A method for the electrolytic production of a polyvalent metal and equipment for carrying out the method

The présent invention relates to a method for the electrolytic production of a polyvalent mntal, such as titanium, zirconium or hafnium, by the cathodic dissolution of a halide of the métal in an electrolyte of alkali or alkaline aarth métal halidns in the fused state and the electro-extraction of the matai from the electrolyte.

The method more particularly concerna the préparation of titanium by the electrolysis of an electrolyte of fused halidas.

The electrolytic production of titanium in a bath of fused salts diffère from that of other, monovalent metals produced in the fused state in many ways which are reflected in particular operative problème.

As regards the aspects of a truly plant-engineering nature, the problème dariving from the cathodic déposition of the matai in the solid state and from the raxtreme reactivity of the mntal. and of its ions with air are weJ.l known. An important contribution to the solution of these problème i3 provider) by the plant described in Turopean patent application

No. EP-A-0210961 in tho name of the AppLicant, whose descriptive content is to be conside.md as being incorporated in the présent description by virtue of its citation. The plant described therein enabl.es the electrolysis process to be operated continuously and tho oxidation by air of the métal produced to be avoided, thus giving a high production yield and a métal product of grod quality,

Ag regards the process, an important charactnristi.c which differentiates the electrolysis of titanium from that of other metals commonly produced in fused salts is the différence between the valence of the titanium in the electrolyte and its valence in the raw matériel, titanium tetrachloride, which is not very soluble in thR electrolyte. To enable efficient electrolytic extraction jt is noenssary to reduce the titanium tetrachl.or.ido to the divalent oxidation state which is soluble in the electrolyte.

Another important aspect of tho electrolysis of titanium is connecter!

with it.'i multivalence in tho electrolyte with the nimultaneous presence

09628 of divalent. and trivalent ions, the equil'brium of which 13 affected by conclitions such as the température and the presence of impuritie3 in the electrolyte. Since the efficiency of the electrolytic production is greater, the greater the percentage of divalent titanium, it is necessary to keep the average valence of the titanium in the electrolyte very low, generally no greater than 2.1.

A further important factor in the electrolysis of titanium is the high reactivity of the titanium ions in the electrolyte with the nascent chlorine, both the dissolved atoms and the dispersed gas, which make it necessary to keep the zone in which the chlorine is evolved separate from the rest of t.hp electrolyte.

Oecause of this reactivity it i.s necessary to prevent the migration of the titanium ions by diffusion into the vicimty of the anode in order to avoid their oxidation to the trivalent oxidation state, their reaction with nascent chlorine, and the formation of TiCl^ which is volatils at the operating température, whilst at the same time maintaining tha ion transfer between the cathode and the anode due to the chlorine ions.

In order to increase the efficiency of thr· titanium extraction, the dif f te il t i^s connected x.'-i tii tho factors described d>nv9 being taken intn account, j t was propooed .in 0‘>-A-2,71--9,945 to interpose a conductlvo dianhragm between thp modo and the cathode, surrounding the anode irid li.nvinq i>ia 1 Is which were perméable tn the electrolyte and ndapt.nd to -uippoiT a depnsit in the form of a panel (overlay ) of the métal tn be produced, and to connect this diaphragm ta the electrical supply circuit, uf the cell. sn ns to givn it a négative potentiel relative to the anode in order to r?.-*«-nn ri>n formolinn of a cathodic deposit of the métal In Lm produced on the perméable walls of the diaphragm which has a per mal· j.J i. !.y ·<ι jeh i s to allow thⁿ ion tmnsfer duo to the chlorine ions Ind: ni.ibsI..anI. ial. l y to uroveni f.iie mjgraî.ii >n of titanium ions hy dif fus ion from t he c t,criards thr· ηιιηιΐο.

09628

European patent LP-B-555M doscr.ibes a method for controlling the permea— bility of the diaphragm covered with tho deposit of the métal to be obtained which is achieved by causing the (notai deposit to increase or dissolve in dépendance on the voltage drop in the electrolyte which imprégnâtes tho diaphragm it3olf.

The first of the methods c.itnd above does not enable continuous operating conditions to be maintained industrially because of the continuous variation in the thickness of the deposited panel which itself constitutn3 the mass of métal produced to be removed periorlically so that the operator has to repeat the sterling up procedure several times a day.

The method according to the aforosaid ΕΡ-Β-^Γ·.5564 does not enahle the oxidation of the divalent titanium in the cathodic compartment and the conséquent increase in the average valence of the titanium in the bath to hn pmvented during the formation nf tho métal dnposit on the diaphragm, and this inevitably leads to a low extraction efficiency.

