898
Ind. Eng. Chem. Process Des. Dev. 1981, 20, 698-704
Literature Cited Berger, W.; Kreutz, K. B. Chem. Tech. (Le&&) 1974, 26, 694-5. Hermans, P. H.;Bredee, H. L. J. Soc.Chem. Ind. London 1936, 55, T 1-4. Kehet, E.; Lln, A.; Kaplen, A. Ind. Eng. Chem. Process Des. D e v . 1967, 6, 48-55. Rushton, A. Chem. €ng. (London) 1870, No. 237, CE 88-94.
Rushton, A.; Rushton, AI. Filtr. Sep. 1972, 9 , 274-8. Tiller, I. M. Chem. Eng. hog. 1977, 73, 65-75.
Received for review December 27, 1979 Revised manuscript received May 11,1981 Accepted June 2, 1981
Extraction of lithium and Magnesium Salts with a Mixed Ionic Extractant Rodrlgo A. Hernbnder' and Juan M. Martinez' Departamento de Tecnok$a &mica, Facuttad de Ci6ncias fisicas y Mstemiticas, UniversHad de Chile, Casilla 2777, Santiago, Chile
Lithium and magnesium salts extraction from aqueous solution is studied using an equimolar mixture of a primary amine and a carboxylic acid diluted in toluene. Effect of extractant concentration, temperature, and pH are determined. Single salt dlstribution curves and the determination of lithium selectivity in relation to other cations give evldence that the carboxylate affinity is in the order Mg2+> Li+ > Na+ > K+. In view of LiCl and LiN03 extraction data,it is shown that lithium is extracted as a dimer while the anions present a monomeric structure. Magnesium is confirmed to be extracted as a monomer, but sodium and potassium carboxyiates are trimers. This indicates that for the cations considered, pdymerlc structures occur whose number of units increases as the cation extraction diminishes, showing the extracted species search of greater stabili in the organic phase.
Introduction The possibility of extracting inorganic salts from brines resulting from seawater desalination planta, or the bitterns produced during the solar evaporation of seawater for d i u m chloride manufacture, has been a subject of considerable interest over the past two decades. One of the most important recoverable species from these occurring solutions or plant waste streams is magnesium chloride, and interesting work has been published in relation to the development of solvent extraction processes for the recovery of this salt from bitterns or saline solutions. In view of these results, it has been considered that solvent extraction techniques might be used to recover not only magnesium but also lithium that exist in natural brines in Northern Chile together with other alkaline and alkaline earth cations and chloride at a high concentration. The composition of a representative sample of the brines occurring at the enormously rich salt deposit called Salar de Atacama is indicated in Table I. The fact that magnesium is present at a relatively high concentration leads to the problem of separating this cation from lithium once sodium and very likely also potassium have been separated by crystallization at a former stage. One method which makes it possible to separate bivalent from monovalent cations has been developed by Grinstead et al. (1969). I t is a liquid-liquid extraction process proposed to recover magnesium chloride from seawater concentrates or natural brines. The active extractant, so-called mixed ionic extractant, is an organic salt which typically comprises a stoichiometric mixture of an amine and an organic acid. According to
* To whom all correspondence should be adGressed at Paulo Abib Engenharia S.A., Divide de Processes Quimicos, Rua Cap. Francisco Teixeira Nogueira, 154, CEP 05038, Si30 Paulo, S.P., Brasil. Compada Acero del Padfico, CAP, Huachipato, ConcepciBn, Chile. 0196-4305/81/1120-0698$01.25/0
Table I. Composition of a Representative Sample from Salar de Atacama (Northern Chile), Analyzed According to Standard Methods component concn, M compn, % w/w Li + 0.26 0.15 Na' 4.22 7.95 0.53 1.70 K' Mg2 0.45 0.885 0.011 0.036 CaZ+ 5.58 c116.2 0.17 S0,Z1.32 0.48 0.095 H3J303 +
