Abstract: Objective By improving the pyrophosphate method for determining the amount of free silica pyrophosphate in dust,the dilution process,and the filtration and washing temperature,the operation process of pyrophosphoric acid method for measuring free silica in dust has been further optimized,so that the influence factors of the determination process are significantly reduced,and the detection speed is improved,so as to ensure the timely and accurate results. Methods Dust samples were heated with 25 mL pyrophosphoric acid to 245-250 ℃ for 15 min,placed it at 60-80 ℃,poured it into 90 ℃ hot distilled water（150-200 mL）. Boil it,filter it while it was hot,and then wash it with 0.1 mol/HCl（70-80 ℃）. Finally,washed with hot distilled water at 70-80 ℃ until neutral. Electric furnace carbonization,ash between 800 ℃ and 900 ℃,and calculate the results after ash. Results The use of 25 mL of pyrophosphoric acid allowed the mercury bulb of the thermometer to be fully immersed in the pyrophosphoric acid,making it easier to operate at a digestion temperature between 245 and 250 ℃,preventing the formation of jelly due to excessive digestion temperature and affecting the normal operation of the next step. Place（60-80 ℃） and pour it into 90 ℃ hot distilled water（150-200 mL） to boil. This dilution process was easy to operate and does not produce gel like substances,avoiding the impact on the next step of operation. Filter while hot,and then wash with about 0.1 mol/L HCl（70-80 ℃）. Finally,washed with hot distilled water at 70-80 ℃ until neutral,accelerating the filtration process,shortening the detection time,and improving work efficiency. Conclusion By changing the pyrophosphoric acid dosage,dilution process and filtration washing temperature,the determination process can be further optimized,the influence factors of the determination process can be significantly reduced,and the determination speed can be significantly accelerated. The experiment proves that the optimized pyrophosphoric acid can be used to detect the free silica content in dust.

Key words: Silica, Temperature, Dilution, Filter, Measurement method, Improve