" ce 2,931,703 Patented Apr. 5, 1960

, 2 preferably, M and N are low molecular weight alkali metals, such as lithium or sodium. ‘Particularly preferred 2,931,703 .as starting materials for the process of the invention are PROCESS FOR-RECOVERY 0F LITHIUM HY- ~ . ' alkali metal phosphates containing at least two lithium ' DROXIDE FROM LITHIUM PHOSPHATES cations, of the formula LigMPO, where M is as de?ned vLawrence J.-Reader, Malvern, Pa., assignor to Foote above. ' ' ~ '. ‘ Mineral Company, Philadelphia, Pa., a corporation of One preferred source of lithium for processing in ac cordance with the present invention is Li3PO4. Trilithium Pennsylvania ' - ' ' . phosphate, which may be converted to lithium hydroxide No Drawing. ApplicationlApril ‘3, 1957 10 as ‘further described hereinbelow,'may be obtained, for §erial No. 650,307 . example, from caustic liquors produced in processing 13 Claims. (Cl. 23-25) . _ ores such as spodumene, lepidolite, petolite, and the like, '- by treatment with phosphoric acid, whereby lithium values are conveniently separated from other alkali metal ' This invention relates to lithium hydroxide recovery, 15 compounds admixed therewith. and more particularly, provides a method for the recovery Another alkalimetal phosphate readily amenable to of lithium values in’ the form of lithium hydroxide from conversion to lithium hydroxide by the present process a lithium phosphate. ’ . and employed in a preferred embodiment of this inven It is a principal object of the present invention to tion is dilithium sodium phosphate, Li2NaPO4, an impure provide a novel method for the recovery of lithium values 20 form of which is .a byproduct vmaterial from Searles Lake from a lithium phosphate. 1 brines sometimes deignated as “Trona Scale.” If de a it is a further object of this invention to provide a ., sired, other dilithiumv alkali metal phosphates,v such as ‘l novel method for obtaining an alkali metal hydroxide Li2KPO4 or Li2RbPO4, may; be utilized in the process of l from an alkali metal phosphate wherein lithium is one the invention. The monolithium alkali metal phosphates, of the cations, of the phosphate. ' ‘exempli?ed by LiNa2PO4, LiK2PO4'and LiCs2PO4, when It is an additional object of this invention to provide available, may alternatively be employed in accordance .a novel processforv producing lithium hydroxide. ‘ ’ with this process, or mixtures of lithium phosphates may A further object of, this invention is to’provide anovel be used. ' process of producing lithium‘ hydroxide from a lithium' In the ?rst step of the present process, the lithium phosphate in‘which losses of lithium are reduced to a 30 phosphate is calcined with alumina and lime. The latter minimum. ‘ ' - '7 ‘a ' two reagents may be added as such, or in the form of A speci?c object of'this invention is to provide a novel materials supplying or giving rise to thedesired com method for the conversion of a lithium phosphate 'to pounds on heating. Thus, for example, the source of lithium hydroxide with accompanying production of alumina may be any desired aluminum compound fur valuable byproducts. . . > > nishing alumina at elevated temperatures, such as alu These and other objects of the invention‘will be ap minum hydroxide; a particularly preferred and inexpen parent from a consideration of the following speci?cation sive source of alumina is an aluminum. ore such as and claims. , i bauxite. The lime, or CaO, may be supplied by quick Alkali metal. phosphates containinglithium as a cation lime or hydrated lime, if desired, or advantageously, lime‘ are obtained as a byproduct or intermediate in many stone or other form of calcium ‘carbonate may be em mineral re?ning processes. Commercially, lithium phos ployed as a source of lime under the reaction conditions. phate has'no ready market, and for sale, is converted to The reactions believed to be taking place on calcina other forms of lithium compounds such as lithium hy tion and digestion of a lithium phosphate in accordance droxide, wThe methods‘proposed in‘rthe prior are for the with the process of the invention, as illustrated with ref release of the lithium values from a lithium phosphate erence to Li3PO4, A1203 and CaO as reactants, are as

generally do not lead directly to the formation of lithium follows: ' ' hydroxide, but- produce lithium salts such as lithium sulphateor, lithium chloride, from which lithium hy- (l) Calcination -, q . droxide' or lithium carbonate can be obtained only by 2Li3P04+ 3Al2O3 +3CaO-> 3Li2O.Al2O3 +Ca3 (P04), proceeding through an additional step. The reaction of 50 lithium phosphate with calcium hydroxide in aqueous (2)’ Digestion solution, which does produce lithium hydroxide as a 3Li2O.Al2O3+ 3Ca0+ 3H2O—> 6LiOH+3CaO.Al2O3 product, is commercially impractical because of an un favorable solubility balance and low yields. When a mixed alkali ‘metal phosphate of lithium‘ is em‘. ‘ployed as a starting material, the reactants interact in In accordance with the present process, lithium hy 55 droxide is obtained by calcining a lithium phosphate with the same proportions as in the above equations, but the lime and alumina, followed by digestion of the calcined corresponding alkali metal hydroxide is formed together mass in water, in the presence of lime. with the lithium hydroxide. >Thus, the overall