GB/T 26520-2021Calcium chloride for industrial use (English PDF)

7.3.2 Reagents or materials

7.3.2.3 Sodium hydroxide solution: 100 g/L.

7.3.2.4 Disodium ethylenediaminetetraacetate standard titration solution: c (EDTA) ~ 0.02 mol/L.

7.3.2.5 Calcium reagent carboxylate sodium salt indicator.

7.3.3 Test steps

Weigh-take an appropriate amount of specimen (10 g of calcium chloride dihydrate, 8 g of anhydrous calcium chloride or 20 g of calcium chloride solution), accurate to 0.0002 g, and place it in a 250 mL beaker. After adding water to dissolve it, transfer it all to a 1,000 mL volumetric flask, use water to dilute to the scale and shake it well. This solution is test solution A, which is used for the determination of calcium chloride content, total alkali metal chlorides and total magnesium content.

Transfer-take 10 mL of test solution A into a 250 mL conical flask, use hydrochloric acid solution to adjust pH to 3 ~ 5, add water to about 50 mL, add 5 mL of triethanolamine solution, 2 mL of sodium hydroxide solution, and about 0.1 g of calcium reagent carboxylate sodium salt indicator; use disodium ethylenediaminetetraacetate standard titration solution to titrate it. The solution turns from red to pure blue, which is the end point.

Meanwhile, carry out a blank test. In the blank test, except that no test portion is added, the type and amount of reagents added in other operations (except the standard titration solution) are the same as the determination of the test solution.

7.3.4 Test data processing

The calcium chloride content, which is calculated as the mass fraction w1 of calcium chloride (CaCl2), shall be calculated in accordance with Formula (1):

Where, V---the value of the volume of the disodium ethylenediaminetetraacetate standard titration solution consumed by titrating the test solution, expressed in (mL);

V0---the value of the volume of the disodium ethylenediaminetetraacetate standard titration solution consumed in the blank test, expressed in (mL);

Where, c1---the accurate value of the concentration of the hydrochloric acid standard titration solution, expressed in (mol/L);

V1---the value of the volume of the added hydrochloric acid standard titration solution, expressed in (mL); c2---the accurate value of the concentration of the sodium hydroxide standard titration solution, expressed in (mol/L);

V2---the value of the volume of the sodium hydroxide standard titration solution consumed during titration, expressed in (mL);

M---the value of the molar mass of calcium hydroxide {1/2[Ca(OH)2]}, expressed in (g/mol) m---the value of the mass of the test portion, expressed in (g).

Take the arithmetic mean of the parallel determination results as the determination result. The absolute difference between the two parallel determination results shall not be greater than 0.005%.

7.5 Determination of Total Alkali Metal Chlorides

7.5.1 Principle

Use potassium chromate as an indicator and use silver nitrate standard titration solution to titrate the total chlorine. Minus the chlorine content in calcium chloride and magnesium chloride and convert it into the total alkali metal chlorides content calculated as sodium chloride (NaCl).

7.5.2 Reagents or materials

7.5.2.2 Sodium bicarbonate solution: 100 g/L.

7.5.2.3 Silver nitrate standard titration solution: c(AgNO3) ~ 0.05 mol/L. Weigh-take 17.5 g of silver nitrate, dissolve it in 2,000 mL of water, and shake it well. Store the solution in a brown bottle. Weigh-take 0.1 g of reference sodium chloride that has been burned in a high-temperature furnace at 500 °C ~ 600 °C to a constant mass, accurate to 0.0001 g. In accordance with the provisions of HG/T 3696.1, calibrate it.

7.5.3 Test steps

Use a pipette to transfer-take 10 mL of test solution A (see 7.3.3) and place it in a 250 mL conical flask. Add 50 mL of water, use nitric acid solution or sodium bicarbonate solution to adjust the pH to 6.5 ~ 10 (use pH test paper to check it). Add 0.7 mL of potassium chromate solution and use silver nitrate standard titration solution to titrate it. The solution turns from light yellow to reddish, which is the end point.

7.5.4 Test data processing

The total alkali metal chlorides content, which is calculated as the mass fraction w3 of sodium chloride (NaCl), shall be calculated in accordance with Formula (3):

Where, V---the value of the volume of the silver nitrate standard titration solution consumed during titration, expressed in (mL); c---the accurate value of the concentration of the silver nitrate standard titration solution, expressed in (mol/L);

M---the value of the molar mass of sodium chloride, expressed in (g/mol) (M = 58.44); m---the value of the mass of the test portion (see 7.3.3), expressed in (g);

1.053---the coefficient for converting calcium chloride (CaCl2) into sodium chloride (NaCl); w1---the value of the mass fraction of calcium chloride determined in accordance with 7.3, expressed in (%);

1.228---the coefficient for converting magnesium chloride (MgCl2) into sodium chloride (NaCl); w7---the value of the mass fraction of total magnesium (calculated as MgCl2) determined in accordance with 7.9, expressed in (%).

Take the arithmetic mean of the parallel determination results as the determination result. The absolute difference between the two parallel determination results shall not be greater than 0.2%.

7.6 Determination of Water-insoluble Matter Content

7.6.1 Principle

Weigh-take a certain amount of specimen and dissolve it in water. After filtration, dry the residue under certain temperature conditions, until reaching a constant mass. After weighing, determine the water-insoluble matter content.

7.6.2 Reagents or materials

Silver nitrate solution: 20 g/L. absolute difference between the two parallel determination results shall not be greater than 0.002%.

7.8.2 Visual turbidimetric method

7.8.2.1 Principle

Same as 4.2 in GB/T 23844-2019.

7.8.2.2 Reagents or materials

Same as 4.2 in GB/T 23844-2019.

7.8.2.3 Test steps

Weigh-take 1.00 g ± 0.01 g of specimen. Place it in a 100 mL colorimetric tube, add water to approximately 30 mL, dissolve it, and perform the following operations in accordance with the provisions of 4.4 in GB/T 23844-2019. In addition, in accordance with the provisions of 4.4 in

GB/T 23844-2019, determine the results.

Transfer-take 3.5 mL of sulphate standard solution [1 mL of solution contains 0.1 mg of sulphate (calculated as SO4)], use water to dilute to the same volume as the specimen, and process it in the same way and at the same time as the test solution of the same volume.

7.9 Determination of Total Magnesium Content

7.9.1 Principle

Use triethanolamine to mask a small amount of ferric iron, trivalent aluminum and divalent manganese ions. When the pH is 10, use chrome black T as the indicator and use disodium ethylenediaminetetraacetate standard titration solution to titrate the total amount of calcium and magnesium, minus the calcium content from it to calculate the magnesium chloride content.

7.9.2 Reagents or materials

7.9.2.1 Triethanolamine solution: 1 + 3.

7.9.2.2 Ammonia-ammonium chloride buffer solution A (pH ~ 10).

7.9.2.3 Disodium ethylenediaminetetraacetate standard titration solution: c (EDTA) ~ 0.02 mol/L.

7.9.3 Test steps

Use a pipette to transfer-take 10 mL of test solution A (see 7.3.3), place it in a 250 mL conical flask, add 50 mL of water, 5 mL of triethanolamine solution, 10 mL of ammonia-ammonium chloride buffer solution A and 0.1 g of chrome black T indicator. Use the disodium Take the arithmetic mean of the parallel determination results as the determination result. The absolute difference between the two parallel determination results shall not be greater than 0.5.