GB/T 1606-2008Sodium bicarbonate for industrial use (English PDF)

7.1 General Provisions

Unless otherwise specified, all reagents and water used in this test refer to analytically pure reagents and Grade III water as specified in Table 1 of GB/T 6682-2008.Unless otherwise specified, standard titration solutions, impurity standard solutions, preparations and products used in the test shall be prepared in accordance with the provisions of HG/T 3696.1, HG/T

3696.2 and HG/T 3696.3.

7.2 Appearance Inspection

Under natural light, on a white-backed watch glass or white porcelain plate, use the visual inspection method to judge the appearance.

7.3 Determination of Total Alkali Content

7.3.1 Principle

Dissolve the test portion in water, use bromocresol green-methyl red indicator solution as the indicator, and use standard hydrochloric acid titration solution for titration to determine the total alkali content.

7.5.2.2 Reagents or materials

7.5.2.2.1 Nitric acid solution. 1 + 1, prepared with analytical grade.

7.5.2.2.2 Nitric acid solution. 1 + 19, prepared with analytical grade.

7.5.2.2.3 Standard iron solution. 1 mL of solution contains 0.010 mg of iron (Fe). Use a pipette to take 1 mL of the iron standard stock solution prepared in accordance with HG/T 3696.2 into a 100 mL volumetric flask, use nitric acid solution (1 + 19) to dilute to the scale, and shake well.

Prepare this solution immediately before use.

7.5.2.2.4 Water. Grade II water conforming to the provisions of GB/T 6682-2008.

7.5.2.3 Instruments and equipment

Inductively coupled plasma optical emission spectrometer (ICP-OES).

7.5.2.4 Test procedures

7.5.2.4.1 Preparation of test solution

Weigh-take an appropriate amount of specimen (2 g for Class I and II, 0.5 g for Class III), accurate to 0.001 g, place it in a beaker, use a watch glass to cover it, add nitric acid solution (see 7.5.2.2.1), until the specimen dissolves, transfer all to a 50 mL volumetric flask, use nitric acid solution (see 7.5.2.2.2) to dilute to the scale, and shake well.

Simultaneously, and in the same way, prepare a blank test solution. Except that no specimen is added, all other operations and the types and amounts of reagents added are the same as the test solution.

7.5.2.4.2 Drawing of standard curve

Respectively transfer-take 0.00 mL, 1.00 mL, 2.00 mL, 4.00 mL, 6.00 mL and 8.00 mL of iron standard solution to six 50 mL volumetric flasks. Use nitric acid solution (see 7.5.2.2.2) to dilute to the scale and shake well. Under optimal instrument determination conditions, at a wavelength of 238.204 nm, determine the emission spectral intensity of iron in the standard curve. With the mass concentration (mg/L) of iron as the x-coordinate and the corresponding emission spectral intensity as the y-coordinate to draw the standard curve.

7.5.2.4.3 Test

Under the same conditions as in 7.5.2.4.2, determine the emission spectral intensity of iron in the test solution and blank test solution. From the standard curve, find out the corresponding mass concentration (mg/L) of iron.

7.5.2.5 Test data processing

The iron content is expressed as the mass fraction w3 of iron (Fe) and calculated in accordance with Formula (7).

Where,

rho---the mass concentration of iron in the test solution obtained from the standard curve, expressed in (mg/L);

rho0---the mass concentration of iron in the blank test solution obtained from the standard curve, expressed in (mg/L);

m---the mass of the test portion, expressed in (g).

Take the arithmetic mean of parallel determination results as the determination result. The absolute difference between two parallel determination results shall not exceed 0.0005% for

Class I and Class II products and not exceed 0.002% for Class III products.

7.6 Determination of Sulfate Content

7.6.1 Barium sulfate gravimetric method (arbitration method)

7.6.1.1 Principle

Dissolve the test portion and separate the insoluble matter. Precipitate the sulfate as barium sulfate in dilute hydrochloric acid medium. Separate the obtained precipitate, ignite it at 800 °C

± 25 °C, and weigh it.

7.6.1.2 Reagents or materials

7.6.1.2.1 Ammonia water.

7.6.1.2.2 Hydrochloric acid solution. 1 + 1.

7.6.1.2.3 Barium chloride solution. 100 g/L.

7.6.1.2.4 Silver nitrate solution. 5 g/L. Use a small amount of water to dissolve 0.5 g of silver nitrate, add 20 mL of nitric acid solution (1 + 1), use water to dilute to 100 mL, and shake well.

7.6.1.2.5 Methyl orange indicator solution. 1 g/L.

7.6.1.3 Instruments and equipment

High-temperature furnace. temperature controllable at 800 °C ± 25 °C.

7.6.1.4 Test procedures

Weigh-take approximately 20 g of specimen, accurate to 0.01 g, place in a beaker, add 50 mL

7.6.2.2.2 Barium chloride solution. 100 g/L.

7.6.2.2.3 Standard sulfate solution. 1 mL of solution contains 0.10 mg of sulfate (SO4). Use a pipette to take 10 mL of the sulfate standard stock solution prepared in accordance with HG/T

3696.2, place it into a 100 mL volumetric flask, use water to dilute to the scale and shake well.

7.6.2.3 Instruments and equipment

Constant-temperature water bath. temperature controllable between 40 °C and 50 °C.

7.6.2.4 Test procedures

7.6.2.4.1 Preparation of test solution A

Weigh-take 5.00 g ± 0.01 g of specimen, place in a 100 mL beaker, add water to dissolve it.

Transfer all to a 100 mL volumetric flask, use water to dilute to the scale and shake well. This solution is test solution A, which is used for the determination of sulfate and calcium contents.

7.6.2.4.2 Test

Use a pipette to take an appropriate amount of test solution A (10 mL for Class I and II; 1 mL for Class III) into a 100 mL beaker. Add hydrochloric acid solution to neutralize to approximately pH 7.Use pH paper for testing, adding 5 drops in excess. Boil for 3 ~ 5 minutes to remove carbon dioxide, then cool to room temperature. Transfer all to a 50 mL colorimetric tube, add 2 mL of barium chloride solution; add water to the scale and shake well. Place in a constant-temperature water bath at 40 °C ~ 50 °C for 10 minutes. Against a black background, compare it with the standard turbidity solution. If the resulting turbidity is not deeper than that of the standard turbidity solution, it meets the requirements specified in this document;

otherwise, it does not meet the requirements specified in this document.

The standard turbidity solution is prepared by taking the standard sulfate solution in accordance with the following provisions, and treating it simultaneously and in the same way as the test portion.

Class I. 1.00 mL; Class II. 2.50 mL; Class III. 2.50 mL.

7.7 Determination of Water-insoluble Matter Content

7.7.1 Acid-washed asbestos Gooch crucible method (arbitration method)

7.7.1.1 Principle

Dissolve the test portion in water. The water-insoluble matter is filtered through an acid-washed asbestos Gooch crucible, washed, dried, and then weighed.

7.7.1.2 Reagents or materials

7.7.1.2.1 Phenolphthalein indicator solution. 10 g/L.

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