US1116865A - Process of producing alkali and alkaline-earth metals. - Google Patents

Description

C. E. ACKER.

PROCESS 0F PRODUCING ALKALI AND ALKALINE EARTH METALS.

APPLICATION FILED AUG.5, 1910.

Patented Nov 2 SHEETS-SHEET l G. E. ACKER. PROCESS 0F PRODUGNG ALKALI AND ALKALINE BARTH METALS.

APPLICATION FILED AUG,5,1910.

Patented Nov. 10, 1914.

K mlweg.

2 SHEETS-SHEET 2.

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spammen of Leners recent. appresi@ ne .Ais1-t .5, me .Sisal .1o- .51ans- Paaeneed Nov. 1o, 1ere.,

T0 all whom t may concern .Be it known that I, ,CHA-#LES E. Afasie., a

:citizen of .the United States, residing at Ossining, in the countyof Westchester State of New York, have inrented certain new7 and useful Improuements in Processes Alkali and Alkaline-llarthv 0f .Producing Metals, of which the following is a full, Clear, and exactdescription. v

This invention relates. to the reduction 0f .igllkalind alkaline-.earth meta s, and has for its object the provision of a .process whereby such .metals may be produced more economicallyand efficiently than heretofore.

United Statespatent to Edgar A. Ash- Croft, No, 801,199, dated .October 10, 1905, discloses a process .for the production of all kali metals; sodium being obtained by electrolyzingfused sodium chlorid over a molten leadcathode, thereby producing an alloy of ,lead and sodium, such alloy being thereafter employed while s till molten Aas an anode ,connection with a secondary `electrolyte consisting of fused sodium hydroxid or ,fusedsodium chlorid; the cathode in this latter operation bein of iron x or nickel and the metal belng liberated thereat,`

subseqtienti;I Erising tothe surface of the sec- Qndary electrolyte whence it Ymay ,be

, dra-Wu eff# :I have .found in practice that .the .above described is open to Ea number of serious objections which have been brought ,notice in ,attempting to use `the various substances ,heretofore Pm use@ .for use as'- secondary electrolytes.. f ile Sodium hydroxidchlorid, bromid or iodid, may on .a to effect Tthe production of sodium in the manner .above described, such electrolytes, and in fact :all others .that :havre thus far been mentioned 'or .proposed for this purpose,

v fail to vmeasure up to the commercial requirements. 'In passing ,a heavy current of electricity from the surface .of molten leadsodum or like alloy through .an .electrolyte of `,fused sodium hydroxid at the temperature at which the alloy was made, to Wit, 70W-800o C., substantially no sodium will be liberated at the cathode, and but very little will be obtained at lall unless the tem- 5discovered, however, that alkaline-earth. metals may be obtained at a 0 which imposes an onerous and Elleconomical condition. Then, .too,.if the current be passed from 'alloy through an electrolyte composed (1f-any chlorid, bro

mid, fluorid, iodid'ior mnrixture thereof, ,mom QL, ,of

? mm is liable t9. 'fsodlum unless ,the

be plate -S Quite @corrales-Stb@ alloy is .quite ri in alkali metal; the Ilatter condition involonperature `be reduced tol approximately 350"l such objectionable features being possible by Yreasll'of 4the fact .that the heavy metal 1n the alloy may combine withy .the liberated anion to form a stable salt at the temperature .of the operation. If, for example, vthe' secondary electrolyte be fused sodium chlorid and the anode be lead-sodium alloy, the anion will be chlorin, .and this will combine with avidity with the sodium in the 4alloy at the surface thereof; but there is the liability, particularly in ,the case of a weak alloy, that unless the current density ybe low, combination nto a greater or less .extent between thelead and chlorin may occur, resulting in ,the formation of lead chlorid,- a Lvery stable conducting salt, which mixes with the molten sodium chlorid .and is then decomposed by the current with deposition of lead at ,the cathode. This and .other objectionable actions are apt to occur not only in connection with the use of lead .alloy Vand a secondary electrolyte of sodium chlorid, but with other alkali or alkalineearth metal alloys and .with numerous salts. The current efficiency in the secondary cell .With chglorid electrolytes is always very low because the liberated metal dissolves therein at the regular Working tem erature. Ihave oth alkali and high efficiency as'a Aresult of electrolysis in the secondary cell at a convenient and ,economical temperature if the electrolyte consists of a metallic compound, containing carbon and nitrogen, such for example as the corresponding metal cyanid or cyanamid, or of a stronger cyanid or cyanamid, or a mixture of such salts, and that by the use of such an electrolyte no portion of the heavy metal in the alloy can be carried along as an impurity. I thus not alone improve the product, but I further obviate the necessity for the very careful regulation of tem perature, current density and composition of alloy necessitated by the use of the elec trolytes heretofore proposed. In producing metallic sodium I regard pure sodium cyanid as the best secondary electrolyte; but potassium cyanid or mixed sodium and potassium cyanids may also be employed owing to the fact that potassium cyanid is a stronger compound than sodium cyanid and is not decomposed by metallic sodium. I

