H. KAKIHANA, N. MARUICHI AND K. YAMASAKI
36
tions involving the internal electrical properties of the adsorbed ion are responsible for the action of inhibitors of the type under consideration. be noted also that, if the proposed Po. It lariaation mechanism has merit, it Can account for the well-known stirnulathe: effect of such ions as c]- and S- upon ~orrosion without {he netessitY for ad hoc In these cases, polariaation under the influence of the net ionic charge would disdace negative charge from the site of adsorption, ihereby&cre&ng"the activation energy of the corrosion for the The negative ions should also facilitate the forma-
ferrous -
Vol. 60
tion and dissolution of metallic cations by electrostatic action.i8J7 (16) A possible objection to the sssumphon of such polariratiolu may be based u w n the reconnition that an __ an - a metal .- behaveg - .__ . _ . in6nita of 3eatrona. is not pertinent, however, for two rBOW. First, actual metals are in no seme homogeneous energetically. so far 88 corrosion proceasea are concerned. Second. almoat certainly under aerated con&tiona the "surface" of the substrate is not metallio, but a conducting or semi-conducting oxide flm in which deotriod &acontinuities are or may be prominent. (17) The author dadly acknowledgea the benefit of many conferencea with Professor Wm. T. Smith, Jr.. of the University of Tenneasee, concerning the chemistry of technetium and rhenium, and a l ~ o his kindness in providing the very pure potassium perrhenate used in certain erperimente.
hi
reservoir
ION EXCHANGE IN CONCENTRATED SOLUTIONS, NaCl-HCl AND LEI-HCl SYSTEMS BY HIDETAKE KAKIHANA, NOBUOMARUICHI AND KAZUO YAMASAKI Contribution from Chemical Institute, Faculty of Science, Nagoya University, Nagoya, Japan Received June 1 , 1066
Ion exchange was studied in the concentrated solutions of NaCl-HCl and LiC1-HCl systems. The amount of water adsorbed in the resin was calculated from the difference of the amount of hydrogen ion before and after the ion-exchan e equilibrium. The amount of adsorbed water decreases as the concentration of chloride ion increases both in NaCl-H& and LiCl-HCl systems. Differences were found between NaCl-HCl and LiCI-HC1 systems. The anomaly found in the latter system was explained b assuming the dehydration of Li ion in concentrated solutions. I n NaCl-HC1 system the Donnan equilibrium was founJto exist between the resin and the solution phases. The same equilibrium exists only in 0.1 and 0.3 N solutions in the LiC1-HCl system.
Although ion exchange in concentrated solutions has been applied successfully by several investigators to the separation of transuranic elements from rare earths' and mutual separation of transition elements,2 etc., very few investigations have been reported on ion-exchange equilibria in solutions of large ionic strength. The present work is an attempt to study the equilibria of ion exchange in concentrated NaCl-HC1 and LiC1-HC1 systems. Experimental (1) The Resin.-The resin used was Amberlite IR-120 (hydrogen form, medium cross-linkage) of mesh size 30-50 obtained by dry screening at 40" and i t contained 17% of water. The amount of resin used in one batch experiment was 3.6 g., i.e., about 15 milliequivalents. (2) Reagents.Sodium chloride was reci itated from its saturated solution by hydrogen chlorig. lithium chloride was prepared by adding hydrochloric acid to lithium carbonate, which has been purified by recrystallization. Hydrochloric acid was distilled twice. (3) Procedure.-A certain amount of resin (exchange capacity E, meq.) was put into a glass-stoppered erlenmeyer flask (capacity 100 ml.) containing a known quantity (V, ml.) of 1-5 N NaCI-HCl Or 0.1-12 N LiCl-HCl mixture:. After shaking for 40 min. in a thermostat at 25.0 f 0.1 , the resin was quicklv separated from the solution by suction on a glass filter. The time required for filtration was 60 sec. An aliquot of the filtered solution was titrated with 0.1 N barium hydroxide solution, and the hydrogen ion concentration (H+)s was determined. If the volume change of the solution can be neglected before and after the ion exchange, the total amount of h drogen ion in the solution, [H +]a, is given by [H+]s= (H& V.. After the aboveproredure, the chloride ion concentration (Cl-)s was determined by Fajans argentometric titration, using fluorescein -
~
_
_
(1) K. Street, Jr., and G. T. SeabOrg, J . Am. Chem. Soc., TO, 4268 (1948). (2) K. A. Kraus, et aI.#ibid., 71, 3263. 3855 (1949); 73,4293, 5792 (1950); 78, 9, 13, 2900 (1951); 74, 843 (1952); 76, 1400.3273 (1953); 76, 984, 5916 (1964); 77. 1383 (1955).
