Effects of humus on the environmental activity of mineral-bound Hg: Influence on Hg volatility

The effects of three humus fractions (fulvic acid, brown humic acid and grey humic acid) on the volatility of five types of mineral-bound Hg were investigated. Fulvic acid was found to strongly promote the volatilization of Hg bound by Fe2O3, MnO2 and kaolinite, but suppressed the volatilization of Hg bound by bentonite and CaCO3. Brown humic acid was found to enhance the volatilization of Hg bound from all the tested minerals, except for Fe2O3. Grey humic acid had the weakest effect in promoting or suppressing Hg volatilization. The influence of the various humus fractions on the volatilization of mineral-bound Hg is closely related to the complexing capacity and complex stability of the particular humus material. The higher the complexing capacity and the lower the complex stability, the more prominent is the humus material in promoting Hg volatility. The Hg sorption capacity and sorption strength of the minerals, as well as their Hg speciation characteristics, limit the effect that humus has to volatilize Hg.