Research On Migration Law Of Heavy Metal Remediated By Woody Plants In Coal Mine Reclamation Area

Phytoremediation, which had been developed in recent years, was one of the important means of regulating the soil heavy metal pollution, and it had been paid attention to by many scholars at home and abroad. Based on the reclamation characteristics of coal mine reclamation areas in Huainan, the thesis selected Datong ecological wetland (DTEW), Panyi mine reclamation area (PYRA) and Xinzhuangzi mine reclamation area (XZRA) as the research objects and analyzed as well as studied the pollution characteristics of soil heavy metals in reclamation areas. It showed that the soil in reclamation areas was contaminated by heavy metals in different degrees and that Cd was the main inducing factor of soil heavy metal pollution in reclamation areas. On the basis, the thesis, sifting through different species of woody plants, researched the migration law of heavy metals in the coal gangue-soil-woody plants system by means of the trend simulation and mathematical modeling.(1) Through the research on the ability of the woody plants in different reclamation areas to absorb and accumulate different heavy metals, it showed the type differences of reclamation. The differences and differentiation occurring among different species happened among the same species, and the different ecotypes were formed, which affected the ability of the same woody plants to absorb and accumulate the same heavy metal.(2) According to the content of heavy metals in gangue collected at the different time in different reclamation areas, the thesis, through the trend analysis, studied the desorption law of heavy metals in gangue under the covering soil. The findings revealed the desorption law in this situation followed the negative exponential equation, and they showed the desorption rate of heavy metals in gangue in reclamation areas mainly repaired by woody plants was higher than that of heavy metals in gangue in reclamation areas mainly repaired by herbaceous plants. It proved that plant roots could accelerate the desorption of heavy metals in gangue in reclamation areas.(3) Through the analysis of the correlation between heavy metals in the underlayer covering soil and the covering soil thickness, pH, water content, hole degree, organic matter, available potassium, available phosphorus as well as cation exchange capacity, the thesis determined the main factors. Adopting the multiple linear regression, the thesis removed abnormal factors, and it established the influence factor migration models of different heavy metals in the system of gangue and the upper covering soil, such as Cd, Cu, Mn and Pb.(4) According to the characteristics of woody plant roots in absorbing and accumulating heavy metals in the soil, the thesis put forward a new sampling scheme in order to study the migration law of heavy metals in the soil-root interface system. The findings could be revealed in the two aspects. On one hand, if the ability of woody plants to absorb and accumulate heavy metals was great, their migration ability was great accordingly, and the migration law followed the cubic curve model along the roots; if the ability of this kind was reduced with roots, their migration ability was gradually weak as well, and the migration law made the transition from a cubic curve model to a linear model. At the same time, the thesis, using the Kriging method, established Kriging models with different profiles at different stages, which had the characteristics of plant accumulation. Through a large number of heavy metal content data in the soil and woody plants, the thesis, using the trend fitting approach, found that the distribution law of heavy metals in the rhizosphere soil-the root zone as well as in the woody plants system followed a cubic curve model:y=a3X3+a2X2+a1x+ao.(5)According to the process during which woody plants absorbed and accumulated heavy metals in the reclamation areas, the thesis, combined with the accumulation mechanism of heavy metals in woody plants, refined the physiological structure characteristics of woody plants. By using the thought about the pharmacokinetic compartment model, it established a two-compartment mathematical model and a three-compartment mathematical model reflecting how woody plants absorbed and accumulated heavy metals, and it built the space-time model about stems as well. They were as follows:Two-compartment mathematical model:Note: The migration rate of heavy metals (The rate at which heavy metals migrate from the soil to the roots was a constant).Note: The content of heavy metals in soil was a fixed value. Three-compartment mathematical model: Space-time model about stems:(6) According to the characteristics of woody plant roots in absorbing and accumulating heavy metals in the soil, in terms of methodology, the thesis brought forth a method and system for determination of heavy metals migration trends in soil. Based on the characteristics of the coal mine reclamation areas, it fully and systematically discussed the migration law of heavy metals in the gangue soil-woody plant system, and it, using the thought about pharmacokinetics, established a migration model of heavy metals in the woody plants system theoretically, thus providing ideas and methods for the quantitative study of the migration and accumulation of heavy metals in woody plants system as well as the reasonable selection of the quantitative calculation models.