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Analytical methods used in studies on continuous separation of ions by countercurrent ion exchange
ANALYTICA
538
ANALYTICAT, SEPARATI-ON
SHIRLEY
METHODS OF IONS
CIIIMICA
ACTA
VOL.
USED I-N STUDIES T3Y COUNTERCURRENT
13. RAI1DING,
RUSSELL
Stunford Rcseavch
Institute,
C. PHILLIk, Stanford,
11
(1954)
ON CONTINUOUS I’ON EXCHANGE
NEVIN
California
(U.S.
I<. HIESTER A.)
Duringt an investigation of the feasibility of continuous ion separation by means of countercurrent contact between ion exchange resin and solution3J4, it bccamc apparent that evaluation of the experimental results in terms of ion concentrations in the solution and on the resin, would bc considerably enhanced by ;L careful study of the analytical procedures involved. The present paper describes the analytical methods used, the problems which were encountered, uncl how they were solved. In order to simplify theoretical problems as much as possible, lithium ion (Li+) and potassium ion (K+) were chosen as the ions to bc separated, and hyclrogcn ion (Hmk)as the carrier and elutant. This particular system was selected the exchange bccausc : (I) the three ions are of equal valcncc, thus simplifying mechanism ; (2) Li+ and K’ are both available in pure form, as the chlorides, at rcnsonable costs: (3) as the second and fourth elements in the alkali metal series, Lie’- and Kf differ sufficiently to make separation feasible; and (4) H+ may be analyscd easily. A nuclear-sulfonic polystyrcnc-base type resin, Chempro C-zo cation cxchangcr, was used because of its homogeneity of structure and uniform exchange strength. The objectives of the analytical program, then, were (I) the accurate determination of the concentrations of the alkali metal ions in solution in the presence of I-Ij- and each other, and (z) the quantitative removal of the alkali metal ions from the resin in a form suitable for solution analysis.
ANALYSIS
01:
SOLUTIONS
The flame photometer was chosen for the analysis of the Li+ and K+ because it offered the highest potential (and speed) available for analysis of the alkali metal ions in the concentration range of interest1J29s. A Beckman DU spectrophotometer with an acctylcnc-oxygen flame attachment was used throughout the program. Rcfcvc?lces
p.
549.
VOL.
11
COUNTERCURRENT
(1954)
ION
EXCI-IANGE
539
The four primary variables that might affect the analytical results were the wavelengths and slit widths used for the two ions and the concentrations of the interfering alkali metal ions and hydrogen ion. As suggested by the instrument manufacturer, the wavelengths of the principal lines (on this instrument, 771 rnp for the potassium and 673 rnp for the lithium) were used throughout. In all of the tests involving the other variables, Li+ or K+ solutions containing I.ON NC1 were used as the standard. These were prepared at 0.01, 0.05, 0.1, and 0.5N. by weighing out the salt, dissolving in water and diluting to volume, and then checking the standardization gravimetrically through precipitation of the chloride with silver nitrate solution. At least five dilutions of each of the above primary standards were then made up by diluting aliquots with hydrochloric acid and water so that the final solutions were r.oN with respect to the hydrogen ion. In general, the calibration procedure consisted of, first, adjusting the instrumcnt to the chosen settings of wavelength ancl slit width for the ion concerned. The primary standard was then aspirated into the flame and the photometer set to a reading corresponding to 100% transmission. The relative transmissions of the diluted solutions were then determined and plotted against the actual concentration of the ion of interest. This plot was then considered the calibration curve for that particular primary standarcl. Fig. I is an example of a calibration curve for pure potassium ion.
Fig. I. Sample calibration curve for potassium ions in r.oN HCI In order to see if thcsc curves were consistent with each other, the rending for 100% transmission on each curve was dropped to the bottom curve (as read against o.gN solution) and all other points on each graph corrected proportionally. When this was done, the points shown on the bottom curve arc obtained and it is seen that they are self-consistent. Effect O/ slit wi&lz. The effect of slit width could not bc checked directly since it was necessary, first, to find the proper slit width to be used with each of the References
p.
549.
S. 13.
540
RADDING,
R.
C.
PIIILLIPS,
N.
K.
VOL.
HIESTER
11 (1954)
primary standards mentioned above. At too small a slit width, the sensitivity became poor bccausc so little of the flame intensity reached the instrument; when the slit width was too large, the interference from other ions became greater. Thus, the proper slit width had to be based on an optimum balance of these two factors, The optimum values obtained for this instrument are given in Table I. TABLE OPTIMUM SLIT WIDTIIS FOR IONS USING THE UECICMAN
I
VARIOUS CONCENTRATIONS DU SPECTROPiIOTOMETEI1 ATTACIIMBNT
OptitiL!?
Actual normality of Lit- nncl I(+ in I .oN HCl 0.01
0.05 0.1 ___
_ _.
_ ____.
0.5 _-._-
___.__.__ .-_-_..-_.-
OF LITHIUM AND POTASSIUM WITH A FLAME PHOTOMETER
_-._. _ -
slit w;
0.15
o.oG
0.15
o.oG
0.08
0.04 0.02
0.05
_
---_
might be expected, the optimum slit width depended on the strength of the flame line, and thus on both the ion and its approximate ionic concentration. The actual effect of slit width was best shown by rechecking one of the primary standards, and its dilutions, on the flame photometer with the slit width set hi&r than optimum. For comparison purposes the instrument was set at IOO~/~ transmission with the primary standard and at the optimum slit width. The slit width was then incrcascd and the pcrccnt transmission of all of the samples was dctcrmined. These values wcrc then used to read the indicated concentrations from the normal calibration curve obtained for the primary standard at the optimum slit width. The results indicated by the new readings arc given in Table II. TABLE II As
EDPPPCT
OF
SLlT
WIDTH _
Actual normality of Li-land Ii+ in I .oN HCl
----
--
VARIATION ON SOLUTIONS -.-.--_._.. . ..---._
Li+ at
Ratio 0.2
I .os
0.020
1.17
CONCENTRATIONS _-__.--
_-_- __..._.. -.
-_
p.
1.13
549.
--
_
r.og 1.01 I.04 0.gG 0.9s .-__ _-_-----
‘Jkse values again confirm the fact that, at larger slit widths, interfcrenccs (“background”) have a greater effect on the results. Rc_fcYemcs
- ____-.
K-t- at 0.1 mm slit width .. -. _.._--.. --. .-. --.--.-.__.No reading
I.15 I.01
OF
of inclicatecl to actual normality
mm slit width ~ _._._._. I .0x
0.005 0.010 0.030 0.040 0.050
APPARIINT
estraneous
11 (1954)
VOL.
COUNTEHCUHREST
54=
101; EXCI-IAXGE
Effect of $veseme of hydrochloric acid. It very quickly became apparent that the hydrochloric acid, always present in the experimental solutions, also interfered with the readings for the metal ions. This effect had also been reported by Pnxucs, JOHNSON ANDLYKKEN 5. For this reason it was decided to check the magnitude of this effect. Standard solutions of o.or!V KC1 and O.OIN LiCl were prepared by weighing out the pure salt, dissolving in distilled water, and diluting to volume with water. The concentrations were checked as before by precipitating the chloride ion with silver nitrate. Aliquots of the standard solutions were diluted with distilled water to volume to give four different concentrations. These solutions were then used to preparc a special calibration curve for the flame photomctcr. Regular acid-containing standards wcrc then checked on the flame photometer against this calibration curve, using the optimum slit widths given above. The results arc shown in Table III.