p have discovered that potassium cyanid is the most suitable cyanid for the production of the metal potassium. In the above electrolytes the corresponding cyanamid salt may be substituted for cyanid, or a mixture of such cyanamids and cyanids may be employed. y

In the production of metallic lithium, calcium, barium, or strontium by this process,

sodium or potassium cyanid may be employed as the electrolyte, at the beginning of the operation, but the liberated. metallithium, calcium, barium, or strontium-will reduce the molten cyanid in whole or in part, in course of time, to the corresponding cyanamid salt, that is to say, sodium or potassium cyanamid. These molten cyanids and cyanamids constitute admirable electrolytes in connection with anodes of leadsodium, lead-potassium, lead-barium, leadlithium, or of any other suitable heavy metal, such, for example, as tin, combined with an alkali or alkaline-earth metal, for the reason that the heavy metals do not form corresponding salts which can existat the temperature of the operation,-normally a moderate read heat,-the only stable cyanids or cyanamids at red heatl being those of alkali or alkaline-earth metals; andfurther, that neither the heavy metals nor alkali or alkaline-earth metals aresoluble in molten cyanid or cyanamid. The molten alkali cyanids and cyanamids, too, are especially suitable for use as electrolytes, because of their low melting points, and great fluidity, and the fact that no narrow limits of ternperature are necessary, which obviates the necessity for extremely careful regulation.

The use of a cyanid is free from objection for the reason that should any molten cyanid runout. into the air or should such substance escape in the form of vapor, it would im# mediately burn to cyanate, which is harmless; and no odor of hydrocyanic acid is apparent, for the reason that the cyanid is not used in solution and there is no hydrolysis. The cyanamids are harmless.

bringing oxids into solution, etc.

Other alloys, more or less suitable for the purpose in question, may be made by electrolyzing various fused salts in connection with a molten metallic cathode, among which may be mentioned alloys of each of the alkali and alkaline-earth metals with not alone lead or tin, but in some cases with zinc, aluminum, etc.. Hence, by the expression heavy metals I mean to include for the purpose of this specification, all metals not included in the alkali or alkaline-earth group of metals.

It has been customary in electrolyzing molten salts of different kinds to add some fluxing agents for the purpose of lowering the melting point, increasing the fluidity, When such a mixture of salts is electrolyzed over a molten metallic cathode the voltage and current density required to economically supply all the heat required in the process, While obtaining'a good current efliciency, etc., are so high that all salts in the mixture are decomposed and all of the metals are liberated in Contact Withthe surface of the alloy. Thus, in the electrolysis of molten sodium chlorid over a lead cathode, as ordinarily practised, the current density is so high that any metallic chlorid or soluble salts whatsoever, whether of potassium, lithium, calcium, barium, strontium, etc.,- will be decomposed simultaneously with the sodium chlorid and their metals will become a part of the alloy.

In the electrolysis of, ordinary sodium chlorid for instance, which contains calcium sulfate as an impurity, which substance however dissolves perfectly in the molten sodium chlorid, thecalcium sulfate is decomposed continuously by the current and the calcium enters the alloy together with the sodium, and if steam be afterward injected into the alloy the calcium will be removed along with the sodium. The other common impurities, such as iron oxids, silica, etc., do-

not fuse perfectlyfbut settle out as impurities.

