Zinc speciation in power plant burning mixtures of coal and tires

Fly ash from the cyclone-boiler co-combustion of high-S, high volatile bituminous coal and tire-derived fuel (tdf) was studied using a variety of chemical, optical, and microbeam techniques. Fly ash, dominated by Al-Si glass with lesser amounts of coalderived carbons, Fe-spinels, and tire-derived carbons, has Zn concentrations ranging from 2200 ppm (1st ESP row) to 6900 ppm Zn (3rd ESP row). Zinc occurs in Zn-rich nanoparticles in the Al-Si glass phases and as ZnO in amorphous and crystalline nanominerals, Fe- and Zn-sulfides, Pb-Al-Fe sulfates, and Zn sulfates. Iron-rich, Al- and Ti-bearing spinels contain accessory Zn2+,Cr3+,Mn2+, and Pb2+. Fe-sulfates and phosphates nanoparticles incorporate As, Cr, V, Ni, and Zn. Fullerenes were not detected in this fly ash, potentially due to the higher temperature of combustion in the cyclone boiler. Zinc was detected by XPS, but the low binding energies mitigated against the determination of the speciation of the element.