

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

The bisulfate content of the final anolyte is necessarily exactly the same as the bisulfate content of the pickling solution used, for in stationary condition is the amount of additive salt entering the electrolysis unit per unit of time exactly equal to the amount of salt leaving it. According to the described mechanism mediates the electrochemical ion exchange thereof the bisulfate-forming salt, however, the salt does not participate in the electrode processes.

Observance of the above process parameters is necessary, otherwise the above-mentioned concentration reduction within the circuit the process does not take place or is not maintained and which a consequence of this would be the separation of ferrous sulphate and residual acid associated electrochemical decomposition of the ferrous sulphate according to it the mechanism described above cannot be implemented. Concentrates of bisulfate-forming salt in the pickling solution to less than 0.5 mol / liter, the amount of salt for catalysis of the electrochemical ion exchange the chain is not sufficient. If, on the other hand, this concentration is greater than 10 mol / liter, the pickling rate and the solubility of the ferrous sulphate are reduced. in a clearly identifiable manner. About the residual acid content in the pickling solution is significantly higher than 100 grams / liter drops the efficiency of the power to a significant extent and the specific energy the demand for regeneration increases significantly. If you would not use any diaphragm, anolyte and catholyte would rapidly mix due to the evolution of gas, which would make it impossible to written electrochemical 'ion exchange process Would one like to completely empty the iron content of the solution, the effect of the electrolysis -Vvu14? 19-o 8 'IO '15 55 40 -none sink and there would be a risk that the catholyte would become alkaline.

If the final catholyte contained more than 15 g of iron ions per liter, it would the divalent iron ions are anodized to the trivalent state, which would also mean a reduction in efficiency and in addition, this would result in an increase in pickling loss.

If the flow direction in the cathode chamber did not correspond to the flow direction in the anode space, the described ion exchange mechanism but completely disrupted and neither the electrodialytic separation the residual acid or the electrochemical decomposition of iron the sulphate could be carried out with satisfactory degree. At a current density of less '15 amperes / dmz is the device not sufficiently productive and in addition it could through the diaphragm diffusion is not sufficiently overcompensated by ionic transport, which would also lead to a reduction in degree. At loads with a current of more than 22 amperes / dm2 the structure of the cathode coating is unsatisfactory and the appear. The transmission rate of the participants in the electricity transport ions depend on the temperature and in the given system are reached the most favorable transfer mechanisms for the described ion exchange mechanism. ring temperatures at temperatures above '70 ° C. At temperatures above 90 ° C foam formation is increased to an undesirable degree, which also leads to operational difficulties. The continuous mode of operation is necessary since setting of the stationary concentration distribution takes 'several hours in use. During this time, the cycle cannot be established maintained with sufficient efficiency. An interruption in the electrolysis is thus always associated with significant loss of time and production Result. _ The iron concentration in the pickling solution used can be in what regeneration matters are chosen arbitrarily. However, except at an iron content of more than 90 grams FeH / liter in the pickling solution If the speed drops, it is not appropriate to exceed it limit already for that reason, that with higher iron concentration as well the risk of heptahydrate separation becomes greater, which separation causes malfunctions.

The flow rate of the solution is regulated accordingly with the requirements for concentration phasing out, for example calculated according to following formula V-: fl aßâ-Y - n- I) reg et In the above formula, V is the flow rate throughout the system expressed in liters / hour, Y is the efficiency of the current in%, n is assumed 55 40 9 7414719-o 'let in series connected electrolytic cells and I is the electrolyzing current strength in amperes. The other symbols have the ones listed above the meanings. The factor 1.85 expresses the amount of sulfuric acid produced by an ampere hour at 100% efficiency.

Whether ammoniumf is used as a bisulfate-forming additive sulphate or another sulphate has no effect on the efficiency, then only the molarity of the additives in the pickling solution in each case is the same. Regarding the structure of the cathodically separated However, the nature of the cation in the additive salt is of great importance. see.

If you use ammonium or magnesium sulphate or one combination of these two salts, a smooth cathode coating is obtained. laying of leaf structure. If you thus want to extract another block workable cathode product, the mentioned additives should be used.

