YS/T 1157.1-2016Methods for chemical analysis of crude cobalt hydroxide—Part 1: Determination of cobalt content—Potentiometric titration method (English PDF)

2.1 Method summary

In the presence of perchloric acid and phosphoric acid, the sample oxidizes manganese to Mn3 to form manganese phosphate to mask the interference of coexisting elemental manganese. In citric acid Salt exists in the ammonia solution, with potassium ferricyanide solution Co2 oxidation Co3, excessive potassium ferricyanide Potentiometric titration with cobalt standard Titration solution back titration.

2.2 Reagents

Unless otherwise stated, only reagents identified as analytical grade were used in the analysis. The water used was either laboratory grade 3 water or water of comparable purity.

2.2.1 Ammonium hydrogen fluoride.

2.2.2 Perchloric acid (rho = 1.67 g/mL).

2.2.3 Phosphoric acid (p = 1.69 g/mL).

2.2.4 Ammonia (rho = 0.90 g/mL).

2.2.5 Hydrochloric acid (1 1).

2.2.6 ammonium citrate solution (300g/L).

2.2.7 Cobalt standard titration solution Weigh 1.0000g cobalt metal (wCo >= 99.95%), add 20mL nitric acid (11), after low temperature dissolved, Add 10mL of sulfuric acid (1 1), steamed to white smoke, remove the cooling, wash the watch glass and cup wall with water, heat to dissolve salt, cooled and moved into 1000mL volumetric flask, diluted with water to the mark, mix well. 1mL of this solution contains 1mg of cobalt.

2.2.8 Potassium ferricyanide standard solution

2.2.8.1 Preparation. Weigh 5.6g potassium ferricyanide, add about 250mL water dissolved, filtered and diluted to 1000mL with water, and mix. Stored in Brown bottle.

2.2.8.2 Calibration In a.200mL beaker, add 30mL ammonium citrate solution (2.2.6), 30mL ammonia (2.2.4), accurately added 15.00mL potassium ferricyanide standard solution (2.2.8.1), mix well. On the potentiometer, place the redox electrode (2.3.2) in the beaker Constantly titrated with cobalt standard titration solution (2.2.7) Titration to the maximum potential jump is the end of the jump.

Calculate the conversion factor of potassium ferricyanide standard solution to cobalt standard titration solution according to equation (1).

k = V1V2

In the formula.

k --- conversion factor, the unit volume of potassium ferricyanide standard solution consumed cobalt standard titration solution volume;

V1 --- back titration consumption of cobalt standard solution ml, in milliliters (mL);