Both tho methods dnscribnd in the patents mentioned above require complex starting procedures which are expensive in terms of time and electrical energy and very difficult to control. In these methods, tho starting-up which is carried out with tho diaphragm open, starting with a mass of electrolyte which does not contain ions of the métal to be produced, requires a sequence of operations which is unaccoptabln for industrial production.

In order to avoir) these problème, a first subject of the présent invention is a mothod of the type indicatod in tho introduction to the présent description, in which the stage of electro-extraction of the métal is carried out in a cell includ.ing at least one anode and one cathode and a conductive framework which acte as an intermediato electrode and surrounds the anode so as to dofine an anodic compartment and a cathodic compartment, and has walls which are perméable to tho electrolyte and are able to support a deposit of tho meta! to be produced in tho form of a panel so as to allow ionic transfer betwoen the cathodic and tho anodic compartments but to limit substantially the transfer of the ions of the métal to be produced from the cathodic compartment to the anodic compartment, characterised

09628 in that it includes the steps of :

a) supplying the extraction cell with électrolyte containing ions of the métal to be produced in solution,

b) confining, within the Framework, a bath of alkali métal or alkaline earth métal halides which is substantially free of iona of the métal to be produced by the electrolyte-tight screening of the permeable walls of the framework with métal partitions which are capable of anodic dissolution,

c) feeding an electric current between the anode and the framework auch as to cause cathodic déposition of the alkali métal or alkaline earth matai on the permeable walls of the framework for a sufflcient pariod of time to cause an accumulation of this métal,

d) feeding an electric current between the anode and the cathode such as to cause déposition of the métal to be produced on the cathode with the simultaneous anodic dissolution of the partitions, so as to enable the diffusion of ions of the métal to be produced from the cathodic compartment towards the anodic compartment with the formation of the depositif of the métal to be produced on the permeable walle of the framework as a resul of the réduction of the métal ions by means of the alkali or alkaline earth métal,

e) maintaining the electric current feed the anode the cathode in order to dépolit the métal at the cathode and simultaneously,

f) regulating the current between the anode and the framework so as to keep the perméabilité of ths deposit substantially constant.

During step f), the intensity of the current between the anode and the framework constituting the intermediate electrode is kept at a magnitude such as to cause the déposition of the alkali métal or alkaline earth métal on the interface of the framework which facee the anodic compartment at a rats sufficient to reduce the ions of the métal to be produced (s.g. Ti ), which flow by diffusion from the cathodic compartment, to the metailic state, and so as to establish a state of substantiel équili— brium between the flow of these ions (Ti ) which are being depoeited and the anodic dissolution flow of the métal (e.g. titanium) being deposited to the interface of the framework which faces the cathodic rompar trient.’

99628

A further subject of the invention is a composite electrode particularly for carrying out the method described above for the electrolytic production of a polyvalent métal in a fused-halide électrolyte, including t at least one anode provided with a terminal for its electrical connection, an electrically-conductiva frametuork insulated from the anode, provided with a terminal for its electrical connection and surrounding the anode in the form of a basket, the frametuork having wall portions facing the anode which are permeable to the electrolyte and adapted to support a cathodic métal depoeit, characterised in that it hae support means associated with the walls of the frametuork for supporting sealing éléments in the form of partitions, adjacent the electrolyte-permeable wall portions, for confining within the frametuork an electrolytic bath which is frwa from the métal to be produced, and for preventing the infiltration of the electrolyte into the interior of the fremework through the permeable wall portions, the partition-like sealing olemwnts being constituted by a métal which is capable of anodic dissolution under the operating conditions of the electrode.

Further characteristics and advantages of the method and of the device according to the invention will becoma clear from the detailed description which follows with référencé to the appendad drawings, provided purwly by way of non-limiting example, in which:

Figure 1 is a frontal section of a composite electrode according to the invention,

Figure 2 is a view taken on the line II—II of Figure 1,

Figuras 3 to 5 are sectional views of a detail of

Figure 1 according to different embodiments,

Figure 6 is a schematic view which shows the mechanism by which the métal is extracted, and

Figure 7 is a schamatic view of the plant for carrying out the method

09628

The electrode illustraded in Figure 1 and 2 is particularly adapted for use in a plant of the type described in the aforesaid Européen patent application N° EP-A-0210961 which describes elec.trodes for suspension in a bath of fused salts supportsd by support means and electrical connection means constituted by a pair of electrically-conductive members which face each other and are supported respectively by opposite walls of the crucible containing the fussd sait bath.

