Note: Descriptions are shown in the official language in which they were submitted.
~7~
-- 1 --
Q~ INV~NTI~
This invention relates to a method for the recovery of lithium
from so1utions and, more particularly, to a method for the
recovery of lithium from lithium containing brines and solutions
5 using electrodialysis.
In the recovery of lithium from ores, ore may be baked with
sulfuric acid, the product leached with water, resulting lithium
sulfate solution treated with lime and soda ash to remove calcium
and magnesium, and lithium precipitated as carbonate. Other ore-
treating methods include the o-called alkaline methods and ion-
exchange methods which yield solutions of lithium as hydroxide,
chloride or sulfate. These methods also include the removal of
; calcium and magnesium by treatment with lime and soda ash.
In the recovery of lithium from natural, predominantly chloride,
15 brines, which vary widely in composition, an economical recovery
; depends not only on the lithium content but also on the
concentrations of in~erfering ions, especially calcium and
magnesium. Magnesium is particularly troublesome because its
chemical behaviour in solution is very similar to that of
~; 20 lithium. If the magnesium content is low, removal by
precipitation with lime is feasible. Evaporation and treatment
with lime and oda ash, is followed by precipitation of lithium
carbonate. In the case of a high magnesium content, removal with
lime is not feasible and various ion exchange and liquid-liquid
ex~raction methods have been proposed. Thus, it i~ obvious that,
although conventional processing of ores and brines makes it
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-- 2 --
possible to eliminate major portions of interfering ions, the
separation of lithium from magnesium remain5 a serious problem.
Lithium brines have also been subjected to electrolysis or to
membrane electrolysis, but usually only after the calcium and
S magnesium contents have been reduced to relatively low values.
Therefore, el~ctrolysis and membrane eleetrolysis of lithium salt
solutions, usually with the object of producing a lithium
compound, not only require the additional step of removing calcium
and magnesium, but have the additional disadvantage of the
evolution of copious amounts of gases such as hydrogen and
chlorine.
It is suggested that the use of electrodialysis alone or in
combination with cation exchange may overcome these difficulties
to some extent and can accomplish a separation of lithium from
15 multivalent cations such as iron, aluminum, calcium and
magnesium. More specifically, in ~.S. Patent 3063924, it is
stated that the removal of univalent ions and multivalent anions
from aqueous solutions is easily accomplished, but the presence
of multivalent cation~ such as calcium and magnesium causes
di~ficulties due to the formation of deposits on membranes.
Hence, multivalent cations are first removed by means of a cation
exchanger whereupon calcium and magnesium deposit after which the
: liquid is passed throu~h an electrodialyzing apparatus to remove
~a portion of at least one monovalent ion and to form a
25 concentrated salt solution. This method still requires the prior
,'
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~729~3~
-- 3
removal of calcium and magne6ium in a separate operation.
G.E. Raplan et al have reported (Chemical Abstracts, volume 60,
6507a) that good separation~ of lithium ions from multivalent
ions, such as ferric, aluminum, magnesium and calcium ions, can
be obtained at ~igh pH in a three-compartment electrodialysis
cell using unipolar and bipolar ion-exchange membranes, a nickel
anode and a lead-antimony alloy cathode. The presented data
show that only relatively dilute solutions have been u edl It is
stated that at hi~h pH hydroxides of the multivalent cation~
lo precipitate, and that at low pH the selectivity toward these
cations is considerably lowered.
~UMMARY QE ~E~ INvENTIoN
We have now found that lithium in solutions can be concentrated
to a high concentration and that a very effective separation of
lithium from brines comprising lithium and high concentrations of
multivalent ions, especially magnesium, can be obtained with high
selectivity by subjecting such solutions and brines to
electrodialy is at low or neutral p~ using monopolar cationic and
anionic permselective membranes.
The cationic membranes that are useful are those that are
permselective for monovalent cations, and the anionic membranes
~: are chosen dependent on the form in which lithium is to be
; recovered from the concentrate and can be permselective for
~-. monovalent or mono and multivalent anions. By carefully
- 25 controlling the operating conditions, such as current densities,
ac1d~ties and flow rate~ a concentrated ~olution of lithium with
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-- 4
a low magne~ium to lithium weight ratio can be recovered. Feed
~olution~ containing as little a~ 30 mg lithium per litre of
brine or solution and a magnesium to lithium weight ratio as high
as ~ixty to one can be processed.
When treating chloride-containin~ lithium brine~, the evolution
of chlorine can be ~uppressed by the choice of an appropriate
rinse ~olution.
