DE1038291B - Process for the electrolytic treatment of sulfuric or phosphoric acid salt solutions of ferrous metals, primarily pickling liquids - Google Patents

Description

There are known methods according to which spent pickling solutions, e.g. B. more or less sulfuric iron sulfate solutions are regenerated. Almost all of these methods involve first the metal salt as much as possible to crystallize by its solubility is ermin changed in the pickling solution by evaporation and cooling, or displacing means of free acid and cooling \ ^r. On the one hand, this results in low-metal, strongly acidic residual liquid which is used to make up fresh pickling acid; on the other hand, solid metal salt falls, e.g. B. iron sulfate heptahydrate, which is usually a very poorly usable product. Recently it has been proposed to convert the iron sulfate into iron oxide and sulfur dioxide by reducing roasting and then to process the latter into sulfuric acid or, after previous partial dehydration, to convert it with hydrogen sulfide or hydrochloric acid gas.

It was obvious that the metal salts would be electrolysed or think of pickling solutions. However, the implementation of such a method is an issue manifold difficulties. It is probably possible to deposit iron or ferrous metals on solid cathodes, but only from neutral or very weakly acidic solutions, since any increase in the hydrogen concentration an evolution of hydrogen at the cathode and thus a deterioration in the current yield evokes.

It would also be possible to create a neutral catholyte with the help of liquid stratification and flow and acidic anolytes, but in this case one obtains e.g. B. in iron sulfate electrolysis, at the anode instead of newly formed sulfuric acid, only iron (III) sulfate, since it is present of iron (II) salt solutions at the anode, practically no sulfate ion is discharged and therefore also no acid is formed (cf. in this connection US Pat. No. 2,389,691). One Iron (III) salt solution has a dissolving effect on metallic iron during pickling, but without the very necessary development of hydrogen. The formation of iron (III) ions on the anode generally leads to another difficulty in carrying out the electrolysis of iron salt solutions, there if the electrolysis room is shared, the unavoidable mixture of the catholyte and the anolyte, for example through rising gas bubbles or thermally induced currents, always iron (II) ions at the anode and iron (III) ions are present at the cathode and thereby the formation of Oxygen, on the latter, the deposition of the metal is largely prevented.

It is known that iron can be removed from mercury cathodes when using insoluble anodes

for electrolytic processing

of sulfuric or phosphoric acids

Ferrous metal salt solutions,

primarily pickling liquids

Applicant:

Siemens & Halske Gesellschaft mbH,
Vienna

Representative: Dipl.-Ing. C. Wallach, patent attorney,
Munich 2, Kaufingerstr. 8th

Claimed priority:
Austria, October 24, 1952

Dr. phil. Hans Hohn,

Dipl.-Ing. Dr. techn. Erich Fitzer

and Dipl.-Ing, Heinrich Müller, Vienna,

have been named as inventors

can divorce. According to German patent specification 545 130, neutral electrolyte is used and the cathode is moved in order to counteract hydrogen deposition. According to German patent specification 692 992 one tries to achieve the same goal by exposing the resting mercury cathode to the action of a strong magnet and thereby pulling the separated iron down to the bottom of the electrolysis vessel in order to enrich it there to a considerable concentration. Both processes work with a moderate cathodic current density, namely with 300 or 200 amps / m ² . In both cases, no attention is paid to the effect of the anode.

The need to separate the anode compartment from the cathode during the electrolysis of iron salt solutions, has already been recognized and confirmed by our own tests. For this purpose, according to the

809 600/413

3 4

German Patent 526 777 a ceramic dia acid content falls, this loss is made up for Phragma proposed, according to the German patent, by the increasing acidity as well Scripture 823 939 a thermally treated plastic- increasing conductivity of the electrolyte and the filter cloth. due to the improved energy yield. the

Surprisingly, in contrast to the temperature dependency of the cathodic currents, it has now been found that the known method has a very good yield, insignificant as long as it is possible to work with cathodic current densities that are high enough with high sulfuric or phosphoric acid.
Salt solutions of ferrous metals with good power output, especially in electrolytic processing

Booty to be processed electrolytically if the iron or salt solutions of metals that can occur in several metals on a mercury cathode with current densities io valencies (e.g. Fe or Cr) that are above 500 Amp./m ² , preferably above disturbing anodic Formation of higher valued ions 1500Amp./m ² and more separated and thereby switching off (eg FeIII), the anode compartment is advantageously separated from the concentration of metal ions in the cathode compartment cathode compartment by a suitable diaphragm not below 0.2 mol Fe or equivalent amounts of an- phragm. The diaphragm has the first of which ferrous metals are allowed to sink. 15 line is given the task of preventing the penetration of, for example, iron (II) -man z. B. using a solution of 540 g / l ions in the anolyte by diffusion or flow FeSO ₄ · 7 H ₂ O and 1.5 percent by volume of H ₂ SO ₄ under largely prevent. Advantageously, the same electrolysis conditions and variations of the filter cloths made of acid-resistant plastic are used for cathodic current density or thin, well-permeable ceramic diaphragms

