Comparative Pollution Toxicity and Chemical Speciation of Heavy Metals in MSWI Fly Ash with Different Particle Size Distribution

Municipal solid waste incineration (MSWI) fly ash is a collection of aggregates with different particle sizes, and the size distribution played an important role in its physicochemical and pollution characteristics. In this work, MSWI fly ash was divided into four size distributions (> 100 mesh, 100-200 mesh, 200-400 mesh, and < 400 mesh) with the negative pressure screen analyzer. The composition, structure, and morphology of MSWI fly ash, the total amounts, leaching toxicity, and chemical speciation distribution of heavy metals in MSWI fly ash varied with size distribution and was investigated. The results uncover that the phase composition of MSWI fly ash is almost the same regardless of size distribution, but the content varied. As the particle size decreases, the spherical particles of MSWI fly ash increase and its surface shape tends to be regular. There is no significant mathematical correlation between the leaching concentration or total amounts of heavy metals and size distribution of MSWI fly ash, but most heavy metals tend to deposit on fine particles. The residual and carbonate fractions form the main chemical speciation of heavy metals in MSWI fly ash, and carbonate states of high proportion facilitate the migration and leaching of heavy metals. This study highlights the importance of size distribution on enrichment of heavy metals on MSWI fly ash. And it also proposes that the influence of the incineration process, municipal wastes composition, and other factors on performances of MSWI fly ash remains to be clarified further.