T H E SYSTEM ALUMIXUM NITRATE-WATER*-HEXYL AT 25°C.
ALCOHOL
CHARLES C. TEMPLETON'
Department of Chemaslry, University of Michigan, A n n Arbor, Michigan Received November 28, 1948
Recently there has been increased interest in the physical chemistry of systems of the type inorganic salt-water-organic solvent. These include the work of W. Fischer (4-7) and coworkers on the salts of the rare earths, scandium, zirconium, and hafnium, that of Wad (29) on cerium(1V) nitrate, that of Garwin and Hixson and Hixson (8) on nickel(I1) and cobalt(I1) chlorides, and that of the author and coworkers (22, 26-28) concerning the separation of thorium nitrate from rare earth nitrates and of the rare earth nitrates from each other. There is also, of course, the well-known use of ether to purify uranyl nitrate. The papers of Nachtrieb and coworkers (19, 20) on the extraction of ferric chloride from concentrated aqueous hydrochloric acid solutions with isopropyl ether come the closest of the studies so far published to being of a fundamental physicochemical nature. Hill, Miller, and Macy (10-13, 15) determined ternary phase diagrams for water and silver perchlorate in conjunction with each of the following solvents: benzene, toluene, aniline, and pyridine. Misciattelli (16) studied the system thorium nitrate-water-ethyl ether, and Misciattelli (17) and Guempel (9) studied the system uranyl nitrate-water-ethyl ether. The water percentages in Misciattelli's studies are not overly precise or consistent. However, the Karl Fischer (3) method for the determination of water now makes it possible to obtain much more accurate results. The present study is presented, apart from the interest of the data themselves, to give more insight into the factors govering the extraction of metallic nitrates from aqueous into organic solutions, a phenomenon which is dependent upon the presence of oxygen-containing functional groups in the solvent molecules. During the course of this study there appeared the very recent work of Katzin and Sullivan (14), which includes complete phase data (obtained with the help of the Karl Fischer method) for water-uranyl nitrate-solvent systems, for several alcohols, ketones, and ethers. Aluminum nitrate was chosen for study because of its appreciable solubility in n-hexyl alcohol (intermediate between that of thorium nitrate and the rare earth nitrates) and because its alcoholic solutions showed no instability after even six months of standing. By contrast, solutions of ferric nitrate in n-hexyl alcohol change their chemical nature so rapidly that, after a week or more, one cannot obtain reproducible distribution data.
* Present
address: Shell Oil Company, 3737 Bellaire Boulevard, Houston 5 , Texas. 1255
1256
CHARLES C. TEMPLETOX
DETERMISATIOX OF PHASE DATA FOR THE SYSTEM ALUYIXUM X1TRATE-W.iTER-nHEXYL ALCOHOL
Materials n-Hexyl alcohol (Eastman Kodak Company, practical grade) was distilled twice through a column of about four theoretical plates, the middle fraction only being retained after each distillation. The product had a boiling range of 0.2"C. No special measures were taken to remove water, since the solvent was eventually again placed in contact with water, and the analytical method was used for obtaining the data. Karl Fischer determinations showed the final solvent to contain 0.1 per cent or less of water. Aluminum nitrate nonahydrate (Mallinckrodt analytical reagent grade) was used without further purification. The maximum impurities, 0.1 per cent of alkali salts and 0.02 per cent sulfate, were less than the general experimental error. All other chemicals used were of analytical reagent grade. Procedure All the systems were agitated and allowed to come to equilibrium in a 25°C. & 0.05" thermostat. Twenty-four hours was abundant time for equilibrating
