Some standard content:
GB/T3558-1996
This standard adds high temperature combustion hydrolysis-potentiometric titration method on the basis of GB3558-83 "Determination of chlorine in coal". At the same time, the writing format, relevant terms and measurement units of the standard are compiled according to GB/T1.1-1993 "Guidelines for Standardization Work Unit 1: Drafting and Expression Rules of Standards Part 1: Basic Provisions for Standard Writing" and GB483-87 "Coal Quality Analysis Test Methods-General Provisions". The two methods specified in this standard have equivalent effects. This standard will replace GB3558-83 from the date of entry into force. Appendix A of this standard is the appendix of the standard. This standard is proposed by the Ministry of Coal Industry of the People's Republic of China. This standard is under the jurisdiction of the National Coal Standardization Technical Committee. The drafting unit of this standard: Beijing Coal Chemistry Institute, China Coal Research Institute. The main drafters of this standard: Gao Ganliang and Qiu Wei. 286
1 Scope
National Standard of the People's Republic of China
Determination of chlorine in coal
Deternination of chlorine in coalGB/T 3558—1996
Replaces GB355883
This standard specifies the key points, reagents, instruments, determination steps, result calculation and method precision of two methods for determining the total chlorine content in coal: high-temperature combustion and hydrolysis of coal sample-potentiometric titration and aldrin molten sample-potassium thiocyanate titration (Volhard method). This standard is applicable to lignite, bituminous coal and anthracite. 2 Method A: High-temperature combustion and hydrolysis-potentiometric titration 2.1 Determination principle
The coal sample is burned and hydrolyzed in a mixed gas flow of oxygen and water vapor, and all the chlorine in the coal is converted into chloride and dissolved in water to a certain extent. Using silver as the indicator electrode and silver-silver chloride as the reference electrode, the concentration of chloride ions in the condensate is directly titrated using the standard silver nitrate potentiometric method, and the chlorine content in the coal is calculated based on the amount of standard silver nitrate solution. 2.2 Reagents and materials
2.2.1 Quartz sand: particle size 0.5~1.0mm. 2.2.2 Sulfuric acid solution: concentration (1+5) (V+V). Pour 20mL of high-grade pure concentrated sulfuric acid (GB625) into 100mL of distilled water and mix. 2.2.3 Sodium hydroxide solution: 10g/L.
Dissolve 1g of high-grade pure sodium hydroxide (GB629) in 100mL of water. 2.2.4 Agar powder: chemically pure.
2.2.5 Saturated potassium nitrate solution: Dissolve a sufficient amount of high-grade pure potassium nitrate (GB/T647) in an appropriate amount of water, and continue to add potassium nitrate until it no longer dissolves.
2.2.6 Ethanol (GB/T678): analytical grade. 2.2.7 Bromocresol green indicator: 10g/L ethanol solution. Dissolve 1g of bromocresol green indicator in 100mL of ethanol. 2.2.8 Standard sodium chloride solution: chloride ion concentration 0.20mg/mL. Accurately weigh 0.6596g of high-grade pure sodium chloride (GB/T1266) that has been pre-calcined at 500~600C for 1h, dissolve it in a small amount of water, transfer it to a 2000mL volumetric flask, dilute to the scale, and shake well. 2.2.9 Standard silver nitrate solution: c(AgNO,)=0.0125mol/L. Accurately weigh 2.1236g of high-grade pure silver nitrate (GB/T670) that has been pre-calcined at 110C for 1h, dissolve it in a small amount of water, transfer it to a 1000mL brown volumetric flask, dilute to the scale, and shake well. 2.2.10 Porcelain boat: 77mm long, 10mm high and wide, temperature resistance above 1100℃. 2.3 Instruments and equipment
2.3.1 High temperature combustion hydrolysis device (see Figure 1), including: Approved by the State Administration of Technical Supervision on December 19, 1996, implemented on July 1, 1997
GB/T3558-1996
Figure 1 High temperature combustion hydrolysis device
. Absorption bottle No. 2; Absorption bottle No. 2; 3. Condenser; 4--single-section furnace; 5-porcelain boat; 6-platinum couple; 7.-quartz tube; 8-injection push rod, 9-oxygen cylinder; 10-adjustable pressure disc furnace; 11-flat bottom flask 2.3.1.1 High temperature furnace: can be heated to above 1100℃, with a constant temperature zone of 80-100mm long (1100±10℃). Equipped with automatic temperature controller.
Combustion tube: transparent quartz tube, temperature resistant above 1300℃, specifications and dimensions see Figure 2.2.3.1.2
2.3.1.3 Condenser: serpentine, specifications and dimensions see Figure 3.288
Figure 2 Quartz tube
GB/T 3558--1996
$25×8
Figure 3 Condenser
2.3.1.4 Steam generator: composed of 500mL flat-bottom flask and adjustable pressure disc electric furnace (0.5kW, 0~220V continuously adjustable). 2.3.1.5 Flowmeter: full scale 1000ml/min, minimum scale 10mL/min. 2.3.2 Potentiometric titration device: see Figure 4, where: 0000
TTTTTTTTTTT
Figure 4 Potentiometric titration device
1-millivoltmeter; 2-stirring bar 3--beaker; 4--silver wire (indicator electrode); 5---burette; 6--salt bridge; 7-silver wire (reference electrode); 8·beaker; 9--silver chloride precipitate; 10--stirrer 2.3.2.1 Millivoltmeter: digital, accuracy 0.1mV. 2.3.2.2 Magnetic stirrer: continuously adjustable speed. 2.3.2.3 Burette: 10mL, Class A.
2.3.2.4 Salt bridge: heat and dissolve 10g potassium nitrate and 1.5g agar powder in 50mL distilled water, and inject into a U-shaped glass tube after cooling slightly. 289
GB/T3558---1996
2.3.2.5 Indicator electrode: 3mm diameter pure silver wire. 2.3.2.6 Reference electrode: 3mm diameter pure silver wire inserted in aqueous solution containing chloride ions (Cl) and silver chloride precipitation. The container is required to have light-proof performance or measures.
