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Determination of silver, bismuth, cadmium, copper, iron, nickel and zinc in lead- and tin-base solders and white-metal bearing alloys by atomic-absorption spectrophotometry
Talanru, Vol. 33, No I. pp. 91-94. 19X6 Prmted in Great Britain. All rights reserved
Copyright
c
0039-9 140 X6 $3.00 + 0.00 1986 Pergamon Press Ltd
DETERMINATION OF SILVER, BISMUTH, CADMIUM, COPPER, IRON, NICKEL AND ZINC IN LEAD- AND TIN-BASE SOLDERS AND WHITE-METAL BEARING ALLOYS BY ATOMIC-ABSORPTION SPECTROPHOTOMETRY CHOW
Geological
Survey
Laboratory. (Received
Scrivenor
CHONG
Road.
P.O. Box 1015, Ipoh.
5 Mrrrch 1985. Acwpred
22 August
Perak,
Malaysia
1985)
simple atomic-absorption spectrophotometry method is described for the determination of silver, bismuth. cadmium, copper, iron, nickel and zinc in lead- and tin-base solders and white-metal bearing alloys, with use of a single sample solution. The sample is dissolved in a mixture of hydrobromic acid and bromine, then fumed with sulphuric acid. The lead sulphate is dissolved in concentrated hydrochloric acid. The method is particularly suitable for the determination of silver and bismuth. which are co-precipitated with lead sulphate. The other elements can also be determined after removal of the lead sulphate by filtration. Summary-A
Lead- and tin-base solders and white-metal bearing alloys differ widely in composition. The major elements range in concentration from 0.1 to 99% for Pb, 0.5 to 95% for Sn and 0.02 to 20% for Sb. The alloys also contain various amounts of trace elements such as silver, bismuth, copper. zinc. nickel, cadmium and iron. Spectrophotometric.’ 5 spectrographic” and polarographic’ methods have been used in the determination of the trace elements. The lead can be separated as lead sulphate’,‘,’ or chloride,’ or complexed with tartrate or EDTA.S Atomic-absorption spectrophotometry (AAS) has also been proposed for the determination of these trace elements after the sample has been dissolved with various acid mixtures and reagents. Farrar* used a mixture of hydrobromic acid and bromine to dissolve lead-base bearing alloys and type metal for determination of copper and zinc by AAS. Hwang and Sandonato’ used a special mixture of nitric acid, fluoroboric acid and water in the ratio 3:2:5 v/v to dissolve tin-lead solders. They claimed that the resulting solutions remained stable for up to 48 hr. Carleer et al.“’ used ayun regicc to dissolve lead- and tin-base solder for the determination of several major, minor and trace elements by AAS. Mixtures of fluoroboric, nitric and tartaric acids,” and of fluoroboric acid and hydrogen peroxide” have been used to dissolve type metal and lead alloys, respectively, for the determination of tin and antimony by AAS. In general. the greatest problem in the dissolution is the stability of the solution, because precipitation of lead and some of the trace elements can occur on dilution or after standing for some time. A mixture of hydrobromic acid and bromine is effective in dissolving lead- and tin-base solders and
white-metal bearing alloys and has the advantage that tin, antimony and arsenic may be removed by volatilization on fuming with sulphuric acid. However, there have been many report?,‘” of the partial co-precipitation of some elements with the lead sulphate produced. In this stuay it was found that the co-precipitation of silver and bismuth with lead sulphate was substantial, rendering invalid any attempt to remove the precipitate and determine silver and bismuth in the solution. However. if the lead sulphate is dissolved in concentrated hydrochloric acid, the solution, after dilution. is stable for some weeks and silver and bismuth can easily be determined by AAS. Other trace elements such as nickel. cadmium, zinc, copper and iron can also be determined in the same solution or, since they are not co-precipitated with lead sulphate, they can also be determined after the lead sulphate has been filtered off.
EXPERIMENTAL
A Varian Techtron model AA875 atomic-absorption spectrophotometer, equipped with a IO-cm air~acetylene burner was used in all measurements. Standard singleelement hollow-cathode lamps were used as line sources. The air and acetylene flows were set at 28 and 9, respectively, the aspiration rate was 6 ml’min and the absorbance read-out integration time was 3 sec. Other conditions used were as indicated in Table I.
