| Wetland is an ecological view which has the richest bio-diversity and also the most important environment for man's living, no other system can replace its functions in resisting the flood, regulating the surface flow, storing floodwater, controlling pollution etc. But the researches in the last few years indicate that the regulating surface flow functions reduce greatly because of the deceasing in the wetland area. Decline of the wetland storage ability causes the reduction of animals and plants kind. The self-purification ability of the wetland is reduced, corrode is serious in the bank, the content of nutriment and the silt content increase in he river. So the researches about wetland nitrogen distribution in space and heavy metal distribution pattern receive the great concern of scientific workers day by day. But the studies in the adsorption of wetland soil and the transformation of the heavy metal pollutant in wetland are still less. At present, the studying of sod layer soil are concentrated on the adsorption of the heavy metal onto the turf layer, there are few reports about the heavy metal adsorption on the sod layer. The sod layer is the top layer of Xianghai wetland soil. The organic matter is relatively high and easy to accumulate on sod layer, thus influences crops growth. On the other hand, the organic matter is blocking the migration of heavy metal pollutant to the deep soil and reduces the gathering of heavy metals in the deep soil. In this paper, the adsorption ability and the adsorption influencing factors of the sod layer were investigated. In this research, the physical and chemical properties of the 4 represent soil samples (Reed sod layer 1, Reed sod layer 2, Cattail sod layer 1, and Cattail sod layer 2) were determined. Classifying the soil sample as 0.076mm, 0.088mm, 0.097mm, 0.105mm, 0.125mm, 0.200mm, 0.300mm refer to《Water & Waste Water Monitor and Analytical Method》. In order to calculate the correcting value of the various kinds of composition according to dried sample, the water content of all particle size soil samples were determined. In this paper, the organic matter content is represented by the total organic carbon, because the total carbon (TC) is made up by the total organic carbon (TOC) and inorganic carbon (IC), so if TC and IC are determined, the difference of the two is TOC. This paper reveals the thermodynamics and dynamics characteristics of the Pb, Cd adsorption on the Xianghai wetland soil, and discusses the factors influencing the adsorption ability, including pH value, absorption time, soil particle size, soil sample weight. Experiments of influence factor were carried out under room temperature, and the solution volume was 50mL. Besides special conditions of each experiment, the samples employed was all Reed sod layer 1, the pH value of the solution before adsorption was 6.0±0.1, shaking time was 3h, filtering, the filtrate was adsorbing balancing solution. The thermodynamics experiment adopted the optimal soil sample weight, pH value and adsorption time. Compounded a series of Pb, Cd solutions separately using 0.005mol/LCaCl2 as the background solution, the concentrations ofCd were: 35, 40, 45, 50, 60, 70, 80, and 90 μmol/L, the solution volume was 50mL. Meanwhile, compounded a mixed solution of Pb and Cd according to the following concentrations: 35, 40, 45, 50, 60, 70, 80, and 90 μmol/L, the solution volume was 50mL, the interference experiment was also adopted the optimal soil sample weight, pH value and adsorption time. The concentration of Pb, Cd in the initial and equilibrium solution were determined by FAAS. The adsorption Γis calculated by difference subtraction. The adsorption results were described using Langmuir and Fruendlich isotherms. The experimental results show that the adsorption of Pb and Cd onto sod layer soils could be described using Langmuir and Fruendlich isotherms with the correlation coefficient significant at the confidence level of p=0.01(n=8), and the adsorption interference existed between Cd and Pb to the sod layer soil. The maximum adsorption of Pb is 3 times greater than that of Cd. The maximum adsorption of Pb and Cd increases with increasing in the contents of TOC, and Fe, Mn oxides in the soils, implying that the soil characteristics, such as TOC, and Fe, Mn oxides in the soils, are important internal factors influencing adsorption of Pb and Cd to wetland soils, and pH is the external parameters influencing adsorption of Pb and Cd to sod layer soils. The kinetic adsorption characters of Pb, Cd onto the soil sod layers were studied through column experiments. Fill 5.0 g (dry weight) 0.3 mm soil samples in 3 columns separately, and the soil sample height was 13mm. There was a thin layer (3mm) absorbent... |
