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A study of the separation of phosphate ion from arsenate ion by solvent extraction
Taianta, 1961, Vol. 7. pp. 276 to 280.
Pergamon Press Lrd
Printed in Northern Ireland
A STUDY OF THE SEPARATION OF PHOSPHATE ION FROM ARSENATE ION BY SOLVENT EXTRACTION HARLEY H. ROSS* and RICHARD B. HAHN Department
of Chemistry,
Wayne State University,Detroit, Michigan,U.S.A. (Received 8 September 1960)
Sac-Theresults pr~en~dcon~ the postuIate of Keggin that o~gen-confining materials are good solvents for heteropoly acids. The results also show that none of the solvents examined will completely separate phosphate ion from arsenate ion with a single extraction. The butanol-chloroform system is studied extensively. The results show that as the percentage of butanol is increased in the mixed solvent, the percentage of phosphate and arsenate extracted also increases. Of the various concentrations of butanol studied, the 10% concentration shows the most promise as a selective extractant for phosphate consistant with a high yield. The results also show that the amount of arsenate ion extracted with any given concentration of butanol is relatively independent of the concentration of phosphate ion in the system. INTRODUCTION
THE separation of phosphate ion from arsenate ion is an important problem in analytical chemistry. The separation is especially di~cult when the amount of arsenate ion is large as compared to that of phosphate. Precipitation methods do not serve to separate phosphate from arsenate, as similar insoluble arsenate compounds are formed. The gathering of phosphate ion on a precipitate of aluminum or iron111 hydroxide has been used to separate phosphorus from other elements but, here again, arsenate interferes. Arsenate can be separated from phosphate by reducing the arsenic to the tervalent state, then boiling with either hydrochloric acid or hydrofluoric acid. In this process the arsenic is volatilised from solution but this method is quite long and is not suitable for removing microgram amounts of arsenate from solution. Of all the various methods solvent extraction procedures have shown the most promise. For this reason, this study has been limited to solvent extraction techniques. There are many methods in which phosphate ion is separated from other elements by extracting phosphomolybdic acid with an organic solvent. Wuf9 and Copaux4 used diethyl ether as the solvent for the heteropoly acid. Scroggie14 found that esters, ketones, aldehydes, and ethers are good extractants but carbon disulphide, carbon tetrachloride, chloroform, benzene, and toluene are not. Keggin postulated that oxygen-containing materials are good solvents for heteropoly acids. Other solvents that have been used to extract heteropoly acids include ethyl acetoacetate,16 ethyl acetate,’ butyl acetate,9 2-methyl-l-propanol,2*3*16 3-methyl-1-butanol,ll I-octanol,13 and l-butano1.l’ Mixtures of 1-butanol in chloroform have also been used to extract In all of the above mentioned phosphomolybdic acid from arsenomolybdic acid. 1*5*6~10 solvents, arsenic was extracted to some extent also and only a limited amount could be tolerated without interference. An article by Wadelin and Mellonl* compares various solvents. * present address: Oak Ridge Institute of Nuclear Studies, Oak Ridge, Tennessee, U.S.A. 276
A study of the
separation of phosphate ion from arsenate ion by solvent extraction
Rosenheim12 gives a general equation for the formation acids : X”0 n(2a- + + 12M00,~
277
of heteropolymolybdic
+ (24 + 2a - n)Hf ---t Ho2 - ,jX(MozOJ6 + (6 + a)H,O
(I)
