Mechanisms governing the fate of trace metals during coal combustion a
re reviewed, and new theoretical results interpreting existing data ar
e presented. Emphasis is on predicting the size-segregated speciation
of trace metals in pulverized coal-fired power plant effluents. This f
acet, which determines how trace metals originally in coal impact the
environment, is controlled by fuel composition and combustion conditio
ns. Multicomponent equilibrium calculations are used to predict vapori
zation/condensation temperatures for antimony, arsenic, beryllium, cad
mium, chromium, lead, mercury, nickel, and selenium compounds in coal
combustion flue gases, for a representative Illinois No. 6 coal. Exper
imental data show that equilibrium provides a good guide on the effect
of chlorine on the partitioning of pure nickel, cadmium, and lead sal
ts, introduced separately into a gaseous turbulent diffusion flame wit
hin an 82 kW combustor. Metal nuclei coagulation mechanisms are examin
ed using existing computer codes, and these predict that coagulation d
oes not allow condensed metal nuclei to be scavenged by existing coal
ash particles. Rather, literature data on trace metal enrichment on sm
all particles are consistent with processes of reactive scavenging of
metals by larger particles, and it is suggested that these processes m
ight be exploited further to convert these metals into environmentally
benign forms.