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Publication numberUS2615838 A
Publication typeGrant
Publication dateOct 28, 1952
Filing dateMay 27, 1946
Priority dateMay 27, 1946
Publication numberUS 2615838 A, US 2615838A, US-A-2615838, US2615838 A, US2615838A
InventorsCyril Presgrave, John Minnick Leonard
Original AssigneeG And W H Corson Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrolytic process of producing alkali and alkaline earth metals
US 2615838 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Oct. 28, 1952 MlNNlcK ETAL 2,615,838

ELECTROLYTIC PROCESS OF PRODUCING ALKALI AND ALKALINE EARTH METALS Filed May 2'7, 1946 MAKE U P SOLVENT l ALKALI METAL OR ALKALINE EARTH ANHYDROUS METAL THIOCYANATE LIQUID SOLVENT OR PERCHLORATE O+-ELECTRICAL H E NERGY CELL CATHODE PRODUCT ANOLYTE con-mums SOLVENT SGN' OR CLO; IONS IN soLvENT ---"T SOLVENT I l l SOLVENT REMOVAL EVAPORATJR:

ALKALI METAL OR ALKALINE EARTH METAL Ho OXIDE HYDROXIDE on I; CARBONATE I V ANHYDRCUS 'SOLVENT REACTOR ALKALI METAL OR ALKALINE EARTH METAL THIOCYANATE on PER- T V cHL RA E DRYER ALKALI METAL OR ALKAL'NE EARTH METAL PRODUCT INVENTORS LEONARD JOHN MINNICK CYRIL PRESGRAVE'. BY THEIR ATTORNEYS Patented Oct. 28, 1952 ELECTROLYTIC PROCESS OF PRODUCING. ALKALLAND ALKALINE EARTHYMETALS Leonard John Minnick, Cheltenham and Cyril Presgrave, East Whitemarsh Township, Mont gomery County, Pa., assignors to G. and W. H.

Corson, Inc., Plymouth Meeting,-..I{a.,=.a corpora rationofiDelaware.

Applioation'May 27,, 1946, Serial No; 6725704 8 Claims. :J-Cl. 20.4.i'59): -.-i

The present invention relates to' a process for the'production of alkali and alkaline earth met als,'-and more particularly itrelates to a process The processes at present available for the preparationof alkali and alkaline earth metals aregenerally divisible into two typesfirst, the

methodsinvolving chemical reactions and, sec- 0nd, those employing the use of an electric current:-- The former type of method involves reduction' reactions conducted in retorts under specialatmospheres or high vacuum, and'many problems are involved in the commercial op-' eration' of this type oi-process. The latter type of method 'involves,-so far as commercial practice is-concerned; chiefly the electrolysis, in the molten state, of an anhydrous salt of the metal.

Other methods for producing alkali and alkaline earth metals by electrolysis in both aqueous and non-aqueous solvents have been suggested.- Usually, the use of an aqueous solution-is impractical since there is a strong tendency for hydrogen to be evolved at the cathode, and the releaseof hydrogen is accompanied by decomposition of the solvent and the conversion of the-metal into the hydroxide. Several ideas have also been described in which a co-deposit of hydrogen and the alkali metal is formed at thecathodeduring the electrolysis of an alkali metal salt dissolved-in a non-aqueous solvent-= such as propyl or other higher alcohol; In such cases; high voltage, with consequent high power consumption,- is required and the co-plating of the hydrogen with the metal is also undesirable.

One object ofthe present invention is to provide an economical process for the production of alkali and alkaline earth metals by the electrolysis ofa non-aqueous liquid comprising anhydrous' liquidammonia; methylami-ne,- prop-yl-- amine, or pyridine combine'd-with a salt. of the A further object of: the invention istoprovide J an electrolytichprocess for the preparation of alkali and :alkaline' earth metals which may be conducted lat relatively high current densities.

andwwith relativ.elyr;-low power consumption to produce ca cathode-product;substantially. free from :contami-nation by: unelectro'lyzed salt:

AnOt11Br. .QbjeCt-;0r the invention: is. to: provide r i a method. for producingaalkalizuand alkaline earth metals as the=cathode productgwin con-t 2 junction'fwith the product'oniofs: an: anode profile-""- uct that mayflireadilyzbe-employed;to":prepare an. alkali; or. alkaline; earth metal salt available'afor recyclingiinwthe process. Anothersobject ofzthetinvention is to. provide P a method for the-production lof;alkalin andalka line. earth 'metalsifrom-z salts; :of the metal -;that: can be prepared: without: difiiculty from; inexapensiveizraw materials:

A still::furtherzobjectmof :the: invention; is to makezeavailable 1a. process for the'fielectrolytic; production-50f alkalitaand alkaline --earth:metalsfrom :salts thereofteven': when :the salts are not; :L: anhydrous. Still anotherv object of. the inventioniis lto. pros 1;. vide a- -.process-'.:by whicht'.;.a..substantially?pure. solution: or paste;-: :xcomprisin'g the 1" :alka'lizl alkalineearthm'etaharld the-solvent of: the'ele trolyte; maybe prepared; twhichnsolutioniior :pa'ste: may: be used :in the industriesrhrimay bereadily converted intoian alkaliior alkaline'earthmetal of a high state of purity, merely by. evaporation of the solvent.

