Logarithmic Distribution Coefficients of Rare Earth Compounds Fractionally Precipitated from Homogeneous Solution F. H. Firsching, Guy W. Aton, Ralph S. Bakowski, Marvin R. Kiotz, Haralambos N. Meggos, Gerald D. Melm, Thomas R. Paul, Michael J. Smith, and James D. White Science and Technology Division, Southern Illinois University, Edwardsville, Ill. 62025 A study of the fractional precipitation of the rare earth iodates from homogeneous solution using double complexation and replacement has been made. The Doerner-Hoskins logarithmic distribution coefficient (lambda) has been found for a variety of combinations of two rare earths and two complexing agents. Lambda values obtained using two complexing agents have been compared with lambda values obtained using only one complexing agent. Additional lambda values have been calculated from these experimentally determined values. A comparison of calculated and experimental values are in good agreement. Approximate lambda values have also been computer calculated with a set of equations using solubility product and formation constant data.
COPRECIPITATION effects have complicated fractional precipitation of the rare earths. Precipitation from homogeneous solution in the presence of a complexing agent has reduced coprecipitation ( I ) . This study shows that when two complexing agents are present further improvement has often been realized. To organize and interpret information on a fractional precipitation process, results are expressed using the DoernerHoskins logarithmic distribution coefficient or lambda. If the system under study obeys the Doerner-Hoskins equation, then the lambda will be the same for a different starting ratio of two ions to be separated or if the amount precipitated varies. This provides a handy means of evaluating what would otherwise be confusing and varied results. The application of the Doerner-Hoskins equation ( 2 ) to coprecipitation studies usually involved oxalates (3). Only limited work on rare earth iodates has been previously published (4-6). This study is similar to that previously reported for lanthanum and praseodymium ( 4 ) and represents the application of double complexation and replacement to many other rare earths. It also shows that double complexation often provides a superior separation over single complexation. EXPERIMENTAL
Reagents. Analytical Grade reagents were used, except as described below. Rare earth oxides were purchased from two sources: Baker and Adamson, Allied Chemical, Morristown, N. J., and Alfa Inorganics Inc., Beverly, Mass. These oxides were generally of 99.9% purity with an occasional oxide of 99.8 %. Three of the complexing agents used in this study were (1) L. Gordon, M. L. Salutsky, and H. H. Willard, “Precipitation from Homogeneous Solution,” Wiley, New York, 1959. (2) H. A. Doerner and W. M. Hoskins, J . Am. Chem. SOC.,47, 662 (1925). ( 3 ) J. Block and L. Gordon, Tuluntu, 10, 351 (1963). (4) F. H. Firsching, ANAL.CHEW,34, 1696 (1962). ( 5 ) M. E. Pruitt, R. R. Rickard, and E. I. Wyatt, Ibid., 34, 283 (1962). (6) F. H. Firsching and T. R. Paul, J . biorg. Nucl. Chem., 28, 2414 (1966). 152
ANALYTICAL CHEMISTRY
purchased from two sources, K & K Laboratories Inc., Plainview, N. Y.,and Geigy Industrial Chemicals, Ardsley, N. Y . The Geigy material had a minimum purity of 98%. The three complexing agents were: N-(carboxymethyl)-N’2-hydroxyethyl-N,N’-ethylenediglycine sold as hydroxyethylethylenediaminetriacetic acid (HEDTA); [(carboxymethylimino)bis(ethylenenitrilo)]tetraacetic acid sold as diethylene triaminepentaacetic acid (DTPA); and (1,2-cyclohexylenedinitri1o)tetraacetic acid sold as diaminocyclohexanetetraacetic acid (DCTA). Equipment. A Cary 14 spectrophotometer was used with matched 5-cm light path quartz end window cells for the spectrophotometric data. Beckman Zeromatic pH meters were used for the pH measurements. Procedure. Either a new unscratched 250-ml beaker was used or one that had been treated with Glasskote silicone spray (this prevents the formation of a tenacious film of precipitate on the glass). One half millimole each of two rare earths and two complexing agents and 5.0 mmole of ammonium acetate was added. The volume was adjusted to about 50 ml and the pH to 5.0 using either ammonia