The formation of inorganic particles during suspension heating of simulated wastes

Abstract

AbstractMeasurements of metal partitioning between the fine condensation aerosol and the larger particles produced during rapid heating of aqueous and organic solutions containing metal additives with widely varying volatilities were made in a laboratory‐scale furnace operated over a range of temperatures (900 to 1500 K). A stream of monodisperse droplets (nominal diameter of 36 μm) was injected into an isothermal, laminar drop‐tube reactor, quickly developing into a stream of droplets with heterogeneous size distribution due to droplet collision and coalescence. Aqueous solutions containing nitrates of cadmium, lead and nickel gave rise to particles with trimodal size distributions. Partitoning of the larger particles between a residual mode (particle aerodynamic diameter, Dp,aero > 7 μm) and an intermediate mode (1 μm > Dp,aero > 7 μm) is suggestive of particle porosity variation. In addition, ultrafine particles, with submicron aerodynamic diameter, were formed, both by the anticipated vaporization pathway and by an unexpected explosive fragmentation mechanism. The higher volatility of the chloride than the oxide was evidenced by an enhanced inorganic aerosol formation during the high temperature treatment of a nickel chloride solution. The oxidative burning of organometallic solutions of nickel and lead produced only particles of submicron aerodynamic size.