CA1044175A - Electrolytic process for the production of metals in molten halide systems - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Metals are produced by electrolysis of their respective metal halides wherein the metals are deposited on one of a pair of spaced substantially parallel electrodes, the opposed surfaces of which are inclined at an angle of between 7° and 15° to the vertical, and wherein gas liberated in the inter-electrode space is discharged upwardly into a gas separation chamber disposed above the inter-electrode space.

Description

This invention relates to a process for the production of metals, particularly aluminium and magnesium, by electrolysis of their respective metal halides, preferably chlorides, contained in alkali halide melts, preferably alkali chloride melts, and the invention also refers to electrolytic cells for use in such processO
Cells of the type discussed are not restricted to produc- -~
tion of aluminium and magnesium, but can be applied in any system where the metal product is heavier than the solvent eleckrolyte, and is formed as a liquid phase - for example, lead, bismuth, zinc, cerium, gallium - from the respective molten halide (prefer-ably chloride) solvents.
Acco-rding to one aspect of the present invention, there is provided an electrolytic cell for use in the electrolytic pxoduction of metals in molten halide systems, which comprises a pair of spaced oppositely charged electrodes, the opposed surfaces of which are substantially parallel to each other and are inclined at an angle of between 7 and 15 degrees to the vertical, and a gas æeparation chamber disposed above the inter-electrode space into which in use of the cell gas is discharged upwardly from the inter-electrode space.
The electrodes may be connected alternately to the -:~ : .... ,:
positive and negative poles of the power supply and hence may con-stitute a system of electrodes in parallel.
In another form of the invention, only the end members ;~ of a system of parallel electrodes need be connected to the power supply and the intervening electrodes would then be made to function as bipolar electrodes.

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It is not necessary, and is in fact undesirable, that -anything but a small portion of the electric current should ~ -pass through the pool of metal accumulated at the bottom of the cell.
3 An important feature of the invention is the provision made for facilitating gas, e.g. chlorine, to be liberated from the inter-electrode space during electrolysis by means of a suitable gas separation chamber so that said gas is substan-tially prevented from "back reacting" with metal in the vicinity lO of the cathode surface.
According to another aspect of the present invention - there is provided a process for the electrolytic production ofmetals in molten halide systems, which comprises depositing metal on one of a pair of spaced oppositely charged electrodes, ,~; .. . .
the opposed surfaces of which are substantially parallel to each ' other and are inclined at an angle of between 7 and 15 degrees --to the vertical, and collecting gas liberated in the inter : .: . , electrode space in a gas separation chamber disposed above the inter-electrode space.
Preferably the gas separation chamber is such that the width in inches of the melt surface in the gas separation chamber is not less than LC

where L is the numerical value of the cathode length in inches, C is the numerical value of the current density in amp/cm2, and ,; : ~ .:,;
M is the numerical value of the inter-electrode spaclng in inches. - ;~
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Preferably, the cathode surface on which the metal is deposited is inclined at a positive angle to the vertical, i.e. faces upwardly, and the spaced anode surface is inclined ~1 at a similar negative angle to the vertical, i.e. faces downwardly. The electrodes are preferably planar, non-consum-` able and closely spaced.
The area of the melt surface and the depth of the ~ liquid electrolyte in the gas separation chamber are prefer-,i ably sufficient to permit separation of gas from the electro-i 10 lyte in the gas separation chamber at substantially the same rate as said gas is produced in the inter-electrode space.
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~ More particularly, the invention in one form relates ~
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to cell designs which take maximum advantage of the compactness -~
made possible by using a system of closely spaced planar ~, electrodes inclined at relatively small angles to the vertical, and operating at high current densities, e.g. in excess of ; 2 2 1 amp/cm (amps per sq.cm), preferably not less than 1.5 amp/cm .
'` The lnter-electrode spacing (A.C.D.)is preferably less than 2 inches and preferably between 1.2 and 1.8 inches. In any given case, the angle at which the electrodes are inclined will vary : , i with the normal operating parameters; for example, it may be -~

`, ~ expected that the angles of inclination will be greater for 1~ higher current densities and for smaller inter- -::i:::