two liquid phases; several days were required for a solid and an organic liquid phase to reach equilibrium. When removed from the thermostat, the phases were immediately separated and placed in dropping bottles; in this condition they could stand indefinitely before analysis. Water was determined by the Karl Fischer (3, 18) method in conjunction with an electrical endpoint indicator. Standardization and operating methods were based on accepted procedures (18). For solutions which were sufficiently concentrated, aluminum nitrate was calculated from the alumina residue obtained by direct ignition of the solution sample in a platinum crucible. For more dilute solutions, aluminum was determined colorimetrically by the use of the ammonium aurintricarboxylate (aluminon) method in acid medium (23) and a Klet t-Summerson photoelectric colorimeter (green filter). In these cases about 10 g. of alcoholic solution was weighed into a 100-ml. volumetric flask and allowed to stand for several days in contact with about 50 ml. of water. The distribution relations are such that the aluminum is quantitatively extracted into the aqueous phase. Later enough water was added t o bring the interface to the mark, the alcohol was pipetted away, and the analysis finished in the usual fashion. pH measurements were made with a glass and saturated calomel electrode system and a Beckman Model H-2 pH meter. Datu and discussion In table 1 are recorded the fundamentaI phase data for the system. I t was demonstrated that Al(SO&. 9H10 was the equilibrium solid phase for both the saturated two-liquid-phase system and for a single alcoholic phase. The solubility of 0.62 per cent for n-hexyl alcohol in water was determined interferometrically by Butler, Thomson, and Maclennan (1).Two independent values
SYSTEM ALUMIKUM KITRATE-WATER-HEXYL
ALCOHOL
1257
for the solubility of aluminum nitrate in water a t 25°C. reported by Seidell (24), e.g., 43.5 and 39.5 weight per cent Al(Kos)s, compare reasonably well with these data. TABLE 1 The system aluminum nitrate-water-n-hezyl alcohol at W C . I RUS
so,
I
PH (AQUEOUS ,
I
7 l(a) 201 8I1 301 9
0.60
'
0.72 0.66
,
0.92 0.90 1.20
I
1.74 2.09 2.20 2.40
I
I
I11 VI 1 2 3
1
VI1 5
6VI11 l
2.64 2.78
AQUEOCS PHASE
I
Weight percentages
* 0.06'
ALCOHOLIC PHASE
1
Weight percentages
HIO
__ HI0 __
2aHirOH
41.2 41.2
58.2 59.2
9.65 9.55
82.4 82.61)
39.9 38.3 38.1 35.6 35.0 31.5 31.3 30.5 26.0 23.0 20.3 17.14 13.84 11.9 9.41 6.27 0.00
60.3 61.2 60.2 63.5 64.7 67.9 69.7 67.9 73.5 76.3 78.8 81.6 84.8 86.8 90.3 92.5 99.4*
9.21 8.53 8.71 7.74 7.07 5.77 5.81 5.66 5.12 5.03 5.14 5.47 5.83 6.05 6.22 6.52 7.117
83.9 85.6 85.3 88.0 89.3 92.3 92.4 92.6 94.2 94.7 94.8 94.5 94.1 93.9 93.7 93.4 92.9
(-0.2)' 6.89 0 . 5 5.84 1.7 5.98 0 . 9 14.27 0 . 2 3.62 0 . 6 1 1.99 (-1.O)I 1.81 1.6 ] 1.78 0 . 5 10.72 0 . 7 0 24 0.9 0:10 1 . 2 0.041$ 1 . 3 I 0.032$
__
~
Ii
0.62'~ 0.00
PELUBYS
Supplementarv d a t a : Found Theoretical A: Solid phase, Run No. I : Al(K03)3,per cent. . . . . . . . . . . .. . . . . . 5 6 . 8 56.8 H20, per cent . . . . . . . . . . . . . . . , . , . , . , 42.7 43.2 This phase was prepared by adding finely ground Al(N03)~.9H20t o the saturated system and allowing crystals t o grow t o moderate size. B. Solubility of AI(NOa)n.SH2O in n-hexyl alcohol alone: .41(503)3 by ignition 7.10 per cent Found Theoretical Solid phase : H20, per cent. . . . . .. . . . . , , . . . . . , . . . . , , , , . . . , , . . , . 41.6 43.2
-
* Butler,
Thomson, and Maclennan (1)
t More accurate than the value of 7.4 previously
reported (26).
$ Determined colorimetrically with aluminon.