Slandard coppr, iron. c~utlnkm and nickel .rolution.r ( 1000 u~:m/). Dissolve 0.25 g of the metal in 12.5 ml of concentrated hydrochloric acid. Add 3 drops of concentrated nitric acid in the case of nickel and copper. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration. 91
CHOW
92 Table
Element
Ag Bi Cd
C” Fe Ni Zn
Wavelength, ntn
CHONG
I. AAS conditions
Band width, nm
Lamp current, mA
0.5 0.2 0.5 0.5 0.2 0.2
3.5 IO 3.5 3.5 5 3.5 5
328.1 223.1 228.8 324.8 248.3 232.0 213.9
I .o
Absorbance expansion factor
1 1
I I I, 10* 2 5
*For very low iron values. Standard silver solution (1000 pggimi). Dissolve 0.25 g of silver metal in 25 ml of 50% nitric acid. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration. Keep in a dark place. Standard zinc solution (1000 pg/m/). Dissolve 0.3112 g of zinc oxide, previously dried for 1 hr at 105”, in 12.5 ml of concentrated hydrochloric acid. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration. Standard bismuth solution (1000 pg/ml). Dissolve 0.2787 g of bismuth oxide, previously dried for 1 hr at 105’, in 12.5 ml of concentrated hydrochloric acid. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration but maintain the acid concentration at 2% to prevent hydrolysis of bismuth. Procedures Method involving the dissolution of lead sulphate. Weigh accurately 0.4 g of lead-base bearing metal or 1.0 g of tin-base bearing metal or 0.5 g of solder into a 150-ml beaker. Add 10 ml of concentrated hydrobromic acid, followed by 2 ml of saturated bromine water. Cover with a watch-glass and heat on a hot-plate with occasional swirling until the sample is completely dissolved. It may be necessary to add a little more hydrobromic acid or a few extra drops of bromine for complete dissolution, depending on the type of sample. Wash down the glass cover and sides of the beaker and add 4 ml of 50% sulphuric acid and heat to strong fuming on top of a thin asbestos sheet on a hot-plate, then until the lead sulphate is white. Direct heating on a hot-plate before this stage may lead to spattering. Heat the beaker directly on the hot-plate until the lead sulphate becomes crystalline and about 0.5 ml of sulphuric acid remains. Allow to cool, add 40 ml of concentrated hydrochloric acid and stir until all the lead sulphate has dissolved. Dilute with distilled water and transfer the solution to a 200-ml standard flask. Cool to room temperature and make up to the mark. Transfer 50.0 ml of the solution as soon as possible into a IOO-ml standard flask and dilute to the mark with distilled water; this step must be done quickly because solutions containing large amounts of lead may yield a small amount of lead sulphate precipitate on standing. However, the diluted 50-m] aliquot is stable for some weeks. The final solution is now suitable for aspiration and AAS deter-
mination of the various elements but may be further diluted where necessary, as in the case of the determination of copper in tin-base bearing metal. Preparation of calibration graph. Prepare a blank and mixed standards of silver, bismuth, cadmium, copper, iron, nickel and zinc by pipetting aliquots (as indicated in Table 2) into a series of 150-ml beakers. Add IO ml of concentrated hydrobromic acid and 2 ml of saturated bromine water and proceed as for samples. Method involving Ihe separation of lead sulphate. Weigh accurately 0.2551.0 g of sample into a 150-ml beaker and proceed as above, up to the point at which about 0.5 ml of sulphuric acid remains. Then cool, add 10 ml of 1% v/v sulphuric acid and filter off the precipitate on a 9-cm Schleicher and Schiill No. 589’ paper (or equivalent, e.g., Whatman No. 40), collecting the filtrate in a IOO-ml standard flask. Wash the precipitate with 40 ml of 1% sulphuric acid. Make the solution up to the mark with distilled water. The solution is now ready for aspiration and the determination of the various elements. It may be diluted with 1% sulphuric acid when necessary to bring the absorbance within the calibration range. Preparation of calibration graph. Prepare a blank and mixed standards of copper, zinc, cadmium, nickel and iron by pipetting ahquots (as indicated in Table 3) into a series of 150-ml beakers. Add 10 ml of concentrated hydrobromic acid, 2 ml of saturated bromine water and 4 ml of 50% sulphuric acid. Heat to fuming until about 0.5 ml of sulphuric acid remains. Allow to cool and transfer to a lOO-ml standard flask with 50 ml of 1% sulphuric acid, and dilute to the mark with distilled water.