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electrode spacing~ (A.C~D's). The invention thus enables the attainment of signifiaant advantage~ in respect of opera~ing and capital co~t~
In the case o~ aluminium, reduction cell size can be reduaed 80 that ~teel ~nd r~fractory require~ents are of the order of a quarter o~ tho6~ ~or convqnti~al cells of the ~me pro~uctive capacity ? and the f 10Qr area requir~d can be reduc~d ~o one-fifth. Typical cell ..
dimen~ion~ ~or po~sible ~ tr~e conflgu~ations obtai~ed 1~ by scalin~ up r~ ult~ o~tain~d ~om the experimenks referred to in khe Examples which ~ollow, are shown in Table I below~

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Because of the simplified design, and greatly reduced size, of cells constructed acaording to this invention, it is calculated that the capital cost could be reduced to about ~ quarter o~ that for conventional cells at the 150,000 amp level, and total electrolysis plant costs could be reduced to about one-third tha~
of c~nventional plant.
With magnesium produation the co~t o~ cells using low density electrolyte~, may be similarly reduced by a 1~ faator of 2 to 3 compared with aell designs used in the conventional proce~ses, or with ~all-type magnesium cells using com~ara~le low den~ity electr~lytas.
A ~i~nificant opera~ing advantage of the dry vertical electrode geometry of this invention, in '~ 15 ge~eral, is the removal of the r~striction on cell .
current or cuxrent density, which is always imposed on . conventional liquid cathode cells by the magnetic stirrin~ ef~ects of the lar~e currents. The removal ~, of this restricti~n by eliminati~n of the liquid cathode ~; 20 and by the impr~ve~ cell geometry ~f this invention, means that cells of sev~ral hundre~ thousand amper~s capacity are now brought wibhin the range of practicality. ~:
In addition, stable values of i~ter-electxode sp:1 are~maintained without the need f~r manipulating the electro~es or adjustin~ the 12vel of the pool of metal accumulated at the base of the oellO

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Because of the stability of inte~-electrode ~istance and the lack of disturbance hy magnetic stirring it becomes possible ~y means of this invention to operate chloride reduction cells with inclined S cathodes at c~nsiderably lower inter-electrode distances than are practicable in conventional cells.
Since a significant proportion of the energy consumed in conventional electrolytic cells is dissipated as heat (due to re~istance effects) the new electrode geometry of this invention makes possible not only savings in electrical energy but also a simplification of the : problem of removing heat from large cells.
We have found that an imp~rtant condi~ion for successfully operating cells with cl~se-packed inclined electrcdes at high current density is the provision of an adequately designed gas separation chamber. MGdels ) of the gas-liquid flow patterns produced by the anode ~ .
;~l reaction have shown that it is necessary to provide - sufficient depth of liquid electrolyte and suficient liquid-gas interfacial area above the cathode to permit complete separation of gas from the electrolyte at substantially the same rate as it is produced in the anode . reaction. The ~as pumping effect of the anode reaction ,1 . ....
rll pro~uces vortexes in the vicinit~ ~f the mel~-gas .. . .
interface. If the rate of evolution of gas from the melt - :
is too low because of inadequate fr~e surface area, then , : gas that has not escaped may continue to circulate in the ~ :

8 - 28/3 G : ::