In the electrolysis of molten sodium chlorid 0n a large scale, it is desirable to add i a certain yproportion of potassium chlorid to the bath for the purpose of slightly lowering the working temperature, and the process may then be advantageously conducted at temperatures ranging from 800o down to 700 C., if desired. The alloy Will then contain both potassium and sodium, but the presence of a small percentage of potassium in metallic sodium is not found to be obj ectionable for the usual purposes for which sodium is required. It is of course not absolutely necessary in electrolyzing molten sodium chlorid, for instance over a lead cathode, to employ any potassium chlorid whatever, but certain advantages are obtained by the use of at least 2% of this compound; and this percentage may be increased up to 25%, if desired. Similarly in electrolyzing molten potassium chlorid it is desirable to add from 2 to 25% of sodium chlorid. Lithium chlorid requires the addition of sodium or potassium chlorid,-,not to lower its melting point, but to increase. the current eiiiciency. If the primary bath is composed principally of molten calcium chlorid it may be desirable in some cases to add 10% or more of sodium or potassium chlorid or iuorid, or one or more of the alkaline-earth chlorids or iuo-rids; and the same procedure may be taken in the case of barium chlorid and strontium chlorid. In general, it may be stated that no hard or fast rule may be laid down to be followed co-ncerning these mixtures of salts, and it must be borne in mind that they all will be decomposed by the cprrent if the voltage and current density be sufficiently high.

The molten metallic cathode should be a body of metal large enough to act as a storage reservoir for the alkali or alkaline-earth metal, as Well as for heat; and it may ordinarily contain from 5% to 25% by Weight of the light metal. It should be kept in constant circulation and this circulation should not be too sluggish in order to preserve au effective balance between the respective cells. This makes it possible to run either half of the furnace for several hours, While thc other half is short circuited; and especiallydocs it tend to equalize the temperature throughout the Whole apparatus. .This is particularly true when the apparatus is compact and well inclosed in non-conducting brick Work, or other heat insulating material, resulting in a conservation of the en' ergy required throughout the process. lt may be here noted that the provision of an electrolyte comprising a suitable metal cyanid or cyanamid, permits of this particularly desirable feature since it allows the secondary cell to be operated at the same or substantially the same temperature as the primary. The principal source of electrical heat should be in the primary bath and the voltage and current density should there be relatively high. If the temperature of the primary bath is 750 C., the temperature of the circulating alloy throughout the furnacel will be approximately 750 C., and the temperature of this moving body of metal will determine to a large eiitent the temperature of the operation in the secondary furnace, which Will ordinarily be but very slightly lower than that of the moving metal; but the temperature of the secondary electrolyte may be, in fact, maintained as much as 100o C. lower than that in the primary, if desired, by employing a very low current density in the secondary, by exposing the iron cover to heat radiation in the air, Aby conducting some of the heatl away through an eXtra heavy cathode With outside copper connections, etc. Here again the use of alkali cyanids and cyanamids is beneficial owing to their low melting points, which, of course permits the electrolyte to remain fluid over a large range of temperature.

Other advantages arising from the use of my process Will be hereinafter set forth and more particularly pointed out in the appended claims.

In the accompanying drawings, which illustrate one form of apparatus adapted to carry out my process: Figure 1 is a vertical section of a double compartment furnace, said section being taken on the line I-I of Fig. 2. Fig. 2 is a horizontal section of said furnace taken on the line II-II of Fig. 1. Fig. 3 is a transverse vertical section taken on the line IIIA-III of Fig. 2. Fig. 1 is a fragmentary section taken on the line IV- IV of Fig. 3.

The furnace casting -or inner container 1 should preferably be made of cast iron or cast steel, and the inner walls of each compartment should preferably be lined with refractory material 2, such as alumina or magnesia. at the bottom and on all sides by heat insulating material 3, preferably brick or the like. The furnace comprises two principal compartments, a primary compartment -t and a secondary compartment 5, these compartments being separated by a septum or wall 6 Which preferably forms an integral part of the casting l. In vertical section, this wall has been shown in the form of an inverted T; the bottom fianges 7 thereof serving to support the adjacent side linings 2. The primary anodes 8 extend through the top of the primary compartment and are preferably made of some form of carbon ;v graphite being particularly Well adapted or the purpose. This primary compartment is covered with a slab 9 of suitable refractory material not affected by chlorin'or other corrosive gas Which may be liberated at the anodes. The gases so liberated are conducted away through the fines or vents 10. The secondary compartment 5 is tted With an overflow spout 11 for the purpose of conducting off metallicsodium for example, if that be the ultimate material desired; and this compartment is preferably fitted With an iron cover 12 insulated from The furnace casting is inclosed the inner container by meansof an asbestos tion with'f'the further-sidesof the respective' mary electrolyte'-15.` -Thebody of heavy metal `or alloy 16, is disposed in the bottom of Hthe respectivecompartments and a plu-- l`'rality .lof conduits are provided 'which are alsoflled by said alloy, such conduits affording means for' effectively circulating the heavy metal or alloy, through the re spective. compartments. In the form` of passage 19, leading from -ittorcompartment 5. As will he observed'from-an inspection of Fig.f2, these passages -18 and 119 are rel-atively elongated :and substantial aline-5 ment, -but have their .remotelends somewhat enlargedin order to equalize the p flow of l 1 alloyithroughfth:chambers.

