INDUSTRIAL AND ENGINEERING CHEMISTRY
916
This is illustrated in the following table for the above example, M = 2 and the minimum theoretical plate difference 6 = 2 ,M = 2 1
N 3 1
2
5
3
3
3
7 5
4
9
Etc.
7
6
1 1 3
1 5
3 7 5
This table shows that for this example where the minimum 6 is supposed to be 2, the following combinations (0,M , AT)of sampling points are permissible in so far as the table has been carried (0 refers to the bottom sample): 0, 2, 5 ; 0, 2, 7 ; and 0, 2, 9. -4 similar calculation using the intermediate sample plate as M = 3 and 6 = 2 gives the following permissible combination of sampling points for j = 2 and 3: 0, 3, 5; 0, 3, 7 ; 0, 3, 8 ; 0, 3, 10. Again, taking the intermediate sample at the third theoretical equilibrium plate from the bottom sample ( M = 3),and requiring the minimum 6 to be equal to 3 instead of 2, the following combinations are permissible for j = 2 or 3: 0 , 3, 7 ; 0, 3, 8; 0, 3, 10.
Higher values of j greater than 3 required more than 8 theoretical plates in the multiplate still. An examination of the permissible groups 0, M , N above reveals that the numbers in a group are prime with respect to one another. That is, M and N in any one permissible group do not contain a common integer factor, and M is not divisible by N to give an integer, and vice versa. For example, the groups 0, 2, 4 will not yield the one-plate curve because 2 is a factor of 4. Similarly, for 0, 2, 6; 0, 3, 6; and 0, 4, 6. In this last instance, although 4 and 6 are not integer multiples of one another, they both do contain the common factor 2. This fact makes the group 0,4,6 unsatisfactory. The plate number six, the sixth theoretical plate from the bottom sample, has an integer factor in common with all numbers between 0 and 10. Thus, a multiplate still of less than eleven theoretical plates should not be sampled a t the sixth theoretical plate when the data are to be treated by the three-sample method. LITERATURE CITED
(1) Fenske, M. R., Myers, H. S., and Quiggle, D., IND.ENQ.CHEM., 42, 649 (1950). (2) Herring, J. P., M.S. thesis, Pennsylvania State College, 1948. RBCEIVED for review January 25, 1851.
ACCEPTED November lQ, 1951.
of Ions in Aaueous
Engineering p ","c:s -, development
Vol. 44, No. 4
I I
Solution with Glass STUDIES WITH RADIOACTIVE TRACERS ARTHUR 0. L O N G AND JOHN E. WILLARD UNIVERSITY
OF W I S C O N S I N , M A D I S O N , WIS.
I
T HAS been shown earlier (11)that radioactive tracers afford a sensitive and relatively rapid means for studying the sorption of ions from solution by surfaces. This exploratory work on techniques and on the sorption and desorption of sodium and cesium ions on glass has now been extended. Particular emphasis has been placed on experiments designed to determine whether the sorption process is an ion exchange process uncomplicated by other processes. I n this work, a8 in the previous investigations, the specimens have been glass squares, 1 inch on a side, cut from soda-lime-silica microscope slides (11). Except where otherwise specified all of the specimens were scrubbed under water, rinsed with carbon tetrachloride, and moderately flamed before use. The radioactive-counting techniques were similar to those previously described (11). Results are given in terms of monolayers sorbed, the monolayer being arbitrarily defined as the number of atoms required' to cover the macrosurface area of the sample if each ion covers an area equal to the square of its ionic diameter. SIMULTANEOUS SORPTION AND DESORPTION O F SODIUM IONS
I n order to observe the rates of simultaneous sorption and desorption of sodium ions, glass specimens were tagged by immersion in a solution of sodium ions tagged with Na2*(15-hour halflife), rinsed, and immersed in a solution of the same concentration tagged with Na22 (3-year half-life). The amount of NaZ4sorbed just prior to immersion in the Na22 solution mas determined by drying and counting one of the samples a t this time. The sum of the Na22 sorbed and the Na24 remaining after immersion in the