2.3.3 Analytical balance: sensitivity 0.1mg.
2.4 Combustion and hydrolysis of coal sample
2.4.1 Instrument preparation:
Assemble the instrument as shown in Figure 1, connect the circuit, gas line and cooling water. Heat the high-temperature furnace to 1100℃. Add about 30mL of distilled water to absorption bottle No. 1. Add about 20ml of distilled water to absorption bottle No. 2. Open the cooling water of the condenser. Plug the rubber stopper of the injection rod, adjust the oxygen flow rate to 500mL/min, and check for leaks. 2.4.2 High-temperature hydrolysis sample:
Accurately weigh 0.5g (accurate to 0.0002g) of air-dried coal sample into a porcelain boat, and then cover it with an appropriate amount of quartz sand. Put the porcelain boat into the combustion tube, insert the sample push rod, plug the rubber stopper, and pass oxygen and water vapor. Push the front end of the porcelain boat to the 300℃ temperature zone, and push the porcelain boat to the constant temperature zone (1100±10℃) in three sections within 15min (300C, 600℃, 800℃, each stay for 5min) and stay for 15min. During the whole operation, the evaporation of water in the steam generator should be controlled to 2mL/min. After the combustion-hydrolysis is completed, stop passing oxygen and water vapor, remove the sample push rod, and use a nickel wire with a hook to take out the porcelain boat. Pour the sample solution in the absorption bottle into a 200mL beaker, rinse the absorption bottle and the gas guide tube with distilled water, rinse bottle No. 1 twice, rinse bottle No. 2 once, and rinse the washing liquid directly into the beaker (control the rinsing water within 15mL), and distilled water to 140±10mL. Add 3 drops of bromocresol green indicator (2.2.7) to the beaker, neutralize with sodium hydroxide solution (2.2.3) until the indicator turns light blue, then add 0.25mL of sulfuric acid solution (2.2.2), 3mL of potassium nitrate solution (2.2.5), and 5mL of standard sodium chloride solution (2.2.8). 2.5 Potentiometric titration
2.5.1 Preparation:
Connect the titration device according to Figure 4. Place the beaker containing 150mL of distilled water on the titration table, insert the indicator electrode, and connect this solution to the reference electrode with a salt bridge. Connect the two electrode leads to the measuring end of the millivoltmeter. Put in a stirrer and start the stirrer. At this time, the millivoltmeter should display the potential difference between the two electrodes (sweep mV), otherwise check whether the measuring circuit connection is correct. 2.5.2 End point potential calibration:
2.5.2.1 Blank solution preparation: Except for not adding coal sample, other conditions are the same as those in 2.4.2. 2.5.2.2 Titration endpoint potential calibration 1)
Place the beaker containing blank solution on the titration table and connect the titration device according to (2.5.1). Drip the standard silver nitrate drip volume (mL) determined by the pre-made titration differential curve at a rate of 0.03mL/s, and record the potential at this time as the titration endpoint potential.
2.5.3 Sample solution titration:
Place the beaker containing sample solution on the titration table and connect the titration device according to (2.5.1). First, drip 0.05ml./s drip standard silver nitrate solution (2.2.9), pay attention to the millivolt number displayed on the millivoltmeter, when the potential is close to the calibrated endpoint potential, titrate at a rate of 0.02mL/s until the calibrated endpoint potential is reached. After stirring for 1min, record the amount of silver nitrate added and the actual endpoint potential. When calculating the result, for every deviation of the actual endpoint potential from the calibrated endpoint potential by ±1mV, ±0.01mL of silver nitrate dripping should be deducted, but the deviation number cannot exceed ±3mV, otherwise 0.50mL of standard sodium chloride solution (2.2.8) should be added and titrated again. 2.6 Calculation of determination results
The chlorine content in coal is calculated according to formula (1), and the determination result is rounded to the third decimal place. Cla V - Vi)c × 0. 035 45 × 100m
1) Due to the reagent blank, the amount of silver nitrate solution dripped to calibrate the endpoint potential should be determined by making a titration differential curve. When measuring for the first time or changing a chemical reagent, a titration differential curve should be made. The preparation method is shown in Appendix A. 290
Formula 4: Clad-chlorine content of air-dried coal towel, %; GB/T3558-1996
Vi--amount of silver nitrate used to calibrate the endpoint potential, mL; V.-amount of silver nitrate used to titrate the sample solution, mL.; -concentration of standard silver nitrate, mmol/ml.; 0.03545--millimolar mass of chlorine, g/mmol; m
2.7Precision
Mass of air-dried coal sample, g.
The repeatability and reproducibility of the determination results of chlorine in coal are as specified in Table 1: Table 1
Repeatability
(Allowable difference in the same laboratory)
Clad, %
3 Method B: Aska mixture melting sample-potassium thiocyanate titration method 3.1 Determination principle
Reproducibility critical difference
(Allowable difference in different laboratories)
Clad, %
Mix the coal sample and Aska mixture, put them into a muffle furnace for melting, and convert chlorine into chloride. Leach with boiling water, add excess silver nitrate solution in an acidic medium, use ammonium ferric sulfate as an indicator, and titrate with potassium thiocyanate solution. Calculate the chlorine content in the coal based on the actual consumption of silver nitrate solution.
3.2 Reagents and materials
3.2.1 Eschka mixture: weigh two parts of magnesium oxide (HG3--1294) and one part of anhydrous sodium carbonate (GB/T639), grind to a particle size of less than 0.2mm, and mix well.
3.2.2 Nitric acid (GB/T626): relative density 1.40. 3.2.3 Chemically pure n-hexanol.
3.2.4 Standard silver nitrate solution: c (AgNO,) = 0.025 mol/L Accurately weigh 4.2472g of high-grade pure silver nitrate (GB670) pre-baked at 110C for 1h, dissolve in a small amount of water, and then transfer to a 1000ml brown volumetric flask and dilute to the mark with distilled water. 3.2.5 Silver nitrate solution: 10g/1.
Weigh 1g of silver nitrate, dissolve it in 100ml of distilled water, and add a few milliliters of nitric acid. 3.2.6 Saturated ammonium ferric sulfate solution: Dissolve a sufficient amount of ammonium ferric sulfate (GB/T1279) in an appropriate amount of distilled water, and continue to add ammonium ferric sulfate until it no longer dissolves. Add a few milliliters of concentrated nitric acid solution to remove the brown color of the solution, and use the supernatant. 3.2.7 Phenolphthalein indicator: 10g/L, 1g of phenolic acid is dissolved in 100ml of ethanol (GB/T678). 3.2.8 Standard potassium sulfate solution:
Weigh 2.5g of potassium sulfate and dissolve it in distilled water, then transfer it to a 1000mL volumetric flask, dilute to the mark with distilled water, and shake well. Use a single-marked pipette to accurately measure several portions of 10 ml silver nitrate solution (3.2.5) and inject them into several beakers respectively. Add 50 ml distilled water, 3 ml concentrated nitric acid (3.2.2) and 1 ml ammonium ferric sulfate (3.2.7) as indicators. Use potassium thiocyanate solution (3.2.7) to titrate until the solution changes from milky white to light orange. This is the end point. Note the amount of potassium thiocyanate solution used and calculate the standard concentration of potassium thiocyanate. 3.2.9 Standard sodium chloride solution: Chloride concentration 0.1 mg/mL. Accurately weigh 0.3298 g of high-grade pure sodium chloride (GB/T1266) pre-calcined at 500-600°C for 1 hour, dissolve in a small amount of water, transfer to a 2000 ml volumetric flask, dilute to the mark with distilled water, and shake well. 3.3 Instruments and Equipment
