GB/T 2449.1-2021Sulphur for industrial use—Part 1: Solid product (English PDF)

6.2 Determination of sulfur mass fraction

6.2.2.1 Principle

The sample is eluted with carbon disulfide and weighed. The mass fraction of sulfur in industrial sulfur is calculated. This method is suitable for the determination of sulfur mass fraction in high-quality sulfur.

6.2.2.2 Reagents

Carbon disulfide.

6.2.2.3 Instruments and equipment

6.2.2.3.1 Glass sand core crucible. No.3, pore diameter 16 µm ~ 30 µm, volume 30 mL.

6.2.2.3.2 Suction filter bottle. 500 mL.

6.2.2.3.3 Vacuum pump.

6.2.2.3.4 Constant temperature drying oven. The temperature can be controlled from 105 °C to 110 °C.

6.2.2.3.5 Balance. Accurate to 0.001 g.

6.2.2.4 Test procedures

Weigh 2 g ~ 3 g of specimen, accurate to 0.0001 g. Place it in a glass sand core crucible, that has been dried to constant weight at 105 °C ~ 110 °C.

Connect the air extraction device. In the fume hood, install the glass sand core crucible containing the sample on the filter bottle. Use a dropper to add an appropriate amount of carbon disulfide into the crucible. Use a glass rod to stir to dissolve the sulfur. Turn on the vacuum pump to filter at a suitable rate. Continue washing and dissolving with carbon disulfide, until most of the sulfur is dissolved. Then use carbon disulfide to wash the crucible wall and bottom. Conduct suction filter.

Move the glass sand core crucible containing the residue into a constant temperature drying oven, which has a temperature of 105 °C ~ 110 °C, to dry for 45 minutes. Take it out and place it in a desiccator, to cool to room temperature. Then use carbon disulfide to wash the crucible 5 ~ 8 times. Move it into a constant temperature drying oven, which has a temperature of 105 °C ~ 110 °C, to dry for 30 minutes. Take it out and place it in a desiccator to cool to room temperature. Then weigh it, accurate to 0.0001 g. Repeat the above operation with carbon disulfide, until the difference between two consecutive weighing does not exceed 0.0003 g.

6.2.2.5 Test data processing

The mass fraction of sulfur (omega1) is calculated according to formula (2).

6.6 Determination of mass fraction of organic matter

6.6.1.3.3 Barium hydroxide solution. c [1/2 Ba(OH)2] = 0.05 mol/L. Prepare freshly when using. Add a few drops of phenolphthalein indicator solution to the solution. The solution needs to be isolated from carbon dioxide in the air with a collection tube filled with alkali asbestos.

6.6.1.3.9 Methyl red-methylene blue mixed indicator solution.

6.6.1.3.12 Alkali asbestos.

6.6.1.3.13 Glass wool.

6.6.1.3.14 Oxygen. Pure oxygen, stored in cylinders, equipped with oxygen pressure reducer.

6.6.1.3.5 Hydrochloric acid standard titration solution. c (HCl) =

0.5 mol/L 6.6.1.3.6 Hydrochloric acid standard titration solution. c (HCl) = 0.05 mol/L. Measure 50.00 mL of hydrochloric acid standard titration solution (6.6.1.3.5) into a 500 mL volumetric flask. Use water to dilute to the mark. Shake well. Prepare this solution before use.

6.6.1.3.8 Sodium hydroxide standard titration solution. c (NaOH) = 0.05 mol/L Measure

50.00 mL of sodium hydroxide standard titration solution (6.6.1.3.7) into a 500 mL volumetric flask. Use water to dilute it to the mark. Shake well. Prepare this solution before use.

6.6.1.3.11 Platinum asbestos. Contain platinum mass fraction of 5% ~ 10%

6.6.1.4 Instruments and equipment

6.6.1.4.1 Porcelain boat. 88 mm × 12 mm.

6.6.1.4.3 Combustion and absorption device. As shown in Figure 1

As shown in Figure 1, connect the entire device with a short rubber tube.

6.6.1.5.2 Blank test

The tube furnace (F) is heated while oxygen is passed through the device at a flow rate of approximately 100 mL/min.

When the temperature of the tube furnace F reaches 400 °C ~ 450 °C for about 30 minutes, remove the G5 and G6 scrubbing bottles. Add 20 mL of barium hydroxide solution, 40 mL of water, 5 mL of hydrogen peroxide solution to each. Then connect the G5 and G6 scrubbing bottles to the device. These operations shall be performed as quickly as possible, to avoid absorbing carbon dioxide from the air.

