Use of fly ash for remediation of metals polluted sediment--green remediation.

The aim of this study was to determine the possibility of using fly ash and combination of kaolinite and fly ash for the solidification/stabilization (S/S) of Ni and Zn contaminated sediment from the Krivaja river basin (Serbia), which represents an extraordinary risk to the environment and belongs to the last quality class in the Serbian sediment classification. Fly ash was used as a stabilising agent because it occurs as a secondary industrial product, so in this way two types of waste are immobilized. Microwave assisted BCR sequential extraction procedure was employed to assess potential of Ni and Zn mobility and risk to the aquatic environment. In order to determine the long-term behavior of the S/S mixture, the semi-dynamic ANS 16.1 leaching test was performed. The existing leaching method was modified and acetic acid and humic acid were also used as leachants instead of deionised water, in order to simulate possible "worst case" leaching conditions for S/S waste being disposed of in a landfill environment (acid rain, floods, etc.). S/S effectiveness was evaluated by measuring the cumulative fractions of metals leached, effective diffusion coefficients - De and leachability indices - LX. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray analyzer (EDS) along with leaching tests were implemented to elucidate the mechanisms responsible for immobilization of the Ni and Zn. The controlling leaching mechanism was found to be diffusion, in all treated samples. Overall, the test results indicated that S/S treatment was effective for immobilization of these two types of waste, and can be considered acceptable for "controlled utilization".