Influence of ignition of waste fishbone on enhancing heavy metal stabilization in municipal solid waste incineration (MSWI) fly ash

Natural fishbone was found effective for heavy metal stabilization (particularly Pb) in municipal solid waste incineration (MSWI) fly ash in a previous study presented by the authors. Natural fishbone containing hydroxyapatite (HAP) could stabilize Pb and Zn under appropriate conditions; however, undesirable release of Cu and P occurred in the presence of non-HAP fraction. Therefore, ignition of fishbone for optimizing this technique was investigated. Based on thermogravimetry and differential thermal analysis, mass loss test, and X-ray diffractometry, it was found that ignition not only removed the non-HAP fraction, but also increased the crystallinity of HAP in fishbone as a function of temperature. Various ignition temperatures were carefully evaluated based on the performance of candidate fishbones in metal stabilization under designated conditions. Accordingly, fishbone ignited at 430 °C (IGN-430) was selected. Both natural and IGN-430 fishbones were involved in the stabilization of heavy metals in fly ash under various scenarios. IGN-430 provided more efficient metal stabilization than natural fishbone under the same conditions, because it supplied more fishbone HAP at the same dose. The non-HAP fraction in fishbone was the main source of released P in the leachate and presumably facilitated Cu and Zn release from fly ash. This facilitation hindered metal stabilization, the influence of which was greater at higher liquid condition. Consequently, IGN-430 fishbone is preferred to natural fishbone used for metal stabilization in fly ash, as it provided a more efficient metal stabilization without undesirable release of the other elements. A solid-like condition was even more beneficial for heavy metal stabilization in fly ash by fishbone HAP.