GB/T 23367.1-2024Methods for the chemical analysis of lithium cobalt oxide - Part 1: Determination of the cobalt content - EDTA titration and potentiometric titration (English PDF)

4.2 Reagents or materials

4.2.1 Water, GB/T 6682, grade 3 and above.

4.2.2 Hydrochloric acid (1 + 1).

4.2.3 Nitric acid (rho =

1.42 g/mL), analytical grade or above.

4.2.4 Perchloric acid (rho =

1.67 g/mL), analytical grade or above.

4.2.5 Cobalt standard solution: WEIGH 1.0000 g of metallic cobalt (wCo >= 99.98 %) in a 400 mL beaker, ADD 30 mL of hydrochloric acid (4.2.2), COVER with a watch glass, DISSOLVE completely at low temperature, COOL to room temperature, TRANSFER to a 1000 mL volumetric flask, DILUTE to the mark with water, and MIX well. 1 mL of this solution contains

1.0 mg of cobalt. Commercially available certified cobalt standard solution can also be used.

4.2.6 Ammonia-ammonium chloride buffer solution (pH ~ 10): WEIGH

54.5 g of ammonium chloride and dissolve in water, ADD 350 mL of ammonia, DILUTE to 1000 mL with water, and MIX well.

4.2.7 Murexide indicator: WEIGH

0.4 g of murexide, ADD 50 g of potassium sulfate, and GRIND thoroughly in a mortar. Store in a desiccator.

4.2.8 Preparation of disodium ethylenediaminetetraacetate (C10H14N2O8Na2 - 2H2O, referred to as EDTA) standard titration solution (about

0.01 mol/L). WEIGH

3.72 g of EDTA into a 400 mL beaker, ADD water to dissolve with slight heat, COOL to room temperature, TRANSFER to a 1000 mL volumetric flask, DILUTE to the mark with water, and MIX well.

4.2.9 Standardization of disodium ethylenediaminetetraacetate (C10H14N2O8Na2 - 2H2O, referred to as EDTA) standard titration solution (about

0.01 mol/L) (calibration before use): TRANSFER

15.00 mL of cobalt standard solution (4.2.5) into the titration cup, record as V1. ADD 50 mL of water and 20 mL ~ 22 mL of EDTA standard titration solution (preferably 3 mL ~ 5 mL before the end point of the reaction process), then ADD 10 mL of ammonia-ammonium chloride buffer solution (4.2.6), and finally ADD about

0.1 g of murexide indicator (4.2.7). If EDTA manual titration is selected, directly titrate with EDTA standard titration solution until the solution changes from orange-yellow to purple-red, which is the end point. If EDTA automatic titration is selected, insert the photometric electrode into the automatic potentiometric titrator, and titrate to the end point with EDTA standard titration solution under stirring according to the titration end point recognition program set by the instrument.

4.5.1 Specimen Weigh

0.10 g of sample (4.4) to an accuracy of 0.0001 g. The mass of the weighed specimen is recorded as m1.

4.5.2 Parallel test Perform two tests in parallel and take the average value.

4.5.3 Blank test Perform a blank test along with the specimen, and the volume of the EDTA standard titration solution consumed is recorded as V5.

4.5.4 Determination

4.5.4.1 PLACE the specimen (4.5.1) in a 100 mL beaker, ADD 10 mL of hydrochloric acid (4.2.2), COVER with a watch glass, and HEAT on a low-temperature electric hot plate until completely dissolved. After cooling, TRANSFER to a 100 mL volumetric flask, DILUTE to the mark with water, MIX well, and RECORD the constant volume as V6.

4.5.4.2 If the specimen cannot be dissolved by hydrochloric acid (4.2.2), take another specimen (4.5.1) and PLACE it in a 100 mL beaker, ADD a mixed solution of 3 mL nitric acid (4.2.3) and 3 mL perchloric acid (4.2.4) to dissolve, COVER with a watch glass, and HEAT on a low-temperature electric hot plate until completely dissolved. Then PLACE the solution at 120 °C ~ 250 °C and HEAT until the solution volume remains 1 mL ~ 2 mL. REMOVE and cool slightly, RINSE the watch glass and the beaker wall with water, and HEAT at low temperature to dissolve the salt until the solution is clear. After cooling, TRANSFER To a 100 mL volumetric flask, DILUTE to the mark with water, MIX well, and RECORD the constant volume as V6.

