Distribution Coefficients and Anion Exchange Behavior of Elements in Oxalic Acid-Hydrochloric Acid Mixtures F. W. E. Strelow, C. H. S. W. Weinert, and Cynthia Eloff National Chemical Research Laboratory, Pretoria, Republic of South Africa
Anion exchange distribution coefficients with AG b X 8 , a strongly basic quarternary ammonium anion exchanger with a polystyrene matrix, are presented for 36 elements in oxalic acid-hydrochloric acid mixtures. The coefficients are presented in two tables ordered according to their numerical value in 1M HCI plus 0.05M (or 0.25M) oxalic acid. When this value is lower than 1, the values in 0.1 or 0.01M HCI are taken. A number of the possibilities of this system for separations are pointed out, and some aspects of the elution behavior of various elements are discussed. The versatility of the system is demonstrated by sequential elution of the mixtures Mn(l1)-Ni(l1)-V(V)-Nb(V)U(VI); Mg-AI-Ga-In; Co(1l)-Cu(l1)-Ti(1V)-Mo(V), and Cu(ll)-AI.
WHILEOXALIC ACID or oxalic acid-mineral acid mixtures have been used successfully for the ion exchange separation of elements such as Sc, Ti(IV), and V(V) ( I ) , Ti(IV), Zr, Nb, Ta, W(VI), and Mo(V1) (2); and Ta and Nb(V) ( 3 4 ) ; and oxalic acid or oxalates have been used for the elution of Te(IV), Sb(V), and Sn(1V) (5); Ga(II1) (6); U(V1) (7); and Cu(II), Ni(II), and A1 (8), the only systematic anion exchange study in oxalate media seems to be that undertaken by De Corte et a[. (9), who have determined distribution coefficients for 12 elements in oxalic acid solutions with Dowex 1-X8 resin. While only separations of radio tracer amounts were reported, separations of milligram amounts should be possible in some cases, though most of the elements investigated have limited solubilities in oxalate solutions. Some common multivalent elements such as Al, Fe(III), and Ti(1V) do form oxalate complexes with stability constants several orders of magnitude larger than those of Cu(II), Ni(II), Mn(II), etc. Oxalic acid in appropriate mixture with a strong mineral acid, which could be used to control the dissociation of the oxalic acid and therefore effect selective complex formation, therefore should offer excellent prospects for the separation of multivalent from divalent elements. Furthermore, the anion of the mineral acid will compete for exchange sites in the resin and the strength of this competition is governed not only by the concentration, but also by the kind of the anion. This provides more variables the analyst can use when looking for selective separations. This paper presents a systematic study of anion exchange distribution coefficients of 36 elements in oxalic-hydrochloric (1) R. I. Walter, J , Znorg. Nucl. Chem., 6 , 58 (1958). (2) W. R. Bandi, E. G. Buyok, L. L. Lewis, and L. M. Melnik, ANAL.CHEM.,33, 1275 (1961). (3) J. Gillis, J. Hoste, P. Cornand, and A. Speeke, Meded. Kon. Vlaam. Acad. Wetensch. Belg., 15,63 (1953). (4) M. Herman, Ind. Chim. Belge, 23, 123 (1958). ( 5 ) R. K. Preobrazhensky and L. M. Moskvin, Radiokhimiya, 3, 309 (1961). (6) E. P. Tsintsevich, I. P. Alimarin, and L. F. Marchenkova, Chem. Abstr., 53,10898 (1959). (7) Z. Dizdar, Recl. Tral;. Inst. Recherches Structure Matiere, 2 , 85 (1953). (8) M. R. Zaki and K. Shakir, 2.Anal. Chem., 185,422 (1962). (9) F. De Corte, P. Van Den Winkel, A. Speeke, and J. Hoste, Anal. Chim. Acta, 42,67 (1968). 2352
acid mixtures. Two oxalic acid concentrations 0 . 0 5 M and 0.25M were selected and the hydrochloric acid concentrations were varied from 0.01M to 4.OM. EXPERIMENTAL
