Distribution Characteristics Of Heavy Metals Speciation And The Mechanism Of Adsorption/Desorption In Poyang Lake Wetland Soil

With the growth of population,industrialization and urbanization becomefaster,the environmental pollution of Poyang Lake is increasingly serious, especiallyin heavy metal pollution of wetland soil.So the research for heavy metals in soil hasbecome a hot spot,However, the same metal as they exist in different forms in the soil,its transport or transformation characteristics and pollution nature are different, heavymetal toxicity is not only related to its total mass, species distribution is determinedby a greater extent.In this paper, the wetland soil of Poyang Lake watershed the object ofstudy,determinated its amount of Cu、Zn, and its content of various forms wasdetermined by using extraction method, and discusses its distribution characteristics,and the status of soil heavy metal pollution in the Poyang Lake wetland wereevaluated by using integrated pollution assessment method.In order to understand themigration and transformation of various forms of heavy metal in the soil, through thecorrelation,determinated the relationships between the total amount and its variousforms of heavy metal and soil properties.By the adsorption kinetics experiments,analysed the heavy metal adsorption rate of wetland soils.By the isothermaladsorption experiments, analysed the heavy metals Cu, Zn adsorption characteristicsof wetland soil.By the isothermal desorption experiments, analyzed the relationshipbetween the amount of desorption and adsorption.By changing the solution pH andtemperature, analyzed the impact of environmental factors on the adsorptioncharacteristics of heavy metals in the wetland soil.By the Cu, Zn coexist adsorptionexperiments, analyzed the strength of the adsorption capacity for the two heavy metalions on wetland soils.The main conclusions are as follows:(1)When Sampling,the water level of Poyang Lake Basin in the transition periodto the dry season, the water content of wetland soil samples are unevendistribution.the maximum is24.77%, located in the Xingzi.the minimum is6.02%, islocated in Jiujiang.Soil organic matter content is very high in Jiujiang which reached0.54mg/g, the organic matter content of other soil samples is between0.02-0.06mg/g. the pH of Poyang Lake wetland soil samples which maximum is8.45located inHukouand. A minimum which located in Ganjiang river is4.94, and the average of allis6.28.(2)The Cu, Zn content distribution of Poyang Lake wetland soil are quitedifferent, the highest value of Cu is342.54mg/kg, located in Caijiawan. Theminimum value is6.83mg/kg, located in Duchang.The content of Cu in wetland soilincleded Southern branch of Ganjiang river, the XinJiang river, Longkouport,Duchang, Xiugan and Hukou is very low within the standard national level, andthe remaining points are within the scope of the national secondary standard.Thecontent of Cu in Caijiawan soil is the highest which reaches342.54mg/kg. Themaximum content of Zn in Wetland soil is282.96mg/kg, located in Jiujiang. Theminimum is34.39mg/kg, located Duchang. The content of Zn in wetland soil ofsouthern branch of Ganjiang river, Longkou port,Duchang, Hukou and Xingzi is verylow within the standard national level, and the remaining points are within the scopeof the national secondary standard.(3)The form heavy metals Cu in Poyang Lake wetland soil is residual fraction,various forms of content in the order: residual> organic> Fe-Mn oxides> carbonatefraction> exchangeable, heavy metals Cu in each sampling point morphologicalvariation coefficients is relatively large, up to1.46.The form heavy metals Zn inPoyang Lake wetland soil is residual fraction, various forms of content in the order:residual> Fe-Mn oxides> organic> exchangeable> carbonate-bound. Sampling pointsof Zn morphological variation coefficient between0.55-0.68, compared to a smallercoefficient of variation of Cu.(4)The average of pollution index in Poyang Lake wetland soil is0.78, accordingto the warning limit pollution evaluation criteria. Which pollution index ofCaijiawanx is up to2.81, Jiujiang soil index reached1.97,so the soil heavy metals Cu,Zn content was significantly exceeded.(5)Analyzing the relevance of that By SPSS software: The relationship betweenthe content of Cu,Zn in Wetland soil showed a significant positive correlation.andshowed a significant positive correlation with the content of soil organic matter. Butshowed no significant correlation with other physical and chemical properties.Heavy metals in soil sampling points Zn carbonate soil PH state and was a significantnegative correlation, the correlation coefficient was-0.693. Heavy metals in soilsampling points Zn, Cu residual layer of soil organic matter and a significant positivecorrelation, the correlation coefficients were0.677,0.746.(6)Researching the adsorption kinetics experiments for heavy metals Cu, Zn inJiujiang, Cai Jia Wan and Rao soil showed that:Three kinds of soil adsorpted heavymetals Cu, Zn at about20min to reaching the saturation.the temperature adsorption ofheavy metals Cu in these soil are available to describe by Langmuir and Freundlichequations.about the correlation coefficient f, it is better fit the Langmuir equation,correlation coefficients were greater than0.9, up to a significant level. Three soiladsorption isotherms of Zn can be used Langmuir equation and Freundlich equation.(7)Under the same initial solution concentrations of heavy metals when the pHfrom5.5to6.5,the adsorption of Cu,Zn growed in soils with the increases ofpH.Changing the temperature, the characteristics of soil adsorption for Cu and Zn isirregular.(8)When Cu, Zn are coexistent, soil adsorption of heavy metal ions adsorbedamount is less than the amount of heavy metal ions under a single condition, there is acoexistence between the two competitive adsorption of heavy metal ions, includingCu adsorption capacity of greater than Zn.