At present, the method of extracting tungsten mostly adopts water immersion method. Before water immersion process, tungsten scrap needs to be sintered. The sintering process directly sinters the mixed powders. During the sintering process, the dust is discharged along with the flue gas, and the valuable metal tungsten is mixed in the dust, which results in the loss of valuable metal tungsten. The unreasonable ratio of raw materials to auxiliary materials leads to the low conversion rate of tungsten when tungsten waste is used to extract tungsten.

Epoxy compounds are important intermediates in organic synthesis and chemical raw materials. The ternary ring of epoxy compounds has special tension, so it is easy to synthesize many substances needed by people through selective ring opening or functional group conversion. Epoxy compounds have been widely used in many fields such as fine chemical industry, petrochemical industry, organic synthesis, pharmaceuticals, spices and so on.

Due to the defects of concentrated sulfuric acid catalysis, scholars at home and abroad have successively used strong acid cation exchange resin, heteropoly acid, inorganic salts, solid superacid as catalysts to prepare tributyl citrate. Comparing various methods, chemists believe that Heteropoly salts with Keggin structure are the best catalytic scheme. For example, phosphotungstic acid with Keggin structure is an oxygen-containing polyacid bridged by heteroatom P and coordination atom W through oxygen atom coordination unit. It has both the function of acid catalysis and oxidation catalysis. It is a protonic acid with uniform strength and high catalytic activity.

With the improvement of science and technology level and the progress of human development level, environmental pollution is becoming more and more serious, toxic and difficult to degrade. Pollutants are more and more widespread in the air, which is harmful to biological safety and ecosystem, and restricts the progress of society.