EFFECT
OF
-._
WATER-CONTAINING
US. ACID-CONTAINING CONCENTHATIONS OF SOLUTIONS . ---__ ___----__-.-.
Actual nor&&y ‘of Ii+ or Li+ in r.oN HCl
------.
Ratio
~--__--0.002
-__-_
IJARDS
.._ -. .-__
ON
_-_-_.---.-._.
.07 1 .ocj I .oG I .oG _ -__---_
_.
----_--
INTERPERENCE
Actual normality of Li+ in 1.0hr HCl _ _-. . . ‘_ 0.001
012
TABLE
IV
LITIIIUM --
Ah’D
Ratio 3L1-t:11<-t
...---_
_. --_
References
0.012 0.018 0.O.z.~ 0.030 0.10 0.20 0.30 0.40 .._ . .-. _..
p. 549.
iLi+
1.02 I *OS I.03
I *cl.+
I .Ol 1 .OI
1.02 I.05 1.02 I.01 o.s7 I.11 I.15 1.12
r.oN
hydro-
IONS
to’ actual :I K+
I .oo I.03
0.004
0.000 0.008 0.010
of indicated.
- ___ _
0.002
0.003
POTASSIUAI
---
**‘3 1.12 I.12 1.12 - _____ -- __-__^---__---.
It is apparent that the use of standards in water, rnthcr than in chloric acid, will give high readings on the cspcrimcntal samples.
MUTUAL
APPARENT
of indicated to actunl normality Li+ K-+
I
0.00.1 o.ooG 0.008
---
STAN
hormality xLi+ :3K+ I .oo 1.01
I.05 I .04 I .04 1.02
S. B.
542
IZADDING,
It.
C.
PHILLIPS,
N.
I<.
HIESTER
VOL.
11
(1954)
Effect of vtdzral intcrfcvcvzce of alkali iom. Li+ and K+ exhibited mutual interferencc, and the effect of this interference was evaluated by the preparation of standard solutions, in x.oN hydrochloric acid, containing both K+ and Li+ levels. Readings were in 1:x, 3:x, and I :3 ratios, and at various concentration then obtained against the pure Ksk or Li’ calibration standards. Some of the Li + results arc given in Table IV. This information indicates that the greater quantities of KC, either ratio-wise or concentration-wise, usually cnuscd increased interfercncc in the Lie’- results. This cffcct is shown in Fig. 2.
0
Pure
LI*
xlLi’.lK’ t. 1 ll’. 3K alLi* SK’ .JLt* IK’
eo60_
l
aoI
0 0001
I
I111111
I 001 meqlml
Fig. 2. Mutual
11
I
11!111
I
III~NI_
O!O Llfhlum
.‘O
Ion
interference
of alkali ions
A comparison of thcsc results with those for K+ indicate that Li+ cause less intcrfcrcncc with the I(+ readings than I(’ with Li+. For example, in the case of I IA+ :I KC, th(: results are given in Table V. TABLE LlTHlUhl .
-
INTEI
-. .-
Actual normality Lit- or I<+ in x.oN __
of HCl __---
Ratio __._- ---
0.001. 0.002
_.
._..--.. ._. _..- ..._-._. . _
of indicntcd J,1-C _ ___
.._
_.
IONS . _
to actual __
_
_^ .._. .._
normality Iit-
_ ._....
1.00
I.01
I .05 I .04 1.01
1.01 1.01
r.03
0.004 0.006 0.005
V
WITH POTASSIUM .__.__ __ _ _._ .___ ._ _._...__
___-..-..-- -
__---_
___..
I.00
._ --_.. __.
0.99 .- .._._._-
Adopted ~rocediwc. The procedure which was finally adopted for the analysis of the solutions encountcrcd in the countercurrent ion cxchangc studies is outlined below : The volume of the snmplc is rccordcd and the acid content dctcrmined on an References
p.
549,
VOL.
11
(1954)
COUNTERCURRENT
ION
EXCHANGE
543
is more than 5% below r.oN, hydrochloric aliquot. If the H+ concentration acid is added to a second aliquot to make the solution I.oN, and the new volume are determined on the acid-adjusted recorded. The K’ and Li+ concentration sample with a flame photometer at predetermined wavelengths using the proper reference solutions. The amounts of K+ and Lit are obtained by reference to the proper calibration curves. Preliminary values for K+ and Li’ were obtained from the calibration curves of the pure ions. The approximate ratio of K+ to Lit was then determined from these results and the corrected K+ and Lit values read from the proper ratio calibration curve. The calibration curves were prepared by plotting readings obtained on solutions of lithium chloride and potassium chloride in r.oN HCl in molar ratios of Li” : I<+ of O:T, I :I, I:Z, x:5, 3:1, 5:1, and x:o. Solutions of o.gN KCl, o.rN KCl, o.ogN KCl, O.OIN KCl, o.5N LiCl, o.rN LiCl, o.ogN LiCl, and O.OIN LiCl wcrc used as reference standards. REMOVAL OF
IONS
FROM
RESIN
In the case of resin* analysis, the principal problem was the quantitative transfer of potassium and lithium from the resin sample to a solution which can be analysed by the standard proccdurc cstablishcd above. The removal (I) clution with an excess of methods tested fell into two general categories: another ion, and (2) dcgradativc oxidation of the resin followed by an ncid leach of the rcsiduc. In the elution method, an aliquot of the resin sample was transferred to a tube, and the chosen volume of elutant was passed through it at a slow rate. The resin was then washed with distilled water, and the combined effluents wcrc analysed for the K+ and Lie removed from the resin. The resin aliquot was then oven-dried, so that the coiicentrations could be expressed on a consistent basis of dry hydrogen-form resin. Since the amount of alkali metal ion originally present on the resin was not known, each set of tests was performed on alicluots of the same resin sample so that the results could be compared. Effect of clulio~ condilions. The elation espcrimcnts involved the effect of clutant quantity and concentration. Each of the elution columns used to check the treatments contained IO g of oven-dried resin. The results obtained arc given in Table VI.
* The resin used in this work was a polystyrene-sulfonic acid ty e resin manufactured by Chcmicsl Process Company, Redwood City, Call*Pornia. Xefeveaces
p.
549.
c-20
544
s.
13. RADDING,
01’ _-
ELUTANT _-------------__
R.
C.
PHILLIPS,
TABLE _ ___ _.--_
IfIrl?KCT ._- .___. -..-
Elution
ON
trcatmentn
IIIESTER
QUALITY
ALTxunt
__._._. __ --__.- ..__.. ._.. ..__ . .IOO ml r.oN HCL 200 ml r.oN I-ICI 400 ml I.ON HCl xoo ml z.oN HCl 400 ml r.oN HCl 1000 ml 2.oN CuCI, .- ..__ -_-- --._------_._- -------.--\vns passed
IC.
through
11
(1954)
OF
EPI:LU&NT
removeci,
rn;ztg
.-_ _ .- - --_--.__-_ 0.078 0.094 o-077 OS’37 0.078 o.rGo 0.158 0.079 0.078 o-159 0.140 0.073 - -.---.--- --_ - _- -- _-._ - __.________ ______
. tllc
VOL.
VI
CONCENTRATION
- - ______
(1 Tlx clutant 5 ml/min.