RESULTS AND DISCUSSION Co-precipitation
of some elements
Lead sulphate has been reportedI to co-precipitate a number of elements such as silver, bismuth, copper, antimony, calcium and strontium under certain conditions. However, there is some disagreement on the co-precipitation of certain elements by lead sulphate.
Table 2. Concentration range of standard solutions used in procedure involving dissolution of lead sulphate Stock solution, Element
Ag Bi Cd C” Fe Ni Zn
PPm 10 100 10 100 100 10 10
with lead sulphate
Aliquot,* ml 4.0, 8.0, 2.0,4.0, 4.0, 8.0, 0.4, 1.2, 0.4, 1.2, 2.0.4.0, 0.8, 1.6,
12.0 6.0 12.0 2.4 2.4 6.0 2.4
*For making up to a volume of 200 ml. tAfter dilution of 50 ml of the 200-ml standard
Concentrationt in 100 ml, ppm 0.1, 0.2,0.3 0.5, 1.0, 1.5 0.1, 0.2,0.3 0.1, 0.3,0.6 0.1, 0.3.0.6 0.05,o. 10,o. 15 0.02.0.04.0.06 solution
to 100 ml.
Analysis
of solders
and white metals
93
Table 3. Concentration range of standard solutions used in procedure involving separation of lead sulphate Stock solution, Element
Aliquot. ml
PPm
Cd CU Fc Ni Zn
10 100 10 10 I
Concentration in 100 ml, ppln
1.0,2.0. 3.0 0.5. 1.0.2.0 I .o. 3.0. 6.0 I .o. I .5. 2.0 2.0. 4.0. 6.0
Karabash et al.’ reported that there was no coprecipitation of some twenty metals, including nickel, zinc, cadmium, copper, bismuth, iron and silver at concentrations of 10~6P10 ‘% of that of the lead. Zhenpu Wang and Cheng4 reported serious coprecipitation of aluminium, bismuth and iron with lead sulphate, but Luke’ and Ota’ determined aluminium and iron, respectively, in tin and lead alloys without considering co-precipitation with lead sulphate. In this study it was found that cadmium, copper, iron, nickel and zinc were co-precipitated to a negligible extent with lead sulphate, as shown in Table 4. The degree of co-precipitation of silver and bismuth seems to depend on the conditions used. If a lead nitrate solution is used and hydrobromic acid and bromine are not added. the degree of coprecipitation of bismuth and silver with lead sulphate is about 19 and 27%. respectively. If hydrobromic acid and bromine are added, however, the degree of
0. I. 0.2, 0.3 0.5. I .o, 2.0 0.1. 0.3. 0.6 0.1.0.15.0.20 0.02.0.04.0.06
co-precipitation respectively. Solubilitl, solution
Amount
Ag cu Ni Cd Zn Fe *The amount
of lead was
NBS value
43 Bi Cd Fe Ni cu Zn
0.052
cadmium.
nickel, cadmium.
found. ,“R
Co-precipitated,
0.020 0.155 0.001 0.001 0.100 0.500 0.101 0.495 0.010 0.046 0.0104 0.0510 0.101 0.500
%
-80 -69 -99 - 100 0 0 +I -I 0 -8 f4 f2 fl 0
I g, added as lead nitrate solution.
NBS 54d tin-base bearing metal
Value found
NBS value
0.024 0.052 0.003 < 0.001 0.004 0.053 0.0005
0.003 0.044 0.027 0.002 3.62
copper,
From Table 4. it is clear that silver and bismuth are considerably co-precipitated with lead sulphate whereas the other elements are not. The results given
of silver, bismuth. cadmium, copper. iron. nickel and zinc (%) in NBS samples by the lead sulphate dissolution method
NBS 53e lead-base bearing metal Element
and the .stubilit~~ of’ its
Drtrrnzination of‘ silcer, bismuth, iron, nickel and :inc
Amount
0.100 0.500 0.100 0.500 0.100 0.500 0.100 0.500 0.010 0.050 0.0100 0.0500 0.100 0.500
lOO%,
The solubility of lead sulphate in hydrochloric acid was studied at room temperature. It was found that to dissolve lead sulphate completely and keep it in solution after dilution to 200 ml with water, at least 13 ml of concentrated hydrochloric acid per 100 mg of lead will be required for the initial dissolution, for 200-500 mg of lead. The 200 ml of solution obtained in this way can be diluted fourfold without reprecipitation of lead sulphate.
