GB2190668A

GB2190668A - Process for removing boron from lithium carbonate

Info

Publication number: GB2190668A
Application number: GB08711842A
Authority: GB
Inventors: Daniel Putout; Gabriel Sarazin
Original assignee: Metaux Speciaux SA
Current assignee: Metaux Speciaux SA
Priority date: 1986-05-22
Filing date: 1987-05-19
Publication date: 1987-11-25
Also published as: FR2599019B1; CA1304564C; FR2599019A1; DE3716557C2; GB2190668B; GB8711842D0; DE3716557A1; AT387560B; ATA128387A

Description

GB 2 190 668 A 1

SPECIFICATION them at around 1 00'C.

Analysis of the Li2C03 crystals collected shows a Processfor removing boron from lithium carbonate boron content markedly lowerthan its initial content.

The invention will be better appreciated by re The present invention concerns the removal of 70 ferring to the single Figure, which shows in solid line boron in the purification of lithium carbonate. a diagrammatic view of the steps of the process ac The attraction of lithium is known, in particular in cording tothe invention. ReactorA is supplied atS, the aeronautical industrywhere, alloyed with alumi- with lithium carbonate to be purified, togetherwith nium, it makes it possibleto produce lightersheets water and carbon dioxide gas. Dissolution of the salt orsolid parts which have certain enhanced mechani- 75 takes place in A, from which a suspension L, issues.

cal characteristics. This is filtered at Bto give a solution L2 and a residue In most cases, lithium is produced electrolytically S2. The solution L2 is passed into the crystallizerC from a bath of molten salts containing LiCl and KCl, where. underthe effect of heat, it desorbs carbon and it is know that the lithium salt subjected to that dioxide gas and forms a suspension S3, which is sep process must contain very little boron, which is con- 80 arated byfiltration D into a mass S4 of wet crystals sidered as a poison of the electrolysis operation. and mother liquors L3 charged with boron. The crys Most of the processes fortreating lithium ores tals are dried in an oven E to give a purified lithium generally result in the production of a lithium car- carbonate S5. The carbon dioxide desorbed in C is bonate Li2C03 which, depending on the sources, con- recycled to Awith an optional make-up of fresh C02.

tains from 10 to 2500 ppm of boron with respectto 85 The invention can be illustrated by means of the lithium. following example.

As moreoverthe production of LiC] from Li2C03, which consists of simple substitution of the anion Example 1 C03---bytheanionCl-does notin anywayalterthe 80 g of Li2C03 containing 1060 ppm of boron with boron content, it is therefore necessary, in orderto 90 respectto the lithium was dissolved in 1000 g of correctly electrolysethe UCI, to remove the boron, if water at WC, into which carbon dioxide gas was notfrom the chloride at leastfrom the initial car- bubbled. Filtration was effected to remove the ex bonate. cess of lithium carbonate which, after drying, repre In accordance with the present invention, boron is sented a residue of 19. 7 g.

at least partially removed from lithium carbonate by 95 The solution obtained contained 11.1 g of Li per dissolving the carbonate in water into which carbon litre, whereas tests carried outwithout C02 gave, at dioxide gas is bubbled at a temperature lowerthan the same temperature, a maximum concentration of or equal to ambient and then, after filtration, heating 2.54 g of Li per litre. Those figures showthe influence the solution thus obtained at a temperature lower of the C02 on the dissolution capacity of the car- than its boiling temperature, separating hotthe re- 100 bonate.

sulting crystals of purified carbonate, and drying Thatsolution was heated at WC and gave a sus them at about 1 OWC. pension of crystals, which wasfiltered. That resulted In a practical manner of carrying outthe inven- in the collection of 48. 37 g of Li2C03 crystals contain tion,Hthium carbonate Li2C03 is dissolved in water at ing 16 ppm of boron with respectto the lithium con ambienttemperature or below, preferably at 1 Oto 105 tent while the mother liquors contained in the dis WC. Carbon dioxide gas is bubbled into that water solved state 11.96 g of Li2C03 containing 5000 ppm of in such an amount as to practically attain the limit of boron with respectto the lithium content.

solubilityto produce a solution that is markedly By reference to the degree of reduction in the more concentrated in respect of lithium than onethat boron content, viz. 98.5%, and the low proportion of would resuitfrom the dissolutoin of carbonate in 110 that element in the carbonate obtained, it is possible hotter purewater. The operation can be carried out tojudgethe effectiveness of the purification process in anytype of reactor provided with a gas dispersion of the invention.

arrangement permitting of saturation of the liquid Those results can be improved by operating con that it containswith C02. tinuously in thefollowing manner:

Then, afterfiltration to separatethe undissolved 115 In the reactor A containing water maintained at be- carbonate,the solution is raised to a temperature of tween 10 and WC and into which carbon dioxide gas lowerthan its boiling point by heating in a crys- is bubbled, impure lithium carbonate is dissolved tallizer, whereupon the C02 is desorbed from the sol- continuously and in an amount such that it cor ution and a suspension of crystals of Li2C03 is responds to that of the pure carbonate produced.