N.
resin at a
superficial
velocity
of
about
It appears that cithcr 400 ml of r.oN HCI l)oth I<+ and Li+ from the resin satisfactorily.
or IOO of z.oN HCl would elutc The copper chloride elutant was not satisfactory, mainly because it caused intcrfercncc in the flame photometer readings. A volume of 125 ml of 2.oN HCI was selcctcd as best for the elution proccdurc, bccausc the resin could bc washed with an equal volume of distilled wotcr and yiclcl just 350 ml of cfflucnt (a standard volumetric flask size) at a hydrochloric acid concentration of I.oN, the desired lcvcl for analysis. Effect of clvy-nsliing comi?itions. The second removal method, destruction of the resin, was accomplished cithcr by dry-ashing or by chemical oxidation (wetnshing). The resin samples wcrc oven-dried prior to thcsc dcstructivc treatments so that the results could bi: cxpresscd on a dry basis. In the dry method, the resin was carcfully pyrolysed at 1000~ C until only a mineral ash rcmaincd. After cooling, this ash was then taken up with I.ON HCl and the solution analyscd as usual. The wet method consisted of treating the resin with nitric acid and sulfuric acid, and in some cases pcrchloric acid, at the boiling point until no residue was apparent. The resultant solution was then evaporated to dryness, taken up with I.ON I-ICl, and analyscd as before. Again, each set of tests was pcrformcd on alicluots of the same resin sample so that the results could bc comparccl. The first cxperimcnts compared the clution method with dry-ashing in porcelain crucibles. TABLE -.
_. -
COhIPAl~ISON __ .
Trcatmen;
017
_
IlLUTION
_
METIIOD
_
VII \VITII --_---
DRY-ASHING
OF
-_-Arnciyt
__-------.-_ ._.__. .-. .-_. _ Gsin elutecl with xoo ml of 2.oN HCl liesin ashccl at 1000~ C 20 ml o.oxN Solution of 1Li-I- : 1 K-l-._ ..__ ._ _ ._ _ ___. _ .__ -_ _Rcferetrccs p. .=jdg,
0.079
0.024 None
RESIN
fou;~id; mcq/g 0.158 0.025 None
_
VOL.
11
COUNTERCURRENT
(195-1)
ION
EXCHANGE
545
As can be seen in Table VII, ashing in porcelain is completely unsatisfactory, probably because the Lif and K+ are taken up in the porcelain glass. Next, for comparison, platinum crucibles were tried for the dry-ashing instead of porcelain crucibles. In some casts, solutions containing known quantities of Lif and Kf were added to the ashing containers before trcatmcnt. In these cases, the results should be high by the amount added. The results of these tests arc given in Table VIII. TABLE __
COMPARISON . ..___ __ ._ _..
OF .-
IlR\--ASCIINC .__. __ _
RESULTS
--_ .--. _. _ _ _ Resin eluted with IOO ml of z.oN I-ICI ashcd
in porcelain
Resin
ashccl in platinum
PORCELAIN
ASD
Li+ _
Predicted
Ii-t-
IN
PLATINUM
mcq/g Li+
Found
K-t
_ . 0.079
0.158
at 1000~
C
0.024
0.025
at
C
0.083
0.757
0.271
0.188
0.256
0.338+ __I-..
0.075 * o-025* -_--..- ._.__- .._. ______
Rain plus known solution num at 1000~ C ashcd
IN
Amount,
Treatment
Resin
VIII
I
in
. . _ . --.----.
+ Concentrations
iire given
1000”
in plati-
0.?02
platinum _.
0.380* _ _ _.__.- _._______
in total
meq
rather
than
meq/g.
Although the platinum crucibles are much more satisfactory than porcelain, poor recoveries of added solutions were obtained. This may hc due to volatilization or to background cffcct on the flame caused by fine particles of incompletely ashcd resin. The wet-ashing tcchniquc was tried next. In LWffecl of wet-ashing con&ions. these experiments some of the treatments were repeated scvcral times to check the reproducibility of the results. In all cases the material was trcntecl with nitric acid and sulfuric acid, at the boiling point, until the solution was essentially clear. These results arc given in Table IX. The wet-ashing method appears to give fairly reproducible results, but poor recoveries of the acldcd solutions were obtained. Again volatilization or flame background interference due to unreacted resin constituents may bc the cause. A second series of wet-ashing cxpcriments was undertaken next. In this series perchloric acid was used, in addition to nitric acid and sulfuric acid. A few elution runs wcrc also included for comparison purposes on the new resin aliquot. As before, the expcrirnents were pcrformcd in rcplicatc. Rcj-c~emcs
p.
549.
s. 13. RAUDING,
546
R.
C.
I’IIILLIPS,
TABLE TA13ULhTION
-. .
__ _.. _
_ ._
--
OIF
_-._.._.._. .
. ..- - -
IN
THE
PRESENCE
. Resin Rcsi n Resin Resin Resin Known solution * l
HCI HCl
in total
VOL.
11
(1954)
EXPERIMENTS
.
0.231 0.271 O-237 O-255 0.220 o a295 0.351 O-343 0.311 o.G76 0.676 None None than
OF
0.500
. ._. meq rather
._.._
meek Li+
Pound
0.103 0.090 0.093 0.089 0.093 0.156 0.213 0.103 0.135 O.I‘(G 0.2G4 o.zGo 0.329 0.240 0.710 0.710 None None 0.079
PEl
.
ACID
meq/g Li-t-
Found
O-055 0.05G 0.059 0.058 0.059 0.500 0.460 o.oGG o.oG8 ._. _.._._. ._.-.than in mcq/g.
Although Table X shows fairly good agreement clution is simpler and faster.
I<+ -. 0.108 0.185 0.183 0.175 0.183 0.237 0.2GG 0.233 0.259 0.220 0.275 0.256 0.3’5 0.301 0.068 0.688 None None 0.158
in incy/g,
Amount, Prcdictccl Ii -+ Li+
Snmplc
*Concentrations
HIESTER
_. .-... -._ .___ Amount, Predicted Li-I-I<+ _ __ . -..
Resin Rain liesin Resin Resm 0.172 liesin plus known solution Resin plus lcnown solution o.zoG 0.179 12csin plus known solution 0.202 liesin plus known solution O.lG5 Resin plus known solution Rain plus known solution 0.254 Resin plus known solution 0.245 Resin plus lcnown solution o-314 12esin plus lcnown solution 0.2 74 0.800 Known solution* Known solution* 0.8Go water None None Water Resin elutctl with IOO ml of t.oN HCl _ . ..- . ....-__..._-.. _ _--.--._ ..-_. _ *Conccntr;ctions arc given in tota! mcq rather
WIZT-ASIIING
I<.
IX
WET-ASHING
Snmplc _.
N.
in this wet-oxidation
K-t0.138 0.142 0.140 0.142 0.141 o-485 o-143 o-145
method,
rl dofited pvocedl6ve. A 25 ml (8.0 g) sample of the resin is placed in a column r/z x 7 inches and cluted with 125 ml of 2iV hydrochloric acid at a rate of 5 ml Referewes
p.
549.
VOL. 11 (1954)
COUNTERCURRENT
ION
EXCHANGE
547
per minute, catching the effluent in a 250 ml volumetric flask. The sample of resin is then washed with distilled water in the same manner, adding the wash effluent to the acid effluent in the volumetric flask. The solution is diluted to exactly 250 ml with distilled water and analyscd as outlined in the analysis of solutions. The resinis transferred to a beaker, dried overnight at 105~ C and weighed. The results are calculated on a milliequivalent per gram dried resin basis. Determination
of tire dtimde
cxclimzge ca$acity
of the rosin.
