MECHANISMS OF INORGANIC PARTICLE FORMATION DURING SUSPENSION HEATING OF SIMULATED AQUEOUS WASTES

The fate of cadmium, lead, and nickel contained as nitrates in aqueous droplets was studied in a laboratory-scale furnace. Trimodal particle size distributions were observed. Metal partitioning between a residual mode (particle aerodynamic diameter, D(p,aero) > 7-mu-m) and an intermediate mode (1-mu-m > D(p,aero) > 7-mu-m) was consistent with the dependence of particle porosity on condensed-phase transformations during nitrate decomposition. In addition, ultrafine particles were produced. In the nickel experiments, where vaporization was not a reasonable mechanism for inorganic aerosol formation, it was found that 30-35% of the particles had aerodynamic diameters of less than 1-mu-m. Furthermore, a preponderance of cenospheres was observed in the large particle size fractions. It is conjectured that the fragmentation process of cenosphere bursting produced the submicron aerosol. In the cadmium and lead experiments, the amount of submicron particles produced was in qualitative agreement with the amount of metal oxide calculated to vaporize.