GB2204062A

GB2204062A - Processing metal chlorine solutions

Info

Publication number: GB2204062A
Application number: GB08809276A
Authority: GB
Inventors: Andreas Mobius; Birgit Streng; Klaus Wiesener; Josef Kerti
Original assignee: Technische Universitaet Dresden
Current assignee: Technische Universitaet Dresden
Priority date: 1987-04-22
Filing date: 1988-04-20
Publication date: 1988-11-02
Anticipated expiration: 2008-04-20
Also published as: ATA92988A; AT394398B; DE3811472A1; GB8809276D0; GB2204062B

Description

j - 1 - A Method of processing metal chloride solutions 2204062 The

invention relates to a method of processing metal chloride solutions by electrolysis in order to exploit the solutions 0+ one or a plurality a+ metal chlorides which occur in the pickling W metals with hydrochloric acid in order to produce alloys or for direct hydrometallurgical recovery 0+ metals.

Specific grades of steel and other metals are preferably pickled with hydrochloric acid. Often there is nD economically worthwhile processing facility +or the metal chloride solutions which occur.in the process. Alongside a.

use as a precipitating agent in the water industry, there is in Tost cases a thermal deccmpnsition which is eypensive in ter-s c+ energy and produces metal oxides some of which be czed as a colour pigment or which may be recycled +or.

Mundry applications. An electrolytic processing such Ra if., tie CSse ci iron sulphate solutions according to USME -2969207 (J. KERTI et. al.) from the sulphuric acid pickling mixture is not possible$ since anodically chlorine is created but the inexpensive anode material lead cannot be used in chloride electralytes5 while if expensive dimensionally stable anodes were used, a gas-tight construction of the electrolysis cell from the electrolysis of alkali-metal chlorides would be very involved.

DEWS 2552512 is a typical example of recovering chlorine.b.y electrolysis c+ metal chlorides. The anodically created chlorine is exteacted by vacuum. The method is suitable only for processing relatively large quantities of metal chloride solutions, since equipment has to be available +or cleaning, storing and transporting the chlorine. For this reason, it has not been possible to date to process metal chloride solutions from pickling baths electrolytically in a direct circuit. The hydrochloric acid +or the pickling process must 2 therwArs to tntstottly =,octet by to the W0 chloride solution iust be broken down thermally to produce oxides and hydrochloric acid.

The literature shows the endeavours which have been undertaken in order to avoid the oxidation & chloride ions on the anode or in order to feed the anodically created chlorine to an electrolytic process. For instance, according to DE-OS 2539137, DEMS 2943533, JP 59-11S92, JP 59-11893, JP 59-11894, the use M membranes and diaphragms is suggested as a means c+ keeping chloride ions away from the anode. To prevent higher-valency metal ions forming, stabilisers and other additives are admixed with the electrolyte.

GB-1576290 describes the recovery of hydrochloric acid in the middle chamber M a three-chamber cell with an ion exchanger oe7hrEne and diaphragm. The anodic oxidation of iron to produce FelMons is utilised in order to extract it frc!rj hydrochloric acid in the form of a chlorine complex with organic solvents. Thus, R pure hydrochloric acid can be obtained.

Where the electrolysis of chloridic baths is concerned, in EP 0170632, the hydrochloric acid is recovered in that the ancdically created chlorine is reacted with hydrogen to produce hydrochloric acid. This appears to be both expensive and complicated. The complication +or the vacuum extraction M chlorine and its bonding or use is not mentioned in any further reference in the patent literature (+or instance in DE-OS 2552512, see above).

If one is successful in processing chlorine-containing baths without developing anodic, chlorine, then the use M such a procedural step, even beyond the processing of by-products, is possible in such processes in which the coupling of a preliminary or intermediate stage (production of a metal chloride solution) with the processing of such a solution 4 creetes economically favourable conditions. Such couplings are typical for instance of the direct hydrometallurgical recovery M metals.

For example, zinc sulphide concentrate can be lixiviated already with hydrochloric acid solutions which contain around 1% free HCl. Thus, the coupling of such a stage with the processing W the resultant metal chloride solution would obviously be more advantageous than taking the route via the known pressure lixiviation W zinc blende concentrate with sulphuric acid under excess oxygen pressure in autoclaves at temperatures of around 150-C and processing nf the sulphuric acid rich electrolyte.

For zinc electrolysis from chloridic solutions, various W=Ibndg EM on =. The anzdes in quest!cn are pure!,.

graphite and the expensive dimensionally stable anodes.

Certainly, as already menticened, considerable problems arise by virtue c+ the anodic chlorine development.

It is evident that for an economic processing of metal chloride solutions by means of electrolysis, a solution must be found whereby the anodic chlorine development is avoided and which M course also operates with long term stability.

