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Precipitation of lead as lead sulphate by destructive oxidation of EDTA
SHORT COMMUNICATIONS
1300 Jahnm,
Vol 21. pp
13W-1302
Pergamon
PRECIPITATION
Press
1974. Prmted
m Great
Br&un
OF LEAD AS LEAD SULPHATE BY DESTRUCTIVE OXIDATION OF EDTA (Received 27 March 1974. Accepted 9 June 1974)
MacNevin and Dunton’ studied the homogeneous precipitation of ferric hydroxide through release of the cation from its EDTA complex by the slow oxidation of EDTA with hydrogen peroxide at constant pH. A dense and easily filterable ferric hydroxide is obtained by this procedure at pH 3.0. Cartwright studied the oxidation of EDTA with hydrogen peroxide in detail and found that certain oxtdes caused decomposition of the hydrogen peroxide, thus stopping the oxidation process. However, by taking advantage of the ability of phosphate to stabilize hydrogen peroxide, he was able to produce bismuth. iron. lead calcium and barium phosphates as dense and readily filterable precipitates from solutions containing the single ions. The method is not selective. as all the metals present in solution are released at the same time from their EDTA complexes. In previous communications we have described procedures for the homogeneous precipitation of lead sulphate through cation replacement by iron, copper and nickel. ‘v4 In these methods many metals which generally accompany lead in its alloys or ores did not interfere. Because oxidation of EDTA also releases the metal ion. it was of interest to study this too for homogeneous precipitation of lead sulphate.
EXPERIMENTAL
Reagents
All reagents were of analytical grade. Aqueous lead nitrate solutions OGOS.0.025 and 0,05M, 55; EDTA solution and 0.2M ammonium sulphate were prepared. Hydrogen peroxide and alkali metal chlorate. bromate and persulphate were used as oxidizing agents for EDTA. For interference studies solutions of aluminium(III), copper(H), mckel(I1). zinc(I1). iron(II1) and manganese(U) were prepared from their sulphates to give metal ion concentrations of 10 mg/ml. Solutions of tin and antimony were prepared by dissolving the metal in a minimal amount of 1: 1 nitric acid-hydrofluoric acid and dilutmg to the required volume to give a concentration of 10 mg/ml. Procedures For pure lead solutions. To a solution contammg Z-100 mg of lead, add 5 ml of SS/, EDTA solution and 5 ml of 0.2M ammomum sulphate, dilute to 45 ml, add 1 ml of nitric acid (1 + 3) and 2 ml of 307; hydrogen peroxide or 0.5 g of sodium bromate. Heat the solution on a boiling water-bath for at least 2 hr. Precipitation starts in 10 min and is complete after 2 hr. Continue heating till the final volume of the solution is about 15 ml. Cool for 30 min, and filter off on a sintered-glass crucible (porosity 4) using 1% sulphuric acid and 500,; ethanol as the initial and the final wash solutions respectively. Continue washing with ethanol until the washings are free from sulphate. Dry the precipitate at 120°C for 1 hr. cool and weigh as lead sulphate. The conversion factor is Pb/PbSOL = 06833. Analysis of type metal. Dissolve a weighed (log) sample of type metal in 15 ml of nitric acid and 15 ml of hydrofluoric acid.’ Boil for a few min to remove nitrous fumes and dilute to 1 litre in a volumetric flask. Take a 10 ml aliquot m a 100 ml beaker and add 5 ml each of 596 EDTA solution and 0.2M ammonium sulphate. adjust the volume to 50 ml, and continue as described above.
DISCUSSION
The precipitates obtained are dense and easily filterable. They have no tendency to creep and do not absorb moisture on exposure to the atmosphere. Various oxidlxing agents such as chlorate, bromate, persulphate and hydrogen peroxide were studied. It was found that precipitates of superior characteristics were obtained only with bromate or hydrogen peroxide as the oxidant. Oxidation of EDTA by bromate or hydrogen peroxide was very slow at higher pH. the rate of reaction decreasine with increasing_.oH. At oH > 3.0. the oxidation was not complete even after boiling for more than 3 hr. However, at pH 1.5-3.0. the oxidation was complete after boiling the solution for at least 2 hr. In this pH range, heating on a water-bath even for more than 3 hr did not result in the complete oxidation of EDTA. At pH < 1.5.