Grinstead et al. (1969), the effectiveness of the amine component is in the order: quaternary > primary > secondary > tertiary; and of the acid: carboxylic > alkylphosphoric > arylsulfonic. Constituenta of inorganic salts in aqueous solution are extracted as separate species but in stoichiometric ratio. The extraction proceeds according to an equilibrium reaction. In the case of magnesium chloride extraction by an organic salt whose constituents are a primary amine and a carboxylic acid, the reaction may be represented as Mg2++ 2C1- 2RNH,+*R'COO- s (aq) (4 (0%) 2RNH3Cl + Mg(R'C0O)Z (1) (erg) (erg) It is made evident through reaction 1that the forward extraction will be enhanced for a large excess of chloride due to the common ion effect. Another advantage of mixed ionic extractants is the possibility of recovering the inorganic salt from the loaded organic phase by stripping with water, which makes the process somewhat simpler and cheaper. Moreover, since anionic and cationic organic components can be chosen independently, selectivity may be increased by means of a suitable choice. Grinstead et al. (1969) found that on the one hand inorganic cations are extracted in the order: Ca2+> Mg2+
+
@ 1981 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 4, 1981 600
> Na+ > K+, and on the other, anions are extracted in the These results suggested to us order: NO3- > C1- > SO-.: that lithium might be extracted preferentially over sodium but to a lesser extent than magnesium, and since nitrate ion is absent from the brines at stake (see Table I), magnesium chloride extraction should proceed prior to lithium chloride extraction. According to the results of Grinstead et al. (1969), promising combinations for magnesium were carboxylic acids with either primary or quaternary ammonium compounds. Actually, though it was known that quaternary amines promoted a higher extractability, in agreement also with the work of Hanson et al. (1975), it was considered that primary amines such as Primene JM-T offered promise through higher selectivity and lower loss of extractant due to solubility in water. In this work, the mixed ionic extractant used was Primene JM-T/naphthenic acid. Consideration has been given to the determination of equilibrium isotherms between the organic and aqueous phases for pure lithium and magnesium salts including chlorides, nitrates, and sulfates for the sake of comparison. Selectivity of lithium chloride in relation to other salts naturally occurring in Salar de Atacama brines has also been studied. The mechanism of extraction of lithium was also elucidated by appropriate treatment of our experimental data. Experimental Section Materials. The extractant used comprises a stoichiometric mixture of Primene JM-T and naphthenic acid E diluted in toluene. Primene JM-T (marketed by Rohm and Haas Chemical Co.) is a mixture of primary amines with a tert-alkyl chain in the C18-C22length range. The equivalent weight determined by acid titration was found to be 342. Naphthenic acid E is a mixture of naphthenic acids of petroleum origin containing cycloalkyl carboxylic acids, such as five-membered ring acids c-C6H9-(CH2),-COOH. The equivalent weight of this material, by titration with base, is about 250. It was purchased from Chevron Chemical Co. Calculated amounts of Primene JM-T and naphthenic acid E were mixed and then diluted in Analar grade toluene. No modifier was used. The extractant concentration was 1 M except when something different is specified. The following synthetic solutions were prepared from standard reagent grade chemicals: LiC1, LiN03, Li2S04, MgCl,, Mg(NO3I2,MgS04, NaCl and KC1. Procedure. Equal volumes of organic and aqueous solutions of given composition were shaken in a thermostat bath at the required temperature (30 "C, except when determining the effect of temperature) during 30 min; this time was considered to be long enough for the system to reach equilibrium, according to experiences performed during different mixture times. Both