or acetic acid. Fifty milliliters of a 0.4M solution of potassium iodate was added while the solution in the beaker was vigorously stirred. The pH was adjusted to 5.0 using either ammonia or acetic acid and the final volume was adjusted to 125 ml. The replacement ion solution was prepared as follows. To a 100-ml beaker was added 1.0 mmole of replacement ion (any salt that will not interfere is suitable, such as nitrate, perchlorate, chloride, acetate) and 2 mmole of ammonium acetate. The volume was adjusted to about 35 ml and the pH to 5.0 using ammonia or acetic acid. The final volume was adjusted to 50 ml and transferred to a buret. The replacement ion was then added dropwise to the stirred rare earth solution. After the replacement ion had been added completely, the precipitate and solution were allowed to stand for several hours before filtering. (This prevented incomplete precipitation.) It was then filtered through a porcelain crucible, medium porosity. DISCUSSION
Throughout this study the total concentration of both rare earths and also of both complexing agents was held constant. One rare earth was substituted for another, and one complexing agent was substituted for another, in the same concentration. This made it possible to compare various combinations of rare earths and complexing agents with one another. The analysis of rare earths remaining in the final solution was complicated by serious interferences. Instead of analyzing the filtrate, the spectrophotometric analysis (3, using the Cary 14, was carried out on the precipitate fraction. The precipitates were ignited to the oxides (850” C) dissolved in perchloric acid and brought to 25.0 ml in a volumetric (7) D. C . Stewart and D. Kato, ANAL.CHEM.,30, 164 (1958).
flask. The spectra of this solution was compared to the spectra of standard solutions of pure rare earth perchlorates. For colorless rare earths cations, an EDTA titration (8) was used to determine the amount precipitated. From this information the amount of both rare earths left in the final solution can be found. With these values the lambda calculation can be made using the Doerner-Hoskins equation (2). The meaning of lambda values as used in the DoernerHoskins equation is given in Table I. This shows the type of fractionation that would occur in a mixture of A and B if half the original amount of B is precipitated. Each increase in lambda corresponds to lowering the concentration of A in the filtrate by a factor of 2, while the concentration of B remains constant. The improvement in the precipitate ratio is not as favorable. Once a lambda value is determined for a binary system obeying the Doerner-Hoskins equation, the most desirable fraction to precipitate for any ratio can be calculated. In the first investigation, differing amounts of replacement solution-20, 30,40, and 50 ml-were added to the complexed rare earths in the presence of iodate. The addition of different volumes of either a zinc or cadmium solution resulted in different final volumes of solution and also produced differing amounts of precipitate. These results are given in Table 11. The logarithmic distribution coefficient (lambda) was essentially the same for all the volumes of replacement ion used, thus indicating that the system was following the Doerner-Hoskins equation. As a result of this preliminary work, a volume of 50 ml was selected as a standard quantity of replacement ion for the remainder of the study. A short series of determinations was made to check the effect of varying ratios of rare earths on the lambda value obtained. The complexing agents were EDTA and DTPA, the replacement ion was cadmium, and the two rare earths were praseodymium and neodymium. When the ratios of Pr to Nd were 4 to 1, 1 to 1, and 1 to 4 the corresponding lambda values were 1.71 =t 0.03, 1.87 f 0.05, and 1.71 rt 0.04. This indicated that the ratio of rare earths had little influence on the lambda value. Various combinations of praseodymium, neodymium, samarium, europium, and holmium, with HEDTA, EDTA, DCTA, and DTPA were studied. In each solution only two rare earths and two complexing agents were present. A few lambda values using combinations involving lanthanum, gadolinium, dysprosium, erbium, and yttrium were also determined.
