" 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.