Anion exchange of metal complexes—I. Anion resin invasion: Dowex 1 × 8 and thiocyanate salts

J. inorg, nu¢l. Chem., 1966, Vol. 28, pp. 1707 to 1713. Perpmon Pre~ Ltd. Printed in Northern Ireland

ANION EXCHANGE

OF METAL COMPLEXES--I

ANION RESIN INVASION: DOWEX 1 × 8 AND THIOCYANATE

SALTS

G. ZACHAiUAWS, W. R. HERRERA* and C. J. CUMMISKEY Department of Chemistry, St. Mary's University, San Antonio, Texas (Received 16 August 1965; in revisedform 7 December 1965)

Abstract--Essential agreement has been found between a direct and an indirect method of evaluating resin invasion usingKSCN as non-exchange electrolyte. The indirect method has been further applied to lithium, sodium and ammonium thiocyanates as non-exchange electrolytes. Results obtained in all cases are similar, with the effects being in the order of apparent ionic size: Na + > NH, + > Li + > K +. Mean activity coefficients in the resin phase have been determined for KSCN from the direct method measurements. INTRODUCTION THE interpretation o f the distribution o f a central metal species, M +n, as a function o f the ligand activity in the anion exchange technique o f studying metal complex ions requires information concerning the invasion o f the resin by the non-exchange electrolyte, ML. One m e t h o d o f securing this information is direct (2) and has been extensively employed by GOTTLIE#3,4) and KRAUS. ~5~ Because o f the tediousness o f this m e t h o d and as a result o f theoretical considerations, MARCUS and CORYELLre) concluded that an indirect m e t h o d employing a secondary, chemically stable, tracer anion could be used as well. This latter m e t h o d has also been employed in several investigations. ¢7) Until recently no comparison between the methods had been made.~S.9~ It is the purpose o f this present w o r k to apply b o t h methods to yet another system for comparison as well as to accumulate invasion data required for the interpretation o f subsequent distribution studies o f the G r o u p I I b metals, n o w in progress. EXPERIMENTAL Materials

The resin used was Dowex 1, a trimethyl benzyl ammonium strongly basic anion exchanger, with the crosslinkage resulting from an 8 per cent divinylbenzene content, 50-100 mesh, analytical reagent grade, as supplied by J. T. Baker, The capacity of the resin in the thiocyanate form, RSCN, was determined to be 2.81 4- 0.03 m-equiv./g of air-dried resin. The mI (8 da) used was sodium iodide as * Direct Invasion Data are from the thesis in partial fulfillment for the degree of Master of Science at St. Mary's University. ~1~ ~x~W. R. FIERm~RA,In: A Study of the Invasion of Dowex 1 × 8 by Potassium Thiocyanate and Sulfuric Acid Solutions, M.S. Thesis in Chemistry, St. Mary's University, San Antonio, Texas (1964). c~ K. W. PI~PER, D. REICHENBEZOand D. K. HALE, d. chem. Soc. 3129 (1952). c*~M. A. GOTTLmB,In: Studies on Cation and Anion Exchange Resins in Equilibrium with Electrolyte Solutions, Ph.D. Thesis in Chemistry, Polytechnic Institute of Brooklyn, Brooklyn, New York (1953). ~*~M. A. GOTTLmnand H. P. G~OOR, J. Am. chem. Soc. 76, 4639 (1954). ~6~F. NF.I.SONand K. A. K ~ u s , d. Am. chem. Soc. 80, 4154 (1958). ~'~ Y. MARcus and C. D. CORYlSLL,Bull. Res. Coun. Israel A8, 1 (1959). ~v~y. MARCUSand I. EIaEZlm, J. inorg, nucl. Chem. 25, 867 (1963). ~s~R. B~mnmm, J. inorg, nucl. Chem. 26, 845 (1964). ~9~R. B ~ , M. GtBSTINIA~and E. CERVO,J. inorg, nucl. Chem. 27, 1325 (1965). 1707

