GB/T 1819.2-2004Methods for chemical analysis of tin concentrates--Determination of tin content--The potassium iodate titrimetric method (English PDF)

3.20 Potassium iodide standard titration solution [c(1/6KIO 3 ) = 5 x 10

-5 mol/mL]

3. 20.1 Preparation; Weigh 1.8 g of potassium iodate, 9 g of potassium iodide,

0.3 g of sodium hydroxide. Place them in a 500 mL beaker. Add 200 mL of water.

Heat until it is completely dissolved. Use glass wool, to filter the solution into a

1000 mL volumetric flask. Use water to dilute it to the mark. Mix well.

3.20.2 Calibration: Weigh three sets of 0.1200 g metallic tin (99.99%). Put them

in a 300 mL conical flask. Do a blank test together. Add 1 g of reducing iron powder, 80 mL of hydrochloric acid solution (3.15). Heat it at low temperature, to dissolve completely. Add 20 mL of water. Proceed calibration according to

6.4.5

~ 6.4.6.

Calculate the actual concentration of potassium iodate standard titration solution, according to formula (1):

Where:

c - The actual concentration of potassium iodate standard titration solution,

5.2

The specimen shall be dried in an oven, at 105°C ± 5°C for 1 h. Then it is placed in a desiccator, to cool to room temperature, for later use.

6.1 Sample

Weigh a 0.2 g of specimen, accurate to 0.0001 g.

6.2 Number of determinations

Perform 2 measurements independently. Take the average value.

6.3 Blank test

Do a blank test with the sample.

6.4 Determination

6.4.1 Place the sample (6.1) in a 250 mL beaker. Add 2 g of potassium chlorate,

20 mL of hydrochloric acid (3.11). Heat to decompose for 20 min, at low temperature.

6.4.2 Add 60 mL of hydrochloric acid (3.15), 1 g of hydrazine sulfate, 0.3 g of potassium bromide. Heat and evaporate for more than 50 minutes. During the evaporation process, add hydrochloric acid (3.15), to keep the volume at about

30 mL. Take it down and cool it slightly. Cover a watch glass. Add hydrogen peroxide dropwise, until a brownish-red bromine gas appears. Add 10 mL of

EDTA solution, 5 mL of beryllium sulfate solution. Use ammonia to neutralize it, to pH9 ~ 10. Use a slow filter paper, which has a little pulp, to filter it. Use ammonia water-ammonium nitrate lotion, to wash the precipitate 7 ~ 8 times.

Use a glass rod, which has a rubber head, to carefully scrub the beaker, to transfer all the precipitate to the filter paper. Then move the precipitate together with the filter paper, into a 5 mL tall corundum crucible (or porcelain crucible).

Dry it. Ash it. Cool it down.

Note: When the sample contains less than 10 mg of arsenic, less than 1 mg of copper, less than 10 mg of tungsten trioxide, less than 2.5 mg of antimony, it may omit the operation of 6.4.1 ~ 6.4.2. It may directly put the sample (6.1) in a 5 mL crucible, which contains 2 g of mixed flux. Follow the operations of 6.4.3 ~ 6.4.6 below.

6.4.3 Add 2 g of zinc powder-borax-boric acid mixed flux to the crucible. Use a thin glass rod to stir it carefully. Use a small brush, to clean the thin glass rod.

Cover with 1 g of mixed flux. Cover with 1 g of sodium chloride. Move it in a box-type resistance furnace, which has been heated to 750 °C. Heat to 820 °C, to melt it for 30 minutes. Take it out. Cool it down.