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Exchange properties of ammonium salts of 12-heteropolyacids. Sorption of caesium on ammonium phosphotungstate and phosphomolybdate
Notes
367
It is difficult in this case to predict how far the substitution has proceeded because there is not a great deal of difference between the polarograms of K~Pt(NOz)4 in I M KNO~ and of KzPt(NO2)2CI3 in 1 M KNO~. Fig. 5 shows the change in the peak current with time at an applied voltage of --0.5 V for the complex 10-3 M K3PtC14 in 1 M KNO~. Dept. of Science, Newcastle University College University of New South Wales Tighe' s Hill, 2N, New South Wales Australia
G. CURTrlOYS J.H. GREEN
Exchange properties of ammonium salts of 12-heteropolyacids. Sorption of caesium on ammonium phosphotungstate and phosphomolybdate (Received 8 October 1959) THE exchange properties of ammonium phosphomolybdate were suggested by BAX~R and GRIFFIN,~1) and later by THISTLETHWAITEt2). BUCHWALOand THISTLETHWAITEla) described the sorption of potassium, rubidium, caesium, thallium and alkaline earths on ammonium phosphomolybdate as being due to isomorphous exchange of an ion in the lattice; the sorbing cation was assumed to be able to replace both ammonium and hydrogen ions present in a molecule of ammonium phosphomolybdate. The exchange properties of ammonium phosphomolybdate were used by Sr~n'r(4) for the column separation of UNa, 4'K, 8eRb and 184Cs, using ammonium nitrate solution in various concentrations as eluant. The determination of radioactive caesium in dilute solutions by sorption on thallium phosphomolybdate has also been described. (s) Our earlier studies on the reaction between alkali metals and heteropolyacids indicated the instability of phosphomolybdic acid and its salts in solutions under certain conditions. On the other hand phosphotungstic acid resists hydrolysis and is stable even in strong acid media. This paper describes the exchange properties both of ammonium phosphotungstate and ammonium phosphomolybdate. Experimental Ammonium phosphotungstate and ammonium phosphomolybdate were prepared by precipitation of commercial 12-heteropolyacids with excess of NH4C1 in 0.I N HCI; they were washed with 0.1 N HCI, then absolute alcohol, and dried at 40-60°C. In the dry product NH~ was determined by Nessler's colorimetric method, W and Mo gravimetrically with oxine or colorimetrically with rhodanide, and water by ignition to constant weight at 450°C. Phosphorus was determined colorimetrically as phosphotungstovanadic acid or phosphomolybdovanadic acid. The analyses correspond to the formulae (NH,)2.eTH0.sa(P W12040).9"8 H a t ,
abbreviated to NH4PW
(NH4)~.95H0.05(P Mox2040).l 1"6 H20
abbreviated to NH4PMo.
(a) The prepared salts (0.1 g) were added to 2 ml of HC1 or HNO3 (0.2-10 N) and after reaching equilibrium solid and liquid phase were analysed (Tables 1 and 2). Whereas in the solid phase of NH4PW the replacement of ammonium ions by hydrogen increases continuously, the calculated values of the ratio N H J P for NH4PMo are irregular, due to decomposition of NH~PMo by the acid. (I) G. P. BAXTERand R. C. GRIrHN, Amer. Chem. J. 34, 204 (1905). (I) W. P, TmSTLETHWAITE,Analyst. 72, 531 (1947). (3) H. BUCrtWALOand W. P. THISTL~THWAITE,J. lnorg. NucL Chem. 5, 341 (1958). (') J. VAN R. SMIT,Nature, Lond. 181, 1530 (1958). 16) HARATADASm,Bull. Chem. Soc. Japan 31, 635 (1958).
368
Notes
TABLE I.--EQUILIBRIUM IN THE SYSTEM: AMMONIUM PHOSPHOTUNGSTATE-HYDROCI-ILORIC ACID, AMMONIUMPHOSPHOTUNGSTATE-NITRIC ACID
atoms of P*
Moles of NH4*
Acid concentration N
g atoms of W* N H J P moles solid phase
Liquid phase
Solid phase
Liquid phase
Solid phase
Liquid phase
Solid phase
HC1 HNO3
11.6 9.8
88.4 90.2
Was not found
37"5 37"5
0'25 0'2
449.75 449.80
2"36 2"41
HC1 HNO8
- -
I'0
Was not found
37.5 37"5
0-3 0"2
449"70 449-80
2'18 2'22
3'0
HCI HNO3
22"7 22.7 24'8
77.3 75'2
37"5 37'5
0-25 0.2
449'75 449"80
2"05 2"0
HC1 6"0 HNO3
25.4
75.2 74"6
I Was not / found Was not found
37-5 37-5
0-2 0.2
449-80 449.80
2'0 1"98
HC1 HNOa
26.4
73"0 73-6
Was not found
37.5 37"5
0.30 0"2
449.70 449.80
1-95 1"96
0'2
18-2 17.0
81.8 __83'0
~
10"0
I
]
/
* Results calculated relative to 100 moles of ammonium in original material.