phases were then separated and centrifuged in order to obtain clear phases. Most chemical analyses were performed by atomic absorption spectrophotometry. Sodium and potassium aqueous samples were also analyzed by flame photometry. All organic samples were directly analyzed by atomic absorption spectrophotometry after due dilution in methyl isobutyl ketone. Results and Discussion Influence of the Nature of Cations and Anions on Single Salt Extraction. In order to compare the extractability of lithium with that of other cations, extraction isotherms for several chlorides have been determined. The
Table 11. Distribution of Various Salts between Water and Primene JM-TINaphthenic Acid 1 M in Toluene at 30 "C ( m = Electrolyte Molality, and 7 = Activity Coefficient) aq phase salt LiCl
NaCl
KCl
LiNO,
M 3.15 2.94 2.36 1.58 0.93 0.66 0.45 0.27 0.09 2.63 2.09 1.38 0.97 0.59 0.36 0.21 3.00 2.08 1.53 1.06 0.62 0.30 3.02 2.56 1.98 1.46 1.00 0.79 0.51
my
4.29 3.66 2.52 1.40 0.73 0.50 0.34 0.20 0.07 1.96 1.47 0.93 0.65 0.40 0.25 0.15 1.88 1.27 0.93 0.66 0.40 0.21 3.45 2.62 1.81 1.20 0.77 0.59 0.38
org phase, M
'
0.0823 0.0767 0.0543 0.0307 0.0150 0.0103 0.0058 0.0027 0.0008 0.0373 0.0250 0.0137 0.0077 0.00383 0.00194 0.00087 0.0085 0.0050 0.0030 0.0019 0.00079 0.00032 0.1040 0.0760 0.0550 0.0359 0.0239 0.0164 0.0092
distribution curves of lithium, sodium, potassium, and magnesium chlorides between water ant 1 M Primene JM-T/naphthenic acid in toluene at 30 "C are shown in Figure 1. (For alkaline salts experimental values are given in Table 11.) For magnesium chloride, our results check those of Grinstead et al. (1969). The lithium chloride extraction curve lies between those for magnesium and sodium chlorides, thus indicating that the order of extraction of these cations is the following: Mg2+> Li+ > Na+ > K+. It is observed that bivalent magnesium is extracted to a greater extent than monovalent ions which, in turn, are extracted in the reverse order of their ionic radii. From these results it could be inferred that the carboxylate ion shows a greater affinity for the cations having a higher charge density. Nevertheless, calcium extraction has been found to be somewhat higher than magnesium extraction (Grinstead et al., 1969). The influence of the anion is illustrated in Figures 2 and 3. In the former, the distribution curves between water and the extractant 1 M in toluene are given for the following lithium salts: chloride, nitrate, and sulfate, while Figure 3 shows the curves for the corresponding magnesium salts. From both sets of curves it is found that the in anion extractability order is NO3- > C1- >> Sod2-, agreement with previous results (Grinstead et al., 1969) for sodium salts extracted with the combination of a quaternary amine and a carboxylic acid. This also confirms the fact that anion and cation extractions take place as separate species, which is typical of mixed ionic extractants. It is relevant to point out that nitrates are extracted at a somewhat higher extent than chlorides, which in turn are extracted from one to two orders of magnitude more effectively than sulfates.
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 4, 1981
700
0.10
d
0.08
-
I
c
\
m
-3P
0.m
5 F
2z
0.04
r
0.002
(I
0.001
a
0
0
2
~
A 0 UEOUS CONCENTRATION (molar/ I t )
0.02
Figure 3. Distribution of magnesium salts between water and Primene JM-T/naphthenic acid 1 M in toluene at 30 O C .
= 0.012
c
\
0 2
I
n
3
AQUEOUS CONCENTRATION ( moles / It )
Figure 1. Distribution of several chlorides between water and Primene JM-T/naphthenic acid 1 M in toluene at 30 O C .
-2z
0.010
0
G
/'1'
EXTRACTANT CONCENTRATION (1) 1.0 M (2) 0.6 M ( 43)) 0.4 0.2 M
0.00%
-.-
0.10
I
/
c c
; ; 0.08-
!
//-
Y
/-
z
0
0.2
0.4
0.6
ae
1.0
AOUEOUS LiCl CONCENTRATION (molrdlt)
Figure 4. Distribution of lithium chloride between water and Primene JM-T/naphthenic acid in toluene, at 30 "C, for several extractant concentrations: 0.2; 0.4; 0.6, and 1.0 M.
