GB/T 17863-2008Determination of thorium in thorium ores (English PDF)

2.1 Principle

The sample is decomposed by fusion with sodium peroxide at high temperature, and an appropriate amount of ferric chloride carrier is added during leaching (for samples with many impurities or a high phosphate content, triethanolamine and EDTA are used instead for a coarse separation). The test solution is passed through an N263 extraction chromatographic column, which removes most of the elements that interfere with the determination of thorium. In acidic solution at pH 1.65 to 1.70, EDTA complexes thorium in the ratio 1+1. Using the xylenol orange - semi-xylenol orange - naphthol green B ternary mixed indicator, which gives a sharp end-point jump, the solution is titrated with EDTA standard solution until it changes from purple-red or bright peach-pink to bright yellow-green, which is the end point.

2.2 Reagents

Unless otherwise stated, use only reagents of recognised analytical grade and distilled or deionised water in the analysis.

2.2.1

Sodium peroxide.

2.2.2

Ferric chloride solution, 150 g/L.

2.2.3

Triethanolamine solution, 1+1.

2.2.4

EDTA solution, 50 g/L.

2.2.5

Hydrochloric acid solution, 1+1.

2.2.6

Sodium hydroxide solution, 10 g/L.

2.2.7 Nitric acid - tartaric acid solution

Dissolve 2 g of tartaric acid in water, add 30 mL of nitric acid (rho = 1.42 g/cm3) and dilute to 100 mL with water.

2.2.8 Nitric acid solution

Place 15 mL of nitric acid (rho = 1.42 g/cm3) in a 100 mL volumetric flask and dilute to 100 mL with water.

2.2.9 Nitric acid - tartaric acid solution

Dissolve 2 g of tartaric acid in water, add 15 mL of nitric acid (rho = 1.42 g/cm3) and dilute to 100 mL with water.

2.2.10

Hydrochloric acid solution, 1+3.

2.2.11

N263 (methyltrialkylammonium chloride).

2.2.12

No. 200 gasoline.

2.2.13

Secondary octanol.

2.2.14

Anhydrous ethanol.

2.2.15

Glass fibre, boiled in hydrochloric acid (2.2.10) for 0.5 h and washed clean with water before use.

2.2.16 N263 extraction chromatographic column

2.2.16.1 DA201 macroporous adsorption resin (divinylbenzene - acrylonitrile copolymer)

Use particles of 0.177 mm to 0.250 mm. Pretreat before use: soak the DA201 adsorption resin in anhydrous ethanol (2.2.14), load it into a large exchange column (2.3.5) padded at the bottom with a suitable amount of glass fibre (2.2.15), and wash it with anhydrous ethanol (2.2.14) to remove the residual initiator, until 5 to 6 drops of eluate collected on a watch glass show no turbidity when 1 drop of water is added. Drain the resin, spread it in a porcelain tray to air-dry, then keep it in an oven at a constant 80 °C until there is no smell of ethanol, and set it aside for use.

2.2.16.2 Preparation of the N263 extraction chromatographic column

Take a number of chromatographic columns (2.3.6) of identical specification. Prepare the packing: weigh 30 g of N263 (2.2.11) into a dry 500 mL beaker, add 45 g of gasoline (2.2.12) and three drops of secondary octanol (2.2.13), stir thoroughly with a glass rod, then add 30 g of DA201 macroporous adsorption resin (2.2.16.1) and stir quickly and thoroughly so that it is adsorbed uniformly; cover with a watch glass, allow to stand for 10 min to 15 min and stir again; allow to stand for 4 h to 5 h until it becomes sand-like. Soak the packing, previously soaked in water, in hydrochloric acid (2.2.10) for 2 h, and wet-pack it without air bubbles into the columns, whose bottom is padded with a suitable amount of glass fibre (2.2.15); cover the top of the column with a further layer of glass fibre (2.2.15). Control the flow rate at 1.3 mL/min to 1.5 mL/min. Before use, equilibrate the column with 20 mL of nitric acid (3.8).

2.2.17 Potassium chloride - hydrochloric acid buffer solution

Weigh 0.3728 g of potassium chloride, add 9 mL of hydrochloric acid (2.2.10), dilute to 1 L with water, and adjust to pH 1.65 to 1.70 with hydrochloric acid (3.5) and ammonia solution (3.19).

2.2.18

Urea solution, 200 g/L.

2.2.19

Ammonia solution, 1+1.

2.2.20

Xylenol orange, 5 g/L.

2.2.21

Semi-xylenol orange solution, 2 g/L.

2.2.22

Naphthol green B solution, 2 g/L.

2.2.23 Standard EDTA titrant

Weigh separately 0.1210 g, 0.2327 g and 3.7226 g of primary standard EDTA reference material (GBW 06102, complexing value 99.979%) into 150 mL beakers, dissolve in double-distilled water, transfer into 500 mL volumetric flasks, dilute to the mark with double-distilled water and mix. One millilitre of these EDTA standard titration solutions titrates 0.0325 mg Th, 0.0625 mg Th and 1.000 mg Th respectively.

