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| Migration of hexavalent chromium ions in soils at low temperatures |
| Received:November 05, 2018 |
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| KeyWord:heavy metal-chromium ions;low temperature environment;ICP-MS;LT-NMR |
| Author Name | Affiliation | E-mail | | ZHANG Cong-hui | College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot 010018, China | | | SHEN Xiang-dong | College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot 010018, China | ndsxd@163.com | | ZOU Yu-xiao | College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot 010018, China | |
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| Abstract: |
| In order to investigate the migration rules of chromium ions in composite soils under low-temperature environments in cold regions, four different soil mix ratios were set by mixing different mass fractions of cement (C)and desulfurized gypsum (S). The composite soils were cooled from upper surface, lower surface and environment directions after standard curing for 28 days. After this time, Inductively Coupled Plasma Mass Spectrometry (ICP-MS)and Low Temperature Nuclear Magnetic Resonance (LT-NMR)experiments were conducted. The results found that the soil temperature showed a trend of firstly a rapid decrease, and then a slow decrease after being cooled by 3℃. The soil temperature transfered the negative heat from the surface to the inside. The chromium ion concentration at both edges of all composite soils was higher than at the center and increased as temperature decreased. The characteristic peak area and the first peak of the T2 relaxation time were significantly reduced, and the corresponding first peak pores between 0.001 μm and 0.117 μm were little changed, from -5.4℃ to -14.4℃. The areas of the second and third characteristic peaks were reduced, while the amount of ice was increased. The temperature had a significant influence on the migration of Cr ions and the correlation coefficient between the amount of ice and ion concentration was as high as 0.91. The freezing rate of macro-pores was far higher than meso-pores and small-pores, and the increasing ice lens led to Cr ions migrating and aggregating at the low temperature. Research indicates that the low-temperature environment has an important influence on the migration of heavy metals in composite soil. |
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