2 2 a
8
0.04
1.002
0 021
1
1.001
I
2
3
AOUEOUS CONCENTRATION (molrs/lt)
Figure 2. Distribution of lithium salts between water and Primene JM-T/naphthenic acid 1 M in toluene at 30 O C .
Effect of Extractant Concentration. Extraction isotherms were determined for lithium chloride at 30 "C using the extractant at the following concentrations in toluene: 0.2, 0.4, 0.6, and 1.0 M. As may be seen from
Figures 4 and 5, the extractant concentration has an approximate linear effect on the equilibrium reaction in the range considered. However, this does not hold true for very small loadings, probably due to the extraction curve shape which is concave upward for alkaline chlorides (see Figure 1). This is usually an indication of the existence of a polymeric structure for the extracted species in the organic phase, a fact that was inferred from our data as discuaeed further on. Extractant concentrations higher than 1 M were not considered in view of the high solvent viscosity, and since lithium extraction is low the extractant saturation point is far from being reached. Effect of Temperature. The effect of temperature has been investigated for lithium chloride and lithium nitrate, for which distribution curves between water and Primene JM-T/naphthenic acid 1M in toluene have been determined at 5, 30, and 60 "C. These results are shown in Figures 6 and 7 for lithium chloride and lithium nitrate, respectively. For both salts the temperature effect is small and almost
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 4, 1981
701
0.008
AQUEOUS LiCl CONCENTRATION AT EOUlLlBRlUM
TEMPERATURE 0.10
A
( I ) 0.5 m o l e s / l t (2) 0.4 m o l e s l l t
-
o
5
OC
30 *C 60%
(3) 0.3 moles11 t
0.006
z
--
k
-u
( 4 ) 0.2 m o l e s / l t
(D
0.08
c
\
0
5
n
-z 0
E
0.004
V
z
0
G
5W
F 0.06
s
8 3
V
z
0
5
0 V
0.002
B 0
0
o
0.2
4
0.e
0.8
1.0
EXTRACTANT CONCENTRATION (MI
Figure 5. Variation of organic lithium chloride concentration with extractant concentration for given lithium chloride contents in the aqueous phase at equilibrium. TEMPERATURE A
o
5 30
*C Oc
60 *c
AQUEOUS LiNO, CONCENTRATION (moles/lt)
Figure 7. Distribution of lithium nitrate between water and Primene JM-T/naphthenic acid 1 M in toluene at 5, 30, and 60 OC. Table 111. Distribution of Lithium Chloride between Water and Primene JM-TINaphthenic Acid 1 M in Toluene (at 30 "C) as a Function of pH in the Initial Aqueous Solution
PH 3 5
7 9
11
Figure 6. Distribution of lithium chloride between water and Primene JM-T/naphthenic acid 1 M in toluene at 5,30, and 60 OC.
negligible below an aqueous phase concentration of about 1.2 M at equilibrium. For lithium chloride, extraction curves for 5 and 30 "C are virtually coincident in the range considered. It is found, as expected, that an increase in temperature diminishes the extracted species concentration in the organic phase. This means that the extraction reaction is exothermic but the enthalpy released is likely to be small. The temperature effect is less significant for lithium chloride than for lithium nitrate. It is noteworthy pointing out that for both salts, but mainly for lithium nitrate for which extraction takes place at a higher extent, a third
concn, M aq 0% phase phase 2.07 2.10 2.06 2.03 2.00
0.0410 0.0461 0.0432 0.0418 0.0422
dist coeff 0.0202 0.0219 0.0210 0.0206 0.0211
phase was observed at 5 "C, which was difficult to analyze but certainly richer in lithium than the organic phase. In order to collect representative samples, distribution curves were determined for both phases after due clarification, neglecting the intermediate phase mentioned above. Effect of pH. Experiments were performed for lithium chloride solutions with different values of pH in the range 3-11. Table I11 indicates the equilibrium concentrations in both phases and the resulting distribution coefficient. Within experimental error, no influence of pH is observed, due to the mixed ionic nature of the extractant. This would allow variations of pH in a wide range without any significant reduction in extraction efficiencies. However, in the magnesium-containing solution the maximum allowable pH value would be of about 8, in order to avoid magnesium hydroxide precipitation. Mixed Salt Extraction and Selectivity Data. Extraction experiments for mixtures of two salts with a common anion (in this case chloride) have been performed using the three following mixtures: LiC1-MgC12; LiC1NaC1, and LiC1-KC1, at equimolar initial ratio. Distributions of lithium and magnesium between water and Primene JM-T/naphthenic acid 1M in toluene at 30