3.3.1 Muffle furnace: equipped with a thermocouple pyrometer, with adjustable temperature and good ventilation. 291
3.3.22 Porcelain crucible: capacity 30~～50mL.
3.3.3 Burette: 10ml, Class A.
3.3.4 Magnetic stirrer: speed continuously adjustable. 3.3.5 Single-marked pipette: 5mL and 10ml. 3.3.6 Analytical balance: sensitivity 0.1mg.
3.4 Determination steps
GB/T 3558---1996
3.4.1 Accurately weigh 1g (accurate to 0.0002g) of air-dried coal sample with a particle size less than 0.2mm, put it into a crucible containing 3g (accurate to 0.1g) of Eschka mixture (3.2.1), mix it carefully, cover it with 2g of Eschka mixture, put it into a muffle furnace, half-open the furnace door, gradually increase the furnace temperature from room temperature to 680±20C, and heat it at this temperature for 3h. 3.4.2 Take the crucible out of the muffle furnace and cool it to room temperature. Transfer the burned material in it into a 250mL beaker, rinse the inner wall with 50~~60mL hot water, and pour the rinse liquid into the beaker. 3.4.3 Filter with qualitative filter paper using the pouring method, rinse the residue with hot water 1-2 times, then transfer the residue into a funnel, and then carefully rinse the filter paper and residue with hot water until there is no chloride ion (check with 1% silver nitrate solution). During the filtering and rinsing process, the final volume of the filtrate should be controlled to be about 110 ml.
3.4.4 Add 1 drop of phenolphthalein indicator (3.2.8) to the filtrate, adjust with concentrated nitric acid (3.2.2) until the red color disappears, then add 5 mL in excess, accurately add 5 mL of sodium chloride standard solution (3.2.9) and 10 mL of silver nitrate solution (3.2.5) with a single-marked pipette, let stand for 2 to 3 minutes, add 2 to 5 mL of n-hexanol to cover the surface blood, place the beaker on a magnetic stirrer and stir rapidly for 1 minute, then add 1 mL of ammonium ferric sulfate solution (3.2.7), and titrate with standard potassium thiocyanate solution (3.2.8). When the solution changes from milky white to light orange, it is the end point, and record the volume of potassium thiocyanate solution.
3.4.5 For each batch of coal samples, two or more empty measurements (without adding coal samples) should be carried out according to the steps (3.4.1 to 3.4.4), and the average value is taken as the white value.
3.5 Calculation of determination results
The chlorine content in coal is calculated according to formula (2), and the determination results are rounded to the third decimal place. Cla - 0. 035 45eV-VI) × 100m
Wherein: Clad-chlorine content in air-dried coal sample, %; 0.03545mmol of fluorine, g/mmol; mass concentration of potassium thiocyanate, mmol/mL; V
-amount of potassium thiocyanate used in coal sample determination, mL; V>
-amount of potassium thiocyanate solution used in blank determination, mL; m
3.6 Precision
Mass of air-dried coal sample, g.
Same as the provisions in 2.7.
.（2）
CB/T3558—1996
Appendix A
（Appendix of the standard）
Drawing of titration differential curve
Place the beaker containing the Baobai solution on the titration table. Connect the titration device according to 2.5.1. Slowly drip the standard silver nitrate solution (2.2.9), and record the indicator electrode potential every time 0.1ml is dripped. When approaching the end point, record it every time 0.05ml is dripped. Draw the differential curve with AmV/Aml. as the ordinate and the volume of the added standard silver nitrate solution (ml.) as the abscissa. Take the milliliters of the standard silver nitrate solution corresponding to the AmV/△mL peak as the amount of silver nitrate added to calibrate the end point potential. 2936 Calculation of determination results
The chlorine content in coal is calculated according to formula (1), and the determination result is rounded to the third decimal place. Cla V - Vi)c × 0. 035 45 × 100m
1) Due to the reagent blank, the amount of silver nitrate solution to be dropped for calibrating the endpoint potential should be determined by making a titration differential curve. When a chemical reagent is measured for the first time or when it is replaced, a titration differential curve should be made. The preparation method is shown in Appendix A. 290
Formula 4: Clad——chlorine content of air-dried coal towel, %; GB/T3558—1996
Vi—-amount of silver nitrate used to calibrate the endpoint potential, mL; V.-amount of silver nitrate used to titrate the sample solution, mL.; -concentration of standard silver nitrate, mmol/ml.; 0.03545-——millimolar mass of chlorine, g/mmol; m
2.7Precision
Mass of air-dried coal sample, g.
The repeatability and reproducibility of the determination results of chlorine in coal are as specified in Table 1: Table 1
Repeatability
(Allowable difference in the same laboratory)
Clad, %
3 Method B: Aska mixture melting sample-potassium thiocyanate titration method 3.1 Determination principle
Reproducibility critical difference
(Allowable difference in different laboratories)
Clad, %
Mix the coal sample and Aska mixture, put them into a muffle furnace for melting, and convert chlorine into chloride. Leach with boiling water, add excess silver nitrate solution in an acidic medium, use ammonium ferric sulfate as an indicator, and titrate with potassium thiocyanate solution. Calculate the chlorine content in the coal based on the actual consumption of silver nitrate solution.
3.2 Reagents and materials
3.2.1 Eschka mixture: weigh two parts of magnesium oxide (HG3--1294) and one part of anhydrous sodium carbonate (GB/T639), grind to a particle size of less than 0.2mm, and mix well.
3.2.2 Nitric acid (GB/T626): relative density 1.40. 3.2.3 Chemically pure n-hexanol.
3.2.4 Standard silver nitrate solution: c (AgNO,) = 0.025 mol/L Accurately weigh 4.2472g of high-grade pure silver nitrate (GB670) pre-baked at 110C for 1h, dissolve in a small amount of water, and then transfer to a 1000ml brown volumetric flask and dilute to the mark with distilled water. 3.2.5 Silver nitrate solution: 10g/1.
