GB/T 16659-2024Determination of mercury of coal (English PDF)

5.2 Atomic absorption spectrophotometer. equipped with a mercury hollow cathode lamp with

a wavelength of 253.7nm.

5.3 Atomic fluorescence spectrometer. equipped with a mercury hollow cathode lamp with a

wavelength of 253.7nm.

5.4 Mercury detector. cold atomic absorption mercury detector or cold atomic fluorescence

mercury detector.

5.5 Solid sampling direct mercury detector.

5.6 Electric heating plate. controllable in the range of 50°C~200°C.

5.7 Microwave digestion system. including microwave digestion instrument, digestion tank, etc.

5.8 Mercury vapor generation bottle. a conical bottle with a scale of 50mL and a tightly fitting plug, with inlet and outlet pipes on the plug and the end of the inlet pipe 5mm~10mm away from the bottom of the bottle.

7.1 Specimens

The coal samples for the general analysis test shall be prepared according to GB/T 474 or GB/T 19494.2.

7.2 Preparation of sample solution

7.2.1 Wet digestion

Weigh about 0.1g (accurate to 0.0002g) of the coal sample for general analysis test into a mercury vapor generator bottle. Add 50mg of vanadium pentoxide (4.6) and a few drops of anhydrous ethanol (4.8) to moisten the specimen; then add 10mL of nitric acid (4.3);

immediately cover the mercury vapor generator bottle with a porcelain cover; leave it overnight.

Add 4mL of sulfuric acid (4.4) and place it on a electric hot plate; first heat at (120±10) °C for about 1.5h; then gradually increase the temperature to (160±10) °C; and continue heating until sulfur trioxide smoke just emerges.

7.2.2 Oxygen bomb combustion

According to the provisions of GB/T 213, weigh about 0.99g~1.01g (accurate to 0.0002g) of coal sample for general analytical test in a dry combustion dish and ignite it for combustion.

After the combustion is completed, wait for the oxygen bomb to cool down, and then slowly and evenly release the gas. The entire release process lasts for no less than 2 min.

7.2.3 Microwave digestion

Weigh about 0.1g (accurate to 0.0002g) of the coal sample for general analysis test into a digestion tank; add 6mL of nitric acid (4.3); stand for 30min. Add 1mL of hydrogen peroxide (4.7); and after the reaction is moderated; tighten the tank cover and place it in a microwave digestion instrument. Digestion is performed according to the digestion procedure in Table A.1 in Appendix A (it can also be determined according to the conditions of the microwave digestion instrument used in the laboratory).

8.1 Method summary

Treat the specimen into a solution to convert mercury into divalent mercuric ions. Under acidic conditions, use stannous chloride as a reducing agent to reduce the mercury ions into mercury atomic vapor; and measure it with an atomic absorption spectrophotometer.

8.2 Test procedures

8.2.1 Drawing of working curve

8.2.1.1 Drawing the working curve of wet digestion method

8.2.1.1.1 Accurately pipette 0.00mL, 0.25mL, 0.50mL, 1.00mL, and 1.50mL of mercury standard working solution (4.20) to five mercury vapor generating bottles respectively; titrate potassium dichromate solution (4.12) until the solution turns yellow; add 2mL of anhydrous ethanol (4.8), and adjust to 30mL with water.

8.2.1.2 Drawing the working curve of oxygen bomb combustion method

8.2.1.2.1 Accurately pipette 0.00mL, 1.00mL, 2.00mL, 5.00mL, and 10.00mL of mercury standard working solution (4.20) to five 50mL volumetric flasks respectively. Add 5mL of nitric acid solution (4.9) and 0.5mL of potassium permanganate solution (4.14); shake well. And slowly titrate hydroxylamine hydrochloride solution (4.15) while shaking the volumetric flask until the color of potassium permanganate just fades; dilute to the scale with water; and make constant volume.

8.2.1.2.2 Transfer the standard solution to the mercury vapor generating bottle; and perform the rest of the operation as in 8.2.1.1.2.

8.2.1.3 Drawing the working curve of microwave digestion method

8.2.2 Determination of sample

Transfer the specimen solution (7.2.1 or 7.2.3) or accurately pipette 50mL of the specimen solution (7.2.2) into the mercury vapor generating bottle; add 1mL of stannous chloride solution (4.11) and immediately cover the bottle with the stopper; and shake well. After standing for a while, connect the mercury vapor generating bottle to the atomic absorption spectrophotometer for determination and record the maximum absorbance; and obtain the mercury content in the specimen solution from the working curve.

8.2.3 Blank test

For each batch of coal samples, prepare two blank solutions (without adding coal samples) according to 7.2; and determine the mercury content in the blank solutions according to 8.2.2;

and take the average value as the blank value.

8.3 Test data processing

8.3.1 Calculation of result

8.3.2 Expression of result

The result is the arithmetic mean of repeated measurements, rounded off to three digits after the decimal point according to GB/T 483.

9.1 Method summary

The sample is treated into a solution. In an acidic medium, potassium borohydride is used as a reducing agent to reduce the mercury in the test solution to mercury vapor. Argon is used as a carrier gas to introduce it into the atomizer and measured by atomic fluorescence spectrometer.

9.2 Test procedures

9.2.1 Drawing of working curve

Except for not adding stannous chloride reducing agent, prepare the standard series solution in five 50mL volumetric flasks according to the requirements of 8.2.1 and dilute with water to the scale. Introduce nitric acid solution (4.10), potassium borohydride solution (4.17) and standard series solution into the electric quartz furnace atomizer; measure the fluorescence intensity of mercury in the standard solution.

9.2.2 Determination of sample

Adjust the instrument to the best working state according to the instrument manual. The reference measurement conditions are shown in Table A.2.Introduce the specimen solution (7.2), nitric acid solution (4.10) and potassium borohydride solution (4.17) into the electric quartz furnace atomizer; measure the fluorescence intensity of mercury in the sample solution;

and obtain the mass concentration (µg/L) of mercury in the specimen solution from the working curve.

9.2.3 Blank test

For each batch of coal samples, prepare 2 blank solutions (without adding coal samples) according to 7.2; and determine the mass concentration (µg/L) of mercury in the blank solutions according to 9.2.2; and take the average value as the blank value.

9.3 Test data processing

9.3.1 Calculation of result

The content of mercury in the coal sample for the general analysis test is calculated according to Formula (3).

9.3.2 Expression of result

The same as 8.3.2.

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