The electrode illustrated in Figure 1 and 2 is similarly provided with a pair of supporte described in greater detail below; it is, however, unders10 tood that the innovative principle of the electrode according to the invention can be applied regardless of the technical details of its electrical connection. The composite electrode iteelf will also be referred to below in the présent spécification by the abbreviation TA, since it is constituted essentially by a Bipolar Titanium Electrode (TEB) wich is formed in situ during the initiating stage of the extraction process, and by an anode A.

Ulith reference to the drawings, the electrode according to the invention includes an anodic graphite cross-member 1 which supports three anodic graphita bars 2 by mortize joint. A generally parallelepipedal métal Framework which surrounds the anodic bars 2 like a basket is indicated 3* The

Framework 3 has fiat side walls 4, 5, 6, and 7 and a basa wall Θ. Th· top portion of the framework 3 eurrounds the anodic cross member 1 and is •lectrically insulated therefrom by means of prismatic sleeves 9 of insulating refractory material. The side walls 6 and 7 and the base wall 8, lik· the upper portions of the side walls 4 and 5, are covered with panels 10 of insulating, refractory material. A concave element 11 is mechanically and electricaliy connected to the framework 3 but is insulated electrically from the anodic cross member and is intended to act ae a support and terminal for the connection of the framework to a supply of electromotive force (rectifier not illustrated).

jg A similar concave supp_Ort element 12, electrically insulated from the Framework 3, is connected electrically to the anodic cross member 1 and acta as

9 6 2 8 the terminal for its electrical connection.

The front walls 4 and 5 of the framework each hâve an aperture in which there is mounted a grating 13 formed by a plurality of tile-shaped éléments 14 arranged in horizontal rows and defining passages 15 between them through which the electrolyte can flow. Figures 3 to 5 show three different configurations _of each tile-shaped element which, as will be 3een in more detail below,are particularly suitable, for enabling the alkali métal or alkaline earth métal deposited by cathodic réduction to accumulate during the operation of the electrode. The configuration of the tile-shaped element of Figure 3, with a V-shaped cross section, is particularly preferred.

A refractory ceramic fibre panel 16 which is permeable to the electrolyte is mounted adjacent each grating 13 of the side which faces towards the anodic bars. A plurality of grid membres 17 are mounted on the opposite side of the grating.

Métal partitions indicated 1B are releasably mounted so as to form an electrolyte-tight seal between two annulai- frame members 19 and 20« Each partition 1θ, which is preferably constituted by a sheet of the very métal which it is intended to produce with the aid of the composite electrode, acts as a sealing member which closes the apertures in the side walls 4 and 5, enabling an electrolytic bath of fused salts in which the anodic bars are immersed to be confined within the cavity defined by the framework 3, while simultaneously preventing the infiltration into this cavity of the production electrolyte which is outside the anode, during the initiating stage of the ^extraction process.

The electrode according to the invention is also provided with deflectors 21 for reducing spray caused by the formation of chlorine bubbles evolved at the anode and the conséquent entrainment of the electrolyte towards the anodic cross member when the electrode is in operation.

The method for the production of a polyvalent métal, which will be given below with particular reference to the production of titanium, is prpferably carried out in a plant of the type described in European patent application N° EP—A—

0210961 in the name of the AppJicant.

09628

As illustrated schemacica.lly in : i .ure 7, a crucible 22 is used which, to advantage, is divided into a first cell 23 for the dissolution of the tstrachloride and a second, extraction cell 24 for the déposition of the metallic titanium at the cathode. The dissolution and extraction celle intercommunicate through valve nnans 25.

With reference initially to the métal extraction stage, an electrolyte is supplied to thn extraction cnil from the dissolution cell and is constituted by a bain of alkali métal halides or alkallne earth métal halides containing titanium in solution. The electrolyte is preferably constituted by sodium chloride. The use of sodium chloride has numerous advantages over other electLOlytes by virtue of the simple structure of the liquid which does not form complexes which would interfère with the titanium déposition mechanism and which, by condensing on the walls of the crucible above the level of the bath, forme î solid, adhèrent layer which forma a good protection for the materiais against the corrosive action of the gaseous chlorine.