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~4~75 vortex pattern where it will accumulate and cause a froth layer to form and to increase in thickness until it extends into the region b~tween the electrodes.
In addition, when the ra~e of gas evolution, in other words current den~ity, is increased in a cell of given A.C.D., a point is reached where gas becomes entrainad in melt returning ~o the inter-electr~de region.
Intex-electrode distance (A.C.D.) has an additional important effect be¢ause melt returning to the inter~electrode space after having been gas-pumped to the surface may interact with the ascending stream ~f gas and liquid. This causes gas ~o be diverted from the upward stream an~ re~dire~d down into the inter-electrodq space. For a yiven rat2 of gas evolution, i.e.
current density, i~çreasing the A,C.D. will eliminate this e~fect. For a ~iv~n total rate o~ gas evolu ion ~' thexe thUS exis~s an ~ptimum ~.~.D. which repxes~ts th~ be~t cQmpromise between av~i~ance ~ gas reci~culation and i~crea3e G~ cell voltage because of the increase of cuxrent phth. For cUrrent densities in the viainity o~ 1.5 a~p/cm2 and with electrodes up ~o 2~ inches in working length inclined at 10 to the ver~iaal an A.C.D.
of 1.5 inches has been found to be near optimum.
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Two critical parameters o~ the gas sepaxation cham~2r are the width o~ the melt ~ur~ace (i-e the sur~a~e be~ween the liquid electrolyte and gas~ in the gas separati~n chambe~, an~ the dep~h of liquid ~ ~ , ,: :
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elec-trolyte in the gas separation chamber above the cathode. These two parameters are shown in Figure 1 of the accompanying drawings as S and D respectively.
In Figure 1, the numeral 1 indicates the anode/ 2 indicates the cathode, 5 indicates the liquid electrolyte in the gas separation chamber above the cathode 2, 8a indicates the quiescent melt level, S indicates the width of the melt surface, D indicates the depth of the -electrolyte in the gas separation chamber above the cathode, L indicates the cathode length, and M indicates the A.C.D. (inter-electrode distance).
Our model studies suggest that, for electrodes inclined at between 7 to 15 degrees to the vertical, conservative or minimum values for S may be attained by applying the empirically derived formula:-~ .
S = 8 x 24 x 1 5 x M = 3C (Formula A) where S is in inches, C is the numerical value of the 20 current density in amps/cm2~ L is the numerical value -of the cathode length in inches, and M is the numerical value of the inter-electrode spacing (A.C.D.) in inches.
The width of the melt surface and the depth of the liquid ` electrolyte in the gas separation chamber are preferably not less than twice the inter-electrode spacing, and are preferably not less than four inches. Preferably, S is not greater than D. -There is evidence of the use of vertical electrodes in cells for the production of both aluminum and magnesium, 30 e.g. in U~S. Patent 2,512,157 (Johnson~. The Johnson cell, ', '.': "
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~ 4~75 however, is limited to refining impure solid aluminium .
anodes in chloride electrolyte with deposition of solid aluminium on aluminium cathodes. The lack o~ provision for adequate gas liberation from be~iween the electro~es S would result in low current e~ficiencies if this cell were adapted for electrowinning of aluminium.
Prior aluminium extraction processes, such as, for example those covered by U.S. patents 2,959/533 and 3,382,166 (de Varda) and 3,352,767 (de Garab et al), ~perate with variable A.C.D. and also ~o not provide adequately for separation of gas. These patents also speci~y the use of the conventional cryolite-A1203 electrolyte, incl~ding the c~nsumable carbon anodes which - are mandat~ry in such a system.