Table I. Meaning of Lambda Values Filtrate ratio Precipitate ratio A to B A to B
X 1
50 50 50 50 50
50 25 12.5 6.3 3.1
2 3 4 5
50 50 50 50 50
50
75 87.5 93.7 96.9
Lambda values using many combinations of the above rare earths were determined with double the usual amount of one complexing agent added instead of single amounts of two complexing agents. Thus a comparison could be made of the effects of using one complexing agent os. the effect of using two complexing agents. Table I11 contains lambda values for various pairs of rare earths with two complexing agents and also with one complexing agent present. These values represent the average of at least three or more individual determinations unless designated otherwise. The most common number of determinations was four, with occasionally a total number as high as 12. Double complexation is usually equal to or more efficient than single complexation in achieving a separation of rare earth cations. In some cases double complexation is remarkably superior. When HEDTA-DTPA and Pr-Sm combinations were used a X of 6.1 was obtained. This is about eight times more efficient than the X of 3.1 obtained with HEDTA, and about five times more efficient than the X of 3.7 obtained with DTPA. The experimentally determined values in Table I11 can be used as a source of additional information. For example, if only the lambda values for combinations involving Pr-Nd and Nd-Sm had been determined, the lambda value for the Pr-Sm combination can be calculated by a simple multiplication. log
[Prlo
~-
Prlf X I = ___
__ log [Ndl, [Ndlf
where [Prl0 = original concentration (1)
[Pr], = final concentration
(8) R. F’ribil and V. Vesely, Tuhrtu, 10, 899 (1963).
Table 11. Effect of Adding Different Amounts of Replacement Ion Complexing agents are HEDTA and DTPA Combination
Nd-Eu
,.
*
X found with cadmium, rnl added
X found with zinc, ml added
of
rare earths Pr-Sm Nd-Sm
20 6 . 0 =k 0.10 2.7 i 0.1 2.5 i- 0 . l a
Sm-Eu Sm-Ho ... Average of two values. Single value.
30 6.2=k00.4a 2.8 =t 0 . 1 2 . 2 f 0.0a 1.2* 4.2 f 0 . 5
40 6.311.2 3.1 f 0.3
50 6.3f1.7
...
1.9 i 0.2 1 . 3 i 0.1 3.4 =k 0 . 4
1.3b 3.3b
...
30 6.O=tO0.3 2.9 =t 0 . 5
40 5.9f0.4 3.1 f 0.2
50 5.4f0.3 3.1 f 0.3
VOL 40, NO. 1, JANUARY 1968
153
~~~~
Table 111. Experimentally Complexing agents Rare HEDTA-EDTA HEDTA-DCTA HEDTA-DTPA EDTA-DCTA EDTA-DTPA earth combinaReplacement ion Replacement ion Replacement ion Replacement ion Replacement ion tions Cd Zn Cd Zn Cd Zn Cd Zn Cd Zn A. Pr-Nd 1 . 5 f 0 . 2 1 . 5 i O . l a 1 . 5 f O . O 1 . 2 ~ 0 . 22 . 2 f 0 . 2 2 . 2 f 0 . 2 1 . 5 f O . l 1 . 4 f O . 1 ~ 1 . 9 f O . 12 . 0 f 0 . 1 4 . 1 f 0 . 2 4 . 4 f 0 . 2 3 . 9 S 0 . 1 4 . 2 & 0 0 . 65 . 2 f 0 . 1 6 . 1 f 1 . 2 3 . 3 S 0 . 1 4 . 3 f 0 . 6 3 . 8 f 0 . 4 4 . 6 f 0 . 7 B. Pr-Sm 4.8 f 0.1. 5.0 f 0 . 5 5.4 f 0.5 5.2 f 0 . O a 6.2 A 0.1 C. Pr-Eu 16.0 f 4 . 0 8.9 & 0.7 D. Pr-Ho 10.4 f 1.4 2.4 f 0.2 2.5 f 0 . 2 E. Nd-Sm 2 . 6 3 = 0 0 . 12 . 6 f 0 . 2 2 . 9 5 0 . 1 2 . 4 f 0 . 4 3 . 1 f 0 . 3 2 . 6 f 0 . 1 2 . 8 f 0 . 3 3.8 f 0.4 3.4 & 1.0 1.9 f 0.2 F. Nd-Eu 8.1 A 0 . 9 9.9 f 0.4 G. Nd-Ho 1.3f 0.1 1.5 f 0.0 H. Sm-Eu 6 . 6 f 0 . 5 6.1 f 0 . 1 3.3 f 0.2a 2.7 A 0.1 2.9 f 0 . 2 I. Sm-Ho 2.0 f 0 . 1 J. Eu-HO The average of two determinations. 0
If XI and Xz are multiplied together a third lambda value is calculated for the Pr-Sm combination.
