Geochemical and Hydrological Reactivity of Heavy Metals in Soils - Chapter 12

Trong ba thập kỷ qua, hai cách tiếp cận chung đã được đề xuất trong các tài liệu mô tả sự tương tác của sulfate trong đất. Các phương pháp tiếp cận đầu tiên là có tính chất hóa học nơi các mối tương quan nhiệt động lực học với sự biệt hóa của các cation và anion có mặt trong dung dịch đất và tương tác với bề mặt đất là các cơ chế chính. Những mô hình này có thể được gọi như các mô hình hóa học. . | 12 Kinetic Modeling of Sulfate Transport in a Forest Soil H. Magdi Selim George R. Gobran Ximing Guan and Nicholas Clarke CONTENTS Introduction Multireaction Kinetic Model Model Formulation Sulfate Transport Case Study Field Site Description and Soil Sampling Sequential Leaching Modeling Equilibrium Sorption Linear and Nonlinear Kinetic Sorption Model Predictions BC Layer Summary Acknowledgments References INTRODUCTION Over the last three decades two general approaches have been proposed in the literature for describing the interactions of sulfate in soils. The first approach is that of a chemical nature where thermodynamic interrelationships with speciation of cations and anions present in soil solution and the interaction with the soil surface are the major mechanisms. These models may be referred to as chemical models. Examples of such models include that of Cosby et al. 1986 Reuss and Johnson 1986 De Vries et al. 1994 among others. A common feature of these models is that both ion exchange and aluminum hydrolysis reactions are similar. Their capability of quantifying these processes varies according to whether the interactions are 2003 by CRC Press LLC under batch conditions vs. when transport is included. In addition transport mechanisms can be the simple mixing cell type or the convective-dispersive type where finite difference or element methods for solving simultaneous sets of equations are included Cosby et al. 1986 . A common theme of all these chemical models is the failure to accurately describe the retention and reactions of sulfate in soils. In addition the sorption of the sulfate in all these chemical models is based on either Freundlich or Langmuir approaches. Both types are empirical where they are included simultaneously with the chemical models. In addition both approaches assume that equilibrium is valid that is that the local equilibrium assumption is dominant.