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1 15 In the case o magnesium, the conventional , electrolytic cells u~ed for the reduction of magnesium 1~ chlori~e employ vertic~l anodes in con~uncti~n with high ~1 density electrolytes, i.e. electrolytes which are heavier ~' than the molten magn~sium produced~ and complex cathode ~.
designs axe thus necqssary to collect the molten magnesium :i at the surface of the melt. Although low-density chl~ride ;`, . electrolytes w~ioh enable magnesium t~ be collected ~n .j ; the cell ~loor are n~w kn~wn, the exis~ing cell designs- `~
for use with such electrolytes are quite diferant from 1 25 ~he noYel and efficient cell desi~ns pr~p~sad in this ~ } ~
~ invention.
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U.S~ patent~ 2,468~022 and 2,696,688 (Blue at al) describe a hipolar electrode magnesium cell of considerable complexity which employs vertic~l electrodes, but dif~ers ~rom the present invention in a number of importan~ ways.
The ob~ectives o~ the ~lue design are to simpli~y electrolysis chamber construction, to provide improved gas sealing, and to increase the oapacity o~ the cells by providing a laryer number o~ elieictrodes than in the conventional app~xatus. However, these ~bjectives are achieved at considerable cost in complicating the overall c~ll structuxe. T~us, a ~eparate two ~r thre~ compartment feed chamber together with a molten salt distributing system consisting either o~ a weir cha~ber mounted above the centre of the cell ar a series of distributing :~ 15 channels incorpor~ted int~ the walls of the cell are required. In additi~n, a molten salt pump for airculation o$ the electr~lyte i9 needed.
The Blue cell relies upQn forced circulation of ;~
~' melt to remove magnesium fr~m the inter-electrode space ~, 20 in cells which u3e melt systiem~ ~f higher density khan :~
:. magnesium. In these cells ~he molte~ me~al fl~ats to .!~ ' .
the surface~ The ~11 is sai~ to ~perate at Q.43 to 0.45 amp~cm2, typical of conventional pra~tice. However, aurrent efficiency is sald t~ b~ about 75%, an~ it i9 t~
25 ~ be noted that no a~tual operating oondi ions are described- ::
The l~w current e~icie~cy i5 not surprisi~iq, because the design is believed to be qui q inadequate for se~uring , - 12 - 28/~ G :-',~
' ''`i ~ ',, separati~n of chlorine from magnesium. Co~siderable entrapment of gas between the electr~des mus~ occur because not ~nly are the ele~trodes devoid of any slope, but the inter-electrode g~p is alsv narrow right up to and beyond the surfaae o~ the melt.
The cell o~ Blue et al does not ~rovide anything approachi~g the compa~tness and e~iaiensy of the cell of the pre~ent i~ven~ion, be~au~ o~ thq use o~ low curre~t den~ity an~ more p~rticularly th~ lack of pr~vision f~x a~equate chl~rine rem~val, which leads to l~w curre~t e~fician~y. F~rth~r, ~he exp~nse o~ the .~ additional comp~nent$ is likely ~ nulli~y to ~ large ex~ent the claimed advanta~e ~f b~in~ able to incorporate more elec~r~des at lower ~.C.~. within the ele¢trolysis cha~ber than in conve~ al plant.
U,S. p~tent 3,396,094 (~ivilo~i et al~ illustrates the l~gths to which i~ is ne~es~ary to go ~o improv~
~urrent effi~ien~y i~ c~venti~nal c~lls by modifying the method of colle~ing magnasium a~ ~he melt su~face. U.S. ~-patent 3,418,223 (L~ve) ~h~ws ~he ~aste o~ space within ~ .
~; a ~ell re~ulting ~r~ ~he ~se Q~ ~ ~wo-pi~ce ~athode ~or ,: aolleating m~tal at ~h~ ~uxf~ce ~ ~hP ~el~ ana alsohow3 ~he ~t~uctural cQ~plexi~y ~ the typical chlorine ; c~llecti~n ch~mber~ In ~o~h ~ivilot~i's and Love's çells, separa~ion o~ chl~rl~e ~rom ~he ~elt may be expected to be ubstantially in~ lete b~c~use ~ the lack o~ adequate ree sur~ace ~or gai~ s~pa~a~io~