w
Bi
Table 5. Determination
added.
to 75 and almost
of leud sulphate
Table 4. Co-precipitation of bismuth. silver. copper. zinc and iron with lead sulphate* Element
increases
Value found 0.004 0.048 0.005 0.028 0.003 3.64 0.0005
NBS 127b solder (Sn 40, Pb 60) NBS value
Value found
0.01 0.06
0.016 0.070
0.012 0.01 I -
94
CHOW
Table 6. Determination
of silver, bismuth, cadmium, by the lead sulphate
NBS 53e lead-base bearing metal Element Ag Bi Cd Fe Ni
cu
NBS value 0.052
Zn Table
CHONC
NBS 54d tin-base bearing metal
Value found
NBS value
0.003 0.044
Value found 0.001 0.020 0.005 0.028 0.003 3.60 0.0006
0.027 0.002 3.62
NBS value
Value found
0.01 0.06
0.012 0.011
added,
Element
1’1:
/x
Recovery, %
Ag Bi Cd cu Fe Ni Zn
25 250 25 150 100 25 IO
25.2 240 26 149 96 24 IO
101 96 104 99 96 96 100
*0.5 g of solder sample method.
Amount
was analysed
in Tables 5 and 6 show that good agreement has been obtained with NBS values for nickel, iron and copper by both the proposed methods, whereas for silver and bismuth the lead sulphate separation method gives exceedingly low results as a result of co-precipitation. Thus the lead sulphate dissolution method is recommended for determination of silver and bismuth. As the silver value in NBS 127(b) is given to only two decimal places, it is not possible to compare the third decimal place. Consequently this sample was analysed for silver seven times by the lead sulphate dissolution method. The silver value was found to range from 0.0158% to 0.0160% with a coefficient of variation of 0.6%. Although the lead sulphate dissolution method can be used to determine a wider range of elements, the lead sulphate separation method has the advantage that a larger sample size can be used and is thus useful for elements that are present in very small amounts and are not coprecipitated with lead sulphate.
To test the validity of the lead sulphate dissolution method, known amounts of silver, bismuth, cadmium, copper, iron, nickel and zinc were added to a solder sample (Sn 60, Pb 40), the mixture was analysed and the recovery (total concentration obtained for the element minus concentration of element present in the sample) was calculated. The results are given in Table 7 and the good recovery obtained shows that the lead sulphate dissolution method is reliable.
dissolution
method
avoids those
dissolution
associated with the coanalytical problems precipitation of other elements and the insolubility of lead sulphate. The only limitation is that it cannot be used for large samples having high lead contents, because reprecipitation of lead sulphate occurs on dilution. AcknorL,/edgemenfs-Grateful acknowledgement is made to the Director-General, Geological Survey, Malaysia, for his permission to publish this paper and to the Assistant Director-General and the Director of Geochemistry for their encouragement.
REFERENCES 1. Chemical
2. 3. 4. 5. 6.
7. 8. 9. IO. Il. 12. 13.
Conclusion
obtained,
by the lead sulphate
test
The lead sulphate
NBS 127b solder (Sn 40, Pb 60)
7. Recovery of silver, bismuth, cadmium, copper, iron, nickel and zinc in a solder sample (Sn 60, Pb 40)* Amount
Recovery
copper, iron, nickel and zinc (%) in NBS samples separation method
Analpis of Metals and Metal Bearing Ores, ASTM, Part 12, 1980, E42 and E57. C. L. Luke, Anal. Chem., 1952, 24, 1122. K. Ota, Bunseki Kagaku, 1956, 5, 3; Anal. Ahstr., 1956, 3, 2731. Zhenpu Wang and K. L. Cheng, Taianla, 1982,29, 551. K. L. Cheng, R. H. Bray and S. W. Melsted, A&. Chem.. 1955, 27, 24. A. G. Karabash, L. S. Bondarenko, G. G. Morozova and Sh. I. Peizulayev, Zh. Analit. Khim, 1960, 15, 623; Anal. Abstr., 1961, 8, 1895. J. R. Bishop and H. Leibmann, Anulyst, 1953, 78, 117. B. Farrdr, At. Absorpt. Newsi., 1965, 4, 325. J. Y. Hwang and L. M. Sandonato, Anal. Chem., 1970, 42, 744. R. Carleer, J. P. Fraqois and L. C. Van Poucke, Bull. SW. Chim. Be/g., 198 1, 90, 357. J. U. Gouin, J. L. Holt and R. E. Miller, Anal. Chem., 1972, 44, 1042. T. M. Quarrell, R. J. W. Powell and H. J. Cl&y, Analyst, 1973, 98, 443. I. M. Kolthoff and P. J. Elving, Trearise on Analyrical Chemistry, Part II, Vol. 6, p. 111. Interscience. New York, 1964.
