YS/T 575.29-2023Methods for chemical analysis of bauxite - Part 29: Determination of available alumina and reactive silica (English PDF)

5.4 Sodium hydroxide solution (50 g/L, calculated as Na2O). Weigh 64.516 g of sodium

hydroxide into a 2000 mL beaker; dissolve in water; cool to room temperature; use water to dilute it to 1000 mL; mix thoroughly; transfer to a polyethylene bottle.

5.5 Acetic acid-sodium acetate buffer solution (pH approximately 5.7). Weigh 121 g of anhydrous sodium acetate into a 2000 mL beaker; dissolve in 700 mL of water; then add 9.6 mL of glacial acetic acid (rho = 1.05 g/mL); use water to dilute to 1000 mL.

5.6 Ammonium molybdate solution (100 g/L).

5.7 Sulfuric acid-oxalic acid-ferrous ammonium sulfate mixed solution. Weigh 10 g of ferrous ammonium sulfate into a 2000 mL beaker; add 400 mL of water to dissolve it.

Then add 60 mL of sulfuric acid (1 + 1). Weigh 10 g of oxalic acid into a 2000 mL beaker; add 300 mL of water to dissolve it. After cooling, mix with the previous solution and use water to dilute to 1000 mL.

5.8 Zinc standard titration solution (0.02942 mol/L). Weigh 2.3945 g of standard zinc

oxide (calcined in a high-temperature furnace at 800 °C ± 50 °C to constant weight);

moisten with a small amount of water; dissolve in 30 mL of hydrochloric acid (1 + 1);

cool it; transfer to a 1000 mL volumetric flask; use water to dilute to the mark; mix thoroughly.

5.9 Prepare and calibrate the disodium ethylenediaminetetraacetic acid (EDTA)

standard titrant solution (c ~ 0.05 mol/L) as follows.

a) Weigh 19.8 g of disodium ethylenediaminetetraacetic acid into a 500 mL beaker.

Dissolve the solution in 200 mL of water. Transfer the solution to a 1000 mL volumetric flask; use water to dilute to the mark; mix thoroughly.

b) Pipette three 15.00 mL portions of the zinc standard titrant solution (5.8) into separate 250 mL conical beakers. Add 80 mL of water and 2 drops of xylenol orange indicator (5.12). Adjust the solution to an orange color with aqueous ammonia (5.3). Add 15 mL of buffer solution (5.5) and 1 drop of bromocresol green indicator (5.11). Titrate with the EDTA standard titrant solution. The endpoint is reached when the solution changes from purple to green. Perform a blank test at the same time.

5.10 Silicon dioxide standard solution. Weigh 0.1000 g of silicon dioxide (wSiO2 >=

99.99%), that has been pre-calcined at 1000 °C for 2 h and cooled to room temperature, into a platinum crucible; add 3 g of anhydrous sodium carbonate; mix thoroughly. Cover the crucible with 1 g of anhydrous sodium carbonate; place it in a 950 °C furnace to melt for 12 minutes. Remove and cool it; place in a plastic cup. Leach with 200 mL of boiling water. Rinse the crucible and lid. Cool to room temperature; transfer to a 1000 mL volumetric flask; use water to dilute to the mark; mix it; store in a plastic bottle. 1 mL of this solution contains 0.1 mg of silica.

6.1 Dissolution apparatus. Microwave digester with 100 mL polytetrafluoroethylene

digestion tubes.

Note. Other dissolution apparatus may be selected based on sample characteristics.

6.2 Spectrophotometer.

8.1 Test material

Weigh 1.00 g of sample (7), accurate to 0.0001 g.

8.2 Parallel test

Perform two parallel tests and take the average value.

8.3 Blank test

Perform a blank test with the sample.

8.4 Determination

8.4.1 Place the sample (8.1) in a digestion tube; add 20.0 mL of sodium hydroxide

solution (5.4); shake well; transfer to the dissolution apparatus (6.1); keep it at 143 °C for 30 min.

Note. The holding temperature and time can be adjusted according to different samples.

8.4.2 Transfer the contents of the dissolution apparatus (8.4.1) to a 250 mL volumetric

flask with water; use water to dilute to the mark; mix thoroughly. Filter the test solution through quantitative filter paper; transfer the entire contents of the volumetric flask into a funnel; set aside the residue; place the filtrate in a 250 mL beaker.