In this case, the cathode plates, the thickness of which increases by precipitation, time after time against new sheets of iron. They out of solution the removed cathode plates are processed by melting, for example in and for casting.

When using sodium or potassium sulphate, optionally a combination of both, is obtained at the cathodes, which are located in the beginning of the cell series, a coherent, not particularly glossy but rare matte coating. At the end of the cell series, where the iron of the cathode halr dropped to below 25 g; FeH / liter and the molarite of the additive salt is greater than 1, the iron separates in the form of powder on the cathodes surfaces. Given the great demand for iron powder is its production per se of great practical importance, this in in the present case, where the extraction of iron powder is with the pickling process, the recovery of the pickling solution used and the solution of environmental problems.

For the production of iron powder, the process according to the invention The procedure is thus carried out in such a way that the additive salts to the pickling solution use sodium and / or potassium sulphate in an amount of 0.5-1.0 mol / liter and in the cathode drums, in which the stationary iron concentration is less than 25 g Fe ++ / liter, uses aluminum, graphite or lead cathodes, so that the iron powder can be easily removed by loosening or brushing from the time after other electrodes removed from the solution. If you use iron electro- there, the precipitated iron particles adhere more strongly to the electrode surface.

If the entire iron content of the pickling solution used is desired, obtained in the form of iron powder, a pickling technique must be applied, at which the iron content of the pickling solution used does not exceed 50 55 Ål-O 7414719-0 10 25 gnamFeHYliter and the acid content is less than 20 g / liter. These conditions can be maintained in the open vessel systems.

One useful for carrying out the method according to the invention device consists of series connected, funnel-arranged cells, which each comprises separate electrode spaces. In the individual cells The cathode and anode spaces follow alternately with each other and between two such rooms there is a diaphragm. Within the individual cells, the todrums are interconnected by means of channels passing through the cell wall and the anoderms are likewise connected to each other by similar means channels. In this way, anolyte and catholyte can flow independently each other. For further transport of the solution from the anode compartment respectively the cathode space in each cell to the anode space and the cathode space in subsequent cell there are in each cell built-in, level-regulating board race. Within the individual cells, the anodes and cathodes are electrical connected in parallel with each other but independently connected to each other to busbars. In this way, it is possible to raise a apparent cathode from the liquid independently of the other cathodes. If one on The method described above desires to produce iron powder was used in cellular early rien iron plates as cathodes. However, it was used in the cell series end or more precisely from the cell in which the iron con- the concentration is only a maximum of 25 g / liter, aluminum, lead or graphite cathodes.

The invention will be illustrated in more detail in the following examples, but it is of course not limited to the details given in examples.

Example 1: When pickling steel pipes in open containers, which steel pipes were intended to be galvanized, the pickling was combined with the the sulfuric acid generation. The pickling was carried out in four, as regards the flow in series , open vessels in sulfuric acid solution at 70 ° C. In stationary equilibrium for the circuit process set in the individual vessels the following concentrations: Vessel number H2SO4, g / liter FeH, g / liter 'l 262, 5 50 2 195.0 50 127.5 70 4 eo, o _ 90 The concentration of ammonium sulphate in all four vessels was 80 g / lit er.

Using the pickling solution, exiting the fourth vessel 50 55 40 14 7414719-0 was fed continuously into the cathode compartment of the electrolytic series. Solution one flowed through the cathode chamber, the iron contained therein being differed from the iron plates trapped in the liquid. While the solution flowed through the cathode chamber, its pH rose to 1.8, at the same time as its iron content dropped to 12 g / liter. The ammonium sulphate content increased 165 g / liter. The anode chamber was separated from the cathode chamber by one of a stretched polypropylene fabric consisting of diaphragm. The cells were made of textile backlit profiles and silicone rubber was used as a seal.