Other: objectstincludihg: the provision of a1; cyclic chemicalrand electrochemical: process for 1 the preparation :of :alkali and alkaline earth-met-: als,. wi1l be apparent-from a consideration"- of this specification and the claims;

The Ilprocess of the present invention "is ap- I plicable for use in the production :of: any 1 of the I various alkali .zor. alkalinei earth. metals; namely-,4, lithium; sodiumppotassium; caesium; rubidium,- i. calcium, strontium, 'and.'barium;::and ofxalloys orrw mixturesthereof; iii.

In accordancmiwith the. invention, a cathode productxcomprisingz anfialkaliaror alkaline earth '1 metal substantially 7 uncontaminated by unelec-z trolyzed salt is: prepared by the electrolysis: ":01? an electrolyterto form a: cathode. and an anode: products The electrolyte is a non-aqueous 1iq-- uid comprising :an anhydrous liquid selected-from: i the group. consisting of. ammonia; methylaminaiethylamine'; and .pyridine 'combined'rwith a salt I of the "metal: selected ifrom'the' group. :consisting of the .perch'loraterand;thiocyanate, and'in such :3 an electrolyte :the concentration of salt-therein v provides a solution .in-zwhich the cathode: prod- T uct is substantially insoluble; rThe cathode 1 product; as will .be. further a discussed; 'may abe a r. bronze liquid, a :paste, or the metal itself v.Since the liquid. orpasteiis' substantiallyinsolubleiin; and hasai-lower specific :gravity than thetelece trolyte; it; floats; thereoni-irand;therefore; theip. product; substantially free ..from-.unelectrolyzed A salt,';1may be, easily separated from the .electro: n:

3 lyte. The anode product comprising the anhydrous liquid, the anion of the metal salt and its associated solvated proton is separated from the cell, and the anion and its associated solvated proton are reacted with the oxide, hydroxide Or carbonate of the desired metal to form the corresponding metal salt. This salt, in substantially anhydrous form, is then used as source material in the process.

The process of the present invention will be more clearly understood from a consideration of the drawing which illustrates the process by means of a flow sheet diagram.

Referring to the drawing, there is shown an electrolytic cell, the cathode and anode of which are connected to a source of electrical energy. The cell is equipped with cooling means. The anhydrous liquid solvent of the type described herein is fed to the cell, and the alkali metal or alkaline earth metal thiocyanate or perchlorate obtained as described herein is also fed to the cell. During electrolysisthere is formed a cathode product comprising the desired metal, and anode product. Nitrogen may also be formed when ammonia is present. The cathode product is removed from the cell and the metal separated from adhering solvent. The solvent may be recycled to the cell as shown. The anode product comprises solvent and the thiocyanate or perchlorate anion, and the anion is converted to the alkali metal or alkaline earth metal salt by reaction between the anion and the oxide, hydroxide or carbonate of the desired alkali metal or alkaline earth metal. This reaction may take place in the cell itself as more fully discussed hereinafter, or may take place outside the cell as shown in the drawing and as also more fully discussed hereinafter. If this reaction takes place outside the cell, the reaction medium may comprise the entire anode product to which water may be added, or excess solvent may first be removed, as in an evaporator, and recycled, following Which the remaining anode product is mixed with water which serves as the reaction medium. Any of the anhydrous solvent remaining after the reaction may be recycled for re-use in the process. In any event, the anion is converted to the alkali metal or alkaline earth metal salt which is dried and reused in the process. In view or the fact that some of the solvent may be destroyed during the electrolysis, make-up solvent may be added as needed. The process generally described above will be described more in detail hereinafter.

In place of using a single anhydrous liquid, a mixture of two or more liquids may be employed, for example, liquid ammonia containing an alkylamine having less than 8 carbon atoms, or pyridine. The solubility of the metal formed as the result of the electrolysis in such mixed liquids is usually less than it is in the case of liquid ammonia alone, and the paste, hereinafter described, forms more readily. Other materials which will not interfere with the desired electrolytic action may be added to the solvent, if desired, provided that they do not decrease the amount of the salt in combination with the anhydrous liquid to such an extent that the desired concentration of the salt cannot be obtained.

The use of an anhydrous liquid of the type described increases the advantages of the use of a non-aqueous medium for the electrolysis of alkali and alkaline earth metal salts and overcomes the objections that have been encountered in --prior methods. Solubility of many of the metal salts is extremely high in this type of liquid and, as will be discussed, concentrations can be reached in excess of any requirements needed for the economic production of the metal. Furthermore, by employing the method described herein, the presence of water does not prevent the production of the metal and the process eliminates the water from the nonaqueous liquid, as will be further discussed. While the elimination of the water consumes a small amount of electrical energy, the cost is nominal and the effect on the operation of the cell is slight. Furthermore, the cost of a liquid,

' such as anhydrous liquid ammonia, is low and I ance being ammonia.

the material is available in large quantities.

