GB/T 39138.1-2020Methods for chemical analysis of gold nickel chromium iron silicon boron alloys - Part 1: Determination of gold content - Potentiometric titration using ferrous sulfate (English PDF)

3.1

Hydrochloric acid (rho=1.19g/mL).

3.2

Nitric acid (rho=1.42g/mL).

3.3

Sulfuric acid (rho=1.84g/mL).

3.4

Phosphoric acid (rho=1.70g/mL).

3.5 Sulfuric acid and phosphoric acid mixed acid

Take 50mL phosphoric acid (3.4) in a 300mL beaker, and slowly add 50mL sulfuric acid (3.3) while stirring.

Mix well, cool, and transfer to reagent bottle for later use.

3.6

Sulfuric acid solution (4 96).

3.7

Sodium chloride solution (250g/L).

3.8

Standard titration solution of ferrous sulfate (0.008mol/L).

a) Preparation. Weigh 10.5g of ferrous sulfate (FeSO4·7H2O) solid and dissolve it in a brown containing 5000mL sulfuric acid solution (3.6)

Mix well in a glass bottle and place it for calibration for more than 7 days.

b) Calibration. Calibration is performed in parallel with the measurement of the sample.

Pipette 10.00mL gold standard solution (3.9) into a 100mL beaker, add 0.5mL sodium chloride solution (3.7), and steam until wet in a water bath

Salty, remove. Add 5mL sulfuric acid and phosphoric acid mixed acid (3.5), add water to 40mL volume. Insert the platinum indicator electrode and

Saturated potassium chloride calomel reference electrode, under electromagnetic stirring, titrate with ferrous sulfate standard titration solution (3.8a)) to near the end point (that is, the potential sudden change)

When the jump value changes greatly), use a microburette to titrate to the potential jump point as the end point.

Three parts are calibrated in parallel, and the range of the volume of the ferrous sulfate standard titration solution consumed should not exceed 0.020mL, whichever is the average.

Calculate the actual concentration of ferrous sulfate standard titration solution according to formula (1).