Chemical analysis method for chloride ions in cement raw materials

Scope of application

This standard specifies the chemical analysis method for determining chloride ions in cement raw materials by phosphoric acid distillation-mercury salt titration.

This standard applies to cement raw materials and other materials specified to adopt this standard.

2 Normative Citation Documents

The provisions in the following documents become provisions of this standard by reference. All referenced documents with dates are not applicable to this standard for subsequent amendments (excluding errata), however, parties who agree to this standard are encouraged to consider whether the *** version of these documents can be used. Referenced documents without dates apply to this standard.

General rules for sampling and sample preparation of bulk mineral products, manual sampling.

GB/T6682 Specifications and test methods for water used in analysis laboratories

The basic requirements of the experiment

Number of experiments

The number of tests for each measurement is specified as two, and the average of the two tests is used to represent the measurement result.

Quality, volume, titration degree, and representation of results

Using "g" to represent mass, accurate to 0.0001g. The volume of the burette is expressed in "mL" accurate to 0.05mL. The titer unit is expressed in "mg/mL", with three significant figures after rounding.

Blank test

Use the same amount of reagents, do not add samples, conduct the experiment according to the same measurement steps, and subtract the blank test value from the measurement results when calculating.

Summary of 4 Methods

Using a specified distillation apparatus, decompose the sample with hydrogen peroxide and phosphoric acid under temperature conditions of 250℃ to 260℃, purifying air as the carrier, distilling and separating chloride ions. Use dilute nitric acid as the absorbing solution. After distilling for 10 to 15 minutes, rinse the condenser tube and its lower end with ethanol into a conical flask, with the addition of ethanol accounting for over 75% (by volume). At around pH 3.5, use diphenylcarbazide as the indicator, and titrate with standard mercury nitrate titration solution.

Reagents and materials

Unless otherwise specified, the reagents used should not be less than analytical grade. Reagents used for standardization and preparation of standard solutions should be reference reagents. The water used should meet the requirements of Grade III water specified in GB/T 6682.

The density of the concentrated liquid reagents listed in this standard refers to the density at 20°C, with the unit in grams per cubic centimeter (g/cm3).

Nitric acid (HNO3), with a density of 1.399 g/cm3 to 1.419 g/cm3, or a mass fraction of 65% to 68%.

Phosphoric acid (H3PO4), density 1.689/cm3 or mass fraction ≥85%.

5.3 Ethanol (C2H5OH), with a volume fraction of 95% or anhydrous ethanol.

Hydrogen peroxide (H2O2), mass fraction 30%.

5.5 Sodium hydroxide (NaOH) solution [C(NaOH)=0.5mol/L]

Dissolve 2g of sodium hydroxide in 100 mL of water.

Nitric acid solution [C(HNO3)=0.5mol/L]

Take 3 ml of nitric acid (5.1), dilute with water to 100 mL.

5.7 Chloride Ion Standard Solution

0.3297g of accurately weighed sodium chloride heated at 105℃—110℃ for 2 hours, dissolved in a small amount of water, then transferred into a 1L volumetric flask, diluted to the mark with water, and shaken. 1mL of this solution contains 0.2mg of chloride ions.

Draw 50.00 mL of the above solution, inject it into a 250 mL capacity bottle, dilute with water to the mark, and shake well. Each mL of this solution contains 0.04 mg of chloride ions.

Mercuric nitrate standard titration solution [C (Hg(NO3)2)=0.001mol/L]

Preparation of standard mercury nitrate titration solution [C(Hg(NO3)2)=0.001mol/L]

Weigh 0.34g of mercuric nitrate [Hg(NO3)2·1/2H2O], dissolve it in 10mL of nitric acid (5.6), transfer it into a 1L volumetric flask, dilute to the mark with water, and shake well.

Standard titration of mercury nitrate standard titration solution [C(Hg(NO3)2) - 0.001mol/L].

Use a microburette to accurately add 5.00mL of 0.04mg/mL chloride ion standard solution (5.7) to a 50mL conical flask, add 20mL of ethanol (5.3) and 1-2 drops of bromothymol blue indicator (5.11), adjust the solution to blue with sodium hydroxide solution (5.5), then adjust the solution to just turn yellow with nitric acid (5.6), add excess 1 drop (pH about 3.5), add 10 drops of diphenylcarbazide indicator (5.12), titrate with standard mercuric nitrate solution until cherry red appears.

Conduct blank experiments simultaneously. Use the same amount of reagents, do not add chloride ion standard solution, and perform the experiment according to the same measurement steps.

The titration degree of standard mercury nitrate titration solution for chloride ions is calculated according to equation (1).

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In the formula:

Mercury nitrate standard titration solution titration degree for chloride ions, unit is milligrams per milliliter (mg/mL).

V2 is the volume of standard mercury nitrate titrant consumed during titration, measured in milliliters (mL).

V1 is the volume of blank test consumed by standard mercury nitrate titration solution, in milliliters (mL).

The concentration of a 0.04 M chloride ion standard solution is 0.04 mg/mL.

The volume of 5.00 added to the chloride ion standard solution, in milliliters (mL).

Mercuric nitrate standard titration solution [C(Hg(NO3)2)=0.005mol/L]

Preparation of standard titration solution of mercury nitrate [C(Hg(NO3)2)=0.005mol/L]

Weigh 1.67g of mercuric nitrate [Hg(NO3)2·1/2H2O], dissolve it in 10mL of nitric acid (5.6), transfer it into a 1L volumetric flask, dilute to the mark with water, and shake well.