Weigh 1g of silver nitrate, dissolve it in 100ml of distilled water, and add a few milliliters of nitric acid. 3.2.6 Saturated ammonium ferric sulfate solution: Dissolve a sufficient amount of ammonium ferric sulfate (GB/T1279) in an appropriate amount of distilled water, and continue to add ammonium ferric sulfate until it no longer dissolves. Add a few milliliters of concentrated nitric acid solution to remove the brown color of the solution, and use the supernatant. 3.2.7 Phenolphthalein indicator: 10g/L, 1g of phenolic acid is dissolved in 100ml of ethanol (GB/T678). 3.2.8 Standard potassium sulfate solution:
Weigh 2.5g of potassium sulfate and dissolve it in distilled water, then transfer it to a 1000mL volumetric flask, dilute to the mark with distilled water, and shake well. Use a single-marked pipette to accurately measure several portions of 10 ml silver nitrate solution (3.2.5) and inject them into several beakers respectively. Add 50 ml distilled water, 3 ml concentrated nitric acid (3.2.2) and 1 ml ammonium ferric sulfate (3.2.7) as indicators. Use potassium thiocyanate solution (3.2.7) to titrate until the solution changes from milky white to light orange. This is the end point. Note the amount of potassium thiocyanate solution used and calculate the standard concentration of potassium thiocyanate. 3.2.9 Standard sodium chloride solution: Chloride concentration 0.1 mg/mL. Accurately weigh 0.3298 g of high-grade pure sodium chloride (GB/T1266) pre-calcined at 500-600°C for 1 hour, dissolve in a small amount of water, transfer to a 2000 ml volumetric flask, dilute to the mark with distilled water, and shake well. 3.3 Instruments and Equipment
3.3.1 Muffle furnace: equipped with a thermocouple pyrometer, with adjustable temperature and good ventilation. 291
3.3.22 Porcelain crucible: capacity 30~～50mL.
3.3.3 Burette: 10ml, Class A.
3.3.4 Magnetic stirrer: speed continuously adjustable. 3.3.5 Single-marked pipette: 5mL and 10ml. 3.3.6 Analytical balance: sensitivity 0.1mg.
3.4 Determination steps
GB/T 3558---1996
3.4.1 Accurately weigh 1g (accurate to 0.0002g) of air-dried coal sample with a particle size less than 0.2mm, put it into a crucible containing 3g (accurate to 0.1g) of Eschka mixture (3.2.1), mix it carefully, cover it with 2g of Eschka mixture, put it into a muffle furnace, half-open the furnace door, gradually increase the furnace temperature from room temperature to 680±20C, and heat it at this temperature for 3h. 3.4.2 Take the crucible out of the muffle furnace and cool it to room temperature. Transfer the burned material in it into a 250mL beaker, rinse the inner wall with 50~~60mL hot water, and pour the rinse liquid into the beaker. 3.4.3 Filter with qualitative filter paper using the pouring method, rinse the residue with hot water 1-2 times, then transfer the residue into a funnel, and then carefully rinse the filter paper and residue with hot water until there is no chloride ion (check with 1% silver nitrate solution). During the filtering and rinsing process, the final volume of the filtrate should be controlled to be about 110 ml.
3.4.4 Add 1 drop of phenolphthalein indicator (3.2.8) to the filtrate, adjust with concentrated nitric acid (3.2.2) until the red color disappears, then add 5 mL in excess, accurately add 5 mL of sodium chloride standard solution (3.2.9) and 10 mL of silver nitrate solution (3.2.5) with a single-marked pipette, let stand for 2 to 3 minutes, add 2 to 5 mL of n-hexanol to cover the surface blood, place the beaker on a magnetic stirrer and stir rapidly for 1 minute, then add 1 mL of ammonium ferric sulfate solution (3.2.7), and titrate with standard potassium thiocyanate solution (3.2.8). When the solution changes from milky white to light orange, it is the end point, and record the volume of potassium thiocyanate solution.
3.4.5 For each batch of coal samples, two or more empty measurements (without adding coal samples) should be carried out according to the steps (3.4.1 to 3.4.4), and the average value is taken as the white value.
3.5 Calculation of determination results
The chlorine content in coal is calculated according to formula (2), and the determination results are rounded to the third decimal place. Cla - 0. 035 45eV-VI) × 100m
Wherein: Clad-chlorine content in air-dried coal sample, %; 0.03545mmol of fluorine, g/mmol; mass concentration of potassium thiocyanate, mmol/mL; V
-amount of potassium thiocyanate used in coal sample determination, mL; V>
-amount of potassium thiocyanate solution used in blank determination, mL; m
3.6 Precision
Mass of air-dried coal sample, g.
Same as the provisions in 2.7.
.（2）
CB/T3558—1996
Appendix A
（Appendix of the standard）
Drawing of titration differential curve
Place the beaker containing the Baobai solution on the titration table. Connect the titration device according to 2.5.1. Slowly drip the standard silver nitrate solution (2.2.9), and record the indicator electrode potential every time 0.1ml is dripped. When approaching the end point, record it every time 0.05ml is dripped. Draw the differential curve with AmV/Aml. as the ordinate and the volume of the added standard silver nitrate solution (ml.) as the abscissa. Take the milliliters of the standard silver nitrate solution corresponding to the AmV/△mL peak as the amount of silver nitrate added to calibrate the end point potential. 2936 Calculation of determination results
The chlorine content in coal is calculated according to formula (1), and the determination result is rounded to the third decimal place. Cla V - Vi)c × 0. 035 45 × 100m
1) Due to the reagent blank, the amount of silver nitrate solution to be dropped for calibrating the endpoint potential should be determined by making a titration differential curve. When a chemical reagent is measured for the first time or when it is replaced, a titration differential curve should be made. The preparation method is shown in Appendix A. 290
Formula 4: Clad——chlorine content of air-dried coal towel, %; GB/T3558—1996
Vi—-amount of silver nitrate used to calibrate the endpoint potential, mL; V.-amount of silver nitrate used to titrate the sample solution, mL.; -concentration of standard silver nitrate, mmol/ml.; 0.03545-——millimolar mass of chlorine, g/mmol; m
2.7Precision
Mass of air-dried coal sample, g.
The repeatability and reproducibility of the determination results of chlorine in coal are as specified in Table 1: Table 1
Repeatability
(Allowable difference in the same laboratory)
Clad, %
3 Method B: Aska mixture melting sample-potassium thiocyanate titration method 3.1 Determination principle
Reproducibility critical difference
(Allowable difference in different laboratories)
Clad, %
Mix the coal sample and Aska mixture, put them into a muffle furnace for melting, and convert chlorine into chloride. Leach with boiling water, add excess silver nitrate solution in an acidic medium, use ammonium ferric sulfate as an indicator, and titrate with potassium thiocyanate solution. Calculate the chlorine content in the coal based on the actual consumption of silver nitrate solution.
