Separation of Lithium from Potassium and Sodium By Treatment of the Chlorides with Higher Aliphatic Alcohols E;kRLE R. CALEY AND HERBERT D. AXILROD Frick Chemical Laboratory, Princeton University, Princeton, Y. J.
0
F T H E various methods for the quantitative separation of lithium from potassium and sodium by extraction of the mixed chlorides with organic solvents, the isoamyl alcohol method of Gooch (2) appears to have had the widest use. Because the boiling point of isoamyl alcohol is considerably above that of water, the aqueous solution containing the alkali chlorides may be evaporated in the presence of this solvent; the water is not only evaporated away without much loss of solvent but the salts are completely dehydrated in the process. Moreover, the lithium chloride gradually dissolves in the isoamyl alcohol while the other alkali chlorides are gradually precipitated out. Hence, for quantitative separation by this general method such a solvent is better than one, such as dioxane, whose boiling point is only slightly above that of water, and much better than one, such as acetone, whose boiling point is below that of m t e r . The only other solvent of relatively high boiling point that has been advocated for this separation is pyridine ( 3 ) ,but its disagreeable odor and the difficulty of obtaining it readily in a highly pure state have apparently restricted its use. The method of Gooch has the disadvantage that neither potassium chloride nor sodium chloride is quantitatively insoluble in isoamyl alcohol, so that relatively large corrections must be applied for the amounts of these salts that dissolve along with the lithium chloride. Furthermore, these corrections differ in accordance with the particular combination of salts present. Though the corrections may be applied with considerable confidence, there is, nevertheless, some uncertainty involved, especially in regard to the amounts of salts dissolved in the washings, and for this no corrections are attempted. Furthermore, the measurement of the volume of solvent present after extraction in order to appIy these corrections is somewhat inconvenient in practice. A solvent that required no such corrections and yet had the high boiling point and other desirable characteristics of isoamyl alcohol would manifestly be better from the standpoint of both accuracy and convenience. Since the solubilities of lithium, potassium, and sodium chloride in the aliphatic monohydric alcohols are known to decrease progressively in ascending the series from methyl t o amyl alcohol, it seemed apparent that the solubilities of potassium chloride and sodium chloride in similar alcohols of more than five carbon atoms might become very small, whereas the solubility of lithium chloride might still remain large enough for analytical separation. Experiment showed this to be true. The higher alcohols chiefly considered were nhexanol and 2-ethylhexanol, since these are now readily available in a technical grade a t low cost. For the purpose of this separation no advantage mould probably result from the use of a grade of these alcohols entirely free from isomers. By reason of these considerations, the experiments here described were all made with the so-called practical or technical grades of these two alcohols.
Solubility Experiments
Before being used for these determinations the solvents n-ere boiled to ensure their freedom from water, and the salts were carefully dehydrated. With one exception each result shown is the result of several concordant determinations. The result for the solubility of potassium chloride in 2-ethylhexanol is merely an estimate based upon the probable limit of measurement of the analytical method used for the determination, since the solubility of the salt in this solvent was so slight that the attempted measurements gave the same results as blank determinations. For convenient comparison the solubilities of the three salts in isoamyl alcohol are also given, calculated from data published by Turner and Bissett (4). With the increase in number of carbon atoms the solubility of sodium chloride in these three alcohols decreases more than the solubility of lithium chloride, and the solubility of potassium chloride decreases much more. From the standpoint of probable sharpness of separation, the n-hexanol is obviously better than isoamyl alcohol, and the Z-ethylhexanol obviously much better. However, since the solubility of lithium chloride in octyl alcohol is considerably less than the solubility of this salt in either amyl or hexyl alcohol, it seemed possible that in actual practice hexyl alcohol might be a more satisfactory solvent. Therefore, analytical experiments were made with both solvents. ANALYTICAL EXPERIMENTS.The general procedure recommended by Gooch was followed except for certain minor variations. The potassium and sodium were weighed out in the form of their chlorides, and the lithium in the form of carbonate, the lithium carbonate in the weighed test mixture then being converted t o chloride by the addition of slightly more than the calculated amount of hydrochloric acid before evaporating the aqueous solutionsof the salts with the alcohol. After evaporation and dehydration, the residual potassium chloride, sodium chloride, or both, was collected on a weighed sintered-glass crucible, and washed thoroughly with successive small portions of the cold alcohol. KO attempt was made t o restrict the total volume of alcohol used in washing, as is the usual practice in using amyl alcohol for this separation. After washing, the crucible and salts were dried in an air oven at a temperature sufficient t o volatilize rapidly the residual solvent. In separations made with nhexanol a temperature of 180" C. was used, and in those with 2ethylhexanol, a temperature of 210" C. The accuracy of separation was judged from the agreement or discrepancy between the weights of the residual salts and their original weight. The lithium chloride that dissolved in the alcohol was not converted t o sulfate and weighed, as is the usual procedure in actual analysis, since this seemed unnecessary for measuring the accuracy of separation. However, in order to make sure that the observed results were not due t o ii compensation of errors, the weighed residual salts were all tested for lithium with a spectroscope. Except when the lithium was preaent in unusually large amounts, these experimental separations were made by TABLE I. SOLUBILITIES OF CHLORIDES OF LITHICU, SODIUM, AHD POTASSIUM ( I n certain amyl, hexyl, and octyl dcohols a t 25' C., expressed in grams dibsolved by 100 mi. of solvelit)
Salt LiCl NaCl KCI
The solubilities of lithium, sodium, and potassium chloride in the two alcohols a t 25' C. are shown in Table I. These results were obtained by conventional procedures. 242
Isoamyl Alcohol
7.3 0.0016 0.0006
n-Hexanol 5.8 0.0008
0,00004
%-Ethylhexan01
3.0 0.0001
0.0368 o.oi5i (1.0699 22Bi
>
tj
1
7
1
8
1 1
!l
10 11 12 13 14
1 1 1 1
1
SIMILAR AMOUKTSO F LITHIUM AS
KCI
Taken
Grank None Sone 0.2213 0 2641 0 . 1324 0.1754 Sone Sone 0,3077 0.2134 0.104!1 0.105ii 0 . 0791 0,1202
I.iC1 Present Gram 0.0608 0,062!1 0,0592 0 OGGY 0.074:i 0,0753
0 0640 0 0030 0.OSlfi 0.06iY 0 0570 0,0435 0.0587 0.0621
Weight,of Extraction Residue Gram 0.2500 0,2470
0,2206 0,2637 0.3122 0.344;
n 2000 0 . 237;) 0.3073 0.2132 0.2626 0.2198 0.1864
0.191s
-
CHLORIDE BY n-IIEXASDL .ZSD 2-ETHYLHEXANOL 13ror
NaCl Gram - 0 . 0007
-0.000.i ,....
...... .. , . .....
-0 . 0 0 0 : ~ - 0.0003
.....
, . . . .
... .
,.....
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