For convenience hereinafter, the process will be described in connection with the use of anhydrous liquid ammonia since this is the cheapest of the non-aqueous liquids available for use in the present process, and for this and other reasons, it is used in the preferred embodiment of the invention. Furthermore, while, if desired, alloys or mixtures of two or more of the alkali or alkaline earth metals may be prepared from a solution of two or more of the salts of the desired metals in the anhydrous liquid, the invention will be discussed from the standpoint of the preparation of a single alkali or alkaline earth metal.

As stated, the concentration of salt in the anhydrous liquid is an important factor and in the process of the invention, the concentration of salt in the electrolyte provides a medium in which the cathode product is substantially insoluble. This permits the production of a cathode product which is substantially iree from contamination by unelectroly-zed salt, and the cathode product removed from the cell in the process of the present invention is to be contrasted with the impure cathod product which would result if a low concentration of salt in the liquid ammonia solvent were to be used. Such impure solutions are blue in color and comprise a small amount of metal, unelectrolyzed salt, and solvent. As will hereinafter be discussed, the desired concentration is preferably obtained by the use of the alkali or alkaline metal salt alone, but if desired, the required concentration may be obtained by the use of another salt in conjunction with the alkali or alkaline earth metal salt.

The cathode product separated from the unelectrolyzed portion of the electrolyte may be in the form of a liquid or a paste or may be the metal itself, depending on the concentration of the electrolyte in contact with the cathode product and the operating conditions of the cell. The liquid is believed to be a blend or solvated compound between the anhydrous ammonia and the metal, and an excess of ammonia may be present. In higher concentrations, some of the metal may be in suspension or in colloidal solution in the compound, and these liquids may contain up to about of the metal, the bal- When the concentration is still higher, the paste is formed and in this case, it is believed that metal resulting from the evaporation of the ammonia from the metalammonia blend or compound is associated with that compound, and the concentration of the metal in the paste usually exceeds about 90% and may be as high as 99%. When the concentration of salt in the electrolyte in contact with self will plate out on the cathode.

,uid is to be distinguished from a simple solution in which a low concentration of salt is dissolved in liquid ammonia. These diilerences between the two types of liquids may be noted, for ex-' ample, if an alkali Or alkaline earth metal is added thereto. In the case of liquid of the type used in the. present invention, a bronze liquid will be formed upon the surface of the liquid by a reaction between a small amount of the ammonia in the liquid and the metal, such bronze liquid being immiscible in the liquid. When, however, an alkali or alkaline earth metal is added to a simple solution in which a low concentration oi salt is dissolved in ammonia, the metal will dissolve in and be distributed throughout the liquid, providing a blue coloration thereof.

The salt employed in producing the electrolyte is selected from the group consisting of they perchlorates and the thiocyanates. These salts are stable and easy to prepare and may be obtained in an anhydrous state, if desired, by simple drying procedures. Furthermore, theammonium perchlorate or thiocyanate formed at the anode may be readily reconverted into the alkali or alkaline earth metal perchlorate or thiocyanate by reaction with the oxide, hydroxide or carbonate of the alkali or alkaline earth metal. This reconversion may take place in the cell by adding the oxide, hydroxide or carbonate to the anolyte and the formation of the alkali or alkaline earth perchlorate or thiocyanate then proceeds simultaneously with the electrolysis of the salt in the same solution. However, since some water is formed by the reaction which requires additional electric current to dissociate it into its constituent parts, it will usually be desirable to treat the anolyte with the alkali or alkaline water can be present in a non-aqueous electrolyte and not interfere with the preparation of metals that are higher'than hydrogen in the electromotive series. This is unique and is to be compared with the attempts that have been made heretofore to produce metals of this type in such solvents as acetone, acetonitrile and phosphorous oxychloride.

In general, the introduction of an alkali meta salt containing more than 5% of water is not recommended and if water is associated with the salt,it is advantageously below 1%. In the case of the alkaline earth metal salts, the use of a salt'containing less than about 1% of water is desirable and, the salt advantageously contains less than about 0.5%,. The alkali and alkaline earth metal salts, if they contain an excessive amount of water or if the use of an anhydrous salt is desired, may be dried by any suitable method, for example, by the methods described hereinafter in conjunction with the treatment of the salt obtained from the anolyte prior to its re-use in the cell.

The cell may be of any suitable design but is sealed by a lid or cover and is provided with a vent which permits the solvent vapor, the nitrogen generated at the anode and any other nonearth metal compound in a separate step. The halides do not possess the requisite solubility in ammonia or other solvent to permit their use as theprimary source of alkali or alkaline earth metal.