EDTA titrants of appropriate concentration shall be prepared for different thorium contents, so that the volume of standard EDTA titrant consumed is as far as possible 80% to 90% of the maximum capacity of the burette.

2.2.24 Thorium standard solution

2.2.24.1

Prepare as follows: weigh an amount of thorium nitrate [Th(NO3)4·4H2O] into a beaker, add 200 mL of hydrochloric acid (2.2.10), dissolve, transfer into a 1 000 mL volumetric flask and dilute to the mark with water. According to the requirements, prepare thorium standard solutions with a thorium content of 0.1 mg/mL to 10 mg/mL.

2.2.24.2

Standardise as follows: accurately pipette at least 5 portions of thorium standard solution of the appropriate concentration into 50 mL tall-form beakers, rinse the inner wall of each beaker with 10 mL of potassium chloride - hydrochloric acid buffer solution (2.2.17), add 1 mL of urea solution (2.2.18) and titrate according to the procedure. The range of the results obtained shall be less than 3% to 5%; the arithmetic mean is taken as the standardised value.

2.3 Apparatus

2.3.1

pH meter, scale division 0.01 pH.

2.3.2

Analytical balance, scale division 0.0001 g.

2.3.3

Magnetic stirrer.

2.3.4

Voltage-regulated electric hotplate: a 0 V to 220 V voltage regulator in series with a 1 000 W electric hotplate.

2.3.5

Glass exchange column, (35 to 40) mm × 400 mm, with a stopcock at the lower end.

2.3.6

Glass chromatographic column, (7 to 8) mm × (70 to 80) mm.

2.3.7

Micro-burettes, 5 mL and 10 mL, class 1, scale division 0.01 mL.

2.3.8

Muffle furnace, 0 °C to 1 100 °C.

2.4 Sample

2.4.1

The particle size of the sample shall be less than 0.097 mm, and the sampling shall be sufficiently representative of the whole.

2.4.2

Before determination, the sample shall be dried at 105 °C to 110 °C for 2 h in a layer 4 mm to 5 mm thick and, after drying, kept in a desiccator. If the sample contains organic matter, after weighing it shall be ignited in a high-temperature furnace at 600 °C for 30 min before decomposition.

2.5 Procedure

2.5.1

Weigh 0.1 g to 0.5 g of sample (to the nearest 0.0001 g) into a 25 mL to 30 mL corundum crucible already containing 3 g of sodium peroxide (2.2.1), mix with a small glass rod, wipe the rod clean with a small piece of quantitative filter paper and place the paper on the mixture, then cover with a layer of about 1.5 g of sodium peroxide (2.2.1). Fuse in a muffle furnace at 800 °C for 5 min to 6 min, take out and cool, and place the crucible in a 150 mL beaker to which 3 drops of ferric chloride (2.2.2) have previously been added; add 3 mL of triethanolamine (2.2.3), then 2 mL of EDTA solution (2.2.4), and add 80 mL of hot water at 50 °C to 55 °C. When the melt has come away from the crucible, wash the crucible with 2 to 3 drops of hydrochloric acid (2.2.5) and water.

2.5.2

Boil the beaker containing the leach solution on a hotplate, remove, allow to cool and settle, and filter through a fast or medium qualitative filter paper. Wash the beaker and the precipitate 4 to 5 times each with sodium hydroxide solution (2.2.6). Then rinse the beaker with hot water, use this rinse water to wash the precipitate, and wash the precipitate once more with hot water; discard the filtrate. Dissolve the precipitate in the original beaker with 20 mL to 25 mL of nearly boiling hot nitric acid - tartaric acid solution (2.2.7). When dissolution is complete, wash the filter paper 1 to 2 times with hot water and combine the filtrate in the original beaker. Cool to room temperature; the solution is ready for loading on the column.

2.5.3

Transfer the test solution in two portions onto the equilibrated chromatographic column (2.2.16), wash the beaker and the column 4 to 5 times each with a total of 25 mL to 30 mL of nitric acid - tartaric acid solution (2.2.9) (about 6 mL each time) and discard the eluate. When the solution in the reservoir above the column has passed through, add 0.5 mL of hydrochloric acid (2.2.10) and discard the eluate. Then elute the thorium with 25 mL of hydrochloric acid (2.2.10) in 5 portions, collecting the thorium eluate in a 50 mL tall-form beaker. Place the beaker containing the thorium eluate on the voltage-regulated hotplate (2.3.4) and heat without boiling to concentrate the volume to about 2.5 mL.

2.5.4

Rinse the inner wall of the beaker with 6 mL to 7 mL of water, add 10 mL of potassium chloride - hydrochloric acid buffer solution (2.2.17) and 1 mL of urea solution (2.2.18), add a stirring bar and mix thoroughly on the magnetic stirrer (2.3.3). Adjust the acidity to pH 1.65 with ammonia solution (2.2.19) and hydrochloric acid (2.2.5), keeping the solution volume at 20 mL to 25 mL. On the magnetic stirrer (2.3.3), while stirring, add 1 drop of xylenol orange (2.2.20), 1 drop of semi-xylenol orange (2.2.21) and 2 drops of naphthol green B (2.2.22); when mixed, the test solution is bright peach-pink or purple-red. Continue stirring and titrate from the micro-burette (2.3.7) with standard EDTA titrant (2.2.23) of appropriate concentration until the test solution turns a distinct bright yellow-green that does not fade within 30 s, which is the end point.