300 Amp./m * 80% current efficiency ^ao used, which does not allow the passage of current

800 amp./m * 89 »/ 0 current ^yield oppose high resistance. The diaphragm

2400 Amp./m * 97 V »Current output ^{can be} arranged so that it is cut along the

Flow direction of the mercury to the cathode

The favorable current yields with a high current surface of the respective cell section parallel densities decrease slightly with falling metal content of the electrical 25 or in the direction of flow of the mercury lyten. An economical electrolytic ascending progresses.

processing of solutions below 0.2 mol / l iron or in the practical execution of the invention

Equivalent content of other metals is hardly possible. According to the method, the following conditions are advantageously

It has also been found that as long as one is observed: One uses one quickly liquid mercury surface is present as cathode, 30 flowing mercury cathode, then the formed at the high current densities described, the amalgam is transported out of the cell and thereby cathodic current yield is not improved, the mercury surface is constantly renewed. In the event of if the deposited metals, insofar as they can be ferro- a non-interfering mercury cathode with are magnetic, during the electrolysis with the help of ferromagnetic amalgams one below or next to a magnet to the bottom of the electrolyzer ge 35 the cell arranged moving magnetic field be pulled. However, it is advantageous to arrange the amalgam transport of the iron amalgam out of the cell, To keep the surface in constant slight movement, Also can be magnetic conveying and flowing how this z. B. in the usual horizontal cells for mercury cathode can be combined as desired. in the the alkali chloride electrolysis through the rapid connection to it can flow into the amalgam itself of mercury is given. 40 known way z. By filtration, centrifugation

Be enriched for the electrolytic deposition of nickel from and / or pressing; the pure Salt solutions it has z. B. as a particularly advantageous mercury or impoverished amalgam is the elec- tric proven when the electrolysis is fed into horizontal trolysis again.

cells is carried out, with a min- The separation of the circulated mercury

Minimum flow velocity of the mercury or 45 silver or the enriched amalgam from the amalgam of 2 cm / sec. removed metal can expediently by removing

Heavy metals that are sparingly soluble in mercury, pre-evaporate in a non-oxidizing atmosphere the ferrous metals, can be taken from pouring. The liquid or Mercury cathodes in horizontal cells with relatively plastic amalgam or a mixture of different low mercury fillings, 50 amalgams are advantageously continuously fed to the heating zone be deposited that the electrolysis at kas. As a result, it can be in the form of a simple device running cathode surface takes place. gen the economic viability of the evaporation Increase the cascade course of the cathodes above the normal level. Another improvement on this surface can be achieved through one or more stages in the process that the ab-cell bottom reach that transversely to the flow direction, the protective gas atmosphere or the vacuum getung of the mercury. It has been shown that the air flows through at the point where the material is introduced that particularly favorable conditions are obtained, the amalgam flow itself, or the outflow at the when the spacing of the steps in the cathode surface material exit point by the condensed mercury takes place from stage to stage in the direction of flow silver.

of the mercury towards the end of the cell to be removed 60 To obtain non-pyrophoric fine to and possibly have an increasing gradient. The anode coarse-grained metal or alloy powder can so surface, it is also expedient to proceed in stages so that the evaporation of the mercury leads be advantageous so that the electrode spacing silver with increasing temperature, but below is practically the same throughout. After each of the melting temperatures of the respective metal resp. Anode stage is expediently a device for collecting the alloy in question without using mecha and dissipation of the cathodically formed niche pressure takes place. It is also possible that Arranged hydrogen. metal to be separated from mercury in the form

It has also been found that the acid concentrations of sintered or presintered are more porous to completely Tration in the electrolyte plays a minor role in the way of dense metal or alloy powder plays. Although the current yield has to be treated further with increasing 70, that the shaping by mechanical

Niche pressure treatment in a manner known per se (e.g. static pressing, extrusion, rolling, etc.) takes place during and / or after the evaporation process in the evaporation space itself, in such a way that that the pressure used is preferably increased as the evaporation treatment progresses.

The electrolyte can be fed into and out of the cathode compartment continuously or discontinuously This can be removed again enriched with re-formed acid. In the anode compartment is at the same time the anolyte was largely kept free of metal salts and kept acidic. If the diaphragm is dense enough, it will run the diffusion of metal ions into the anode compartment is very slow due to their electrical charge, and that in the electrolysis of salt solutions of the metals with several valencies in the anolyte generated and migrating back to the cathode small amounts of higher-valued metal ions are on the Current yield without any significant influence. When using very permeable diaphragms with ao a minimum of voltage drop can be achieved by periodic or continuous acid and / or Additions of water to the anolyte result in a constant, low flow of liquid from the anolyte to the catholyte be maintained, thereby successfully countering the diffusion of metal ions into the anode compartment will. When pickling liquids are regenerated, the addition of water should not significantly increase the loss of water go out during work-up so as not to unnecessarily dilute the pickling acid.