In the preferred embodiment of the invention, an anhydrous or substantially anhydrous salt is employed. However, limited amounts of water may be associated with the salt, if desired, without seriously affecting the reactions that take place in the electrolysis of the salt, due to the fact that, as an initial step and before the metal plates out, the cell will purge itself of water. In purging itself of water, electric current is required and a sludge of the hydroxide of the metal will be H stantially anhydrous salt. The type of salt employed and the ease with which it may be dried are obviously the governing factors. The water content of. the salt should be kept lower in the case of alkaline earth metal salts than in the case of alkali metal salts due to the fact that there is a greater tendency for the alkali earth metal to react with the solvent to form amides or thelike, the reaction being catalyzed by the I presence of the hydroxide formed whenthe cell purges itself of water. Theimportant point to be noted in connection with the water is that, in the pliesentinyention,,.a reasonable amount of condensable gas to pass out of, but will not permit moisture to enter, the cell; for example, a mercury trap or a trap containing a moistureabsorbing material inert to ammonia may be used. The cell may be constructed of a wide variety of relatively cheap and available materials, for example, iron or steel, glass or enamelled material, rubber or synthetic rubber-like materials, and ceramics. This advantage itself makes the process of the present invention highly desirable as compared to other methods in use for the production of alkali and alkaline earth metals. 7

' For most operations, it will be desirable to 'maintain a temperature below the boiling point of liquid ammonia at atmospheric pressure (33.35 C.) and, therefore, the cell will usually be provided with refrigeration means, for instance, refrigeration coils around the cell, or in the electrolyte, or within the electrodes, the last named being preferred as the heat is then removed at the point of its chief source. If desired, the cell may be a pressure cell, in which event refrigeration is not required, or the cell may be operated under conditions where the conversion of the liquid ammonia into the gaseous phase is relied upon to provide self-refrigeration of the cell. While in most operations, the temperature of the cell, as stated, will be maintained by refrigeration means below the boiling point of liquid ammonia, the electrolysis can be conducted at much higher temperatures, for instance, where a very high concentration of the alkali or alkaline earth salt is employed so that the. cathode product will be formed as a paste or a metal, temperatures as high as 30 C. or higher may be used. Thus, a solution of sodium perchlorate of relatively high concentration, for example 4.2 molar has been employed with the result that bright metallic sodium metal has been plated out on and adhered to the cathode.

The use of relatively low temperatures of operation, as contrasted with those required in the processes employing a bath of molten salt, possesses several advantages in addition to the saving of the energy required to maintain the bath in a-fused state. For example, in the processes of the, present invention, there is no difiiculty 9 ierioountered due to sublimation or vaporization of the metal from the cell and there is no d'ahger of:losing metal by burning. which is a hazard in v the production of metals'from molten "baths.

Furthermore; the use'of relatively low temperaturesifpermi'ts the cell to "operate 'isubstan'tially uniformly and without local electrode resistance,

and th'e uniformity of operation is 'enhanced by operating at a low temp'erature, for example, 7 below theboilingpoint of liquid-ammonia. l --'The cell may, except-as noted, be a 'c'onventiona'l electrolysis cellwith a 'cathode'x'and an anode, and the electrode'slimay'fbe ot any-shape desired; 'such "as" fiatsheets rods, cylinders, or T the' -like; Sin'ce in -most instances; the' anode -product will be reactive-with the eathode prod uct a permeable"Ldiaphragm'} such "as a; porous 1 ceramicsheet, will usually beer'nployed to-divide the cell into'- 'cathodeand anode compartments. 'lngthe cas'e o'i the thiocyanatesxhowever w here there is little or' 'n'o tendency for reaction with thecatho'de p'rodutit', the use of a-- diapl iragm is i il'ot feq il-ired.

T Th'e cathode*may be any ooii'dllb'to'ri for" exar'hple, pl'atinuinfiron; 7S1 er, eop 'erg' earbong and the llki- I i The anode i {p'r e'ferably rnade ot a I nateriaPtvl'iieh is 'siibstantially no -l"a'tive towardthe anode liiluor' tr'olytic carbon?-boromitireoriium, or tantalum. Of this g rouin oarbon -is' the preferid material. The 'anode, howeverf inay, if desired, be of the typ'e 'that is reactive With the anolyte't for exampl'e, 'an' iron; nick'elg" copper; 'zinc, or alum-i num anode may be" usedi This second type=has not only the disadvantage that-it is eonsu'mea "rela- "=tively rapidly; but also" that, when it is employed, the -anolyt'e'-k-zo'ntaii'iing' the *ammonium salt "will becoritaminated by a secondsaltivhichmus't be removed-in an additional step-before the Values resem in the anolyte 'maybeuseda's the cell "feed. Referring" to the "electrical operating characteristic's of the 'cell,' while the 'eurrentdens'ity i's immaterial so far as oprabilityis concerned and thecell may *be operated at anycurrent density --aes1ree,:-a hasbe'en found-that th'epurrent dens'ities re-lower thanrequiredanaqu ous systems. This is importantfrom the standpoint of economy of operation and the dimensions of the cell: In "a -ty'p ical base, it is "entirely "feasible "to bperate cells inf thefcom'mercialproductionof the metal mvabdut to 100 'ampere's -per" square 'deeimeter. Likewise, the voltage; may "be" Varied as" :desired, but'sincetheam'ount of voltageyisiadactor of the-power "cost-ibis advantageouslykept as low as feasible'and it'has'-been"found"'tliat the'"voltage may beabouthalfof"thatirequired -iii'other typespfpro'c'esses making the'same'metalsl In -"'a'typical' -caseusing current densities-with the range mentioned," the'volta'ge may be a'slow as 4 volts.

