GB/T 1510-2016Manganese ores - Determination of aluminium content - EDTA titrimetric method (English PDF)

4.3 Hydrochloric acid, rho =

4.4 Hydrochloric acid, 1+1.

4.5 Hydrochloric acid, 1+2.

4.6 Hydrochloric acid, 1+5.

4.7 Hydrochloric acid, 2+98.

4.8 Sulfuric acid: 1+1.

4.9 Hydrofluoric acid, rho =

4.10 Hydrogen peroxide, mass fraction of 30%.

4.11 Ammonia water, 1+1.

4.12 Hydrochloric acid-hexamethylenetetramine solution (pH = 5 ~ 5.5): Weigh 40 g of hexamethylenetetramine and dissolve it in water; add 20 mL of hydrochloric acid (1+1); use water to dilute to 100 mL; mix well.

4.13 Hexamethylenetetramine solution, 5 g/L.

4.14 Sodium hydroxide solution, 500 g/L: Weigh 500 g of sodium hydroxide; use water to dissolve and dilute to 1 L; store in a plastic bottle.

4.15 Sodium fluoride saturated solution: Store in a plastic bottle.

7.4.1 Preparation of sample solutions

7.4.1.1 Put the sample (see 7.2) in a 400 mL beaker; add 20 mL of hydrochloric acid (see 4.3); heat the solution until there is no obvious reaction,; then, add 5 mL of nitric acid (see 4.2). Continue to heat to dissolve until nearly dry; remove and cool slightly; add 20 mL of hydrochloric acid (see 4.4) and 100 mL of water; heat to dissolve the salts. Remove it; use medium-speed filter paper to filter while it is still hot; use hot water to wash the filter paper 10 ~ 15 times. Keep the filtrate as main liquid A.

7.4.1.2 Transfer the filter paper and residue into a platinum dish or platinum crucible; dry and carbonize at low temperature; put it into a high temperature furnace at about 550 °C for ashing; then, burn it in a high temperature furnace at 850 °C for 10 minutes; remove it for cooling. Add 2 mL of sulfuric acid (see 4.8); add 3 mL ~ 5 mL of hydrofluoric acid (see 4.9) dropwise; after heating to evaporate the silicon, heat it on an electric hot plate until the sulfuric acid emits smoke; remove it. Slightly cool; blow a small amount of water around the platinum dish; then, heat until the sulfuric acid smokes and is almost dry. Remove it; add 10 mL of hydrochloric acid (see 4.4); heat to dissolve the salts; combine the test solution with the main solution A.

7.4.2 Separation of hexamethylenetetramine

7.4.2.1 Adjust the volume of the solution (see 7.4.1.2) to about 100 mL ~ 150 mL; boil and remove. Use ammonia water (see 4.11) to neutralize until a precipitation occurs; then, use hydrochloric acid (see 4.4) to adjust until the precipitate just dissolves; add 5 ~ 10 drops in excess. Add 20 mL of hydrochloric acid-hexamethylenetetramine solution (see 4.12); heat to slightly boil and keep at a temperature (80 °C ~ 90 °C) for 15 min ~ 20 min. Remove and cool slightly; use a medium-speed filter paper to filter (in two funnels when there are a lot of precipitations of hydroxide of iron and aluminium); use hot hexamethylenetetramine solution (see 4.13) to wash the beaker and precipitate 5 ~ 8 times respectively. Use 30 mL of hot hydrochloric acid (see 4.5) to dissolve the precipitate in the original beaker; use hot hydrochloric acid (see 4.7) to wash the filter paper until it is no longer yellow; then, use hot water to wash the filter paper for 10 ~ 15 times. Keep the solution as the main liquid B for strong base separation.

7.4.2.2 Transfer the filter paper and residue into a platinum dish or platinum crucible; put it into a high temperature furnace at about 550 °C for ashing; then, burn it in a high temperature furnace at 850 °C for 10 minutes; remove it for cooling. Add 3 g of mixed solvent (see 4.1); put it in a high temperature furnace of 950 °C for 10 min; take it out and cool it slightly; add hydrochloric acid (see 4.4) dropwise; heat until the frit is separated from the platinum crucible; pour it into the main liquid B and combine them.

7.4.3 Strong base separation Heat and evaporate the solution (see 7.4.2.2) to a volume of about 80 mL ~ 120 mL; add 10 mL of sodium hydroxide solution (see 4.14); use ammonia water (see 4.11) to neutralize until a precipitation occurs; then, use hydrochloric acid (see 4.4) to adjust until the precipitate dissolves, and exceed for 10 mL; boil for 1 min ~ 2 min. Remove it and cool it down; add 40 mL of sodium hydroxide solution (see 4.14) at one time under constant stirring; add 8 ~ 10 drops of hydrogen peroxide (see 4.10) dropwise; boil for 3 min ~ 5 min. Remove and cool to room temperature; transfer to a 250 mL volumetric flask; use water to dilute to the mark; mix well. Use a double-layer medium-speed filter paper for dry filtration. Discard the initial filtrate.

7.4.4 Acidity adjustment and titration Pipette the above filtrate (see 7.4.3) accurately according to Table 2 into a 500 mL conical flask; add 2 drops of phenolphthalein indicator solution (see 4.19); use hydrochloric acid (see 4.4) to adjust it to red; shake while adding; continue to add hydrochloric acid (see 4.4) until the red color disappears and the solution is clear (a large amount of hydrochloric acid is used in this process) and exceed for 5 mL of hydrochloric acid (see 4.6); add EDTA solution (see 4.17) with an excess of 5 mL ~ 10 mL over the theoretical calculation value (see 4.17); the pH value of the solution, at this moment, is about 2; then, add 25 mL of hydrochloric acid-hexamethylenetetramine solution (see 4.12); heat and boil for 3 min ~ 5 min. Remove and cool to room temperature. Add 4 drops of xylenol orange indicator solution (see 4.20); use zinc standard titration solution (see 4.18.1) to titrate to red as the end point (do not record the consumption of zinc standard titration solution). Add 25 mL of saturated sodium fluoride solution (see 4.15); boil for 2 min ~ 3 min. Remove it; cool to room temperature; add 1 drop ~ 2 drops of xylenol orange indicator solution (see 4.20); use zinc standard titration solution (see 4.18.1) to titrate again to red as the end point.