3.2 Reagents and materials
3.2.1 Eschka mixture: weigh two parts of magnesium oxide (HG3--1294) and one part of anhydrous sodium carbonate (GB/T639), grind to a particle size of less than 0.2mm, and mix well.
3.2.2 Nitric acid (GB/T626): relative density 1.40. 3.2.3 Chemically pure n-hexanol.
3.2.4 Standard silver nitrate solution: c (AgNO,) = 0.025 mol/L Accurately weigh 4.2472g of high-grade pure silver nitrate (GB670) pre-baked at 110C for 1h, dissolve in a small amount of water, and then transfer to a 1000ml brown volumetric flask and dilute to the mark with distilled water. 3.2.5 Silver nitrate solution: 10g/1.
Weigh 1g of silver nitrate, dissolve it in 100ml of distilled water, and add a few milliliters of nitric acid. 3.2.6 Saturated ammonium ferric sulfate solution: Dissolve a sufficient amount of ammonium ferric sulfate (GB/T1279) in an appropriate amount of distilled water, and continue to add ammonium ferric sulfate until it no longer dissolves. Add a few milliliters of concentrated nitric acid solution to remove the brown color of the solution, and use the supernatant. 3.2.7 Phenolphthalein indicator: 10g/L, 1g of phenolic acid is dissolved in 100ml of ethanol (GB/T678). 3.2.8 Standard potassium sulfate solution:
Weigh 2.5g of potassium sulfate and dissolve it in distilled water, then transfer it to a 1000mL volumetric flask, dilute to the mark with distilled water, and shake well. Use a single-marked pipette to accurately measure several portions of 10 ml silver nitrate solution (3.2.5) and inject them into several beakers respectively. Add 50 ml distilled water, 3 ml concentrated nitric acid (3.2.2) and 1 ml ammonium ferric sulfate (3.2.7) as indicators. Use potassium thiocyanate solution (3.2.7) to titrate until the solution changes from milky white to light orange. This is the end point. Note the amount of potassium thiocyanate solution used and calculate the standard concentration of potassium thiocyanate. 3.2.9 Standard sodium chloride solution: Chloride concentration 0.1 mg/mL. Accurately weigh 0.3298 g of high-grade pure sodium chloride (GB/T1266) pre-calcined at 500-600°C for 1 hour, dissolve in a small amount of water, transfer to a 2000 ml volumetric flask, dilute to the mark with distilled water, and shake well. 3.3 Instruments and Equipment
3.3.1 Muffle furnace: equipped with a thermocouple pyrometer, with adjustable temperature and good ventilation. 291
3.3.22 Porcelain crucible: capacity 30~～50mL.
3.3.3 Burette: 10ml, Class A.
3.3.4 Magnetic stirrer: speed continuously adjustable. 3.3.5 Single-marked pipette: 5mL and 10ml. 3.3.6 Analytical balance: sensitivity 0.1mg.
3.4 Determination steps
GB/T 3558---1996
3.4.1 Accurately weigh 1g (accurate to 0.0002g) of air-dried coal sample with a particle size less than 0.2mm, put it into a crucible containing 3g (accurate to 0.1g) of Eschka mixture (3.2.1), mix it carefully, cover it with 2g of Eschka mixture, put it into a muffle furnace, half-open the furnace door, gradually increase the furnace temperature from room temperature to 680±20C, and heat it at this temperature for 3h. 3.4.2 Take the crucible out of the muffle furnace and cool it to room temperature. Transfer the burned material in it into a 250mL beaker, rinse the inner wall with 50~~60mL hot water, and pour the rinse liquid into the beaker. 3.4.3 Filter with qualitative filter paper using the pouring method, rinse the residue with hot water 1-2 times, then transfer the residue into a funnel, and then carefully rinse the filter paper and residue with hot water until there is no chloride ion (check with 1% silver nitrate solution). During the filtering and rinsing process, the final volume of the filtrate should be controlled to be about 110 ml.
3.4.4 Add 1 drop of phenolphthalein indicator (3.2.8) to the filtrate, adjust with concentrated nitric acid (3.2.2) until the red color disappears, then add 5 mL in excess, accurately add 5 mL of sodium chloride standard solution (3.2.9) and 10 mL of silver nitrate solution (3.2.5) with a single-marked pipette, let stand for 2 to 3 minutes, add 2 to 5 mL of n-hexanol to cover the surface blood, place the beaker on a magnetic stirrer and stir rapidly for 1 minute, then add 1 mL of ammonium ferric sulfate solution (3.2.7), and titrate with standard potassium thiocyanate solution (3.2.8). When the solution changes from milky white to light orange, it is the end point, and record the volume of potassium thiocyanate solution.
3.4.5 For each batch of coal samples, two or more empty measurements (without adding coal samples) should be carried out according to the steps (3.4.1 to 3.4.4), and the average value is taken as the white value.
3.5 Calculation of determination results
The chlorine content in coal is calculated according to formula (2), and the determination results are rounded to the third decimal place. Cla - 0. 035 45eV-VI) × 100m
Wherein: Clad-chlorine content in air-dried coal sample, %; 0.03545mmol of fluorine, g/mmol; mass concentration of potassium thiocyanate, mmol/mL; V
-amount of potassium thiocyanate used in coal sample determination, mL; V>
-amount of potassium thiocyanate solution used in blank determination, mL; m
3.6 Precision
Mass of air-dried coal sample, g.
Same as the provisions in 2.7.
.（2）
CB/T3558—1996
Appendix A
（Appendix of the standard）
Drawing of titration differential curve
Place the beaker containing the Baobai solution on the titration table. Connect the titration device according to 2.5.1. Slowly drip the standard silver nitrate solution (2.2.9), and record the indicator electrode potential every time 0.1ml is dripped. When approaching the end point, record it every time 0.05ml is dripped. Draw the differential curve with AmV/Aml. as the ordinate and the volume of the added standard silver nitrate solution (ml.) as the abscissa. Take the milliliters of the standard silver nitrate solution corresponding to the AmV/△mL peak as the amount of silver nitrate added to calibrate the end point potential. 293%
Mix the coal sample and the Eschka mixture, put it into a muffle furnace for melting, and convert the chlorine into chloride. Leach it with boiling water, add an excess of silver nitrate solution in an acidic medium, use ammonium ferric sulfate as an indicator, and titrate with potassium thiocyanate solution. Calculate the chlorine content in the coal based on the actual consumption of the silver nitrate solution.
