The phosphorylation of chrysotile asbestos fibers with phosphorus oxychloride (POCl3): mechanism of reaction and chemical composition of the external coating

Abstract

Magnesium hydroxide and silica, which are at the base of the chemical composition of chrysotile asbestos fibers, have been treated with phosphorus oxychloride vapors and compared to chrysotile asbestos treated similarly. Thermogravimetric, evolved gas analyses, and Fourier Transform infrared spectroscopy techniques were used to identify the compounds formed and (or) adsorbed on the surface of the minerals phosphorylated at room temperature and after a heat post-treatment at 300 °C. The results obtained show that the reaction of silica with phosphorus oxychloride can be considered negligible. However, the modifications induced on magnesium hydroxide and chrysotile asbestos fibers are similar. After the chemical treatment at room temperature, it was possible to identify the presence of hydrochloric acid, phosphorus oxychloride, magnesium chloride (nH2O), and acid orthophosphate salts. In comparison, the compounds formed after the 300°C heat post-treatment were only hydrated polyphosphate salts and magnesium chloride (nH2O). It is postulated that a polyphosphorus coating is formed at the surface of the chrysotile asbestos fibers when these are treated with phosphorus oxychloride at room temperature and then treated at 300 °C after the phosphorylation process.