A hiyh recovery of lithium and a satisfactory rejection of
multivalent cations~ especially magnesium, can be achieved by
carrying out ~he method in a single stage. With feed brines with
high ratios of magnesium to lithium, it ~ay be necessary to carry
out the method in more than one stage. In one embodiment, the
lithium content in the concentrate is raised partially in a first
stage while lowering the magnesium content. Subsequently, a
major portion of the magnesium in the concentrate is removed with
lime. The remaining solution is 5ubjected to a second stage
electrodialysis to concentrate the lithium content further.
Accordingly, there is provided a method for the recovery of
: litbium from brines containing monovalent cations including
; 20 lithium, multivalent cations including magnesium and monovalen~
and multivalent anions which method comprises the steps of
subjecting brine to electrodialysis; feeding brine to diluate
cells of an electrodialysis unit comprising a multiplicity of
:
alternating monopolar cationic permselective membranes and
monopolar anionic permselectiYe membranes, said membranes
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-- 5 --
defining alternating diluate and concentrate cells, an anode
compartment and a cathode compartment, an anode positioned in the
anode compartment and a cathode positioned in the cathode
compartment; applying an electrical cur-ent between the anode and
the cathode at a value such that the value or the corresponding
current density is in the range of about 10 to 500 A/m2;
maintaining the temperature in the electrodialysis in the range of
about 0 to 60C; maintaining the pH of the brine fed to the unit at
a value of less than about 7; passirlg flows of solutions through
the diluate and concentrate cells at a linear velocity sufficient
to maintain turbulent flow in said cells; removing a lithium-
depleted diluate from the diluate cells; withdrawing a lithium-
enriched concentrate from the concentrate cells, said concentrate
containing magnesium and lithium in a weight ratio of about 5:1 or
less; and recovering lithium from withdrawn concentrate.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Brines that can be treated according to the method of the
.
invention are natural brines such as occurring at Searle's Lake,
:; the Great Salt Lake and Clayton'Valley in the United States and
: 20 at various locations in Argentina, Bolivia and Chile. Other
~ brines that can be treated are oilfield brines, geothermal brines
:' ~
; ~and intermediate solutions and brines obtained in the processing
o~ ores and natural brines. Such brines contain varying amounts
~: : of monovalent cations includlng lithium, multivalent cations
~ ~25 including calcium, magnesium, iron, copper and zinc and anions
including sulfate, borate and chloride.
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Although the method of the invention i8 ~uitable ~or the recovery
of lithium from above-mentioned solution~ and brines1 the me~hod
is e~pecially u~eful in the treatment of brines which contain
high ratios of m~gnesium to lithium as well a~ r tho~e that
S eon~ain very low concentrations of lithium. Su~h lithium-high
magnesium ~rine~ are usually first treated by evaporation in
conventional evaporator~ or in solar ponds, whereby sub~tantial
amounts of ~alt~ other th~n the lithium and magnesium ~alts have
:
:~ been precipi ated and re~oved from the brine. Low-llthium
10~ bcines, such aB oilfield or geothermal brines, can also be
:
~: : treated advantageously by the method of the present invention.
:Thus, the lithi~um brines ~uitable a~ feed for the treatment by
the method:of the present invention are brines containing lithium
in a concentration as low as 30 mg/L. A practical upper limit
15~ for the ~lithium concentration in a feed brine i~ about 15 g/L,
:: which is~ he practically attainable concentration for most brines
n so:lar evaporation. Typicall~, feed brines contain about û.5
to;7 g/L lithium. Brines containing high concentrations of
mono:valent cations other than llthium may be first. at ~east
~:;20 pa~tially, evaporated to reduoe the concentrations of the
: monovalent cation~ other than lithium. During such partial
evaporation, major portions of sodium and po~assium salts
precipitate and can be removed.