As stated;thecathdde product ;may be readily separated "therefrom; 1 either periodically I when a sufficient amount has been produced ofco ntinuously. The cathode roduct 'ifT'a .bronze' liquid or a"pa ste'may be readuyprdc'essed obtain the free substantially puremetal'; merely'by removin the ammonia associated therein by evaporatioriI Inthecase ofmetals of'low'melting *point such as" sodium',li'thium;"or potassium; this is readily accomplishedby evaporation atatem- -peratu'resuflicient to produce themetal in liquid state. 'J It-Lmayal'so be accomplished byevaporating the ammonia at a low temperature-which ==Iesu1ts Y in (a' 'spon'gy solid :mass -o'f metal. This S ration df lithium plumbideglead may-b espresso can be melted to form ahomogeneous-mass by .1 the application of I heat. The metals whiclrpossessshignmelting points; for'=example-calcium, strontium,- and "barium; 'may generally be most 5' readily. recovered from the bronze'liquid-or paste Iby evaporation in a vacuum-stilloperating-at a temperaturesufficientlyt high so that the-metal can sublime and be re'covere'd. on -a "cooled con- -denser in a section of thestill.-- The recovery in "19 this fashion overcomes the-difficulty of producing the metal in a pyrophoric state which'is usu- F ally the casefwhen' metals of high melting-point i: rare.-*rec'ove'red'by "drdinaryrevaporatidrrprocedure. I A further method that-may be employed for the 1 5 :s'eparation. of the-"metal from the liquid product "is' "-to' p1 cipitatei= the material" out" chemically. fThis, in general, .ire'quiresr that the: precipitating agent-"be miscible with the solvent present in the .liquid, although: this is not required in all-cases.

201 If a paste'iscobtainedas thecathode'produot or if the bronze solution is too viscous fortl'iis' purpose;- additibnal amounts of solvent may be used to convert th'prodiictinto athir'rbronze or even a blue'solution; :Thus," for example, a solution .25 of calcium in liquid ammonia inathe formpf a :blue solutiondue to the addition of liquid am- --"monia to-a calcium-bronze liquid or paste: may

be treated' with toluene to precipitate the calciurrrfrom the -solution in the-'form'ofva' spongy mass. Asecondexample ofthis type ofwp'rocedure is the precipitation of-lithium in finely divided'formfrom-a--"-lithium-bronzesolution in i'liquielammonia by the-addition of= an -amine, such as ,propyla'mine, in which -the metal is-"substan- .35 tially insoluble.

It is to be understood thatno limitation is to be placed on the method of recovering the metal e sfromv thefbronze liquid or paste' andvgenerally the "methodwmployediwill be d'eterinin'ed' by the 'economics and'the usefor'whi'ch the :metal-i's'pror'espondingto the desired-form.

productionof alloys ina ehemieal ractieiig ln the production of alloys; roe" amplethe repawith thelithium bronze solution in -li'qu 13 inonia; and the l ammonia -subseduenn rated; Alloy s of l variousalkali and/ earth metals may also be prepared merelyby mixiing: solutions ot the" desired metals f followed by evaporation-of the ammoniai' The :liquid er -pasty 'cathode produ'ct also' p'osse'sses hi'eh-"deg-ree of fractivitylandyrmay, therefore, be-used' directly in chemical reactions; for exa'mple; asa pow'erful 1' reducing agent.

l t The?'liqui'd brrlpasty'kcathode product may be i-haindled withoilt difiloulty and the conditions of -its =storage -Wi11- depen-d Ion the particular metal. F or exam le; the p l 'oduot maybe's'tor :or enamelled container :i...per, su'ch v glass,- -bein '-employed, or in' -iron ohtai hei sl "such as ca'stiromr'et orts, steel eyundersem the like The preeuct is relwhen the material is stored for long periods of time in a room, a refrigerated or water-cooled container or compartment may be employed to store the material. The product may be stored in pressure containers, if desired. By the use of cooled containers or pressure vessels, the ammonia or other solvent content of the product may be increased, for example, the use of such containers or vessels is recommended when a blue solution is prepared from the bronze liquid or the paste.