3.2 Reagents and materials
3.2.1 Eschka mixture: weigh two parts of magnesium oxide (HG3--1294) and one part of anhydrous sodium carbonate (GB/T639), grind them to a particle size of less than 0.2mm, and mix them evenly.
3.2.2 Nitric acid (GB/T626): relative density 1.40. 3.2.3 n-hexanol chemically pure. bzxZ.net
3.2.4 Standard silver nitrate solution: c(AgNO,)=0.025mol/L Accurately weigh 4.2472g of high-grade pure silver nitrate (GB670) that has been pre-baked at 110C for 1h, dissolve it in a small amount of water, transfer it to a 1000ml. brown volumetric flask, and dilute it to the mark with distilled water. 3.2.5 Silver nitrate solution: 10g/1.
Weigh 1g of silver nitrate, dissolve it in 100ml. distilled water, and add a few milliliters of nitric acid. 3.2.6 Saturated ammonium ferric sulfate solution: Dissolve a sufficient amount of ammonium ferric sulfate (GB/T1279) in an appropriate amount of distilled water, and continue to add ammonium ferric sulfate until it no longer dissolves. Add a few milliliters of concentrated nitric acid solution to remove the brown color of the solution, and use the supernatant. 3.2.7 Phenolphthalein indicator: 10g/L, 1g of phenolic acid is dissolved in 100ml. ethanol (GB/T678). 3.2.8 Standard potassium thiocyanate solution:
Weigh 2.5g potassium sulfate and dissolve it in distilled water. Transfer it to a 1000mL volumetric flask, dilute it to the mark with distilled water, and shake it well. Use a single-marked pipette to accurately measure several portions of 10ml silver nitrate solution (3.2.5) and inject them into several beakers respectively. Add 50ml distilled water, 3ml concentrated nitric acid (3.2.2) and 1ml ammonium ferric sulfate (3.2.7) as indicators. Use potassium thiocyanate solution (3.2.7) to titrate until the solution changes from milky white to light orange. This is the end point. Note the amount of potassium thiocyanate solution used, and you can calculate the standard concentration of potassium thiocyanate. 3.2.9 Standard sodium chloride solution: The concentration of chloride ion is 0.1mg/mL. Accurately weigh 0.3298g of high-grade pure sodium chloride (GB/T1266) pre-calcined at 500~600C for 1h, dissolve it in a small amount of water, transfer it to a 2000ml volumetric flask, dilute it to the mark with distilled water, and shake it well. 3.3 Instruments and Equipment
3.3.1 Muffle furnace: with thermocouple pyrometer, adjustable temperature, good ventilation. 291
3.3.22 Porcelain crucible: capacity 30~～50mL.
3.3.3 Burette: 10ml, Class A.
3.3.4 Magnetic stirrer: continuously adjustable speed. 3.3.5 Single-marked pipette: 5mL and 10ml. 3.3.6 Analytical balance: sensitivity 0.1mg.
3.4 Determination steps
GB/T 3558---1996
3.4.1 Accurately weigh 1g (accurate to 0.0002g) of air-dried coal sample with a particle size less than 0.2mm, put it into a crucible containing 3g (accurate to 0.1g) of Eschka mixture (3.2.1), mix it carefully, cover it with 2g of Eschka mixture, put it into a muffle furnace, half-open the furnace door, gradually increase the furnace temperature from room temperature to 680±20C, and heat it at this temperature for 3h. 3.4.2 Take the crucible out of the muffle furnace and cool it to room temperature. Transfer the burned material in it into a 250mL beaker, rinse the inner wall with 50~~60mL hot water, and pour the rinse liquid into the beaker. 3.4.3 Filter with qualitative filter paper using the pouring method, rinse the residue with hot water 1-2 times, then transfer the residue into a funnel, and then carefully rinse the filter paper and residue with hot water until there is no chloride ion (check with 1% silver nitrate solution). During the filtering and rinsing process, the final volume of the filtrate should be controlled to be about 110 ml.
3.4.4 Add 1 drop of phenolphthalein indicator (3.2.8) to the filtrate, adjust with concentrated nitric acid (3.2.2) until the red color disappears, then add 5 mL in excess, accurately add 5 mL of sodium chloride standard solution (3.2.9) and 10 mL of silver nitrate solution (3.2.5) with a single-marked pipette, let stand for 2 to 3 minutes, add 2 to 5 mL of n-hexanol to cover the surface blood, place the beaker on a magnetic stirrer and stir rapidly for 1 minute, then add 1 mL of ammonium ferric sulfate solution (3.2.7), and titrate with standard potassium thiocyanate solution (3.2.8). When the solution changes from milky white to light orange, it is the end point, and record the volume of potassium thiocyanate solution.
3.4.5 For each batch of coal samples, two or more empty measurements (without adding coal samples) should be carried out according to the steps (3.4.1 to 3.4.4), and the average value is taken as the white value.
3.5 Calculation of determination results
The chlorine content in coal is calculated according to formula (2), and the determination results are rounded to the third decimal place. Cla - 0. 035 45eV-VI) × 100m
Wherein: Clad-chlorine content in air-dried coal sample, %; 0.03545mmol of fluorine, g/mmol; mass concentration of potassium thiocyanate, mmol/mL; V
-amount of potassium thiocyanate used in coal sample determination, mL; V>
-amount of potassium thiocyanate solution used in blank determination, mL; m
3.6 Precision
Mass of air-dried coal sample, g.
Same as the provisions in 2.7.
.（2）
CB/T3558—1996
Appendix A
（Appendix of the standard）
Drawing of titration differential curve
Place the beaker containing the Baobai solution on the titration table. Connect the titration device according to 2.5.1. Slowly drip the standard silver nitrate solution (2.2.9), and record the indicator electrode potential every time 0.1ml is dripped. When approaching the end point, record it every time 0.05ml is dripped. Draw the differential curve with AmV/Aml. as the ordinate and the volume of the added standard silver nitrate solution (ml.) as the abscissa. Take the milliliters of the standard silver nitrate solution corresponding to the AmV/△mL peak as the amount of silver nitrate added to calibrate the end point potential. 293%
Mix the coal sample and the Eschka mixture, put it into a muffle furnace for melting, and convert the chlorine into chloride. Leach it with boiling water, add an excess of silver nitrate solution in an acidic medium, use ammonium ferric sulfate as an indicator, and titrate with potassium thiocyanate solution. Calculate the chlorine content in the coal based on the actual consumption of the silver nitrate solution.