(3)
xs =
Similarly, if the lambda values for combinations using Pr-Nd and Pr-Sm had been determined, then the lambda value for the Nd-Sm combination can be calculated by a simple division. A series of these calculations are given in Table IV. Examination of this data shows a good correlation between the experimental values (Table 111) and calculated values (Table IV). Slightly more than half of the calculated values are within 20 of the experimentally determined value. This calculation of lambda values should prove to be very useful, If three lambda values are determined experimen-
tally, then an additional three values can be calculated, if four are determined then six more can be calculated. Further work was done on two other rare earth systems using the same general procedure. The major change was that oxalate and arsenate were substituted for iodate. Because of inherent differences in solubilities, the same concentration of all precipitants could not be achieved. While the original solutions contained 20 mmoles of iodate, only 10 mmoles of arsenate and 0.75 mmoles of oxalate could be added without causing a heteregeneous precipitation. To maintain the ionic strength sodium acetate was added t o the arsenate solution and ammonium chloride was added to the oxalate solution. The arsenate solution had one additional difference. To produce a manageable precipitate, 0.1 mg of diatomaceous earth was added to prevent the formation of a gelatinous precipitate. The results using these two precipitants are given in Table V. Both the oxalate and arsenate systems were more repro-
Table IV. Calculated Rare earth combinations pr-Nd Pr-Sm Pr-Eu Pr-Ho
HEDTA-EDTA Replacement ion Cd
Zn
Complexing agents HEDTA-DCTA Replacement ion cd Zn
Nd-Sm Nd-Eu Nd-Ho
6.9 S 1 .O (D/A)
Sm-Eu
1.2 f 0 . 1 (C/B)
1.5 =k 0.2(F/E)
1.4 f 0.4(F/E)
Sm-Ho
2.6 i 0.4(D/B) 3.1 i 0.4 (G/E) 2.2 =k 0 . 4 (D/C)
3.8 & 0.4(G/E)
3.8 f 0 . 9 (D/B)
12 f 2
18 f 1
( E X I)
13 i.4
2.6 A 0 . 3 (G/F)
Combinations from Table I11 used for calculation are given in parenthesis.
