# The Levels, Speciation, and Influencing Factors of Mercury in MSWI Fly Ashes of a High Geological Background Area

## TL;DR

This study examines mercury levels in fly ash from waste incineration in Guizhou, China, finding high mercury content and environmental risks.

## Contribution

The study provides new insights into mercury speciation and influencing factors in fly ash from a region with high geological mercury background.

## Key findings

- Total mercury in fly ash ranged from 0.52 to 444 mg/kg, with a weighted geometric mean of 22.14 mg/kg.
- Most mercury exists in elemental form (over 80%), but up to 26–29% is in water-soluble or ion-exchangeable forms.
- Mercury enrichment is influenced by heterogeneous waste compositions and transient thermochemical conditions.

## Abstract

Fly ash (FA) captures most mercury (Hg) in the waste stream during municipal solid waste incineration (MSWI), and the content and speciation of Hg in MSWI fly ash (MSWI-FA) have a significant impact on the ecological environment. In this study, 245 fly ash samples were collected from 18 MSWI facilities in Guizhou Province, a fragile karst area with a high Hg background in Southwest China. The results indicate that total Hg ranged from 0.52 to 444 mg/kg among samples, while the geometric means varied from 0.85 to 223.33 mg/kg for different incinerators, with a weighted geometric mean of 22.14 mg/kg, more than double the national average. Substantial temporal variability in Hg content suggested intermittent inputs of Hg-rich waste into the MSW stream. While positive correlations (p < 0.05) were observed between Hg and chlorine, potassium, and cadmium, the moderate to low R2 values indicate that Hg enrichment is a complex multi-factor system influenced by heterogeneous waste compositions and transient thermochemical conditions. Speciation analysis revealed that most of the Hg exists in its elemental form (F4), constituting over 80% of the total Hg. However, the water-soluble fraction (F1) and the ion-exchangeable fraction (F2) each reached up to 26–29% in some samples, indicating substantial environmental mobility. These findings demonstrate that MSWI-FA in Guizhou contains elevated Hg levels, posing considerable ecological and environmental risks. Enhancing the classification and management of Hg-containing waste in MSW is critical to mitigating the environmental risks of fly ash, particularly in karst ecological areas.