Improvement On Determination Of Silica Using Pyrophosphoric Acid Method And Study On Influencing Factors

Dust impairs the health of the workers in the workplace, which is the most severe occupational hazard factor in our country. Free silica contained in dust is a major cause of leading silicosis, analyzing the content of silica in dust is an important substance in occupational health monitoring. The origin of dust samples is different, and their particle sizes and substrate compositions are not the same, too. Some substrates have influence on the determination of free silica, which brought many difficulties to the monitoring works, without giving an objective evaluation for the existence of free silica in the workplaces.This topic mainly improved on pyrophosphoric acid method for the determination of free silica in dust, and researched on the influence factors for the determination of silicon dioxide, including indissolvable materials with pyrophosphoric acid, glassy materials, amorphous silica, different crystalline silicon dioxide, dust filtration and sulfide minerals.Through the above research, the pyrophosphoric acid method has been improved as follows: using phosphoric acid instead of pyrophosphoric acid, the particle size of samples is to be 200 meshes, phosphoric acid treatment temperature is controlled at the range of 235 ℃to 245 ℃temperature range, the improved method is easier to operation, and the determination results are more stable. In the study of influencing factors, we find that there is no loss in hydrofluoric acid for topaz, corundum, zircon in the indissolvable materials with pyrophosphoric acid, however, aquamarine, tourmaline and silicon carbide have different degrees of dissolution loss in hydrofluoric acid, which can affect the detection results; the combined silica contained in Glassy materials can also affect the determination of free silica; the insoluble parts of diatomite in phosphoric acid will interfere with the determination of free silica; the filtration experiments make us discover that floating dust samples can produce filtration phenomenon, so microporous membrane filtration operation should be done in the detection of floating dust samples. In the determination of dust samples containing sulfide minerals, hundreds of milligrams of ammonium nitrate are needed to make the sulfide dissolve.