where X is Pv, AsV, SiIv, or Ge Iv. Inspection of equation (I) shows that a large excess of molybdate ions or hydrogen ions will force the reaction to the right. Wadelin and Mellon, however, were unable to utilise a high concentration of molybdate ion to enhance the formation of the heteropoly acid because it exhibits strong absorption in the same region as the complexes they measured. In the present work, various solvents were studied using radiochemical methods. The chloroform-butanol system was examined extensively. Unlike the spectrophotometric method, none of the solution variables affect the accuracy of the measurements made on the system. EXPERIMENTAL Reagents In addition to standard laboratory reagents, the following solutions were used: Phosphorus-32 and Arsenic-76 tracer solutions: Solutions of these isotopes, in the form of phosphate and arsenate, were diluted to the desired activity with O.OlN hydrochloric acid. Phosphorus carrier: Dissolve 2.8657 g of pure potassium dihydrogen phosphate @U&PO3 in 100 ml of water and dilute to 1 litre. The resulting solution contains 2.00 mg of phosphate ion per ml. Arsenic carrier : Dissolve about 45 g of disodium hydrogen arsenate (Na,HAsO~~7H,O) in 100 ml of water and dilute to 1 litre. The resulting solution contains about 2 mg of arsenate ion per ml. Magnesia mixture: Dissolve 55 g of magnesium chloride (MgCle.6HaO) and 140 g of ammonium chloride in 500 ml of water. Add 130 ml of concentrated ammonium hydroxide and dilute to 1 litre. Organic solvents: All organic solvents were chemically pure or reagent-grade. Mixed solvents were prepared on a volume percentage basis by adding the required volumes of each component using a pipette. Apparatus Various methods were used to detect and count the activities of the isotopes used in this work. Beta activity was measured with end-window Geiger tubes of both the halogen and organic quenched types. Gamma radiation was measured with a thallium-activated sodium iodide crystal in the form of a well-type scintillation detector. The counts were recorded with a variety of commercial scalers. General procedure Various concentrations of reagents are recommended in the literature for the extraction of heteropolymolybdic acids. The following concentrations were decided upon as being representative and consistent with a large molybdate and hydrogen ion concentration. The hydrochloric acid concentration was 50 % (V/V) and the sodium molybdate was 0.31 M (15 ml of 20 % sodium molybdate solution in 40 ml of final solution). All extractions were performed with 40 ml of solution in each phase. After preliminary experimentation, the following general procedure was developed to determine the amount of phosphate extracted. Procedure (1) Pipette exactly 5 ml of phosphate carrier into a 250-ml separatory funnel. (2) Add an amount of szP tracer solution (lo-50 ,ul) to give an activity of lO,OOO-15,000cpm. (3) Add 15 ml of 20 % sodium molybdate solution. (4) Add 50 ml of the solvent being examined. (5) Add 20 ml of concentrated hydrochloric acid, stopper the funnel, shake for 2 min, and allow the phases to separate.
278
andRtc~.4xn
HARLEYH.ROSS
B. HAHN
(6) Separate the layers, discard the aqueous phase, and add 50 ml of 3Mammonium hydroxide-1M ammonium chloride buffer solution to the organic phase, shake 2 min, and allow the phases to separate. (7) Drain the aqueous layer into a 1%ml beaker and heat to boiling. (8) Add 10 ml of magnesia mixture and allow to stand until cool. (9) Collect the precipitate of magnesium ammonium phosphate on a tilter disc in a Hirsch funnel. Wash the precipitate with three lo-ml portions of buffer solution and three 5-ml portions of acetone. (10) Aii dry the precipitate and beta count. (11) The percentage of phosphate extracted is found using the equation :
Al x 100 ‘A extracted = Aa where A, = the activity of the precipitate (cpm), and Az = the activity of the original tracer solution (cpm). A procedure similar to the above was used to determine the percentage of arsenate extracted with the same solvents. The numbered steps in the general procedure were replaced by the following: (la) Pipette exactly 5 ml of arsenate carrier into a 250-ml separatory funnel. (2a) Add an amount of 7BAstracer solution (10-50 ~1) having a total activity of 70,000-80,000 CPM. Steps 3,4, and 5 are the same as above. (6a) Pippette a 5-ml portion of each layer into different test tubes suitable for use in a well-type scintillation counter. (7a) Count each layer. The percentage of arsenate extracted is calculated by means of the following equation: A, x 100 ‘A extracted = A, + Aa where