While continuing to pass oxygen through the device at a flow rate of about 100 mL/min, energize the tube furnace (E), to raise the temperature to 400 °C ~ 450 °C. Maintain this temperature for about 10 minutes. Then continue to raise the temperature to 800 °C ~ 900 °C. Maintain this temperature for about 30 minutes. Cut off the power supply of the tube furnace (E). Continue to supply oxygen for about 30 minutes. Then cut off the power supply of the tube furnace (F).

Remove the G5 and G6 scrubbing bottles. Open the bottle caps. Use a small amount of water to rinse it. Merge the washing liquid into the absorption liquid. Then perform blank titrations according to the following steps.

Using phenolphthalein indicator solution as indicator, use hydrochloric acid standard titration solution (6.6.1.3.6) to titrate the absorption solution to the end point.

Then add 2 ~ 3 drops of methyl red-methylene blue mixed indicator solution to each scrubbing bottle. Add a certain volume (usually 10.00 mL) of excess hydrochloric acid standard titration solution (6.6.1.3.6). Shake well. Use sodium hydroxide standard titration solution (6.6.1.3.8) to make back titration.

The hydrochloric acid standard titration solution (6.6.1.3.6), which is consumed in the blank test, shall be less than 0.2 mL.

The volume V0 of the hydrochloric acid standard titration solution (6.6.1.3.6), which is consumed for the blank test of the absorption liquid in the G5 and G6 scrubbing bottles, is expressed in milliliters (mL), which is calculated according to formula (7). Where.

V0 - The volume of hydrochloric acid standard titration solution consumed in the blank test, in milliliters (mL);

V1 - The volume of the hydrochloric acid standard titration solution added, in milliliters (mL);

V2 - The volume of sodium hydroxide standard titration solution consumed by back titration, in milliliters (mL).

In the calculation, if the actual concentration of the hydrochloric acid and sodium hydroxide standard titration solution is not exactly 0.05000 mol/L, V1 and V2 shall be converted into the volume when the concentration of the hydrochloric acid and sodium hydroxide standard titration solution is 0.05000 mol/L.

6.6.1.5.3 Specimen weighing and burning

Weigh 1.0 g ~ 1.5 g of specimen in a porcelain boat, accurate to 0.001 g.

The tube furnace (F) is heated and oxygen is passed through the device at a flow rate of approximately 100 mL/min.

When the temperature of the tube furnace (F) reaches 400 °C ~ 450 °C for about 30 minutes, remove the G5 and G6 scrubbing bottles. Add 20 mL of barium hydroxide solution, 40 mL of water, 5 mL of hydrogen peroxide solution to each of them, to oxidize any sulfite which is possibly generated. Then connect the G5 and G6 scrubbing bottles back to the device. These operations shall be performed as quickly as possible, to avoid absorbing carbon dioxide from the air.

Send the porcelain boat, which is loaded with the sample, to the unheated part of the combustion tube (D) in front of the tube furnace E. Immediately introduce oxygen at a flow rate of 100 mL/min. Heat the tube furnace (E).

When the temperature of tube furnace E reaches 450 °C, maintain this temperature and no longer rise. Slowly move the tube furnace (E) toward the porcelain boat, to burn the sulfur, whilst trace amounts of carbonaceous matter remain in the porcelain boat and combustion tube (D). If the combustion is too intense, the chromium trioxide solution in the G2 absorption bottle may be drawn back, then the oxygen flow rate shall be increased to prevent this. If the sulfur sublimates outside the porcelain boat and condenses between the porcelain boat and the platinum asbestos, the tube furnace (E) shall be moved to allow complete combustion of the sulfur.

After the sulfur is slowly burned, move the tube furnace (E) to the position where the porcelain boat is heated. Raise the temperature to 800 °C ~ 900 °C. Heat the combustion tube (D) and porcelain boat for about 30 minutes, to burn the remaining carbon and carbonate. break down. Cut off the power supply to the tube furnace (E). Continue to supply oxygen for about 30 minutes. Blow out the device. Then cut off the power supply to the tube furnace (F).

6.6.1.5.4 Determination of the amount of carbon dioxide released

When all the carbon dioxide is absorbed (observe whether the precipitation in the G5 used are soaked in 8 mol/L nitric acid for more than 12 hours, rinsed with tap water, finally rinsed with ultrapure water.