In the electrolytic processing of sulfuric or phosphoric acid salt solutions of the ferrous metals with insoluble anodes and mercury cathodes, despite the possibility of the cathodically co-deposited Allow hydrogen to rise only in very limited places and expedient arrangement of the diaphragms a partial electrical blocking of the diaphragm surface by hydrogen bubbles enter. This can be avoided by keeping the electrolyte and the mercury cathode in the same Direction of flow and the flow velocity of the electrolyte at least almost the same, advantageous however, is larger than that of the mercury cathode. This also has the further advantage that the distance between the diaphragm and cathode can be reduced to a few millimeters. Through this the anodes can be lowered so that the cell voltage is as low as possible Values can be decreased. To increase the current yield has been found to be advantageous proved to be suitable for the electrolyte during and / or after passage through the electrolytic cells Way to continuously replenish with metal salts. The electrolytic regeneration of the pickling solution is advantageously coupled with the pickling process by continuously adding the low-acid pickling solution withdrawn from the pickling apparatus and fed its fresh, acid-rich pickling solution from the electrolysis will. So has z. B. the withdrawal of pickling solution from the pickling bath with a concentration of sulfur and / or phosphoric acid from 6 to 8%> and the electrolytic regeneration thereof up to one Proven acid content of 10 to 14%. In the case of the possibility of using cheap night electricity, can pickling solution consumed during the day stored or from this z. B. excreted iron sulfate heptahydrate and regenerated during the night. The inventive method is for electrolytic Processing of all pure or mixed salt solutions of ferrous metals, especially Fe, Ni, Co, Cr and others applicable with sulfuric and / or phosphoric acid.

Claims (14)

Patent claims: 1. Process for working up acidic solutions of the sulfates and / or phosphates of the metals iron, nickel and / or cobalt or one of these metals with one or more corresponding salts of their alloy metals, e.g. B. the sulfates of Fe with Cr and / or Ni and / or Mn, in particular of spent pickling liquids by electrolysis on moving mercury cathodes, characterized in that the electrolysis is carried out with a cathodic current density over 1500 Amp./m ² and an electrolyte is used containing at least 0.2 mol of iron in liters or an amount equivalent to the iron content of one of the metals mentioned or one or more of the alloy components. 2. The method according to claim 1, characterized in that the electrolysis at separate Cathode and anode compartments by using a diaphragm, which primarily facilitates diffusion the anodically oxidizable ions to a higher valency level in the anode compartment practically prevented, is carried out and the electrolyte is fed into the cathode compartment and is also taken from the cathode space. 3. The method according to claim 2, characterized in that a penetration of catholyte is prevented in the anode compartment that the from an aqueous sulfur or phosphoric acid solution existing anolyte is supplemented with water to the extent of the anodic oxygen evolution that possibly by adding more from liquid to anolyte an additional flow of liquid from anolyte to catholyte is maintained, with the extent of the possible outflow to the cathode compartment the anolyte is supplemented with dilute acid. 4. The method according to claim 1 or the following claims, characterized in that the Electrolysis in horizontal cells and with a minimum flow rate of mercury or amalgam of 2 cm / sec is carried out. 5. The method according to claim 1 or the following claims, characterized in that the Electrolysis takes place in a horizontal cell with a cascading cathode surface. 6. The method according to claim 1 or the following claims, characterized in that the Distances of the steps in the cathode surface from step to step in the direction of flow of the Of mercury towards the end of the cell. 7. Horizontal cell for performing the method according to claim 5 or 6, characterized through one or more steps in the cell bottom transversely to the direction of flow of the mercury. 8. Horizontal cell according to claim 7, characterized in that the sections between the individual steps in the cell floor have increasing incline towards the end of the cell. 9. Horizontal cell for performing the method according to claim 5 or 6 or according to claim 7 or 8, characterized in that the anode surface is also offset in height is arranged, advantageously so that the electrode spacing is practically the same throughout. 10. Horizontal cell for performing the method according to claim 5 or 6 or according to one of claims 7 to 9, characterized in that after each anode stage a device for Collection and division of the cathodically formed hydrogen is arranged. 11. Cell for performing the method nadh claim 2 or the following, characterized in that that the diaphragm in section along the flow direction of the mercury to the cathode surface of the respective section is arranged parallel or horizontally or slightly rising in the direction of flow of the mercury. 12. The method according to claim 1, characterized in that the separation of the circuit guided mercury from the absorbed metal by evaporation in non-oxidizing Atmosphere is made and the liquid or plastic amalgam or the mixture of different Amalgam is continuously fed to the heating zone. 13. The method according to claim 12, characterized in that during the decay of the Mercury can optionally be shaped into a semi-finished or prefabricated product. 14. The method according to claim 1, characterized in that the continuously from the electrolysis room removed electrolyte is saturated with solid metal salts or as dissolving acid or pickling acid is used in the circuit to be re-fed to the electrolysis. Considered publications:
German patent specification No. 545 130. 809 600/413 9.5S