A,, = the activity of the organic phase (cpm),
and
A, = the activity of aqueous phase (cpm). RESULTS
the above procedures, several solvents were examined to determine how much phosphate and arsenate was extracted by each. The results of these experiments are shown in Tables I and II. The results obtained in the first two sets of experiments indicated that 20 % butanol in chloroform was a promising solvent, in that a large percentage of phosphorus was extracted while only a small amount of arsenic was carried through. It was thought Using
TABLEI.-PERCENTP;GEOFPHOSPHATEEXTRACTEDUSINGVARIOUS ORGANIC SOLVENTS
Solvent
‘A Phosphate extracted h 5 ‘A*
Ethyl acetoacetate 20 % Butanol in chloroform Ethyl acetate Butyl acetate 50% Zsobutanol in benzene Zsobutanol 1-Butanol 1-Octanol Chloroform Benzene
lOOGO 94.97 79.92 73.58 72.63 67.21 60.63 29,86 00.00 OOGO
* Average oftwo determinations
A study of the separation
of phosphate
TABLE II-PERCENTAGE
ion from arsenate ion by solvent extraction
279
OF ARSENATEEXTRACTED USING VARIOUS ORGANIC SOLVENTS
Solvent
%
Arsenic extracted &5 %*
20 % Butanol in chloroform Butyl acetate 1-0ctanol Ethyl acetate 50 % Isobutanol in benzene Zsobutanol I-Butanol Ethyl acetoacetate Chloroform Benzene
4.74 849 14.39 29.46 36.76 87.05 87.91 96.67 00.00 OOGO
* Average of two determinations
that a more favourable mixture of 1-butanol might exist for this extraction. To this end, the same procedures were used to determine the percentage of phosphate and arsenate extracted with various concentrations of 1-butanol. The extractions of arsenate were made with three concentrations of this ion. Extractions were performed both in the presence and absence of phosphate ion to determine the effect of this variable. The experimental conditions and results are shown in Tables III, IV, and V. TABLE III.-PERCENTAGE
OF PHOSPHATE EXTRACTED USING VARIOUS
CONCENTRATIONS OF 1-BlJTANOL IN CHLOROFORM % Butanol
% Phosphate extracted &5 %*
20
94.97
19
95.04
18
97.23
17
93.26
16
92.99
15
96.31
10
8560
7.5
55.01
5.0
18.30
* Average of two determinations TABLE IV.-PERCENTAGE
OF ARSENATEEXTRACTED USMG VARIOUS
CONCENTRA~ONS OF l-BUTANOL IN CHLOROFORM ‘A
Arsenic extracted at indicated level*
% Butanol
5 10 15 20 30 * Average of 10
IO-mg
loo-Pug
0.20 0.36 1.56 5.16 13.57
0.27 1.42 2.45 4.58 13.15
two determinations
Tracer 0.076 0.78 1.99 4.17 13.06
280
HARLEYH. Ross and RICHARDB. HAHN TABLEV.-PERCENTAGEOFARSENATEEXTRA~DUSINGVARIOUSCONCENTRA~ONS OF l-BCJTANOLINCHLOROFORMWITH~~ mg OFADDEDPHOSPHATE 'A Arsenic extracted at indicated level*
% Butanol
5 10 15 20 30
lO-mg
lOO+g
Tracer
0.073 0.69 2.30 4.32 12.12
0.14 0.88 1.61 3.62 12.38
0.12 0.80 1.77 4.50 12.38
* Average of two determinations Zusammenfass~-Das Postulat von Keggin, wonach sauerstoffhaltige verbindungen gute Liisemittel fti Heteropolysauren sind, wird bestatigt. Keines der untersuchten Losemittel kann eine viillige Tremmng von Phosphat und Arsenat in einem Extraktionschritt bewirken. Das System Butanol-Chloroform wurde eingehend studiert. Mit an&gender Butanolkonzentration steigen die extrahierten Phosphat und Arsenatmengen an. Eine Butanolkonzentration von 10 % scheint meistversprechend ftir eine selektive Phosphatextraktion zu sein. Die extrahierte Arsenatmenge ist weitgehend unabhangig von der vorherrschenden Phosphatkonzentration. R&u&-Le postulat de Keggin, a savoir que les substances contenant de l’oxygene sont de bons solvants des htteropolyacides, est confirm&. Aucun des solvants etudib ne &pare completement l’ion phosphate de l’ion arseniate en une seule extraction. Le systeme butanol-chloroforme a et6 tres ttudit. Quand le pourcentage de butanol augmente dam le melange de solvants, le pourcemage de phosphate et d’arseniate extraits augmente aussi. Parmi les concentrations vari&s de butanol &udi&es, 10 pour cent offrcnt le plus de promesses comme produit extrayant selectivement le phosphate, avec un rendement important. La quantit6 d’arseniate extraite par toute concentration de butanol est relativement independante de la concentration d’ion phosphate dans le systeme. REFERENCES 1 R. I. Akkseev, Zavodskuya Lab., 1945,11, 122. a R. J. L. Allen, Biochem. J., 1940,34,858. a I. Berenblum and E. Chain, ibid., 1938,32,287. 