702
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 4, 1981 ( I ) MgCI,
( L i C I -MgCI,)
( I ) LiCl ( LiCl ( 2 ) LiCl (LiCl
(I)
( 2 ) MgClp (single =It) 0.15
( 3 ) LiCl
(single salt)
( 4 ) LiCl
(LiCI
( 3 ) LiCl (aingte s o l t ) ( 4 ) NaCl (single salt )
0.007
- MgClzl
-
- NaCl ) - KCI
(5) NaCl ( LiCl 0.006
f a
\
- NaCl)
( 6 ) KCI
(single s a l t )
( 7 ) KCI
(LiCl
- KCI)
0
E 0.005
8
5
a8
0.004
0
:
0.005
d
0.002
0.001
0
I
2
AQUEOUS CONCENTRATION ( m o l r s / l t )
Figure 8. Distribution of lithium chloride and magnesium chloride between water and Primene JM-T/naphthenic acid 1 M in toluene at 30 OC, for the single-salt systems and for the LiC1-MgCI2 mixture at initial 1:l molar ratio.
"C for the LiC1-MgC12 mixture and for the corresponding single salt curves are shown in Figure 8. It may be observed that, when compared with the single-salt extraction curves, magnesium extraction is highly enhanced while lithium extraction is deterred as a consequence of the common ion effect. Actually, a high chloride concentration increases the extraction of the cation for which the amine shows a greater affinity, in this case magnesium. Comparable situations are found for the mixtures LiC1-NaCl and LiC1-KC1 also at initial 1:l molar ratio. In these cases, though, the high chloride concentration increases lithium extraction, decreasing that of sodium or potassium, as shown in Figure 9. It is interesting to observe that lithium extraction is more effectively enhanced for the LiC1-NaCl than for the LiC1-KC1 system, although the difference is not very significant. Moreover, it may also be noticed that, while sodium extraction decreases to about one-half compared with the single-salt system, potassium extraction, which is very low, is only slightly depressed due to the presence of lithium. It must be pointed out that while these curves are drawn as a function of molar concentration in the final aqueous phase, extraction actually depends on electrolyte molalities and on activity coefficients which are difficult to evaluate for mixed salt systems and whose determination is beyond the scope of this work. Selectivity of an ion M1+ in relation to M2+is defined as the ratio between the two distribution coefficients, which results in eq 2
The selectivity values for magnesium in relation to lithium (S89,and for lithium in relation to sodium and potassium concentrations are shown in Figure 10. It may be observed that magnesium over lithium selectivity is very high for low values of lithium concentration. This can be explained in view of the shapes of the extraction curves,
0
2
I
3
AOUEOUS CONCENTRATION (molrs/lt)
Figure 9. Distribution of lithium, sodium, and potassium chlorides between water and Primene JM-T/naphthenic acid 1 M in toluene at 30 "C, for the single-salt systems and for the LiCI-NaCl and LiCI-KCI mixtures at initial 1:l molar ratio. IO0
50
;20 5
5w
1
w IO v)
5
2
4
I I
2
AQUEOUS LiCl CONCENTRATION( m o b d l t )
Figure 10. Selectivity of magnesium in relation to lithium and of lithium in relation to sodium and potassium, for the extraction with Primene JM-T/naphthenic acid 1 M in toluene at 30 OC, as a function of the aqueous lithium chloride concentration at equilibrium.
since the magnesium extraction curve is concave downward while the lithium curve is concave upward. The selectivity curve reaches a minimum of about 4.7 for a lithium aqueous concentration of about 1.3 M and then increases again due to the rise in the magnesium extraction, which is probably a result of the extraction of MgCl- species (Grinstead et al., 1969).