: The lithium br~ne, whether or nct partially evaporated, is fed to
an electrodialysi~ unit. The electrodialysis unit or
~ ~,
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~;272~382
electrodialyzer comprise~ a multiplicity of vertically arranged,
alternating anion permselective exchange membrane~ and univalent
cation permÆelective 2xchanse membranes, a ca~hode compartment
and an anode compartment. The choice of membranes i5 very
5 important. Suitable cationic membranes must have a high
permselectivity (to be defined) for lithium, a low
permselectivity for multivalent cations, especially magnesium, a
high resi~tance against chemical deterioration, biological
fouling and thermal degradation, a low electrical resistance and
lO a high mechanical strength. We have found that ~uitable ca~ionic
permselective membranes are, for example, strongly acidic
membranes which have a membrane matrix of a styrene di-vinyl
benzene co-polymer on a polyvinyl chloride base and possess
sulphonic acid radicals ~R-SO3~) as active groups~ The active
15 groups comprise 3-4 milli-equivalents per gram of dry resin which
is satisfactory to provide the desired selectivity for univalent
ions. In particular, we have found that suitable cationic
permselective membraneæ are treated Selemion ~M CMR, Selemion TM
Experimental A (specially treated on one face) and Selemion TM
20 Experimental B (both surfaces specially treated). Suitable
anionic permselective membranes must have properties similar to
those for the cati~nic membranes. Suitable anionic permselective
membranes are, for example, strongly basic membranes with active
~roups derived from trimethylamine (for example, R-N(cH~)3.Cl)
2s at 3-4 milli-equivalents per gram of dry resin, and having a
matrix of a styrene di-vinyl benzene co-polymer on a polyvinyl
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chloride base. In particular, Selemion TM ASV, which is
permselective for univalen-t anions, or Selemion TM AMV which is
non-selective for univalent anions (i.e. permeable to mono and
multivalent anions) are suitable, the choice being dependent on
5 the particular embodment of the method (to be described). A
combination of the preferred membranes will, therefore, make it
possible to concentrate the monovalent cations, such as Li, Na
and K, and monovalent anions such ~s Cl or mono and multivalent
anions such as Cl, S04, and borates. The Selemion TM membranes,
lO which are manufactured by the Asahi Glass Company of Tokyo, Japan,
have the desired properties. It is understood that membranes
with similar properties produced by other manufactures such as
Neosepta TM CM-l and Neosepta TM CMS membranes that have sulphonic
acid active groups and are produced by the Tokuyama Soda Co. Ltd.
15 of Japan, are similarly suitable and that the use of combinations
of other membranes may yield the desired results.
The alternating cationic and anionic membranes form alternating
diluate cells and concentrate cells situated between the anode
compartment and the cathode compartment. The anode and cathode
20 are made of suitable materials. For example, the anode can be
made of platinum coated titanium and the cathode of stainless
steel. A source of direct current is connected to the electrodes.
The lithium brine is fed to the diluate cells, preferably after
removal of suspended solids. A lithium-depleted diluate is
2S withdrawn from the diluate cells. It is important to maintain
turbulent conditions in the concentrate and diluate cells. This
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can be achieved by passing solution through the cells at a
sufficient rate. At least a portion of the diluate may be
recycled and fed into the diluate cells mainly to en~ure
turbulent conditions. A lithium-enriched concentrate i~ withdrawn
5 from the concentrate cells as product~ If desired, at leas~ a
portion of the withdrawn concentrate may be circulated as feed to
~he concentrate cells to ensure turbulent conditions. Instead of
concentrate, a quantity of a dilute receiving solution of an
acidic substance may be fed to the concentrate cells, mainly for
reason of pH controln If desired, a quantity of acidic substance
solution may be fed to the concentrate cells alone or together
with and in addition to a circulated portion of the lithium
concentrate. Whether the feeding of a solution of an acidic
substance is necessary depends on the net water transfer in the
electrodialyzer.
During electrodialysls, water i~ transferred by osmosis from the
diluate to the concentrâte ~ides of the membranes and by electro
osmosis, which takes place in the direction of the transferring
ions. Feed brines with a high salt concentration (e~g. molar
concentration of about 20) have a high osmotic pressure and thus a
high rate of osmotic transfer can be expected. For such feeds, the
water transfer caused by osmosis is in the opposite direction to
that caused by electro-osmosis and, thus, tends to reduce the net
; water transfer. For dilute feed brines, both osmosis and electro-
osmosis are in the same direction to augment the net water
transfer which can be as high as 20 g mol/h or higher.
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With relatively concentrated feed brines it may be necessary to
feed a make-up solution of an acidic substance or sodium sulfate
to the concentrate cells, while for relatively dilute brinss the
feeding of an acidic make-up solution to the concentrate cells
may be unnecessary. Generally, the feeding of an acidic make-up
solution is necessary when the net-water transfer rate to ~he
conc~ntrate cells is less than the withdrawal rate of concentrate
from the concentrate cells.
The nature of the acidic substance in the make-up solution
depends on the form in which the lithium is to be recovered from
the concentrate. If recovery as lithium chloride is desired, the
acidic substance is a hydrochloric acid. If recovery as lithium
carbonate is desired, the solution may contain sodium sulfate,
sodium bisulfate or sulfuric acid, the use of sulfuric acid being
preferred.
The cathode and anode compartments are rinsed with a circulating
rinse solution. It was discovered that the anodic reaction
yields mostly oxygen when the chloride ion concentration in the
circulating anode rinse solution is kept at less than about 3
g/L. The rinse solution is preferably acidified to increase the
electrical conductivity. The rinse solution can be water or a
salt solution acidified to a pH of about 2. A pH of about 2 also
prevents the formation of basic precipitates. The use of sodium
sulfate solution with a concentration in the range of 0.1 to 1.0
molar, preferably 0.2 to 0.5 molar sodium sulfate, acidified with
,
~7~
sulfuric acid to a pH of about 2, is preferred. Thi~ rin~e
solution also cau~es evolution of oxygen~ thereby minimizing the
evolution of chlorine~ which, unle~s recovered, con~titutes an
undesirable byproduct. The same rin~e solution is circulated to
5 both the anode compartment and the cathode compartment.
