Mechanochemical treatment of incinerated municipal bottom ash in CO₂-rich environment for sustainable waste management practices

Incineration of the municipal solid waste produces huge amounts of fly and bottom ash annually. Added-value utilization of those ashes has been of great interest to many researchers worldwide. In this line, this study examined incinerated municipal solid waste under various milling conditions and in presence of CO2 environment. Thermogravimetric analysis of samples milled under air atmosphere revealed higher content of portlandite of finer particle size as observed in scanning electron microscopy images. In contrast, samples milled under CO2 environment demonstrated the presence of dolomite that its content is dependent on the rotation speed of the ball mill. The dolomite structure was confirmed with the X-ray diffraction, and it results from the chemical reaction of CO2 with different component of the waste during milling. To further understand the potential of the treated ash for different applications, we investigated the possibility of heavy metals leaching in acetic acid from the samples. The CO2-treatement of the samples greatly helped to remove heavy metals such as Pb, Co, Cr, Ni, and Zn, with about 99 % removal efficiency. While the air-treated sample did not show significant removal of those metals after the leaching test. This result is significant for targeted applications of the municipal solid waste in construction sector considering the simplicity of the combined CO2/milling treatment and which could be done at large industrial scales.