6.7 Determination of arsenic mass fraction

6.7.2 Principle

After the sample is digested by microwave and acid-driven, the pentavalent arsenic in the test solution is reduced to trivalent arsenic, in the presence of thiourea and ascorbic acid. After the volume is fixed, the arsenic is transferred to the atomic fluorescence spectrometer; the trivalent arsenic is reduced to arsenic hydride by using potassium borohydride, then measured at a wavelength of 193.7 nm. Its fluorescence intensity is proportional to the arsenic content. It can be compared quantitatively with the standard solution.

6.7.3 Reagents or materials

6.7.3.1 Nitric acid. Superior grade pure.

6.7.3.2 Hydrochloric acid. Superior grade pure.

6.7.3.3 Hydrochloric acid solution. 5 + 95.It is prepared using high-grade pure hydrochloric acid or special hydrochloric acid for atomic fluorescence.

6.7.3.4 Potassium borohydride solution (20 g/L).

Weigh 20 g of potassium borohydride. Dissolve it in 1000 mL of sodium hydroxide solution (5.0 g/L). Prepare this solution immediately before use.

6.7.3.5 Thiourea-ascorbic acid solution. 50 g/L

Weigh 5 g of thiourea and ascorbic acid respectively into a beaker. Dissolve it using warm water and dilute to 100 mL.

6.7.3.7 Arsenic (As) standard solution. 1 µg/mL

Measure 1.00 mL of arsenic standard solution (6.7.3.6). Place it in a 100 mL volumetric flask. Use water to dilute it to the mark. Shake well. Prepare this solution immediately before use.

6.7.4 Instruments and equipment

6.7.4.1 Atomic fluorescence photometer. The detected mass concentration of arsenic (As) shall not be greater than 0.02 µg/L.

6.7.4.2 Microwave digestion instrument. The power is adjustable, the maximum power shall not be less than 1200 W; or the temperature is adjustable, the maximum temperature shall not be less than 200 °C.

6.7.4.3 Electric heating plate. 220 V, 500 W or more.

6.7.4.5 Evaporation concentrator. Evaporation concentrator matched with microwave digestion.

6.7.4.4 Acid-catching device

The acid-catching device matched with microwave digestion has adjustable temperature, wherein the maximum temperature shall not be lower than 150 °C.

6.7.5 Test procedures

6.7.5.1 Preparation of sample solution

Accurately weigh 0.2 g (accurate to 0.0002 g) of sulfur specimen into the polytetrafluoroethylene inner cylinder. Add 3 mL of superior grade pure concentrated HNO3.Put it into a sealed vessel. Digest it at 1000 W or 180 °C for 15 minutes. A blank test is performed at the same time.

6.7.5.2 Sample acid removal

After the sample digestion is completed, transfer the digested sample to the beaker.

Then place the beaker on the electric heating plate (6.7.4.3) for acid removal. When the sample solution reaches 1 mL, use 2 mL ~ 3 mL of ultrapure water to wash it. After washing for 4 ~ 5 times, carry out acid removal to make the sample solution remain about 1 mL. After cooling, transfer the solution to a volumetric flask. Dilute to volume.

According to the arsenic content concentration in the specimen, the solutions are treated as follows.

a) When the mass fraction of arsenic in the specimen is between 0.000001% and 0.00025%, transfer the test solution after microwave digestion and acid removal to a 50 mL volumetric flask, which has a dilution coefficient n = 1.

b) When the mass fraction of arsenic in the specimen is between 0.00025% and 0.0025%, transfer the test solution after microwave digestion and acid removal to a 100 mL volumetric flask. Accurately pipet 10.00 mL into a 50 mL volumetric flask, which has a dilution coefficient n = 10.

c) When the mass fraction of arsenic in the specimen is between 0.0025% and 0.025%, transfer the test solution after microwave digestion and acid removal to a 500 mL volumetric flask. Accurately pipette 5.00 mL into a 50 mL volumetric flask, which has a dilution coefficient n = 100.

d) When the mass fraction of arsenic in the specimen is greater than 0.025%, transfer 6.8.1.2.7 Iron (Fe) standard solution. 10 µg/mL. Measure 10.00 mL of iron standard solution (6.8.1.2.6) into a 100 mL volumetric flask. Use water to dilute it to the mark. Shake well. Prepare this solution immediately before use.