Copyright
c
0039-9 140 X6 $3.00 + 0.00 1986 Pergamon Press Ltd
DETERMINATION OF SILVER, BISMUTH, CADMIUM, COPPER, IRON, NICKEL AND ZINC IN LEAD- AND TIN-BASE SOLDERS AND WHITE-METAL BEARING ALLOYS BY ATOMIC-ABSORPTION SPECTROPHOTOMETRY CHOW
Geological
Survey
Laboratory. (Received
Scrivenor
CHONG
Road.
P.O. Box 1015, Ipoh.
5 Mrrrch 1985. Acwpred
22 August
Perak,
Malaysia
1985)
simple atomic-absorption spectrophotometry method is described for the determination of silver, bismuth. cadmium, copper, iron, nickel and zinc in lead- and tin-base solders and white-metal bearing alloys, with use of a single sample solution. The sample is dissolved in a mixture of hydrobromic acid and bromine, then fumed with sulphuric acid. The lead sulphate is dissolved in concentrated hydrochloric acid. The method is particularly suitable for the determination of silver and bismuth. which are co-precipitated with lead sulphate. The other elements can also be determined after removal of the lead sulphate by filtration. Summary-A
Lead- and tin-base solders and white-metal bearing alloys differ widely in composition. The major elements range in concentration from 0.1 to 99% for Pb, 0.5 to 95% for Sn and 0.02 to 20% for Sb. The alloys also contain various amounts of trace elements such as silver, bismuth, copper. zinc. nickel, cadmium and iron. Spectrophotometric.’ 5 spectrographic” and polarographic’ methods have been used in the determination of the trace elements. The lead can be separated as lead sulphate’,‘,’ or chloride,’ or complexed with tartrate or EDTA.S Atomic-absorption spectrophotometry (AAS) has also been proposed for the determination of these trace elements after the sample has been dissolved with various acid mixtures and reagents. Farrar* used a mixture of hydrobromic acid and bromine to dissolve lead-base bearing alloys and type metal for determination of copper and zinc by AAS. Hwang and Sandonato’ used a special mixture of nitric acid, fluoroboric acid and water in the ratio 3:2:5 v/v to dissolve tin-lead solders. They claimed that the resulting solutions remained stable for up to 48 hr. Carleer et al.“’ used ayun regicc to dissolve lead- and tin-base solder for the determination of several major, minor and trace elements by AAS. Mixtures of fluoroboric, nitric and tartaric acids,” and of fluoroboric acid and hydrogen peroxide” have been used to dissolve type metal and lead alloys, respectively, for the determination of tin and antimony by AAS. In general. the greatest problem in the dissolution is the stability of the solution, because precipitation of lead and some of the trace elements can occur on dilution or after standing for some time. A mixture of hydrobromic acid and bromine is effective in dissolving lead- and tin-base solders and
white-metal bearing alloys and has the advantage that tin, antimony and arsenic may be removed by volatilization on fuming with sulphuric acid. However, there have been many report?,‘” of the partial co-precipitation of some elements with the lead sulphate produced. In this stuay it was found that the co-precipitation of silver and bismuth with lead sulphate was substantial, rendering invalid any attempt to remove the precipitate and determine silver and bismuth in the solution. However. if the lead sulphate is dissolved in concentrated hydrochloric acid, the solution, after dilution. is stable for some weeks and silver and bismuth can easily be determined by AAS. Other trace elements such as nickel. cadmium, zinc, copper and iron can also be determined in the same solution or, since they are not co-precipitated with lead sulphate, they can also be determined after the lead sulphate has been filtered off.