reaction Practically complete (over 90%) recovery of the lith may be represented by the general equation ium in the lithium phosphate may be obtained by oper 60 ating in accordance with the process of the invention, and as a byproduct of the present reaction, there are obtained calcium salts useful in the ceramics and glass ' wheredM and N are lithium or other alkali metal, as industries and also useful, for example, as afertilizer. ‘ de?ned above. ' , The present process is‘ applicable to the recovery of 65 ‘As will be evident from the above equations, the lithium lithium hydroxide from a variety of alkali metal phos ‘phosphate, alumina and lime are consumed in the process phates wherein at least one of the cations of the phos 7 in ,the molar proportions respectively of 2:3 :6, three moles phate is lithium. The presently useful alkali metal phos of the lime being consumed in the calcination step and phates may be represented by the general formula and three in the subsequent digestion. The total quan LiMNPO4 Where each of M and N is an alkali metal. 70 tity of lime or'source of lime required for the overall The alkali metal represented by each of M and (N may reaction is preferably added to the lithium phosphate be lithium, sodium, potassium, rubidium or caesium; prior to the calcination step, thus allowing for the con 3,931,793 4 version of a source of lime such as limestone into lime by to minimize contact time with the water. If the product the heat of calcination. However, the lime required for from calcination does not contain the desired amount of the digestion step may, if desired, be added to the product lime, additional lime may be added and mixed with the of the calcination step before digestion. . ' ' ' calcined material. The lime-containing calcined ma ‘T he exact ratios ‘of the reactants are not critical. The terial is then digested in water, advantageously with stir phosphate-alumina-lime overall proportions, that‘ is, the ring, until a solution of lithium hydroxide is obtained. If proportions in the calcination and digestion steps con desired, the entire calcined mass can be stirred with water side‘red together, may be as low as 2:224, but in this case in a batch-type operation until the alkali has been ex not enough lime and alumina will be present to produce tracted therefrom, or alternatively, the digestion may be complete conversion of the ‘phosphate to the. hydroxide, 10 carried out in leaching tanks whereby the alkali is ex and yields will be correspondingly lowered. Accordingly, tracted in successive washings; the aqueous extracts from the overall proportions are preferably at least the. theo-, succeeding stages may be utilized for the digestion of the retical molar proportions referred to above. Advanta- . calcined mass in a multistage countercurrent procedure. geously, lime and alumina are employed somewhat in ex The temperature in the digestion step is advantageously cess of the theoretical requirements, so as to ensure maxi 15 elevated to accelerate the reaction. Temperatures as low a‘ mum recovery of the lithium. Thus, for example, the -' as 60° C. are operable; temperatures in the range of from overall phosphate-alumina-lime ratio may range up to about 85° C. to about 95° C. are preferred. If desired, about 1:2:6, if desired. ' ' temperatures above 100° C., even up to about 115° C. As noted above, the calcination charge need not con can be used, due allowance being made for loss of water tain all the lime required by the overall reaction, since 20 by evaporation, or with prevention of the loss of water additional lime may be added to the calcination product by application of superatmospheric pressures. prior to digestion to remedy any de?ciency thereof with The lithium hydroxide is obtained in aqueous solution respect to the reaction occurring in the latter step. Thus, as the liquor from the digestion step. This liquor may in the calcination, the phosphate-alumina-lime propor be separated, for example, by ?ltration or decantation tions may if desired be as low as 2:2:2, although prefer 25 and employed as such, or evaporated to precipitate lithium ably the proportions will in general be at‘least the theo hydroxide. If the lithium phosphate starting material retical molar ratio shown in the first equation above, is. a mixed alkali metal phosphate, the digestion liquor 223:3, and desirably the alumina and’ lime will exceed will be a caustic solution containing thehydroxides of the minimum theoretical requirements, to produce pro lithium and the other alkali metal forming the cations of portions up to 214:6 or more. In the subsequent diges 30 the original phosphate. The lithium hydroxide may then tion step, the ratio of lithium aluminate in thecalcina be separated from the admixture by conventional pro tion product to the lime present, either as a component cedures; for example, by evaporating the digestion liquor of the calcination product or as a separately added re to concentrate it, whereupon lithium hydroxide is pre actant, may‘range from proportions of 3:2 to 3:6; ad cipitated out by virtue of its low solubility. vantageously, su?icient lime will be present to supply 35 The residue from the digestion, containing calcium at least the theoretically required ratio, 3:3. phosphate and calcium aluminate, is a valuable source of In preparing