Apparatus. Borosilicate glass tubes of 20-mm i.d. with fused-in glass sinters of No. 2 porosity and a buret tap at the bottom and a B 19 ground glass joint at the top were used as columns. A Zeiss PMQ I1 and a Perkin-Elmer 303 instrument were used for spectrophotometric and atomic absorption measurements, respectively. Reagents. Analytical reagent grade chemicals were used whenever possible. Hafnium oxide, the chlorides of Ti(V), Ta(V), Nb(V), Ga, and In(II1) and chloroplatinic acid were obtained from Fluka A.G. ; Buchs, Switzerland. Standard solutions containing 1 millimole of the element in 25 ml of 0.10M HCl were prepared. Solutions of W(VI), Mo(VI), Fe(III), and V(V) also contained 1 of hydrogen peroxide, and those of Ti(IV), Nb(V), Ta(V), and Sn(1V) 0 . 5 0 M oxalic in addition to HC1 and hydrogen peroxide. Less concentrated solutions were prepared by dilution when required. The resin used was AG 1-X8 strongly basic anion exchanger supplied by Bio-Rad Laboratories, Richmond, Calif. Resin of 100- to 200-mesh particle size was used for determination of distribution coefficients and of 200- to 400-mesh for column work. Procedure. Distribution coefficients were determined by equilibrating in a mechanical shaker 250 ml of a solution containing 1 millimole of the element and the given concentrations of oxalic and mineral acid with 2.500 grams of AG 1-X8 resin in the chloride form, which had been dried at 60 "C in a vacuum pistol with phosphorus pentoxide as drying agent. Solutions of W(VI), Mo(VI), Fe(III), V(V), Ti(IV), Nb, Ta, and Sn(1V) contained 0.1% of hydrogen peroxide. Only 0.05 millimole of the element was used in the case of the elements Bi(III), Cu(II), Ni(II), Co(II), Zn, Pb(II), and Cd because of the limited solubility of their oxalates. Equilibration time was 24 hours and equilibration temperature 25 "C, except in the case of Fe(II1) where an equilibration time of 2 hours was used to minimize the amount of reduction to the divalent state. After separation of the resin from the aqueous phase, the amounts of the elements in both, aqueous phase and resin, were determined by appropriate analytical methods and weight equilibrium distribution coefficients were calculated from the results.
D =
amount of element in resin amount of element in solution
ml solution gram dry resin (1)
The coefficients are presented in Tables I and 11.
RESULTS The coefficients in Tables I and I1 indicate numerous possibilities for separations. A few of these were selected for further investigation and a few typical multielement elution curves using synthetic mixtures were prepared to demonstrate the versatility of the system. Separation of Mn(I1)-Ni(I1)-V(V)-Nb(V)-U(V1). A solution containing 0.5 millimole each of Mn(II), V(V), Nb(V),
ANALYTICAL CHEMISTRY, VOL. 44, NO. 14, DECEMBER 1972
Table I.
Element Sn(1V) W(V1) Pd(I1) MO(VI)~ Bi(III)b,c WI) Mo(V1) Ta(V)a Cd(II)b In(II1) Nb(V)a U(V1) Zn(II)b Ti(IV) Fe(I11p Zr(1V) Ta(V) Hf(IV) Ga(II1) Ti(IVp Pb(II)bfc sc
WV) V(V)
0.01M
> 104 3450 >io4 >io4
... 1500 >io4
3 78
51
> 104 > 104 > 104 28.7 >io4
>io4
> 104 103 4030 >io4
> 104
60 5180 5370
Al(II1) >io4 Cu(1I)b 620 Be(I1) 68 Ni(II)b 84 9.2 Co(I1)b Mn(II), Mg, Ca, Sr, Ba, Li, Na, K, Rb, Cs 1 ml of 30% HZOZ present. 0.05 millimole of element. 2-hour equilibration time.
Anion Exchange Distribution Coefficients in Oxalic Acid-HC1 Mixtures 0.05M Oxalic Acid Various Concentrations of HCl Molarity HCI 0.1M 0.2M 0.5M 1.OM 2.OM 3.OM > 104 > 104 >io4 > 104 > 104 9700 7610 6720 699 163 > 104 9170 2850 440 >104 >io4 >io4 867 2310 920 660 > 104 >lo4 > 104 1900 1330 900 590 567 700 1230 1370 1500 1470 1480 837 1270 >io4 650 4100 487 >io4 303 367 364 201 17.7 118 269 171 195 48.9 289 472 2900 44.4 28.8 828 80 173 11.5 3410 7100 675 4.7 78 24.2 1630 66 250 6800 38.1 30.6 3.3 2.9 5.3 35.3 61 26.5 > 104 >io4 639 io4 0.5 11.4 138 39.5 102 10.9 104 5.5 6.1 3560 85 0.9 1700 8.1 1.7 43.5 6.6 485 1.2 >io4 7.9 1420 38.6 6.4 0.5 320