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An important feature of one form of our invention is that the cathode surface is inclined at a positive anyle, (i.e. the surface faces upwardly), of plus 7 to 15 degrees, to the vertical and faces a parallel or substantially parallal planar anode surface inclined at a negative angle, (i.e. the surface faces downwardly) of minus 7 to 15 degrees, to the vertical. In other words, it is important in the system of this form of the invention that the working surface of the cathode is arranged to face slightly upwards and the corres-ponding surface of the anode is arranged to face slightly downwards.
The inter-electrode spacinq is preferably less than 2 inches, and desirably between 1.2 and 1.8 inches. As discussed in detail above, study of melt circulation paths leads to the preferred specification of an anode-cathode spacing of about 1.5 inches at current densities of 1.5amp/cm2 to 2.0 amp/cm2.
Other parameters of importance in the design of the gas separation chamber are the electrolyte depth above the cathode and the width or area of the surface of the electro-lyte in the gas separation chamber. It was found that provis~
ion of a gas separation chamber extending back 4 to 5 inches from the anode shoulder, across the inter-electrode gap and ~:
extending over the top of the cathode structure, was adequate ~ -for 12-inch cathodes. For other values of the cell parameters, Formula A referred to above is applicable, within the range of electrode inclinations stated.
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' ' ' ' . . . ' ' i ' ' '. ~ , " ' ' 17Si The very c~n~ ra~le an~ somewhat unexpectedly bene~icial ef~ect o~ thç electrod~ arran~ement of this i~vention is ~emons~ra~ed by ~omparison o~ Figures 2 and 3 o ~he ac~ompanying drawings whi~h illu~rate ~he operation o~ a ~eg~ ~a~ourabl~ and m~re favourable ~ell a~n~i~ura~io~, ~espectively.
In Figure~ 2 and 3 the numeral 1 indicates the ~ having ac~lve ~no~ ~u~aces 1~, ~ indicates ~he cath~s ~avi~g a~iv~ ~a~ho~ ~u~ as 2a, 8 indica~es 1~ th~ p~ol~te, 8a ~he upper ~ur~ace o~ ~he elec~olyte, a~ 10 ~ te~ ctr~d~ spaae.
A in~icat2~ reg~ns Q~ ere gas formati~n and .! ~ in~cate~ regi~s o~ $e~e~e g~s foxmatisn- In Fi~ur~ 3l 9 is the gas ~e~atio~ ~hamber immediately :-lS ab~v~ the ~h~d~ ~.
In Figures 2 a~d 3 the in~lination of th~ active i el~c~rade surfa~ o ~he ve~tical ~as a~ut 10 an~ ~he ! in~er-eleo~rod~ tan~e ~ ,D~) ~as 1.$ inches. In Figur~ 2 the ~u7~r~n~ der~,si~y was 1 amp!~m~ and in ~igure : :
3 it wa6 2 ~mp/~m~c ~ ~igure 2 th~ depth ~ the , quiesa~nt ~le~r~lyt~ ~b~v~ the w~king ca~hode sur~ace, ~
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'~ within thç i~ter~ a~ e spa~e, was 2 inahes; an~
in Flguxe ~ th~ depth o~ ~he qui~ae~t el~ctrvly~e above ~ the w~kin~ ~a~had~ $ur~ , wi~hi~ ~h~ gas ~eparation `~ ~ 2S ~mb~, w~ 4 inah~s. Th~ wid~h ~ ~h~ u~per sux~ac~ of ~h~ ela~xoly~ w~æ 1.5 i~he~ in Fi~ure 2 and ~ inches in Fi~e 3.
.~ ~; , 1 -- 'l$ 28/3 G