2.5.5

The blank test is carried out at different times by placing about 2.5 g of sodium peroxide (2.2.1) in a corundum crucible, without sample, and fusing in a muffle furnace at 800 °C for 5 min. After cooling, carry out the determination according to the procedure using standard EDTA titrant (2.2.23) of which 1 mL titrates 0.0325 mg Th; the mean value is the blank value. Since the actual blank (generally less than 0.02 mL of titrant) corresponds to a thorium content of less than 0.0001%, it may be neglected. If the blank value is high, it shall be subtracted.

2.6 Quality control

When this standard is used, the recovery of the method shall be controlled (the recovery shall be maintained above 97%; otherwise the cause shall be found and resolved before continuing). Accurately pipette several portions of thorium standard solution (2.2.24) onto the corresponding equilibrated chromatographic columns (2.2.16) and proceed according to the procedure. Comparing the thorium content determined after passage through the column with that without passage gives the mean recovery for that batch of columns. For accurate measurements, the measured value may be divided by the actual recovery to give the result; quality control may also be carried out with the corresponding national primary certified reference materials.

2.7 Calculation of analytical results

The mass fraction of thorium is calculated using formula (1); the analytical result is reported to three decimal places:

w = V × T(Th/EDTA) / m × 100 ... (1)

where:

w - mass fraction of thorium in the thorium ore, %;

V - volume of EDTA titrant consumed by the sample, in millilitres (mL);

T(Th/EDTA) - mass of thorium, expressed in grams, equivalent to 1.00 mL of EDTA standard titrant, in grams per millilitre (g/mL);

m - mass of the test sample, in grams (g).

2.8 Precision

The precision of this method is given in Table 1.

Table 1 - Precision r, R of the N263 separation - EDTA titration method: Level 1: mean thorium content 0.0634%, repeatability critical difference r 0.0042, reproducibility critical difference R 0.0112; Level 2: mean thorium content 0.2317%, r 0.0095, R 0.0251; Level 3: mean thorium content 1.0850%, r 0.0317, R 0.0838.

3.1 Principle

The sample is fused with sodium peroxide, the melt is leached with water and filtered. The precipitate is dissolved in nitric acid solution containing tartaric acid. The test solution is passed through an N263 (methyltrialkylammonium chloride) extraction chromatographic column, on which thorium is quantitatively adsorbed; the impurities are washed off with nitric acid (15%) solution containing tartaric acid (2%), the thorium is eluted with hydrochloric acid (4 mol/L), the colour is developed with arsenazo III and the absorbance is measured at a wavelength of 660 nm.

3.2 Reagents and materials

Unless otherwise stated, use only reagents of recognised analytical grade and distilled or deionised water in the analysis.

3.2.1

Thorium nitrate [Th(NO3)4·4H2O].

3.2.2

Sodium peroxide.

3.2.3

Tartaric acid.

3.2.4

Urea solution, 200 g/L.

3.2.5

Oxalic acid solution, 50 g/L.

3.2.6

Ascorbic acid.

3.2.7

DA201 adsorption resin, 0.177 mm to 0.250 mm.

3.2.8

N263 (methyltrialkylammonium chloride).

3.2.9

No. 200 solvent kerosene.

3.2.10

Secondary octanol.

3.2.11

Nitric acid, rho(HNO3) = 1.42 g/cm3.

3.2.12

Nitric acid solution: place 15 mL of nitric acid (3.2.11) in a 100 mL volumetric flask and dilute to 100 mL with water.

3.2.13

Hydrochloric acid, rho(HCl) = 1.18 g/cm3.

3.2.14

Hydrochloric acid solution: place 33.3 mL of hydrochloric acid (3.2.13) in a 100 mL volumetric flask and dilute to 100 mL with water.

3.2.15

Sodium hydroxide solution, 20 g/L.

3.2.16 Nitric acid - tartaric acid solution

Dissolve 2 g of tartaric acid in water, add 15 mL of nitric acid (3.2.11) and dilute to 100 mL with water.

3.2.17

Ferric chloride solution, 150 g/L.

3.2.18

Triethanolamine solution, 1+1.

3.2.19

Hydrogen peroxide.

3.2.20

Anhydrous ethanol.

3.2.21 Ammonium nitrate solution

Dissolve 15 g of ammonium nitrate in water and dilute to 100 mL with water.

3.2.22 Pyridine - nitric acid solution

Dissolve 34 mL of pyridine in water, add 15 mL of nitric acid (3.2.11) and dilute to 100 mL with water.

3.2.23 Pyridine - ammonium nitrate solution

Dissolve 3 g of ammonium nitrate in water, add 5 mL of pyridine and dilute to 100 mL with water.