[ COVTRIBUrIOS F R O M
THE O A K
RIDGES A T I O N A L LABORATORY, CHEMISTRY DIVISION]
Anion-exchange Studies. XVIII. Germanium and Arsenic in HC1 Solutions’n2 BY FREDERICK NELSOXAND RCRTA. KRAUS RECEIVED FEBRUARY 23, 1955 The anion-exchange behavior of Ge(IV), As(II1) and As(V) in hydrochloric acid solutions was studied with a strong base quaternary amine anion-exchange resin Both Ge(1V) and As(II1) show little adsorption at low ,M HCI and rapidly increasing adsorption with increasing 31 HCl above ca 5 &’ HC1 Adsorption of As(V) was low throughout t h e HCI conceritration range studied (0 1 t o 12 .lf) Application of these d a t a t o separations is discussed
I t was demonstrated in previous papers that anion exchange is a powerful tool for the separation of many elements. .I systematic study of essentially all metals has been carried out in hydrochloric acid solutions and the present paper summarizes the results for Ge(IV), ,Is(III) and As(V). Distribution coefficients D have been measured in the range 0.1 to 12 HC1. Considerable differences in adsorbability were found which may be used as the basis of a number of separations. Experimental
properly acidified aliquots of a stock solution prepared by dissolving C.P. As203 in 0.5 111 S a O H . The elution maxima were located by spot testing successive aliquots of the effluent (SnC12 method5). T h e experiments with As(V) mere carried out with the arsenic tracer. It originally contained both As(II1) and As(\’). T o prepare essentially pure As(V) solutions the tracer was oxidized with chlorine and to avoid possible reduction, particularly at high hydrochloric acid concentrations,e chlorine was added t o all the solutions as a “holding oxidant.” All experiments were carried o u t in a n air-conditioned room at 25 & 2“. Further experimental details will be given in connection with the discussion of the various systems.
Adsorbabilities were measured by the equilibrium or column technique^.^ In the equilibrium technique measured amounts of solution and resin were agitated for a t least one day, after which the solution phase was analyzed. From the change in concentration after equilibration, distribution coefficients D (amount per kg. d r y resin/amount per liter solution) were calculated. All resin weights and distribution coefficients refer to resin dried over “Anhydrone” a t 60” in a vacuum desiccator. The resin was from the same batch of relatively highly cross-linked polystyrene divinylbenzene quaternary amine resin (Dower-1 , 200-230 mesh) which was used in most of the earlier studies and which was characterized previously. Most concentrations were determined radiometrically with the tracers Ge” ( T I / ?= 12 hr.); As7’ (Tils = 40 hr.) = and the mixed tracer AsT3-Asi4(T = 76 day and 19 d a y ) . The Ge77-As77 tracer T s prepared by neutron irradiation of GeOa in the ORNL Low Intensity Training Reactor ( L I T R ) . Aliquots of a stock solution, prepared by dissolving the irradiated oxide in 0.5 J 4 NaOH, were used after appropriate acidification. Half-life determinations indicated t h a t the tracer was of satisfactory purity. All final counting in the Ge(IV) equilibration experiments was carried out after secular equilibrium with the daughter activity As77 had been reached. Since Ge(IV) is easily volatilized from strong HC1 solutions, both the resin and solution phases were counted t o ensure t h a t no serious loss of Ge(I\.) had occurred during sampling. For this purpose the shaking experiments were carried out in 2-1111. tubes. Samples of the solution (1 ml.),were counted, a s well as the remaining liquid-resin mixture. The fractiofl‘ of germanium in the resin could then be computed and material balance” checked. S o experiments arc recorded where loss exceeded 2OY0 of the activity. The As’3--As7; tracer in HC1 solution was obtained from the Radioisotopes Division of ORKL and analyzed by them for radiochemical purity. I t contained 2070 As“, 80% and negligible amounts of other activities. The adsorbabilities of As(I1I) and As(V) were determined by the column method. I n this method elution bands characteristic of only one oxidation state can be followed and errors from possiblc oxidation-reduction reactions and resulting cross-contamination by the various oxidation states can be avoided. The method is thus more reliable than the equilibrium method which in the absence of separate oxidation state analyses yields only average adsorbabilities. Most experiments with As(II1) were carried out with
Results and Discussion 1. Adsorbability of Ge(IV), As(II1) and As(V). -The observed distribution coefficients D (amount per kg. dry resin/amount per liter of solution) are summarized in Fig. 1. The adsorbability of Ge(1V) is essentially negligible from 0.1 to ca. 4 M HC1 and then rises sharply with increasing M HC1 to D = 185 in 10 M HC1. There is indication that D continues to increase a t higher HC1 concentrations. However, the high volatility of Ge(IV) under these conditions precludes accurate measurements. The adsorbability of As(II1) is essentially negligible in the region 0.1 to ca. 4 *If HC1. There is indication that a t lower HCl concentrations its adsorbability rises with decreasing M HCl, possibly due to adsorption of arsenite ions. *4t HCl concentrations larger than 4 M , adsorbability of As(IT1) increases with increasing M HC1 ( D = ca. 26 in 11 ,I6 HCl). The adsorbability of -4s(V) is low throughout the entire range of HC1 concentrations studied. Distribution coefficients increase slightly with J6 HC1 from D = ca. 1.8 in 0.1 111 HCl to D = ca. 4 near 10 -1IHCl. The strong adsorption of Ge(1V) and As(II1) a t high hydrochloric acid concentrations suggests that both elements form negatively charged complexes. In the case of Ge(1V) these negatively charged complexes are apparently not yet completely formed in 10 A6 HC1 since adsorption appears to continue to increase with increasing Jf HC1 in this region. For .4s(III), on the other hand, above 10 M HCI negatively charged complexes may become dominant since the distribution coefficients tend to level off. Qualitatively the adsorption behavior of AS(111) and Ge(1V) is essentially in agreement with the known continued increase in the volatilities of both Ge(1V) and As(II1) with IIif HC1, and one might further conclude by cornbination of the observations on volatility and anion exchange that formation of the negatively charged complexes for
(1) This document is based on work performed for t h e U . S. Atomic Energy Commission at the Oak Ridge Sational Laboratory. (2) Previous communication: F . Pl’elson and K A . Kraus, THIS J O U R N A I , , 7 7 , 3972 (195.5) (3) See e.g., K. .I.Kraus, l?,Selson and G. \V Smith, J . P h y s . Cht‘n7 , 68, 11 (1954). ( 4 ) K , A . K r a u s and G . 13, hloore, 1”ili J O U R N A I . , 7 5 , 1457 ( 1 9 5 3 ) .
