Determination of Tungsten Trioxide in Tungsten Ore--The Thiocyanate Colorimetric Method

The determination of low content of tungsten in ore mainly includes ICP-AES, ICP-MS and visible spectrophotometric method. ICP-AES and ICP-MS instruments are expensive and operating costs are high, and they are not fully popularized at present. The most widely used method is thiocyanate colorimetry. This method is fast, simple, stable, and has wide application scope.

Step 1: preparation of instruments and reagents
1. sodium peroxide.
2. potassium thiocyanate (50%), used after filtration.
3. hydrochloric acid (2. 2 + 3).
4. hydrochloric acid (2.2+3) - titanium trichloride (0.038%) mixed solution: take 0.25mL commercially available titanium trichloride (15%) diluted with hydrochloric acid (2.2+3) to 100mL.
5. standard tungsten trioxide solution:

(1)Weighed 1.0000g tungsten trioxide (high purity reagent) burned at 750 C in advance, placed in a 200mL beaker, and 20mL20% sodium hydroxide solution, heated to dissolve, cooled to room temperature, and moved into the 1000mL bottle, diluted with 2% sodium hydroxide solution to the scale and shake well. This solution 1mL contains 1.00mg tungsten trioxide.

(2)Remove 100.00mL solution (1) in 1000mL volumetric flask and dilute it with 2% sodium hydroxide solution to scale. Shake well. The solution 1mL contains 100 W G tungsten trioxide.

Step 2: analysis.
A sample of 0.5000 ~ 1.0000g (with the same sample as a reagent blank) was placed in a 30mL iron crucible with 5g sodium peroxide, mixed with a small wire hook, and then covered with a thin layer of sodium peroxide at 750 C in a muffle furnace to a transparent and uniform state. Remove it, slightly cold, and place it in a 250mL beaker, which is pre heated with 50mL water, to extract the frit. Wash the crucible with water and move into the 100mL capacity bottle. The water is cooled to room temperature, then diluted to scale with water, shake well, dry or static clarification.

Remove the 2.00-10.00mL test solution into the 50mL colorimetric tube and fill the 10mL with water when the test solution is less than 10mL. Add 2.0mL50% potassium thiocyanate solution, shake well and dilute the mixture with hydrochloric acid and titanium trichloride to scale. Shake well. After 20min, the 1cm colorimeter was used as reference. The absorbance of Yu Bo was measured at 430nm for spectrophotometer. The corresponding amount of tungsten trioxide is found from the work curve.

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