Mineralogical analysis of MSWI bottom ash

It is well known that Municipal Solid Waste Incineration (MSWI) bottom ash is a very inhomogeneous material that can contain high levels of contaminants such as Cl, SO4, As, Pb or Ni. For this reason legislation in the Netherlands classifies MSWI bottom ash based on the amount of contaminants that are mobilized in leeching tests. To reduce contamination treatments, usually done in the form of washing, can be applied.

Knowing the mineralogical composition of MSWI bottom ash and its changes during washing can be very helpful in explaining this leeching behavior and predicting the behavior of bottom ash in building materials. However, determining the composition using only XRD can be difficult due to a great variability of the composition and the presence of many minerals in small amounts. For this reason additional methods were employed to characterize the bottom ash. Heavy density liquid separation was applied to remove the main components quartz and calcite and enrich other fractions for easier identification via XRD. SEM and EDX were used to get an overview of the elemental distribution and the composition of specific minerals. This information was then applied to identify all components in MSWI bottom ash, examine changes during washing and correlate this with the leeching behavior.