TABLE 2.--EQUILIBRIUM IN THE SYSTEM: AMMONIUMPHOSPHOMOLYBDATE-HYDROCHLORIC ACID~ AMMONIUM PHOSPHOMOLYBDATE-NITRIC ACID
Acid concentration N
0-2
HC1 HNO3
Moles of NH**
_
g atoms~ of P*
g atoms of Mo*
Liquid phase
Solid phase
Liquid phase
Solid phase
Liquid phase
Solid phase
8.5 9.5
J 91"5 " L 90"5
4'06 3-97
29"27 29'36
2-95 2'33
397"05 397"67
82"9 82-0
5'39 6'06
--27---~--94 27"27 I
18"75 20'6
381 "25 374.4
1"0 HC1 HNOa
N H d P moles solid phase
3"13 3.08 2'98
3'0
HCI 3.0 HNO3
21"0 23.5
79-0 76-5
4-6 5"26
28-73 28'07
22-7 43"8
377'3 356'2
2"27
HC1 HNO3
23'0
77'0
6"82
26"51
24"8
375 "2
2"90
HC1 10-0 HNO3
17-1
82"9
9"68
23-65
6"56
393"44
3.50
6"0
2"82
--t
* Results calculated relative to 100 moles of ammonium in original material. t Under these conditions NH4PMo decomposes strongly.
Notes
369
(b) In caesium phosphotungstate (CsPW) and phosphomolybdate (CsPMo), the exchange between Cs ions and H ions was investigated in a similar way (3 atoms of Cs were originally present in 1 molecule of the heteropolysalt. The content of Cs in the solid phase decreased with increasing acidity of the medium. CsPW does not decompose; the CsPMo decomposes in 8-10 N HCI. (c) The exchange between Cs and NH~ in NH4PMo and NH4PW was examined by shaking 0-1 g of precipitate of NH4PW or NH4PMo with 2 ml HC1 of varying concentration containing excess 3 M Cs labelled with x87Cs. The precipitate was washed with acid and analysed; Cs was determined radiometrically using an end-window counter. The results are shown in Tables 3 and 4. TABLE 3.--EQUILIBRIUM IN THE SYSTEM; AMMONIUM PHOSPHOTUNGSTATE-CAESIUM CHLORIDE-HYDROCHLORIC ACID
HC1 Concentration N
Cs/P moles solid phase
NHa/P moles solid phase
Cs/NH4 moles solid phase
H20
1.73
0"01 0'1 0.9 3"0 5"2
1'72 1'64 1.51
0-99 1-05 0"95 0.89 0'86 0"83
1"75 1"64 1-73 1 '70 1"84 1 '80
1.58 1"49
TABLE 4.--EQUILIBRIUM IN THE SYSTEM; AMMONIUM PHOSPHOMOLYBDATE-CAESIUM CHLORIDE--HYDROCHLORIC ACID
HC1 concentration N
Cs/P moles solid phase
N H J P moles solid phase
Cs/NH4 moles solid phase
H20
1 "29 1.22 1.24 1.16 1.15
1"59 1"41 1 "56 1"43 1 "39 1 "28
0.81 0.87 0.79 0.81 0-83 0"87
0"01 0"1 0"9 3'0 5'2
1-12
The Cs/NH4 ratio in CsNH4PMo (0'79-0'87), which is also given approximately by BUCHWALD and THISTLETHWAITE,tS) is lower than that in CsNH4PW (1"64-1.84) under similar conditions. The sorption capacity of NH4PW is thus higher, whether expressed in moles or by weight.