4 H. Copaux, Compt. rend, 1921,173,656. 5 K. T. H. Farrer and S. J. Muir, Austral. Chem. Inst. J., and Proc., 1944, 11,222. BN. A. Filippova and L. I. Kuznetsova, Zavodskuyu Lab., 1950,16, 536. ’ J. Hure and T. Ortis, Bull. Sot. chim. France, 1949, 834. * J. F. Keggin, Proc. Roy. Sot., 1934, 144, 75. 8 T. Koto, et al., Technol. Repts. Tdhoku Univ., 1950, 15,70. loR. V. Mervel, Zavodrkaya Lab., 1945, 11,135. I1 C. Rainbow, Nature, 1946, 157,268. le A. Rosenheim, in Abegg and Auerbach’s Handbuch der anorganischen Chemie, Leipzig S. Hirzel 1921, Bd. IV, 1 Abt., 2 Halfte, pp. 977-1065. I11F. L. Schaffer, et al., Analyt. Chem., 1953, 25, 343. I4 A. G. Scroggie, J. Amer. Chem. Sot., 1929, 51, 1057, I5 C. Sideris, Znd. Eng. Chem. Analyt., 1942, 14,762. I6 K. Stoll, Z. analyt. Chem., 1938, 112, 81. I7 C. Wadelm and M. G. Mellon, Analyst, 1952, 77, 708. I8 Zdem, Analyt. Chem., 1953,25, 1668. I4 H. Wu, J. Biol. Chern., 1920, 43, 189.
Pergamon Press Lrd
Printed in Northern Ireland
A STUDY OF THE SEPARATION OF PHOSPHATE ION FROM ARSENATE ION BY SOLVENT EXTRACTION HARLEY H. ROSS* and RICHARD B. HAHN Department
of Chemistry,
Wayne State University,Detroit, Michigan,U.S.A. (Received 8 September 1960)
Sac-Theresults pr~en~dcon~ the postuIate of Keggin that o~gen-confining materials are good solvents for heteropoly acids. The results also show that none of the solvents examined will completely separate phosphate ion from arsenate ion with a single extraction. The butanol-chloroform system is studied extensively. The results show that as the percentage of butanol is increased in the mixed solvent, the percentage of phosphate and arsenate extracted also increases. Of the various concentrations of butanol studied, the 10% concentration shows the most promise as a selective extractant for phosphate consistant with a high yield. The results also show that the amount of arsenate ion extracted with any given concentration of butanol is relatively independent of the concentration of phosphate ion in the system. INTRODUCTION
THE separation of phosphate ion from arsenate ion is an important problem in analytical chemistry. The separation is especially di~cult when the amount of arsenate ion is large as compared to that of phosphate. Precipitation methods do not serve to separate phosphate from arsenate, as similar insoluble arsenate compounds are formed. The gathering of phosphate ion on a precipitate of aluminum or iron111 hydroxide has been used to separate phosphorus from other elements but, here again, arsenate interferes. Arsenate can be separated from phosphate by reducing the arsenic to the tervalent state, then boiling with either hydrochloric acid or hydrofluoric acid. In this process the arsenic is volatilised from solution but this method is quite long and is not suitable for removing microgram amounts of arsenate from solution. Of all the various methods solvent extraction procedures have shown the most promise. For this reason, this study has been limited to solvent extraction techniques. There are many methods in which phosphate ion is separated from other elements by extracting phosphomolybdic acid with an organic solvent. Wuf9 and Copaux4 used diethyl ether as the solvent for the heteropoly acid. Scroggie14 found that esters, ketones, aldehydes, and ethers are good extractants but carbon disulphide, carbon tetrachloride, chloroform, benzene, and toluene are not. Keggin postulated that oxygen-containing materials are good solvents for heteropoly acids. Other solvents