( 5 ) F. Feigl, “Qualitative Analysis b y Spot Tests,” Elsevier Publishing Co., Xew York, S . Y . , 1946. (6) J. W. Mellor, “Inorganic and Theoretical Chemistry,” Vol. I X , Longmans, Green a n d Co , S e w York, N . V.,p , 1-14.
Sept. 5 , 1955
GERMANIUM AND ARSENICIN HCl SOLUTIONS
4,509
5
0 2
4
2 3 4 5 6 COLUMN VOLUMES OF EFFLUENT,
Fig. 2.-Separations
io
7
involving germanium and arsenic.
erable, adsorption of As(II1) becomes sufficiently large to necessitate inconveniently large volumes I I for its elution, although separation is feasible. The 1 I 0.5 I 0 2 4 6 8 (0 12 separation of As(V) from Ge(IV), on the other hand, MOLARITY OF HCI. readily can be achieved a t high HCl concentraFig. 1.-Adsorption of Ge(IY), As(I1I) and As(V). tions. Even a t low HC1 concentrations, where D A ~ ( v> ) D G e ( I V ) , this separation is still feasible. these elements proceeds through the neutral species Under ), low, is high these conditions D A ~ ( vthough (GeC14and XsC13). enough to delay appearance of the As(V) elution It is interesting to note that both Ge(1V) and band until essentially all the Ge(1V) (or any other As( 111) are extractable from strong hydrochloric "non-adsorbable" element) has been removed. acid solutions by organic solvents,' which is in acA typical separation involving Ge(1V) and As(V) cordance with these considerations, although it is felt that for these elements the fact that solvent is illustrated in Fig. 2a. For this experiment, Feextraction occurs cannot be taken as an indication (111)was added, as well as a typical non-adsorbable that singly negatively charged complexes are element. For the latter Eu(II1) was chosen since f~rmed.~ I t is likely that in these cases solvent its tracer (EulS5)was conveniently available. An extraction involves the neutral species GeC14 and 0.5-ml. aliquot of a solution containing Eu(II1) lS5 As(V)'?, Ge(IV)77,0.01 M Fe(III), 6 M HC1 and AsCl3. One might be tempted to conclude that the ad- chlorine was added to an 0.45 cm.2 X 9.0 cm. colsorption of Xs(V), though small, indicates existence umn of resin pretreated with 6.2 ilf HCl and Cl?. of negatively charged complexes. However, this is Elution was carried out with 6.2 34 HCl(C12). unlikely in view of the instability of AsC16 and the The non-adsorbable element, E u ( I I I ) , appeared in apparent non-existence of As(V)-chloride com- a sharp band with a maximum near 0.4 column volplexes8 More probably the slight adsorption is ume and was separated from As(V), Ge(1V) and due to extraction of arsenic acid ( H a s o , ) by the Fe(II1). As(V) appeared in a reasonably sharp resin. The small increase in adsorption with M band with a maximum near 2.2 column volumes. HCl probably reflects a relatively minor change in Ge(1V) was removed with 3 ill HC1 and then Fethe ratio of the activity coefficients of the species (111)with 0.4 Jf HC1. The differences in the adsorbability of As(II1) H3As04in the two phases. 2. Separations Involving Arsenic and Ger- and As(V), particularly a t high J4 HCl, permit sepmanium.-The differences in adsorbability between aration of these oxidation states, as demonstrated As(II1) and Ge(1V) a t low HCl concentrations are in Fig. 2b. -in 0.1-ml. aliquot of a solution contracer and 9 >If too small to permit separations with small col- taining .~s(III)~~-~~-As(V)~~-~~ umns. A t high HCl concentrations where the HC1 was added to an 0.24 cm.? X 7 . 2 cm. column differences between these two elements are consid- of resin which had been pretreated with 9 M HC1. Elution was carried out with 9 M HC1. As(V), as (7) (a) K . Rohre, 2 . nwal. Chem., 65, 108 (1824), (extractability of expected, appeared in the effluent in a reasonably AsC18 b y CClr f r o m HCI solutions); (h) H . 51. Irving, Q u a r t . Rens., I, sharp band near 2.2 column volumes of emuent, 200 (1951). while As(II1) remained adsorbed. Removal of the ( 8 ) See e . g . , (a) Gmelin's "Handhuch der anorganischen Chemie," Eighth Edition, System No. 1 7 , Verlag Chemie, Weinheim. Germany, Xs(II1) was accomplished with 0.1 M HCI.
1 9 5 2 , p. 391; (b) N. 1'. Sidgwick, "The Chemical Elements and their Compounds," Vul. 1 , Clarendon Press, Oxford 1950, p. 7 8 1 .
OAK RIDGE,TBSN.