An important factor in ion exchange studies is the ultimate capacity, or total exchange capacity, of the ion cxchangc resin. It is a mcasurc of the number of positions available for exchange in a given quantity of resin. Since its cletermination involves the measurement of a resin concentration the techniques involved are similar to those for the removal of ions from a resin. Two fundamentally different methods for determining ultimate capacity were evaluated. In one, resin in the hydrogen form was convex-fed to a mctol ion form by contact with a large excess of metal salt solution. The amount of l-I+ displaced from the resin into the solution was dctcrmincd by titration, thereby indicating the capacity of the resin. The alternative method involved the incrcmcntal titration of a hydrogen resin slurry with sodium hydroxide to obtain a titration curve. The amount of sodium hydroxide solution required to titrate to the point at which the PH changes rapidly, upon the addition of base, was converted to the I-I4 prcscnt and thus to the ultimate capacity of the resin. In the elution procedure a quantity of resin was first converted rilmost completely to the hydrogen form by extensive elution with hydrochloric acid in a fixed bed. This resin was thoroughly mixed and clutcd further with zN I-ICl. Finally it was washed with distilled water until the effluent was neutral to methyl orange. After further mixing, the resin was divided into eight portions of about 25 ml (IO g) and treated as follows: (I) Two aliquots were transferred to small glass columns, and one liter of saturated sodium chloride solution was passed through each. The resin samples then were washed with distilled water. Alicluots of the effluent solutions were titrated with standard sodium hydroxide to the phenolphthalein end-point to obtain the quantity of H+ released by the resin. The resin samples were treated with 250 ml 2.oN HCl, washed with distilled water, and dried overnight at 105’ C to obtain the ultimate capacity in terms of the dry weight of hydrogen form resin. (2) Two aliquots were trcatcd as in proccdurc (I) except that two liters of saturated sodium chloride solution were used. (3) Two aliquots were similarly trcatcd with one liter each of 5’y0 calcium chloride solution. (4) Two aliquots were titrated in increments to pr! r4 with standard sodium
I~efc7e72ccs p. 549.
538
S. B. IZADI>ING,
I<. C. PHILLIPS,
N.
I<. HIESTEH
VOL.
hydroxide. The resin was back-titrated with standard hydrochloric resin samples were washed with distilled water and dried overnight The results of thcsc tests arc given in Table XI. TABLE COMPARISON
_. -
OF
hlETIfOIJS
FOR
11
(1954)
acid. The at 105~ C.
XI
ULTIMATE
.
CAPACITY
Ultimate
Trcntment .- .- -. __-. -- ..----.- -.-.-__..___ -..---_ One liter snturatcd NaCl One liter saturated NaCl Two liters saturated NnCl
DETERMINATIONS
capacity,
meq/g -
$2 5.14 S.06
NaCl
;::, %
5.00
Titration to plr 1.1 Average ___ _. _. _.-- -_._--- __-..._.-. .
5.10
__-.
.__._
____
5.11 -
In the sodium hydroxide titration procedure, the break in the pH curve occurred bctwcen per 7 and px II, as is shown in Fig. 3. The reverse titration with hydrochloric acid to prr 2 did not give a satisfactory end-point. No definite break was observed, and the apparent end-point resulted in an erroneously high capacity. The proccdurc selcctcd as the standard method was that of using one liter of 5% calcium chloride solution. This method was economical of the analyst’s time and of rcagcnts and gave satisfactorily reproducible results.
Pig.
3. Dctcrmination
of ultimate
capacity
by incremental
titration
ACKNOWLEDGEMENTS
Portions
of the cspcrimcntnl
LYDIA PlzTlzRS of the Analytical gratefully acltnowlcdgecl.
References
p. 549.
work were conducted by OLIVER D. SMITH and Section of the Institute and their assistance is
VOL.
11 (1954)
COUNTERCURRENT
ION
EXCHANGE
549
SUMMARY The hydrogen ion concentration exhibited a pronounced effect on the apparent alkali ion concentrations as determined with a Beckman DU spectrophotometer with a flame attachment. Lithium and potassium ions showed a mutual interference, which appeared small, but was sufficient to affect the theoretical evaluation of exchange systems, especially under trace conditions. Control of slit widths eliminated some of the interferences, but further corrective measures had to be applied by the use of prepared calibration curves. from the resins were explored. Several methods for removing ions quantitative1 While cop cr salts were effective elutants, they cou Yd not bc used in routine analysis ions analyses and elution because o P*mtcrference with the lithium and potassium with hydrochloric acid was finally chosen. A simple and economical method was found for detcrminiug the ultimate capacity of the resin. La concentration en ions liydrogtine a une forte influence sur la concentration apparentc des ions alcnlins, dCtermm6e au spectrophotom&tro de flamme Beckman ui, bien DU. Les ions lithium et potassium pr6sentcnt une mutuelle interfbrence, quc falble, cst sufflsante pour fausser 1’6valuation tli6orique dessystemes d ? *change, spt5cialemcnt lors u’il s’agit de traces. Certaines interfbrences pcuvent Otre bliminbes par un contrOle 3 e l’ouverture de la fcnte, mais l’emploi de courbes d’&alonnagc, est n6cessaire. Diffbrentes m6thodes furent essay&es pour 1’Climination quantitative d’ions clans dcs r&sines. Bien que les sels de cuivre soient efficaces comme bluants, ils nc peuvent ctre utilis6s pour dcs analyses en s&rie car ils gOnent les dosages dc lithium et potassium. I1 est plus avantageux d’utiliser l’aclde chlorhydrique. Une mQthodc simple et pratique est utilisee pour la dbtermination dc la capacitG finale des r&sines. ZUSAMMENFASSUNG Die Konzentration der: Wasserstoffionen hat einen grossen Einfluss auf die welche mit dem Flammen-Spcktroscheinbare Konzcntration an Alkaliionen, und Kalium photometer Beckman DU bestlmmt wird. Die Ionen von Lithium zcigcn eiuc gegcnseitige Intcrferenz, welche, obwohl sie sehr schwach ist, ausreicht, urn die thcoretische Bewertung des Austausch-Systcmes zu stijren, speziell sofern es sich urn Spuren handelt. Gewisse Interferenzen kdnnen vermieden werden durch Kontrollc der offnung, aber die Verwendung von Eichkurven ist notwendig. Verschicdene Methoden wurden versucht flir die quantitative Entfernung dcr Ionen aus Harzen. Obwohl die Kupfersalze wirksame kluierungsmittel darstcllen, lccjnnen sic flir Serienanalysen nicht verwendet werden, da sic die Bestimmung von Lithium und Kalium stbren. Es ist vorteilhafter die Salzsjiure zu verwenden. Eine einfachc und praktische Methode wird verwendet flir die Bestimmung dcr Kapazitiit von Harzcn. REFERENCES 1 J. W.
BEIIIIY, D. G. CIIAPPOLL AND R. B. BARNES, Ind.
123 (x+$6)
E71g.
19.
Chcnt.,
Amal.
Ed.,
* P. T. GILUIZRT, JR., R. C. H,\wss
AND A. 0. BECI~MAN, An&. Chem., 22 (1950) 772. 3 N. K. HiEs*rm<, R. C. PIXILLIPS, E. F. FIELDS, R. C. COHEN ANI) S. 13. RADDING,
Id. Eng Chem., 45 (1953) 2402. 4 N. K. HIESTER, E. F. Frowns, R, C. PIIIL’LIPS AND S: 13. RA-SDING, Chem: Eng. Pvog., So (1954) 139. 0 T. D. P,\HKs, H. 0. JOHNSON AND L. LYICKISN, Anal. C/tern., 20 (1948) 822.
