| With the development of the social economy,Chromium is largely applied in industry,and Chromium salt production has been a certain development as well.But large quantities of chromium-containing solid waste-chromium residue were also generated,hexavalent chromium in the leachate is a kind of strong migration,toxic pollutants.Due to large quantities of long-term and open-dumping of chromium slag,hexavalent chromium will infiltrate into soil and groundwater following with the rain or surface runoff,this will pollute the surrounding soil,groundwater and surface water,and pose a threat to human health.the safety of animals and plants around.In this research,a chromium plant in Beichen District of Tianjin was taken as study object,we study on the migration and transformation of hexavalent chromium in soil-groundwater system through the way of on-site survey,field sampling,indoor experiments and numerical simulation,and forecast and analyze the range and intensity of chromium pollution in the study area over the next 30 years furtherly.The main work and results of this resaerch are as follows:(1)We selected Tianjin Beichen District as the research area,and investigate the hydrogeological conditions,soil structure and physicochemical properties of the study area.In this study,the soil characteristics and hydrodynamic parameters of the study area were obtained by field survey.The dynamic monitoring of soil and groundwater chromium pollution in the study area was carried out,and we analyzed the pollution status.(2)The experimental study on the transformation of chromium in the soil was carried out,we selected the untreated silty and silty clay in the study area;The soil column was placed in a constant temperature and humidity incubator for dark culture to study on the transformation of chromium in soil under different moisture.The result shows that the higher the water content,the faster the rate of reduction of hexavalent chromium is.(3)Combined with the pollution and geological conditions of the surrounding areas of chromium slag,we select the uncontaminated silt and silty clay for indoor experiment to do dynamic soil column leaching.The results show that the adsorption capacity of silty clay to heavy metal chromium is greater than that of silt.We also calculate the the diffusion coefficient of chromium in the silty clay and silt were 7.49×10-4m2/d and 1.17×10-4m2/d,to provide parameters for the establishment of numerical simulation model.(4)Through the field investigation of the study area,the topography,hydrogeology,land use,chromium residue distribution and the relationship between pollution and the surrounding area are determined.We determined the crop area,calculated the irrigation system to determine the irrigation volume.(5)the study area was divided into three subranges as contaminant source,living-area and farml-area;and Hydrus-1D software was used to build a numerical model of water flow and the transport process of Cr(?)in shallow soil(0-200cm)of these three subranges;and this paper predicted the transport process of Cr(?)in the coming 30 years.The results show that Cr(?)distributes in the shallow soil randomly;and the Cr(?)in the shallow soil of study area is below the inorganic secondary pollution standards,in other words,it is pollution-free.(6)We established the Three-dimensional model of transformation of Cr in Groundwater by Visual MODFLOW.The trend forecast results show that:By the distribution of groundwater flow and geological conditions,the pollution distrubuties to the are around,and the high concentration range is constantly expanding.The content of hexavalent chromium in the pollution source is seriously excessive,so some measures still need to be taken to block or slow the spread of pollution halo. |
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