DE1106085B - Process for the electrolytic processing of iron-containing amalgams - Google Patents

Description

Process for the electrolytic processing of iron-containing amalgams Amalgam metallurgical processes have been increasing in recent years Interest. It has been shown that the manufacture and processing of those metal amalgams could be brought to industrial maturity, which both a simple production as well as dismantling of the amalgams in question. For such operations the amalgams of the metals soluble in mercury are well suited.

The metals of the iron group, however, form amalgams, which are essentially from suspensions of the metal in question or its sparingly soluble in mercury Mercury compounds exist and are therefore difficult to access anodic decomposition are. Likewise, it is not possible to use the important and convenient process step of the so-called "phase exchange" to be carried out with these amalgams, since such Reactions due to the nature of the amalgams are very sluggish. If you bring z. B. zinc amalgam with copper sulfate solution in contact, then immediately sets a phase exchange reaction one, which ideally results in copper amalgam and zinc sulfate solution. This reaction proceeds with great intensity, which can be illustrated by compares it with an electrical current passage equivalent in effect. The intensity of the Zn-Cu phase exchange corresponds to a current passage of several thousand A / m2 through the phase boundary amalgam-aqueous solution. If on the other hand nickel or If iron amalgam is brought into contact with copper sulphate solution, the phase exchange takes place so slowly that at most it can be equated to a current passage of a few A / m2 can, which is insufficient for technical purposes.

For this reason it is for the processing of the iron-containing amalgams So far only the route of thermal treatment (distillation) has been available. However, this method is not only difficult to carry out in terms of equipment, but also mostly also uneconomical, because of the necessary automation of the operation smaller devices require a technical and financial outlay that is in bears no relation to their performance.

Iron amalgam is now produced as an intermediate product in various electrochemical processes. Most important is the process of electrolytically regenerating used iron pickling acid solutions with the help of mercury cathodes with the formation of iron amalgam and free acid. B. aluminum sulfate solutions can easily be freed from their undesirable content of noble metals (Fe, Cu, Ni, Zn) by electrolysis with mercury cathodes. It was therefore obvious, in fact even necessary because of the difficulties in thermal separation already mentioned, to develop an aqueous process for the decomposition of iron amalgam. A step towards solving the problem is provided by the method described in USA. Patent 1970 973, according to which iron amalgam is reacted with an acidic aqueous solution of an oxidizing agent, e.g. B. of iron (III) sulfate to be cleaned.

According to equation 2 Fe +++ + FeHg = 3 Fe ++ + Hg, iron amalgam is broken down at a technically useful speed. However, if the subsequent oxidization described there was used, an equivalent amount of iron (II) sulfate would always accumulate to the extent of the iron removed from the amalgam, which on the one hand is unusable, on the other hand binds acid, so that a regeneration process for acid would be pointless. In fact, the process according to US Pat. No. 1970 973 is only intended for the separation of heavy metals from salt solutions of base metals for cleaning purposes. If, on the other hand, you want to electrolytically separate large amounts of iron from strongly acidic solutions and at the same time further acidify them, it is necessary to remove the iron in elemental form from the process in accordance with the process according to the invention of iron, whereby the iron-containing amalgam produced in electrolysis cells with mercury cathodes (primary cells) is brought into contact with iron (III) sulphate-containing solution, consists in that the resulting, essentially iron sulphate-containing solution is fed into the cathode spaces of electrolysis cells (secondary cells) , which are equipped with solid metal cathodes and, separated from these in a known manner by filter diaphragms, unassailable anodes, the electrolyte in the secondary cells flowing from the cathodes to the anodes, being removed from the anode compartment as a solution containing iron sulfate or flows off and is fed back to the iron-containing amalgam.

It has proven advantageous to implement the iron (III) sulfate-containing Solution with the iron-containing amalgam at a higher temperature, preferably between 40 and 100'C, with vigorous movement of the phase boundary amalgam-aqueous solution and to be carried out at a pH value between 0 and 4.

The mercury and aqueous phases are expediently countercurrent or in cocurrent, in filled or empty towers and / or in filled or empty with impact bodies, horizontal or in the direction of flow of the mercury inclined trough-shaped apparatus and / or stirred vessels (reaction vessels) for the reaction brought.

To prevent iron (III) sulphate solution from mercury If it attacks oxidatively, it is advantageous not to have too low an iron content in the amalgam to sink. It is therefore necessary to note that the iron content of the amalgam after completion of the reaction with the aqueous phase kept at at least 0.05 ° (o will.

