The potential use of sorbents to manage emissions of ultrafine metal nuclei from residual oil combustion was investigated by using an 82-kW-rated laboratory-scale refractory-lined combustor. Without sorbent addition, baseline measurements of the fly ash particle size distribution (PSD) and chemical composition indicate that most of the metals contained in the residual oil form ultrafine particles (~0.1 μm diameter). These results are consistent with particle formation via mechanisms of ash vaporization and subsequent particle nucleation and growth. Equilibrium calculations predict metal vaporization at flame temperatures and were used to define regions above the dew point for the major metal constituents (iron [Fe], nickel [Ni], vanadium [V], and zinc [Zn]) where vapor-phase metal and solid-phase sorbents could interact. The addition of dispersed kaolinite powder resulted in an approximate 35% reduction in the ultrafine nuclei as determined by changes to the PSDs as well as the size-dependent chemical composition.