<td> At the start of i concentration of 2.1.</td><td colspan="2"> zhfj extraction opui·: between 3 '-nH W\: ,</td><td colspan="2"> ition, the bath preferably has a titanium &gt;ith an average valence of no more than</td>

<td> The extraction c</td><td> Ίχ include· ,,r</td><td> t ¹ .’· S </td><td> one cathode 26 and at least</td><td> one</td>

<td> composite electru</td><td> '&gt; · ( Γ &lt; ) of’ f he</td><td> t_y!.u</td><td> - described above. During the</td><td> stage of</td>

initiation of ihf· eloc.lro-extract.iun, tue framework 3 οΓ the composite electrode is provide·! with partitions lb constituted by titanium sheets, and an electrolytic both of fusnri 1. d ido salts of alkali or alkaline earth metals, preferably sodium chloride, substantially without titanium ions, is confined withl-) ibs fimiKSMGrk .

The température _>f the el ctrob/ln ï > regulated to a value preferably between 800 and ΗΗΟ’Γ., The p' -nmms i a carried out in a sub-atmosf eric pressure environment.

Q

99628

After t.hp compnr.lt.-> plnctrortn hn$ hoen position-d in the electrolyte, a pnt.rntial in applied, through a rectifier '-'7, between thn anode 2 and the meta] fγο^ιπϊιόγ’>- 3 whirh assurons a nwidiwn potcntial relative to the anode, thp iη l <>n ^: i tv nf the eurent proihr»·! being such as tn cause the cathodic. déposition nf thp al.ka] i met.-·.! ni- alkaline earth métal, preferably sodium, on the gr>t ings I ’ . The til ed structure of the gratings encourages the ocç'.iæ'il-d: ion d met.i.lltc sodium in thn downward-fneing concavit.y of each til.n~-ti.aped nl-nmnt, rince t.hn podium, which is 1 ighter than the elortrnlytn, tend·· t·¹ rino .-uid r-mains t.r.ijipod undor thn archnd walJ. of

1Π each ti .le-ehapnd · · ’ ’i’nt . Th»· potentiel, is applied between thn anode and th···· fr-amnwnrk noti. 1. a mbat m'i-] accumulâtj on of sodium has been obtained.

Λ potentiel is then applied hntwnen the anode ’’ and the cathode 26, so as to cmn» titanium to hp d, o i i 1ι>> I -od th a i.mi 11. taneous anodic dissolution of the ronfining parti Fions î Π. ·’η a γ<·ίη! t of thp anodin dissolution of the parti tini’s 1î._} a transfer of material is estahlîshnd between tha electrolyte outside thn f r.nmework, wh.ich contain-' t itanium ions, and the ,7.i.

bath within t,h<· fr.-vwnr¹'.. rhe Ti ions luiprate by diffusion towards the anode and are reduced tn métal.] in titanium wihn thn help of the sodium which hnn aecumul -t.-d within th- gratin»; s-t.rurture 13, t.hus forming a micro-cryst.a 1 1 > ne rlnpos i t in thn form nf pornos ponds which act as perméable diaptiragm-. tn thp innin transfrr nf t.h>? chloride inns hut are ? .1, suhstanti a L.l y i .npermonljl n tn l-h r> fl.ow nf Ti .ions hy diffusion towards thp anode.

Figure 6 show- _S(-hematicalSy F!<^ mnehanism whirh is set up as a resuit of the formation nf .» p >rr»n p-nd af mirrn-rrystalJinn titanium indicated 28.

It should bn rnmamlmi -d that l.h»· panel simultaneously becomes the saat _of sev-ral prn^r'^p'^?n on that the p.-npl its-lf op-rates like an electrode with t.hn follciwiog fonctions î ) th·¹ -surfnco nf thn panel which faces the anode acte as a monnpolar nathndo· there h a 1 imitnd production of mntaJl.ic sodium on the panel .with in'in'mnUpnt ni n-tr.i-ni pjipplyj

1Π

09628 mentioned above

2) the oppos· tr· fiirv nf th&lt;?' panel Fies that

<td> acts as a moni'polar</td><td> cathodn</td><td> at</td><td> uihich</td><td> tl m</td><td> réaction</td>

<td></td><td colspan="2"> _ .3 +</td><td></td><td></td><td> / 4&gt;</td>

<td></td><td> Ti</td><td> +</td><td> e —</td><td> —&gt;</td><td> Ti</td>

takes place, wheroby t.lm avorage valence nf thp electrolyte is kept low ;

5) the interior of the panel acte ns a monopolar cathode, in billion the h.nlf reaction ;

<td></td><td>_T.? + T i -h</td><td> ? P</td><td> ----&gt; Ti</td><td></td>

<td> takes place with</td><td> t.he formation of</td><td> fine</td><td> crystalline</td><td> titanium ;</td>

<td> 4 ) as '&gt;</td><td> hipolar electrode</td><td> f or</td><td> a fraction</td><td> of the current</td>

supplied between

t.iin production cathodes and the anodes, with a limited production and oxidation of cathode; and also ) as a the the ions

