HANDLING AND USES OF THE ALKALI METALS

Recovery of Lithium from Complex Silicates JOHN W. COLTON

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: January 1, 1957 | doi: 10.1021/ba-1957-0019.ch001

Scientific Design C o . , N e w Y o r k , N . Y .

Lithium ores of major economic importance are spodumene, lepidolite, Trona concentrates, and amblygonite. Spodumene is the most abundant source, occurring in a complex matrix named pegmatite, which is inert to chemical treatment at room temperature. The industrially important processes of recovery of lithium from silicate minerals involve either high temperature ion substitution reactions or volatilization, and yield the sulfates, carbonates, hydroxides, or chlorides. These salts are readily interconvertible. Metallic lithium is made by electrolysis of lithium chloride.

Lithium, u n l i k e s o d i u m a n d potassium, does not generally occur as a simple salt or b r i n e . T h e m a j o r sources of l i t h i u m are c o m p l e x silicates, such as spodumene or lepidolite. S o d i u m , o n the c o n t r a r y , occurs as concentrated salt brines a n d i n v i r t u a l l y p u r e beds at m a n y locations throughout the w o r l d . If these brines d i d not exist, or i f there were no s i m p l e r source of s o d i u m than feldspar, then c o n c e i v a b l y soda ash m i g h t cost 80 cents p e r p o u n d , as l i t h i u m carbonate actually does today. E v e n t h o u g h l i t h i u m ores are moderately abundant, l i t h i u m salts are e x t r e m e l y difficult to produce. L i t h i u m minerals f a l l into t w o general classes: phosphates a n d c o m p l e x a l u m i n u m silicates. T h e l i t h i u m minerals listed i n T a b l e I are k n o w n to occur i n North America.

Table I. North American Lithium Sources Name T r o n a concentrate Amblygonite Spodumene Lepidolite

Empirical Formula L i . N a . PO* L i . A l . F . PO4 L12O . AI2O3 . 4 S i 0 3 L i F . K . 2AI2O3 . 7 S i 0

L i t h i a Content, W t . % L12O 20 - 21 8-9 4.5-7 3-5

2

2

2

2

T r o n a concentrate is not technically classified as a m i n e r a l , b u t is rather the b y - p r o d u c t of potassium a n d b o r a x r e c o v e r y f r o m Searles L a k e b r i n e i n C a l i fornia. T h e concentration of l i t h i u m i n this b r i n e is l o w ( a p p r o x i m a t e l y 0.03% L i C l ) , a n d it w o u l d be u n e c o n o m i c a l to process this b r i n e for l i t h i u m values alone. T h e n a m e T r o n a comes f r o m the m i x e d c r y s t a l NaHCOs . N a C 0 . 2 H 0 , w h i c h is one of the products of Searles L a k e . 2

3

2

A m b l y g o n i t e , w h i c h is a l i t h i u m a l u m i n u m fluorophosphate, does not occur i n large enough deposits to be w o r k e d independently. It is often f o u n d i n association w i t h spodumene ores. S p o d u m e n e , because of its abundance, is unquestionably the most i m p o r t a n t domestic source f o r l i t h i u m . It is a n e x t r e m e l y stable l i t h i u m a l u m i n u m silicate. 3

In HANDLING AND USES OF THE ALKALI METALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1957.

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A D V A N C E S IN CHEMISTRY SERIES

L e p i d o l i t e is a l i t h i u m potassium m i c a ; it also belongs to the class of a l u m i n u m silicates. V a r i o u s e m p i r i c a l formulas have been proposed for it, p r o b a b l y because its actual composition varies somewhat. I n fact, none of these minerals are p u r e crystals of definite composition. O f the lepidolite deposits w h i c h have been discovered i n the U n i t e d States so far, none w a r r a n t m i n i n g today. L e p i d o l i t e is processed i n the U n i t e d States, b u t the ore is i m p o r t e d f r o m southern A f r i c a . O t h e r important minerals are petalite a n d zinnwaldite, w h i c h f a l l into the class of a l u m i n u m silicates; a n d t r i p h y l i t e , w h i c h is a l i t h i u m ferrophosphate. These are f o u n d p r i n c i p a l l y i n E u r o p e a n d A f r i c a .


