LAWRENCE DRESNER AND KURTA. KRAUS
990
The stability of the complexes found in this xork may be compared to the findings of other JTorkers in Table I. h critical survey by Carleson and Irving's showed TABLE I Author
N e t h o d , conditions
log p-1'"
CarlesonZ0 Cation exchange, 20°, 0.69 &I' H(C104 C1) medium, pH 0.16 -1.82 Diete7 Ether extraction, varying HC1 medium Mendee* Kitrobensene extraction, varying HC1 medium This work Anion exchange, amine extraction, varying HC1 and KaCl media - 0 50
log p i ' *
log pi'*
+
-0 43
-
.53
-1 26
.32
-1 12
.45 - 1 . 6
that earlier values of constants for formation of IiiClz+ and Inc13 probably are incorrect. I n particular, the polarographic work of Schuff e, Stubbs, and WitinanZ2 may be reevaluated, taking account of the irreversibility of the wave in absence of Referring the half wave poteiitials E,/,, in mv., to the extrapolated value for zero hydrochloric acid concentratioii23 instead of to the perchlorate solution,22permits the calculation of the left side of the eq.
- log ;r;pir*az= const.
+ 3 log a 3(E,,i, - El/,O):'0.059
(11)
as function of log a, giving values agreeing with those obtained in the present work (Fig, 3 ) . The present work leads to the conclusion that InCl2+ is relatively less important than found by Carleson, while IiiCl3 (19) B. G. F. Carleson and H. Irving, J . Chem. hoc., 4390 (1954). (20) The values reported b y Carleson'g are valid for constant ionic strength, a n d hence are n o t truly pz'* values. To conveit them, --z log YtHci a t ionic strength 0.69 was added to the constants.21 (21) G. P. Haigt, Jr., J. Zoltevica, and K. Evans, Acta Chem. Scand., 16, 311 (1962). ( 2 2 ) J. A. Schufle, hl. E". Stubbs, and R . E. TT-itman, J . Am. Chsm. Sac., '73, 1013 (1951). (23) E. D. Jloorhead and \T. 11.RIachevin, Anal. Chem., 34, 209 (19G2).
T'ol. G7
is more important than found by Dietz and Rfendez. In any case, this work agrees with previous work in showing the absence of InC1S2- and 111Cle3- in aqueous solutions. If in aqueous solutions higher anionic complexes are not formed, it is reasonable that this would also be the case in the anion-exchange resin phase, with its lower effective dielectric coiistant, because of the repulsion of the negative charges. This argument holds, however, only if the species are ionic, as they probably are at the dielectric constants encountered in the resin and aqueous solutions. In xylene solutions of triisooctylainmonium chloride, however, the dielectric coiistant is presumably so low that no ionic dissociation occurs. Under such conditioiis it is conceivable that amine hydrochloride molecules react with neutral indium chloride molecules to give neutral species with more thaii four chloride ligands. If indeed indium tends to retain hexacoordination. the species RIn(H20)zC1, and RsInClc are likely in the organic phase (with possibly some of the intermediate R~Iii(HzO)C16, although the present results do not require its coiisideratioii). The important point here is, that contrary to former belief,11,*4it is not possible to conclude from the species found in the organic phase in amine extraction experiments on the species predoniinaiit in the resin in the corresponding anion-exchange experiments. The different mechanisms of distribution, due to great differences in the effectiye dielectric constant, would make such a direct comparison generally invalid. Acknowledgments.-The authors thank Miss S. Yitshaki and Mrs. N. Bauman for technical help in carrying out the experiments. D. RI. thanks Prof. G. Stein of the Hebrew University, Jerusalem, and the Scientific Director, Israel Atomic Energy Commission, for making possible the use of the work as part of a Ph.D. thesis. (24) P.Marcus, Bull. Res. Counctl I s r a d , SA, 17 (1959).
