GB2206356A - Anodic structure for the electrolytic refining of nonferrous heavy metals - Google Patents

Description

k 1 2206350 "CONTINUOUS ANODIC STRUCTURE FOR THE ELECTROLYTIC REFINING OF

NONFERROUS HEAVY METALC The present invention relates to a continuous anodic structure for electrorefining nonferrous heavy metal such as, e.g., lead, copper and tin.

It is known that the electrolytic refining of, e.g lead is carried out in electrolytic cells to which massive anodes are charged, which are constituted by impure lead; and lead or stainLess-steel cathodes are installed, on which refined lead will be deposited: in this case, the electrolyte is, preferably, but not 10. mandatoriLy, an aqueous solution of Lead fLuosilicate with free fLuosiLicic acid,' with the addition of gelatin or other deposit-leveLing colloids.

The massive anodes of the type known from the prior art are affected by several drawbacks, and a rather large is number of practical Limitations: first of all, it is necessary. at rather frequent intervals, to replace the consumed anodes; this causes interruptions in the production cycle..

Furthermore, the so-said "anodic residues" must be smelted again, and this is another factor of cost.

often, the anodic sludges get detached from the anodes and collect themselves on the bottom of the electrolytic cell, and must be periodically discharged:

furthermore, the sLudges may be dispersed in the bath, and thus constitute a polluting agent.

If, on the contrary, the sLudges remain adhering to the anodes, the electrical voltage of dissolution increases, and the sludges have to be detached from the anodes, in order that the electrolysis. may satisfactoriLy 1 1 continue.

1 t should massive anodes of the anode surface area is surface area of anodic current 2.

be furthermore observed that with he impure metal known from the prior art, strictly correlated with the so that the density has a value very close to that of the cathodic current density, and this fact causes limitations in the increase in cathodic density i n s i d e the cell, and an increase in refining costs.

purpose of the present invention is b a s i c a L 1 y providing an anodic structure which does not have in the prior consumed anodes f with new anodes the confronting cathode, The that of a discontinuous nature, as it occurs that periodically removing the cell, in order to replace them longer necessary.

In such way, those dead times would be avoided, w h i c h a r e caused by the dismantling and replacement c', the anodes, thus making it possible the electrorefining to be carried out as a The present invention solving all the other above the anodes known from o r d e r art, so rom the IF is no practically uninterrupted cycle.

rthermore aiming at drawbacks affecting is 1 U reminded the prior art.

In to achieve the above purposes, invention proposes an anodic structure electrolytic refining cell for the eLectrcrefi nonferrous heavy metal, inside which cell the power is fed to the eLectr by one or more anodic and characterized in that i perforated plates, of a rnateri the electrolyte, suitable the present f o r a n ning of a e 1 e c t r i c a 1 odes plunged cathodic t comorises at in an electrolyte current carriers, least a couple of al chemically inert towards for being transversely 3.

the cell by the sides, and in the nearby, of each of said anodic current carriers, so as to define inside the cell a chamber closed 1Rterally and at -its bottom, which contains s?id anodic current carrier, with said chamber being suitable for being filled with the metal to be refined in a loose form.

The outer faces of said perforated plates are coated by a thin cloth made from a thread permeable to t h e electrolyte, but acid-proof.

The anodic current carrier contained in the anodic structure according to the present invention is advantageously a strap of a conductor metal bent to an "L"-shape, or to an "U"-shape, but it can anyway be given any other shapes suitable for the characteristics of the present invention.

Preferably, the Irom, and paraLle coated by an acid-proof plastic from said plastic mater perforated plates, spaced apart to, each other, are made fror.. a metal material, or even si,-,.ply The metal.to be refined is preferably in a granular form, or has the form of drops or fragments, obtained., e.g., by granulation in water,- or by any other suitable processes for supplying loose metal particles: in that way, the considerabLe savings operations costs.

The anodic metal form of scraps, fragments, or any other anyway comminuted forms, and the individual pieces, fragments or drops have a size preferably contained within the range of from 1 to 20 mm. The fragments or small pieces of anodic metal to expensive casting of the anodes is avo are achieved in investmenz id-ed, and and o be purified may also be in the 1 1 be purified are then interior chamber of the In such way, the use, once that p a r t i c 1 e s restored charged in bulk t c t h e em p 'L y anodic structure in question.

anodes are continuously renewed, beca the electrolysis has been started, o t h e r m e t a L are charged and t lie anode i s continuosly and practically becomes a true continuous anodic structure. BY operating becomes i S t 1.1 o v a 1 u e s: large su whi ch Layer, adopting the ceL possible, or thus, anodic chamber question is drops, particles or an optimum contact envisaged current of the anodic material, contained between the and parallel plates, and portion of ensures a a f a c t intolerable Dotential bottom wall of the loose perforated horizontal c a r r i e r, generating, such L at even when the cathodic c three times as large as the by operating with an anode rface area, the anodic passivation would be caused by an excessively whilst the cell voltage is kept within as to prevent dangerous impurities from being from the anode and being subsequently deposited on cathod, with the consequent pollution of this latter.