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It will be see~ that x~n~ion vf gas between ~h~ elect~Gdes is v~ry s~vere under the conditions shown in Figure 2, e~en at a m~ra~ely low current density of 1 ~mp/cm2. O~era~ n~r ~his con~i~ion is found to S result i~ ~ack reactio~ o~ ~b~ut 30 p~r cent o~ product, i~ Q~her word~ a ~urre~ efficiq~cy ~ 70 per cent or less.
Figu~e 3 illustra~s th~ e~fec~ of electr~ly~i~
; : u~in~ ~ ~$11 d~sign a~d ~a~ ~ep~ra~i~n chamber con~truate~
i~ a~rd~ wl~h one ~m of ~his lnven~lo~. Operation h i~p~oved ~a~ liberatio~ u~er ~he ~onditions shown :; .
i~ Fiyur~ 3 x~ h~ cux~nt e~iaiency ~o about 90~.
A ~atur~ he f~ o~ th~ inY~nti~n shown in igu~e 3, a~ ¢~mpax~d wl~h ~he c~ll de~ign shown in : Fi~2 ~ h~ e wi~h ~nd dep~h of the gas sepaxzti~n ' 15 ~h~m~r ~ ~mmedia~e~ ab~v~ ~h~ w~rkins cathode surf~ce ; : ~a a~ ~u~ici~t t~ e~6~re ~a~ tha~ the ~a$ ~ormed in the in~er-ele~ dq space 10 durin~ elec~rolysis is ~ :
di~cha~qd or liber~ed t~ a u~s~an~ial degxee fxom ~u~h spac$ 10 i~to ~e gas sepaxa~i~n chamber 9, and ~b) ~a~ said g~$ ~ llbexa~çd ~o ~ su~stan~ial degree ' ~rGm ~hq el~ctr~ly~e i~ ~aid ga~ $epa~ation ~hamb~r 9.
.
P~ rabl~ ~he wl~h and/~r d~h o~ ~h~ gas s~para~i~n h~m~ 9 ~X~ ~t l~as~ ~wi~ ~h~ i~te~ xod~ ~istance t~,$.~ 2 ~ d~s~ d ~11 ar~a~gem~t ~h~t~nti~lly r~u~S ~e ~ak Xqa~io~ ~hic~ w~uld oth~rwis~ occu~ ~kw~n ~h~ ~as ~n~ kh~ me~al in tha -.
vi~ h~ c~thodç s~ s~ 2a ~as i~dica~ed in ~ 16 ~ 28~3 G
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Figure 2) and ~hus substantially increases the curren~
e~icie~cy o~ the cell.
Figu~ 4 repr~sents a diagxammatic side elevatisn o~ a ty~e o~ mul~i-el~ctrode cell designed S aacording to the pres~n~ inven~io~. Overall dimensions o~ ~he cells are prefe~ably a~ indicated in Table I.
1 ~esi~ate~ the graphite anodas wi~h el~ctrolytically ~tiv~ ~u~faqes la l~ali~ed a~ a neyative angle of ab~u~ 10~ ~o ~he ve~ al, an~ provided with ~ecesses 4 ;~ lQ to ~Qr~ ~ ~as liberati~ cha~b~r 5 which is pre~erably : pr~o~ti~n~d accordin~ oxmula ~ and ~hich a~ford~ an a~e~Uat~ ra~e o~ ~a~ e~luti~n ~rom ~he melt sur~ace 8a.
~ 2 desi~ s ~he ~akh~d~s, which for aluminium p~oduction ; ar~ 4~ ~r~phi~ and ~ m~e~ium ~oduction may be ~5 holl~w ~ab~i~ated ~te~l s~xuot~re~ ~r plain ~eel shaets, h~,ving ca~h~de surfa~e~ 2a which are at a positive anS3le o~ abou~ lQc ~ the vex~i¢al and arq sub~tantially ~, ~axall~l to the a,n~e suxfac~s la, and 3 represents the re~ra~t~?ry lined ~teel sh~Il. 8 de~igna~es ~he elec:~rolyte 2d an~ 6 the elec~rical ~ur~ent c~nne~tion~ ~or the anQdes.
~nea~iQn~ ~o~ the cathoa~ 2 are n~t sh~wn; these may, ii~ d~ir~d, be mad~ ~lre~tly ~ ~he ~hell 3, It will 13e '~ undex~Q~d that in ~ny oall con~igu~a~iQn the anodets) .~ i m~y be ~d~u~ted i~ a ver~i~al ~r subska~ially vertical !