Conclusion The results indicate quantitatively that ammonium phosphomolydate and ammonium phosphotungstate are able to exchange part of their ammonium for caesium. Equilibrium is attained between ammonium, alkali and hydrogen ions. Ammonium phosphotungstate is stable in neutral and strong acid media and Cs sorption may be influenced over a wide range by the concentrations of both ammonium and hydrogen ions. On the contrary the stability of ammonium phosphomolybdate is lower, and the sorption capacity of ammonium phosphotungstate for caesium is higher than that of ammonium phosphomolybdate. Detailed data will be published later. J. KRTIL Institute of Nuclear Research V. KOU~M
Czechoslovak Academy of Sciences Prague
367
It is difficult in this case to predict how far the substitution has proceeded because there is not a great deal of difference between the polarograms of K~Pt(NOz)4 in I M KNO~ and of KzPt(NO2)2CI3 in 1 M KNO~. Fig. 5 shows the change in the peak current with time at an applied voltage of --0.5 V for the complex 10-3 M K3PtC14 in 1 M KNO~. Dept. of Science, Newcastle University College University of New South Wales Tighe' s Hill, 2N, New South Wales Australia
G. CURTrlOYS J.H. GREEN
Exchange properties of ammonium salts of 12-heteropolyacids. Sorption of caesium on ammonium phosphotungstate and phosphomolybdate (Received 8 October 1959) THE exchange properties of ammonium phosphomolybdate were suggested by BAX~R and GRIFFIN,~1) and later by THISTLETHWAITEt2). BUCHWALOand THISTLETHWAITEla) described the sorption of potassium, rubidium, caesium, thallium and alkaline earths on ammonium phosphomolybdate as being due to isomorphous exchange of an ion in the lattice; the sorbing cation was assumed to be able to replace both ammonium and hydrogen ions present in a molecule of ammonium phosphomolybdate. The exchange properties of ammonium phosphomolybdate were used by Sr~n'r(4) for the column separation of UNa, 4'K, 8eRb and 184Cs, using ammonium nitrate solution in various concentrations as eluant. The determination of radioactive caesium in dilute solutions by sorption on thallium phosphomolybdate has also been described. (s) Our earlier studies on the reaction between alkali metals and heteropolyacids indicated the instability of phosphomolybdic acid and its salts in solutions under certain conditions. On the other hand phosphotungstic acid resists hydrolysis and is stable even in strong acid media. This paper describes the exchange properties both of ammonium phosphotungstate and ammonium phosphomolybdate. Experimental Ammonium phosphotungstate and ammonium phosphomolybdate were prepared by precipitation of commercial 12-heteropolyacids with excess of NH4C1 in 0.I N HCI; they were washed with 0.1 N HCI, then absolute alcohol, and dried at 40-60°C. In the dry product NH~ was determined by Nessler's colorimetric method, W and Mo gravimetrically with oxine or colorimetrically with rhodanide, and water by ignition to constant weight at 450°C. Phosphorus was determined colorimetrically as phosphotungstovanadic acid or phosphomolybdovanadic acid. The analyses correspond to the formulae (NH,)2.eTH0.sa(P W12040).9"8 H a t ,
abbreviated to NH4PW
(NH4)~.95H0.05(P Mox2040).l 1"6 H20
abbreviated to NH4PMo.
(a) The prepared salts (0.1 g) were added to 2 ml of HC1 or HNO3 (0.2-10 N) and after reaching equilibrium solid and liquid phase were analysed (Tables 1 and 2). Whereas in the solid phase of NH4PW the replacement of ammonium ions by hydrogen increases continuously, the calculated values of the ratio N H J P for NH4PMo are irregular, due to decomposition of NH~PMo by the acid. (I) G. P. BAXTERand R. C. GRIrHN, Amer. Chem. J. 34, 204 (1905). (I) W. P, TmSTLETHWAITE,Analyst. 72, 531 (1947). (3) H. BUCrtWALOand W. P. THISTL~THWAITE,J. lnorg. NucL Chem. 5, 341 (1958). (') J. VAN R. SMIT,Nature, Lond. 181, 1530 (1958). 16) HARATADASm,Bull. Chem. Soc. Japan 31, 635 (1958).
368
Notes
TABLE I.--EQUILIBRIUM IN THE SYSTEM: AMMONIUM PHOSPHOTUNGSTATE-HYDROCI-ILORIC ACID, AMMONIUMPHOSPHOTUNGSTATE-NITRIC ACID
atoms of P*
Moles of NH4*
Acid concentration N
g atoms of W* N H J P moles solid phase
Liquid phase
Solid phase
Liquid phase
Solid phase
Liquid phase
Solid phase
HC1 HNO3
11.6 9.8
88.4 90.2
Was not found
37"5 37"5
0'25 0'2
449.75 449.80
2"36 2"41
HC1 HNO8
- -
I'0
Was not found
37.5 37"5
0-3 0"2
449"70 449-80
2'18 2'22
3'0
HCI HNO3
22"7 22.7 24'8
77.3 75'2
37"5 37'5
0-25 0.2
449'75 449"80
2"05 2"0
HC1 6"0 HNO3
25.4
75.2 74"6
I Was not / found Was not found
37-5 37-5
0-2 0.2
449-80 449.80
2'0 1"98
HC1 HNOa
26.4
73"0 73-6
Was not found
37.5 37"5
0.30 0"2
449.70 449.80
1-95 1"96
0'2
18-2 17.0
81.8 __83'0
~
10"0
I
]
/
* Results calculated relative to 100 moles of ammonium in original material.