E - [H+]R [Cl-IO [cl-]Q - [Cl-IS [Cl-IQ - [H'IO [Na+lo - [ N ~ + ] Q - [ N ~ + ] R= I(Cl-)s - (H+)sIV [H+ls = (H+)s VI [cl-]s 3 [Cl-]O - [cl-]Q [CI-IO = [H+]o - [Na+]o [N~+]R [Cl-]R = [Na+lQ [Na+Is =
-
'
(1)
SOLUTIONS ION EXCHANGE IN CONCENTRATED
Jan., 1956
outer solution phase, is important in ion exchange and many authors have tried to determine its amount by various methods.'-? However, the methods used by previous investigators in dilute solutions cannot be used in the present ion-exchange studies in concentrated solutions. The amount of adsorbed water was therefore estimated indirectly by the following calculation. The total amount of hydrogen ion in the resin and the solution is equal to (H+)E(V - A )
+ [H+]Q-k [H+]R
where A is the volume of water adsorbed in the resin phase at equilibrium, and the first term denotes the amount of hydrogen ion in the outer solution. The total amount of hydrogen ion is also equal to E [H+]o. Thus
+
(H+)E(V- A ) -k
@+]Q
f [H+]R = E f [H+lo
By arranging the equation
- (E+
A = (H+)8V -k [H+lQf m + l R (H+h
[H+101 A[H+l (2)
most concentrated solution the amount of adsorbed water is not negligible, so we had to replace V with (V - A ) in formula (1) in the following calculation. (2) Adsorption of Complex Species.-If some complex species were captured by the resin so firmly that they could not be washed out with water, [Cl-]R, namely, [Cl-lo - [Cl-]Q - [Cl-Is would not be nero. And if some complex species were captured by the resin so loosely that they could be washed out easily with water, there might be some quantitative relations between [ N ~ + ] Q(or [L~+]Q),[cl-]Q and [H+]Q or at least those values would be rather high compared with normal surface adsorption. However, neither of these cases was observed in our experimental data. We can therefore conclude that, within the experimental error, we are dealing only with H+(+H20)-Na+(+H20) or -Li+(+HaO) exchange. (3) NaCl-HC1 System.-We shall assume that in this NaCI-HCI system Donnan equilibria are established between ions in the resin and the outer solution. Then we have
(Pm
As all the terms in (2) are determined experimen-
tally, the amount of adsorbed water A can be calculated. Values of A thus determined for NaC1-HC1 and LiC1-HC1 systems are shown in Table I. The
NaCl
(N)
0.5
1.00
2.00 3.00
HCl
(N) 0.53 1.05 2.06 0.00 1.05 2.01 3.01 4.02 0.00 1.01 2.02 3.00 0.00 1.01 2.01
1 .00 0.99 0.89 0.92 -87 .77 .71 .73 0.89 .79 .69 -69 0.85 .73 .65
LiCl
(N)
0.10
1.00
2.00
4.00
6.00
A$.+A&- = A$s+A&AE+A& A&+A&-
HC1
(N)
0.00 1.18 3.53 7.42 11.5 0.00 0.93 2.78 7.19 11.6 0.00 0.93 3.95 8.53 10.3 0.00 1.97 4.31 7.29 0.00 1.95 3.93 4.86
1.06 0.89 .87 .67 .53 0.51 .96 .96 .68 .33 0.55 .93 .69 .39 .32 0.73 .56 .45 .16 0.12 .47
.28 .05
amount of adsorbed water decreases as the concentration of C1- ion increases both in NaC1-HC1 and LiC1-HC1 systems. However, even in the
(5)
Ai,+/AZ+ = A$.+/Ai+
Adsorbed water/g.
dry reain, ml.