When using monovalent cation permselective and anion
permselective membranes, the monovalent cations and anions in the
feed solution pass from the diluate cells to the concentrate
cells through the cationic and anionic membranes respectively,
10 leaving multivalent cations and anions in the diluate cells. The
use of monovalent permselective cationic and anionic membranes is
: desired when lithium is to be recovered from concentrate as
lithium chloride. When llthium is to be recovered as lithium
sulfate, the use of monovalent cation permselective membranes and
15 multiYalent anion permselective membranes is preferred~ The
gases evolved at the electrodes are carried from the cathode and
anode compartments in the rinse solution. Unlike membrane
electrolysis, the volume of ga~es evolved in electrodialysis is
small, especially also in relation to the volume of brine
. 20 treated.
:~ The permselectivity PMl/M2 of a membrane is defined as the ratio
between the specific transport rate of a first element Ml and
that of a ~econd element M~ through the membrane; the specific
transport rate being the quotient of the transfer rate of the
25 element over the concentration of that element. In the present
method, to effect separation of lithium from magnesium into a
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32
- 12 -
lithium-enriched concentrate, PLi/Mg should be greater than one,
and preferably much greater than one. Desirable values of PLi/Mg
are related to the weight ratio of Mg:Li and the number of electro
dialysis steps.
For brines containing both lithium and multivalent cations,
especially magnesium, the conventional processing of such brines
by lime addition to precipitate magnesium limits the Mg:Li weight
ratio from about 0.5:1 to as high as about 7:1. The ratio is
preferably limited to 5:1. Ratios of higher than about 7:1 can cause
formation of unmanageable precipitates. The Mg:Li weight ratio in
concentrates obtained as final product by electrodialysis and to be
subjected to further treatment should, therefore, also be restricted
to an upper value of about 5:1 or less to avoid difficulties in
subsequent processing. However, by establishing the number of
electrodialysis steps in relation to the PLi/Mg value, feed brines
with much higher Mg:Li ratios can be processed. For example, a brine
containing magnesium and lithium in a weight ratio of 20:1 can be
treated by electrodialysis using membranes having values for PLi/Mg
of > 4, 1.5, or 1.1 in 1, 4 and 15 steps of electrodialysis
preferably arranged in series, respectively, to give a final
concentrate product with a maximum Mg:Li weight ratio of about 5:1 or
less. In multi-stsp electrodialysis to improve the Mg:Li ratio, the
concentrate ~rom one step i5 used as feed in a subsequent step, the
last electrodialysis giving a final concentrate having the preferred
Mg:Li ratio of not ~reater than about 5:1.
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- 13 -
A~ stated above, the lithlum feed brine may contain a~ little as
30 mg/L l~thium and as much as 15 g/L lithium, typically 0.5 to 7
g/L. With lithium-high magnesium feed brines, the magnesium to
lithium weight ratio in the feed is in the range of about 1:1 to
60~ he ratio i~ usually higher than about lsl but should
preerably not exceed a~out 60:1, to give the preferred ratio in
the final concentrate of about 5:1 or le6s. ~he lithium in ~he
concentrate can be concentrated up to a value just below its
solubility, but the precipitation of lithium or any other salt
should, of course, be avoided. The recovery of lithium can be
increased by subjecting the diluate from the electrodialysis to
one or more additional electrodialysis steps~ Thus, lithium
recovery can be maximized by ~ubjecting brine to multiple-step
electrodialysis, feeding diluate from one step as feed to the
next electrodialysis step. If desired, an amount of magnesium
: can be removed in an intermediate precipitation, wherein solution
is treated with lime. Suitable concentrations of lithium in the
; f inal concentrate can be as high as about 40 ~/L, at, as stated,
a magnesium to 1ithium weight ratio of about S:l or less.
20 Lithium is recovered from the concentrate as its chloride,
carbonate or sulfate according to known methods.
The electr~dialyzer may be operated with brine temperatures in
the range of from just above the f reezing temperature to as high
as 60C. At the higher temperatures, the process is more
25 efficient but the life of the membranes is reduced. The process
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is preferably operated with brine temperatures in the range of
about 5 to 50C, the optimum temperature with optimum membrane
. life being about 30C.
The method is conducted at low or neutral apparen$ pH. We have
5 found that a pH above about 7 results in the undesirable
precipitation of magnesium when relatively high magnesium
concentrations are presentO The pH of the feed brine is,
therefore, maintained at a value of less than about 7 and
preferably in the range of about 2 to 6, a value of about 4 being
10 most preferred. Within the preferred range of about 2 to 6I the
method proceeds without any precipitation and feed solutions with
a Xg con~ent as high as 145 g/L can be processed.