that have been used to extract heteropoly acids include ethyl acetoacetate,16 ethyl acetate,’ butyl acetate,9 2-methyl-l-propanol,2*3*16 3-methyl-1-butanol,ll I-octanol,13 and l-butano1.l’ Mixtures of 1-butanol in chloroform have also been used to extract In all of the above mentioned phosphomolybdic acid from arsenomolybdic acid. 1*5*6~10 solvents, arsenic was extracted to some extent also and only a limited amount could be tolerated without interference. An article by Wadelin and Mellonl* compares various solvents. * present address: Oak Ridge Institute of Nuclear Studies, Oak Ridge, Tennessee, U.S.A. 276
A study of the
separation of phosphate ion from arsenate ion by solvent extraction
Rosenheim12 gives a general equation for the formation acids : X”0 n(2a- + + 12M00,~
277
of heteropolymolybdic
+ (24 + 2a - n)Hf ---t Ho2 - ,jX(MozOJ6 + (6 + a)H,O
(I)
where X is Pv, AsV, SiIv, or Ge Iv. Inspection of equation (I) shows that a large excess of molybdate ions or hydrogen ions will force the reaction to the right. Wadelin and Mellon, however, were unable to utilise a high concentration of molybdate ion to enhance the formation of the heteropoly acid because it exhibits strong absorption in the same region as the complexes they measured. In the present work, various solvents were studied using radiochemical methods. The chloroform-butanol system was examined extensively. Unlike the spectrophotometric method, none of the solution variables affect the accuracy of the measurements made on the system. EXPERIMENTAL Reagents In addition to standard laboratory reagents, the following solutions were used: Phosphorus-32 and Arsenic-76 tracer solutions: Solutions of these isotopes, in the form of phosphate and arsenate, were diluted to the desired activity with O.OlN hydrochloric acid. Phosphorus carrier: Dissolve 2.8657 g of pure potassium dihydrogen phosphate @U&PO3 in 100 ml of water and dilute to 1 litre. The resulting solution contains 2.00 mg of phosphate ion per ml. Arsenic carrier : Dissolve about 45 g of disodium hydrogen arsenate (Na,HAsO~~7H,O) in 100 ml of water and dilute to 1 litre. The resulting solution contains about 2 mg of arsenate ion per ml. Magnesia mixture: Dissolve 55 g of magnesium chloride (MgCle.6HaO) and 140 g of ammonium chloride in 500 ml of water. Add 130 ml of concentrated ammonium hydroxide and dilute to 1 litre. Organic solvents: All organic solvents were chemically pure or reagent-grade. Mixed solvents were prepared on a volume percentage basis by adding the required volumes of each component using a pipette. Apparatus Various methods were used to detect and count the activities of the isotopes used in this work. Beta activity was measured with end-window Geiger tubes of both the halogen and organic quenched types. Gamma radiation was measured with a thallium-activated sodium iodide crystal in the form of a well-type scintillation detector. The counts were recorded with a variety of commercial scalers. General procedure Various concentrations of reagents are recommended in the literature for the extraction of heteropolymolybdic acids. The following concentrations were decided upon as being representative and consistent with a large molybdate and hydrogen ion concentration. The hydrochloric acid concentration was 50 % (V/V) and the sodium molybdate was 0.31 M (15 ml of 20 % sodium molybdate solution in 40 ml of final solution). All extractions were performed with 40 ml of solution in each phase. After preliminary experimentation, the following general procedure was developed to determine the amount of phosphate extracted. Procedure (1) Pipette exactly 5 ml of phosphate carrier into a 250-ml separatory funnel. (2) Add an amount of szP tracer solution (lo-50 ,ul) to give an activity of lO,OOO-15,000cpm. (3) Add 15 ml of 20 % sodium molybdate solution. (4) Add 50 ml of the solvent being examined. (5) Add 20 ml of concentrated hydrochloric acid, stopper the funnel, shake for 2 min, and allow the phases to separate.