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 4, 1981 703
For LiC1-NaC1 and LiC1-KC1 systems all curves are concave upward. At very small loadings they are almost coincident, giving a low selectivity value. A t higher loadings, since lithium is extracted to a higher extent than sodium or potassium, selectivity curves increase in both cases, giving flat maxima of about 17 for lithium-to-potassium selectivity and 6 for lithium-to-sodium selectivity. The extractability of lithium in relation to magnesium, sodium, and potassium may be roughly compared through the selectivity maximum values that are 0.21,6,and 17, respectively. This confirms the fact that the extraction of the referred cations occur in the decreasing order Mg2+, Li+, Na+, K+,as mentioned before. Mechanism of Extraction. The mechanism of inorganic salt extraction using mixed ionic extractants has been studied by Grinstead and Davis (1968,1970).It has been made clear that: (a) the cation and anion of the inorganic salt are extraded as unassociated species; (b) in the organic phase, the divalent cations as well as the anions such as nitrate, chloride and sulfate present a monomeric structure; (c) sodium and potassium carboxylates form aggregates in the organic phase, which are trimers in most of the cases; (d) a t low loadings, the extracted species are associated with several unused extractant molecules. According to Hanson et al. (1975),who also studied the magnesium chloride extraction, a t high loadings the extracted species are most unlikely to be associated to any free molecules of extractant. It seems as well that water is co-extracted, leading to nonstoichiometric solvent loadings. In the light of our data it was considered interesting to elucidate the mechanism of lithium salt extraction since to our knowledge no data have been reported in relation to it. According to the mechanism presented by Davis and Grinstead (1970)the extraction reaction for a monovalent cation and anion salt such as lithium chloride, may be written as
I
IO"
mil FOR AQUEOUS LiCl
Figure 11. Organic lithium chloride concentration aa a function of my for aqueous lithium chloride at different extractant concentrations: 0.2, 0.4, 0.6, and 1.0 M,at 30 "C. IO"
,
(x/n + Y/q + 1) M+ + X(RNH3R'COO), e P 1 1 -(R'COOM),*x(RNH,R'COO) + ;(RNH,X),* n y(RNH3R'COO) (3)
+
where n and q are aggregation numbers of the species containing M+ and X-, respectively, x and y indicate the corresponding degrees of solvation, and p is the number of extractant molecules taking part in the reaction. All species in reaction 3 are in the organic phase except M+ and X-. If the assumption is made that the extractant concentration remains constant, which is reasonable at low loadings, the equilibrium constant expression may be simplified and lead to the equation 0 2
In eq 4, m is the aqueous molality of the inorganic salt at equilibrium, y is the electrolyte mean activity coefficient, and K'is a constant. If log (MX), is plotted as a function of log (my)m, a line of slope 2nq/(n + q ) should be obtained, where n and q are integers. The minimum value of the slope is 1.0 when n and q are both equal to 1, that is when no aggregation occurs. The data log (MX), vs. log my for lithium chloride at 30 "C for different concentrations of the extractant are shown in Figure 11. On the other hand, Figure 12 represents the data for lithium nitrate extraction at 30 "C,
0.5
I
2
my FOR AQUEOUS LiN03 Figure 12. Organic lithium nitrate concentration aa a function of my for aqueous lithium nitrate (extraction with Primene JM-T/ naphthenic acid 1 M in toluene at 30 'C).
corresponding to the distribution of this salt between water and the extractant 1 M in toluene. Experimental values of concentrations and calculated my values are given in Table I1 for lithium chloride and lithium nitrate extractions at 30 "C with the extractant at 1 M concentration. Activity coefficients were taken from the work of Robinson and Stokes (1959).
