地下煤火土壤典型重金属砷迁移规律

通过火区土壤采样，研究了不同温度条件（25，50，70 ℃）目标火区各土壤层（Ⅰ，Ⅱ，Ⅲ，Ⅳ，Ⅴ，Ⅵ）对砷的吸附解吸特性。实验结果表明：火区各土壤对砷的吸附量随外加砷浓度的增加而增大，并随温度增加而增加；解吸量变化趋势一致，即解吸量随吸附量的增减而增减。结合实验数据，采用Freundlich模型拟合火区土壤对砷的等温吸附过程，分析了拟合参数KF及其变化趋势：25 ℃时，各土壤层对As吸附的KF值大小依次为Ⅳ>Ⅴ>Ⅵ>Ⅲ>Ⅱ>Ⅰ，与各土壤层的CaCO3含量基本一致；50 ℃时各土壤层对As吸附的KF值大小依次为Ⅵ>Ⅳ>Ⅲ>Ⅴ>Ⅱ>Ⅰ，与各土壤层pH和CaCO3含量基本一致；70 ℃时各土壤层对As吸附的KF值大小依次为Ⅰ>Ⅲ>Ⅱ>Ⅳ>Ⅵ>Ⅴ，与pH基本呈相反的变化趋势；形态分析表明残渣态As含量随土壤有机质含量增加而增加，随土壤pH值变化则呈相反的趋势。采用火区土壤样，构建不同土壤柱开展了各土壤层及复合土壤层土柱淋滤实验，结果表明淋滤初期土壤对砷的释放速度最快，砷跟随淋滤液快速向下迁移；淋滤中、后期土壤对砷的释放速度减小，砷在土壤中的迁移逐渐平衡；在火区土壤砷吸附解吸特性与土柱林滤实验基础上，采用COMSOL软件，模拟研究了内加砷源、表层土壤加砷、外加砷源条件下土壤柱内重金属砷的迁移，结果表明：单层土壤柱数值模拟结果与实际土壤柱淋滤实验结果基本相符；内加砷、表层加砷及外加砷复合土柱数值模拟结果表明，土柱砷含量随土柱温度增加而增加，土壤温度是影响土壤砷迁移的主要因素之一。

Migration of typical heavy metal As in the soil of underground coal fire

In the present paper，the authors conducted experiments on the samples of the soil of the Daquanhu coal fire at different temperatures (25，50，70 ℃) for analyzing the adsorption and desorption characteristics of typical heavy metal to the soil layers (Ⅰ，Ⅱ，Ⅲ，Ⅵ，Ⅴ，Ⅳ) at different depth for the same sampling site of the fire zone.Results show that the amount of adsorption of As to soil increases with the increase of As concentration added to the soil.And it also varies up and down with the increase and decrease of temperature.Desorption of As varies up and down with the same trend of the adsorption.With the experiment data，the authors fitted the trend of the isothermal adsorption of typical As to these soil layers by using the Freundlich model.The key parameter KF for this model，which indicates the capacity of As adsorption to soil layers，was quantified as different equations for each soil layer.At the temperature of 25 ℃，the parameter KF for each layer has the trend of Ⅳ>Ⅴ>Ⅵ>Ⅲ>Ⅱ>Ⅰ，which shows the same change as the change of the CaCO3 content for each layer.At the temperature of 50 ℃，the parameter KF for each layer has the trend of Ⅳ>Ⅵ>Ⅲ>Ⅴ>Ⅱ>Ⅰ，which shows the same change as the change of the pH value and the CaCO3 content of soil layers.At the temperature of 70 ℃，the parameter KF for each layer has the trend of Ⅰ>Ⅲ>Ⅱ>Ⅵ>Ⅳ>Ⅴ，which shows the opposite change with the change of the pH value.With these soil samples，soil columns for each layer were established，including a column for the integrated soil layer with all layers.Result from leaching experiments show that the releasing rate of As was fast at the beginning of leaching which indicates the As move downward quickly with the leaching liquid movement.At the middle and late stage of leaching，the releasing rate reduces slowly to reach an equilibrium sate.In the present paper，numerical simulations also were made to study the change of migration of As at different conditions，i.e.，the inner As adding condition，the surface As adding condition，and the external As adding condition.Single layer simulation shows the same movement of As as the experiments which verified the reliability of simulation method.Integrated soil simulation shows that the As content within the soil column increases with the increase of temperature which indicates the soil temperature is the major factor for the As migration.