As anodes, semi-hard lead plates containing one percent silica were used. ver. The final catalyst was transported back to a pump the beginning of the cell series and was fed there into the anode space, from where it in series flowed through the anode spaces in the subsequent cells. Thereby rose the acid content of the solution to 294 g / liter and the ammonium sulphate content dropped to 80 g / liter. The electrolysis was carried out with a current density of 18 amperes / dm2, whereby the temperature in the electrolyte vessels through change of cooling water flow rate was maintained at about 85 ° C.

The final anolyte was added with sulfuric acid for the purpose of replacing the after the discharge, the sulphate loss occurs, until its acidity concentration was 550 g / liter. Thereafter, the re- generated the acid to the first pickling vessel, whereby the pet closed. In the electrolysis or in the vessels it was replaced by evaporation lost the water and the ammonium lost through the discharge the sulfate. During the electrochemical regeneration, a current was obtained. efficiency of 64% and the per 1 kg of recovered cathode iron calculated specific energy demand amounted to 6.1 kWh. The cathode plates were replaced Daily. The cathode plates removed from the solution, which by precipitation thickened into blocks, melted.

Example 2: Electrochemical work-up of it in the preparation of iron bars formed, the used pickling solution was combined with position of iron powder.

The pickling was carried out batchwise in open vessels, with the pickling the treatment in each individual vessel was carried out independently of the pickling in the other vessels but in all vessels at 80 ° C. The pickling solution used contained 80 g of acid, 80 g of Fe ++ ions and 90 g of sodium sulphate, all per liter. Design and operation of the electrolysis device were identical to those described in Example 4. The final catholyte contained per liter 42 g of iron and 174 g of sodium sulphate. The final surface contained per liter 199 g of sulfuric acid and 90 g of sodium sulphate. 9 The electrolytic device consisted of 46 series-connected cell units. ter. The stationary concentrations, which set in in the eleventh cell, were as follows: 16 g sulfuric acid, 24 g Fe ++ ions and 148 g 49 7414719-o 42 NaiZSO4 per liter; In the first ten vessels, iron plates were hung as which were treated in the manner described in Example 1. I de other vessels: Soft lead plates were hung as cathodes. These lead- plates were removed in each shift once from the liquid and brought to pass through the nip between rollers, raising the lead plates slightly.

The adhesive iron powder was loosened and collected. Kato- were removed from the solution while energized. Since one in var- The cell working with several cathodes was formed when a cathode was removed. flat no power outage. The efficiency of the electricity was calculated on block iron to 60% and on iron powder to 66%. The energy demand was for block iron 7.0 kWh / kg and for iron powder fiber 6.4 kWh / kg.

Claims (2)

10 15 20 25 1; 7414719-0 Patent claims Process for working up pickling solutions containing per liter not exceeding 100 g of sulfuric acid and not less than 2% g of iron ions, carried out in cycles or batches, in combination with pickling of iron and by a combination of electrolytic decomposition of ferrous sulphate and electrodialytic insulation of the acid and sulphate components in the sulfuric acid-containing pickling solution used, characterized in that an ammonium, magnesium or alkali metal sulphate concentration of 0.5-1.0 mol / liter is set in the used sulfuric acid-containing pickling solution by adding salt. and feeds it into the cathode chamber in a cellular electrolysis device containing by means of diaphragms spaced apart anode and cathode spaces, and allows it to flow through said cathode space, during which the iron content of the solution is drained to 7-15 g Eb * Vliter, anode space and thereby in the same direction as the current maintained through the cathode space, whereby current the density of the diaphragm is maintained at 15-22 A / dmg and the operating temperature of the electrolysis at 70-90 ° C. Process according to Claim 1, characterized in that the volume velocity of the circulating solution is chosen in direct proportional proportion to the efficiency of the current, to the number of electrolyte cells and to the current, but in inverse proportion to the difference between the acid concentration in the electrolysis system the effluent solution and the acid concentration in the solution entering the said system, and by measuring the pH of the solution emerging from the last cathode chamber, the flow rate being reduced if this pH is less than 1,8, but increasing if said pH is above 1 , 8. PROMISED PUBLICATIONS: US 984,703 (204-112), 1,954,664 (204-112), 2,865,823 (204-151)