SHORT COMMUNlCATlONS
Table 1. Determination
Lead taken. rrtg
of lead in pure solutions Mean deviation. ‘ng
Lead found. mil
Hydrogen peroxide method 52 10.4 25.9 51.8 777 103.6 Sodium bromate method 5.2 1@4 25.9 51.8 77.7 103.6
1301
No. of experiments
5.2
10.2 25.9 52.1 77.7 103.6 5.0 10.4 25.8 51.9 77.8 103.5
a gradual release of lead from tts EDTA complex was achieved by heating even on a water-bath. At pH 1~0the EDTA complex is unstable to acid and a precipitate of lead sulphate and EDTA is slowly formed on heating, but precipitation is incomplete even on prolonged heating, so cation-release by lowering the pH is not applicable. Judging from the rate of precipitation, the oxidative degradation of EDTA is the predominant factor in the liberation of the lead ions. At pH c 1. rapid precipitation of lead sulphate occurs and hence the oxidation should always be done at pH l*O-15. Varying concentrations of EDTA and sulphate ion did not affect the quantitative precipitation oflead sulphate. It was found that 1 or 2 ml of 307; hydrogen peroxide or 05g of sodium bromate could oxidize 5 ml of 5% EDTA solution. For other concentrations of EDTA the optimum quantities of oxidant have to be found by trial and error, but an excess of either bromate or hydrogen peroxide has no adverse effect. Interferences were studied on mixtures of 50 mg of foreign ion with 5 or 50 mg of lead. The results in Tables 1-3 clearly mdicate the usefulness of the method for the determination of lead in the presence and absence of Interfering metals. Determination of lead in type metal gave an accurate value. It is noteworthy that tin and antimony do not interfere. Chloride does not interfere when present in up to tenfold amount relative to lead. The method can also be used to determine sulphate.
Table 2. Interference studies for the hydrogen peroxide method
Lead taken. “YJ
Lead found W
Mean deviation, W
No. of experiments
AI(III) Al(II1) Cu(II) CU(I1)
51.8 5.2 51.8 5.2
51.6 5.2 51.7 5.1
PO 03 0.2 0.2
4 4 4 4
Ni(I1) N1(11) Zn(II) Zn(I1) Fe(II1) Fe(II1) Mn(I1) Mn(I1) Sri(H) Sn(I1) Sb(III) Sb(II1)
5.2 51.8 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2
5.0 51.6 51.9 4.9 52.0 5.0 51.9 5.1 51.8 5.2 51.9 5.1
@2 0.2 @O @I 01 0.1 0.1 0.1 0.1 0.1 0.2 0.1
: 3 3 4 4 3 3 4 4 4 4
Metal added
.
1302
SHORTCOMMUNICATIONS
Table 3. Interference studies for the bromate method Metal added AI(II1) AI Cu(I1) Cu(I1) Ni(I1) Ni(I1) Zn(I1) Zn(I1) Fe(II1) Fe(II1) Mn(I1) Mn(I1) Sn(I1) Sn(I1) Sb(II1) Sb(II1)
Lead taken, lng 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 52
Lead found ‘ng 51.7 5.1 51.9 5.0 51.7 5.1 51.7 5.1 52.0 5.1 52.0 5.3 51.7 5.0 51.6 5.1
Mean deviation. fag 0.2 0.2 0.2 0.2 0.4 @3 0.3 0.3 0.2 @l 0.1 01 0.1 @I 0.1 0.1
No. of experiments 4 4 4 4 4 4 4 3 4 4 4 4 3 3 3 3
Acknowledgements-Grateful thanks of the authors are due to Professor P. K. Jena. Director, Regional Research Laboratory, Bhubaneswar, for facilities and interest in the work. J. RAJAG~PALA RAO A. SURYANARAYANA
Regional Research Laboratory Bhubaneswar-4, India
B.R.SAm REFERENCES 1. W. H. MacNevin and M. L. Dunton, Anal. Chem.. 1954.26, 1246.
