Mineralogy Characteristics and Heavy Metal Distribution of MSWI Fly Ash

Abstract

Fly ash from municipal solid waste incineration (MSWI) plants can be categorized as a highly toxic mineral material due to the potential for leaching heavy metals. The mineralogical properties of MSWI fly ash visually reflect the heavy metals distribution in the ash, and are closely related to the release and migration behaviors of heavy metals in fly ash disposal or utilization scenarios. In order to understand the distribution of heavy metals in MSWI fly ash and provide support for heavy metals control technology, comprehensive tests on the macroscopic and microscopic mineralogical characteristics of the fly ash were conducted using X-ray diffraction (XRD), scanning electron microscope, a mineral liberation analysis system, and other methods. The results showed that MSWI fly ash was a heterogeneous material of closely combined mineral and non-mineral phases. The main mineral phases identified by XRD included chlorides and calcium-bearing minerals, mainly calcite and portlandite. The element distribution analysis, conducted with a mineral liberation analyzer, revealed that heavy metals of MSWI fly ash were mainly present in three forms:uniform distribution in the non-mineral amorphous phase, isomorphism in calcite and other minerals, and adsorption on the surfaces of quartz and hematite. Most content of Cu and Cr were distributed in the non-mineral phase due to their lower volatility, while most of semi-volatile heavy metals (43.92% of Zn and 60.61% of Cd) were present in mineral phases. In particular, Cd, Cr and Zn were mainly present in calcite, hematite and silicates respectively.