Na22 solution was determined from the total count due to the two isotopes when each sample was removed from the Na22 solution. The NaZ2was determined from the residual count after the Na24 had decayed. Corrections were made for Na24 decay and for the long-lived impurity (11) which was found on the Ns24 control sample and was assumed to remain in equal quantity on the samples immersed in the Na22 solutions. The results of such teste made for different times of immersion, different temperatures, and different pH's suggest a t first sight that the rates of simultaneous sorption and desorption of sodium ion are qualitatively similar (Figure 1). In each case the initial rate of desorption at 72" 6. appears to be greater than the corresponding rate of sorption. After this initial interval the sum of the monolayers represented by the sorbing and desorbing curves remains approximately constant. This constancy does not, however, indicate that sodium ions were entering and leaving the surface at equal rates. The plotted values for monolayers of Na24 are calculated on the assumption that the specific activity (disintegrationsper minute per milligram of sodium) of this isotope during desorption was the same as before it was sorbed, Ghereas it quite certainly had been decreased by inactive sodium in the glass. If such dilution occurred, the rate of departure of sodium from the glass was greater than indicated by Figure 1 and significantly greater than the rate of sorption, indicating a continual net loss of sodium from the glass. LEACHING O F NEUTRON-IRRADIATED GLASS SAMPLE§
I t may be calculated that a 1.63-gram glass square of the type used in this work, bombarded with a thermal neutron flux of 1012
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
April 1952
917
A
Hours
1
O.O1'
Minutes
2.9
3.0
3.1
L x T
I
3.2
I
33
103
Figure 2. Sorption of Sodium Ions on Soft Glass as a Function of Temperature and Presoaking of Glass
0 06 5L
Immersion time, 25 minutes Initial pH, 7.2 0.023 M NaNOa Final oH. 8.5 Ea Apparent activation energy B Not oresoaked d Presoakea inwater for 50 hours 0 Presoaked i n 6 M HCl for 50 hours 0 Presoaked i n 0.2 M HNOa for 86 hours 0 T w o 0 falling a t same point Double circle Two 0 fallins a t same point All samples moderately flamed before treatment
-7 1 1-
2
3
Hours immersion l i m o
'4
5
Figure 1. Simultaneous Sorption and Desorption of Sodium Ions
--
Na+ 0.023 M 0 Naa2 pH 10 for B and C,7.5 for A 0 Nags Just prior towimmersion i n Naaa solution, t h e samples were immersed int0.023 M Na+ solution containing Na24 for 5 hours for A and C, for 10 minutes for B ; temperature and H of t h e Naan solution same as used i n t h e subsequent immersion; times of immersion in Na22 solution shown i n Figure 1
b a
neutrons per square cm. per second for 4 hours, will give 1.9 X 1010 disintegrations per minute of Na*4 and lesser amounts of activity of Si, Ca, K, and other elements. This amounts to about 2000 disintegrations per minute per Angstrom thickness of the glass; thus, such samples should be useful in studying the rate of removal of surface atoms from glass by leaching solutions. Two sets of SAMPLES WITHOUT FOREIQN IONPRETREATMENT. $lass specimens were irradiated with thermal neutrons, one for 1hours at a flux of about 7 X 10'0 neutrons per square cm. per second and another for 4 hours a t a flux of about 1019 neutrons square cm. per second. Each specimen was then immersed n a leaching solution in a Teflon container; the solution was evaporated t o a small volume in the container and transferred to a counting plate where it was evaporated to dryness for counting. R i s i n g tests showed that the transfer was essentially quantitative. Some results of these tests are given in Table I. The relative counting ratee shown in the last column of the table were obtained by choosing one sample of leached activity from each bombardment as a standard and comparing the counting rates of the other samples to it. It was assumed that the distribution of radiospecies in the different samples was the same and that their decay rates were therefore the same. A decay curve of sample B-1 plotted from 8700 to 100 counts per minute showed a half-life of 15
hours throughout. Although the sodium accounts for less than 10% by weight of the glass it may be calculated that it contributes more than 90% of the activity for about 6 days after bombardment. It seems possible to draw the following conclusions from the data: Activity is leached from the bombarded slidesmuch more rapidly during the first interval of immersion in 0.1 N nitric acid than during successive intervals but leaching continues a t a lower but approximately constant rate during several immersions followin5 the initial immersion. This behavior is observed a t both 80 and 23' C.
