土壤中六价铬离子在低温环境中的迁移规律研究

Migration of hexavalent chromium ions in soils at low temperatures

为了探究复合土体中六价铬离子在寒区低温环境中的迁移规律,设置了4个不同土体配合比,掺入不同质量分数的水泥(C),脱硫石膏(S),对标准养护28 d后的复合土体进行上表面、下表面和环境3个方向的降温处理,而后进行电感耦合等离子质谱仪(ICP-MS)和低温核磁共振仪(LT-NMR)实验。结果表明,进行三温降温后的土体温度曲线呈现出先快速下降后缓慢下降的趋势,土体温度通过热传递由表及里传递负温;不同配合比下的土体均呈现两侧边缘处离子浓度高于中心处,随温度降低铬离子浓度增加;T 2弛豫时间的特征峰面积和第一峰值明显减小,所对应的第一峰孔隙区间0.001~0.117μm在-5.4℃至-14.4℃时基本不变,第二峰与第三峰面积减小,结冰量增加;温度对铬离子迁移具有重要影响且结冰量与铬离子浓度相关系数高达0.91;大孔隙的结冰速率远高于中孔及小孔隙,冰透镜体的增加导致了Cr^6+的迁移并在低温区聚集。研究表明,低温环境对复合土体中重金属离子迁移有重要影响。

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 T 2 relaxation time were significantly reduced,and the corresponding first peak pores between 0.001μm and 0.117μm 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.