704
Ind. Eng. Chem. Process Des. Dev., Vol. 20, No. 4, 1981
In all the cases, the log-log graph presents a straight line portion at low loadings. At higher loadings, the assumption that the extractant concentration is constant is not valid and the slope of the curve decreases progressively. The value found for the straight line portion of all curves is 1.33 f 0.02. This means that 2nq/(n + q ) = 4/3. The only possible integer solutions are 1 for one parameter and 2 for the other. Davis and Grinstead’s results (1970) indicate that the anions are extracted as monomeric species. Since no aggregation occurs between the cation carboxylate and the alkylammonium salt it is reasonable to think that the latter will have the same structure regardless of the cation extracted. Thus, it may be concluded that in eq 4, g = 1and consequently n = 2. This is valid as well for lithium chloride as for lithium nitrate, one result providing a means of checking the other. Lithium carboxylate is thus extracted as a dimer ( n = 2) which is in agreement with the tendency of lithium cation to form chelates of such a structure, in search of a greater stabilization of the species. It is important to note that the dimeric structure is observed for the different extractant concentrations tested and for the different temperatures in the range studied. Plots of log (LiCl), vs. log ( m ~ )at~5 aand 60 “C have also given a slope value of 1.33 within the experimental error. The slope analysis approach has also been used in the cases of sodium chloride and potassium chloride. In both cases the value found is 1.5 that fits with the combination 3 and 1 for the two integers of eq 4. If we again ascribe the value 1 to the alkylammonium chloride, previously identified as a monomer, we deduce that n = 3. This means that both the sodium and the potassium carboxylates are extracted as trimers. These results check those of Grinstead et al. (1968) for sodium salts extracted using several mixed extractants. Chloride and nitrate are thus extracted as monomers, and as far as the cations are concerned, magnesium is extracted as a monomer, lithium as a dimer, and sodium and potassium as trimers. Conclusions A mixed ionic extractant comprising an equimolar mixture of Primene JM-T and naphthenic acid diluted in
toluene provides a means of extracting lithium salts from brines. Lithium is extracted to a higher extent than sodium and potassium, but less than magnesium. The effects of temperature and pH are not very significant and the influence of the nature of the anion is in agreement with previous results. For systems containing a mixture of cations, extraction is shown to be enhanced by the high chloride concentration. Selectivity studies confirm that the cation extraction order is Mg2+> Li+ > Na+ > K+. The mechanism of lithium salts extraction has been elucidated showing that no aggregation occurs between cation carboxylate and alkylammonium. Lithium carboxylate presents a dimeric structure, while sodium or potassium are extracted as trimers and magnesium as a monomer, regardless of the anion. This technique could be applied for separating magnesium from lithium in brines, but further research is required to assess its practical availability. Nevertheless, our experimental data duly complete previous results in relation with mixed ionic extractants.
Acknowledgment The authors gratefully acknowledge Dr. Richard L. Bell for his assistance and helpful discussion, Dr. Manuel Young for his participation in the experimental work, and Mr Juan Manuel PBrez, who performed most of the chemical analyses. The authors would like to express their gratitude to the University of California and to the University of Chile for financial support.
Literature Cited Davis, J. C.; Grinstsad, R. R. J. PhyS. Chem. 1970, 74, 147-151. Grinstead, R. R.; Davis, J. C. J. phys. Chem. 1966, 72, 1630. Grinstead. R. R.; Davis, J. C.; Lynn, S.; Charlesworth, R. K. Ind. Eng. Chem. Prod. Res. Dev. 1969, 8 . 218-227. Grinstead, R. R.; Davis, J. C.; Snider, S. W. “Recovery of Salts from SaUne Water via Solvent Extractlon”; Flnal Report to the Office of Sallne Water, Department of the Interior, U.S.A., 1968. Hanson, C.; Hughes, M. A,; Murthy, S. L. N. J . Inorg. Nucl. Chem. 1975, 37, 191-198. Robinson. R. A.; Stokes, R. H. “Electrolyte Solutions”,2nd ed.; Acadetnlc Press: London, 1959.
Received for review October 10, 1980 Accepted May 26, 1981
