Characterization of MWI bottom ash and its potential use as alkali-activated material precursor

Nowadays, European Union (EU) policies are focused on maintaining the value of products, materials and resources for as long as possible, moving towards a circular economy. The priority of the member states is to continue... [ view full abstract ]

Nowadays, European Union (EU) policies are focused on maintaining the value of products, materials and resources for as long as possible, moving towards a circular economy. The priority of the member states is to continue developing systems and infrastructures for selective collection. Unfortunately, there is still not enough awareness in the Europe population and most of the waste ends up mixed in landfill. According to the EU waste management hierarchy, landfilling is the least preferable option and should be limited to the necessary minimum. The most attractive option thus far to avoid waste landfilling is the incineration in waste-to-energy plants (WtE), since as well as generating energy, the volume of waste is reduced by up to 90 %. Municipal Waste (MW) can be incinerated producing the main by-product Bottom Ash (BA) as non-hazardous residue as well as Air Pollution Control (APC) as hazardous by-product. With the weathering stabilization from Municipal Waste Incineration (MWI) during 2 - 3 months, the weathered Bottom Ash (WBA) is generated. Then, its main construction application is as secondary aggregate for road sub-base. Nevertheless, this research aims to go one step forward in order to contribute in the EU’s objectives in waste management and valorisation fields. Therefore, the present study is focused on the potential use of WBA as the only precursor in the synthesis of new alkali-activated materials (AAM). Previous studies published by the authors revealed that WBA is composed by the crucial AAM components, i.e.: SiO₂, Al₂O₃, and CaO. Likewise, the bigger the particle sizes, the higher content in SiO₂. Consequently, the smaller the particle size, the higher the heavy metal content. Hence, higher potential as a AAM precursor is expected in bigger fractions. Then, the chemical characterization of WBA was conducted as a function of its particle size (0-2 mm, 2-4 mm, 4-8 mm, 8-16 mm, >16 mm, and >30 mm) by means of XRD, XRF, FT-IR, and ICP-OES. The WBA was sorted as a function of particle size, and milled below 80 µm. In addition, the availability of reactive phases has been analysed through chemical attacks with NaOH solutions. The obtained results of chemical attacks demonstrate the availability of reactive phases in all the studied fractions.