O f the two classes of l i t h i u m sources i n N o r t h A m e r i c a , the phosphates are less interesting. Phosphate sources are somewhat l i m i t e d i n scope. T h e ores present no r e a l p r o b l e m of recovery, as phosphates c a n be decomposed b y m i n e r a l

Figure 1. Three pegmatite samples containing spodumene Sample at bottom shows more t h a n two thirds spodumene. U p p e r samples are m o r e t y p i c a l , w i t h feldspar, quartz, a n d m i c a i n t e r m i x e d w i t h spodumene

acid. In some cases a l u m i n a or l i m e must be added to tie u p the phosphate a n d p r e v e n t reprecipitation of l i t h i u m phosphate (15, 18). H o w e v e r , silicates are a n other matter a n d this report is p r i m a r i l y concerned w i t h silicate processing. S p o d u m e n e is one of m a n y constituents of pegmatite. Pegmatite itself is a c o a r s e - g r a i n e d m i x t u r e of crystals of quartz, feldspar, spodumene, a n d m i c a . V a r y i n g proportions of the different crystals occur i n different pegmatites. A t y p i c a l pegmatite m i g h t contain 12 to 30% spodumene, 22 to 2 7 % quartz, 30 to 5 0 % feldspar, a n d 3 to 5% m i c a , w i t h smaller quantities of apatite, t o u r m a l i n e , a n d b e r y l , plus occasional traces of cassiterite, columbite, monazite, p y r i t e , p y r r h o t i t e , a n d r u t i l e . Pegmatites u s u a l l y exist i n the f o r m of dikes, w h i c h are v e r t i c a l slabs


5

COLTON—LITHIUM FROM COMPLEX SILICATES


of v a r y i n g size between adjacent masses of granite. often susceptible to surface strip m i n i n g .

These veins or dikes are

A n idea of the abundance of spodumene m a y be obtained b y the estimate that i n the N o r t h C a r o l i n a pegmatite belt alone m o r e t h a n 5,000,000 tons of p e g matite are available i n dikes of sufficient size to w a r r a n t m i n i n g (14, 16). T h i s is r o u g h l y equivalent to 1,000,000 tons of spodumene or 100,000,000 pounds of l i t h i a ( l i t h i u m oxide) equivalent. T h i s is m o r e t h a n 80 times the 1951 c o n s u m p t i o n of a l l l i t h i u m compounds. C o m m e r c i a l deposits also exist i n the B l a c k H i l l s r e g i o n of S o u t h D a k o t a , a n d have been discovered recently i n Quebec (10), M a n i t o b a , a n d O n t a r i o , C a n a d a . A s m a l l deposit has b e e n k n o w n for m a n y years i n N e w H a m p s h i r e . R e c e n t l y spodumene deposits of u n k n o w n m a g n i t u d e have been a n nounced i n A r i z o n a , N e w M e x i c o , a n d C o l o r a d o (1). T h e prospecting for l i t h i u m m i n e r a l s n o w i n progress m a y indicate that m o r e deposits w i l l be f o u n d i n the near future. A c t u a l l y , spodumene is available i n v i r t u a l l y u n l i m i t e d quantities. T h e first step i n the processing of l i t h i u m silicates is to extract the spodumene f r o m the pegmatite — i n other words, to concentrate the l i t h i u m values. W i t h one possible exception a l l producers concentrate the ore near the m i n e site i n order to save o n freight costs for s h i p p i n g the m i n e r a l to the processing k i l n . T h e r a w pegmatite contains o n l y 0.8 to 2.0% l i t h i a ; the spodumene contains 4.5 to 7.0%. T h r e e p r a c t i c a l processes for separating spodumene f r o m the other ingredients of pegmatite are h a n d sorting, flotation, a n d h e a v y m e d i a separation. H a n d sorting is still practiced at certain mines i n S o u t h D a k o t a , w h e r e the crystals of s p o d u mene are e x c e p t i o n a l l y large. O c c a s i o n a l l y single crystals of spodumene h a v e been f o u n d i n the E t t a M i n e as large as 4 feet i n diameter, w e i g h i n g as m u c h as 40 tons (12, 17). A t least t w o types of flotation have been attempted o n spodumene pegmatites. C o n v e n t i o n a l flotation, i n w h i c h the v a l u a b l e m i n e r a l is discharged i n the f r o t h a n d the worthless gangue is depressed, utilizes cationic soaps as the frother (20). M o r e recently a rather u n c o n v e n t i o n a l type of flotation, i n w h i c h most of the worthless components are floated off i n the froth, was developed (1), a n d appears to be m o r e successful.

