Adsorption and Desorption of Mercury(II) in Three Forest Soils in Shandong Province, China

As one of the most toxic heavy metals with persistence, bioaccumulation, and toxicity in environment, mercury and its environmental problems have caused a global concern. To fully understand the behavior and fate of mercury (Hg)(II) in forest soils, a series of batch experiments were conducted to determine the adsorption and desorption characteristics of Hg(II) by three dark brown forest soils from Mount Taishan, Laoshan Mountain, and Fanggan Village in Shandong Province, China. The adsorption solution was prepared using 0.1 mol L−1 NaNO3 as background electrolyte, with Hg(II) at rising concentration gradients of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mg L−1. Fourier transform infrared (FTIR) spectroscopy was adopted to characterize the soil samples and soil-Hg complexes. It was found that Hg(II) adsorption isotherms could be well fitted with both Langmuir and Freundlich equations. The soil from Mount Taishan had the largest potential Hg(II) adsorption capacity, though with less adsorptive intensity. The percentages of Hg(II) desorbed from all soil samples were less than 0.6%, which suggested that all the soils studied had a high binding strength for Hg(II). The soil from Mount Taishan had a higher Hg(II) desorption capacity than the other soils, which indicated that the Hg(II) deposited on the topsoil of Mount Taishan from atmosphere may easily discharge to surface water through runoff. Results of the FTIR spectroscopy showed that the three soils contained the same functional groups. The relative absorbencies of soil-Hg complexes changed significantly compared with those of the soil samples and the adsorption of Hg(II) mainly acted on the O–H, C–O, and C=O groups of the soils.