Utilization of waste natural fishbone for heavy metal stabilization in municipal solid waste incineration fly ash

Waste fishbone that is a rich source of hydroxyapatite (HAP) was investigated for the stabilization of heavy metals (mainly Pb) in municipal solid waste incineration (MSWI) fly ash, which has not been particularly studied to date. In the present study, the original status of fishbone and fly ash was preserved. The stabilization was initially conducted during a leaching process (Scenario A). Greater doses of fishbone and longer contact times benefited the stabilization in this scenario, and the highest Pb stabilization efficiency reached 59.31% after a 72 h-leaching process at fishbone dose of 100% (w/w). The abundant supply of Pb relative to fishbone HAP might affect the efficient stabilization. Therefore, the influence of liquid/solid (L/S) was examined for improving the stabilization under a settling condition (Scenario B). Lower L/S conditions were beneficial to the stabilization, and the highest Pb stabilization efficiency achieved was 66.35% at L/S of 1 mL/g for 24 h of settling when fishbone dose was 50% (w/w). Additionally, as the second most leachable metal, Zn was also considerably stabilized at L/S < 1.5 mL/g (solid-like conditions) in Scenario B. Cu in the leachates of both scenarios increased in the presence of fishbone. The facilitation of Cu release undesirably hindered Pb stabilization; however, this impediment presumably occurred during the leaching process rather than settling period. The solid-like condition was found to be more favorable for using fishbone HAP on the stabilization of heavy metals in fly ash. L/S and settling period were identified as the critical factors for the efficient stabilization of Pb and Zn, respectively. It is suggested that this technique not only helps treat MSWI fly ash in a low-cost and environmental-friendly approach, but also helps reduce the problems associated with waste fishbone disposal.