DD283164A5 - PROCESS FOR PROCESSING METAL CHLORIDE SOLUTIONS - Google Patents

Abstract

The invention relates to a process for working up of metal chloride solutions by means of electrolysis for the utilization of the solutions of one or more metal chlorides resulting from the pickling of metals with hydrochloric acid. The object of the invention is achieved by using a tungsten carbide-catalyzed hydrogen diffusion electrode as the anode for the electrolysis. A tungsten carbide catalyzed hydrogen diffusion electrode encased in a diaphragm should be used to restrict the access of anodically formed hydrogen ions to the cathode. With the method according to the invention it is possible to work up metal chloride solutions economically. {Method; refurbishment; Metal chloride solution; Electrolysis; recovery; pickling; Metal; Hydrochloric acid; tungsten carbide catalyzed hydrogen diffusion electrode; Anode; diaphragm}

Description

The invention relates to a method for the workup of Metallchlo ridlösungen by electrolysis for the recovery of the pickling of metals with hydrochloric acid resulting solutions of one or more metal chlorides or for the production of alloys.

Characteristic of the known state of the art

Certain types of steel and other metals are preferably pickled with hydrochloric acid. For the resulting metal chloride solutions there is often no economically viable processing option. In addition to a use as precipitant in the water industry is usually an energy-consuming thermal decomposition to metal oxides, which are sometimes used as a color pigment or recycled smelting. An electrolytic work-up as in iron sulfate solutions according to US-PS 3939207 (J. KERTI et al) from the sulfuric acid pickling is not possible because anodic chlorine is produced, the cheap anode material lead can not be used in chloride electrolytes and when using expensive dimensionally stable anodes from the Chloralkalielektrolyse gas-tight construction of the electrolytic cell very expensive wäru. DE-OS 2552512 is a typical example of the chlorine extraction by electrolysis of metal chlorides. The anodic chlorine is sucked off. The process is suitable only for the processing of large amounts of metal chloride solutions, since facilities for the purification, storage and transport of the chlorine must be present. For this reason, metal chloride solutions from pickling baths are not processed electrolytically in the direct cycle until today. The hydrochloric acid for the pickling process must therefore constantly supplemented by new acid or the metal chloride solution are thermally decomposed to oxides and hydrochloric acid.

The literature shows what efforts have been made to avoid the oxidation of chloride ions at the anode or to supply the anodic chlorine to the electrolysis. Thus, e.g. to DE-OS 2539137, DE-OS 2943533, JP 59-11892, JP 59-11893, JP 59-11894 proposed the use of membranes and diaphragms, the chloride ions from the anode Fernl. old. In order to prevent the formation of relatively small amounts of metal, stabilizers and further additives are added to the electrolyte.

GB-1576280 describes in a 3-chamber cell with ion exchange membrane and diaphragm the recovery of hydrochloric acid in the central space. The anodic oxidation of iron to Fe ³⁺ ions is exploited to extract it from the hydrochloric acid in the form of a chlorine complex with organic solvents. Thus, a pure hydrochloric acid can be obtained. In EP 0170632, the hydrochloric acid is recovered in the electrolysis of chloride baths characterized in that the anodic chlorine is reacted with hydrogen to hydrochloric acid. At the same time, this seems expensive and expensive. The effort for the suction of chlorine and its binding or \ uwendung is not further elaborated in the patent literature (as well as in DE-OS 2552512, see above).

Object of the invention

The aim of the invention is an economical process for the utilization of metal chloride solutions, in particular of hydrochloric pickling baths of the metal industry.

Explanation of the essence of the invention

The object of the invention is an energetically favorable recovery of hydrochloric acid and electrolyte metal.

It turns out that for a cost-effective treatment of metal chloride solutions by means of electrolysis, a solution can be found in which the anodic chloride development is avoided and which, of course, also works with long-term stability.

This object is achieved by de ^1! for electrolysis, a tungsten carbide catalyzed hydrogen diffusion electrode is used as the anode.

At these anodes (1) gaseous hydrogen is oxidized directly to hydrogen ions, so that

H ₂ = 2H ⁺ + 2e "U," = O, 00V (I)

for example, in comparison to the anodic process in the iron sulphate electrolysis (2)

H ₂ O = 2H ⁺ + V ₂ O ₂ + 20 " _Ueq = 1.23V (2)

or the evolution of chlorine in an ethylene chloride electrolysis (3)

2Cr = Cl ₂ + 2e "Π", = 1.36 V (3)

a significantly lower anode potential is realized. Since in the inventive use of hydrogen diffusion anodes, the chloride ions are not discharged due to the low anode potential, hydrochloric acid is produced in the anode compartment, which can be used again for pickling. The metal or metals are deposited cathodically in good quality.

