GB/T 3558-2014Determination of Chlorine in Coal (English PDF)

2.2.9 in 1996 version);

-- Add a potentiometric titration assembly, using the silver-silver chloride reference

electrodes available on the market (see 3.3.2).

Using re-drafting method, this Standard is compiled with reference to ISO 587.1997 Solid

mineral fuels – Determination of chlorine using Eschka mixture. This Standard is not

equivalent to ISO 587.1997.

Determination of chlorine in coal

3.1 Summary of method

A coal sample is combusted and hydrolyzed in the mixed gas flow of oxygen and water

vapor. All chlorines contained in the coal are converted to chlorides and dissolved in the

water quantitatively. Titrate the concentration of chlorine ions in the condensate directly by

silver nitrate potentiometric method. Use the silver as an indicator electrode and the silver-

silver chloride as a reference electrode. Calculate the total chlorine content in the coal

sample according to the consumed volume of silver nitrate standard solution.

3.2 Reagents and materials

During analysis, unless otherwise stated, use only reagents of recognized analytical grade

and only distilled water or deionized water or water of equivalent purity.

3.3 Instruments and equipment

3.3.1 High temperature combustion hydrolysis device (Figure 1)

3.3.1.4 Water vapor generator. It is consisted of a 500 mL flat bottom flask and an

adjustable electric disc furnace (0.5 kW, AC 0 V ~ 220 V, adjustable continuously).

3.3.1.5 Absorber. It is consisted of two 250 mL conical flasks, glass tubes and rubber

stopper.

3.3.1.6 Oxygen flow meter. 1 000 mL/min at full scale, having the minimum division value

of 10 mL/min.

3.3.2 Potentiometric titration assembly. as shown in Figure 4, using the self-made silver-

silver chloride reference electrodes. The silver-silver chloride reference electrodes

available on the market may also be used, and the potentiometric titration assembly is

shown in Figure 5.

3.4 Combustion hydrolysis coal sample

3.4.1 Preparation of apparatus

Assemble the apparatus as shown in Figure 1.Stuff a little of refractory wool into the gas

outlet of combustion tube. Connect the electric circuit, gas circuit and condensate water.

Add about 30 mL of distilled water to No.1 absorption flask, and about 20 mL to No.2

absorption flask. Raise the high temperature furnace to 1 100°C. Mark the 300°C, 600°C

and 800°C zones of the combustion tube. Plug up the rubber stopper of sample injection

rod. Regulate the flow rate of oxygen to 500 mL/min and the evaporation capacity of water

vapor generator to about 2 mL/min. Check if there is gas leakage.

3.4.2 High temperature hydrolysis sample

3.5.2 Potentiometric calibration of end point

3.5.2.1 Preparation of blank solution. Same as 3.4.2, except that no coal sample is added.

3.5.2.2 Potentiometric calibration of titration end point. Place a beaker containing the

blank solution on a titration set. Drip the silver nitrate standard solution that has a definite

dripping quantity at a rate of 0.03 mL/s. Record the potential value at this point. Carry out

the potential determinations twice as above. The difference between the measured values

shall not exceed ±3 mV.

3.5.3 Titration for sample solution

Place a beaker containing the sample solution on a titration set. Firstly, drip the silver

nitrate standard solution at a rate of 0.05 mL/s;

3.6 Calculation of results

The chlorine content of the coal is calculated according to Formula (1), and is recorded

with the mean of two repeated determinations by rounding off to the third decimal places

in according with GB/T 483.

3.7 Precision of this method

The precision of this method for the determination of chlorine in coal is shown in Table 1.

4.1 Summary of method

Mix the coal sample and Eschka mixture. Melt them in a muffle furnace. Convert the

chlorine to chlorides.

4.2 Reagents and materials

During analysis, unless otherwise stated, use only reagents of recognized analytical grade

and only distilled water or deionized water or water of equivalent purity.

4.2.1 Eschka mixture. Weigh two portions of mass of magnesium oxide AND one portion

of mass of anhydrous sodium carbonate. Grind to the granularity less than 0.2 mm. Mix

well. Or, the Eschka mixture available on the market may be used.

4.2.2 Nitric acid. rho20°C=1.40 g/mL.

4.2.3 Hexyl alcohol. chemically pure.

4.2.4 Saturated ammonium iron sulfate solution. add the ammonium iron sulfate to a

certain amount of water till it does not dissolve anymore, and there is certain amount of

solid ammonium iron sulfate in the solution. Add several milliliters of nitric acid to remove

the brown colour. Take the supernatant liquid for use.

4.2.5 Silver nitrate solution. 10 g/L. Weigh out 1 g of the silver nitrate and dissolve in 100

mL of water, and add several milliliters of nitric acid.

4.2.6 Silver nitrate standard solution. c(AgNO3) = 0.025 00 mol/L. Weigh out accurately

4.247 2 g of reference reagent silver nitrate that has been pre-dried at 110°C for 1 h and

cooled to room temperature in a drier. Dissolve in a little of water. Then transfer to a 1 000

mL brown measuring flask. Dilute to scale with water.

4.2.7 Potassium hydrogen sulfate standard solution

4.2.8 Sodium chloride standard solution. the concentration of chloride ion is 0.10 mg/mL.

Weigh out accurately 0.329 8 g of reagent grade sodium chloride that has been pre-burned

at 500°C ~ 600°C for 1 h and cooled to room temperature in a drier. Dissolve in a little of

water. Then transfer to a 2 000 mL measuring flask.

4.2.10 Crucible. made of porcelain, having a 30 mL ~ 50 mL capacity.

4.2.11 Titration tube. 10 mL, grade A.

4.2.12 One-mark pipette. 50 mL and 10 mL, grade A.

4.3 Apparatus

4.3.1 Muffle furnace. having a thermocouple pyrometer and temperature control device,

capable of being maintained at a temperature of 800°C, and with good circulation of air.

4.3.2 Electromagnetic stirrer. having a rotating speed of 500 r/min, adjustable continuously.

4.3.3 Analytical balance. sensitivity is 0.1 mg.

4.4 Procedure

4.4.1 Weigh (1 ± 0.1)g of the coal sample (accurate to 0.000 2 g) for general analytic test.

Place in a crucible in where 3 g (to the nearest 0.1 g) of the Eschka mixture is contained.

Mix thoroughly. Then, cover with a further 2 g of the Eschka mixture. Place the crucible in

the muffle furnace. Keep the furnace door half-opened. Raise the temperature to (680 ±

20)°C. Maintain this temperature for 3 h.

4.4.5 Determination of blank value

Determine each lot of coal samples. Carry out two or more blank determinations by using

the same procedure as described in 4.4.1 ~ 4.4.4.Take the mean as the blank value (V4).

4.5 Calculation of results

The chlorine content of the coal is calculated according to Formula (3) and is recorded

with the mean of two repeated determinations by rounding off to the third decimal places

in according with GB/T 483.

4.6 Precision of this method Same as 3.7.