Individual and inter-particle heterogeneity analysis of the surface and inner matrices of chelate-treated MSWI fly ash particles employing water extraction

While leaching behaviours of heavy metals in municipal solid waste incineration (MSWI) fly ash has been investigated, the impacts of heterogeneous characteristics of MSWI fly ash particles on leaching behaviours of heavy metals are uncertain. Therefore, this study investigated intra/inter-particle heterogeneity of MSWI fly ash particles using scanning electron microscope (SEM) and energy dispersive X-ray (SEM-EDX). Water extraction by Japan Leaching Test 46th (JLT46) was employed in order to remove soluble components and analyze inner matrices of MSWI fly ash particles. Therefore, heterogeneity of the surface and inner matrices of MSWI fly ash particles were investigated in this study.
Intra-particle heterogeneity analysis shows that coefficient of variation (CV values) of major elements exceeded 1.0 in some case. This means that MSWI fly ash particles are heterogeneous at even micro-scale level although they have been considered as homogeneous owing to fine particles. The results also showed that intra-particle heterogeneity might depend on mineralogical compositions of particle surface and inner matrices. Inter-particle heterogeneity analysis also shows that weight percent of major elements widely distributed. This means that fly ash particles contain major elements in widely different concentration. It suggests that MSWI fly ash particles are heterogeneous among fly ash particles. Therefore, intra/inter-particle heterogeneous characteristics of MSWI fly ash might have non-negligible impacts on leaching behaviours of heavy metals.