ION EXCLUSION ,ASD ShLT FILTERISG ITITH POROUS IOS-EXCHA%SGE MATERIALS' BYLATVRENCE DRESXER AND KURTA. Bix-ius Oak Ridge Satzonal Laboratory, Oak Ridge, Tennessee Received August 20, 1962 A theoretical analysis is given of the salt filtering properties of microporous bodies composed of particles with ion-exchange active surfaces. The computations are based on solutions of the Poisson-Boltzmann equation for uniformly charged cylindrical micropores and for a regular lattice of charged rods; point charges are assumed for the interstitial solution. The results are discussed in terms of anticipated salt rejection as a function of effective pore radius.
Ion-exchange materials hare long been known to have the property of excluding electrolytes. In general, the coiicentration of invading electrolyte I n an ion exchanger is less than in the surrounding aqueous phase provided the concentration of the latter is not too high. The ability of exchangers to exclude electrolytes forms the basis of the ion exclusion process2 (1) Work performed for the Offioe of Saline Water, U. S. Department of the Interior, a t the Oak Ridge National Laboiatory, Oak Ridge, Tennessee, operated by Union Carbide Corporation for the U. S. Atomic Energy Commission.
and of the electrodialysis method for desalination. It should also be useable for desalination in a hyperfiltration (reverse osmosis) method, since the relative transport of water and salts through an exchanger membrane should be closely related to their relative amounts in the membrane. Salt filtration by ion-exchange membranes was discussed in considerable detail, and with good coverage of the earlier literature, by lIcKelvey, (2) See e . g . , R. A l . Wtieaton and W. C Bauman. Ind. Eng Chem., 45, 228 (1953): Ann. &V. Y . Acad. Scz., 5'7, 159 (1953).
SALTFILTERING WITH POROCS IOK-EXCHANGE MATERIALS
hlay, 1963
Spiegler, and W ~ l l i e . ~These authors studied filtration of NaCl solutions ((1.01 to 1 AI) and CaClz solutions (1 M ) with commercial membranes of the type used in electrodialysis equipment. They found reasonably good salt rejection but extremely low flow rates a t pressures of 1000 p.s.i. It thus appeared of interest to examine the principles of salt screening by somewhat more “porous” materials and, in particular, to evaluate the properties of microporous bodies consisting of small surface-charged (ion-exchange active) particles. Such a configuration may be expected to act as a “salt filter” which combines reasonable salt rejection with good flow. Even a relatively small increase in the effective pore size of a “salt filter” compared with the effective pore size of an ion-exchange membrane should cause considerable increase in flow, since, for example, according to Poisseuille’s law, laminar flow varies with the fourth power of the pore radius. 1. Thermodynamic Considerations.-The exclusion of electrolytes from ion-exchange materials can readily be understood by considering the condition of equilibrium for any component J PJ =
rUJ(r)
(1)
where 1.1 is the chemical potential and the subscript (r) designates the resin .phase. When the reference states of J in both phases are the same, eq. 1 yields aJ =
aJ(r)
(2)
where a is the activity of J. Equation 2 holds point by point in each phase and across the phase boundary. When J is a 1-1 electrolyte, then rnlmzyd
‘ = m1(r)’m2w’y+(r)‘z
(3)
where m denotes concentration in grams per kg. of water, y& denotes the mean activity coefficient, and the subscripts 1 and 2 denote counter- and co-ions, respectively. The primes on ml(r)’ and ma(,)’ are to remind the reader that the actual ionic concentrations in the exchanger phase may be strongly non-uniform fuiictions of position, Associated with the actual concentrations is a mean activity coefficient yrt(r)’ assumed space-independent. A more convenient formulation of the equilibrium condition (2) entirely in terms of space-independent (stoichiometric) quantities is
(4) where the unprimed concentrations ml(r) and m2(,) are mlmzy.+2 = micr)mz(r)yh(r)2
spatial averages of m l ( r ) ’ and m2(,)‘ over the liquidfilled volume of the exchanger phase or porous body and yh(r) is the associated mean activity coefficient. I n addition to eq. 4, the average concentrations in the two phases satisfy the electroneutrality requirements ml = m2 = mJ mlw = mqr)
+ mocr)
(54
tioiis 4 and 5 can be solved for the ionic concentrations in the resin and yield4
When the capacity of the exchanger mo(,) is high enough or the external electrolyte concentration mJ is low enough, the second term in the square root of eq. 6 will be small compared to the first, and eq. 6 may be written with good accuracy as
Another form of the condition Qf validity of eq. 7 is m2(r)> 1).
