Ultraviolet broadband light scattering by single metal-containing droplets

The thermal evolution of monodisperse droplets of simulated metal containing wastes was studied in a drop-tube reactor by means of spectrally resolved analysis of ultraviolet broadband light scattering and Scanning Electron Microscopy techniques. The use of the broadband light source in the ultraviolet range allowed us to retrieve information on the dimensions as well as on the physico-chemical properties of the droplets/particles. Aqueous droplets of three metal salts: Ni(NO3)2*6H2O, Pb(NO3)2, Cd(NO3)2*4H2O were analyzed as a function of their concentration at ambient temperature. It was found that they could be characterized in terms of optical behaviours within two distinct spectral bands. The first one, in the deep ultraviolet, accounts for their surface properties; whereas, the second one, in the middle ultraviolet range, gives insights on the inner (volume) properties of the droplets. Preliminary studies were performed to follow the thermal history of the droplets in a temperature range of 300-800 K which covered the process of spray-drying and the transition from aqueous droplets to high viscosity and/or solid particles.