Referring to the formation of the anolyte, the anions of the alkali or alkaline earth metal salt during the electrolysis move toward the anode and when the electron charges of the anions are given up, the anions, in the case an inert anode is used, react with ammonia to form the ammonium salt with the concurrent release of nitrogen gas. This may be represented by the following equation where A- is the anion of the metal salt:

(minus 6 electrons) 6A +8NI-I's- 6NH4A+N2 HA+S+ SETH-A- where I-IA represents the acid of any anion A, Where S represents any solvent, where SH represents the solvated proton, and where A represents the acid anion. In the case of ammonia, the equation may be written as follows:

Therefore, it is evident that the addition or the formation of any ammonium salt to or in liquid ammonia forms precisely the same compound in solution that is formed when free acid is added. Thus, for example, when ammonium perchlorate is dissolved in liquid ammonia, it dissociates into ammonium ions and perchlorate ions and thus is precisely the same thing that happens when ipure anhydrous perchloric acid is added to liquid ammonia.

As stated, it is usually advantageous to place a porous diaphragm around the anode so that, as the ammonium salt forms, it may be kept isolated from the remainder of the cell and either periodically or continuously drawn off. The anode material removed from. the cell is a highly concentrated solution of the ammonium salt in the presence of some of the unelectrolyzed alkali or alkaline earth metal salt and is ideally suited for use in converting alkali or alkaline earth metal carbonate, oxide or hydroxide to the metal salt for re-use as a cell feed. This treatment of the anolyte will be further discussed hereinafter.

The anolyte removed from the cell possesses a boiling point considerably higher than that of an anhydrous liquid ammonia. solvent and, in fact, in most instances possesses a boilingpoint considerably above room temperature. This is a further illustration of the different properties of the electrolyte used in the present invention as compared to an electrolyte in which a low coni2 centration of salt is employed in liquid ammonia solvent.

When, however, instead of an inert anode, an anode, such as iron, copper, or nickel, which is attacked by acid, is employed, no free acid is produced but rather the metal salt of the acid. In the case of the use of an iron anode, for example, the solution quickly develops a dark red coloration, due to the formation of an iron salt, immediately adjacent the anode. While the use of an inert anode is preferred, the use of an anode such as an iron anode may be deemed to possess certain advantages, for example, the condition of the anolyte can be visually observed and there is no solvent waste due to the formation of nitrogen gas. However, as pointed out, an additional recovery step is required to separate the contaminating metal from the other materials, as will also be further discussed hereinafter.

In making up the original electrolyte, the alkali or alkaline earth metal salt, either anhydrous or containing a small amount of water as has been described, obtained from any suitable source, may be dissolved in the anhydrous liquid to provide the requisite concentration. One convenient method of obtaining a lithium salt, such as lithium perchlorate, is to react calcium perchlorate and dilithium calcium phosphate (obtained, for example, by reacting dilithium sodium phosphate in an autoclave under pressure with lime in the presence of water) forming lithium perchlorate and insoluble tricalcium phosphate. The lithium perchlorate solution is separated from the insoluble phosphate and the lithium salt is recovered from the solution and dried. This method of obtaining a lithium salt is not claimed herein but is the subject-matter of copending application Serial No. 666,187, filed April 30, 1946, now Patent No. 2,548,037.

Various methods may be employed in the treatment of the anolyte to prepare it for re-use in the cell. For example, when an inert anode has been used, the anolyte may be rendered suitable for re-use merely by the addition of the desired amount of alkali or alkaline earth carbonate, oxide or hydroxide thereto. In general, however. it will be desirable to employ a series of steps including a reaction in the aqueous phase between the ammonium perchlorat and the alkali or alkaline earth metal carbonate, oxide or hydroxide. In such a procedure, the ammonia is removed from the anolyte, by heating it necessary,

and the residue is dissolved in water and reacted with the carbonate, oxide, or hydroxide of the desired alkali or alkaline earth metal. In the case a carbonate is employed, ammonium carbonate is obtained as a by-product. The solution containing the alkali or alkaline earth metal salt is then evaporated, advantageously after the addition of a small amount of the acid of the anion to make sure that all the ammonia has been removed and to serve as a make-up for any small loss of the anion. The salt recovered may be further dried if desired by any of the methods hereinafter discussed and is then mixed with anhydrous liquid ammonia to provide a cell feed containing the requisite amount of salt. The ammonia initially removed from the anolyte together with any other ammonia available from other portions of the process, for example, that which may be evaporated from the cell, is collected and condensed and is reused, with a small amount of make-up ammonia, to prepare the cell feed.

In the case the anode is not inert, the anolyte of themetal introduced to the anolytejby-the' anode, for example, ferric hydroxide. The-hydroxide i then-removed fromthe solution and the solution is treated with the carbonate, oxide or hydroxide as described.