~ : 25 ~1r~ction ~r ~tking ~ ~e-~attln~ o~ A.C,~, .~: , : .', ' - 17 - 2~3 G
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~4~L75 Figure 5 represents a ~iagrammatic side elevation of a mo~e compact electrode configura~ion, namely that empl~ying bipolar electrodes. The connotations of the de~ignating numerals used are no~ the same as in Fi~ure ~. 1 desiynates the graphite anode, with w~rking surfaces la inclined according to the invenkion,

2 the bip~lar electrodes with working sur~aces 2a, which electrodes 2 may 4e monolithia graphi~e blocks supported at their ends by the insulati~g walls of the cell. ~ -

3 deFignate~ the c~llqctor cathodes, which may be of ~te21 in ~he c~se of mag~esium, but of graphite in the case o~ aluminlum cells, and 3a repr~sents the workin~ surface~ o~ the cathoaes 3~ 4 represents the ~:
r~fraa~ory lin~d ~ut~r s~eel sh~ll and S the gas libe~ati~n chamber, pr~erably proportioned according ~Q For~ula ~. T~e insula~ing lGwer supp~rts 6 for the bipolar eleçtrGdes 2 s~rve as barriers for reducing leakage c~rre~t. ~.

. .
A ru~ wa~ ¢arrie~ o~t in a cell havi~g a .qlngle i inclined ~node, and o the general ~orm shown in .~ Figure 3. The ~e~tive el~trode area was a~proximately 1~00 ~m2, Electroly~e c~mpo~i~ion was 21~ MgC12-75% :~.
KC~ Gl, an~ a t~tal ~li current of ~00 amps wa~
~us~, a~ a temp~rature o~ ~$0C~

- 18 - 30~3 G
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The anode-cathode slope was 9 to the vertical and was within the rec~mmended range for efficient operation. The other parameters were chosen to test . ~ some o~ the le~s fav~urable conditions ~or gas release.
The most adverse ~ature was the u~e ~ a melt depth ~ .
of ~nl~ 1.5 ins. above the ~athoaç, togPther with a cuxrent densit~ o~ ~nly 0.36 amp/cm2. Under these condi~i~ns, ~on~ide~able back reac~ion was an~iaipa~ed to oGcur because o~ ba~k ~ir~ulation o~ chlorine into the in~ el~ctro~e spac~.
During a run ~f 61 mln~tes duration, 404 ~ of `~ C12 were produced a~d 543 g ~ Mg~12 were consumed.
. The current ef~iciency was 75~.

.~ lS A run was caxried ~u~ using a single an~de cell of the gen~ral form shown in Figur~ 3 and havlng an ;~ effec~ive electrode area ~f app~oximately 1000 cm2.
' The eleo~rolyte composition was ~l~ MgC12, 75% K Cl and 4S LiC1.
., 20 The anode~cathode slope was 9Q to the vertical Z ~nd was within the re~mm~nd~d range ~or e~ficient ~, op~ration. ~he c~th~de leng~h L w~s 12 inches, S and D
; were aach 4 inahes~ The ~p~r~ing tempera~ure was 850~, curr~nt density was 0.84 amp/~m2 and a ~otal ~ell current o~ 700 amps was maintained during the 60 minu~e duration i: :
~ . of th~ run.

I
,~ .
~ 19 28~3 G
'.
, : ..... .. , : ..... : .. , ~ . ~, . ... . .. .

~4~75 S01 g ~f C12 were p~odu~e~ and 1077 g o~ MgC12 ..
were cc~nsumed sc that cu~rent ef~i~iency was 88%~
'.' ~
~ se~ond ~url was ca~xied ou~ in the same cell as .ir. ~xa~nple 2 u~ing a~ elec~rolyte cont~ining 22~ MgC12, 2~ KÇl, and 50~ ~iCl. Operatlng ~onditions were ahosen ~ demonstrat~ oXIe ~ ~h~ tim~lm cc:mbinatio2~s of parame~exs a~ai~akle in a ~11 m~el, ~:~
~'! Current d~nsi~y w~ in~xea~ed ~a 1 S amp~c:m~
a~ ~he ~11 was op~atq~ with a mel~ dep~h of 4 in. -ov~r ~he cat:hode at a ~Inp~at~u~ ~f 850~ L was 12 ~ .
.~ ~nch~s and ~ ~,nd ~ w~r~ ea~h 4 lnahes~ Duri~g th~ 4S minuke rurl a ~te~dy ~11 aur~nt o~ 16$~ amp~ was us2d~ ~.
1477 g ~ Cl;~ we~ ~ec~v~xed, and. 1981 g of MgC12 :I LS were co2~sumed s~ khat the ~u,rrqsl~ e~ici~nay was ~%.

i, A run wa~ carrle~ ~u~ in ~he cell of the general . . ., ~
~orm shown in Fi~lxq 3 usirg ~ melt G:c~mpositic;n averaging 10% ~1 $13, ~5~ NaCl, 4$~ KCl. The di~ne~siQn$ of the cell ., , `' ~ 20 were as st~,ted in ~ampl~ 3 . Th2 tear~p~ra~ure was 730C . ~ -ing ~he run o~ ur the ae~,l aurxent was l~ûO amps.
s la57 ~ ~ Cl~ w~xe ~over~d ~nd 23~3 g o~ ~1 C13 W9~ um~.
'1:
h~ av~ra~ cu~er~ ie~ wa~ 8~

1"

0 - 28~3 G

,~i .
~.. ~ . . - .

Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the electrolytic production of metals in molten halide systems, which comprises depositing metal on one of a pair of spaced oppositely charged electrodes, the opposed surfaces of which are substantially parallel to each other and are inclined at an angle of between 7 and 15 degrees to the vertical, and collecting gas liberated in the inter-electrode space in a gas separation chamber disposed above the inter-electrode space.

2. A process according to claim 1 wherein the gas separation chamber is such that the width in inches of the melt surface in the gas separation chamber is not less than where L is the numerical value of the cathode length in inches, C is the numerical value of the current density in amp/cm2 M is the numerical value of the inter-electrode spacing in inches.

3. A process according to claim 1 wherein the metal is deposited on the cathode surface which is inclined at an angle to the vertical and faces upwardly, and the spaced anode sur-face is inclined at a similar angle to the vertical and faces downwardly.

4. A process according to any one of claims 1 to 3 wherein the electrodes are planar and non-consumable and are closely spaced.

5. A process according to any one of claims 1 to 3 wherein the area of the melt surface and the depth of the liquid electrolyte in the gas separation chamber are suf-ficient to permit separation of gas from the electrolyte in the gas separation chamber at substantially the same rate as said gas is produced in the inter-electrode space.

6. A process according to any one of claims 1 to 3 wherein the width of the melt surface and the depth of the liquid electrolyte in the gas separation chamber are each not less than twice the inter-electrode spacing.

7. A process according to any one of claims 1 to 3 wherein the width of the melt surface and the depth of the liquid electrolyte in the gas separation chamber are each not less than four inches.

8. A process according to any one of claims 1 to 3 wherein a pool of molten metal is formed below the electrodes but said pool does not serve as a cathode on which metal is deposited.

9. A process according to any one of claims 1 to 3 wherein the metal deposited is aluminium or magnesium.

10. A process according to any one of claims 1 to 3 wherein the metal is deposited by electrolysis of its halide contained in an alkali halide melt.

11. A process according to any one of claims 1 to 3 wherein the metal is deposited on the cathodes of a plurality of pairs of electrodes arranged in parallel.

12. A process according to any one of claims 1 to 3 wherein the electrolysis is carried out at a current density of not less than 1 amp/cm2.

13. A process according to any one of claims 1 to 3 wherein the inter-electrode spacing is less than two inches.

14. A process according to any one of claims l to 3 wherein the inter-electrode spacing is between 1.2 and 1.8 inches.

15. An electrolytic cell for use in the electrolytic production of metals in molten halide systems, which comprises a pair of spaced oppositely charged electrode, the opposed surfaces of which are substantially parallel to each other and are inclined at an angle of between 7 and 15 degrees to the vertical, and a gas separation chamber disposed above the inter-electrode space into which in use of the cell gas is discharged upwardly from the inter-electrode space.

16. An electrolytic cell according to claim 15 wherein the cathode surface is inclined at an angle to the vertical and faces upwardly and the anode surface is inclined at a similar angle to the vertical and faces downwardly.

17. An electrolytic cell according to claim 15 wherein the electrodes are planar and non-consumable and are closely spaced.

18. An electrolytic cell according to any one of claims 15 to 17 wherein the inter-electrode spacing is less than two inches.

19. An electrolytic cell according to any one of claims 15 to 17 wherein the inter-electrode spacing is between 1.2 and 1.8 inches.

20. An electrolytic cell according to any one of claims 15 to 17 and having a plurality of pairs of electrodes arranged in parallel.

21. An electrolytic cell suitable for use in the electro-lytic production of metals in molten halide systems, which com-prises a pair of closely spaced non-consumable oppositely charged electrodes, the opposed surfaces of which are planar and substantially parallel to each other, and are inclined at an angle between 7 and 15 degrees to the vertical, the cathode surface being inclined at an angle to the vertical and facing upwardly, and the anode surface being inclined at a similar angle to the vertical and facing downwardly, the inter-electrode spacing being less than two inches, and a gas separation chamber disposed above and in communication with the inter-electrode space into which in use of the cell gas is discharged upwardly from the inter-electrode space.