Inasmuch as the anodic material which fills or compartment of the anodic structure constituted by an extremely a continuous an extremelv 1 fragments, a current be with it should c a r r i e a n o d i c anodic, structure, ow current density urrent density normally having a is prevented, thick sludge such limits d i s s o 1 v e d t h e u s e d very the in large amount of carrier ensuring provided; the herein r substantially constitutes the chamber, to that the own weight two on the t h e "L"-shaped a n o d i c current very good electrical contact, without which was not easy to expect, drops due to ohmic resistance.- r r e s t i n 9 t 1 I n m e t a 1 v o 1 t a 9 e 1 n thi 5 W a YA. electrorefining strongly i m p u r e nonferrous heavy metals becomes possible, without having to be afraid of the passivation of the anodes, or of the contamination of the pure metal collected on the cathodes.

Besides the above, the possibility is achieved that as the anodic material to be refined, comminuted scraps o f m e t a L a L L o y and scraps c f mi xed ffi e t a L s t o b e separated, always as smaLl-sixe pieces having a size comprised within the.above suggested Limits, can be used.

The invention is now better explained as regards its aspects by the figures of the hereto attached i o n, general p a r t i c 1 e s the smaller the average size c f t h e t o be purified, t h e L owe r t h e c e 11 i c a 1 and by some examples of pract the electro'lyti c ref ining of drawings:

practical drawings relating to In the Figure 1 shows a schematic view of an electrolytic ref ining f aci lity using the continuous anodi c stru.-cture according to the present invention; and Figure 2 shows a partially sectional, perspective a continuous anodic structure view, 'exemplifying according to the present invention a facility is In Figure. 1, an electrolytic and continuous invention: in the depicted sectional views tures 12, the loose particulate masses refined can be clearly depicted, cell 10, with cathQdes of anodic structures 12 ac s t r u c to be f aci lity seen the has the usual structure known ir a p p 1 i c a t lead and copper.

which compr known type cordina to s e s 11 t h e of the anodic 20 of metal emainder of.the the art, and 1 1 6.

the electrolytic bath 15, a tank 16 for said electrolytic bath, a circulation pump for the electrolyte, with the delivery line 17 on the bottom wall of the cells, provided wi.th delivery-nozzles 19, and a discharge and recycle line 18 can be observed in it. Furthermore, a line 9 of recycle of the anodic sludges, with a tank. 8 and a relevant recycle pump, and a filter-press 7 are depicted. The continuous current to feed the cells 10 is fed by the usual cathodic bus-bars 13 and anodic bus-bars 14.

I t i S operation what o n c ont i nuou - the prior F i 9 u r e 2 not necessary to describe in detail the of the facility, because it is at all normal:

the contrary thoroughly changes, is the anodic structure, which is neither present in art, nor is suggested by it.

of the hereto attached drawings shows in r detail the continuous anodic structure of the present invention: it will be observed at once that it is a structure very simple from a structural viewpoint, and hence cheap to build.

It comprises the greate two perforated parallel pl made from a plastic-coated metal, or simply suitable plastic material, the lining of acid-proof cloth 22 (one linif?9 on each outer face of the anodic chamber 24), the loose anodic material 20 (also shown in Figure 1 the anodi c current carrier 23 bent to an "L"-shape, and a wall 25 of the electrolytic cell. It can be observed that the structure forms a chamber closed laterally and at the bottom, which contains said current carrier strap 23 (of stainless steel), whilst the top de is open in order to allow - the periodic charging of.

tes 21, 1 1 1 7 the comminuted anodi c m etal.

In order to better understand the practical application of the continuous anodic structure according to the invention, some examples of practical application a r e supplied hereinunder, f rota w h i c h t h e important technical and f i n a n c i a 1 advantages can be f J1 I y understood, that the invention has provided to those ski L led in the art. - According to traditional anodes, Sb Cu Sn As Bi e wor average size of 5-6 mm, compartment of a cell, perf crated plasti c materi a L the drons the process of e lect roref i ni rig w i t h a work lead having the composition:

1.67% 0.11% 0.29% 0.042% 0.014% Aq 0.0029% must be deprived of copper and tin before being cast into anodes, in order to prevent Cu and Sn f rom beinadissolved,, and depositing on the cathode, polluting it.

The sam k lead was directly cast into drops of and was charged to the anodic constituted by two walls of a which restrain the mass of to be refined to rest on the bottom current c a r r i e r The electrolyte was a bath of lead fLoborate w i t h f ree f luoboric acid and boric acid, and with t h e usual gelatin added.

The parent cathodes were, stainless-steeL p 1 a t e s w i t h PVC peripheral rims.

Throughout -the t e s t, the cathodic current density w a 5 o n t h e contrary., 1 1 8.