Received
June
10th.
1954
-
538
ANALYTICAT, SEPARATI-ON
SHIRLEY
METHODS OF IONS
CIIIMICA
ACTA
VOL.
USED I-N STUDIES T3Y COUNTERCURRENT
13. RAI1DING,
RUSSELL
Stunford Rcseavch
Institute,
C. PHILLIk, Stanford,
11
(1954)
ON CONTINUOUS I’ON EXCHANGE
NEVIN
California
(U.S.
I<. HIESTER A.)
Duringt an investigation of the feasibility of continuous ion separation by means of countercurrent contact between ion exchange resin and solution3J4, it bccamc apparent that evaluation of the experimental results in terms of ion concentrations in the solution and on the resin, would bc considerably enhanced by ;L careful study of the analytical procedures involved. The present paper describes the analytical methods used, the problems which were encountered, uncl how they were solved. In order to simplify theoretical problems as much as possible, lithium ion (Li+) and potassium ion (K+) were chosen as the ions to bc separated, and hyclrogcn ion (Hmk)as the carrier and elutant. This particular system was selected the exchange bccausc : (I) the three ions are of equal valcncc, thus simplifying mechanism ; (2) Li+ and K’ are both available in pure form, as the chlorides, at rcnsonable costs: (3) as the second and fourth elements in the alkali metal series, Lie’- and Kf differ sufficiently to make separation feasible; and (4) H+ may be analyscd easily. A nuclear-sulfonic polystyrcnc-base type resin, Chempro C-zo cation cxchangcr, was used because of its homogeneity of structure and uniform exchange strength. The objectives of the analytical program, then, were (I) the accurate determination of the concentrations of the alkali metal ions in solution in the presence of I-Ij- and each other, and (z) the quantitative removal of the alkali metal ions from the resin in a form suitable for solution analysis.
ANALYSIS
01:
SOLUTIONS
The flame photometer was chosen for the analysis of the Li+ and K+ because it offered the highest potential (and speed) available for analysis of the alkali metal ions in the concentration range of interest1J29s. A Beckman DU spectrophotometer with an acctylcnc-oxygen flame attachment was used throughout the program. Rcfcvc?lces
p.
549.
VOL.
11
COUNTERCURRENT
(1954)
ION
EXCI-IANGE
539
The four primary variables that might affect the analytical results were the wavelengths and slit widths used for the two ions and the concentrations of the interfering alkali metal ions and hydrogen ion. As suggested by the instrument manufacturer, the wavelengths of the principal lines (on this instrument, 771 rnp for the potassium and 673 rnp for the lithium) were used throughout. In all of the tests involving the other variables, Li+ or K+ solutions containing I.ON NC1 were used as the standard. These were prepared at 0.01, 0.05, 0.1, and 0.5N. by weighing out the salt, dissolving in water and diluting to volume, and then checking the standardization gravimetrically through precipitation of the chloride with silver nitrate solution. At least five dilutions of each of the above primary standards were then made up by diluting aliquots with hydrochloric acid and water so that the final solutions were r.oN with respect to the hydrogen ion. In general, the calibration procedure consisted of, first, adjusting the instrumcnt to the chosen settings of wavelength ancl slit width for the ion concerned. The primary standard was then aspirated into the flame and the photometer set to a reading corresponding to 100% transmission. The relative transmissions of the diluted solutions were then determined and plotted against the actual concentration of the ion of interest. This plot was then considered the calibration curve for that particular primary standarcl. Fig. I is an example of a calibration curve for pure potassium ion.
Fig. I. Sample calibration curve for potassium ions in r.oN HCI In order to see if thcsc curves were consistent with each other, the rending for 100% transmission on each curve was dropped to the bottom curve (as read against o.gN solution) and all other points on each graph corrected proportionally. When this was done, the points shown on the bottom curve arc obtained and it is seen that they are self-consistent. Effect O/ slit wi&lz. The effect of slit width could not bc checked directly since it was necessary, first, to find the proper slit width to be used with each of the References
p.
549.
S. 13.
540
RADDING,
R.
C.
PIIILLIPS,
N.
K.
VOL.
HIESTER
11 (1954)
primary standards mentioned above. At too small a slit width, the sensitivity became poor bccausc so little of the flame intensity reached the instrument; when the slit width was too large, the interference from other ions became greater. Thus, the proper slit width had to be based on an optimum balance of these two factors, The optimum values obtained for this instrument are given in Table I. TABLE OPTIMUM SLIT WIDTIIS FOR IONS USING THE UECICMAN
I
VARIOUS CONCENTRATIONS DU SPECTROPiIOTOMETEI1 ATTACIIMBNT
OptitiL!?
Actual normality of Lit- nncl I(+ in I .oN HCl 0.01
0.05 0.1 ___
_ _.
_ ____.
0.5 _-._-
___.__.__ .-_-_..-_.-
OF LITHIUM AND POTASSIUM WITH A FLAME PHOTOMETER
_-._. _ -
slit w;
0.15
o.oG
0.15
o.oG
0.08
0.04 0.02
0.05
_
---_
might be expected, the optimum slit width depended on the strength of the flame line, and thus on both the ion and its approximate ionic concentration. The actual effect of slit width was best shown by rechecking one of the primary standards, and its dilutions, on the flame photometer with the slit width set hi&r than optimum. For comparison purposes the instrument was set at IOO~/~ transmission with the primary standard and at the optimum slit width. The slit width was then incrcascd and the pcrccnt transmission of all of the samples was dctcrmined. These values wcrc then used to read the indicated concentrations from the normal calibration curve obtained for the primary standard at the optimum slit width. The results indicated by the new readings arc given in Table II. TABLE II As
EDPPPCT
OF
SLlT
WIDTH _
Actual normality of Li-land Ii+ in I .oN HCl
----
--
VARIATION ON SOLUTIONS -.-.--_._.. . ..---._
Li+ at
Ratio 0.2
I .os
0.020
1.17
CONCENTRATIONS _-__.--
_-_- __..._.. -.
-_
p.
1.13
549.
--
_
r.og 1.01 I.04 0.gG 0.9s .-__ _-_-----
‘Jkse values again confirm the fact that, at larger slit widths, interfcrenccs (“background”) have a greater effect on the results. Rc_fcYemcs
- ____-.
K-t- at 0.1 mm slit width .. -. _.._--.. --. .-. --.--.-.__.No reading
I.15 I.01
OF
of inclicatecl to actual normality
mm slit width ~ _._._._. I .0x
0.005 0.010 0.030 0.040 0.050
APPARIINT
estraneous
11 (1954)
VOL.
COUNTEHCUHREST
54=
101; EXCI-IAXGE
Effect of $veseme of hydrochloric acid. It very quickly became apparent that the hydrochloric acid, always present in the experimental solutions, also interfered with the readings for the metal ions. This effect had also been reported by Pnxucs, JOHNSON ANDLYKKEN 5. For this reason it was decided to check the magnitude of this effect. Standard solutions of o.or!V KC1 and O.OIN LiCl were prepared by weighing out the pure salt, dissolving in distilled water, and diluting to volume with water. The concentrations were checked as before by precipitating the chloride ion with silver nitrate. Aliquots of the standard solutions were diluted with distilled water to volume to give four different concentrations. These solutions were then used to preparc a special calibration curve for the flame photomctcr. Regular acid-containing standards wcrc then checked on the flame photometer against this calibration curve, using the optimum slit widths given above. The results arc shown in Table III.