Any remaining low iron (III) ion content in the converted electrolyte is used up by the ferrous salt solution reduced with metallic iron after leaving the reaction vessels. To be towers filled with scrap iron are advantageously used, which provide the solution flows through. The scrap towers are between the reaction vessels and the secondary electrolysis cells switched.

To remove small amounts of dissolved mercury if necessary To remove the iron (II) sulfate-containing solution, this will be done after the treatment with scrap iron, brought into contact with copper. This procedural step leads one through by the th electrolyte after leaving the filled with scrap iron "Turmes leads through a tower filled with copper shavings. On the copper or copper amalgam surface the copper shavings precipitate mercury, while an equivalent amount of copper goes into solution. To remove contaminants, e.g. B. originating from scrap iron Carbon, becomes the electrolyte after leaving the with or with scrap iron Copper waste filled tower before entering the cathode chambers of the secondary cells filtered.

The flow rate of the electrolyte from the cathode compartments to the anode spaces of the secondary cells through the filter diaphragms is more appropriate higher than the speed of migration in the electric field The fastest migrating cation in the electrolyte at the operating temperature (up to 100'C). This prevents hydrogen or iron (III) ions from the Anode spaces can get into the cathode spaces, which there by lowering the Current yield or precipitation could give rise to disturbances. This electrolyte flow is maintained by making the liquid level in the cathode compartments higher holds than in the anode compartments, which according to known methods, for. B. by regulation the height of the liquid level in the cathode compartments or the anode compartments or can be done in both at the same time.

The primary cells and secondary cells are advantageously current-wise connected in series, with one to compensate for the different current yields both cell types either part of the current through a resistor in parallel leads to the cell which has the higher cathodic current efficiency, or with higher cathodic and anodic current yield of the secondary cell that in the Secondary cell formed iron (III) -sulphate solution not entirely with iron-containing one Amalgam reduced, but before branching off a part and directly to the scrap iron tower feeds. If the anodic current yield in the secondary cell [measured in With regard to iron (III) ions formed] the cathodic (deposited iron), the correction is made by adding acid and possibly lowering the iron salt concentration of the electrolyte. Usually it is necessary to use these adjustment methods at the same time or to use together.

Technically, the method is carried out as follows: A mercury cathode cell (primary cell), which z. B. iron sulfate solution is processed into free acid and iron amalgam (regeneration of used pickling acids), an electrolysis cell (secondary cell) with sheet iron cathodes, filter diaphragms made of plastic cloth and lead anodes is connected in series. The mercury in the primary cell is circulated through the cell, the mercury pump and a reaction tower filled with glass spheres at a rate such that a single flow through the cell leads to a loading of 0.1 % iron. The iron content of the amalgam during operation is preferably 0.5 to 0.8% Fe.

At the same time flows through the reaction tower in countercurrent to the mercury the anolyte from the secondary cell, which, for example, contains 60 g of iron as sulfate, 20 g ammonium sulfate and 0.1 g per liter of one under the trade name »Erkantol BX« sulfonated products manufactured and sold by the Bayer A. G. paint factories Contains naphthalene derivative as a wetting agent, the amount reacted of iron (III) ions is sufficient to remove 0.1% iron from the amalgam flowing through. The now partially reduced anolyte is successively through the scrap tower and passed the copper tower, filtered and abandoned the cathode compartment of the secondary cell. The solution becomes catholyte in this way through cathodic iron deposition about 10 g Fe / 1 taken before it flows through the diaphragm to the anode. At the Lead anode will simultaneously double the amount of iron, i.e. H. about 20 g Fe / 1 to Iron (III) sulfate oxidized. The remaining iron remains in the electrolyte as Ferrous sulfate. The anolyte, which consists of iron (III) sulfate, passes through a Again pump to the reaction tower.

If the primary cell works cathodically and the secondary cell cathodically and anodically with 100% current yield with regard to amalgam formation, iron deposition and iron (III) ion formation, it can be seen that the deposition of iron as amalgam in the primary cell results in the same high deposition of electrolyte iron in the secondary cell, with the corresponding required amount of iron (III) sulfate also being produced in the latter. However, this ideal case is technically unattainable. All three mentioned electrode processes proceed with different current yields. In the primary cell, a current yield of 80% can practically be expected, while both the anode and the cathode of the secondary cell work with current yields of over 90%.

