Simulation experiments were conducted by using soils in the northeastern Qinghai-Tibet Plateau to explore the effects of freeze-thaw cycles on soil physicochemical properties, Pb and Cr distribution and fraction transformation. Soils were incubated at -15 ℃ for 24 h and at 5℃ for 24 h to complete a freeze-thaw cycle. The soil physicochemical properties and the fractions of Pb and Cr in soils were analyzed after serial freeze-thaw treatments. The results showed that different freeze-thaw cycles and water content affected soil physicochemical properties and fractions of Pb and Cr in soils to some extent. The cation exchange capacity increased significantly in agricultural and pastoral soils after five freeze-thaw cycles. The sand proportion of soil in an urban area decreased at 60 freeze-thaw cycles. Freeze-thaw cycles did not change the functional groups and mineral constituents of soils. The infrared peaks of soils with different freeze-thaw conditions were very similar. The freeze-thaw treatment influenced the mobility, chemical fractions of Pb and ecological risk in most of soils. The exchangeable Pb in agricultural and pastoral area increased from 0.19% to 1.52%/0.90% after 5/10 freeze-thaw cycles with 60% water content. The ecological values of Pb in urban soil were 8.32%/7.38% higher at 10/15 freeze-thaw cycles compared with the control treatment. Hence, these findings provided useful information on physicochemical properties and fraction transformation of Pb and Cr in soils undergoing freeze-thaw cycles to offer an additional insight on Pb and Cr behaviors in cold and freezing environments.

Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

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