EFFECT
OF
-._
WATER-CONTAINING
US. ACID-CONTAINING CONCENTHATIONS OF SOLUTIONS . ---__ ___----__-.-.
Actual nor&&y ‘of Ii+ or Li+ in r.oN HCl
------.
Ratio
~--__--0.002
-__-_
IJARDS
.._ -. .-__
ON
_-_-_.---.-._.
.07 1 .ocj I .oG I .oG _ -__---_
_.
----_--
INTERPERENCE
Actual normality of Li+ in 1.0hr HCl _ _-. . . ‘_ 0.001
012
TABLE
IV
LITIIIUM --
Ah’D
Ratio 3L1-t:11<-t
...---_
_. --_
References
0.012 0.018 0.O.z.~ 0.030 0.10 0.20 0.30 0.40 .._ . .-. _..
p. 549.
iLi+
1.02 I *OS I.03
I *cl.+
I .Ol 1 .OI
1.02 I.05 1.02 I.01 o.s7 I.11 I.15 1.12
r.oN
hydro-
IONS
to’ actual :I K+
I .oo I.03
0.004
0.000 0.008 0.010
of indicated.
- ___ _
0.002
0.003
POTASSIUAI
---
**‘3 1.12 I.12 1.12 - _____ -- __-__^---__---.
It is apparent that the use of standards in water, rnthcr than in chloric acid, will give high readings on the cspcrimcntal samples.
MUTUAL
APPARENT
of indicated to actunl normality Li+ K-+
I
0.00.1 o.ooG 0.008
---
STAN
hormality xLi+ :3K+ I .oo 1.01
I.05 I .04 I .04 1.02
S. B.
542
IZADDING,
It.
C.
PHILLIPS,
N.
I<.
HIESTER
VOL.
11
(1954)
Effect of vtdzral intcrfcvcvzce of alkali iom. Li+ and K+ exhibited mutual interferencc, and the effect of this interference was evaluated by the preparation of standard solutions, in x.oN hydrochloric acid, containing both K+ and Li+ levels. Readings were in 1:x, 3:x, and I :3 ratios, and at various concentration then obtained against the pure Ksk or Li’ calibration standards. Some of the Li + results arc given in Table IV. This information indicates that the greater quantities of KC, either ratio-wise or concentration-wise, usually cnuscd increased interfercncc in the Lie’- results. This cffcct is shown in Fig. 2.
0
Pure
LI*
xlLi’.lK’ t. 1 ll’. 3K alLi* SK’ .JLt* IK’
eo60_
l
aoI
0 0001
I
I111111
I 001 meqlml
Fig. 2. Mutual
11
I
11!111
I
III~NI_
O!O Llfhlum
.‘O
Ion
interference
of alkali ions
A comparison of thcsc results with those for K+ indicate that Li+ cause less intcrfcrcncc with the I(+ readings than I(’ with Li+. For example, in the case of I IA+ :I KC, th(: results are given in Table V. TABLE LlTHlUhl .
-
INTEI
-. .-
Actual normality Lit- or I<+ in x.oN __
of HCl __---
Ratio __._- ---
0.001. 0.002
_.
._..--.. ._. _..- ..._-._. . _
of indicntcd J,1-C _ ___
.._
_.
IONS . _
to actual __
_
_^ .._. .._
normality Iit-
_ ._....
1.00
I.01
I .05 I .04 1.01
1.01 1.01
r.03
0.004 0.006 0.005
V
WITH POTASSIUM .__.__ __ _ _._ .___ ._ _._...__
___-..-..-- -
__---_
___..
I.00
._ --_.. __.
0.99 .- .._._._-
Adopted ~rocediwc. The procedure which was finally adopted for the analysis of the solutions encountcrcd in the countercurrent ion cxchangc studies is outlined below : The volume of the snmplc is rccordcd and the acid content dctcrmined on an References
p.
549,
VOL.
11
(1954)
COUNTERCURRENT
ION
EXCHANGE
543
is more than 5% below r.oN, hydrochloric aliquot. If the H+ concentration acid is added to a second aliquot to make the solution I.oN, and the new volume are determined on the acid-adjusted recorded. The K’ and Li+ concentration sample with a flame photometer at predetermined wavelengths using the proper reference solutions. The amounts of K+ and Lit are obtained by reference to the proper calibration curves. Preliminary values for K+ and Li’ were obtained from the calibration curves of the pure ions. The approximate ratio of K+ to Lit was then determined from these results and the corrected K+ and Lit values read from the proper ratio calibration curve. The calibration curves were prepared by plotting readings obtained on solutions of lithium chloride and potassium chloride in r.oN HCl in molar ratios of Li” : I<+ of O:T, I :I, I:Z, x:5, 3:1, 5:1, and x:o. Solutions of o.gN KCl, o.rN KCl, o.ogN KCl, O.OIN KCl, o.5N LiCl, o.rN LiCl, o.ogN LiCl, and O.OIN LiCl wcrc used as reference standards. REMOVAL OF
IONS
FROM
RESIN
In the case of resin* analysis, the principal problem was the quantitative transfer of potassium and lithium from the resin sample to a solution which can be analysed by the standard proccdurc cstablishcd above. The removal (I) clution with an excess of methods tested fell into two general categories: another ion, and (2) dcgradativc oxidation of the resin followed by an ncid leach of the rcsiduc. In the elution method, an aliquot of the resin sample was transferred to a tube, and the chosen volume of elutant was passed through it at a slow rate. The resin was then washed with distilled water, and the combined effluents wcrc analysed for the K+ and Lie removed from the resin. The resin aliquot was then oven-dried, so that the coiicentrations could be expressed on a consistent basis of dry hydrogen-form resin. Since the amount of alkali metal ion originally present on the resin was not known, each set of tests was performed on alicluots of the same resin sample so that the results could be compared. Effect of clulio~ condilions. The elation espcrimcnts involved the effect of clutant quantity and concentration. Each of the elution columns used to check the treatments contained IO g of oven-dried resin. The results obtained arc given in Table VI.
* The resin used in this work was a polystyrene-sulfonic acid ty e resin manufactured by Chcmicsl Process Company, Redwood City, Call*Pornia. Xefeveaces
p.
549.
c-20
544
s.
13. RADDING,
01’ _-
ELUTANT _-------------__
R.
C.
PHILLIPS,
TABLE _ ___ _.--_
IfIrl?KCT ._- .___. -..-
Elution
ON
trcatmentn
IIIESTER
QUALITY
ALTxunt
__._._. __ --__.- ..__.. ._.. ..__ . .IOO ml r.oN HCL 200 ml r.oN I-ICI 400 ml I.ON HCl xoo ml z.oN HCl 400 ml r.oN HCl 1000 ml 2.oN CuCI, .- ..__ -_-- --._------_._- -------.--\vns passed
IC.
through
11
(1954)
OF
EPI:LU&NT
removeci,
rn;ztg
.-_ _ .- - --_--.__-_ 0.078 0.094 o-077 OS’37 0.078 o.rGo 0.158 0.079 0.078 o-159 0.140 0.073 - -.---.--- --_ - _- -- _-._ - __.________ ______
. tllc
VOL.
VI
CONCENTRATION
- - ______
(1 Tlx clutant 5 ml/min.
