Melting solidification of oily sludge with coal fly ash: Fusion characteristics, phases transformation and metals leaching behavior

Melting solidification is a promising method to achieve the harmless treatment of oily sludge (OS). In this study, the coal fly ash (CFA) was used as an additive to co-treat with OS. The effects of CFA addition on the fusion characteristics and phases transformation of OS were studied, and the leaching behavior of heavy metals after melting solidification was also evaluated. The results indicated that the addition of CFA had a synergistic effect on the thermal characteristics of OS. SiO2 and Al2O3 in CFA reacted with CaO in OS to form gehlenite (Ca2Al2SiO7), which reduced the ash fusion temperatures (AFTs) of OS. But the AFTs of mixed samples increased with the addition of CFA from 10 wt% to 50 wt%, and this might be due to more anorthite (CaAl2Si2O8) for-mation based on the gehlenite. As the increase of CFA into OS, the microstructures of co-treated mixtures were gradually loose. In addition, the leaching concentrations of heavy metals in the co-melting samples were reduced by 13.22-76.70 mg/L, which were lower than the standard limit, and the products presented low ecological risk indices. The obtained results indicated that the CFA effectively regulated the melting behaviors of OS and promoted the solidification of heavy metals, which provided a safe and stable disposal approach for OS treatment.

Automated summary

This study investigated the effects of coal fly ash (CFA) addition on the fusion characteristics and phases transformation of oily sludge (OS), and evaluated the leaching behavior of heavy metals after melting solidification. The results showed that CFA effectively regulated the melting behaviors of OS and promoted the solidification of heavy metals, providing a safe and stable disposal approach for OS treatment.