TABLE 2.--EQUILIBRIUM IN THE SYSTEM: AMMONIUMPHOSPHOMOLYBDATE-HYDROCHLORIC ACID~ AMMONIUM PHOSPHOMOLYBDATE-NITRIC ACID
Acid concentration N
0-2
HC1 HNO3
Moles of NH**
_
g atoms~ of P*
g atoms of Mo*
Liquid phase
Solid phase
Liquid phase
Solid phase
Liquid phase
Solid phase
8.5 9.5
J 91"5 " L 90"5
4'06 3-97
29"27 29'36
2-95 2'33
397"05 397"67
82"9 82-0
5'39 6'06
--27---~--94 27"27 I
18"75 20'6
381 "25 374.4
1"0 HC1 HNOa
N H d P moles solid phase
3"13 3.08 2'98
3'0
HCI 3.0 HNO3
21"0 23.5
79-0 76-5
4-6 5"26
28-73 28'07
22-7 43"8
377'3 356'2
2"27
HC1 HNO3
23'0
77'0
6"82
26"51
24"8
375 "2
2"90
HC1 10-0 HNO3
17-1
82"9
9"68
23-65
6"56
393"44
3.50
6"0
2"82
--t
* Results calculated relative to 100 moles of ammonium in original material. t Under these conditions NH4PMo decomposes strongly.
Notes
369
(b) In caesium phosphotungstate (CsPW) and phosphomolybdate (CsPMo), the exchange between Cs ions and H ions was investigated in a similar way (3 atoms of Cs were originally present in 1 molecule of the heteropolysalt. The content of Cs in the solid phase decreased with increasing acidity of the medium. CsPW does not decompose; the CsPMo decomposes in 8-10 N HCI. (c) The exchange between Cs and NH~ in NH4PMo and NH4PW was examined by shaking 0-1 g of precipitate of NH4PW or NH4PMo with 2 ml HC1 of varying concentration containing excess 3 M Cs labelled with x87Cs. The precipitate was washed with acid and analysed; Cs was determined radiometrically using an end-window counter. The results are shown in Tables 3 and 4. TABLE 3.--EQUILIBRIUM IN THE SYSTEM; AMMONIUM PHOSPHOTUNGSTATE-CAESIUM CHLORIDE-HYDROCHLORIC ACID
HC1 Concentration N
Cs/P moles solid phase
NHa/P moles solid phase
Cs/NH4 moles solid phase
H20
1.73
0"01 0'1 0.9 3"0 5"2
1'72 1'64 1.51
0-99 1-05 0"95 0.89 0'86 0"83
1"75 1"64 1-73 1 '70 1"84 1 '80
1.58 1"49
TABLE 4.--EQUILIBRIUM IN THE SYSTEM; AMMONIUM PHOSPHOMOLYBDATE-CAESIUM CHLORIDE--HYDROCHLORIC ACID
HC1 concentration N
Cs/P moles solid phase
N H J P moles solid phase
Cs/NH4 moles solid phase
H20
1 "29 1.22 1.24 1.16 1.15
1"59 1"41 1 "56 1"43 1 "39 1 "28
0.81 0.87 0.79 0.81 0-83 0"87
0"01 0"1 0"9 3'0 5'2
1-12
The Cs/NH4 ratio in CsNH4PMo (0'79-0'87), which is also given approximately by BUCHWALD and THISTLETHWAITE,tS) is lower than that in CsNH4PW (1"64-1.84) under similar conditions. The sorption capacity of NH4PW is thus higher, whether expressed in moles or by weight.
Conclusion The results indicate quantitatively that ammonium phosphomolydate and ammonium phosphotungstate are able to exchange part of their ammonium for caesium. Equilibrium is attained between ammonium, alkali and hydrogen ions. Ammonium phosphotungstate is stable in neutral and strong acid media and Cs sorption may be influenced over a wide range by the concentrations of both ammonium and hydrogen ions. On the contrary the stability of ammonium phosphomolybdate is lower, and the sorption capacity of ammonium phosphotungstate for caesium is higher than that of ammonium phosphomolybdate. Detailed data will be published later. J. KRTIL Institute of Nuclear Research V. KOU~M
Czechoslovak Academy of Sciences Prague