YS/T 820.8-2012Methods for Chemical Analysis of Laterite Nickel Ores - Part 8: Determination of Silica Content - Potassium Silica fluoride Titrimetric Method (English PDF)

4.7 Saturated potassium chloride-ethanol lotion: mix absolute ethanol and carbon

dioxide-free water according to (1+2), and add potassium chloride (4.2) to saturation.

4.8 Neutral water: in 2000mL carbon dioxide-free boiling water, add 1mL of bromothymol blue-phenol red mixed indicator solution (4.9); adjust to a bright blue-violet by sodium hydroxide standard titration solution (4.11).

4.9 Bromothymol blue-phenol red mixed indicator solution: take 0.1g of bromothymol

blue [C27H28O5Br2S] and phenol red [C19H14O5S] indicators, respectively; and dissolve them in 20mL of absolute ethanol; add 30mL of hot water; and stir to complete dissolve and mix evenly.

4.10 Sodium hydroxide stock solution (cNaOH ~1.0mol/L): take 40g of sodium hydroxide

and dissolve it in carbon dioxide-free water; dilute to 1000mL; mix evenly; store in a polyethylene container; and place it tightly until the solution is clear.

4.11 Sodium hydroxide standard titration solution (cNaOH~0.1mol/L).

4.11.1 Preparation

Pipette 100mL of sodium hydroxide stock solution (4.10); dilute to 1000mL by carbon dioxide-free water; mix evenly; and store in a tubulated bottle equipped with soda asbestos tube.

4.11.2 Calibration

Take 0.50g (accurate to 0.0001g) of reference potassium hydrogen phthalate [KHC8H4O4] (dried to constant weight at 105°C ~110°C); place it in a 250mL conical flask; add 100mL of carbon dioxide-free hot water and dissolve it. After cooling, add 4 drops of phenolphthalein indicator (10g/L); titrate by sodium hydroxide standard titration solution (4.11) to pink; and keep it for 30s without fading. Do a blank test at the same time. Three portions are calibrated in parallel, and the volume range of the

6.2 The number of determinations Perform 2 determinations independently, and take their average value.

6.3 Blank test

Do the blank test with the testing material.

6.4 Determination

6.4.1 Place the testing material (6.1) in a 30mL nickel crucible; add 4g of potassium

hydroxide (4.1); heat it on a hot plate to expel the moisture; cover the crucible lid with a small gap; and move it into a 650°C high temperature furnace to melt for 10min~15min. Take it out, cool to room temperature; place it in a 250mL polyethylene beaker; leaching the frit with a small amount of boiling water for several times. And then wash out the crucible with hydrochloric acid (4.5); control the volume not to exceed 50mL. Under constant stirring, quickly add 20mL of hydrochloric acid (4.3); and stir until the solution is clear.

6.4.2 Add 10mL of nitric acid (4.4); place the beaker in a cold-water bath till it reaches

room temperature; add 3g of potassium chloride (4.2) and a little filter paper pulp; and stir well. Slowly add 10mL of potassium fluoride solution (4.6) under stirring; continue stirring for 1min~2min; and stand for about 15min.

6.4.3 Use a plastic funnel with absorbent cotton and filter paper pulp (previously rinse

with saturated potassium chloride-ethanol lotion (4.7) for 2~3 times) to filter; and use saturated potassium chloride-ethanol lotion (4.7) to purge the polyethylene beaker.

Completely transfer the precipitate to the funnel and wash until the precipitate has no acid reaction.

NOTE: The acid-free reaction refers to taking 3mL~4mL of the filtrate for washing the precipitate;

adding 1 drop of indicator solution (4.9); adding 1 drop of sodium hydroxide standard titration solution (4.11); showing bright blue-purple, then it indicates that it has been cleaned.

6.4.4 Place the precipitate and absorbent cotton in a polyethylene beaker; add 6 drops

of indicator solution (4.9); add 150 mL of boiling neutral water (4.8); stir evenly; and immediately use sodium hydroxide standard titration solution (4.11) to titrate till a stable bright blue-violet appears.