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)

4.1 Principle

After the sample is dissolved in hydrochloric acid (or a mixed solution of nitric acid and perchloric acid), in an ammonia-ammonium chloride buffer solution, with murexide as the indicator and EDTA standard titration solution as the titrant, the cobalt content is calculated based on the volume of EDTA standard titration solution consumed. It can use EDTA manual titration or EDTA automatic titration.

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.

5.3 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 Test steps

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.

5.5.3.2 If the specimen cannot be dissolved by hydrochloric acid (5.2.2), TAKE another specimen (5.5.1) and place it in a 100 mL beaker, ADD a mixed solution of 5 mL nitric acid (5.2.3) and 5 mL perchloric acid (5.2.4) to dissolve, COVER with a watch glass, and HEAT at low temperature until the specimen is completely dissolved. Then PLACE the solution at 120 °C ~ 250 °C, HEAT to drive out the acid until the solution volume is about 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 salts until the solution is clear. After cooling, TRANSFER to a 250 mL volumetric flask, DILUTE to the mark with water, SHAKE well, and RECORD the constant volume as V12. […]