EXPERIMENTAL
A Varian Techtron model AA875 atomic-absorption spectrophotometer, equipped with a IO-cm air~acetylene burner was used in all measurements. Standard singleelement hollow-cathode lamps were used as line sources. The air and acetylene flows were set at 28 and 9, respectively, the aspiration rate was 6 ml’min and the absorbance read-out integration time was 3 sec. Other conditions used were as indicated in Table I.
Slandard coppr, iron. c~utlnkm and nickel .rolution.r ( 1000 u~:m/). Dissolve 0.25 g of the metal in 12.5 ml of concentrated hydrochloric acid. Add 3 drops of concentrated nitric acid in the case of nickel and copper. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration. 91
CHOW
92 Table
Element
Ag Bi Cd
C” Fe Ni Zn
Wavelength, ntn
CHONG
I. AAS conditions
Band width, nm
Lamp current, mA
0.5 0.2 0.5 0.5 0.2 0.2
3.5 IO 3.5 3.5 5 3.5 5
328.1 223.1 228.8 324.8 248.3 232.0 213.9
I .o
Absorbance expansion factor
1 1
I I I, 10* 2 5
*For very low iron values. Standard silver solution (1000 pggimi). Dissolve 0.25 g of silver metal in 25 ml of 50% nitric acid. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration. Keep in a dark place. Standard zinc solution (1000 pg/m/). Dissolve 0.3112 g of zinc oxide, previously dried for 1 hr at 105”, in 12.5 ml of concentrated hydrochloric acid. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration. Standard bismuth solution (1000 pg/ml). Dissolve 0.2787 g of bismuth oxide, previously dried for 1 hr at 105’, in 12.5 ml of concentrated hydrochloric acid. Make up accurately to 250 ml with distilled water. Dilute to the desired concentration but maintain the acid concentration at 2% to prevent hydrolysis of bismuth. Procedures Method involving the dissolution of lead sulphate. Weigh accurately 0.4 g of lead-base bearing metal or 1.0 g of tin-base bearing metal or 0.5 g of solder into a 150-ml beaker. Add 10 ml of concentrated hydrobromic acid, followed by 2 ml of saturated bromine water. Cover with a watch-glass and heat on a hot-plate with occasional swirling until the sample is completely dissolved. It may be necessary to add a little more hydrobromic acid or a few extra drops of bromine for complete dissolution, depending on the type of sample. Wash down the glass cover and sides of the beaker and add 4 ml of 50% sulphuric acid and heat to strong fuming on top of a thin asbestos sheet on a hot-plate, then until the lead sulphate is white. Direct heating on a hot-plate before this stage may lead to spattering. Heat the beaker directly on the hot-plate until the lead sulphate becomes crystalline and about 0.5 ml of sulphuric acid remains. Allow to cool, add 40 ml of concentrated hydrochloric acid and stir until all the lead sulphate has dissolved. Dilute with distilled water and transfer the solution to a 200-ml standard flask. Cool to room temperature and make up to the mark. Transfer 50.0 ml of the solution as soon as possible into a IOO-ml standard flask and dilute to the mark with distilled water; this step must be done quickly because solutions containing large amounts of lead may yield a small amount of lead sulphate precipitate on standing. However, the diluted 50-m] aliquot is stable for some weeks. The final solution is now suitable for aspiration and AAS deter-
mination of the various elements but may be further diluted where necessary, as in the case of the determination of copper in tin-base bearing metal. Preparation of calibration graph. Prepare a blank and mixed standards of silver, bismuth, cadmium, copper, iron, nickel and zinc by pipetting aliquots (as indicated in Table 2) into a series of 150-ml beakers. Add IO ml of concentrated hydrobromic acid and 2 ml of saturated bromine water and proceed as for samples. Method involving Ihe separation of lead sulphate. Weigh accurately 0.2551.0 g of sample into a 150-ml beaker and proceed as above, up to the point at which about 0.5 ml of sulphuric acid remains. Then cool, add 10 ml of 1% v/v sulphuric acid and filter off the precipitate on a 9-cm Schleicher and Schiill No. 589’ paper (or equivalent, e.g., Whatman No. 40), collecting the filtrate in a IOO-ml standard flask. Wash the precipitate with 40 ml of 1% sulphuric acid. Make the solution up to the mark with distilled water. The solution is now ready for aspiration and the determination of the various elements. It may be diluted with 1% sulphuric acid when necessary to bring the absorbance within the calibration range. Preparation of calibration graph. Prepare a blank and mixed standards of copper, zinc, cadmium, nickel and iron by pipetting ahquots (as indicated in Table 3) into a series of 150-ml beakers. Add 10 ml of concentrated hydrobromic acid, 2 ml of saturated bromine water and 4 ml of 50% sulphuric acid. Heat to fuming until about 0.5 ml of sulphuric acid remains. Allow to cool and transfer to a lOO-ml standard flask with 50 ml of 1% sulphuric acid, and dilute to the mark with distilled water.