Figure 2.

North American lithium sources


6



H e a v y m e d i a separation takes advantage of the difference i n specific g r a v i t y between spodumene a n d the other components of pegmatite. A l p h a spodumene, w h i c h is the native variety, has a density of a p p r o x i m a t e l y 3.15. F e l d s p a r has a density of about 2.6, quartz about 2.6, a n d m i c a 2.7 to 3.0. W h e n a water s l u r r y of finely d i v i d e d ferrosilicon is m a i n t a i n e d at the p r o p e r concentration it behaves i n m a n y respects l i k e a true l i q u i d . Its specific g r a v i t y c a n be m a i n t a i n e d at 2.9. In this m e d i u m spodumene sinks a n d the other components of pegmatite float. C o m m e r c i a l plants u t i l i z i n g h e a v y m e d i a separation are i n operation throughout the country, mostly for large v o l u m e commodities such as coal. H o w e v e r , a h e a v y m e d i u m has been used for spodumene separation, a n d it is reported to be used currently. T h e r e is a n active m a r k e t today i n spodumene concentrates. T h e quoted price is $11 to $12 p e r unit, w i t h a unit defined as 1 t o n of ore m u l t i p l i e d b y the p e r centage of l i t h i a ( l i t h i u m oxide) contained i n the ore. F o r example, a n ore of 5% l i t h i a content w o u l d be sold at $55 to $60 p e r ton. S t a r t i n g w i t h spodumene, there still is a l o n g w a y to go to m a k e simple ionized l i t h i u m chemicals. S p o d u m e n e is v i r t u a l l y i m m u n e to o r d i n a r y c h e m i c a l treatment. It is not dissolved b y m i n e r a l acid at r o o m temperature, nor b y caustic. A l l processes of r e c o v e r y of l i t h i u m values f r o m spodumene or lepidolite i n v o l v e h i g h temperature reactions. A t y p i c a l process w o u l d i n v o l v e two roasting k i l n s . In the first k i l n the spodumene is heated to 1100°C. for conversion to the softer beta phase. T h e beta crystal is then finely g r o u n d to between 100 to 200 mesh, i n p r e p a r a t i o n for the next step. A l p h a spodumene is h a r d a n d tends to fracture into splinters. T h i s p r o p e r t y makes it difficult to g r i n d to the r e q u i r e d fineness. T h e beta spodumene, after g r i n d i n g , is m i x e d w i t h another reagent w h i c h m a y be either l i m e or limestone, s u l f u r i c acid, potassium sulfate, or a n y of several more exotic reagents. T h e m i x t u r e is then calcined at h i g h temperatures, as s h o w n i n T a b l e II.

Table II. Calcining Temperatures for Recovery of Lithium from Complex Silicate Ores Lithium Mineral Spodumene Lepidolite Spodumene Spodumene Spodumene • L i t h i u m sublimed as chloride.