154
Cd
Zn
1.6fO.l(B/E) 1.7&00.2(B/E) 1 . 3 S O . l ( B / E ) 1.8&0.3(B/E) 1.7&0.2(B/E) 2.3&00.5(B/E) 2.6 f 0 . 3 (C/F) 1.3 f 0.2(D/G) 3 . 9 i 0 . 7 ( A X E ) 3 . 9 & 0 . 3 ( A x E ) 4 . 3 f 0 0 . 2 ( A X E ) 2 . 6 f 0 0 . 2 ( A X E )6 . 8 f 0 . 7 ( A X E ) 5 . 7 f 0 . 6 ( A X E ) 4.2 f 0 . 5 (C/H) 4.1 f 1.3 (A X F) 5 . 5 f 0.6 (A X F) (A X G ) 15 A 2 (A X G) 24 f 2 (B X I) 29 f 3 (B X I) 2 . 7 f 0 0 . 3 ( B / A ) 2 . 9 f 0 0 . 3 ( B / A ) 2.6SO0.1(B/A) 3.5A00.7(B/A) 3.2 i 0.5 (C/A)
Eu-HO
HEDTA-DTPA Replacement ion
ANALYTICAL CHEMISTRY
(D/A)
17 f 1
(B X I)
2.0*0.4(B/A) 2.3 f 0.3 (C/A) 1OA 1
2.810.5(B/A) 2.5 S 0 . 3 (C/A) 3.4 It 0 . 3 (E X H)
(E X I)
1.0 f O.l(C/B) 0 . 6 f 0.1 (F/E)
0.9 f 0.2(C/B)
-~
Determined Lambda Values DCTA-DTPA Replacement ion Cd Zn 1.9 f 0.1 2.2 f 0.1 5.lf0.8 7.0f1.3 4.5 f 1.0 5.0 i 0.2 2.9 i 0.1 2 . 4 f 0.1 4.1 i 0.2
HEDTA Replacement ion Cd Zn 2.1 0.1 2.1fO.2 3.1f0.2 4 . 0 1 0.8
*
Complexing agents EDTA Replacement ion Cd Zn 3.1
f 0.2 5.2 f 0 . 2 10.5 i 0.4 2.6f0.6
2.2 i 0.3
-
DCTA DTPA Replacement ion Replacement ion Cd Zn Cd Zn 1.8f0.2 1.5fO.O 2 . 4 f 0 . 3 2.010.1 2.5 f 0.5 2 . 5 f 0.2 3.7 f 0.1 3.5 i 0.4 4.0 f 0.2 10.1 f 0.1
2.Of0.1.
2.2fO.2
2.5fO.4
2.1fO.2
2 . 1 1 0.1 2.4f0.1 2.4f0.1
ducible than the iodate system. Three-figure accuracy was justified because of this reproducibility, while for the iodate the third figure was seldom justified. When the lambda values of the various combinations are compared for the arsenate, oxalate, and iodate, no single precipitant is best for all combinations. Usually the iodate produces the better separation. The data show an excellent correlation between calculated and experimental lambda values for both the arsenate and oxalate systems. The arsenate system is exceptionally close. Thus all three systems-arsenate, oxalate, and iodate-adhere quite well to the Doerner-Hoskins equation in all the combinations studied. A reasonable assumption would be that the precipitaton of insoluble rare earth compounds from homogeneous solution using double complexation and replacement follows the Doerner-Hoskins equation. Additional experimental lambda values involving combinations with lanthanum, gadolinium, dysprosium, erbium, and yttrium are given in Table VI.
From these data a short series of lambda values has been calculated. An examination of this calculated data, given in Table VII, shows a correlation with data in Table VI and also in Table 111. By combining the data from Tables 111 and VI, it would be possible to calculate many other combinations involving all 10 rare earths. The dramatic improvement in separation efficiency that is occasionally realized with two complexing agents as compared to one is quite remarkable. Attempts to account