4.5.4.3 TRANSFER

25.00 mL of the test solution (

4.5.4.1 or 4.5.4.2) to the titration cup, RECORD it as V7. ADD about 50 mL of water and 19 mL ~ 21 mL of EDTA standard titration solution (depending on the cobalt content of lithium cobaltate, preferably 3 mL ~ 5 mL before the end of the reaction process). After stirring, ADD an appropriate amount of ammonia-ammonium chloride buffer solution (4.2.6) to adjust the pH of the solution to be tested to ~ 10. Finally, ADD about

0.1 g of murexide indicator (4.2.7). If EDTA manual titration is selected, titrate with EDTA standard titration solution (4.2.8) until the solution changes from orange-yellow to purple-red, which is the end point. If EDTA automatic titration is selected, insert the photometric electrode (4.3.2) into the automatic potentiometric titrator (4.3.1), and titrate to the end point with EDTA standard titration solution(4.2.8) under stirring according to the titration end point recognition program set by the instrument.

5.2.2 Hydrochloric acid (1 + 1).

5.2.3 Nitric acid (rho =

1.42 g/mL), analytical grade and above.

5.2.4 Perchloric acid (rho =

1.67 g/mL), analytical grade and above.

5.2.5 Cobalt standard solution: WEIGH 3.0000 g of metallic cobalt (wCo >= 99.98 %) into a 400 mL beaker, ADD 30 mL of hydrochloric acid (5.2.2), COVER with a watch glass, DISSOLVE completely at low temperature, COOL to room temperature, TRANSFER to a 1000 mL volumetric flask, DILUTE to the mark with water, and MIX well. 1 mL of this solution contains

3.0 mg of cobalt. Commercially available certified cobalt standard solution can also be used.

5.2.6 Ammonium chloride-ammonium citrate-ammonia mixed solution (pH ~ 10): WEIGH

62.5 g of ammonium chloride and 50 g of ammonium citrate, DISSOLVE in water, ADD 350 mL of ammonia water, DILUTE to 1000 mL with water, and MIX well.

5.2.7 Preparation of potassium ferrocyanide (K3[Fe(CN)6]) standard solution (about

0.05 mol/L). WEIGH

17.8 g of potassium ferrocyanide, DISSOLVE in water, FILTER and TRANSFER into a 1000 mL brown volumetric flask, DILUTE to the mark with water, MIX well, and STORE in a dark place.

5.2.8 Standardization of potassium ferrocyanide (K3[Fe(CN)6]) standard solution (about

0.05 mol/L) (calibration before use): ADD

25.00 mL of potassium ferrocyanide standard solution (5.2.7) to a 250 mL beaker, RECORD it as V9, and then ADD 80 mL of ammonium chloride-ammonium citrate-ammonia mixed solution (5.2.6), and MIX well. INSERT the electrode into the potentiometric titrator and titrate with the cobalt standard solution (5.2.5) under stirring until the potential jump, which is the end point. The volume of the cobalt standard solution consumed is recorded as V8. Calculate the titration coefficient of the potassium ferrocyanide standard solution equivalent to the cobalt standard solution according to formula (3): where: K - titration coefficient, the volume ratio of the cobalt standard solution consumed by a unit volume of potassium ferrocyanide standard solution; V8 - volume of the cobalt standard solution consumed during titration, in milliliters (mL); V9 - volume of the potassium ferrocyanide standard solution added, in milliliters (mL). Perform three parallel calibrations. The range of the volume of the cobalt standard solution consumed shall not be greater than

0.05 mL. Take the average value. Otherwise, recalibrate. The calculation result is retained to four decimal places, and the rounding off of numerical values is carried out in accordance with the provisions of GB/T 8170.

5.3 Instruments and equipment

5.3.1 Automatic potentiometric titrator with stirring device.

5.3.2 Redox electrodes matching the instrument.

5.4 Samples

5.4.1 The sample particle size shall not be greater than 100 µm.

5.4.2 Before analysis, the sample shall be dried at 110 °C ± 5 °C for 2 h and placed in a desiccator to cool to room temperature.

5.5.1 Specimen Weigh

1.00 g of sample (5.4) to an accuracy of 0.0001 g. The mass of the weighed specimen is recorded as m2.

5.5.2 Parallel test Perform two tests in parallel and take the average value.

5.5.3 Determination

5.5.3.1 PLACE the specimen (5.5.1) in a 100 mL beaker, ADD a small amount of water to moisten it, slowly ADD 20 mL of hydrochloric acid (5.2.2), COVER with a watch glass, and HEAT at low temperature until the specimen is completely dissolved. After cooling, TRANSFER to a 250 mL volumetric flask, DILUTE to the mark with water, SHAKE well, and RECORD the constant volume as V12.