Other Reagent H2SO4 CaCOs (limestone) KHSO* C a C O s (limestone) CaCb a

Maximum Kiln Temperature, ° C . 250 - 300 850 900 1050 1100

C a l c i u m carbonate decomposes into c a l c i u m oxide a n d c a r b o n d i o x i d e at about 900 ° C . Most l i m e k i l n s operate w i t h a m a x i m u m temperature of 1300° to 1500°C. P o r t l a n d cement k i l n s operate at about 1450° to 1500°C. T h e h i g h temperature reaction frees the l i t h i u m f r o m the silicate b y a v a r i e t y of i o n substitution or i o n exchange. T h e c a l c i u m i o n , h y d r o g e n i o n , or potassium i o n replaces the l i t h i u m ion i n the silicate m a t r i x . These p y r o l y t i c substitutions are a l l accomplished i n the solid phase. H e n c e they r e q u i r e fine g r i n d i n g of feedstocks to give large surface areas a n d m i n i m u m time of diffusion to the interior of the particle. T h e nearest equivalent process of c o m m o n knowledge is p o r t l a n d cement manufacture. B y a m a z i n g coincidence, l i t h i u m k i l n s look just l i k e cement k i l n s . A t y p i c a l k i l n , s h o w n i n F i g u r e 3, is processing lepidolite, b u t the general principles of operation are the same as w i t h spodumene. C o m m e r c i a l plants operating today extract their soluble l i t h i u m salt, either h y d r o x i d e or sulfate, f r o m the residue b y water leaching. It is also possible to r e m o v e the l i t h i u m f r o m the k i l n b y s u b l i m i n g it i n the f o r m of l i t h i u m chloride. S o m e w h a t h i g h e r temperatures are r e q u i r e d , about 1100°C. T h e v a p o r pressure of l i t h i u m chloride is h i g h e r than that of any other a l k a l i m e t a l chloride, as s h o w n i n F i g u r e 4. T h e c h l o r i d e v o l a t i l i z a t i o n process is not yet p r a c t i c e d c o m m e r c i a l l y , a l t h o u g h i t has been successfully tested o n a large scale. S o m e trials apparently f a i l e d because of certain unforeseen m e c h a n i c a l problems. F o r example, p a r t i a l h y d r o l y s i s of the c a l c i u m chloride resulted i n the evolution of h y d r o g e n c h l o r i d e



COLTON—LITHIUM

FROM COMPLEX SILICATES

7

Courtesy A m e r i c a n L i t h i u m C h e m i c a l s F i g u r e 3.

Lithium r e c o v e r y k i l n

i n the k i l n gas. T h e h y d r o g e n chloride was v e r y corrosive to steel equipment. In addition, the l i t h i u m chloride fume, being of s u b m i c r o n diameter, was e x t r e m e l y difficult to recover. H o w e v e r , these problems a n d others have been overcome recently. A l l spodumene roasting reactions y i e l d a m a t e r i a l w h i c h has potential v a l u e as a n ingredient of p o r t l a n d cement; b u t none is so used at present. T h i s situation offers a n opportunity for r e d u c i n g cement k i l n operating expenses. T h e i n c r e m e n t a l profit is substantial. In the future, w i t h the anticipated h i g h l y competitive cement m a r k e t , the m a r g i n a l revenue f r o m a l i t h i u m operation c o u l d be c r i t i c a l i n cement profitability. T h e c h l o r i d e v o l a t i l i z a t i o n process is especially adaptable to cement production, since w i t h slight adjustments to k i l n feedstock a n d o p e r ating temperature the calcined residue is cement c l i n k e r without f u r t h e r t r e a t ment (7, 12). A l l processes of l i t h i u m r e c o v e r y y i e l d sulfates, h y d r o x i d e s , or chlorides i n a contaminated water solution. These salts c a n be r e a d i l y converted f r o m one f o r m to the other b y w a y of the carbonate. L i t h i u m , i n m a n y respects, is more l i k e a n a l k a l i n e earth t h a n a n a l k a l i m e t a l . Its carbonate, fluoride, a n d phosphate salts are r e l a t i v e l y insoluble i n water. Its h y d r o x i d e has a l i m i t e d affinity for water, as contrasted w i t h the v e r y hygroscopic nature of caustic soda.

Table III. Some Properties of Common Lithium Salts Salt

S o l u b i l i t y , G r a m s p e r 100 G r a m s Solvent Melting point, ° C .

LiCl L12CO3 L i O H . H2O L12SO4 . H2O LiF LisPO*

613 615 — 860 870 837

C o l d water, 20°C.

H o t water, 100°C.

84.0 1.33 22.4 24.0 0.27 0.031

127.5 0.72 30.7 22.2

A m y l Alcohol

9.0 6.5 — — — —

A n y solution of l i t h i u m sulfate, chloride, or other w a t e r - s o l u b l e salt c a n be converted to the carbonate b y the addition of soda ash solution. L i t h i u m c a r bonate precipitates a n d c a n be filtered off. L i t h i u m h y d r o x i d e i n solution c a n be converted to the carbonate b y b u b b l i n g c a r b o n dioxide gas t h r o u g h it. T h e c a r bonate is converted into sulfate or chloride b y treating w i t h the corresponding




8

Figure 4.