N.
resin at a
superficial
velocity
of
about
It appears that cithcr 400 ml of r.oN HCI l)oth I<+ and Li+ from the resin satisfactorily.
or IOO of z.oN HCl would elutc The copper chloride elutant was not satisfactory, mainly because it caused intcrfercncc in the flame photometer readings. A volume of 125 ml of 2.oN HCI was selcctcd as best for the elution proccdurc, bccausc the resin could bc washed with an equal volume of distilled wotcr and yiclcl just 350 ml of cfflucnt (a standard volumetric flask size) at a hydrochloric acid concentration of I.oN, the desired lcvcl for analysis. Effect of clvy-nsliing comi?itions. The second removal method, destruction of the resin, was accomplished cithcr by dry-ashing or by chemical oxidation (wetnshing). The resin samples wcrc oven-dried prior to thcsc dcstructivc treatments so that the results could bi: cxpresscd on a dry basis. In the dry method, the resin was carcfully pyrolysed at 1000~ C until only a mineral ash rcmaincd. After cooling, this ash was then taken up with I.ON HCl and the solution analyscd as usual. The wet method consisted of treating the resin with nitric acid and sulfuric acid, and in some cases pcrchloric acid, at the boiling point until no residue was apparent. The resultant solution was then evaporated to dryness, taken up with I.ON I-ICl, and analyscd as before. Again, each set of tests was pcrformcd on alicluots of the same resin sample so that the results could bc comparccl. The first cxperimcnts compared the clution method with dry-ashing in porcelain crucibles. TABLE -.
_. -
COhIPAl~ISON __ .
Trcatmen;
017
_
IlLUTION
_
METIIOD
_
VII \VITII --_---
DRY-ASHING
OF
-_-Arnciyt
__-------.-_ ._.__. .-. .-_. _ Gsin elutecl with xoo ml of 2.oN HCl liesin ashccl at 1000~ C 20 ml o.oxN Solution of 1Li-I- : 1 K-l-._ ..__ ._ _ ._ _ ___. _ .__ -_ _Rcferetrccs p. .=jdg,
0.079
0.024 None
RESIN
fou;~id; mcq/g 0.158 0.025 None
_
VOL.
11
COUNTERCURRENT
(195-1)
ION
EXCHANGE
545
As can be seen in Table VII, ashing in porcelain is completely unsatisfactory, probably because the Lif and K+ are taken up in the porcelain glass. Next, for comparison, platinum crucibles were tried for the dry-ashing instead of porcelain crucibles. In some casts, solutions containing known quantities of Lif and Kf were added to the ashing containers before trcatmcnt. In these cases, the results should be high by the amount added. The results of these tests arc given in Table VIII. TABLE __
COMPARISON . ..___ __ ._ _..
OF .-
IlR\--ASCIINC .__. __ _
RESULTS
--_ .--. _. _ _ _ Resin eluted with IOO ml of z.oN I-ICI ashcd
in porcelain
Resin
ashccl in platinum
PORCELAIN
ASD
Li+ _
Predicted
Ii-t-
IN
PLATINUM
mcq/g Li+
Found
K-t
_ . 0.079
0.158
at 1000~
C
0.024
0.025
at
C
0.083
0.757
0.271
0.188
0.256
0.338+ __I-..
0.075 * o-025* -_--..- ._.__- .._. ______
Rain plus known solution num at 1000~ C ashcd
IN
Amount,
Treatment
Resin
VIII
I
in
. . _ . --.----.
+ Concentrations
iire given
1000”
in plati-
0.?02
platinum _.
0.380* _ _ _.__.- _._______
in total
meq
rather
than
meq/g.
Although the platinum crucibles are much more satisfactory than porcelain, poor recoveries of added solutions were obtained. This may hc due to volatilization or to background cffcct on the flame caused by fine particles of incompletely ashcd resin. The wet-ashing tcchniquc was tried next. In LWffecl of wet-ashing con&ions. these experiments some of the treatments were repeated scvcral times to check the reproducibility of the results. In all cases the material was trcntecl with nitric acid and sulfuric acid, at the boiling point, until the solution was essentially clear. These results arc given in Table IX. The wet-ashing method appears to give fairly reproducible results, but poor recoveries of the acldcd solutions were obtained. Again volatilization or flame background interference due to unreacted resin constituents may bc the cause. A second series of wet-ashing cxpcriments was undertaken next. In this series perchloric acid was used, in addition to nitric acid and sulfuric acid. A few elution runs wcrc also included for comparison purposes on the new resin aliquot. As before, the expcrirnents were pcrformcd in rcplicatc. Rcj-c~emcs
p.
549.
s. 13. RAUDING,
546
R.
C.
I’IIILLIPS,
TABLE TA13ULhTION
-. .
__ _.. _
_ ._
--
OIF
_-._.._.._. .
. ..- - -
IN
THE
PRESENCE
. Resin Rcsi n Resin Resin Resin Known solution * l
HCI HCl
in total
VOL.
11
(1954)
EXPERIMENTS
.
0.231 0.271 O-237 O-255 0.220 o a295 0.351 O-343 0.311 o.G76 0.676 None None than
OF
0.500
. ._. meq rather
._.._
meek Li+
Pound
0.103 0.090 0.093 0.089 0.093 0.156 0.213 0.103 0.135 O.I‘(G 0.2G4 o.zGo 0.329 0.240 0.710 0.710 None None 0.079
PEl
.
ACID
meq/g Li-t-
Found
O-055 0.05G 0.059 0.058 0.059 0.500 0.460 o.oGG o.oG8 ._. _.._._. ._.-.than in mcq/g.
Although Table X shows fairly good agreement clution is simpler and faster.
I<+ -. 0.108 0.185 0.183 0.175 0.183 0.237 0.2GG 0.233 0.259 0.220 0.275 0.256 0.3’5 0.301 0.068 0.688 None None 0.158
in incy/g,
Amount, Prcdictccl Ii -+ Li+
Snmplc
*Concentrations
HIESTER
_. .-... -._ .___ Amount, Predicted Li-I-I<+ _ __ . -..
Resin Rain liesin Resin Resm 0.172 liesin plus known solution Resin plus lcnown solution o.zoG 0.179 12csin plus known solution 0.202 liesin plus known solution O.lG5 Resin plus known solution Rain plus known solution 0.254 Resin plus known solution 0.245 Resin plus lcnown solution o-314 12esin plus lcnown solution 0.2 74 0.800 Known solution* Known solution* 0.8Go water None None Water Resin elutctl with IOO ml of t.oN HCl _ . ..- . ....-__..._-.. _ _--.--._ ..-_. _ *Conccntr;ctions arc given in tota! mcq rather
WIZT-ASIIING
I<.
IX
WET-ASHING
Snmplc _.
N.
in this wet-oxidation
K-t0.138 0.142 0.140 0.142 0.141 o-485 o-143 o-145
method,
rl dofited pvocedl6ve. A 25 ml (8.0 g) sample of the resin is placed in a column r/z x 7 inches and cluted with 125 ml of 2iV hydrochloric acid at a rate of 5 ml Referewes
p.
549.
VOL. 11 (1954)
COUNTERCURRENT
ION
EXCHANGE
547
per minute, catching the effluent in a 250 ml volumetric flask. The sample of resin is then washed with distilled water in the same manner, adding the wash effluent to the acid effluent in the volumetric flask. The solution is diluted to exactly 250 ml with distilled water and analyscd as outlined in the analysis of solutions. The resinis transferred to a beaker, dried overnight at 105~ C and weighed. The results are calculated on a milliequivalent per gram dried resin basis. Determination
of tire dtimde
cxclimzge ca$acity
of the rosin.