In a typical case, in the production loin-1 0 pounds of lithium metal per hour, by a; cyolic=,-process,.;a cell having an iron-cathode, a carbon-;,ano.de,;and operating Witha. current density of 20- amperes per square decimeter of electrode surfaceiisemployed. This cell requires 18,000, amperes and operatesat 5 volts. The .feedto the cell {18 2, l quid comprisingv liqu d ammon a: .W c' rhi h; i combined lithium :ner hlorat rth canc r; atien being 2 mols of lithium-;;perchlorate;;per;l e of feed, and the rateof feedisqsuch that the -cell is supplied with; 54 poun s o thium perchlorat perhour. tion containing 12 /2% c f,-; 1' .mcl aligbalance iquid'a m n and fioat o electro rtei n is removed from the cell. The ammonia r is a te f o th brenz rso uti mce livered to the compressor. contains ammonia, ammonium perchlorate, and lithium perchlorate. Th liquidammonia is also evaporated from the product and is returned to the compressor. "Water and lithium carbonate equivalentto the ammonium perchlorate is then added to "the residue and ammonium carbonate is obtained as a by-product. Following evaporation of the solution and drying of the salt, substantially-anhydrous lithium perchlorate is obtained. In this example;approximately- 4%;; 0f the lithium perchlorate is recycled-as theresult of the presence of this salt in the anolyte as it is removed from the cell. The necessary makeup ammonia is added to the recovered liquid ammoniaand the .cell feed .isprepared. by mixing the required amount of lithium perchlorate and the ammonia to provide a cell feed of the stated concentration.

As has been stated, the process is operative when limited amounts of water are associated with the alkali or alkaline earth metal salt dissolved in the anhydrous liquid solvent to form the electrolyte, but, in the preferred embodiment of the invention an anhydrous or substantially anhydrous salt is employed. In the processing of the anolyte to convert it into a material for re-use as the cell feed, the alkali or alkaline earth metal salt is dried and this drying reduces the water content so that only a limited amount remains with the salt or it may remove the water substantially completely.

In the preparation of the salts from aqueous media, it has frequently been found desirable to crystallize, from a concentrated solution, a crop of hydrated crystals and then to subject them to dehydration, thus producing a product which is nearly free from impurities. The mother liquor from this separation can be further concentrated to produce more of the crystals and usually the mother liquor from several batches is accumulated into one large batch which is treated as stated. It is also possible to prepare anhydrous salts in a manner similar to that described, for example, by mixing solid lithium carbonates with solid ammonium perchlorate in the presence of Water and applying heat until the water is removed.

The salts may be dried by any suitable method at atmospheric pressure or under a vacuum. The use of vacuum drying will result in the re- The-cathod rr si cti za-b nze:sel w Th e-anod produ mov,al -'of moisture eat --temperatul1es .plower can be used at atmospheric ipressurcnand 111 7 211 case of thermally sensitive salts, the use of; yacuum drying may be found to beiadrantageous. I

h p cu met od e ployedinthe dryin of the salt ,will depend ontheiextent -o f;dryness desired and the characteristics-of the part cular salt. In the case of the perchlorates,it'is-usually only necessary'to heat the material to a sufiicient temperature to drive out :allor .substantiall y all of the water. Thus, in the preparationof lithium perchlorate, the wet salt may-be;-heatedto, as.tem-.., perature of about 300'C.'and then cooleddown to room temperature in W ich-casethe material frozen to :a solid state can be brokenup .readily and dissolved in-the.solvent. In: the case :ofithe thiocyanates, which. are subject ,to thermal ,dee composition, :other vmethods. areegenera'llyemployed.

One ofthe-methods whichemaysbecused -the production of ;a.substantial-ly anhydrous. 1358M],

where; there is .a: tendency tor the ;salt;being treated ,to decompose, :involves ;.the;rstep.rof am! moniating the partially .drie -d :salt :at lthensame' time that the -residu a1-..water. is, removed; =I his; is accomplished, for instance,.x;by:passi-ngearnmonia gas,.; for;- example, that-which may .beeevolvedlas excess ammonia in the electrolysis vstep; (usually mixed with nitrogen). ,ovcrthepartiallw driedsalt.

which is maintained :at .an; eleyateditemperature. Thus,-;in thepreparation of lithium thiocyanate.

iorexample, the partiallyidried saltiiszplaced in a closed -contai-ner maintained .=:at,=a temperature in excess of about .150? -1 C.iandzintocwhichlammania-gas is passed. vAfter:aiperioclof:time suflie;

cient :to drive outathe residual water; loweringnof the temperature will result ;:in a ,vrelatively :zhot solution of lithium thiocyanate .in ammonia-and, on cooling, this, solution ;ser.ves 58.5, 1 a highly con- 1 centrated cell feed which can be added-i410 :the

0 1 in-i heliquid state or-canzbe further dilutedbefore its; addition to :the;cell. Alternativel-y,:the material can be treated by crystallizing the ammoniated salt from the ammonia solution. This crystalline product may then be used as a cell feed either directly or in a dissolved condition. Furthermore, this salt may be de-ammoniated to form an anhydrous salt if that should be desired.