V a p o r pressure o f a l k a l i chlorides

acid. T h e h y d r o x i d e m a y be obtained b y reaction of carbonate w i t h l i m e s l u r r y . It is theoretically possible to calcine l i t h i u m carbonate to l i t h i u m oxide i n the same w a y that l i m e is p r o d u c e d f r o m c a l c i u m carbonate. H o w e v e r , o w i n g to the l o w m e l t i n g point of l i t h i u m carbonate ( 6 1 5 ° C . ) n o satisfactory c l i n k e r c a n b e p r o d u c e d . T h e carbonate fuses before it decomposes, a n d the resulting solid is a d e a d - b u r n e d , w a t e r - i n s o l u b l e glass of little v a l u e outside the ceramic field. L i t h i u m exhibits one m o r e p e c u l i a r c h e m i c a l p r o p e r t y w h i c h distinguishes it f r o m the other a l k a l i metals. M a n y of its salts are soluble i n organic solvents such as p y r i d i n e a n d a m y l alcohol. A crude c h l o r i d e solution containing l i t h i u m , sodium, a n d potassium ions m a y be extracted w i t h a n i m m i s c i b l e organic solvent to y i e l d l i t h i u m chloride free of other cations. T h i s p r o p e r t y is used i n l a b o r a t o r y analysis, a n d presents interesting possibilities f o r c o m m e r c i a l processes (8). T o obtain metallic l i t h i u m , l i t h i u m chloride is d r i e d , m i x e d w i t h potassium chloride to f o r m a l o w m e l t i n g eutectic, fused (ca. 4 5 0 ° C ) , a n d t h e n e l e c t r o l y z e d (18). T h e d r y i n g of l i t h i u m chloride involves h i g h temperatures because this salt is v e r y hygroscopic.

References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)

B a n k s , M . K . , M c D a n i e l , W . T . , Sales, P . N . , A m . Inst. M i n i n g M e t . E n g r s . T e c h P u b . 3488h; Mining Eng. 5, 181-16 (1953). C a m e r o n , A. E., J. Am. Chem. Soc. 77, 2731-33 (1955). Chem. Eng. News, 32, 1760-61 (1954). C h e m . Engr., 62, N o . 12, 113-14 (1955). Ibid., 63, N o . 1, 110 (1956). C o l t o n , H. S., U. S. Patent 2,021,987 (1935). C u n n i n g h a m , G. L., Ibid., 2,627,452 (1953). Ibid., 2,726,138 (1955). C u n n i n g h a m , J. B., G o r s k i , C . H., U. S. B u r . M i n e s Rept. Invest. 4321 (1948). D e r r y , D . R., E c o n . Geol., 45, 95-105 (1950). E i g o . D . P . , F r a n k l i n , J. W . , C l e a v e r , G. H., Eng. Mining J. 156, N o . 9, 75-89 (1955). F r a a s , Foster, R a l s t o n . O . C . , U. S. B u r . M i n e s , Rept. Invest. 3344 (1937). H a y e s , E. T., W i l l i a m s , F. P . , Sternberg, W . M., U. S. Patent 2,533,246 (1950). Hess, F. L., Εcon. Geol. 35, 942-66 (1940). K a l e n o w s k i , L. H., R u n k e , S. M., U. S. B u r . M i n e s Rept. Invest. 4863 (1952). K e s t l e r , T . L., Bull. 936-J., Strategic M i n e r a l s Investigations (1942). L a n d o l t , P . E., J. Electrochem. Soc. 102, 285c (1955). M o t o c k , G . T., U. S. B u r . M i n e s I n f o r m . C i r c . 7361 (1946). N i e l s e n , R. L., H e r r e , M. G., Ind. Eng. Chem. 43, 2636-46 (1951). N o r m a n , James, Gieseke, E. W., A m . Inst. M i n i n g M e t . E n g r s . , T e c h . P u b l . 1161 (1940). Rosett, Walter, B i c h o w s k y , F. R., U. S. Patent 2,020,854 (1935).


HANDLING AND USES OF THE ALKALI METALS

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