GB/T 16484.13-2017Chemical analysis methods for rare earth chloride and light rare erath carbonate--Part 13: Determination of ammonium chloride content (English PDF)

2.1 Method principle

Add excess sodium hydroxide solution to the aqueous solution of rare earth chloride and light rare earth carbonate (dissolved with hydrochloric acid). Heat and distill to absorb the decomposed ammonia and water vapor with excess sulfuric acid standard solution. Titrate the excess sulfuric acid with sodium hydroxide standard solution to calculate the amount of ammonium chloride.

2.2 Reagents

Unless otherwise specified, the reagents used in this Part are analytically pure reagents that meet national standards or industry standards. The water used is ammonia-free water. It can be prepared by ion exchange or distillation.

2.2.1 Hydrochloric acid (1+1).

2.2.2 Sulfuric acid (rho = 1.84 g/mL).

2.2.3 Phenolphthalein indicator: Weigh 0.1 g of phenolphthalein and dissolve it in 100 mL of ethanol (3+2).

2.2.4 Sodium hydroxide solution (250 g/L): Weigh 250 g of sodium hydroxide. Add 1 000 mL of water to dissolve. Stir thoroughly and set aside.

2.2.5 Sodium hydroxide standard titration solution [c (NaOH) ~ 0.2 mol/L]:

a) Preparation: Transfer 15 mL of sodium hydroxide solution (2.2.4) into a 500 mL volumetric flask. Dilute to volume with water. Mix well.

b) Calibration: Weigh 0.50 g of potassium hydrogen phthalate dried at 105°C for 2 h, accurate to 0.0001 g, into a 300 mL conical flask. Dissolve in 100 mL of water. Add a few drops of phenolphthalein indicator (2.2.3). Titrate with the above sodium hydroxide solution [2.2.5a)] until the red color does not fade, which is the end point. Titrate 4 times in parallel. When the difference in the volume of the consumed sodium hydroxide solution [2.2.5a)] is not greater than 0.10 mL, take the average value.

Calculate the actual concentration of the sodium hydroxide standard titration solution according to formula (1):

Where, c1 - actual concentration of sodium hydroxide standard titration solution, in moles per liter (mol/L); m - mass of potassium hydrogen phthalate, in grams (g);

V1 - volume of sodium hydroxide standard solution consumed during titration, in milliliters (mL);

204.22 - relative molar mass of potassium hydrogen phthalate, in grams per mole (g/mol).

2.2.6 Bromocresol green-methyl red indicator: Weigh 0.1 g of bromocresol green and dissolve it in 100 mL of ethanol (1+4). Weigh 0.1 g of methyl red and dissolve it in 100 mL of ethanol (3+2). Take 30 mL of the prepared bromocresol green solution and 10 mL of the methyl red solution. Mix them thoroughly.

2.2.7 Sulfuric acid standard solution [c (1/2H2SO4) ~0.2 mol/L]

a) Preparation: Take 5 mL of sulfuric acid (2.2.2). Transfer it into a 500 mL volumetric flask. Dilute to volume with water. Mix well.

b) Calibration: Pipette 25.00 mL of sodium hydroxide standard titration solution (2.2.5) into a 250 mL conical flask. Add 80 mL of water. Add 3 drops of bromocresol green-methyl red indicator (2.2.6). Titrate with sulfuric acid standard […]

2.5.3 Blank test

Carry out a blank test along with the specimen.

2.5.4 Determination

2.5.4.1 Dissolution of test material

2.5.4.1.1 Rare earth chloride test material: Place the test material (2.5.1) in a 100 mL beaker. Dissolve it in water. Transfer it to a 100 mL volumetric flask. Dilute to the volume with water. Mix well.

2.5.4.1.2 Light rare earth carbonate test material: Place the test material (2.5.1) in a 100 mL beaker. Add 30 mL of water. Add hydrochloric acid (2.2.1) dropwise to dissolve. After complete dissolution, transfer to a 100 mL volumetric flask. Dilute to the volume with water. Mix well.

2.5.4.2 Distillation

Take the test solution according to Table 1 and inject it from the feed port into the distillation flask pre-filled with 20 mL of sodium hydroxide solution (2.2.4). Rinse the wall of the flask several times with a small amount of water to make the volume of the solution in the distillation flask about 100 mL. Connect the distillation device. Heat and distill to boiling and keep it for 40 min. The outlet of the condenser (immersed below the liquid surface) is received by a conical flask pre-filled with 15 mL of sulfuric acid standard solution (2.2.7) and 60 mL of water. After the reaction is completed, rinse the wall of the condenser 5 times with water until the volume of the receiving liquid is about 150 mL.

