DETERMINATION OF SULFUR (SULFATE) BY TURBIDIMETRY METHOD (PHOTOMETRIC)
Scope
This test method covers the determination of the sulfur concentration, which exists as sulfate in uranyl nitrate solutions, in the range from 100 to 1000 µg S / g of uranium.
Summary of test method
The uranium in the sample is removed by extraction with tributhyl phosphate (TBP). The sulfate is then precipitated as barium sulfate in the presence of excess salt and acid is held in suspension in glycerin matrix. Sulfate is determined turbidimetrically using spectrophoto .
Meter.
Interferences.
· Any anions that from insoluble precipitates with barium, such as phosphate, axalate, , and chromate, will interfere.
· Many variables, although not classed as interferants, effect the precision of this test method. Careful control of the following parameters must be maintained to achieve the stated precision: particle size of the BaSO4 formed, total ionic concentration of the final solution, degree of mixing of sample and reagents (number of times the flask is inverted), concentration of hydrogen ion in the final solution, and the length of time of standing of the supernatant before the absorbance is measured.
Equipment
Spectrophotometer.
Reagents
· Barium chloride (BaCl2) crystals. Sift the salt and use only the portion that passes through a 28 mesh screen and is retained on a 35 mesh screen.
· Sodium Chloride –Glycerin Solution (16 g/L). Dissolve 40 g of NaCl in 60 mL of HCl (sp gr 1.19). Add 833 mL of glycerin and dilute to 2.5 L with water.
· Sulfate Standard Solution (1 mL = 1000 µg SO4 -). Dissolve 1.1813 g of K2SO4, dried at 110 oC for 1 h, and dilute to 1 L with water.
· Tributyl Phosphate Solution (3+7). Dilute 300 mL of TBP with 700 mL of kerosene and equilibrate with 8 M HNO3
Procedure
· Transwer a weighed aliquot of sample that contains approximately 1 g of uranium to a 60 mL separatory funnel. Adjust the nitric acid concentration to 4 to 5 M and the volume to 5 mL.
· Add 10 mL of TBP solution and equilibrate the solutions
· Allow the layers to separate and transfer the equeous layer to 50 mL volumetric containing 30 mL of distillate water. Use a minimum volume of 1 N HNO3 wash solution to ensure quantitative transfer of the aqueous layer to the 50 mL flask.
· Pipet 10 mL of NaCl-glycerin solution into the 50 mL flask and dilute to volume with water.
· Add 0.50 g of BaCl2, stopper the flask, and invert the solution 20 times to dissolve the BaCl2.
· Allow the solution to stand 60 ± 5 min. then measure the absorbance at 450 nm in 5 cm cells with a blank containing all of the reagents axcept sample as the reference.
· Prepare calibration curve by transferring 0.2, 0.5, 1.0, 1.5, and 2.0 mL aliquots of the standard sulfate solution into 60 mL separatory funnels that contain 5 mL of 4 to 5 M nitric acid and process in accordance with step 2 to step 6 at procedure.
Calculation
Calculate the sulfur content in micrograms per gram of uranium as follows :
Sulfur = (AxB) / C :2: µg/g
Where :
A = SO4 = found in the sample solution, µg
B = 0.334, the gravimetric factor converting SO4 = to S,
C = uranium in the sample solution aliquot, g
Precision
The limit of error at the 95% confidence level for a single determination is ± 3%
Literature
ASTM-C799, Standard Methods for “Chemical, Mass Spectrometric, Spectrochemical, Nuclear, and Radiochemical analysis of Nuclear-Grade Uranyl Nitrate solution”
Scope
This test method covers the determination of the sulfur concentration, which exists as sulfate in uranyl nitrate solutions, in the range from 100 to 1000 µg S / g of uranium.
Summary of test method
The uranium in the sample is removed by extraction with tributhyl phosphate (TBP). The sulfate is then precipitated as barium sulfate in the presence of excess salt and acid is held in suspension in glycerin matrix. Sulfate is determined turbidimetrically using spectrophoto .
Meter.
Interferences.
· Any anions that from insoluble precipitates with barium, such as phosphate, axalate, , and chromate, will interfere.
· Many variables, although not classed as interferants, effect the precision of this test method. Careful control of the following parameters must be maintained to achieve the stated precision: particle size of the BaSO4 formed, total ionic concentration of the final solution, degree of mixing of sample and reagents (number of times the flask is inverted), concentration of hydrogen ion in the final solution, and the length of time of standing of the supernatant before the absorbance is measured.
Equipment
Spectrophotometer.
Reagents
· Barium chloride (BaCl2) crystals. Sift the salt and use only the portion that passes through a 28 mesh screen and is retained on a 35 mesh screen.
· Sodium Chloride –Glycerin Solution (16 g/L). Dissolve 40 g of NaCl in 60 mL of HCl (sp gr 1.19). Add 833 mL of glycerin and dilute to 2.5 L with water.
· Sulfate Standard Solution (1 mL = 1000 µg SO4 -). Dissolve 1.1813 g of K2SO4, dried at 110 oC for 1 h, and dilute to 1 L with water.
· Tributyl Phosphate Solution (3+7). Dilute 300 mL of TBP with 700 mL of kerosene and equilibrate with 8 M HNO3
Procedure
· Transwer a weighed aliquot of sample that contains approximately 1 g of uranium to a 60 mL separatory funnel. Adjust the nitric acid concentration to 4 to 5 M and the volume to 5 mL.
· Add 10 mL of TBP solution and equilibrate the solutions
· Allow the layers to separate and transfer the equeous layer to 50 mL volumetric containing 30 mL of distillate water. Use a minimum volume of 1 N HNO3 wash solution to ensure quantitative transfer of the aqueous layer to the 50 mL flask.
· Pipet 10 mL of NaCl-glycerin solution into the 50 mL flask and dilute to volume with water.
· Add 0.50 g of BaCl2, stopper the flask, and invert the solution 20 times to dissolve the BaCl2.
· Allow the solution to stand 60 ± 5 min. then measure the absorbance at 450 nm in 5 cm cells with a blank containing all of the reagents axcept sample as the reference.
· Prepare calibration curve by transferring 0.2, 0.5, 1.0, 1.5, and 2.0 mL aliquots of the standard sulfate solution into 60 mL separatory funnels that contain 5 mL of 4 to 5 M nitric acid and process in accordance with step 2 to step 6 at procedure.
Calculation
Calculate the sulfur content in micrograms per gram of uranium as follows :
Sulfur = (AxB) / C :2: µg/g
Where :
A = SO4 = found in the sample solution, µg
B = 0.334, the gravimetric factor converting SO4 = to S,
C = uranium in the sample solution aliquot, g
Precision
The limit of error at the 95% confidence level for a single determination is ± 3%
Literature
ASTM-C799, Standard Methods for “Chemical, Mass Spectrometric, Spectrochemical, Nuclear, and Radiochemical analysis of Nuclear-Grade Uranyl Nitrate solution”
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