In figure 1 the data are plotted in triangular coordinates. The system has been completely investigated between the limits water, n-hexyl alcohol, and Al(N0&.9H20, but no measurements have been made for the remaining region of the plot. Evidence will now be presented that the system is not stable in the water-poor region. According to Young (30) A1(NOs)a.9H~0is converted to A1(N0&.6H20 when confined over Dehydrite for 5 days. The author left the nonahydrate over Dehydrite for 2 weeks and obtained a product which give
1258
CHARLES C. TEMPLETON
16.2 per cent Al2O3on ignition (theoretical for the hexahydrate, 15.87 per cent A120a).This product was mixed with n-hexyl alcohol and allowed to stand with occasional agitation for two months. A clear solution resulted, but the residual solid was gelatinous and could not practically be dried for analysis. The solution contained 3.52 per cent A1203(or 14.70 per cent Al(?rTO,)a),a value about twice as large as the solubility in alcohol when the solid phase has the maximum amount of water of crystallization.
H2° FIG.1. System aluminum nitrate-water-n-hexyl alcohol at 25°C. (weight percentage). Regions: A , two liquid phases; B, single water-rich liquid phase; C, single alcohol-rich liquid phase; D, A ~ ( N O ~ ) ~ . ~and H Ztwo O liquid phases; E, AI(NOJ)J.~HZO and water-rich liquid phase; F, AI(NO&.9H20 and alcohol-rich liquid phase.
The salt after standing for two months over Dehydrite was found to contain 25.2 per cent A1203 and 33 per cent H20. The corresponding empirical formula is A120s.1.57N20s.7.4H20,which approximates AI~(OH)3(NO~)3~6Hz0. The study of the water-poor region was then abandoned, since the attempts to remove water appear also to remove nitrate, and a system results of which aluminum nitrate is no longer a proper phase rule component. In table 2 are included the mole fractions of Ala+ in the aqueous phase (counting Ala+ and NO3- as molecular entities), and of Al(NO& in the alcoholic phase (considering the solution to consist of HzO, CaHlsOH, and Al(N0s)s “molecules”). As in previous distribution studies (22, 27, 28) these modes of expression are
SYSTEM A L C M I S U Y NITRATE-WATER-HEXYL
1259
ALCOHOL
mainly an arbitrary means of making comparisons on a molar basis. The molalities are referred to 1000 g. of the richer solvent in each phase. In the right-hand section of figure 2, the true mole fraction of aluminum nitrate in the alcoholic phase, alcX[A1(NOl),], is plotted on a log-log scale versus the true mole fraction of AIS+in the aqueous phase, a q X A 1 3 + . In past studies (22, 26, 28) in which no determinations of water were made, one could calculate only the corresponding apparent mole fractions based on the assumption of immiscibility of the two solvents. In the left-hand portion of figure 2 the distribution of aluminum nitrate is plotted on this apparent mole fraction basis, TABLE 2 Concentrations calculated froin table 1 AQCEOUS PEASE
XUN
XO,
1 True mole ' fraction. of AI:+
I. . . . . . . . . . . . . . 7. . . . . . . . . . . . . l(a) . . . . . . . . . .' 201. . . . . . . . . .
11. . . . . . . . . . . . 8 . . . . . . . . . . . . .1 301 . . . . . . . . . . ~
I11 . . . . . . . . .
v. . . . . . . . . . . . . VI... . . . . . . . . . 1. . . . . . . . . . . . . . 2. . . . . . . . . . . . . . 3. . . . . . . . . . . . . 4 . . . . . . . . . . . . .,
VI1 . . . . . . . . . . . . . . . . . . . . '. ~
5. 6.
1
......... VIII... . . . . . . .
i
0,0482 0.0482 0.0461 0.0436 0.0433 0.0396 0.0388 0.0338 0.0334 0.0325 0.0267 0.0231 0.0199 0.0161 0.0129 0.0110 0.0085 0,0056 0.0000
1
ALCOHOLIC PEASE
Molality of [AI(NOhl
3.32 3.32 3.14 2.94 2.92 2.62 2.555 2.18 2.16 2.08 1.663 1.414 1.204 0.979 0.759 0.638 0,491 0.316
o.oooo
* Calculated on the assumption of
1
'rue mole fraction 01 IAI(N0i)rl
btolality of H,O
0.0269 0.0267 0.0237 0.0205 0.0208 0.0152 0.0132 0.0074 0,0069 0.0068 0,0028 0.0009 0.0004 0 000156 0 000120