2. 3. 4. 5.
P. F. S. Cartwright Analyst, 1961,86,688. 692; 1962.87, 163; 1967.92, 319. A. Suryanarayana, J. R. Rao and B. R. Sam, Anal. Chim. Acta. 197259,481. J. R. Rao. A. Survanaravana and B. R. Sant. Z. Anal. Chem.. 1973.265. 128. E. Garate and T.‘Garate, Chim. Anal. (Paris), 1958.40, 7. Summary-Gravimetric determination of lead (%I00 mg) by homogeneous precipitation of lead sulphate from a solution containing lead(II), EDTA and sulphate by destructive oxidation of EDTA with hydrogen peroxide or sodium bromate is described. Aluminium(III), iron(II1). zinc(H). manganese(II), copper( nickel(II), tin(I1) and antimony(II1) do not interfere in the method. The method can successfully be applied to the analysis of type metal.
R&m&-On decrit le dosage gravimetrique du plomb (5-100 mg) par precipitation homogtne du sulfate de plomb a nartir dune solution contenant du nlomb(II), de I’EDTA et du sulfate, par oxydation destructive de I’EDTA par le peroxyde d’hydrogene ou ie bromate de sodium. Les aluminmm(III), fer(III), zinc(II), mangantse(I1). cuivre(I1). nickel(I1). etam(I1) et antimoine(II1) n’interferent pas dans cette methode. La mtthode peut etre appliquee avec succes h I’analyse d’alliage pour caract&es d’imprimerie. Zusammenfaasung-Die gravimetrische Bestimmung von Blei (5-100 mg) durch homogene Fallung von Bleisulfat wird beschrieben. Es wird aus einer Losung gefallf die Blei(II), EDTA und Sulfat enthllt und in der EDTA mit WasserstoRperoxid oder Natriumbromat oxidativ zerstort wird. Aluminium(II1). Eisen(III), Zink(I1). Mangan(I1). Kupfer(I1). Nickel(II), Zinn(I1) und Antimon(II1) storen nicht. Das Verfahren kann mit Erfolg fur die Analyse von Letternmetall verwendet werden.
1300 Jahnm,
Vol 21. pp
13W-1302
Pergamon
PRECIPITATION
Press
1974. Prmted
m Great
Br&un
OF LEAD AS LEAD SULPHATE BY DESTRUCTIVE OXIDATION OF EDTA (Received 27 March 1974. Accepted 9 June 1974)
MacNevin and Dunton’ studied the homogeneous precipitation of ferric hydroxide through release of the cation from its EDTA complex by the slow oxidation of EDTA with hydrogen peroxide at constant pH. A dense and easily filterable ferric hydroxide is obtained by this procedure at pH 3.0. Cartwright studied the oxidation of EDTA with hydrogen peroxide in detail and found that certain oxtdes caused decomposition of the hydrogen peroxide, thus stopping the oxidation process. However, by taking advantage of the ability of phosphate to stabilize hydrogen peroxide, he was able to produce bismuth. iron. lead calcium and barium phosphates as dense and readily filterable precipitates from solutions containing the single ions. The method is not selective. as all the metals present in solution are released at the same time from their EDTA complexes. In previous communications we have described procedures for the homogeneous precipitation of lead sulphate through cation replacement by iron, copper and nickel. ‘v4 In these methods many metals which generally accompany lead in its alloys or ores did not interfere. Because oxidation of EDTA also releases the metal ion. it was of interest to study this too for homogeneous precipitation of lead sulphate.