To compensate for these differences, one can either divert a corresponding part of the total current from it by bridging the secondary cell with a controllable resistor (which is equivalent to destroying energy) or, advantageously, not allowing a corresponding part of the anolyte formed in the secondary cell to flow through the reaction tower, but directly over it return the scrap tower to the secondary cell. As a result, a larger amount of scrap is consumed, but valuable electrolyte iron is also generated with the energy that would otherwise have to be destroyed. The balancing is checked by checking the iron content of the amalgam from time to time and by regulating the amount of anolyte diverted to prevent the iron content of the amalgam from falling below 0.5% as well as rising above 0.8%.

Is the ratio of the cathodic current yields of the two cells known? and the regulation of the diverted or diverted electricity Electrolytes are then made approximately accordingly, so once a day is sufficient analytical control and readjustment fully. As a result of the considerable amount of iron in the circulating amalgam volume there are only very slow changes in the iron content.

Also the different current yields of the cathode and anode of the Secondary cell must be taken into account. Is the current efficiency of the cathode higher than that of the anode, the anolyte becomes more and more acidic and contains less Iron (III) ions. In this case, the regulation is carried out by reducing the Junction from anolyte to the scrap tower. On the other hand, the released one consumes Acid a little more scrap and dulls itself as a result. Should be dulling do not run completely enough in the scrap tower, so sinks as a result of the higher Acid content in the catholyte, the cathodic current yield somewhat, which increases the Automatically adjust power yields.

However, if the cathodic current efficiency of the secondary cell is lower as the anodic so the content of free acid in the electrolyte decreases, whereby at the same time the iron ion content increases. In this case, the corrections are made, if necessary, by adding sulfuric acid and possibly draining part of the electrolyte carried out in the electrolyte circuit of the primary cell and replaced by water.

Usually regulations are in due to different power yields the secondary cell is not necessary, as the current yield of the cathode depends heavily on the acid content depends on the electrolyte and the system thereby largely regulates itself, d. H. the cathodic current yield adapts to the anodic one.

Claims (9)

PATENT CLAIMS: 1. Process for reprocessing iron-containing amalgams by electrolytic deposition of iron, whereby the iron-containing amalgam produced in electrolysis cells with mercury cathodes (primary cells) is brought into contact with iron (III) sulfate-containing solution, characterized in that the resulting essentially iron sulfate-containing solution Solution is fed into the cathode compartments of electrolytic cells (secondary cells), which are equipped with solid metal cathodes and, from these in a known manner separated by filter diaphragms, unassailable anodes, the electrolyte in the secondary cells flowing from the cathodes to the anodes, from which The anode compartment is removed as a solution containing iron sulfate or drains and is fed back to the iron-containing amalgam. 2. Procedure according to claim 1, characterized in that the reaction of the iron sulfate-containing Solution with the iron-containing amalgam at a higher temperature, preferably between 40 and 100 ° C, with vigorous movement of the phase boundary amalgam-aqueous solution and is carried out at a pH between 0 and 4. 3. The method according to the claims 1 or 2, characterized in that the mercury and aqueous phase in countercurrent or in cocurrent in filled or empty towers and / or in filled or empty with impact bodies, horizontal or in the direction of flow of the mercury inclined trough-shaped apparatus and / or stirred vessels (reaction vessels) for the reaction to be brought. 4. The method according to any one of claims 1 to 3, characterized in that the iron content of the amalgam is kept at least 0.05% at all points in the circuit. 5. The method according to any one of claims 1 to 4, characterized characterized in that the iron sulfate-containing solution after leaving the reaction vessels is subsequently reduced with metallic iron. 6. The method according to any one of the claims 1 to 5, characterized in that the iron sulfate-containing solution after the treatment metallic iron is also brought into contact with copper. 7. Procedure according to one of claims 1 to 6, characterized in that the electrolyte before Entering the cathode spaces of the secondary cell is filtered. B. Procedure according to one of claims 1 to 7, characterized in that the electrolyte in the secondary cells at a rate from the cathodes to the anodes through the filter diaphragm which is higher than the migration speed of the fastest cation (hydrogen ion) from the anode to the cathode at 100 ° C in aqueous solution, with the flow rate of the electrolyte by adjusting the liquid level in the cathode compartments and / or anode spaces is regulated. 9. The method according to any one of claims 1 to 8, characterized in that the different cathodic current yields of primary and secondary cells and the different cathodic and anodic current yields in the secondary cells are compensated for in that a corresponding part of the cells operating with a higher cathodic current yield of the total current is shunted parallel to this cell and / or part of the anolyte from the secondary cells is reduced by metallic iron and / or acid is added to the iron sulfate-containing solution in the secondary cell. Contemplated references: French Patent No. 1 085 609th.