Cl sodium at the interface which faces the anode nt to fi d i.aphragm ions carrying t.he onodps, with siilistitit, i ··!

at the interface i or, i p reaction desc^ri|lod a be ve mainte ineri to ,ιΝιΐρνρ

t.he interface which faces the a I lows current fj tr¹ r i· ’I end the current. between the s imulteneously -o .m to anode and substantially com l. >η':. Fnr t h i current. between thr¹ the unimpeded passage of hetweon the cathodes and précipitation of the titanium cat.hodo, t>y the

t.he tianel

l.lw t h>

caiised by the processes ) and 4) cathode is then is regulated the cathode, regulated panel of the preferably >n flow of sodium at the i

, i ^r;

s

<td></td><td colspan="2"> inter fnon</td><td> f ac i i v | 111-. -ipm g. hil i icî</td><td> in</td><td> ”JÎ fi r i -&gt;</td>

<td></td><td> f 1 ow</td><td> nf</td><td> -.2-1 . ... T1 inn:’ 1 cl| ! o i(:t,</td><td> the</td><td> 0 1 ll&lt;&gt;&gt;, i f</td>

<td> 30</td><td> by</td><td> (ti.f fus</td><td> i on f rom the cathe i y 1.1</td><td></td><td> o.ich t.li</td>

jot n_rf:æ_F nt ta precipitate the of the panel of substantial ions and ϊηΐρΓ^!'··θΡ fac ing the cathode

1

09628 with the use of a plant of the type described in application No. EP-A-0210961, it is particularly easy to replace a mature cathode by a new cathode, without interrupting the production cycle.

A further innovative aspect of the. method of the invention lies in the stops for the dissolution of the raw material for enriching the titanium concentration in the electrolyte to be supplied to the extraction cell. The dissolution is carried out with the help of a dissolution cathode 28 connected to a rectifier 27 and ^constituted by a métal structure with a large surface area immersed in the electrolyte and into which, outside which or adjacent which, liquid titanium tetrachloride is supplied by means of a nozzle 29. The operation may, to advantage, the aid of a TA composite eler.trode of be carried ou with

<td> the</td><td> type</td><td> described</td><td> above,</td>

<td> i of</td><td colspan="2"> titanium and</td><td> including</td>

<td> free</td><td> f rom</td><td> titanium</td><td> ions</td>

initially provided with cnnfining partitions a bat. h of sodium chloride substantially within the framowork.

If one starts, for example, with an exhausted electrolyte having a titanium ion concentration of the order of 2%, with an average valence of approximately 2.1, a potentiel is applied between the anode and the f imiimiiork so as to cause the déposition of sodium by the merhanism described .above with reference to the extraction stage, and a potentiel is then applied between the dissolution cathode and the anode in order to cause t.h-> formation of the panel of titanium.

Titanium tetrachloride ïs then supplied to the dissolution cathode at a rate which is essnntially in a stoichimetric ratio with the electrical currmit supplied to the dissolution cathode in order to enrich thr· electrolyte to give the desired concentration of the titanium ion.s in snjul.ion, which is generally approximately 10%.

The dissolution prncpns m>)' hn represented by the réactions :

Cl„ i

that is, by the cathodic half réaction

9 6 2 8

<td></td><td> T1C1 + 2e ---&gt;</td><td> Ti^{2 +}</td><td colspan="3"> + 4C1</td>

<td> and the</td><td> anodic half reaction</td><td> • •</td><td></td><td></td><td></td>

<td></td><td> 2C1”</td><td></td><td></td><td></td><td></td>

<td></td><td colspan="2"> ----Cl + 2e</td><td></td><td></td><td></td>

<td> It should</td><td> be remembered that,</td><td> in</td><td> reality,</td><td> the</td><td> cathodic</td>

<td> process</td><td> 3*4 involves the Ti</td><td colspan="2"> ion according</td><td> to</td><td> the</td>

<td> reaction :</td><td></td><td></td><td></td><td></td><td></td>

<td></td><td> 3 4 — «</td><td> ? +</td><td></td><td></td><td></td>

<td></td><td> 2Ti 2e ---</td><td> 2Ti^{Z +}</td><td></td><td></td><td></td>

<td> the Ti³⁺</td><td> ion being produced</td><td> by the</td><td colspan="3"> chemical reaction :</td>

