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Effect of Freeze-Thawing Cycles on Lead and Cadmium Adsorption-desorption in Soil and Mechanism

Author: ZhangYingXin
Tutor: GuoPing；LiZhiMin
School: Jilin University
Course: Environmental Engineering
Keywords: Freeze-thaw action Pb Cd Adsorption / desorption DOM
CLC: X53
Type: Master's thesis
Year: 2011
Downloads: 223
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Abstract


Freezing and thawing process changes in soil physical phenomenon common as in northern China in many aspects affect biogeochemical processes of the ecosystem. Previous studies have reported unilateral focus on the freezing and thawing of the soil physical and chemical properties of freezing and thawing of soil heavy metal adsorption / desorption impact studies are few and far between, the thesis freezing and thawing of soil Pb and Cd adsorption / desorption the impact from the freezing and thawing of soil physical and chemical properties, adsorption equilibrium solution and the the desorption solution pH change to illustrate the freezing and thawing of soil adsorption / desorption mechanism of heavy metals; also investigated after freezing and thawing of contaminated soil, exogenous DOM (straw and sludge) leaching of heavy metals from contaminated soils and mechanisms. The main conclusions are as follows: (1) freeze-thaw action on different types of soil adsorption / desorption of heavy metals, soil adsorption and desorption of Pb and Cd are increased with the increase of Pb and Cd concentrations, Pb and Cd in four treatments soil adsorption isotherm can be very good to fit the Langmuir equation, Freundlich isotherm equation either good description of the temperature adsorption process can also be described isothermal desorption of heavy metals. Pb and Cd in the relationship between the adsorption equilibrium concentration and the amount of adsorption, there are significant differences between the amount of adsorption and desorption of the relationship between the amount and the desorption rate. Not been freezing and thawing of the soil, in the same Pb and Cd in the initial concentration of the freeze-thaw action to reduce the adsorption capacity of the soil Pb and Cd the Black Soil adsorption capacity greater than the brown earth. Freezing and thawing of the soil and has not been compared to the freeze-thaw action to promote the desorption of heavy metals in the soil and black soil in the same freeze-thaw conditions desorption capacity is less than the brown earth, the freeze-thaw action to reduce soil Pb and Cd retaining capability. The causes may change the soil pH, organic matter, cation exchange capacity and free iron oxide content of Frozen Soil decrease in the adsorption equilibrium pH of the solution is greater than the freezing and thawing of soil freezing and thawing. 2 different freezing and thawing of soil adsorption / desorption of heavy metals with the rise of the freezing temperature, the increase in the number of freeze-thaw cycles, the amount of black soil adsorption of Pb and Cd gradually reduced, but still less than the non-freeze-thaw black soil, desorption and desorption rate is gradually increased, the freezing and thawing of different moisture content of soil adsorption of Pb and Cd thermodynamic processes affect more complex, with the increase in freezing and thawing of soil moisture, heavy metals increase in the amount of adsorption, desorption reduced, when freezing and thawing of soil moisture content was 120%, the freezing and thawing of soil Pb adsorption is greater than not black soil freezing and thawing, freezing and thawing of soil moisture content within the range studied in this paper, is always less than the amount of adsorption of Cd No black soil freezing and thawing. The nature of the different freezing temperatures, different number of freeze-thaw and freeze-thaw moisture content of soil pH, organic matter, cation exchange capacity, t-test results show that the difference between them reached a significant or very significant level, which explains the different The role of freezing and thawing conditions on soil properties affect the main mechanism of soil adsorption / desorption of heavy metals. 3 freeze-thaw action on different types of soil adsorption of heavy metal equilibration time, the amount of soil adsorption of heavy metals increased with the extension of adsorption time to flatten; whole adsorption process is divided into two stages, namely rapid adsorption stage and slow adsorption phase. Whether after freeze-thaw treatment, Phaeozem and Pb adsorption equilibrium time is greater than Cd adsorption equilibrium time. After freezing and thawing of soil adsorption amount of Pb and Cd reduced and extended the time to reach equilibrium. Regardless of the freeze-thaw or not, the Elovich equation fitting heavy metal adsorption kinetics process optimal equation. Freeze-thaw action on contaminated soil leaching of heavy metals and not freezing and thawing soil, after freezing and thawing, DOM of heavy metals in the Phaeozem and dissolution rate of increase in black than brown soil. Same DOM concentration, sludge application is greater than the dissolution rate of the soil Pb straw application of Pb dissolution rate, the dissolution rate of the straw Cd in the soil is greater than the dissolution rate of the sludge Cd. With the increase of soil heavy metal pollution in time and the contamination of heavy metals, straw and sludge DOM increase in the dissolution rate of Pb and Cd showed a significant difference. The causes of that change to the freeze-thaw action contaminated soil physical and chemical properties (pH, organic matter, cation exchange capacity, and redox potential), but also by the impact of the DOM molecular size and hydrophilic component content.

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CLC: > Environmental science, safety science > Environmental pollution and its prevention > Soil Contamination and Control
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