An important factor in ion exchange studies is the ultimate capacity, or total exchange capacity, of the ion cxchangc resin. It is a mcasurc of the number of positions available for exchange in a given quantity of resin. Since its cletermination involves the measurement of a resin concentration the techniques involved are similar to those for the removal of ions from a resin. Two fundamentally different methods for determining ultimate capacity were evaluated. In one, resin in the hydrogen form was convex-fed to a mctol ion form by contact with a large excess of metal salt solution. The amount of l-I+ displaced from the resin into the solution was dctcrmincd by titration, thereby indicating the capacity of the resin. The alternative method involved the incrcmcntal titration of a hydrogen resin slurry with sodium hydroxide to obtain a titration curve. The amount of sodium hydroxide solution required to titrate to the point at which the PH changes rapidly, upon the addition of base, was converted to the I-I4 prcscnt and thus to the ultimate capacity of the resin. In the elution procedure a quantity of resin was first converted rilmost completely to the hydrogen form by extensive elution with hydrochloric acid in a fixed bed. This resin was thoroughly mixed and clutcd further with zN I-ICl. Finally it was washed with distilled water until the effluent was neutral to methyl orange. After further mixing, the resin was divided into eight portions of about 25 ml (IO g) and treated as follows: (I) Two aliquots were transferred to small glass columns, and one liter of saturated sodium chloride solution was passed through each. The resin samples then were washed with distilled water. Alicluots of the effluent solutions were titrated with standard sodium hydroxide to the phenolphthalein end-point to obtain the quantity of H+ released by the resin. The resin samples were treated with 250 ml 2.oN HCl, washed with distilled water, and dried overnight at 105’ C to obtain the ultimate capacity in terms of the dry weight of hydrogen form resin. (2) Two aliquots were trcatcd as in proccdurc (I) except that two liters of saturated sodium chloride solution were used. (3) Two aliquots were similarly trcatcd with one liter each of 5’y0 calcium chloride solution. (4) Two aliquots were titrated in increments to pr! r4 with standard sodium
I~efc7e72ccs p. 549.
538
S. B. IZADI>ING,
I<. C. PHILLIPS,
N.
I<. HIESTEH
VOL.
hydroxide. The resin was back-titrated with standard hydrochloric resin samples were washed with distilled water and dried overnight The results of thcsc tests arc given in Table XI. TABLE COMPARISON
_. -
OF
hlETIfOIJS
FOR
11
(1954)
acid. The at 105~ C.
XI
ULTIMATE
.
CAPACITY
Ultimate
Trcntment .- .- -. __-. -- ..----.- -.-.-__..___ -..---_ One liter snturatcd NaCl One liter saturated NaCl Two liters saturated NnCl
DETERMINATIONS
capacity,
meq/g -
$2 5.14 S.06
NaCl
;::, %
5.00
Titration to plr 1.1 Average ___ _. _. _.-- -_._--- __-..._.-. .
5.10
__-.
.__._
____
5.11 -
In the sodium hydroxide titration procedure, the break in the pH curve occurred bctwcen per 7 and px II, as is shown in Fig. 3. The reverse titration with hydrochloric acid to prr 2 did not give a satisfactory end-point. No definite break was observed, and the apparent end-point resulted in an erroneously high capacity. The proccdurc selcctcd as the standard method was that of using one liter of 5% calcium chloride solution. This method was economical of the analyst’s time and of rcagcnts and gave satisfactorily reproducible results.
Pig.
3. Dctcrmination
of ultimate
capacity
by incremental
titration
ACKNOWLEDGEMENTS
Portions
of the cspcrimcntnl
LYDIA PlzTlzRS of the Analytical gratefully acltnowlcdgecl.
References
p. 549.
work were conducted by OLIVER D. SMITH and Section of the Institute and their assistance is
VOL.
11 (1954)
COUNTERCURRENT
ION
EXCHANGE
549
SUMMARY The hydrogen ion concentration exhibited a pronounced effect on the apparent alkali ion concentrations as determined with a Beckman DU spectrophotometer with a flame attachment. Lithium and potassium ions showed a mutual interference, which appeared small, but was sufficient to affect the theoretical evaluation of exchange systems, especially under trace conditions. Control of slit widths eliminated some of the interferences, but further corrective measures had to be applied by the use of prepared calibration curves. from the resins were explored. Several methods for removing ions quantitative1 While cop cr salts were effective elutants, they cou Yd not bc used in routine analysis ions analyses and elution because o P*mtcrference with the lithium and potassium with hydrochloric acid was finally chosen. A simple and economical method was found for detcrminiug the ultimate capacity of the resin. La concentration en ions liydrogtine a une forte influence sur la concentration apparentc des ions alcnlins, dCtermm6e au spectrophotom&tro de flamme Beckman ui, bien DU. Les ions lithium et potassium pr6sentcnt une mutuelle interfbrence, quc falble, cst sufflsante pour fausser 1’6valuation tli6orique dessystemes d ? *change, spt5cialemcnt lors u’il s’agit de traces. Certaines interfbrences pcuvent Otre bliminbes par un contrOle 3 e l’ouverture de la fcnte, mais l’emploi de courbes d’&alonnagc, est n6cessaire. Diffbrentes m6thodes furent essay&es pour 1’Climination quantitative d’ions clans dcs r&sines. Bien que les sels de cuivre soient efficaces comme bluants, ils nc peuvent ctre utilis6s pour dcs analyses en s&rie car ils gOnent les dosages dc lithium et potassium. I1 est plus avantageux d’utiliser l’aclde chlorhydrique. Une mQthodc simple et pratique est utilisee pour la dbtermination dc la capacitG finale des r&sines. ZUSAMMENFASSUNG Die Konzentration der: Wasserstoffionen hat einen grossen Einfluss auf die welche mit dem Flammen-Spcktroscheinbare Konzcntration an Alkaliionen, und Kalium photometer Beckman DU bestlmmt wird. Die Ionen von Lithium zcigcn eiuc gegcnseitige Intcrferenz, welche, obwohl sie sehr schwach ist, ausreicht, urn die thcoretische Bewertung des Austausch-Systcmes zu stijren, speziell sofern es sich urn Spuren handelt. Gewisse Interferenzen kdnnen vermieden werden durch Kontrollc der offnung, aber die Verwendung von Eichkurven ist notwendig. Verschicdene Methoden wurden versucht flir die quantitative Entfernung dcr Ionen aus Harzen. Obwohl die Kupfersalze wirksame kluierungsmittel darstcllen, lccjnnen sic flir Serienanalysen nicht verwendet werden, da sic die Bestimmung von Lithium und Kalium stbren. Es ist vorteilhafter die Salzsjiure zu verwenden. Eine einfachc und praktische Methode wird verwendet flir die Bestimmung dcr Kapazitiit von Harzcn. REFERENCES 1 J. W.
BEIIIIY, D. G. CIIAPPOLL AND R. B. BARNES, Ind.
123 (x+$6)
E71g.
19.
Chcnt.,
Amal.
Ed.,
* P. T. GILUIZRT, JR., R. C. H,\wss
AND A. 0. BECI~MAN, An&. Chem., 22 (1950) 772. 3 N. K. HiEs*rm<, R. C. PIXILLIPS, E. F. FIELDS, R. C. COHEN ANI) S. 13. RADDING,
Id. Eng Chem., 45 (1953) 2402. 4 N. K. HIESTER, E. F. Frowns, R, C. PIIIL’LIPS AND S: 13. RA-SDING, Chem: Eng. Pvog., So (1954) 139. 0 T. D. P,\HKs, H. 0. JOHNSON AND L. LYICKISN, Anal. C/tern., 20 (1948) 822.
Received
June
10th.
1954
-