278
andRtc~.4xn
HARLEYH.ROSS
B. HAHN
(6) Separate the layers, discard the aqueous phase, and add 50 ml of 3Mammonium hydroxide-1M ammonium chloride buffer solution to the organic phase, shake 2 min, and allow the phases to separate. (7) Drain the aqueous layer into a 1%ml beaker and heat to boiling. (8) Add 10 ml of magnesia mixture and allow to stand until cool. (9) Collect the precipitate of magnesium ammonium phosphate on a tilter disc in a Hirsch funnel. Wash the precipitate with three lo-ml portions of buffer solution and three 5-ml portions of acetone. (10) Aii dry the precipitate and beta count. (11) The percentage of phosphate extracted is found using the equation :
Al x 100 ‘A extracted = Aa where A, = the activity of the precipitate (cpm), and Az = the activity of the original tracer solution (cpm). A procedure similar to the above was used to determine the percentage of arsenate extracted with the same solvents. The numbered steps in the general procedure were replaced by the following: (la) Pipette exactly 5 ml of arsenate carrier into a 250-ml separatory funnel. (2a) Add an amount of 7BAstracer solution (10-50 ~1) having a total activity of 70,000-80,000 CPM. Steps 3,4, and 5 are the same as above. (6a) Pippette a 5-ml portion of each layer into different test tubes suitable for use in a well-type scintillation counter. (7a) Count each layer. The percentage of arsenate extracted is calculated by means of the following equation: A, x 100 ‘A extracted = A, + Aa where
A,, = the activity of the organic phase (cpm),
and
A, = the activity of aqueous phase (cpm). RESULTS
the above procedures, several solvents were examined to determine how much phosphate and arsenate was extracted by each. The results of these experiments are shown in Tables I and II. The results obtained in the first two sets of experiments indicated that 20 % butanol in chloroform was a promising solvent, in that a large percentage of phosphorus was extracted while only a small amount of arsenic was carried through. It was thought Using
TABLEI.-PERCENTP;GEOFPHOSPHATEEXTRACTEDUSINGVARIOUS ORGANIC SOLVENTS
Solvent
‘A Phosphate extracted h 5 ‘A*
Ethyl acetoacetate 20 % Butanol in chloroform Ethyl acetate Butyl acetate 50% Zsobutanol in benzene Zsobutanol 1-Butanol 1-Octanol Chloroform Benzene
lOOGO 94.97 79.92 73.58 72.63 67.21 60.63 29,86 00.00 OOGO
* Average oftwo determinations
A study of the separation
of phosphate
TABLE II-PERCENTAGE
ion from arsenate ion by solvent extraction
279
OF ARSENATEEXTRACTED USING VARIOUS ORGANIC SOLVENTS
Solvent
%
Arsenic extracted &5 %*
20 % Butanol in chloroform Butyl acetate 1-0ctanol Ethyl acetate 50 % Isobutanol in benzene Zsobutanol I-Butanol Ethyl acetoacetate Chloroform Benzene
4.74 849 14.39 29.46 36.76 87.05 87.91 96.67 00.00 OOGO
* Average of two determinations
that a more favourable mixture of 1-butanol might exist for this extraction. To this end, the same procedures were used to determine the percentage of phosphate and arsenate extracted with various concentrations of 1-butanol. The extractions of arsenate were made with three concentrations of this ion. Extractions were performed both in the presence and absence of phosphate ion to determine the effect of this variable. The experimental conditions and results are shown in Tables III, IV, and V. TABLE III.-PERCENTAGE