Calibration of standard titration solution of mercury nitrate [C(Hg(NO3)2)=0.005mol/L]

Use a microburette to accurately add 7.00 mL of 0.2 mg/mL chloride ion standard solution (5.7) to a 50 mL conical flask, and follow the steps in section 5.8.2.

The titration degree of standard mercury nitrate titration solution for chloride ions is calculated according to formula (2):

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In the formula:

Mercury nitrate standard titration solution titration degree for chloride ions, unit is milligrams per milliliter (mg/mL):

V4 - The volume of standard mercury nitrate titration solution consumed during calibration, in milliliters (mL);

V3 - Volume of blank test consumed standard mercury nitrate titration solution, in milliliters (mL);

The concentration of 0.2- chloride ion standard solution is in milligrams per milliliter (mg/mL).

The volume of the standard solution containing chloride ions added, in milliliters (mL).

Silver nitrate solution 5g/L

Dissolve 5g of silver nitrate (AgNO3) in 1L of water.

Bromophenol blue indicator solution (1g/L)

Dissolve 0.1g of bromophenol blue in 100 mL of ethanol (1+4).

5.12 Diphenylcarbazide solution (10 g/L)

Dissolve 1g of diphenylcarbazide in 100 mL of ethanol.

Instruments and Equipment

6.1 天平 translates to "Libra" in English.

0.001g accurate

Glass capacity vessel

Burette, volumetric flask, pipette, weighing bottle.

Chlorine distillation device

The chlorine distillation device is shown in Figure l.

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1. Blowing pump 2. Rotor flowmeter 3. Gas washing bottle, filled with silver nitrate solution (5.10)

4. Temperature controller 5. Electric furnace 6. Quartz distillation tube 7. Furnace insulation cover 8. Serpentine condenser

9、50ml conical flask

The output contains only the result "7 samples are made"

Sampling methods according to GB/T2007.1. The sample must be representative and uniform. The sample obtained after laboratory sample reduction should not be less than 200g, reduced to not less than 50g using quartering or sample divider, then ground to pass through a square sieve with a pore size of 0.08mm, thoroughly mix the sample, pack it into a sample bottle, seal and store it for testing. The remaining portion is sealed and stored as the original sample for backup.

8 Analysis Steps

Add about 3ml of water and 5 drops of nitric acid (5.6) to a 50ml conical flask, place it under the condenser to collect the distillate, and insert the silica gel tube at the lower end of the condenser into the solution in the conical flask.

Weigh out about 0.3g of the sample, accurate to 0.0001g, place it in a dried quartz distillation tube, and avoid the sample from adhering to the tube wall.

Add 5 drops of hydrogen peroxide (5.4) solution to the distillation tube, shake, then add 5mL of phosphoric acid (5.2). Cover with a grinding mouth stopper. After most of the carbon dioxide gas generated by the decomposition of the test material has escaped, place the fixed frame on the quartz distillation tube and place it in the furnace of the chlorine distillation device (6.3) at a temperature of 250°C to 260°C. Quickly connect the inlet and outlet parts of the distillation tube with a silicone rubber tube (connect the outlet tube first, then the inlet tube), and cover the furnace lid.

Start the air pump, adjust the air flow rate to 100mL/min to 200mL/min, after distilling for 10min to 15min, turn off the air pump, remove the connecting tube, and place the distillation tube in the test tube rack.

Wash the condenser tube and the conical flask at the bottom with ethanol (approximately 15mL of ethanol). Take out the conical flask at the bottom of the condenser tube to collect the distillate, add 1-2 drops of bromophenol blue indicator (5.11), adjust to a blue solution with sodium hydroxide solution (5.5), then adjust to a yellow solution with nitric acid (5.6), add excess 1 drop, add 10 drops of diphenylcarbazide indicator (5.12), titrate with mercuric nitrate standard titration solution (5.8 or 5.9) until cherry red appears.

When the chloride ion content is 0.2% - 1%, the distillation time should be about 15 minutes - 20 minutes: titrate with standard mercury nitrate titration solution [C(Hg(NO3)2)=0.005mol/L].

When conducting sample analysis, blank tests should be carried out simultaneously, and the measurement results should be corrected.

Results show calculation.

The content of chloride ions is calculated according to formula (3): The test results are expressed in mass percentage, and the test results of chloride ions are shown to three decimal places.

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In the formula:

Xc1 - Mass fraction of chloride ions, %

Tc1 - The number of milligrams of chloride ions equivalent to each milliliter of standard mercury nitrate titration solution, in milligrams per milliliter (mg/mL).

V5 - Volume of blank test consuming standard mercury nitrate titration solution, in milliliters (mL):

V5 - The volume of mercury nitrate standard titrant consumed during titration, in milliliters (mL):

The quality of the sample M, in units of grams (g).

Allow deviation

The allowable deviations listed in this standard are all represented by quality scores.

The allowable difference in the same laboratory refers to the allowable difference specified when the same sample is analyzed by the same analyst (or two analysts) in the same analytical laboratory using this standard method. If it exceeds the allowable range, a third test (or a test by a third party) should be conducted within a short period of time. If the difference between the test result and the previous two times or any one of the analysis results meets the allowable difference requirement, the average value should be taken. Otherwise, the cause should be investigated, and the analysis should be re-conducted according to the above requirements.

The allowable difference between different laboratories refers to the requirement that the difference between the average analysis results obtained when two laboratories analyze the same sample using this standard method should comply with the specified allowable difference. In case of disputes, the sample shall be sent to a quality supervision and inspection institution accredited by the provincial and national authorities for arbitration analysis, and the result reported by the arbitration unit shall prevail.

Allowable deviations of chloride ion determination results are shown in Table 1.