According to the invention, this problem is resolved in that +or electrolysis a tungsten carbide catalysed hydrogen diffusion electrode is used as the anode.

At these anodes, gaseous hydrogen according to (1) is oxidised directly to produce hydrogen ions, so that 1 H. 2 2 H' + 2 e LIW, = 0. 00 V ( i 11 +or example in comparison with the anode process in the case of iron sulphate electrolysis (2) 1 1 H20 = 2 H4" + 112 0= + 2 e- Ll., = 1. 22, V (2) or the chlorine development in an iron chloride 2 Cl- = Cl;! + 2 e- U., = 1.36 V (3) a signi+icantly lower anode potential is achieved. Since in the case o+ the use of I.i.),,drogen dif-Fusion anodes according to the i nvention, the chloride ions are not discharged by reason o+ thie low anode potential, hydrochloric acid is produced in t h e ar, ow d e space and can be used again f or p i c k, 1 i n 9. T h e rr. e t e: 1 or. mJetals islare cathodicall- deposited i n a good qL, 2 1 i t C c r. 5 e q _ e n t 1 y ' w i t 1-1 a c orrib i n a t i o n D+ p i c k 1 i n -3 U a, t 1-1 electrolysis and 1-2 y el r og e- n d i + + us i o n anodes, t he + C31 1 ow i ng c r. u d e r e ac t i o n r e su 1 t s (w i t h i r. c) n as a me t a 1). 1 FeO + 2 HCl =. FeC12 + HnO FeC 1 m + H= F e + 2 HCl FEO + H2 Fe + HnO 0+ perticular importance is the use of a tungsten carbide catalysed hydrogen di++usiDn electrode. On the one hand, the tungsten oxides are the actual catalytic compounds. They are present c n the sur+ace cs+ tungsten carbide. Or, the other hand, a high long-term stabi 1 ity was surprisingly +Dund, In the past, it had been assumed that the tungsten oxides were subj ect to marked corrosion and t h a t a. 1 so impurities wou 1 d form accDrdi.rjc31y. The e+4ective li+e o4 tungsten carbide catalysed hydrogen di++usior.s electrodles was not previously estimated as being adequate. In contrast to this, the authors I-save succeeded in establishing t 1-1 a. t t 1-1 e tLkt'!CStC-rl carbide catalysed hydrogen anodes tested operated lc)r-,3 period 0+ t i Tlic- extending to more t 1-1 a n 7 0 0, C0 1 - 5 1 hcurs, in chloridic electrolyte at a constant potential and that the metals were cleanly deposited on the cathode.

Thus it is, all in all, possible economically to process met 1 chloride solutions.

Preferably, a tungsten carbide catalysed hydrogen diffusion electrode encased in a diaphragm should be used in order to restrict the access M anodically formed hydrogen ions to the cathode.

The water can be removed from the circuit by atmospheric evaporation in the pickling bath or by a concentration of the e3ectrolyte in conjunction. with the use M waste heat from electrolysis, in order to prevent diluticn 0+ the pickling As an electrolysis vessel, it is possible to use any cell currently used in metal recovery electrolysis while the cathodes should be periodically withdrawn and replaced by fresh base plates.

Where the processing of iron chloride solutions is concerned, in order to avoid a rapid corrosion, the electrolyte iron is fused in under a barrier gas and fed to the intended use.

Similarly, processing of other metal chlorides is also possible.

It has been demonstrated that also alloys can be precipitated from multi-metal chloride solutions without any complicated electrolyte compositions, with bu44ers, complex formers and inhibitors.

The method can also be very advantageously used +or the hydrometallurgical recovery of metals by electrolysis +romi chlcridic baths. For example, a batch of zinc sulphide concentrate and hydrochloric acid can be lixiviated in closed 1 cont2i ners and the i. esul tat-it hydrogen sul ph ide cat-, be f urther processed either to produce su 1 phur. or sulphuric acid (or.

SO=). Instead of Pure sulphuric acid, i t is pc, ss, i b 1 e d i rect ly t C3 U E e the final acid electrolyte obt a i ned + r orn 0 e 1 ectr c) I ys is.

1 n c ompar i so n with the anode reactions in t 1,1 e c ase c) + previous zinc electrolysis Tnethods it is possible from the su 1 phate e 1 ect ro 1 yte or from the chloride electrolyte, t CD obtain a significantly 1 C3 w er an o d e p c t c- n t i a 1 and t 1-1.k 5 a considerable 52,v i ng on energy, Above a 11 however ri o ch 10 r i n e d. e v e 1 o p 5 5. n o'd i c a 11 -Y 1-1 e h Y d r o c h 10 r i c &C id p, I- Z J uk c e Q i ri the a...!-;ride space i s 'Led fri--- 1 ixiviat ion.