'The second 4'conduit 20 fs 4m commin iicad` compartments through passages'lQ-l :and 22,

such passages also having the forml elon.- gated' slotsand theconduit'QO leading there-A` `pump `isV from 'to a suitable -pumpl 23. This preferably of the centrifugal type, u't any suitable apparatusmay -be employed for this purpose which is adapted yto eiciently .circulate the mass ofalloyr' The movement of the -mass -of fluid alloythrough the -co1n' partments results in stirring'up the `respective electrolyte bodies,- since such bodiesl float lupon -the surface .of the alloy :in the re# spective compartments, The circulation of the alloy may be effected either intermittently or continuouslyy by mechanical means or otherwise, and suitable means, such as a hopper 24,"may be provided for permitting the continuous-or intermittent introduction 'of the' salt required in the lprimary compartment.

For the. production of metallic sodium', I prefer to empio fused sodium chlorid, or a mixture thereo with other compounds, as the electrolyte 15, While the electrolyte 14 should be a cyanogen compound. The heavy molten metal, such for instance as Vleadsodium alloy, extends up into and covers the bottom of each compartment and 'thereby serves to separate the respectivexelectrolytes .by eiiiciently sealing the channels or conduits connecting the primary and secondary cells.

The process may be carried out either in tcrmittently or continuously in the double compartment furnace described; or thetwo compartments or cells may be entirely dis tinct and separate from each other g-that is, the alloy may be made in one furnace and afterward transferred bodily to a separate furnace and there decomposed, such procedure being obviously Within the scope of the invention.

In operation, should it be decided to inancathode risin :ufacture simply sodium, so that such mate- Vrialm'ay -be accumulated, sodium chlorid,

for example, would be introduced through- E'the `hopper 24 and electrolyzed by suitable current, chlorin being evolved and passing oil' through thevent 10 While the sodium Acombines With-the lead or'other `heavy'metal which forms the'cathode in the primary cell,

to/formx-the" `lead-sodium alloy, This alloy in :turn xbecomes" the anode v'of the .secondary vcell, molecules 'of thesodium-c'yanid there- 1n 4vbeing momentarily"dissociated", the -released sodiurrr being deposited upon 'thecathode While the cyanogen anions combine with fresh sodium from the surface' of the alloy; fthe accumulated sodium -upon the 0 tothe surface of the electrolytefat 25 rom whence it may be drawn ,off continuously or intermittently; and the electrolyte *hence 'remaining substantially *unconsum'edf Thisaction is the same with all dfithealkalimetals,such for example as sodium, antV ro uct'g-being delivered through the "The closures 9 and '12arepreferably covered With-a la e'rlof 'suitable material tov form a seal .an 'further to aid in retaining the heat. vI prefer to use common salt v (NaCl) for this lpurpose when using sodium Chlorid as an electrolyte in the primary cell.

In'conclusion I particularly Wish also to call-attention 'to the low melting vpoints of the cyanids, which are considerably below the temperature required for the formation ofthe alloy.- These compounds, too, being free' from Water or Water-forming constituentsiand also being non-halogen compounds are not subject -to the objection hereinbefore referred to, to Wit, a liability to attack the heavy metal .of the alloy, 'to vform soluble compounds therewith at the temperature of the operation, which temperature -as aforesaid approximates a red-heat.

vWhat I claim, is:

'1.The process of producing metal which comprises electrolyzing a fused compound containing carbon, nitrogen and the metal to be produced, by passing a current of electricity therethrough from a body of material containing thefdesired metal and another metal. v

2. The process of obtaining a metal which lcomprises electrolyzing a salt containing thc -'potassium,ilithiu'm, etc., the resultl" sired metal in combination with a nitrogenA ing of a body of molten alloy containing the desired metal and another metal which is incapable of forming a combination With a carbon and nitrogen radical 'which is stable at the temperature of the operation. 4e. The process of producing alkali metal which comprises electrolyzing a fused cyanogen compound of said alkali metal, by passing current from a fused alloy comprising said alkali metal and another metal.