for this improvement have met with limited success. The explanation of results using single complexation is fairly simple. The cation that forms the least stable complex is selectively released by the replacement ion. If it also forms the most insoluble precipitate, then this accounts for experimental results. For double complexation with improved separation over single complexation this explanation is unsatisfactory. If one rare earth cation were almost exclusively complexed by one
Lambda Values“ Complexing Agents EDTA-DTPA Replacement ion
EDTA-DCTA Replacement ion
cd
Zn
cd
1.2 f 0.2 (B/E)
1.6 i 0 . 2 (B/E)
4.2 =t 0.5 (A X E)
5.1 =t 0 . 4 ( A X E)
1Oi1 2.2
z!=
0 . 2 (B/A)
3.1 i 0 . 5 (B/A)
(BXI)
2.0 1 0.3 (B/A) 2.7 & 0 . 0 (C/A)
6.5 f 0.6(E X I) 2.0 1 0 . 2 (C/B)
Zn 1.8 f 0.4(B/E) 5.0 f 0 . 5 ( A X E) 4 . 2 f 0 . 1 (C/H) 6.9 f l.O(B X H) 4.5 i 0.5 (D/J)
9.61O0.5(CXJ) 13 f 2 (B X I) 2.3f00.5(B/A) 3.1 =t0 . 2 (CIA) 3.8 5 0 . 4 ( E X H) 4.5 f 0 . 5 (D/A) 7.2 i 0.8 (E X I) 1.4 f 0.2 (C/B) 1.5 f 0 . 2 (I/J) 1.9 f 0.4(D/B) 1.4f00.2(D/C) 1.9 f 0.2 (I,”)
DCTA-DTPA Replacement ion cd
Zn
1 . 8 f 0.3 (B/E) 1 . 1 i 0.2(C/F) 5 . 5 f 0 . 3 ( A x E) 2.4 f 0.2 (D/I) 2.1 i 0.2(D/J)
2.9 i 0 . 6 (B/E)
l l i 2
(CXJ) (B x I) 2.7&0.4(B/A) 2 . 4 f 0.5 (C/A) 12 f 2
2 . 6 f 0.2(D/A) 0 . 9 f 0 . 2 (C/B)
0.9 f 0.1 (I/J) 1 . 4 f 0.1 (F/E) 1 . 0 5 0 . 2 (D/B) 1.1 i O . I ( D / C )
VOL. 40, NO. 1, JANUARY 1968
155
Table V. Lambda Values Using Arsenate and Oxalate Rare earth Exptl Calcd ARSENATE, EDTA AND DTPA, Cd AS REPLACEMENT 1.74 f 0.05 1.74 (C/E) A. Pr-Nd 1.75 (B/D) 3.34 zt 0.04 3.32(A X D) B. Pr-Sm 3.29 (C/F) 5.30 f 0.18 5.38 (B X F) C. Pr-Ho 5.31 (A X E) D. Nd-Sm 1.91 f 0.05 1.92 (B/A) 1.89 (EjFj E. Nd-Ho 3.05 zt 0.08 3.08(D X F) 3.05 (C/A) F. Sm-Ho 1.61 i 0.05 1.59 (C/B) 1.60 (E/D) OXALATE, DCTA AND DTPA, Cd AS REPLACEMENT G. Pr-Nd 1.33 zt 0.01 1.36 (H/J) H. Pr-Sm
2.48 f 0.02
I. Pr-Ho
5.41 & 0.31
J. Nd-Sm
1.82 f 0.02
K. Nd-Ho
3.82 f 0.07
L. Sm-Ho
2.76 f 0.02
Rare earth combinations
cd
ComDlexina agents HEDTA-~TPA Replacement ion Zn
La-Y Pr-Nd
54.0 (AX C) 1 . 3 (B/C)
Pr-Sm Pr-Eu Pr-Gd Pr-Dy Pr-Er Nd-Sm Nd-Eu Nd-Gd Nd-Dy Nd-Er Sm-Eu Sm-Dy Sm-Er Eu-Gd Gd-Dy
3 . 4 (B/D) 4.4 (B/E)
1 . 5 (F/G) 1 . 3 (J/K) 3.9 (F/H) 4.9 (J/L) 6.1 (J/M) 8 . 4 ( F X M) 12.O(F X I) 2 . 6 (G/H) 4 . 1 (K/L) 5 . 2 (K/M) 5 . 5 (M X G) 8 . 2 ( G X I)
2 . 6 (C/D) 3.4 (C/E)
1 . 3 (D/E) 2 . 2 ( H X M) 3 . 2 ( H X I) 1 . 3 (L/M) 1.3 (J/F) 1 . 7 (K/G) 1 . 5 (I/M)
Dy-Er
Table IX. Final Concentration in Moles per Liter of All Forms of Both Rare Earths Zinc replacement Rare earths Exptl Computer calcd EDTA-DTPA 3.8 i 0.7 x lo-' Pr 7 . 6 x 10-4 1.2 i 0.1 x 10-3 Nd 1.2 x 10-3 1.8 zt 0 . 3 x Pr 4.0 x 10-4 Pr Eu Nd Sm
2.2 i0.0 x 2.1 f 0 . 3 x 2.5 f 0.0 x 6.8 i 1 . 7 x 2.0 + 0.1 x