(3) (4)
where A denotes the activity of an ion. Dividing (3) by (4) or
TABLE I Adsorbed water/& dry reain, ml.
37
A$.+/A,R+= A$.+ AP+
+ At.+
+ A$+
or (7)
We can use analytical concentrations in place of activities in equations 6 and 7. Then either of the following relations holds
As shown in Fig. 1, our experimental data are expressed by a straight line with the slight deviations in the region of larger values of [Na+]o/{ [H+lo E ] , if [N~+]R/[H+]R is plotted against [Na+]o/ { [H+]o E ) ,while the deviations are much more enlarged, if ([N~']R -k [N~+]Q)/{[H+]Rd[H+]Q)is plotted against [Na+]o/( [H+]o E). Again straight lines with gradient 1 are obtained if [Na+Is/[H+ls and { (Na+ls [ N ~ + ] Q }W+Is /{ [H+]Q) are plotted against [Na+lo/( [H+]o 4- E } as in Fig. 2. These facts show that the Donnan equilibria of Na+ ion and H + ion exist between the resin phase and the solution phase and the differences of activity coefficients are not so large even in the resin phase. It is rather difficult t o decide which is the better expression, (8) or (9), in our
+
+
+
+
+
(4) K. W. Pepper and D. Reichenberg, 2. Elsklrochem., 07, 133 (lQK3); B. R. Sundheim, M. H. Waxman and H. P. Gregor, THIE JOWNAL. 57, 874 (18Ka). (K) K.W. Pepper., D. Reichenbergand D. K. Hale. J . Chem. SOC., 3128 (1852). (6) H. P. Gregor, K.'M. Held and J. Beilin, A d . Chem., 411, 620 (1861). (8) At the preaent stage the quasi-exchange phase oannot be treated b (7) C. W. Daviei and G. D. Yeoman, Trans. Faradav Soe., 40, 868 independently, EO it ia added to either solution phase ( 8 ) or reain 875 (lSK2). phase (8) in the following treatment.
H. KAKIHANA, N. MARUICHI AND K. YAMASAKI
38
VOl. 60
1.6
. 1.4
1 N NaCl
1.2 1.0
0.8 0.2
0.4
0.8
0.6
1 .o
BNa.
Fig. 3.-Effects of concentrations of NaCl on the relations between KI" and molar fraction of Na in the resin, BNs.
0
1 2 3 [Na+lo/([H+lo E ) . Fig. 1.-Values of [ N ~ + ] R / [ H + ]are R shown by full line /( 4and crosses and those of { [ N ~ + ] R [ N ~ + ] Q )[H+]R [H+]Q]by broken line and circles.
+
system too. If we assume the Donnan equilibrium, relations similar to equation 8 and 9 are obtained. Figures 4 and 5 show that relations between
+
present case, though the former seems to be a little better than the latter.
T U C U T zg2
++ a m
0
1
+
2
[Li+]o/([H+]o E ) . Fig. 4.-Full and broken lines show the ratios of Li and H ions in the resin and the outer solution phases, respectively. Values of 1 and 6 N LiCl solutions are shown.
is nearly a constant in the case of dilute solutions, but in the case of concentrated solutions its values vary considerably with the molar fraction of Na+ ion in the resin (&a)' (Fig. 3). K p varies very little with increase of HC1 in 1 N NaCl solution, whereas it variep considerably in 2 and 3 N NaCl solutions. These phenomena correspond to the fact that [N~+]R/[H+]R deviates from a straight line in the region of large values of [Na+]o/( [H+]o +El. (4) LiC1-HCl System.-The existence of the Donnan equilibrium was found in the LiCl-HCl
+
(9) BNa = [ N a + l ~ / ( [ N a + l ~ [H+l)R.
1 2 3 [Li+l~/(IH+lo E ) . Fig. 5.-Full and broken lines show the values of ( [ L ~ + ] Rf [L~+IQ)/([H+IR [H+]Q) and ([Li'Is -k ILi+la)/(lH+la [H+la). resoectivelv. The values of 1 .-.. .. and 6 N LiCl'ioluti6ns are'shown.