2.5.4.3 Titration

Add 5 drops of bromocresol green-methyl red indicator (2.2.6) and titrate with sodium hydroxide standard titration solution (2.2.5) until the solution turns blue-green, which is the end point.

2.6 Calculation and presentation of analysis results

Calculate the mass fraction of ammonium chloride w(NH4Cl) according to formula (3):

Where, c2 - concentration of sulfuric acid standard solution, in mol/L; […]

3.1 Method principle

Add excess sodium hydroxide solution to an aqueous solution of rare earth chloride and light rare earth carbonate (dissolved with hydrochloric acid). Heat and distill. The decomposed ammonia and water vapor are absorbed by excess sulfuric acid solution.

In a strong alkaline system, nitrogen in the form of free ammonia or ammonium ions reacts with Nessler's reagent to form a yellow-brown complex. Measure its absorbance at a wavelength of 420 nm on a spectrophotometer to calculate the amount of ammonium chloride.

3.2 Reagents

Unless otherwise specified, the reagents used in this Part are analytically pure reagents that meet national standards or industry standards. The water used is ammonia-free water. It can be prepared by ion exchange or distillation.

3.2.1 Hydrochloric acid (1+1).

3.2.2 Sodium hydroxide solution: Pass 20 mL of sodium hydroxide solution (250 g/L) through a distillation apparatus to remove nitrogen.

3.2.3 Sulfuric acid: 0.2 mol/L.

3.2.4 Potassium sodium tartrate solution: Weigh 50 g of potassium sodium tartrate. Dissolve it in 100 mL of water. Heat to boil to drive off nitrogen. Cool thoroughly and dilute to 100 mL.

3.2.5 Nessler's reagent:

a) Weigh 16 g of sodium hydroxide and dissolve it in 100 mL of water. Cool to room temperature.

b) Weigh 7 g of potassium iodide and 10 g of mercuric iodide and dissolve them in 200 mL~300 mL of water. Then slowly add this solution to the sodium hydroxide solution [3.2.5a)] while stirring. Dilute to 500 mL. Store in a brown bottle. Seal with a rubber stopper. If precipitation occurs, take the supernatant when using. […]

3.5.6 Determination

3.5.6.1 Accurately transfer 5.00 mL to 25.00 mL of receiving solution (depending on the content) into a 50 mL colorimetric tube. Add water to make up to 25 mL.

3.5.6.2 Add 1 mL of potassium sodium tartrate (3.2.4). Shake well. Add 5 mL of Nessler's reagent (3.2.5). Dilute to the volume with water. Shake well. Let it stand for 10 min.

3.5.6.3 Pipette part of the solution (3.5.6.2) into a 2 cm cuvette. Use the blank solution as a reference. Measure its absorbance at a wavelength of 420 nm on a spectrophotometer. Obtain the amount of ammonium chloride from the working curve.

3.5.7 Drawing of working curve

3.5.7.1 Pipette 0 mL, 0.50 mL, 1.00 mL, 2.00 mL, 4.00 mL, 6.00 mL, and 8.00 mL of ammonium chloride standard solution (3.2.7) into a set of 50 mL colorimetric tubes. Dilute to 25 mL with water. Proceed as in 3.5.6.2.

3.5.7.2 Pipette part of the solution (3.5.7.1) into a 2 cm cuvette. Use the reagent blank solution as a reference. Measure its absorbance at a wavelength of 420 nm on a spectrophotometer. Draw a working curve with the amount of ammonium chloride as the horizontal axis and the absorbance as the vertical axis.

3.6 Calculation and presentation of analysis results

Calculate the mass fraction of ammonium chloride w (NH4Cl) according to formula (4):

Keys: m1 - amount of ammonium chloride obtained from the working curve, in micrograms (µg);

V0 - volume of the dissolved test solution, in milliliters (mL);

V1 - volume of the test solution taken out, in milliliters (mL);

V2 - volume of the receiving solution, in milliliters (mL);

V3 - volume of the receiving solution taken out, in milliliters (mL); […]