The flow rate of ~olutions through the concentrate and diluate
cells should be such that the linear velocity is sufficient to
15 obtain turbulent flow. The value of the linear velocity is
dependent on equipment used. The flows of solutions through the
concentrate and diluate cells and the anode and cathode
; compartments should be substantially balanced in order to
- maintain a differential pressure across the membranes which is as
20 low s possible to maintain membrane integrity. The differential
pressure should not exceed about 100 kPa and is preferably in the
: range of from 0 to about 100 kPa.
The current applie~ to the electrodes i5 controlled such that the
membrane current density (applied current per membrane surface
25 area) is such that water splitting is minimized. The current is
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preferably equivalent to a current dens~ty ln the range of about
10 to SQ0 A/m2. Below about 1 A/m2, ~he ionic transfer rat~ ls
too low (the rates approach those o difusive transport). Above
about ~00 A/m2 there are not enough lithium ions to replenish the
5 lithium transferred from the diffusion layer at the membrane and,
as a result, water splittin~ oecurs to an undesirable extent
under severe concentration polarization conditions. The hi~her
values of current density are required for efficient use of the
equipment. Water splitting can be substantially obviated when
lo operating with current densities in the range of about 100 to
450 A/m2 under conditions of turbulence in the concentrate and
diluate cells. Current densitie~ in this range also provide
optimum efficiency and equipment size for the most economical
operation.
15 In one embodiment of the method of the invention, the lithium
content in the concentrate is raised only partially in a first
electrodialysis stepl while simultaneously lowering the magnesium
and other multivalent cations content to a relatively low val~e.
The concentrate f rom the f irst electrodialysis step is subjected
20 to a treatment with lime in an amount sufficient to precipitate
at least a major portion of the magnesium in the concentrate.
The excess calcium in the lime reacts with sulfate already
present an~ is r~moved a~ gypsum. The so-treated concentrate,
ater removal of precipitate, is subjected to one or more further
25 electrodialysis steps to raise the concentration of the lithium
in the concentrate, while simultaneously removing substantially
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-- 16 --
all ~emaining magnesium and oth*r r~ultivalent cation~3 with he
diluate. ~hls embGdiment can be carried out batch-wise, in
which case one electrodialy~s unit can be used, or eontinuou~ly
using two or more electrodialy~i~ uni~sO
S ~he permselective membrane~ used i n this embodiment are
pref erably univalent cationic permselective ~nembranes and
multi~lent anionlc perm . elective membrane~, the use of
multivalent anionic perm~elective membranes being advantageou~ in
~che removal of any exces5 calcium that may be present as a result
10 of the lime treatment. In continuous operationD the type s)f
membrane~ used is~ th~ second electrodialysis step can be the ~ame
~: ;as in batch operati9n when it is desired to recover lithium as
lts sul~ote. In case of the recovery of lithium as chloride the
~: membranes ~re monovalent permselective.
15 l'he: in~ention will now be illu~trated by means of the :Eollowing
,~ ~
~: non-limitative examples, All tests were carried out at ambien~
, ~
'emper atur es .
, ~
A number of tests was eonducted to determine the permselectivity
20 of cationic membranes. The electrodialy~is unit corlsisted o~ a
:
rectangular I,ucite TM cell partitioned into two compartment~ by
: he cationic ~embrane to be tested. The effective membrane area
!
wa~ 80cm~. The two compartments were filled with the brine feed
and water respectively~ and the two liquid~ were slowly agitated
; ~ 2s ino turbulence) to promote d~ffu~ive tran~fer (no current wa~
, ,,
~2~72~3~32
- 17 -
applied). The brine eed to the cell in te ts l, 2 and 3 assayed
7.S g/L Ll, 120 g/L Mg, 1~0 g/L Na and 1.3 g~L ~, the feed in
test 4 assayed 7,3 g/L Li and 104 g/L Mg and that in test 5
assayed 6.2 g/L Li and 33 g/L Mg. The trarlsfer of Li and Mg to
the water side was monitored by as~aying samples of the water-
containing compartment. The results are tabulated in Table Ir
Apparent
Test Time mg/~ mg/l Permselectivity
Mem~rane h~ur~ _Li_ _~9_ Pl~ gL
lSelemion TM CMR 5 66 73 1307
24 360 460 12.9
28 410 60~ lO.g
2 Selemion TM Exp'tal A 6 84 72 1707
2~ 340 270 lg.8
3 Selemion TM Exp'tal B 6 76 65 17.8
24 330 255 20~4
4 Selemion ~ CMv 5 86 300 4.0
24 430 ll~ 5.6
Ionac TM MC3470 5 lO 23 2.3
2~ 34 6~ 2.9
~ Supplied by Sybron Chemieal Division
It can be seen that the three membranes tested ~n tests l, 2 and
3 displayed an apparent perm electivity (PLi/Mg~ in the range of
ll to 20, while those tested in tests 4 and 5 had a PLiJM9 which
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- 18 -
were in6uffisient to expect ef$icient Li-Mg separation by
electrodialy~is. The diffusion transfer rate without the
application o~ current was very low and resulted in inefficient
use of equipment.