6.8 Determination of mass fraction of iron

6.8.1.3 Instruments and equipment

6.8.1.3.1 Spectrophotometer. It has a wavelength of 510 nm.

6.8.1.3.2 High-temperature electric furnace. The temperature can be controlled at 600 °C ~ 650 °C.

6.8.1.4 Test procedures

6.8.1.4.1 Drawing of working curve

Take five 50 mL volumetric flasks. Add 0 mL, 2.50 mL, 5.00 mL, 7.50 mL, 10.00 mL of iron standard solution (6.8.1.2.7), respectively. Treat the solution in each volumetric flask as follows. Add water to approximately 25 mL. Add 2.5 mL of hydroxylamine chloride solution and 5 mL of acetic acid-sodium acetate buffer solution. Add 5 mL of 1,10-phenanthroline solution after 5 minutes. Use water to dilute to the mark. Shake well. Let it stand for 15 min ~ 30 min. Develop color.

At a wavelength of 510 nm, use a 1 cm cuvette and a blank solution without adding iron standard solution as a reference. Use a spectrophotometer to measure the absorbance of the above solution.

Taking the mass of iron in the above solution (in micrograms) as the abscissa and the corresponding absorbance value as the ordinate, to draw a working curve; OR calculate a linear regression equation, based on the obtained absorbance value.

6.8.1.4.2 Preparation of test solution

Weigh about 25 g of the specimen, accurate to 0.01 g. Place it in a 50 mL porcelain crucible. Slowly heat and burn the sulfur in the crucible on a sand bath (or adjustable temperature electric furnace). After the combustion is completed, move it into a high-temperature electric furnace, to burn it at 600 °C for 30 minutes. Take it out and cool it.

Add 5 mL of sulfuric acid solution. Heat it on a sand bath (or adjustable temperature electric furnace) to dissolve the residue. Evaporate the sulfuric acid to dryness. After cooling, add 2 mL of hydrochloric acid solution and 20 mL of water. Reheat to dissolve the residue. Transfer it into a 100 mL volumetric flask after cooling. Use water to dilute it to the mark. Shake well.

6.8.1.4.3 Determination

Measure a certain volume of the test solution (6.8.1.4.2). Place it in a 50 mL volumetric flask, so that the corresponding iron mass is between 50 µg and 100 µg. Add water to dilute it to about 25 mL. Then proceed according to the steps in 6.8.1.4.1 "Add 2.5 mL 6682.

6.8.2.2 Principle

Dissolve the ash after sulfur burning in dilute nitric acid. Measure the absorbance of the solution using an atomic absorption spectrophotometer, at a wavelength of 248.3 nm, using an air-acetylene flame. Use the standard curve method to calculate the measurement result. Impurities in sulfur do not interfere with the measurement.

6.8.2.3 Reagents

6.8.2.3.2 Nitric acid solution. 1 + 2.

6.8.2.3.3 Iron (Fe) standard solution. 100 µg/mL. Weigh 0.864 g of ferric ammonium sulfate [NH4Fe (SO4)2 ·12H2O]. Dissolve it in 600 mL water. Add 10 mL of nitric acid solution (6.8.2.3.2). Transfer it to a 1000 mL volumetric flask. Use water to dilute it to the mark. Shake well.

6.8.2.4 Instruments and equipment

6.8.2.4.1 Porcelain crucible. Capacity is about 50 mL.

6.8.2.4.2 High-temperature electric furnace. The temperature can be controlled at 600 °C ~ 650 °C.

6.8.2.4.3 Atomic absorption spectrophotometer

(equipped with iron hollow cathode lamp).

6.8.2.5 Test procedures

6.8.2.5.1 Drawing of working curve

Take six 50 mL volumetric flasks. Add 0 mL, 0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL of iron standard solution (6.8.2.3.3), respectively. Add 25 mL of nitric acid solution to each. Use water to dilute it to the mark. Shake well.

On the atomic absorption spectrophotometer, according to the working conditions of the instrument, use an air-acetylene flame to zero with a blank solution, without adding iron standard solution. Measure the absorbance of the solution at a wavelength of 248.3 nm.

Taking the mass of iron in the above solution (in micrograms) as the abscissa and the corresponding absorbance value as the ordinate, draw a working curve; OR calculate a linear regression equation, based on the obtained absorbance value.