the calcination mixture, the lithium phos minerals of utility in the glass and ceramics industries phate is mixed with‘ the sources of alumina and lime in and as a fertilizer. If desired, the digestion residue may proportions to supply the desired molar ratio of re be treated by conventional methods for the recovery of actants. When a surce of alumina such as aluminum 40 aluminum and phosphate values, or alternatively, the hydroxide is utilized, this will obviously require 6 moles residue may be dried and ground for use in applications of ‘the aluminum hydroxide for each 2 moles of phos requiring the calcium compounds contained therein. phate, to allow for the production of 3 moles of alumina The invention is further illustrated but not limited'by per mole of lithium phosphate on heating; and similarly, the following examples: ’ the amount of, for example, limestone used will be ad 45 Example I. justed in accordance with the quantity of lime supplied thereby. Su?icient lime should also be employed to This example illustrates the low yields oflithium hy satisfy additional reactive materials associated with the droxide obtained when a lithium phosphate is calcined reactants. For example, when bauxite is used. as the ' and digested with lime in the absence of alumina. , source of alumina, each mole of SiOz associated'there 50 In separate, parallel test procedures, mixtures of lithium with consumes two moles of CaO. ' phosphate with‘ lime (21/2 times theory for the equation To effect the ?rst step of the present process, the re 6Li3PO4+4CaO-—>2Ca2(PO4)3+9Li2O) were calcined for actants are mixed together and calcined. Preferably, the one hour at 1800° F; and at 2100° F., respectively. ingredients are utilized in a ?nely-divided condition. If Digestion of‘ these calcined products for 16 hours. in desired, the lithium phosphate, source of aluminavand 55 water at 95° C. gave yields of less than 10% of the lithia source of lime may be mixed before grinding and pul asv lithium hydroxide in each case. ‘ ' . v'erized together, which results in an intimate admixture Example 2 of the ingredients. The calcination of the mixture may be carried out in any of the well-known types of kilns or This example illustrates the superior results obtained on furnaces. The degree of heat and length of time re 60 treating a mixture of lithium phosphate with lime and quired will depend on the ?neness of the grind, the size a source of alumina in accordance withthe process of of the charge, the type of furnace used and other factors. this invention. ' i The temperature used should be at least high enough to To 20' partsvby weight of a previously prepared mix allow formation of alumina and lime fromthe respective ture of 21 parts by weight of trilithium phosphate with sources thereof and high enough so that reaction of the 43 parts by weight of aluminum hydroxide was added components of the mixture occurs. Generally tempera ‘60 parts by weight of calcium carbonate, andthe re tures in the range of about 1600 to 2500f’ F. are operable sulting mixture was calcined-for 2 hours at 22000 F. and temperatures between about 1800" F. and about The calcination product was ?nely ground and then di 2300° F. are preferable. Reaction may be complete in ~ gested in vWaterat 95° C. for 4 hours. Assay of the times as short as about one half-hour or less, or it may 70 liquor fromthe digestion showed that 98% of the lithia require several hours, depending on the size of the furnace ‘had beenrecovered as lithium hydroxide in solution. charge . and other considerations. The calcined mass is then digested with water .in the Example 3 presence of lime. Preferably the product obtained from This example illustrates the process of the invention the, calcination step is ground prior to digestion in order 75 utilizing an alumina ore in the calcination. aesgros 5 6 A mixture of trilithium phosphate with a commercial 4. The process of claim 3, wherein the said lithium grade of bauxite (10% excess of theory) and commercial phosphate is a phosphate, the cations of which are low lime (1.66 times theory) was calcined at 2200” F. for molecular weight alkali metals selected from the group one hour. On digestion of the ground product in. water consisting of lithium and sodium. at 95° C. for 4 hours, 64% of the lithia was recovered; ' 5. The process of claim 4 wherein the said lithium a 94.8% yield of the lithia was obtained by a 16 hour phosphate is Li3PO4. digestion, as determined by assay of the digestion residue. 6. The process of claim 4, wherein the said lithium Example 4 phosphate is~a mixed alkali metal phosphate. 7. The process of claim 6, wherein the said lithium This example illustrates the process of the invention .as 10 phosphate is a dilithium sodium phosphate. applied to a mixed alkali metal phosphate of lithium. 