G. ZACIIARIADES,W. R. I4_~RgF.aAand C. J. CtrMMtSr~y

1708

supplied in medical grade capsules by Nuclear-Chicago and was essentially carrier free. All other chemicals were analytical reagent grade except for lithium thiocyanate which was the purified grade supplied by City Chemical Co. of New York. The resin as received in the chloride form was treated first with 5 ~o NaOH and then with 20 Yo NaSCN to convert it to the thiocyanate form. Methods

The "batch" equilibration technique was used. One gram of the air-dried resin in the thiocyanate form was shaken over night at room temperature with 40 ml of solution in a polyethylene stoppered Erlenmeyer flask. In the direct procedure, centrifugation was employed to separate the resin and aqueous phases. Potassium concentrations were determined with a Beckman DU Flame Spectrophotometer. In the indirect procedure, since a radioactive tracer, Na181I, was used, the activity in the aqueous phase was determined using a well-type scintillation counter. Efforts to use NaCN as the source of the secondary anion were unsuccessful. Attempts to follow CN- spectrophotometrically required concentrations in excess of the trace envisioned in the theory thus giving rise to considerable disagreement. Using tracer Na14CN did not give satisfactory results either. This was due both to poor selectivity of the resin for CN- over SCN- as well as to difficulties in liquid scintillation counting whether Bray's or a toluene based scintillation solution were used. tl0~ RESULTS F o r the s t u d y o f invasion o f D o w e x 1 × 8 by K S C N solutions, b o t h the direct a n d indirect m e t h o d s were used. T h e f o r m e r m e t h o d m a y evaluate the invasion in terms o f a l o g a r i t h m i c correction t e r m rFa = l o g A - - log A ° (1) where the b o l d face (A) indicates the resin phase a n d A = mzY±. A ° is a small b u t m e a s u r a b l e invasion w h e n A = 1. T a b l e 1 gives the results o f the e x p e r i m e n t a l TABLE 1.~INVASION OF DOWEX 1 × 8 BY KSCN SOLUTIONS KSCN m

log A

m-mole (ML) g resin

0-48 1.00 1"50 1"78 2"10 2"70 3"25 4"05 4"78 5"50

--0"505 --0"222 --0'065 0'000 0-067 0"169 0.244 0"334 0.404 0"462

0"08 0.18 0.35 0.50 0.66 0"99 1.18 1.61 1'86 2"28

gH20 g resin

m~L

mL

y+

log A

,F,

0.276 0-264 0.253 0.248 0"242 0.233 0.228 0"216 0'208 0.200

0-28 0-65 1"39 2-01 2-73 4"24 5"16 7"46 8"93 11"43

10"46 11'02 12"48 13"35 14"32 16"28 17"52 20"46 22.44 25"50

0"182 0"225 0-207 0"193 0"18Y 0"177 0-184 0"176 0"179 0"170

0"28 0"39 0.40 0"41 0'43 0"46 0"52 0.55 0"61 0"64

--0-13 --0"02 --0"01 0.00 0"02 0-05 0"11 0"14 0.20 0"23

m e a s u r e m e n t s as well as the calculations m a d e f r o m them. T h e a m o u n t o f w a t e r u p t a k e b y the a i r - d r i e d resin, R - S C N , was f o u n d to be 0.289 _-k 0.002 g H 2 0 / g resin. T h e m o i s t u r e c o n t e n t o f the air-dried resin, i.e. the weight loss on t a k i n g a i r - d r i e d samples to " b o n e - d r y n e s s , " was f o u n d to be 0.008 q- 0.001 g H~O/g a i r - d r i e d resin.(z) T h u s the d e t e r m i n a t i o n o f the w a t e r content o f the resin allows the calculation o f resin p h a s e molalities as well as activity coefficients. F i g u r e 1 shows the r e l a t i o n between the d a t a herein r e p o r t e d a n d previous literature values. T h e resulting values o.o)

C. J. CUMMISrO/Yand I. SANCHEZ,In: The Determination of Anion Resin Invasion Using a Trace Anion. Paper A-22 Southwest Regional Meeting A.C.S., Houston, Texas, Dec. 1 (1963).