Pr Nd
3.1 =k 0 . 4 x 10-4 1 . 3 i 0.2 x 10-3
Sm
8.6 x 2.7 x 1.3 x 4.7 x 1.3 x
10-3 10-4 10-3 10-4 10-3
10-4 10-4 10-3 lo-' 10-a
HEDTA-DTPA 7.5 x 10-4 1 . 2 x 10-8
Table VIII. Comparison of Experimental and Computer Calculated Lambda Values Zinc replacement EDTA-DTPA HEDTA-DTPA DCTA-DTPA DTPA Exptl Calcd Exptl Calcd Exptl Calcd Exptl Calcd 2.0 4.6 2.5 6.0 2.7
Pr-Dy
156
Table VII. Calculated Lambda Values
1.41 (I/K) 2.42(G X J) 1.96 (I/L) 5.08(G X K) 6.84 (H x L j 1.86 (HIG) 1.38 (K)Lj 4.06 (I/G) 5.02(J x L) 2.18 (I/H) 2.10 (K/J)
Table VI. Additional Lambda Values Complexing agents EDTAEDTADCTA DTPA Replace- ReplaceRare HEDTA-DTPA ment ment earth combinaReplacement ion ion ion tions cd Zn Zn Zn A. La-Nd 11 f. 3 B. Pr-Y 6.4 f 0.2 C. Nd-Y 4 . 9 f 0 . 2 D. Sm-Y 1 . 9 f 0.0 E. Eu-Y 1.45 f 0.05 F. Pr-Gd 6.2 i0.3 G. Nd-Gd 4.1 f 0.6 H. Sm-Gd 1.6 i 0.0 I. Gd-Er 2.0 f 0 . 1 J. Pr-Dy 8.3 f0.8 K. Nd-Dy 7.0 i 0 . 8 1.7 f0.1 L. Eu-Dy M. Gd-DY 1.35 i 0.05 9.5 f 1.6 N. Nd-E; 5 . 5 f0.3 0. Sm-Er 6.0 f 0.4 P. Nd-Er 2.7 i0.2 Q. Sm-Er
Rare earth combinations Pr-Nd Pr-Sm Nd-Sm Nd-Er Sm-Er Pr-Gd Sm-Gd
complexing agent this could account for results. However, equilibria calculations indicate that the cations are usually about equally distributed between both complexes. Apparently kinetics are involved. If one cation is released more quickly than the other then the overall effect would be the preferential precipitation of one cation, which does fit experi-
ANALYTICAL CHEMISTRY
1.5 2.6 1.9 9.8 2.6
2.3 5.4 3.1
1.3 2.6 1.9
6.2 1.6 8.3
3.6 1.6 8.1
2.2 7.0 2.4
1.5 2.6 1.9
2.0 3.7 2.1
1.7 3.9 2.4
mental results. Unfortunately, there is little information about the kinetics of such a reaction. Neither a pair of complexing agents nor one precipitant is superior throughout the rare earth series. One or more selective processes are operating. Somehow one rare earth cation is preferentially released in solution while the other tends to remain complexed. How this selectivity is achieved has not been deduced. A determined attempt was made to develop an equation that would predict lambda values for the system under study. Such an equation would provide a theoretical basis for understanding the separations achieved as well as having practical utility. Using solubility product (6) and formation constant expressions (9, I O ) , a set of equations was developed. Despite the awkward form of the final equations, the calculation of approximate lambda values was made with a computer. The (9) E. V. Kleber, "Rare Earth Research Developments," Uni-
versity of California, Conference Center, Lake Arrowhead, Calif., October 1960, p. 1. (10) S. Chaberek and A. E. Martell, "Sequestering Agents," Wiley, New York, 1959, p. 505.