2 maintained equal to 300 Alm The cell voltage at remained approximately equal to 0.90 V.

After 200 hours of electrolysis, with the cathodes being removed every 70 hours, and the corresponding.charge of metal drops-being added, the lead obtained from re-smetting had the following average composition:

Sb less than 10 ppm Sn less than 5 ppm As less than 10 ppm Cu Less than 3 ppm Bi less than 5 ppm Ag less than 5 ppm Ni less than 3 ppm Lead titre resulted to be of 99.995+.

At test end, the sludge was removed from the anodic compartment, and refining was regularly re-started, after charging a new batch of drops.

Examole-2 The scraps from grids and poles, obtaining from the fine crushing of the old batteries, and from the subsequent sorting by hydrodynamic separator, generate, by re-smelting, an alloy containing 3.85% of Sb, 0.05% of Sn, 0. 20% of Cu, 0.10% of As, 0.020% of Bi, 0.004% of Ag.

If one wishes to obtain electrolytic Pb by casting traditional anodes, t he metal has to be preliminarily refined (copper and arsenic removaL), in order to prevent these impurities from entering the anodes. Furthermore, at approximately half anode life, it is necessary to remove the sludge from the anodic surface, in order to prevent the cell voltage frora increasing.

In our tests, we charged the grid scraps directly to J 9.

anodic compar tment of the cell disclosed in Example t a cathodi c t h e 1, and electrolysed them at 25 density of 300 AIM 2 in the above The volt.age remained to be 0.8 to 1.15 V throughout the test time (24 days); the test was carried out according to the same modalities as of the previous example.

The cathodic deposit, re-smelted into ingots, confirmed the analysis already reported in Example 1, i.e., a 99.995+ Pb was obtained.

Example-3

The copper wire scraps, obtained by crushing coated cables and by the following sorting in air and on a vibrating table, constitute a high--quality material suitable for obtaining electrolytic copper, or furnace refined copper. The low content of Pb (0.5-1%) and of Sn (up to 0.2%), as well as the fortuitous presence of Cd, obliges anyway a long refining step to be carried out, which causes an expensive slag formation, with the recycle of at least 7-10 copper units. it is known that the electrorefining of Cu by operating at 200 Alm 2 requires anodes with Pb -Contents lower than 0.20%, in order to make sure that the same impurity is contained within the limits as stated by the copper cathodes governing regulations.

In our test, we used a fine scrap from copper wire deriving from cable crushing, which contained 2.3% of Pb, 0.25% of Sn and 0.15% of Cd (the raw material was constituted by mized telephone and energy cables).

The electrolyt disclosed electrolyte.

within the range of from electrolysis carried out in the usual e based on copper sulphate with free sulphuric 1 i 1 1 1 t 10.

0 acid at temperatures of approximatelu 50 C yielded good quality cathodes, and, in particular, with Pb impurity lower than 5 ppm. 1 The total impurities were Lower than 65 ppm.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of this invention.

i c 1 1 1 1 c e 11 w h i c h plunged cathodic comprises from a material chemically suitable for cell by the sides, anodic current carriers, so.as a chamber closed laterally and contains said anodic current car suitable for being filled with the metal a loose form.

2. characteri coated said chamber, by a cloth made' impermeable, acidproof thread.

3. A n o d i c C-1-a-i-m-5 Anodic structure for an electrolytic refining for electrorefining a nonferrous heavy metal, inside cell the elect.rical power is fed to the electrodes in an electrolyte by one or more anodic and current carriers, characterized in that it at least a couple of perforated p 1 a t e s, made towards the electrolyte, positioned inside the nearby, of each of being i ne rt transversely and in the s a i d to define inside the cell at its bottom., which rier, said chamber being to be refined in Anodic structure according to claim zed in that,each of said perforated plates on its own face'directed towards the exterior electrolyt 1 ' i S of f rom an structure according to clairll characterized in that said anodic current carrier is a strap of a conductor metal bent to an "L"-shape, or to an "U"-shape.

4. Anodic structure according to claim characterized: in hat said perforated plate constituted by a metal plate coated by an electrolyt proof plastic material.

5. A n c d i c characterized in constituted by structure according to claim 1, that said perforated plate is a' plate of electrolyte-proof plastic 12.

materiaL.

6. Anodi c characterized Loose form has a of from 1'to 20 mm - 7. Anodic characterized metaL.

8. An anodic structure substantially as herein described with reference to the acdompanying drawings.

structure according to claim 1, in that said metal to be purified in a particle size comprised within the range structure according to claim- 1, in tha t said metal is a nonferrous heavy -A Published 19813 at ihe Patent Office. State House. 66 71 High Holborn. London WC1R 4TP- Further copies maybe obtained from The Patent Office, Sales Branch, St Mar7 Cray. Orpington, Xent BR5 3RD. Printed by multiplex techniques ltd, St MarY Cray, Kent- Con. 187-