<td></td><td> 2.4</td><td></td><td> 3+</td><td></td><td></td>

<td></td><td> TiCl + Ti —&gt;</td><td> 2Ti</td><td> +</td><td> 4C1</td><td></td>

<td> After the</td><td colspan="2"> first stage in which the</td><td colspan="2"> concentration</td><td> of the</td>

titanium dissolved in the electrolyt.e is enhanced, it is préférable to provide for a further réduction in the average valence of the a ”soak.ing operation, dissolved titanium by means of by stopping the supply of titanium tetrachloride, reduc i ng the current supoli ed to the dissolution cathode and adjusting the i nionsi ty of the current at the composite elni'trodn, hotnieen the

<td> anode and the panel,</td><td colspan="2"> to a v ilue</td><td> such</td><td> a s t o</td><td> maintain the</td>

<td> production of métal lie</td><td> sod i um</td><td> at</td><td> t i 1 ^r&gt;</td><td> mort j c</td><td> interface</td>

<td> of thn panel and to</td><td> conti nue</td><td colspan="2"> th'· n</td><td>¹71 je¹ i on</td><td> of the</td>

<td> tr.i.v ib'-rH· t Itanium tn</td><td> tlv-·</td><td> H val</td><td> rpt</td><td> a ta t¹'</td><td> al. the</td>

<td> cathodic int-τΓ n</td><td> f the</td><td> i r&lt; ’</td><td> p ΓΙ'¹]'/¹</td><td> i . &gt; f o</td><td> al &gt;&gt;r- trode.</td>

During this npi'î atior., the chlor inc pvolvmj at the anode is convey'd to the outside and the sodium produced within th” Γ¹ h rouets with the high valence

<td colspan="2"> electrolyt.e</td><td> ar'cnrd i nn to</td><td> thn ranci i.ari :</td>

<td> 5)</td><td> TiCl₃</td><td> 4- N 8 ———</td><td> T iCI., t NaCl</td>

<td> or</td><td> bel. ter</td><td> • »</td><td></td>

<td> 1)</td><td> TiCl_n</td><td> + 2'!a — —</td><td> Ti + XiPCl</td>

2)

Π

-ι

2TiCl^ λ T j ^r: i • ' ^J · e.

5

09628

Alternatively, it may be thought that efficiency of the cathodic interface direct réaction of the Ti^⁺ with the the high is due électrons reducing to the Supplied to the .intermediate TEB electrode describej above, this react ion being more favoured from an energy point of view than the déposition of metallic sodium, in 9pite of the configuration of the current paths with greateet résistance.

After the soaking operation it is possible to achieve not only the cheminai equilibrium of the reaction 2) given above with an average valence at R25° of 2.07 but, _Tp+ by continuing the valences

When the nientrochernieal _T.2 +

Ti , without equilibrium dissolut i on stage reaction average valence has means 25 are opened

e.lectroly tn in dissolution ce) l it of is is possible between 2.00 ccmpleted and to and heen renched in the for sufficient thime achive average

2.07 suitable hath, the valve to allow the the extraction cell and in tha to becomn hornogennnus

According to one variant, the dissolution process may be carried out without the supp.ly of current to the dissolution cathode but with the use of a TA composite electrode described above, to which thern is suppliad,

<td> between</td><td> the</td><td colspan="2"> anode and the intormediate</td><td> ΤΓ.Β electrode,</td><td> a</td>

<td> total</td><td> current</td><td> which is</td><td> mode up of</td><td> the sum of two</td><td></td>

<td> currents</td><td> :</td><td></td><td></td><td></td><td></td>

<td></td><td>^a)</td><td> a first</td><td> current which</td><td> corresponds to</td><td> the</td>

<td colspan="2"> s toichlomntri c</td><td> rati.” with</td><td> the flow of</td><td> the tetrachlovide</td><td></td>

<td>^s tipp l i ed</td><td> to t</td><td> he flic sol ver</td><td> according to</td><td> the réaction î</td><td></td>

<td> 21 i +</td><td> 2p</td><td> ----271</td><td> 2 (</td><td></td><td></td>

<td> and</td><td></td><td></td><td></td><td></td><td></td>

<td></td><td> h)</td><td> a second</td><td> ciirrnrd luhicli</td><td> corresponds to</td><td> the</td>

<td> c u rrent</td><td> nendei i</td><td> to main*, a in</td><td> su f Γ i c lent p</td><td> réduction of</td><td></td>

<td></td><td></td><td></td><td></td><td> 2 + _T . 0</td><td></td>

<td> metallic</td><td> ' î n d ί 11</td><td colspan="2"> n e_Or t.hp precipifati m of</td><td> the '1 as Tl .</td><td></td>

4

In this variant, it is possible to eliminate the dissolution cathode, retaining only the injection nozzle.