~ample 2
This test was carried out in order to increase the difusion
transfer rate with the same feed as in Test No. 1 of Example 1.
An electrodlalyzer with an effective membrane area of 1548 cm2
was used, with turbulent flow conditions in the cells. No
: 10 current was applied. The membranes were Selemion TM Experimental
A and Selemion TM ASV as the cation and anion permselective
membranes, respectively. The dil~ate and concentrate circulating
streams af~er 7 hours assayed as shown in Table II.
Table II
,' ~ ~ .
Diluate 3.1 72
Concentrate 2.8 16
As can be seen from the results, the Li ionic flux ~transfer rate
15 per area o~ membrane) was doubled compared to results obtained in
Example 1 with the improved cell hydrodynamics. However, the
'. increase in;the flux of the more concentrated Mg in the feed was
approximately tenfold. The P~i/M9of 4.1 obtained was
satisfactory to achieve a desirable Li-Mg separation in one stage
20 with a Mg.Li weight ratio of 16 in the feed brine.
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.E.xample 3
This te~t ~hows the effect of applied dc potential. An
electrodialy~is unit with two diluate and one concentrate
compar'cments, equipped with Selemion Tl!q CMR ~cationic) and
5 Selemior~ TM ASV (anionic) membrane8 having an effective membrane
atea of 80cm~, was used. Electrode~ were placed in separate
compartment~. The cathode was made of stainless steel and the
anode of platlnum. With the exception of the electrode
compartments the cell was static (i.e. no through-flow3, bu~ the
10 compartments were agitated. A circulating electrode rinse
solution was used and controlled at pH 2 by the addition of ~Cl~
A current of 0.5 A was passed for 120 minutes and the ionic flux
was monitored by sampling the content of the concentrate cell for
Li and Mg assay. Resul s are shown in Table III.
~',
Tal21 e I Il
Time oncentr ate
min . msl~ mg/L Mg ~ ~i/~SI
. 30 46 83 7.6
:~,
`~ : 120 250 350 10.1
,.
15 It can be seen that the application of the relatively small
: current of 62.5 A/m2 resulted in an approximately tenfold
increase i~ the ionic 1ux, compared to results in Example 1.
~`~ The application of current and the reQulting increased ionic flux
due to :electro transport enabled efficlent use of equipmentO
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- 20 -
A multi-cell electrodialyzer containing 11 pairs of 5elemion T~
CMR cationic and Selemion TM ASV anionic membrane~ was used. The
unit had intermembrane distances of 0.7~ mm and contained 10
diluate and 9 concentrate cells. The electrodes were positioned
in separate electrode compartments. The anode was made of
platinum-plated titanium and the cathode of stainless steel.
The initial feed to the diluate cells consisted o~ lOL brine
containing 7 g/L Li and 135 g/L M9O The diluate was recirculated
to the diluate cells. The concentrate stream was circulated to
the concentrate cells and consisted initially of 0.8L 0.05 M HCl~
The electrode rinse solution was circulated to the electrode
compartments and consisted initially of watPr adjusted with HCl
to p~ 2.
The circulation flow rates of the concentrate and diluate streams
were adjusted to give a linear velocity of S cmJsec which was
sufficient to ensure turbulent c~nditions in the cells. The
electrode rinse streams were adjusted ~o that the differential
pressure between the concentrate and the rinse streams was 3 kPaq
; 2a The electrodialyzer was operated at a curr nt density of 100 A/m2
for S hoursr .~he resulting concentrate and diluate streams were
analyzed for Li and ~9 and the Mg to Li weight ratios were
calculated. The results are given in Table IVq
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Diluate 5.6 132 23.6
Concentrate 16 40 2.5
PLi/~g was calculated to be 9.4. The re~ults show that a Mg:Li
ra~io in ~he concentrate product ~tream as low as 2.5 can be
: obtained.
.~
5 This example illustrates that dilute iEeed solutions can be
successfully treated. The equipment was the same as for Example
4. A feed brine ~olution containing 0.07 g/l Li and 1.35 9/1 Mg
; was fed at 18 L/hr, and the diluate stream was recycled at a rate
sufficient to maintain a linear velocity of ~ cm/sec in the
10 dilua~e cells. The concentrate stream was recirculated through
~: ~he concentrate cells at 5 cm~sec and drawn off at 260 mL/hr.