details of the derivation and the Fortran program will be furnished upon request. Limited success was realized in making computer calculations. The chief correlation is in systems using the chelating agent DTPA. The order of magnitude of the calculated values is fairly good and the trends are obvious (Table VIII). With other chelate systems the calculations were of questionable value. Even though a wide variety of concentrations of all forms of both rare earths could satisfy a given lambda, the computer calculation came close to predicting the actual concentrations (Table IX). ACKNOWLEDGMENT
The authors thank Orville Goering and D. W. Kraushaar for their assistance with the Fortran programming and calculations. RECEIVEDfor review January 6, 1967. Accepted September 29, 1967. Supported by the U. S. Army Research OfficeDurham through grant number DA-ARO(D)-31-124-G517. Symposium on Analytical Chemistry, St, Louis Society of Analysts, March 1965, St. Louis, Mo.
Viscosity of Liquid Water from 25" to 150" C Measurements in Pressurized Glass Capillary Viscometer Alexander Korosi and Bela M. Fabuss Monsanto Research Corp., Boston, Laboratory, Ecerett, Mass.
An apparatus containing a pressurized glass capillary viscometer has been developed for application in the measurement of the viscosity of liquids over, or near, their atmospheric boiling point. The assembly is pressurized with hydrogen and the diffusion of hydrogen through a palladium-silver membrane is used to lift the test liquid into the efflux bulb of the viscometer. The apparatus provided relative measurement, with an estimated precision of &0.2%, on liquid water in the temperature range 7 5 O to 150' C. I t can be used wherever the presence of hydrogen is compatible with the test liquid. Measured water viscosities, over the range 25" to 150" C, were correlated. The correlation represented the data with an average deviation of &0.17% and a maximum deviation of 0.49%. Recommended values for water viscosities are given. A detailed description of the apparatus, the experimental method, and results of measurements on liquid water are reported.
KNOWLEDGE OF THE VISCOSITIES of sea water brines is important in the development and operation of desalination processes. To obtain systematic information on the electrolyte solutions involved a new apparatus was developed that allows viscosity measurements on these and on other liquids under hydrogen pressure at temperatures up to 150O C . The apparatus was first used to determine the viscosity of water in the 75-150" C temperature range. The experimental results were evaluated and compared with literature information. T t h this new set of measurements, the uncertainty among -the generally used reference data was reduced, and we feel strongly that the precision of water vis-
02149
cosity data, especially in the 75" to 150" C temperature range, has improved. Numerous high temperature viscosity measurement methods, devoted mainly to establishing the pressure dependence of viscosity, are reported in the literature (1-8). With few exceptions, these measurements were of limited precision and required elaborate equipment. However, a simple and accurate method was reported by Hardy and Cottington (9) for measuring the viscosity of water and deuterium oxide up to 125" C. They used a pressurized glass capillary viscometer and found that pressurization to 35 psig, to prevent boiling, had no effect on the efflux time measured. Their results were confirmed by Heiks et af. ( I O ) , who used a falling body viscometer equipped with a radioactive plummet. (1) E. Kuss, Z. Angew. Phys., Bd. IV., 203 (1955); Ibid.,Bd. VII, p. 372. (2) N. H. Spear and L. P. Herrington, ANAL.CHEM.,23, 148 (1951). (3) F. Glaser and F. Beghardt, Chem.-lng-Tech.,31,743 (1959). (4) P. E. Parisot and E. F. Johnson, J. Chem. Eng. Data, 6, 263 (1961). (5) B. E. Eakin and R. T. Ellington, Trans. Am. Inst. Mining Met. Perrol. Engrs., 216, 85 (1959). (6) F. Walter and W. Weber, Angew. Chemie ( E ) , Bd. 19, 123 (1947). (7) W. Weber, Rheol. Acta, 2,131 (1962). (8) W. Weber, 2.Angew. Phys., Bd. XV, 342 (1963). (9) R. C. Hardy and R. L. Cottington, J . Res. Natl. Bur. Std., 42, RP1994 (1949). (10) J. R. Heiks, M. K. Barnett, et al., J . Phys. Chem., 58, 488 (1954). VOL 40, NO. 1, JANUARY 1968
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