Anion exchange of metal complexes--I

1709

t

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FIG. 1.--Resin phase activity coefficients as a function of concentration of invading KSCN solutions: O Dowex 2 x 8 (mesh undetermined), Reference (3); ~ Ambeflite CG 400, 200 mesh, Reference (9); • Dowex 1 × 8, 50 to 1011 mesh.

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FIG. 2.---Comparison of direct and indirect measurement of resin invasion function, rF,, for Dowex 1 × 8 and KSCN solutions. © direct; A indirect.

1710

G. ZACIOdtt~ES, W. R. HERmmA and C. J. CvMmsI~g

of,ar'a as a function of log A are given in Fig. 2. In the indirect method, the distribution of tracer azlI in the chemical form of NaI was determined as a function of KSCN concentration. Table 2 shows the experimental data. The observed information is TABLE 2.~INvASION OF DOWEX 1 × 8 BY KSCN EMPLOYING x3t[- AS SECONDARY TRACER ANION

(INDIRECTMETHOD) c, m

log A

Std. 0-112 0.112 0-227 0.486 0.486 0.958 1.420 1.660 1.660 1.919 2.399 3.130 3.130 3-740

--1.062 --1.062 --0.796 --0-517 --0.517 --0.238 --0.086 --0.026 --0.026 0.031 0.119 0.228 0.228 0.301

(G - c,)

(count• × Wt., min)-bkg 40 ml soln (g resin) 10,278 4- 86 = C1" 6966 132,840 7088 127,960 8434 74,120 9056 49,240 9074 48,520 9522 30,600 9667 24,800 9717 22,800 9074 22,440 9730 19,040 9811 22,280 9903 15,360 9922 14,600 9917 14,800

1.0132 0.9848 0.9839 0.9867 1.0034 1.0001 1.0007 1.0073 0.9828 1.0080 0.8482 1.0032 0.9807 1.0070

Ca, × wt.r

Dn

7060 6900 8280 8930 9110 9522 9667 9760 9650 8270 9860 9950 9720 9980

18.80 18.50 8.95 5.51 5.33 3.21 2.56 2"33 2.32 1.93 2.60 1.54 1.50 1"48

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log Dn°t

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1.27"

1.40

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0.21

0.95

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0.73*

0.86

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0.21

0.51 0.41

0.58 0-43

--0.07 0.02

0.27 0.32

0.37*

0"37

0.00

0.34

0-36 0.35

0.31 0.22

0"05 0.13

0.39 0.47

0-18"

0.11

0.07

0.41

0"17

0.04

0'13

0"47

* Average of replicate runs is shown t Log Dsca_x ~ = 0.34, estimated from data (CL Fig. 4).

used to evaluate log DB, where D is the distribution of the species as [(count/rain per g resin)/(count/min per ml soln)] and the B subscript refers to the secondary anion. It can be shown (eJ that: ~Fa = log D~ -- log DB°

(2)

where log DB° = log Dn(a=l) -- log A. The resulting indirect evaluation of ,Fa is also shown in Fig. 2 for comparison with the direct evaluation. The alternate expression of the invasion as: F B = ,F~ + log D n ° (3) is also given. (7) The remaining thiocyanate salts have been investigated by the indirect method. Figure 3 gives the experimental results as D a vs. m. It will be noticed at low concentrations up to 0.1 m that the resin shows considerable affinity for the tracer and that the effect is practically independent of the non-exchange cation. Between 0.1 and 1.5 m the SCN- is effective in outcompeting the I- for the resin. Beyond 1.5 m the distribution is practically constant. Throughout the region beyond 0" 1 m, the effectiveness of MSCN in outcompeting NaI for the resin varies in the order: M + -----Na + > NH4 + > Li + > K +, which would suggest this same order of decreasing size of the hydrated ions. Figure 4 presents the data in terms of log D B as a function of the log A, i.e. effective concentration in the aqueous phase of the non-exchange electrolyte. The

A n i o n exchange o f metal complexes---I

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FIG. 3.--Distribution o f 131-iodide as a function o f M S C N concentrations where M + is: • K+; A Na+; O NH4+; [] Li +.