8. The process for the recovery of lithium values from The dilithium sodium phosphate employed in this ex an alkali metal phosphate wherein at least one of the ample, analyzing for 21.4% LiZO, 23.6% NazO, and cations of said phosphate is lithium, of the formula 53.2% P205, was identi?ed as “Trona Scale.” To 13.2 LiMNPO, where each of M and N is an alkali metal, parts by weight of this dilithium sodium phosphate were 15 which comprises calcining a mixture of said alkali metal added 30 parts by weight of bauxite (60.0% A1203, phosphate with added alumina and lime in molar propor 14.5% SiO2) and 72 parts by weight of limestone (98% tions respectively within the range of from about 1:1:2 CaCO3). The mixture was calcined for one hour at ' up to about 122:6; digesting the resulting calcination 2100° F., and the calcined product was ground and product with water, said digestion being carried out in digested in 6 parts by weight of water per weight of cal 20 the presence of lime; and recovering lithium hydroxide , cined product for 16 hours at 95° C. It was found that from the digestion liquor. 85% of the lithia present in the original phosphate salt 9. The method of claim 8 wherein the resulting prod had been recovered in the digestion liquor as lithium uct of calcination is digested with hot water, at a tem hydroxide. ' , perature of from about 60° C. to about 115° C., until Similar results are obtained when the process is car 25 substantially all the lithia contained therein is recovered ried out in the same fashion, but the mixture of phosphate, as lithium hydroxide in aqueous solution. alumina and lime sources is calcined at 2200° F. 10. The process of claim 8 wherein the lithium phos By treatment of LiKNaPO, in accordance with the phate is heated with bauxite as a source of alumina. present process, lithium hydroxide is similarly recovered. 11. The process of claim 8 wherein the said phosphate it is obvious that in recovering lithium hydroxide by 30 is heated with limestone as a source of lime. the present process, it is possible to convert phosphates 12. The process for the recovery of lithium values from of lithium economically to a more readily saleable com trilithium phosphate consisting of the steps of intimately pound of lithium, and that the phosphates may be equally mixing comminuted trilithium phosphate with a calcium well utilized whether they contain only lithium or repre containing material that yields calcium oxide at least in sent a mixed phosphate wherein. a plurality of alkali 35 part on heating and an aluminum-containing material that metal cations, including lithium, are present. Further yields alumina at least in part on heating, in proportion to more, it is evident that the agents used in the process produce a molar ratioof Li3PO,:CaO:Al2O3 of at least are readily obtainable in any desired quantity at low about 222:2; heating said mixture at from 1800 to 2300° cost, and the use of expensive chemicals in any step of F. for at least about one-half hour; comminuting the the process is avoided. It is further obvious that a. 40 resulting product of calcination; digesting said product process has been devised for the recovery of lithium of calcination with hot water at a temperature of from hydroxide from phosphates thereof in which a residue about 60° C. to about 115° C. in the presence of lime in the form of a valuable byproduct is obtained, and until said product is substantially free of alkali metal thus the entire cost of the recovery of lithium hydroxide values; and separating the digestion liquor from the in is not borne exclusively by the latter. 45 soluble residue. While the invention has been described with particular 13. The process for the recovery of lithium values from reference to various preferred embodiments thereof, it dilithium sodium phosphate comprising the steps of inti will be appreciated that modi?cations and variations can mately mixing comminuted dilithium sodium phosphate be made within the scope of the invention. with a calcium-containing material that yields calcium What is claimed is: 50 oxide at least in part on heatingand aluminum-containing l. The process for the recovery of lithium values from material that yields alumina at least in part on heating an alkali metal phosphate which comprises calcining a in proportion to produce a molar ratio of lithium phosphate of the formula LiMNPO4 where each of M and N is an alkali metal with added alumina and lime in a molar ratio of at least 2:2:2 and’ then digesting 55 of at least 222:2; heating said mixture at from 1800 to the resulting calcination product with water in the pres 2300° F. for at leastVone-half hour; comminuting the ence of lime, thereby forming an aqueous solution of resulting product of calcination; digesting said product lithium hydroxide as the digestion liquor. of calcination with hot water at a temperature of from 2. The process for the recovery of lithium values from about 60° C. to about 115° C. in the presence of lime an alkali metal phosphate wherein at least one cation of 60 until said product is substantially free of alkali metal the said phosphate is lithium, of the formula LiMNPO4 values; and separating the digestion liquor from the in where each of M and N is an alkali metal, which com soluble residue. prises heating said alkali metal phosphate with added alumina and lime in a molar ratio of at least 2:2:2 at References Cited in the ?le of this patent 1600 to 2500° F., digesting the resulting calcination product with water in the presence of lime, and recover UNITED STATES PATENTS ing lithium hydroxide from the digestion liquor. 2,424,512 Stautfer ______.__ July 22, 1947 3. The process of claim 2 wherein said heating is car 2,548,037 Minnick et al. ______.. Apr. 10, 1951 ried out at from about 1800" to about 2300° F. 2,776,201 Mazza ...... Jan. 1, 1957