in which the titanium confining partitions electrode are dissolved, in the absence

99628

As regards the stage of the TA composite of the dissolution cathode, cathodic crucible to

The soaking current can be supplied to the métal wall of the cause the anodin dissolution of these partitions.

opérât ion for reducing the average valence of the titanium disoolvnd in the electrolyte may, according to one variant, be carried out: by allnwing tha electrolyte containing TiCl^ and

TiCl₅ and having an average valence spontaneously with metallic titanium grnater than 2.1 to react constituted, for example, by scraps or by titanium recycler! from the extraction cell, in the absence of current., according to the reaction :

2TiCl₃ + Ti ---y 3TiCl₂

This operation may be carried mit Cor a period of between 12 and 16 hours.

In summary, the preferred procedures are as follows î

1) Dissolution cell including metallic titanium added to the bath

<td></td><td></td><td> injection of</td><td colspan="2"> titanium</td><td> tetrachlbride</td><td> for approximately B hours</td>

<td> with</td><td> the</td><td> mechanical</td><td> vc.l ver.</td><td> n ^r )</td><td> between the</td><td> extraction cell and the</td>

<td colspan="3"> dissolution cdl clos</td><td> or!;</td><td></td><td></td><td></td>

<td></td><td> b)</td><td> soaking for</td><td> apprnx</td><td> i ma 1</td><td> ,ely 16 h mrs</td><td> without current, during</td>

<td> the</td><td> last</td><td> two hours</td><td> of whi</td><td> f’h</td><td> the mechani.c'i</td><td> 1 valves 25 are open;</td>

<td></td><td> ?)</td><td> D Issol i it i nn</td><td colspan="2"> coli not</td><td colspan="2"> trie lui l'rig added metallic titanium :</td>

<td></td><td></td><td> injection nf</td><td> the</td><td colspan="2"> tetrachloridn for</td><td> approximately 16 hours</td>

<td> with th</td><td> h mechanical</td><td> valves closed;</td><td></td><td></td>

<td> b)</td><td> snaking far</td><td> npp rox i m i te] y piuht</td><td> hnurs with a</td><td> limited current</td>

<td> t.0 the</td><td> ΤΠΙ, Ιυν ing</td><td> the 1-t t. tur&gt; hours</td><td> of whinh the</td><td> mechanical</td>

<td> valves</td><td> a r o nn r 11.</td><td></td><td></td><td></td>

It is also ρου i.lile to .iiaintalr. tl>-' e v t T Of: t i un singe and the dis-

<td> go lotion</td><td> stage</td><td> s j mul t aneou-îly hy</td><td> iv i i d. a i n i no</td><td> the c</td><td> irculation</td><td> of the</td>

<td> electrob</td><td> 'te bel·</td><td> ''un th« ex ¹ r ir t i</td><td> nn ce 1 ! --n&lt; !</td><td> the r¹</td><td> résolution</td><td> cell</td>

<td> through</td><td> th? v·'</td><td> lue nriri reput</td><td colspan="2"> a ! i ng t h ' opéra t i ng</td><td> parameters</td><td> of the</td>

628

<td colspan="2"> cathodic dissolution</td><td colspan="4"> cell, in particular the supply</td><td> of</td><td> the halide,</td>

<td> the</td><td> current to th^</td><td> dissolver</td><td> and the</td><td> current</td><td> to</td><td> the</td><td> Framework of</td>

<td> the</td><td colspan="2"> intermndiate electrode, so</td><td> as to</td><td> maintain</td><td> thp</td><td colspan="2"> concentration and</td>

<td> the</td><td> average valence</td><td> of the di</td><td> ssolved</td><td> titanium</td><td> ions</td><td> at</td><td> their opéra-</td>

tional values.

Example

The method for the production of titanium is carried out with the use of the pl'.nt described in patent application No. EP-A-0210961 in which the crucible is divided into an extraction cell and a dissolution cell. The extraction cell inrludes 6 iron cathodes each a

with a surface area of 2 m‘ and 5 TA composite électrodes provided with titanium confinement partitions and including a bath of sodium chloride within the f ramewnrk, as descrlberi .above. The electro.ly tic hsth is const Itut.ed by sodium chloride and titanium chloride with 5% by weight of Ti.