T h e Z i n C: i S in conventional mannet. deposited on Et.ILkTilirliLkTf. .g J. t t a n i t a S E, n U 1 h c _an b c- +.t-t r. t h e- r Lk Z- e d ac c c r d i n t C) i n d Lk s t al r. e q u i r. e e n t s Th.e inveriticin will be explained in greater. detail with reference to examples c+ embodiment.

Example 1

A hydrogen diffusion anode and an iron plate serving as the cathode werie disposed in a thermostatical ly control lable electrolysis vessel. T h e hydrogen di++usict.s anode consisted c+ a +1at synthetic plastics box or, in the case c+ bypolar c c n s t r. u c t i D n, a + 'L a --'- +rame carrying two + 1 anges +cl-- t h e sup,p 1 y d, i sc harge of iatei-. The gas diffusion c-lc-cti-cde 91Lied in gas-tight fashion in this + rame was moulded +rom a m i - t u r s-- of tungsters carbide powder, carbon black, activated c h ar c c. p 1 a. n d polytc-tr-a,+1Ltc)r.cc-thylc-i-ie i n pr.Dpol- t i ons c)+ go: 1 GI: 51. 5. For amp 1 i + i c at i 01,9 aa n d c: 1-k r r e n t d i s p e r s a 1 Z_.

c c) r. r 3 s i c rt - r e s i -- t a, n t m e t a 1 gauze was integrated. T h e e.x. c e s s.

hydrc:,-,e.,.! pressut-e arriounted fm 6.7 kFa. The electrolyte spEcc- 7 was divided by an acid resistant fabric into an anode spacerr and a cathode space. The electrolyte entering the cathode space had a composition of 130 9 Fe/l and 2 g HCl/l. By connecting a plurality o+.cells in series, a leaning down of the iron to 10 g/1 and an enrichment of the hydrochloric acid to 76 g/1 could be achieved. In this case, the electrolyte first flowed through the cathode spaces and then the anode, spaces. The anodic current yield amounted to 100% since no anodic oxidation of iron-00-to. iron KIN-ions, as whet-, lead anodes are used in traditional electrolysis. The cathodic current yield amounted to 85%. The current density had a value c+ 40-mA/cmO. The cell voltage was around 1.1 V, the temperature of the electrolyte was maintained at Eys-ple 2 Iron-chrome-nickel steel waste was dissolved in boiling hydrochloric acid. The chromium content was adjusted by thc addition of CrClz6H=O to, higher value than in the steel.

Sodium citrate was added to the solution and in at-, electrolysis cell according to Example 1, at', iron-chromium-nickel alloy was deposited on an iron base plate. The current density amounted to 100 McmO, the cell voltage was 1.6 V and the temperature of the electrolyte was SOM The cathodic current yield was ascertained as 45%.

Example 3

In a thermostatically controlled electrolysis cell according to Example 1, at I temperature of SO-C, with a current density of 40 M/cm2 and while using a nickel plate as the cathode and a hydrogen gas diffusion anode, and using art electrolyte containing 130 g/1 CrCl3.6HzO, 30 9 FeClz.4H=O, g NHAW and 500 g NHqCH,COO, an Fe/Cr/Ni alloy was deposited. The approximately 10 microns thick coating adhered well and sHowed a metallic gloss.

Example 4

The electrolysis conditions were chosen similar to those in Example 1. The electrolyte which entered the cathode space had a composition of three moles zinc chloride/I (hydrochloric pH=1-2) with a colloid additive of approximately 3 kg/ton of metal. By serially connecting a plurality of cells, it was possible to lean down the zinc to I mole zinc chloride/l and to enrich the hydrochloric acid to 4 mole hydrochloric acid/I. The solution flows thereby firstly through the cathode spaces and then the anode spaces.

The anodic current yield amounted tp 100%. The cathodic current yield was ascertained as being 67%. With a current density of 40mA/cm' and an electrolyte temperature of 40-C, a cell voltage of 1.4 V was measured. The hydrochloric acid rich electrolyte leaving the anode space can then be used again for lixiviation of ores or metal compounds..

Claims

C 1 a i TA S

1 1. Method of processing metal chloride solutions by electrolysis and using a metal base plate as a cathode, characterised in that the anode used is a tungsten carbide catalysed hydrogen diffusion electrode.

2. Method according to Claim 1, characterised in that the tungsten carbide catalysed hydrogen diffusion electrode is encased in a diapl.iragrri.

3. Method of processing metal chloride solutions by electrolysis substantially as described in any of the examples disclosed herein.

Published 1988 at The Patent Office, State House, 6671 High Holborn, London WC1R 4TP. Purther copies may be obtained from The Patent Office, Sales Branch. St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.