There was no need for fresh input because of water tran~fer from
'che diluate stream. The electrodialyzer was operated at a
current density of 205 A/m~. The pH in the electrode rinse
15 solution was controlled at a value of 2. The Li and ~9 content
.
of the var~ous streams were analyzed and the Mg to Li weight
: : ratio0 were calculated. The results are shown in Table v as follows:
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- 22 -
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Peed 0.07 1.35 19.3
Diluate 0.029 0.87 30
Concentrate 2.8 33 11.8
It can be seen that the electrodialysis was effectiYe in
concentratin~ lithium from a dilute feed brine.
Example ~:
This example illustrates Li recovery versu~ Li-Mg separation.
5 The equipment employed was as described for example 4. The
initial feed brine contained 6.8 g/L Li and 122 g/L Mg. 1500 mL
feed brine was circulated through the diluate cells at a linear
velocity of 5 cm/sec. The concentrate solution, initially ~00 ml
of 0.05 M HCl,was also circulated at the same linear velocity.
10 The electrodialyzer was operated at 200 A/m2 and at 300 A/m2.
Sample6 of the concentrate and diluate recirculating streams were
taken for ~i and Mg analyses at certain time intervals. The pH
of these two streams was not controlled, but the electrode rinse
stream was maintained at pH 2.
15 The results obtained at 200 A/m2 are shown in Table VI~
:
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- 23 -
~1* Vl
Li
Time Recovery* ~ LLD ~_5L~ n~n~e S~ mL
~miBL ~g~L.h~ Q/h-Mq n~ Li a/L hi ~ M~oLi
0 0 6.8 122 17.9 0 0
32 4.3 90 20~9 2.7 10.0 3.7
120 53 3.3 7~ 21.2 5.0 16.~ 3.2
180 64 2.5 6~ 24. 7.0 30.0 4.3
300 74 1.8 ~ 33.3 8.5 38.0 4.
360 79 1.5 5~ 37.3 8.7 40.~ 4.6
* Calculated on the feed solution
The results obtained at 300 A/m2 are shown in Table VII.
T~
LiDuluate Stream Concentrate Stream
Rec~veryMg.Li Mg:Li
~ %weight ratio wei~h~_ra~io
: 25 24 3
26 6
~: 80 ~4 12
It can be seen from the results tabulated in Tables VI and YII
that the Mg:Li weight ratio in the concentrate stream increased
~;~with the extent of Li removal from the original brine feed. The
~:S results in ~able VI show a satisfactorily low ratio of less than
5 coul~ be obtained at a current density of 200 AJm2 in a single
stage with a 79~ recovery of lithium. The results in Table VII,
however, show that at the higher current density of 300 A/m2, the
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- 24 -
Li recovery must be restricted to less than 50~ in order to
obtain the desired low Mg:Li weight ratlo in the concentrate. It
follows that, in order to obtain the desired low ratio as well as
a high recovery, the el ctrodialysis must be carried out in more
5 than one step.
Example 7
This example illustrates that diluate from a f irst stage
electrodialysis can be subjected to further electrodialysis to
give increased Li recovery with substantial separation f rom Mg.
lo The equipment employed was as described for Example 4. A first
; stage electrodialysis with a feed brine containing 7 g/L Li and
135 g/L Mg wa~ carried out at 290 A/m2. 45% of the lithium was
recovered in a concentrate with a Mg:Li weight ratio of 3.3:1 g/L
Li and 105 g~L Mg, circulating diluate stream of a second stage
15 electrodialysis carried ou~ at 290 A/m2~ The circulating
concentrate ~ream in this second s~age was initially 700 mL of
0.05 M HCl, but slowly gained volume as a result of the net water
transfer from the diluate, reaching a total volume of 950 mL
: after 5 hours. The Li and Mg contents of the diluate and
20 concentrate from the second stage electrodialysis were determined
: `
after 2.5 and 5 hours and analyses and calculated ~g:Li weight
ratios are bho~n in Table VIII.
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- 25 -
~able VIII
Time
Stream
Feed: 2.5 4.0 105 26.3
Diluate: 2c5 3.0 96 32
Concentrateo 2.5 7.0 40 5,7
Feed: 5.0 4.0 105 26.3
Diluate: 5.0 3.0 100 33.3
Concentrate: 5.0 9.5 54 5.7
In the second electrodialysis stage, 28% of the input Li was
recovered giving a concentrate with a Mg:Li weight ratio of 5.7.
Thus, by employing two electrodialysi~ stages a concentrate
stream with the desired Mg:Li weight ratio was produced in the
5 first stage and the lithium recovery was improved in the second
stage.
~amRle ~
This example ill~stra~es that by u~ing a non-chloride solution
for the anode rinse solution, chlorine evolution can be
10 minimized~ A 0.25 Molar Na2so~ solution, adjusted to p~ 2 by the
addition of ~ulphuric acid, was used as electrode rinse solution.