TABLEI. RELATIVEACTIVITYLEACHEDFROM BOMBARDED GLASSSAMPLES BY DIFFERENT SOLUTIONS of Leachin-Relative Soh. Temp., C. Activity0 GLASSFROM FIRSTBOMBARDMENT 1 30 0.1 N "Os 80 1.0 1) 30 0.1 N HNOs 80 0.1 2 30 0.1 N HNOa 80 1.1 2) 30 0.1 N HNOa 80 0.1 3 30 Ha0 p H 6 80 1.2 GLASSFROM SECONDBOMBARDMENT 1 lo 0.1 N "0: 80 1 0.1 N "01 80 0.1 lo 0.1 N HNOa 80 0.07 ld l12 o 0.1 N H N O a 80 0.1 2 0.1 N "01 23 0.8 lo 0.1 "NO: 23 0.15 10 lo 0.1 N HNOs 23 0.04 0 . 1 N HNO; 23 0.03 10 lo 0.1N H N O t 23 0.06 Ha0 23 0.4 3 10 4 210 He0 23 0.5 52 10 0.1 N HNO: 23 0.25 62 0.1 N HNO: 80 0.51 6b 10 lo 0.1 N H N O a 80 0.09 For an estimate of absolute amounts of sodium removed see Table 111, b c v d s e Successive immersions of a single glass sample. f Specimens 5 and 6 were heated nearly t o fusion prior t o bombardment.
Sample
No.
:t
it
It
Q
-Conditions Time, min.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
918 0.20-
Water is approximately as effective a leaching agent under the conditione tried as is 0.1 N nitric acid. Glass heated nearly to fusion prior to bombardment is leached somewhat leea readily than that which is only moderately flamed. SAMPLES WITH FOREIGN IONPRETREATMENT. If sorption processes at a glass surface are reversible ion exchange reactions uncomplicated by other processes, it would be expected that glass which had been subjected to prolonged soaking in a solution of a cation foreign to the glass would have a11 of the readily available sodium in the glass replaced. I n this case it should not be possible to remove further sodium in a subsequent short leaching period. In order to determine whether glass behaves in accordance with this prediction, glass slides were soaked for 330 hours at room temperature in solutions of 0.2 M barium nitrate, 0.2 M potassium nitrate, 0.2 M nitric acid, and 0.2 M sodium nitrate, following which they were bombarded in the Argonne pile for 4.2 hours at a Pax of about lo1*neutrons per square cm. per second. They were then immersed in water and the leached activity was a n t e d . The activity leached from the samples representing each of the four types of presoaking decayed with the 15-hour halflife typical of Na24. The counting rates of the leached activities corrected t o the same time after the end of bombardment are given in Table 11. These data indicate that a 10-minute leaching with water removed appreciable and approximately equal
Vol. 44. No. 4
amounts of sodium from glass which had been presoaked in 0.2 N solutions of potassium, barium, or hydrogen ions for 330 hours. Approximately twice as much was removed from the samples presoaked in a 0.2 N solution of sodium ion6 and seven times aa much from those which had not# been soaked. The specific activity of the sodium in the glass at the time represented by the data of Table I1 wasabout 4200 counts per minute per microgram or 2750 counts per minute "monolayer," calculated from the approximate data for the neutron exposure. The leached sodium activity WBS sufficient so that it probably would not have been possible to distinguish the maximum amounts of barium and potassium activity which could have been present. ESTIMATED DEPTHOF LEACHINQ.If the total disintegration rate of the sodium in a bombarded glass slide is estimated from the bombardment data, and the disintegration rate of the leached activity is estimated from the counting rate, the ratio of these values can be used as an estimate of the fraction of the sodium originally present which has been leached out. Such estimates for each of the three bombardment8 discussed above are given in Table 111. Since neither the neutron flux to which the samples were exposed nor the absolute counting yield under the conditions of these experiments is accurately known, these estimates are meant to serve more aa an illustration of a potentially useful method for such studies than as n quantitative evaluation. More reliable estimates could be obtained if the specific activity of the glass were experimentally determined b y dissolving a weighed sample and counting a thinly spread aliquot evaporated on an inactive glass plats. POSSIBILITY OF RADIATION DAMAGB.It is important to note that the leaching data of Tables I, 11,and I11 were obtained with glase which had been exposed to a sufficient neutron irradiation so that the microsurface structure may have been altered. Furthermore, Na24 atoms which constituted the activity leached out and measured probably had a kinetic energy of recoil of several thousand kg.-cal. per mole at the time of formation by the Na*a ( n , ~Na24 ) reaction. All of the neutron-bombarded glass samples were visibly darkened.