Consequently, the combination of pickling bath electrolysis with hydrogen diffusion anodes results in the following gross reaction (with iron as metal):

FeO + 2 HCl = FeCl ₂ + H ₂ O FeCl ₂ + Hj = Fe + 2 HCl

FeO + H ₂ = Fe + H ₂ O

Of particular importance is the use of a tungsten carbide catalyzed hydrogen diffusion electrode. On the one hand, the tungsten oxides are you, the actual catalytic compounds. They are imine on the surface of tungsten carbide. ' available. On the other hand, surprisingly, a high long-term stability was found. So far, it has been assumed that the tungsten oxides are subject to severe corrosion and, accordingly, contaminants are also formed. The lifetime of tungsten carbide-catalyzed hydrogen diffusion electrodes has hitherto been considered to be insufficient. In contrast, it was found by the authors that the tested where> mcarbidkatalysierten hydrogen anodes over a long period of more than 7000 hours in chloride-based electrolyte "· yJ. Worked constant potential and the metals are clean deposited at the cathode.

This makes it possible overall to work up metal chloride solutions economically.

Preferably, a diaphragm-encased tungsten carbide catalyzed hydrogen diffusion electrode should be used to restrict the access of anodically-formed hydrogen ions to the cathode.

The water can be removed from the slurries by atmospheric evaporation in the pickling bath or by concentration of the electrolyte in combination with the use of electrolysis heat, to prevent dilution of the pickling solution.

The electrolysis vessels used may be those which are customary in the metal extraction electrolysis cell 3, the cathodes are drawn periodically and replaced by new base plates.

In the work-up of iron chloride solutions, the electrolytic iron is melted under inert gas to avoid rapid corrosion and fed to the intended use. In an analogous manner, a workup of other metal chlorides is possible.

It has also been found that alloys without complicated electrolyte compositions can be deposited with buffers, complexing agents and inhibitors of multimetal chloride solutions.

Ausführungsbelspiele

example 1

In a thermostatable electrolysis vessel, a hydrogen diffusion anode and an iron sheet were arranged as a cathode. The Hydrogen Di.'iusionsanode consisted of a flat plastic box or in bipolar design a flat frame, which carried two flanges for hydrogen supply and discharge. The gas-diffusion bonded in this context gas diffusion electrode was pressed from a mixture of tungsten carbide powder, carbon black, activated carbon and polytetrafluoroethylene in the ratio 80/10/5/5. For reinforcement and power dissipation, a corrosion-resistant metal mesh has been integrated. The hydrogen overpressure was 6.7 kPa. The electrolyte compartment was divided by an acid-resistant fabric in the anode and cathode compartments. The electrolyte which entered the cathode compartment had a composition of 130g Fe / I and 2g HCl / I. The series connection of several cells led to a depletion of the iron to 10 g / l and an enrichment of the hydrochloric acid to "/ 6 g / l." The electrolyte first flowed through the cathodes and then the anode compartments.The anodic current yield was 100%, since no anodic Oxydation of iron (II) to iron (III) ions occurs as in the case of lead anodes in traditional electrolysis, the cathodic current efficiency was 85%, the current density was 40mA / an ^{2, the} cell voltage was 1, 1 V, the electrolyte temperature was maintained at 8O ⁰ C.

Example 2

Waste iron-chromium-nickel steel was dissolved in boiling hydrochloric acid. The chromium content was adjusted to a higher value by adding CrCl ₃ .6H ₂ O than in the steel. Sodium citrate was added to the solution, and an iron-chromium-nickel alloy was deposited on an iron base plate in an electrolytic cell according to Example 1. The current density was 100 mA / cm ^2, the cell voltage of 1.6V, and the electrolyte temperature was 80 ⁰ C. The cathodic current efficiency was found to be 45%.

Example 3

In a thermostatted electrolytic cell according to Example 1 were at a temperature of 80 ° C, a current density of 40mA / cm ² , using a nickel plate as a cathode and a hydrogen gas diffusion anode, with a 1M electrolyte, which 130g / lCrCI ₃ · 6H ₂ O, 30g FeCl ₂ · 4H ₂ OIOOgNH ₄ Clund500gNH ₄ CH ₃ COO containing a Fe / Cr / Ni alloy deposited. The approximately 10, π thick coating adhered well and showed metallic luster.

Claims (2)

1. A method for Aufarbaitung of metal chloride solutions by means of electrolysis and using a metal base plate as the cathode, characterized in that a tungsten carbide catalyzed Wasserstoffdiffusioncelektrode is used as the anode. 2. The method according to claim 1, characterized in that the tungsten carbide-catalyzed hydrogen diffusion electrode is enveloped by a diaphragm. Field of application of the invention