EXPERIMENTAL
Reagents
All reagents were of analytical grade. Aqueous lead nitrate solutions OGOS.0.025 and 0,05M, 55; EDTA solution and 0.2M ammonium sulphate were prepared. Hydrogen peroxide and alkali metal chlorate. bromate and persulphate were used as oxidizing agents for EDTA. For interference studies solutions of aluminium(III), copper(H), mckel(I1). zinc(I1). iron(II1) and manganese(U) were prepared from their sulphates to give metal ion concentrations of 10 mg/ml. Solutions of tin and antimony were prepared by dissolving the metal in a minimal amount of 1: 1 nitric acid-hydrofluoric acid and dilutmg to the required volume to give a concentration of 10 mg/ml. Procedures For pure lead solutions. To a solution contammg Z-100 mg of lead, add 5 ml of SS/, EDTA solution and 5 ml of 0.2M ammomum sulphate, dilute to 45 ml, add 1 ml of nitric acid (1 + 3) and 2 ml of 307; hydrogen peroxide or 0.5 g of sodium bromate. Heat the solution on a boiling water-bath for at least 2 hr. Precipitation starts in 10 min and is complete after 2 hr. Continue heating till the final volume of the solution is about 15 ml. Cool for 30 min, and filter off on a sintered-glass crucible (porosity 4) using 1% sulphuric acid and 500,; ethanol as the initial and the final wash solutions respectively. Continue washing with ethanol until the washings are free from sulphate. Dry the precipitate at 120°C for 1 hr. cool and weigh as lead sulphate. The conversion factor is Pb/PbSOL = 06833. Analysis of type metal. Dissolve a weighed (log) sample of type metal in 15 ml of nitric acid and 15 ml of hydrofluoric acid.’ Boil for a few min to remove nitrous fumes and dilute to 1 litre in a volumetric flask. Take a 10 ml aliquot m a 100 ml beaker and add 5 ml each of 596 EDTA solution and 0.2M ammonium sulphate. adjust the volume to 50 ml, and continue as described above.
DISCUSSION
The precipitates obtained are dense and easily filterable. They have no tendency to creep and do not absorb moisture on exposure to the atmosphere. Various oxidlxing agents such as chlorate, bromate, persulphate and hydrogen peroxide were studied. It was found that precipitates of superior characteristics were obtained only with bromate or hydrogen peroxide as the oxidant. Oxidation of EDTA by bromate or hydrogen peroxide was very slow at higher pH. the rate of reaction decreasine with increasing_.oH. At oH > 3.0. the oxidation was not complete even after boiling for more than 3 hr. However, at pH 1.5-3.0. the oxidation was complete after boiling the solution for at least 2 hr. In this pH range, heating on a water-bath even for more than 3 hr did not result in the complete oxidation of EDTA. At pH < 1.5.
SHORT COMMUNlCATlONS
Table 1. Determination
Lead taken. rrtg
of lead in pure solutions Mean deviation. ‘ng
Lead found. mil
Hydrogen peroxide method 52 10.4 25.9 51.8 777 103.6 Sodium bromate method 5.2 1@4 25.9 51.8 77.7 103.6
1301
No. of experiments
5.2
10.2 25.9 52.1 77.7 103.6 5.0 10.4 25.8 51.9 77.8 103.5
a gradual release of lead from tts EDTA complex was achieved by heating even on a water-bath. At pH 1~0the EDTA complex is unstable to acid and a precipitate of lead sulphate and EDTA is slowly formed on heating, but precipitation is incomplete even on prolonged heating, so cation-release by lowering the pH is not applicable. Judging from the rate of precipitation, the oxidative degradation of EDTA is the predominant factor in the liberation of the lead ions. At pH c 1. rapid precipitation of lead sulphate occurs and hence the oxidation should always be done at pH l*O-15. Varying concentrations of EDTA and sulphate ion did not affect the quantitative precipitation oflead sulphate. It was found that 1 or 2 ml of 307; hydrogen peroxide or 05g of sodium bromate could oxidize 5 ml of 5% EDTA solution. For other concentrations of EDTA the optimum quantities of oxidant have to be found by trial and error, but an excess of either bromate or hydrogen peroxide has no adverse effect. Interferences were studied on mixtures of 50 mg of foreign ion with 5 or 50 mg of lead. The results in Tables 1-3 clearly mdicate the usefulness of the method for the determination of lead in the presence and absence of Interfering metals. Determination of lead in type metal gave an accurate value. It is noteworthy that tin and antimony do not interfere. Chloride does not interfere when present in up to tenfold amount relative to lead. The method can also be used to determine sulphate.
