Solidification/stabilization of toxic metal wastes using coke and coal combustion by-products

A study has been conducted to evaluate the potential of a special scrubber waste, NISCO Cyclone Ash (NCA), which contains substantial calcium oxide and calcium sulfites/sulfates for solidification/stabilization (S/S) of toxic metal wastes. The mineralogical compositions of the NCA and a class “C” fly ash have been characterized by X-ray diffraction (XRD). Hydrated mixtures of these wastes have been examined by XRD and found to form ettringite. Low concentrations of As (15 μg ml−1), Ba (500 μg ml−1), Cr (15 μg ml−1), Pb (15 μg ml−1), and Zn (1000 μg ml−1) were added to these hydrated mixtures and found to be successfully immobilized and solidified, as determined by the Toxicity Characteristic Leaching Procedure (TCLP). In addition, the mineralogy, chemistry and leaching characteristics of these combined waste products and their interactions with toxic metals are discussed.