5, The process of producing alkali metal Which comprises electrolyzing a fused cyanogen compound of said alkali metal, by passing current from a fused alloy comprising said alkali metal and another metal which does not form a stable cyanid at the temperature of the molten alloy.

6. The process of obtaining a metal Which vcomprises electrolyzing a Huid y'mass containing a cyanogen compound, by passing an electric current through said mass from an anode comprising a body of alloy con-- taining the desired metal and another metal which does not form a stable cyanogen coinpound at the temperature of the operation.

7. The process of obtaining a metal which comprises electrolyzing a fluid mass containing a cyanid, by passing an electric current through said mass from an anode coinpri'sing a body of alloy containing the desired metal and another metal Which does not form a stablecyanid at the temperature of the operation.

8. The process of obtaining a light metal .belonging to 'the group of metals which form .stable cya-nids when molten, which comprises` passing an electric through a molten bath containing one or more stable cyanogen compounds non-de' composable by the desired metal, from an anode consisting of a molten alloy containing a heavy metal and the desired light metal. f

9. The process of obtaining a light metal belonging to the group of metals Which f form stable cyanids When molten, lwhich comprises passing an electric' current oilthrough a molten bath containing one or more stable cyanids non-decomposable by ,the desired metal, from an anode consisting of a molten alloy containing a heavy metal and the desired light metal. l

10. The process of obtaining a light metal belonging to the group of metals which form both stable cyanids and chlorids when molten, ywhich consists in electrolyzing a fused chlorid of the light metal in a primary electrolytic cell over a cathode which forms a fusible alloy With said metal, and thereafter using said alloy as an anode in a secondary electrolytic cell containing an electrolyte comprising a molten cyanid of the current iight. man, depositing the ugae'meai at at the cathode Without consuming the electrolyte.

12. The process of obtaining an alkalil metaly which comprises electrolyzing a primary electrolyte containing `a fused chlorid over a cathode which forms a fusible alloy with the alkali metal, thereafter dissolving said alkali metal out of said alloy by electrolyzing a secondary electrolyte containing an alkali metal cyanid While using the alkali metal alloy as an anode'therein, the alkali metal depositing at the cathode without consuming said secondary electrolyte.

13. The process of producing sodium which comprises electrolyzing a fused cyanogen compound of sodium by passing current from a fused alloy comprising sodium and another metal.

14. The process of obtaining sodium which comprises electrolyzing a fluid mass containing a cyanid by passing an electric current through said mass Vfrom an anode comprising a body of alloy containing the desired metalv and another metal which does not form -a stable cyanid at the temperature of operation. i

15. The process of obtaining a metal belonging to either the alkali or alkalineV earth groups which comprises electrolyzing a Huid vmass of the desired metal belonging to said groups in a primary electrolytic cell over a cathode which forms a fusible alloy with said metal and thereafter using said alloy as an anode in a secondary electrolytic cell containing an electrolyte comprising a molten cyanid of the light metalt thereby depositing the light metal at the cathode.

16. The process of obtaining sodium which consists in electrolyzing fused sodium chlorid in an electrolytic cell over a\ cathode which forms a fusible 'alloy with said sodium and thereafter usingsaid alloy as i an anode in a secondary electrolytic cell containing an electrolyte comprising a molten sodium cyanid, depositing the sodium at the cathode.

17. The process of obtaining an alkali or alkaline earth metal which comprises 'electrolyzing a mass of the metal cyanid containing the desired alkali or alkaline earth metal by passing a current therethrough from an alkali or alkaline earth metal alloy, dissolving the alkali or alkaline earth metal out of said alloy and depositing said metal at the cathode Without consuming the electrolyte.

'finesse 18. The process of obtaining sodium which cathode Without consuming said secondary l0 comprises eleotrolyzing a primary electroelectrolyte. lyte containing fused sodium chlorid over In Witness whereof, subscribe my signaa cathode which forms a uible alloy with ture in the presence of two Witnesses. 5 said sodium theres. ter ssolving said f sodium out of the alloy by eleotrolyzing ay CHARLES E AGREE' secondary electrolyte containing sodium Witnesses: cyand while using the sodium alloy as an YALDO M. CHAPIN, anode therein, the sodium depositing at the JAMES DE ANTONIO.

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