1712

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4.--Distribution of 131-iodide as a function of the log A for various M + thiocyanates: • K+; [] Na+; A NH4+. Resin invasion correction function, ,F,, as a FIG.

function of log A for the various M + thiocyanates: @ K+; • Na +; © NH4+. mean activity coefficients for KSCN and NaSCN are available in the literature. (1I-lo For NH4SCN, no source of mean activity coefficients was available. However, the values were estimated by comparison of the mean activity coefficients of ammonium and potassium chlorides followed by appropriate approximation of the values o f ammonium thiocyanate from those of potassium thiocyanate. The lithium thiocyanate values were not available either, but no acceptable way of approximating them has been found. Figure 4 also gives the invasion correction function, rF,, as evaluated employing Equation (2) for the various non-exchange electrolytes. DISCUSSION The results summarized in Fig. 2 show that the two methods of estimating resin invasion are in essential agreement at least over the concentration range from log A = -- 0.5 to +0.5. The invasion effects for the M + thiocyanates all follow the same general pattern with slight variations due to size of the cation varying in the order: Na + > NH4 + > Li + > K +. This order has Li+ out of place from the regular lyotropic series of cations. Its natural high charge density together with the fact that the thiocyanate anion is low (lz) j. KIELLAND, J. Am. chem. Soc. 59, 1675 (1937). (i=) H. S. HARI,a~D and B. B. OWEN,in: The Physical Chemistry of Electrolyte Solutions (2nd Ed.) Reinhold Publishing Corp. New York (1950). (~8)R. A. RonnqSONand R. H. STOKES,in: Electrolyte Solutions, Academic Press, New York (1955). (1~) L. M. MILI~g and L. C. SI~RIDAN, J. phys. Chem. 60, 184 (1956).

Anion exchangeof metalcomplexcs--I

1713

in the regular lyotropic seriesof anions might combine to give a somewhat associated species having much lesswater of hydration and thereforea smaller sizethan the free hydrated Li+. This in effectwould bc a more readily invading species as the experimental resultsindicate. The initialrise of ¥± as noted with increasingm on Dowcx 2 × 8 and Ambcrlite G G 400 in the literatureis not continued at the higher concentrations employed in this work with Dowex I × 8. A m a x i m u m seems to occur at 1.0 m followcd by a dropping offto an approximately constant value beyond 2.5 m. This effectseems to be related to the amount of water the resin is capable of absorbing. The resinhereinemployed was similarin crosslinkage to the Dowcx 2 employed by GOTTLmB, however, this relationshipas to mesh sizeis not determinable. The onset of this effectseems to be delayed but the final experimental point indicates that it may be beginning. The amberlitc resin has probably somewhat lesscrosslinkagct15)and certainlymuch more surface area due to the larger mesh sizeand thus a much greatercapacity for water so that changes in its water content duc to salt invasion are not nearly as effectivein increasing the saltmolality in the resin phase (and thus lowering the y±) as the salt molality in the aqueous phase increases. Acknowledgements--The authors wish to thank the Robert A. Welch Foundation for Grant U-087 which supported this work. We are grateful to Mr. ISAACSANCrmZ for much of the preliminary work in this study.

~16~Amberlite Ion Exchange Resins Laboratory Guide, No. IE-85-64, p. 18, Rohm & Haas, Philadelphia (1964).