formed in the crystallizer. The heating operation is 120 The suspension obtained isfiltered in B where a re preferably carried out at a temperature of 60to WC sidue S2 is separated, which is recycled to Aforcom so asto precipitate a maximum quantity of crystals pletely dissolving the incoming carbonate S,. Afrac withoutcausing excessive evaporation of the sol- tion OfS2 can be periodically purged byway of P'.

ution. It is advantageous to recoverthe C02formed Thefiltrate L2 issuing from B isfed continuouslyand for re-use for dissolution of the initial carbonate. The 125 at a given flow rate into the crystallizer C, which is suspension formed in the crystallizer isthen im- maintained at between 60 and WC and where a sus mediately separated in the hot condition into its pension S3 of crystals isformed, while the desorbed components, viz. crystals and mother liquors, by C02 is recycled to the dissolution step aftercooling, means of a suitable filtration device, and the residual separation of the condensed water and recompres moisture is removed from the crystals by drying 130 sion. That suspension isfiltered in Dto give purified 2 GB 2 190 668 A 2 crystals S4,which are continuously extracted from carbonate in water into which carbon dioxide gas is the installation and dried to the state of purified car- bubbled at a temperature lowerthan or equal to bonate S5 and a solution L3 impoverished in respect ambient and then, after filtration, heating the sol of lithium but enriched in respect of boron, which is ution thus obtained at a temperature lowerthan its recycled to A after cooling. The whole of L3 is re- 70 boiling temperature, separating hotthe resulting cycled until a given boron content has been attained. crystals of purified carbonate, and drying them at Atthat moment, a fraction of L3 is discharged from about 1 OWC.

Claims

the circu it continuously or discontinuously by way of
2. A process as

claimed in Claim 1, carried out purge P, and is compensated for by a make-up continuously.

amount of water atA so asto maintain the boron 75
3. A process as claimed in Claim 2, comprising concentration in the recycled liquor lower than the dissolving lithium carbonate S, containing boron, limit content, which has been fixed and which is pre- continuously and in an amount such that it cor ferably about 2 g/L A make-up of water at A is also respondsto the amount to be produced, in water necessaryto compensate forthe losses of water re- maintained at 10 to WC and into which carbon sulting from entrainment by the desorbed C02 and 80 dioxide gas is bubbled; filtering the suspension ob the moisture content of the crystals passed tothe tained and recycling the residue S2tO the dissolution drying operation. step while the filtrate L2feeds at a given flow rate a The supplementary circuits required to causethe crystallizer maintained at 60to WC and in which C02 discontinuous installation tofunction in a con- is given off,which is recycled to the dissolution step, tinuous mode are shown in broken lines in the 85 and a suspension S3 of crystals is produced; filtering Figure. the suspension S3 and obtaining crystals S40f Thefollowing example is an illustration of that lithium carbonate purified in respect of boron while continuous process. the boron-enriched solution L3 is recycled with the residue S2 after cooling until the boron concentration Example 2 90 reaches a value of close to 2 g/], at which moment a Lithium carbonate containing 1060 ppm of boron fraction of L3 is purged and replaced by an equivalent with respectto the lithium was treated in an installa- quantity of water, and drying the purified carbonate tion comprising a dissolution reactorwith a useful crystals atabout 1000C.

capacity of 2.5 litres, maintained at a temperature of
4. A process as claimed in Claim 1 substantially 120C; a filter for separation of the u ndissolved im- 95 as herein described in Example 1.

pure carbonate; a crystallizer with a useful capacity
5. A process as claimed in Claim 2 substantially of 0.95 litre, heated at WC; a filter for separation of as herein described in Example 2.

the purified crystals; and an oven permitting of dry ing of the crystals at 1 OOOC. The assembly of those devices was equipped and interconnected by a system of conduits similarto those shown in Figure. Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd, 10187, D8991685.

The dissolution reactorwas fed at a rate of 3.5 g/h Published by The Patent Office, 25 Southampton Buildings, London, WC2A I AY, of carbonate, that is to say 0.65 g/h of lithium, and a from which copies maybe obtained.

circulation of the materials involved was produced such thatthe flow rate of liquid passing into the crystallizerwas about 0. 138 Wh, the flow rate of liquor recycled atAwas 0.116 Ilh, the make-up amount of water atAwas 0.021 11h and the production of purified carbonatewas 3.49 glh.

After99 hours of operation, the solution passing into the crystallizer contained 7.21 g/1 of lithium and 4160 ppm of boron with respectto the lithium.

The purified lithium carbonate collected then contained only 0.2 ppm of boron with respectto the lithium and the solution recycled to A had a lithium content of 2.9 g/] with 11470 ppm of boron with respectto the lithium.

The degree of reduction in the boron contentwas therefore greaterthan 99. 9%, showing the improve- ment made by going from a discontinuous process to a continuous process.

That process finds application in the production of Li2CO3for obtaining, particularly by electrolysis, lithium intended more particularly for alu miniu m alloys used in the aeronautical industry.

CLAIMS 1. A process for at least partially removing boron from lithium carbonate comprising dissolving the