0
+
+
+
ION EXCHANGE IN CONCENTRATED SOLUTIONS
Jan., 1956
0
0.2
0.6
0.4
0.8
39
1.0
[Li+lo o1 [Na_+10. rJ-10 [Cl 1 0 Fig. 6.-Full lines show the values in NaCl and broken lines the values in LiCl system: 0, 1 N ; A, 2 N , X, 3 N,of NaCl 0 , 0.1 N, 0 , 1 N , 0 , 6 N of LiCl solution.
+
++
I n the neighborhood of these limiting points the [Li+]s/[H+]s or { [Li+ls [ L i + l ~ } /[H+ls { [H+]Q}and [Li+]o/( [H+]o E ) are expressed by values of KE vary greatly. This can be seen from a straight line. These imply the existence of a Figs. 7 and 8 which show the relations between Kg Donnan equilibrium. There is a minimum in the relation between [L~+]R/[H+]Ror { [Ll+]R [ L i + ] ~ ) /[H+]R f -k [H+]Q] and [Li+Io/( [H+lo E ) when the value of [Li+]o/{[H+]o E) is small, ie., the hydrogen ion concentration is large compared with lithium ion concentration. In order to examine this phenomenon further, the 3 relation between [Li+]o/[cl-]o and [Li+]~/[cl-]Q was plotted in Fig. 6. The same relations found for NaC1-HC1 system are also shown in the same figure. I n Fig. 6, curves for various concentrations of NaCl coincide with each other especially for small values of [Na+]o/[Cl-]o, while curves of the LiCl system do not coincide a t all. For the same values of [Li+]o/[Cl-lo, [Li+]Q/[Cl-]Q is not always con2 stant and the value of [Li+]Q/[c1-]Q increases with increase of Li+ ion concentration. In other words, ad in the region of higher concentrations of T i + ion, % more Li+ ion is captured in the quasi-exchange phase. This may suggest that the hydration of the Ili+ ion decreases in concentrated solution, and its ionic radius decreases and it is, therefore, captured by the resin more easily than in dilute solution. The same phenomenon may occur if some com1 plex ions such as LizCl+are formed. However, as mentioned in (b), we could not confirm the existence of such complex ions from our experimental data. Although a t the present stage we cannot tell definitely which is the case, dehydration or complex formation, the hypothesis of dehydration appears to be more probable. When the hydrogen form of the resin is in contact with LiCl HCl solution, [L~+]R/[H+]R(or 0 { [Li+]R -k [ L ~ + ] Q ) [H+]R /( f [H+]Q}>decreases to a limiting value as [Li+]o/([H+]o E ] de0 0.2 0.4 0.6 0.8 1.0 creases as shown in Fig. 4. For example the limitULi. ing value is 1.3 when the concentration of Li+ is 6 Fig. 7.-Relations between exchange coefficient and molar
+ + +
+
+
N.
fraction of Li ion in the outer solution phase.
H. KAKIHANA, N. MARUICHI .4ND K. ~ A M A S A K I
40
Vol. 60
1.0
3
2 0.5
Q l
2 39
%
0 0
0.5
1.o
aLi.
Fig. 9.-Relations between molar fractions of Li ion in the resin and outer solution phases.
1
phase, but as the concentration increases, K g is no longer a constant. K g is calculated, as follows, taking the Donnan equilibrium into consideration
0 0
0.2
0.4
0.6
0.8
1.o
PLi.
Fig. 8.-R.rlntions between exchange coefficient and molar fraction of Li ion in the resin phase.
and the molar frarttionof Li+ ion in the outer solution phase (aT,i) or that in the resin phase ( p ~ i ) . ' O 'l'hcse figurcs show that the variation of Kg does not depend on the molar fraction of Li+ in the resin phase ( p ~ , i )but , on the change of the molar fraction of thc out,cr solut,ion ( c r ~ i ) (Figs. 7 a.nd 8). In rdat.ivcly tliluto solutions (c.g., 1 or 2 N of total vonccntrstion) l