In the electrodialy~er operated at 6 A (345 A/m2), 2L of the
rinse solution was circulated through both the anode and cathode
compartments. The p~ wa~ maintained at 2 by sulphuric acid
15 addition. Chlorine evolution from the electrodialysis was
monitored by measuring chlorine levels in the air in the
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- 26 -
immediate vicinity of the unit. The result0 obta~ned are
compared to the case of u in~ dilute hydrochloric acid having a
p~ of 2 for electrode rinse ~olution. The re~ult~ are given in
Table IX.
Table IX
~hlorine l~vels in_th~iai~
TLmet min ~ s_~L~ ~Y~L Q.2~ Q~_
0.5 ppm no~ detectable
1.0 ppm not detectable
1.5 ppm trace
2 ppm 0.5 ppm
12~ ~ ppm 1 ppm
5 A~ can be seen from the result~ for an operation at 6 A, the 0.25
M Na2so4 electrode rinse solution gave much lower chlorine levels
in the air than a hydrochloric acid rinse solution. It was
further determined that replacement of 20 ml/min of the sulfate
solution with fresh solution allowed the chloride concentration
~; 10 in the rinse solution to be maintained at 3 g/L or less
~- throughout the operation.
Example g:
This example illustrates ~he deportment of other brine
constituents. The electrodialyzer and membranes employed were as
15 described in Example 4. The brine feed contained 7 g/L Li, 130
:~ : g/L ~g, 3 g~L Na, 2.6 g/L R, 6.3 g/L B and 42 g/L SO4 with
~ chloride as the predominant anion. 3 L of the brine feed was
,: circulated through the electrodialyzer at a linear velocity of 5
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cm/sec. The concentrate stream (0.9 Ll initially 0.05 M HCl) was
also circulated a~ the same rate. Electrode rinse solution,
initially containing 0.25 M Na2so~, was fed at 20 mL/min and
circulated at a sufficient rate to obtain approximately zero
5 differential pressure between the rinse and the other streams.
The electrodialyzer was operated at a c~rrent density of 260
A/m2. After 5 hours the various streams were analysed and the
results are given in Table X.
Table X
Diluate S~am Conçentra~ Stream
E~emen~Con~entFa~iQn in_~L~Qncentration in g/~
Li 203 15.0
Mg 93. 50.0
Na 0.39 6.5
K 0.2 4.0
5.8 1.9
~ S04 41.6 0.45
; It can be seen from the results that Na and R reported
10 substantially with Li in the concentrate stream. The value of
PLi/Mg was 12.1 compared with a value for PLi/Na f 0.4 and a
value of P Li/~ of 0.3. It follows that the apparent ease of
: tra~sport (i.e. to the concentrate stream) was in the order R >
Na > Li Mg. Only 0.3% of the S04 and less than 10% of the
15 boron in the feed brine r~ported to the concentrate stream.
Ex~mpl~ 10
This example illustrates that Li can be recovered in a highly
concentrated solution, substantially free of multivalent cations,
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particularly Mg and Ca, by multi-step electrodialy~is and removal
of Mg by treatment with lime. A brine containing 7 g/L Li and
135 g/L Mg was fed to a first electrodialysi~, using the unit as
used in Example 4, carried out at 200 A/m2. The concentrate,
5 which contained 9 g/L Li and 42 g/L Mg (Mq:Li weight ratio
4~67~y was treated with a ~0~ calcium hydroxide ~olution until
the plE3 reached a value of 11. Calcium remaining in solution was
precipitated ~y adding sulfuric acid. The precipi~ate of
magnesium hydro~ide and gypsum wa~ removed by filtration.
10 Calcium remaining in solution was precipitated with sulfuric acid
and precipitate removed. The filtrate, which contained 6.5 g/L
Li, 0.0009 g/L Mg and 0.04 g/L Ca,was adjusted with hydrochloric
acid to a p~ of 4. The adjusted iltrate was fed to the diluate
cells for a second electrodialysis~ The second electrodialysis
15 was carried out for 2 hours at 405 A/m2 and yielded a diluate
containing 0.05 g/L Li, 0.0007 g/L Mg and 0.03 g/L Ca, and a
concentrate containing 15.5 g/L Li, 0.0014 g/L Mg and 0.008 g/L
Ca. The Li recovery in the concentrate of the first
electrodialysis was 83% and oE the second 95% for an overall
20 recovery of 78.9% of the Li from the original brine. During each
electrodialysis step~ diluate and concentrate solutions were
circulated to the diluate and concentrate cells, respectively.
~ The electrode compartments were rinsed with a 0.25 M Na2so~
:~solution ~djusted to pH2. Flow rates were such that turbulent
25 conditions were maintained.
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