f
TEMPERATURE COEFFICIENT AND DH EXPERIMENTS
EFFECTOF ACIDA N D WATERPRESOAKING. If the rate-controlling step in the sorption of sodium ions on glass were a cation replacement reaction with ion pairs of the surface, it might be expected that the temperature coefficient of sorption would be difTABLE11. RELATIVE ACTIVITYLEACHEDFROM BOMBARDED ferent for a surface composed predominantly of -SiOH groups, GLASSSAMPLES PRESOAKED IN DIFFERENT SOLUTIONS obtained by prolonged soaking in acid, than for unsoaked glass Conditions of Leaching (11). Exploratory experiments [Figure 4 of (11)] suggested Preaoaking w --ht,i Water--Na24 Activityn, 8oln. Time, min. Temp., C. Counts/Min. that soft glass samples which had been soaked in 6 N hydrochloric Ba++ 10 Room temp. 910 acid had a higher temperature coefficient for sorption of sodium Ba++ 10 80 1230 10 Room temp. 740 K ions than samples which had not been presoaked. More comRoom temp. 620 K+ 0.25 plete measurements over the same range of conditions have now 10 Room temp. 780 H+ 10 80 1150 H+ been made. The results, given in Figure 2, seem to indicate that, Room temp. 1470 Na 15 10 80 2300 Na within the experimental error, there is no difference between the 10 Room temp. 5000 None temperature coefficients for the samples soaked in 6 N hydro10 80 5500 None Noneb 10 Room temp. 2280 chloric acid or 0.2 N nitric acid and those which were not soaked. a 58 hours after bombardment. As in the earlier tests, the sorption is about b Flamed nearly t o fusion after bombardment. fourfold lower in the case of the presoaked samples than in the case of the nonsoaked DEPTHOF GLASSLBACHBD TABLE 111. ESTIMATED Neutron Fraction of samples. Soaking in 0.2 N nitric acid and Length of Flux, c Conditions of Leaching-Total Ne Depth of in water seems to have about the same efBomb., Hr. Cm. -1 Sec.-l Time, min. Soh. Temp., C Removed Leaching, A. fect as soaking in 6 N hydrochloric acid. 21 7 x 10'0 30 0.1 N HNOa 80 1.1 x 10-6 55 1 x 10'2 10 0.1 -4' HNOa Room temp 1.6 X 10-6 80 These results eliminate any poRitive basis 4 4 1 x 10'2 10 Ha0 Room temp. 0.69 X 10-6 35 for speculating (11)that the temperature1 x 10'2 10 Hi0 Room temp. 1.2 X 10-5 60 4 .a dependent step of the reaction is related to +
+ +
+
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
April 1952
0.10 -
01
c 0
-n 0
0 C
0
5
;O 0 5 . L
B
n
5
z
4 /
4
.
Immersion time, 1 minute 0.023 M Na+ 0 25'C. 45oc.
the physical condition of the surface or to the ratio of -SiOH to -SiONa groups in the surface. It is pertinent to note, however, that a silica surface shows both lower sorption than a silicate surface and a negat