3.2 Reagents and materials
3.2.1 Eschka mixture: weigh two parts of magnesium oxide (HG3--1294) and one part of anhydrous sodium carbonate (GB/T639), grind them to a particle size of less than 0.2mm, and mix them evenly.
3.2.2 Nitric acid (GB/T626): relative density 1.40. 3.2.3 n-hexanol chemically pure.
3.2.4 Standard silver nitrate solution: c(AgNO,)=0.025mol/L Accurately weigh 4.2472g of high-grade pure silver nitrate (GB670) that has been pre-baked at 110C for 1h, dissolve it in a small amount of water, transfer it to a 1000ml. brown volumetric flask, and dilute it to the mark with distilled water. 3.2.5 Silver nitrate solution: 10g/1.
Weigh 1g of silver nitrate, dissolve it in 100ml. distilled water, and add a few milliliters of nitric acid. 3.2.6 Saturated ammonium ferric sulfate solution: Dissolve a sufficient amount of ammonium ferric sulfate (GB/T1279) in an appropriate amount of distilled water, and continue to add ammonium ferric sulfate until it no longer dissolves. Add a few milliliters of concentrated nitric acid solution to remove the brown color of the solution, and use the supernatant. 3.2.7 Phenolphthalein indicator: 10g/L, 1g of phenolic acid is dissolved in 100ml. ethanol (GB/T678). 3.2.8 Standard potassium thiocyanate solution:
Weigh 2.5g potassium sulfate and dissolve it in distilled water. Transfer it to a 1000mL volumetric flask, dilute it to the mark with distilled water, and shake it well. Use a single-marked pipette to accurately measure several portions of 10ml silver nitrate solution (3.2.5) and inject them into several beakers respectively. Add 50ml distilled water, 3ml concentrated nitric acid (3.2.2) and 1ml ammonium ferric sulfate (3.2.7) as indicators. Use potassium thiocyanate solution (3.2.7) to titrate until the solution changes from milky white to light orange. This is the end point. Note the amount of potassium thiocyanate solution used, and you can calculate the standard concentration of potassium thiocyanate. 3.2.9 Standard sodium chloride solution: The concentration of chloride ion is 0.1mg/mL. Accurately weigh 0.3298g of high-grade pure sodium chloride (GB/T1266) pre-calcined at 500~600C for 1h, dissolve it in a small amount of water, transfer it to a 2000ml volumetric flask, dilute it to the mark with distilled water, and shake it well. 3.3 Instruments and Equipment
3.3.1 Muffle furnace: with thermocouple pyrometer, adjustable temperature, good ventilation. 291
3.3.22 Porcelain crucible: capacity 30~～50mL.
3.3.3 Burette: 10ml, Class A.
3.3.4 Magnetic stirrer: continuously adjustable speed. 3.3.5 Single-marked pipette: 5mL and 10ml. 3.3.6 Analytical balance: sensitivity 0.1mg.
3.4 Determination steps
GB/T 3558---1996
3.4.1 Accurately weigh 1g (accurate to 0.0002g) of air-dried coal sample with a particle size less than 0.2mm, put it into a crucible containing 3g (accurate to 0.1g) of Eschka mixture (3.2.1), mix it carefully, cover it with 2g of Eschka mixture, put it into a muffle furnace, half-open the furnace door, gradually increase the furnace temperature from room temperature to 680±20C, and heat it at this temperature for 3h. 3.4.2 Take the crucible out of the muffle furnace and cool it to room temperature. Transfer the burned material in it into a 250mL beaker, rinse the inner wall with 50~~60mL hot water, and pour the rinse liquid into the beaker. 3.4.3 Filter with qualitative filter paper using the pouring method, rinse the residue with hot water 1-2 times, then transfer the residue into a funnel, and then carefully rinse the filter paper and residue with hot water until there is no chloride ion (check with 1% silver nitrate solution). During the filtering and rinsing process, the final volume of the filtrate should be controlled to be about 110 ml.
3.4.4 Add 1 drop of phenolphthalein indicator (3.2.8) to the filtrate, adjust with concentrated nitric acid (3.2.2) until the red color disappears, then add 5 mL in excess, accurately add 5 mL of sodium chloride standard solution (3.2.9) and 10 mL of silver nitrate solution (3.2.5) with a single-marked pipette, let stand for 2 to 3 minutes, add 2 to 5 mL of n-hexanol to cover the surface blood, place the beaker on a magnetic stirrer and stir rapidly for 1 minute, then add 1 mL of ammonium ferric sulfate solution (3.2.7), and titrate with standard potassium thiocyanate solution (3.2.8). When the solution changes from milky white to light orange, it is the end point, and record the volume of potassium thiocyanate solution.
3.4.5 For each batch of coal samples, two or more empty measurements (without adding coal samples) should be carried out according to the steps (3.4.1 to 3.4.4), and the average value is taken as the white value.
3.5 Calculation of determination results
The chlorine content in coal is calculated according to formula (2), and the determination results are rounded to the third decimal place. Cla - 0. 035 45eV-VI) × 100m
Wherein: Clad-chlorine content in air-dried coal sample, %; 0.03545mmol of fluorine, g/mmol; mass concentration of potassium thiocyanate, mmol/mL; V
-amount of potassium thiocyanate used in coal sample determination, mL; V>
-amount of potassium thiocyanate solution used in blank determination, mL; m
3.6 Precision
Mass of air-dried coal sample, g.
Same as the provisions in 2.7.
.（2）
CB/T3558—1996
Appendix A
（Appendix of the standard）
Drawing of titration differential curve
Place the beaker containing the Baobai solution on the titration table. Connect the titration device according to 2.5.1. Slowly drip the standard silver nitrate solution (2.2.9), and record the indicator electrode potential every time 0.1ml is dripped. When approaching the end point, record it every time 0.05ml is dripped. Draw the differential curve with AmV/Aml. as the ordinate and the volume of the added standard silver nitrate solution (ml.) as the abscissa. Take the milliliters of the standard silver nitrate solution corresponding to the AmV/△mL peak as the amount of silver nitrate added to calibrate the end point potential. 2933 Burette: 10ml, Class A.
3.3.4 Magnetic stirrer: continuously adjustable speed. 3.3.5 Single-marked pipettes: 5mL and 10ml. 3.3.6 Analytical balance: sensitivity 0.1mg.