For salts highly sensitive to thermal decomposition, it is also possible to dry the salt from the frozen state at temperatures substantially lower than the freezing point. In such a case, the drying is conducted under conditions of high vacuum and the water sublimes from the solid mass.

Considerable modification is possible in the nature of the cathode product, as well as in the conditions of the process and the structure and operative characteristics of the cell, without departing from the essential features of the invention, and it is to be understood that such modifications and variations fall within the scope of the claims.

We claim:

1. A cyclic process for producing a metal selected from the group consisting of the alkali metals and the alkaline earth metals which comprises electrolyzing between substantially inert electrodes in a cell a solution of a salt of said metal selected from the group consisting of the perchlorate and thiocyanate in an anhydrous liquid selected from the group consisting of ammonia, methylamine, ethylamine and pyridine to produce a cathode product and an anode product, the concentration of salt in said anhydrous liquid at least in contact with said cathode product being at least 2 mols of salt per litre of anhydrous liquid to provide a medium in which the cathode product is substantially insoluble; separating the cathode product from the electrolyte, whereby a cathode product comprising the metal substantially free from salt is obtained; separating the anode product comprising the anhydrous liquid, the anion of said metal salt and its associated solvated proton, SH+, where S is said anhydrous liquid, from the cell; reacting the anion of said metal salt and its associated solvated proton with a compound of said metal selected from the group consisting of the oxide, hydroxide and carbonate to form the corresponding metal salt, and utilizing said metal salt, in substantially anhydrous form, as source material in the process.

2. The process of claim 1 wherein said anhydrous liquid is ammonia.

3. A cyclic process for producing a metal selected from the group consisting of the alkali metals and the alkaline earth metals which comprises electrolyzing between substantially inert electrodes in a cell a solution of ,a salt of said metal selected from the group consisting of the perchlorate and the thiocyanate in an anhydrous liquid selected from the group consisting of ammonia, methylamine, ethylamine and pyridine to produce a cathode product and an anode product, the concentration of salt in said anhydrous liquid at least in contact with said cathode product being at least 2 mols of salt per litre of anhydrous liquid to provide a medium in which the cathode product is substantially insoluble; separating the cathode product from the electrolyte, whereby a cathode product comprising the metal substantially free from salt is obtained; separating the anode product comprising the anhydrous liquid, the anion of said metal salt and its associated solvated proton, SH+, where S is said anhydrous liquid, from the cell; reacting in an aqueous medium said anion and its associated solvated proton with a compound of said metal selected from the group consisting of the oxide, hydroxide and carbonate to form the corresponding metal salt; removing water from said metal salt to render it substantially anhydrous; and utilizing said metal salt as source material in the process.

4. The process of claim 3, wherein said anhydrous liquid is ammonia.

5. The process of claim 3, wherein the metal produced is lithium, wherein the said metal salt is lithium perchlorate, and wherein the said anhydrous liquid is ammonia.

6. The process of claim 3, wherein the metal produced is lithium; wherein the said metal salt is lithium thiocyanate, and wherein the said anhydrous liquid is ammonia.

7. The process of claim 3, wherein the metal produced is calcium; wherein the said metal salt is calcium perchlorate, and wherein the said anhydrous liquid is ammonia.

8. The process of claim 3, wherein the metal produced is calcium; wherein the said metal salt is calcium thiocyanate, and wherein the said anhydrous liquid is ammonia.

LEONARD JOHN MINNICK. CYRIL PRESGRAVE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 788,315 Hoopes Apr. 25, 1905 1,538,390 Ewan May 19, 1925 2,313,408 Vingee et a1 Mar. 9, 1943 OTHER REFERENCES "Journal of Physical Chemistry, vol. 35 (1931), page 2289.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
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US1538390 *Mar 31, 1924May 19, 1925Thomas EwanTreatment of alkali-metal amalgams, especially for the production of alkali metals
US2313408 *Aug 12, 1939Mar 9, 1943Solvay Process CoElectrolytic production of alkali metals
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3006824 *Sep 29, 1958Oct 31, 1961Ethyl CorpProduction of metals by electrolysis
US3897317 *Jun 24, 1974Jul 29, 1975Texas Instruments IncProcess for making hyperpure gallium
US3953302 *Aug 16, 1973Apr 27, 1976P. R. Mallory & Co. Inc.Prevention of dendritic plating of lithium
US4801363 *Jan 5, 1987Jan 31, 1989The Dow Chemical CompanyHigh purity alkaline earths via electrodeposition
EP0164254A2 *May 31, 1985Dec 11, 1985Amoco CorporationPorous lithium electrodes and their use in nonaqueous electrochemical cells
Classifications
U.S. Classification205/560
International ClassificationC25C1/00, C25C1/02
Cooperative ClassificationC25C1/02
European ClassificationC25C1/02