Determination of Tungsten Trioxide in High Molybdenum Tungsten Ores

Tungsten and molybdenum often coexist together, therefore, often contain high amounts of molybdenum in the tungsten ore, tungsten containing more than 0.5% interferes with the determination of molybdenum in tungsten ore will influence, if Mo is not removed, can not accurately determine the content of tungsten trioxide.

However, due to similar properties of tungsten and molybdenum, it is difficult to separate, using ammonium tungstate ignition gravimetric method for the classic molybdenum effect on the determination results in significantly higher and is very unstable, and 8- hydroxyquinoline gravimetric method through two filters, two adjustment solution pH, long process, and platinum in the dish precipitation in the furnace should be strictly grasp the ashing temperature, often due to operational condition is not good grasp of temperature and pH which were not stable, significantly lower.

Recently, a new method of determination has been proposed by some scholars. The specific steps include:

(1) The sample is weighed 200 ~ 300mL beaker, add ammonium fluoride, hydrochloric acid, placed in boiling water bath decomposition, removed, placed on the electric furnace concentration volume, adding perchloric acid, nitric acid, smoke, remove, slightly cold, diluted with water to 30 ~ 40mL, boil, remove, let stand cooling;

(2) Filter paper filter in the volumetric flask, washed with perchloric acid washer and filter paper 3 to 6 times, washed 1 to 4 times, remove the volumetric flask;

(3) The weighed platinum dish is placed under the funnel, the hot ammonia solution is used to purge the beaker and the filter paper to dissolve the tungstic acid;

(4) Platinum plates placed in boiling water bath to evaporate to dry, move to the electric heating furnace to drive the salt, into the high temperature furnace, burning, remove and cool. Add hydrofluoric acid, placed in a boiling water bath and evaporated to dryness, then transferred to a high temperature furnace for ignition, removed, cooled to room temperature in a desiccator, weighed and repeatedly burned to constant weight;

(5) Sodium hydride solution is added to the weighing platinum dish, placed in boiling water bath and heated to dissolve, dissolved completely removed, transferred to a volumetric flask, water to volume, mix;

(6) Pipette 2.00 ~ 10.00mL solution in 50mL colorimetric tube, add oxalic acid, sulfuric acid mixed sulfuric acid, potassium thiocyanate solution, diluted with water to the mark, mix, place 30min, the reagent blank as a reference, measure its absorbance on the spectrophotometer and find the corresponding amount of molybdenum trioxide from the working curve.

(7) The step (2) filter the resulting residue and filter paper into the iron crucible, placed on the electric oven drying, ashing, cooling after adding sodium peroxide in a high temperature furnace melting until red transparent, step (2) filter the resulting filtrate was poured into the original beaker, the liquid leaching melt, after the leaching is complete, washed with water crucible, cooled and moved into the volumetric flask, water to volume, mix, static set to clarify;

(8)Pipette the supernatant 2.00 ~ 10.00mL (less than 10.00mL water make up) in 50mL colorimetric tube, add potassium thiocyanate solution to titanium chloride - hydrochloric acid mixture was diluted to the mark, mix, place after 30min, take reagent blank as reference, measure the absorbance on the spectrophotometer and find the corresponding amount of tungsten trioxide from the working curve. Calculate the result of the analysis.

This method overcomes the conventional analysis for molybdenum trioxide effect on the determination results of tungsten was high or low, unstable and shortcomings, is a method of tungsten trioxide content simple and accurate and stable analysis and detection of high molybdenum and tungsten ores.

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