3.4 Determination steps
GB/T 3558---1996
3.4.1 Accurately weigh 1g (accurate to 0.0002g) of air-dried coal sample with a particle size of less than 0.2mm, put it into a crucible containing 3g (accurate to 0.1g) of Eschka mixture (3.2.1), mix it carefully, cover it with 2g of Eschka mixture, put it into a muffle furnace, half-open the furnace door, gradually raise the furnace temperature from room temperature to 680±20C, and heat it at this temperature for 3h. 3.4.2 Take the crucible out of the muffle furnace and cool it to room temperature. Transfer the burned material into a 250mL beaker and rinse the inner wall with 50~60mL hot water. Pour the rinse liquid into the beaker. 3.4.3 Filter with qualitative filter paper using the pouring method. Rinse the residue with hot water 1~2 times, then transfer the residue into a funnel and carefully rinse the filter paper and residue with hot water until there is no chloride ion (check with 1% silver nitrate solution). During the filtering and rinsing of the residue, the final volume of the filtrate should be controlled to be about 110 mL.
3.4.4 Add 1 drop of phenolphthalein indicator (3.2.8) to the filtrate, adjust with concentrated nitric acid (3.2.2) until the red color disappears, then add 5 mL in excess, accurately add 5 mL of sodium chloride standard solution (3.2.9) and 10 mL of silver nitrate solution (3.2.5) with a single-marked pipette, let stand for 2 to 3 minutes, add 2 to 5 mL of n-hexanol to cover the surface blood, place the beaker on a magnetic stirrer and stir rapidly for 1 minute, then add 1 mL of ammonium ferric sulfate solution (3.2.7), and titrate with standard potassium thiocyanate solution (3.2.8). When the solution changes from milky white to light orange, it is the end point, and record the volume of potassium thiocyanate solution.
3.4.5 For each batch of coal samples, two or more empty measurements (without adding coal samples) should be carried out according to the steps (3.4.1 to 3.4.4), and the average value is taken as the white value.
3.5 Calculation of determination results
The chlorine content in coal is calculated according to formula (2), and the determination results are rounded to the third decimal place. Cla - 0. 035 45eV-VI) × 100m
Wherein: Clad-chlorine content in air-dried coal sample, %; 0.03545mmol of fluorine, g/mmol; mass concentration of potassium thiocyanate, mmol/mL; V
-amount of potassium thiocyanate used in coal sample determination, mL; V>
-amount of potassium thiocyanate solution used in blank determination, mL; m
3.6 Precision
Mass of air-dried coal sample, g.
Same as the provisions in 2.7.
.（2）
CB/T3558—1996
Appendix A
（Appendix of the standard）
Drawing of titration differential curve
Place the beaker containing the Baobai solution on the titration table. Connect the titration device according to 2.5.1. Slowly drip the standard silver nitrate solution (2.2.9), and record the indicator electrode potential every time 0.1ml is dripped. When approaching the end point, record it every time 0.05ml is dripped. Draw the differential curve with AmV/Aml. as the ordinate and the volume of the added standard silver nitrate solution (ml.) as the abscissa. Take the milliliters of the standard silver nitrate solution corresponding to the AmV/△mL peak as the amount of silver nitrate added to calibrate the end point potential. 2933 Burette: 10ml, Class A.
3.3.4 Magnetic stirrer: continuously adjustable speed. 3.3.5 Single-marked pipettes: 5mL and 10ml. 3.3.6 Analytical balance: sensitivity 0.1mg.
3.4 Determination steps
GB/T 3558---1996
3.4.1 Accurately weigh 1g (accurate to 0.0002g) of air-dried coal sample with a particle size of less than 0.2mm, put it into a crucible containing 3g (accurate to 0.1g) of Eschka mixture (3.2.1), mix it carefully, cover it with 2g of Eschka mixture, put it into a muffle furnace, half-open the furnace door, gradually raise the furnace temperature from room temperature to 680±20C, and heat it at this temperature for 3h. 3.4.2 Take the crucible out of the muffle furnace and cool it to room temperature. Transfer the burned material into a 250mL beaker and rinse the inner wall with 50~60mL hot water. Pour the rinse liquid into the beaker. 3.4.3 Filter with qualitative filter paper using the pouring method. Rinse the residue with hot water 1~2 times, then transfer the residue into a funnel and carefully rinse the filter paper and residue with hot water until there is no chloride ion (check with 1% silver nitrate solution). During the filtering and rinsing of the residue, the final volume of the filtrate should be controlled to be about 110 mL.
3.4.4 Add 1 drop of phenolphthalein indicator (3.2.8) to the filtrate, adjust with concentrated nitric acid (3.2.2) until the red color disappears, then add 5 mL in excess, accurately add 5 mL of sodium chloride standard solution (3.2.9) and 10 mL of silver nitrate solution (3.2.5) with a single-marked pipette, let stand for 2 to 3 minutes, add 2 to 5 mL of n-hexanol to cover the surface blood, place the beaker on a magnetic stirrer and stir rapidly for 1 minute, then add 1 mL of ammonium ferric sulfate solution (3.2.7), and titrate with standard potassium thiocyanate solution (3.2.8). When the solution changes from milky white to light orange, it is the end point, and record the volume of potassium thiocyanate solution.
3.4.5 For each batch of coal samples, two or more empty measurements (without adding coal samples) should be carried out according to the steps (3.4.1 to 3.4.4), and the average value is taken as the white value.
3.5 Calculation of determination results
The chlorine content in coal is calculated according to formula (2), and the determination results are rounded to the third decimal place. Cla - 0. 035 45eV-VI) × 100m
Wherein: Clad-chlorine content in air-dried coal sample, %; 0.03545mmol of fluorine, g/mmol; mass concentration of potassium thiocyanate, mmol/mL; V
-amount of potassium thiocyanate used in coal sample determination, mL; V>
-amount of potassium thiocyanate solution used in blank determination, mL; m
3.6 Precision
Mass of air-dried coal sample, g.
Same as the provisions in 2.7.
.（2）
CB/T3558—1996
Appendix A
（Appendix of the standard）
Drawing of titration differential curve
Place the beaker containing the Baobai solution on the titration table. Connect the titration device according to 2.5.1. Slowly drip the standard silver nitrate solution (2.2.9), and record the indicator electrode potential every time 0.1ml is dripped. When approaching the end point, record it every time 0.05ml is dripped. Draw the differential curve with AmV/Aml. as the ordinate and the volume of the added standard silver nitrate solution (ml.) as the abscissa. Take the milliliters of the standard silver nitrate solution corresponding to the AmV/△mL peak as the amount of silver nitrate added to calibrate the end point potential. 293
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