Table 2. Interference studies for the hydrogen peroxide method
Lead taken. “YJ
Lead found W
Mean deviation, W
No. of experiments
AI(III) Al(II1) Cu(II) CU(I1)
51.8 5.2 51.8 5.2
51.6 5.2 51.7 5.1
PO 03 0.2 0.2
4 4 4 4
Ni(I1) N1(11) Zn(II) Zn(I1) Fe(II1) Fe(II1) Mn(I1) Mn(I1) Sri(H) Sn(I1) Sb(III) Sb(II1)
5.2 51.8 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2
5.0 51.6 51.9 4.9 52.0 5.0 51.9 5.1 51.8 5.2 51.9 5.1
@2 0.2 @O @I 01 0.1 0.1 0.1 0.1 0.1 0.2 0.1
: 3 3 4 4 3 3 4 4 4 4
Metal added
.
1302
SHORTCOMMUNICATIONS
Table 3. Interference studies for the bromate method Metal added AI(II1) AI Cu(I1) Cu(I1) Ni(I1) Ni(I1) Zn(I1) Zn(I1) Fe(II1) Fe(II1) Mn(I1) Mn(I1) Sn(I1) Sn(I1) Sb(II1) Sb(II1)
Lead taken, lng 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 5.2 51.8 52
Lead found ‘ng 51.7 5.1 51.9 5.0 51.7 5.1 51.7 5.1 52.0 5.1 52.0 5.3 51.7 5.0 51.6 5.1
Mean deviation. fag 0.2 0.2 0.2 0.2 0.4 @3 0.3 0.3 0.2 @l 0.1 01 0.1 @I 0.1 0.1
No. of experiments 4 4 4 4 4 4 4 3 4 4 4 4 3 3 3 3
Acknowledgements-Grateful thanks of the authors are due to Professor P. K. Jena. Director, Regional Research Laboratory, Bhubaneswar, for facilities and interest in the work. J. RAJAG~PALA RAO A. SURYANARAYANA
Regional Research Laboratory Bhubaneswar-4, India
B.R.SAm REFERENCES 1. W. H. MacNevin and M. L. Dunton, Anal. Chem.. 1954.26, 1246.
2. 3. 4. 5.
P. F. S. Cartwright Analyst, 1961,86,688. 692; 1962.87, 163; 1967.92, 319. A. Suryanarayana, J. R. Rao and B. R. Sam, Anal. Chim. Acta. 197259,481. J. R. Rao. A. Survanaravana and B. R. Sant. Z. Anal. Chem.. 1973.265. 128. E. Garate and T.‘Garate, Chim. Anal. (Paris), 1958.40, 7. Summary-Gravimetric determination of lead (%I00 mg) by homogeneous precipitation of lead sulphate from a solution containing lead(II), EDTA and sulphate by destructive oxidation of EDTA with hydrogen peroxide or sodium bromate is described. Aluminium(III), iron(II1). zinc(H). manganese(II), copper( nickel(II), tin(I1) and antimony(II1) do not interfere in the method. The method can successfully be applied to the analysis of type metal.
R&m&-On decrit le dosage gravimetrique du plomb (5-100 mg) par precipitation homogtne du sulfate de plomb a nartir dune solution contenant du nlomb(II), de I’EDTA et du sulfate, par oxydation destructive de I’EDTA par le peroxyde d’hydrogene ou ie bromate de sodium. Les aluminmm(III), fer(III), zinc(II), mangantse(I1). cuivre(I1). nickel(I1). etam(I1) et antimoine(II1) n’interferent pas dans cette methode. La mtthode peut etre appliquee avec succes h I’analyse d’alliage pour caract&es d’imprimerie. Zusammenfaasung-Die gravimetrische Bestimmung von Blei (5-100 mg) durch homogene Fallung von Bleisulfat wird beschrieben. Es wird aus einer Losung gefallf die Blei(II), EDTA und Sulfat enthllt und in der EDTA mit WasserstoRperoxid oder Natriumbromat oxidativ zerstort wird. Aluminium(II1). Eisen(III), Zink(I1). Mangan(I1). Kupfer(I1). Nickel(II), Zinn(I1) und Antimon(II1) storen nicht. Das Verfahren kann mit Erfolg fur die Analyse von Letternmetall verwendet werden.