<td> At</td><td> the</td><td> .initiât</td><td> ) ΟΙΊ 9</td><td> a current of approximately 4000 A/m</td><td> of</td>

<td colspan="2"> cathndic</td><td> sur f an</td><td> a a r ° a i h</td><td colspan="2"> supplied tn tho TA of tire extraction</td>

<td> ca 11</td><td> for</td><td colspan="2"> n period rif 1</td><td colspan="2"> horiiT after which th·-· opnrating conditions</td>

<td> a re</td><td> ne! i i</td><td> ver! by</td><td> tlia Clip, il</td><td> y of a crjrri’nt of 15:10 '&gt;/m to the</td><td></td>

<td colspan="2"> cathodes</td><td> a r π I</td><td> orront o</td><td> Γ 5&gt; m riym' nf caflindic surface area</td><td> to the</td>

<td colspan="2"> TEfl, and</td><td> cell</td><td> r ii r 1 L ni] rie ri</td><td> Γ l'.ti· or-rl' r of 6,5 1/ between the</td><td> anode</td>

<td> and</td><td> U ic</td><td> rat. h' ’d</td><td> O l'.irri 3,5</td><td> \f bet.wnon t.br· cathode thn TEB are</td><td> set.</td>

In thⁿ dissolution c°l l , i.ihidi io cnnetH.uh:··! by three dissolution g

<td> cathode, o</td><td> V'Ir having</td><td> a</td><td> géométrie surface</td><td> arr&gt;a of</td><td> 2 m' and two TA</td>

<td> compn-, it.o</td><td> o 1.^r,c trnrjns,</td><td> λ</td><td> ruromt. of 40ΠΩ ;</td><td colspan="2"> o ./iri o f cathodic surface</td>

<td> area in ;</td><td> l in ; &gt; 1 i ç’d tn</td><td> tJ</td><td> m T/i dr.ir.ing Ηυ.</td><td> in id. ration</td><td> stage for a</td>

<td> period n f</td><td> 1 h n Π' n i</td><td> !1-IJ 1</td><td> 1.nnonualy '.ri ('.h th'</td><td> ’ starting</td><td> of the extraction</td>

<td> cells, an '</td><td> thon -_η</td><td> Πι ) ‘</td><td> •rating erreront ni</td><td> 2'51)1) d/m</td><td> is supplied to</td>

<td> the Hio'.ol</td><td> r it i nn i tho</td><td> .4 A'</td><td> r : nd Ί ei.li rr nt r</td><td> , ? }f 511(1 li/rn</td><td> nf cathodic</td>

i l.o voltages of the

Sljrf’Cr¹ ητο.Ί the

I.

'· >

p r rjp r ο Γ ¹ -:i

O(J ^r’,5 \/ between cf 2-.,5 kg/hour of

In 12 hours approximately 12 kg of collected per square meter of cathode, leaching, is of the quality indicated

09628 titanium are which, after in Table 1.

ANALYSIS OF THE ELECTROLYTIC DEPOSITION OF TITANIUM

TABLE 1

Concentration of impurities (ppm)

<td></td><td> Element</td><td> Conventional</td><td> Method Accordinq</td>

<td> 5</td><td></td><td> Value</td><td> to the invention</td>

<td></td><td> Oxygen</td><td> 650</td><td> 390</td>

<td></td><td> Nitrogen</td><td> 35</td><td> 25</td>

<td></td><td> Carbon</td><td> 85</td><td> 50</td>

<td></td><td> Chloride</td><td> 1400</td><td> 160</td>

<td> 10</td><td> Iron</td><td> 200</td><td> 50</td>

<td></td><td> Hydrogen</td><td> 325</td><td> 217</td>

<td></td><td> Aluminium</td><td> 100</td><td> 50</td>

<td></td><td> Vanadium</td><td> 100</td><td> 50</td>

<td></td><td> Manganèse</td><td> 100</td><td> 50</td>

<td> 15</td><td> Nickel</td><td> 100</td><td> 50</td>

<td></td><td> Chromium</td><td> 100</td><td> 50</td>

<td></td><td> Molybdenum</td><td> 100</td><td> 50</td>

<td></td><td> Tin</td><td> 100</td><td> 50</td>

<td></td><td> Copper</td><td> 100</td><td> 50</td>

<td> 20</td><td> Silicon</td><td> 100</td><td> 50</td>

<td></td><td> Z irconium</td><td> 100</td><td> 50</td>

<td></td><td> Boron</td><td> 100</td><td> 30</td>

<td></td><td> Yttrium</td><td> 100</td><td> 10</td>

<td></td><td> Magnésium</td><td> 100</td><td> 10</td>

<td> 25</td><td> Sodium</td><td> 1100</td><td> 100</td>

<td></td><td> Phoephorus</td><td> 30</td><td> 30</td>

<td></td><td> ΘΗΝ</td><td> 90/100</td><td> 85/86</td>

09628