OF PHOSPHATE EXTRACTED USING VARIOUS
CONCENTRATIONS OF 1-BlJTANOL IN CHLOROFORM % Butanol
% Phosphate extracted &5 %*
20
94.97
19
95.04
18
97.23
17
93.26
16
92.99
15
96.31
10
8560
7.5
55.01
5.0
18.30
* Average of two determinations TABLE IV.-PERCENTAGE
OF ARSENATEEXTRACTED USMG VARIOUS
CONCENTRA~ONS OF l-BUTANOL IN CHLOROFORM ‘A
Arsenic extracted at indicated level*
% Butanol
5 10 15 20 30 * Average of 10
IO-mg
loo-Pug
0.20 0.36 1.56 5.16 13.57
0.27 1.42 2.45 4.58 13.15
two determinations
Tracer 0.076 0.78 1.99 4.17 13.06
280
HARLEYH. Ross and RICHARDB. HAHN TABLEV.-PERCENTAGEOFARSENATEEXTRA~DUSINGVARIOUSCONCENTRA~ONS OF l-BCJTANOLINCHLOROFORMWITH~~ mg OFADDEDPHOSPHATE 'A Arsenic extracted at indicated level*
% Butanol
5 10 15 20 30
lO-mg
lOO+g
Tracer
0.073 0.69 2.30 4.32 12.12
0.14 0.88 1.61 3.62 12.38
0.12 0.80 1.77 4.50 12.38
* Average of two determinations Zusammenfass~-Das Postulat von Keggin, wonach sauerstoffhaltige verbindungen gute Liisemittel fti Heteropolysauren sind, wird bestatigt. Keines der untersuchten Losemittel kann eine viillige Tremmng von Phosphat und Arsenat in einem Extraktionschritt bewirken. Das System Butanol-Chloroform wurde eingehend studiert. Mit an&gender Butanolkonzentration steigen die extrahierten Phosphat und Arsenatmengen an. Eine Butanolkonzentration von 10 % scheint meistversprechend ftir eine selektive Phosphatextraktion zu sein. Die extrahierte Arsenatmenge ist weitgehend unabhangig von der vorherrschenden Phosphatkonzentration. R&u&-Le postulat de Keggin, a savoir que les substances contenant de l’oxygene sont de bons solvants des htteropolyacides, est confirm&. Aucun des solvants etudib ne &pare completement l’ion phosphate de l’ion arseniate en une seule extraction. Le systeme butanol-chloroforme a et6 tres ttudit. Quand le pourcentage de butanol augmente dam le melange de solvants, le pourcemage de phosphate et d’arseniate extraits augmente aussi. Parmi les concentrations vari&s de butanol &udi&es, 10 pour cent offrcnt le plus de promesses comme produit extrayant selectivement le phosphate, avec un rendement important. La quantit6 d’arseniate extraite par toute concentration de butanol est relativement independante de la concentration d’ion phosphate dans le systeme. REFERENCES 1 R. I. Akkseev, Zavodskuya Lab., 1945,11, 122. a R. J. L. Allen, Biochem. J., 1940,34,858. a I. Berenblum and E. Chain, ibid., 1938,32,287. 4 H. Copaux, Compt. rend, 1921,173,656. 5 K. T. H. Farrer and S. J. Muir, Austral. Chem. Inst. J., and Proc., 1944, 11,222. BN. A. Filippova and L. I. Kuznetsova, Zavodskuyu Lab., 1950,16, 536. ’ J. Hure and T. Ortis, Bull. Sot. chim. France, 1949, 834. * J. F. Keggin, Proc. Roy. Sot., 1934, 144, 75. 8 T. Koto, et al., Technol. Repts. Tdhoku Univ., 1950, 15,70. loR. V. Mervel, Zavodrkaya Lab., 1945, 11,135. I1 C. Rainbow, Nature, 1946, 157,268. le A. Rosenheim, in Abegg and Auerbach’s Handbuch der anorganischen Chemie, Leipzig S. Hirzel 1921, Bd. IV, 1 Abt., 2 Halfte, pp. 977-1065. I11F. L. Schaffer, et al., Analyt. Chem., 1953, 25, 343. I4 A. G. Scroggie, J. Amer. Chem. Sot., 1929, 51, 1057, I5 C. Sideris, Znd. Eng. Chem. Analyt., 1942, 14,762. I6 K. Stoll, Z. analyt. Chem., 1938, 112, 81. I7 C. Wadelm and M. G. Mellon, Analyst, 1952, 77, 708. I8 Zdem, Analyt. Chem., 1953,25, 1668. I4 H. Wu, J. Biol. Chern., 1920, 43, 189.