| Dissolved organic carbon(DOC)was an important component of soil organic carbon,which charactered as high mobility,poor stability,easy oxidation of pollutants.It can easily adsorpted the pollutant especially for the heavy metals and affected the adsorption and desorption behavior of heavy metals in soil.In this study,heavy metal cadmium(Cd)was selected as the typical representative of pollutants in PanYi coal mining area in Huainan.By determination of the selected physicochemical properties of coal gangue weathering matter and soil,Cd and DOC contents and the influencing factors,the migration and distribution characteristics of DOC were systematically analyzed in the coal gangue weathering matter-soil system.The mechanism and dynamic model for the adsorption and desorption of DOC and Cd were also summed in this research.In addition,the mechanism and dynamic model of the adsorption and desorption of Cd affected by DOC in the system were investigated as well,and established multifactor coupling function model in small scale.(1)The distribution characteristics of DOC in coal gangue weathering matter-soil system showed that the content of DOC in coal gangue weathering matter was higher than that of soil.Under the leaching of rainwater,the migration trend of DOC from coal gangue dump to surrounding soil was obvious.The coal gangue weathering matter has a great contribution to the DOC content in the surrounding soil,and the rate of contribution decreased with the increasing of the distance from the coal gangue dump.In vertical direction,the content of DOC in coal gangue weathering matter gradually increased with the increase in depth.The content of DOC in soil decreased first followed by increased.On the other hand,the content of DOC increased with the increase of temperature,pH and moisture content,and had extremely significant or significant positive correlation with organic matter,total nitrogen and available phosphorus.(2)The adsorption and desorption characteristics of DOC in coal gangue weathering matter and soil showed that the adsorption and desorption capacity of DOC on coal gangue weathering matter was lower than that of the soil,and increased with the increasing of DOC concentration.However,the desorption rate of DOC from coal gangue weathering matter was higher than that from soil.Therefore,DOC was easy to enter soil and increased the content of DOC in soil via leaching and rainwater runoff.The adsorption and desorption dynamics curves of DOC showed that there were 2 stages of adsorption and desorption,categorized as the rapid reaction stage and the slow reaction stage.The adsorption process included the rapid adsorption of 0?1h and the slow adsorption of 1.2?6h.The desorption process included a rapid desorption of 0?1h and a slow desorption of 1.2?6h.(3)The adsorption and desorption characteristics of Cd in coal gangue weathering matter and soil showed that the adsorption and desorption capacity of Cd was higher than that of the soil,and increased with the increasing of Cd concentration.On the other hand,the desorption rate of Cd from coal gangue weathering matter was higher than that of soil.Therefore,Cd was easy to entered into the soil?surface water and groundwater by leaching and rainwater runoff,leaded to secondary pollution.The adsorption and desorption dynamics curves of Cd from coal gangue weathering matter and soil showed that there were 2 stages of adsorption and desorption,categorized as the rapid reaction stage and the slow reaction stage.The adsorption process included the rapid adsorption of 0?0.5h and the slow adsorption of 1?12h.The desorption process included a rapid desorption of 0?2h and the slow desorption of 2.5?12h.(4)The adsorption and desorption characteristics of Cd in coal gangue weathering matter and soil under the influence of DOC showed that the results showed that the addition of DOC could inhibit the adsorption capacity of Cd on the coal gangue weathering matter and soil,which reduced the adsorption rate by 7.55%?15.04%.With the addition of DOC,the desorption ability of Cd for the coal gangue weathering matter and soil was improved,with the desorption rate increased by 20.10%?50.29%.Under the influence of different concentrations of DOC,with the increasing of DOC concentration,the adsorption of Cd by coal gangue weathering matter and soil decreased gradually and the desorption capacity increased gradually as well.Under the influence of DOC,the dynamics curves based on the adsorption and desorption of Cd by coal gangue weathering matter and soil showed that there were 2 stages of adsorption and desorption,categorized as the rapid reaction stage and the slow reaction stage.The adsorption process included the rapid adsorption of 0?0.5h and the slow adsorption of 1?12h.The desorption process included a rapid desorption of 0?2h and a slow desorption of 2.5?12h.(5)The model established from adsorption and desorption multifactor coupling model of Cd in coal gangue weathering matter-soil system showed that the grey correlation analysis was carried out by using grey theory to analyze the influence factors of the adsorption and desorption quantity of Cd could build the order was as follows:Cd concentration>DOC concentration>pH>temperature.Based on the regression analysis method,the model of adsorption and desorption multifactor coupling function of Cd in coal gangue weathering matter-soil system could be established under the influence of DOC,as,Y=a+bXHA+cXT+dXpH+eXcd.The relative error between the model and the measured value was small and it could be applied to the prediction and verification of the reclamation area in Huainan or similar mining areas.In conclusion,Cd was easy to be adsorbed in soil environment and could result in long-term soil contamination.Addition of DOC could significantly inhibit the adsorption ability of Cd in coal gangue weathering matter-soil system,effectively reduce the adsorption capacity of Cd and improve the Cd desorption.It provided a new idea and method in remediation technology of Cd contamination in soil. |
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