Thus w ~ o ( ~is) pthe same as in the related capillary. In such a case, eq. 45 becomes identical with eq. 37 aiid the lattice cell and the equivalent capillary have the same value of (e-?. Thus when R'IR, calculated from eq. 45 and 41 is plotted against ( e - < ) for the lattice cell, the curve of Fig. 4 is again obtained. Secondly, the geometric relation (46) between ?TLO(~ ) p and the radius R' from eq. 45 i s identical with eq. 42. Thus to each capillary radius R' determined by a given u and yk2m~2/mZ(r) there corresponds a manifold of lattice cells (with void fractions not exceeding 36%) whose parameters R and ROmust satisfy eq. 45. This is a very satisfactory state of affairs, first because the lattice model is presumably a much better replica of a porous bed than the capillary model, and second because a good way to compare these tmo dissimilar models is through eq. 45 which says that the volumeto-surface ratio is the same in both models. It is plausible to expect that to every capillary radius R' detcrmined by a u and a ratio there corresponds a porous bed with a volume-to-surface ratio equal to R' '2. Acknowledgment.-We wish to extend our heartfelt gratitude to Prof. George Scatchard for a series of illuminating discussions.
THE STRUCTURE OF ACTIVE CENTERS IX NICKEL CATALYST. 11. BY ITURO UHARA, SHOZO KISHIMOTO, TADASHI HIKIXO, YOICHIKAGEYAMA, HIDEBUMI HAJIADA, BXD YOSHIHIKO xUX4T.4
Chemzstry Department, Faculty of Science, Kobe Unaversnty, Milzage, Kobe, Japan Received August 2'0, 1962' When slightly cold-worked nickel is annealed, the disappearance of vacancies and dislocations takes place a t different temperature ranges, T , and TO,respectively, and the influence of the degree of cold-working and the existence of impurities on TOis considerable. The change of the catalytic activities of cold-worked nickel due to annealing at various temperatures wa9 measured for the following reactions: ( A ) hydrogenation of cinnamic acid, (B) dehydrogenation of ethanol, (C) decomposition of hydrogen peroxide, (D) para-ortho conversion of hydrogen, and (E) electrolytic generation of hydrogen (overvoltage). The activities decreased in two steps a t temperature ranges, Tal and T k 2 , and these temperatures coincided approximately with T , and TO, respectively, when specimens of the same material were employed for the measurements of both physical properties and catalytic activities. It was concluded that the active centers annealed a t Tal are point defects at the surface which coexist and vanish together with vacancies in the bulk metal, and that those annealed a t TA?are the terminations of dislocations at the surface.
Introduction The structure and the temperature of disappearauce of lattice defects in metals -which were subjected to cold-Jvorking, etc., have been studied in recent years by measuring the rate of release of defect energy (AP),'
changes of density (D), extra-resistivity (Ap), and hardness ( H ) 011 annealing. ' Typical behavior of twisted (1) L. M. Clarebrough, M. E. Haryreaves, and G . W.\Test, I'roe. k!oii. sot. (London), A232, 252 (1955); 'wag., 1, ,528 (1956); TT-. B ~ "Defects in Crystalline Solids," The Physical Society, 1 ~ 5 5p. , 212.
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