Monitoring the species of arsenic, chromium and nickel in milled coal, bottom ash and fly ash from a pulverized coal-fired power plant in western Canada

The concentration of As, Cr and Ni and their speciation (As3+:5+, Cr3+:6+ a nd Ni0:2+) in milled coal, bottom ash and ash collected by electrostatic pr ecipitator (ESP)From a coal fire-power plant in western Canada were determi ned using HGAAS, ICP-AES and XANES. The chemical Fractionation of these ele ments was also determined by a sequential leaching procedure, using deioniz ed water, NH(4)OAC and HCl as extracting agents. The leachate was analyzed by ICP-AES. Arsenic in the milled coal is mostly associated with organic ma tter, and 67% of this arsenic is removed by ammonium acetate. This element is totally removed from milled coal after extraction with HCl. Arsenic occu rs in both the As3+ and the As5+ oxidation states in the milled coal, while virtually all (> 90%) of the arsenic in bottom ash and fly ash appears to be in the less toxic arsenate (As5+) form. Both Ni and Cr in the milled coa l are extracted by HCl, indicating that water can mobilize Ni and Cr in an acidic environment. The chromium is leached by water from fly ash as a resu lt of the high pH of the water, which is induced during the leaching. Ammon ium acetate removes Ni from bottom ash through an ion exchange process. Chr omium in milled coal is present entirely as Cr3+, which is an essential hum an trace nutrient. The Cr speciation in bottom ash is a more accentuated ve rsion of the milled coal and consists mostly of the Cr3+ species. Chromium in fly ash is mostly Cr3+, with significant contamination by stainless-stee l from the installation itself.