RESULTS AND DISCUSSION Co-precipitation
of some elements
Lead sulphate has been reportedI to co-precipitate a number of elements such as silver, bismuth, copper, antimony, calcium and strontium under certain conditions. However, there is some disagreement on the co-precipitation of certain elements by lead sulphate.
Table 2. Concentration range of standard solutions used in procedure involving dissolution of lead sulphate Stock solution, Element
Ag Bi Cd C” Fe Ni Zn
PPm 10 100 10 100 100 10 10
with lead sulphate
Aliquot,* ml 4.0, 8.0, 2.0,4.0, 4.0, 8.0, 0.4, 1.2, 0.4, 1.2, 2.0.4.0, 0.8, 1.6,
12.0 6.0 12.0 2.4 2.4 6.0 2.4
*For making up to a volume of 200 ml. tAfter dilution of 50 ml of the 200-ml standard
Concentrationt in 100 ml, ppm 0.1, 0.2,0.3 0.5, 1.0, 1.5 0.1, 0.2,0.3 0.1, 0.3,0.6 0.1, 0.3.0.6 0.05,o. 10,o. 15 0.02.0.04.0.06 solution
to 100 ml.
Analysis
of solders
and white metals
93
Table 3. Concentration range of standard solutions used in procedure involving separation of lead sulphate Stock solution, Element
Aliquot. ml
PPm
Cd CU Fc Ni Zn
10 100 10 10 I
Concentration in 100 ml, ppln
1.0,2.0. 3.0 0.5. 1.0.2.0 I .o. 3.0. 6.0 I .o. I .5. 2.0 2.0. 4.0. 6.0
Karabash et al.’ reported that there was no coprecipitation of some twenty metals, including nickel, zinc, cadmium, copper, bismuth, iron and silver at concentrations of 10~6P10 ‘% of that of the lead. Zhenpu Wang and Cheng4 reported serious coprecipitation of aluminium, bismuth and iron with lead sulphate, but Luke’ and Ota’ determined aluminium and iron, respectively, in tin and lead alloys without considering co-precipitation with lead sulphate. In this study it was found that cadmium, copper, iron, nickel and zinc were co-precipitated to a negligible extent with lead sulphate, as shown in Table 4. The degree of co-precipitation of silver and bismuth seems to depend on the conditions used. If a lead nitrate solution is used and hydrobromic acid and bromine are not added. the degree of coprecipitation of bismuth and silver with lead sulphate is about 19 and 27%. respectively. If hydrobromic acid and bromine are added, however, the degree of
0. I. 0.2, 0.3 0.5. I .o, 2.0 0.1. 0.3. 0.6 0.1.0.15.0.20 0.02.0.04.0.06
co-precipitation respectively. Solubilitl, solution
Amount
Ag cu Ni Cd Zn Fe *The amount
of lead was
NBS value
43 Bi Cd Fe Ni cu Zn
0.052
cadmium.
nickel, cadmium.
found. ,“R
Co-precipitated,
0.020 0.155 0.001 0.001 0.100 0.500 0.101 0.495 0.010 0.046 0.0104 0.0510 0.101 0.500
%
-80 -69 -99 - 100 0 0 +I -I 0 -8 f4 f2 fl 0
I g, added as lead nitrate solution.
NBS 54d tin-base bearing metal
Value found
NBS value
0.024 0.052 0.003 < 0.001 0.004 0.053 0.0005
0.003 0.044 0.027 0.002 3.62
copper,
From Table 4. it is clear that silver and bismuth are considerably co-precipitated with lead sulphate whereas the other elements are not. The results given
of silver, bismuth. cadmium, copper. iron. nickel and zinc (%) in NBS samples by the lead sulphate dissolution method
NBS 53e lead-base bearing metal Element
and the .stubilit~~ of’ its
Drtrrnzination of‘ silcer, bismuth, iron, nickel and :inc
Amount
0.100 0.500 0.100 0.500 0.100 0.500 0.100 0.500 0.010 0.050 0.0100 0.0500 0.100 0.500
lOO%,
The solubility of lead sulphate in hydrochloric acid was studied at room temperature. It was found that to dissolve lead sulphate completely and keep it in solution after dilution to 200 ml with water, at least 13 ml of concentrated hydrochloric acid per 100 mg of lead will be required for the initial dissolution, for 200-500 mg of lead. The 200 ml of solution obtained in this way can be diluted fourfold without reprecipitation of lead sulphate.
w
Bi
Table 5. Determination
added.
to 75 and almost
of leud sulphate
Table 4. Co-precipitation of bismuth. silver. copper. zinc and iron with lead sulphate* Element
increases
Value found 0.004 0.048 0.005 0.028 0.003 3.64 0.0005
NBS 127b solder (Sn 40, Pb 60) NBS value
Value found
0.01 0.06
0.016 0.070
0.012 0.01 I -
94
CHOW
Table 6. Determination
of silver, bismuth, cadmium, by the lead sulphate
NBS 53e lead-base bearing metal Element Ag Bi Cd Fe Ni
cu
NBS value 0.052
Zn Table
CHONC
NBS 54d tin-base bearing metal
Value found
NBS value
0.003 0.044
Value found 0.001 0.020 0.005 0.028 0.003 3.60 0.0006
0.027 0.002 3.62
NBS value
Value found
0.01 0.06
0.012 0.011
added,
Element
1’1:
/x
Recovery, %
Ag Bi Cd cu Fe Ni Zn
25 250 25 150 100 25 IO
25.2 240 26 149 96 24 IO
101 96 104 99 96 96 100
*0.5 g of solder sample method.
Amount
was analysed
in Tables 5 and 6 show that good agreement has been obtained with NBS values for nickel, iron and copper by both the proposed methods, whereas for silver and bismuth the lead sulphate separation method gives exceedingly low results as a result of co-precipitation. Thus the lead sulphate dissolution method is recommended for determination of silver and bismuth. As the silver value in NBS 127(b) is given to only two decimal places, it is not possible to compare the third decimal place. Consequently this sample was analysed for silver seven times by the lead sulphate dissolution method. The silver value was found to range from 0.0158% to 0.0160% with a coefficient of variation of 0.6%. Although the lead sulphate dissolution method can be used to determine a wider range of elements, the lead sulphate separation method has the advantage that a larger sample size can be used and is thus useful for elements that are present in very small amounts and are not coprecipitated with lead sulphate.
To test the validity of the lead sulphate dissolution method, known amounts of silver, bismuth, cadmium, copper, iron, nickel and zinc were added to a solder sample (Sn 60, Pb 40), the mixture was analysed and the recovery (total concentration obtained for the element minus concentration of element present in the sample) was calculated. The results are given in Table 7 and the good recovery obtained shows that the lead sulphate dissolution method is reliable.
dissolution
method
avoids those
dissolution
associated with the coanalytical problems precipitation of other elements and the insolubility of lead sulphate. The only limitation is that it cannot be used for large samples having high lead contents, because reprecipitation of lead sulphate occurs on dilution. AcknorL,/edgemenfs-Grateful acknowledgement is made to the Director-General, Geological Survey, Malaysia, for his permission to publish this paper and to the Assistant Director-General and the Director of Geochemistry for their encouragement.
REFERENCES 1. Chemical
2. 3. 4. 5. 6.
7. 8. 9. IO. Il. 12. 13.
Conclusion
obtained,
by the lead sulphate
test
The lead sulphate
NBS 127b solder (Sn 40, Pb 60)
7. Recovery of silver, bismuth, cadmium, copper, iron, nickel and zinc in a solder sample (Sn 60, Pb 40)* Amount
Recovery
copper, iron, nickel and zinc (%) in NBS samples separation method
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