Multi-reaction Model Research Articles

Kinetics of Mercuric Chloride Retention by Soils

AbstractA nonlinear multireaction model was used to describe kinetic data for HgCl2 retention by five soils. A three‐parameter version of the model consisting of a reversible nonlinear (nth order, n < 1) reaction and an irreversible first‐order reaction was capable of describing HgCl2 retention data for Cecil (clayey, kaolinitic, thermic Typic Kanhapludult) and Windsor (mixed, mesic Typic Udipsamment) soils at all initial solution Hg concentrations, and data for Norwood, [fine‐silty, mixed (calcareous), thermic, Typic Udifluvent], Olivier (fine‐silty, mixed, thermic Aquic Fragiudalt), and Sharkey (very‐fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) soils at initial solution Hg concentrations below 5 mg/L. A five‐parameter version of the model, with an added reversible nonlinear reaction, provided a more accurate description of the retention data for the Norwood, Olivier, and Sharkey soils at initial solution Hg concentrations above 5 mg/L. The second reaction needed to describe the data at higher Hg concentrations suggests the presence of a second type of sorption sites, or a precipitation or coprecipitation reaction not encountered at lower Hg concentrations. Release of Hg from the soils was induced by serial dilution of the soil solution, but not all the soil Hg was reversibly retained. This was also indicated by the model. Release of soil Hg depended on the concentration of retained Hg with significant Hg release occurring only at high concentrations of retained Hg. A multireaction model is needed to describe Hg retention in soils because of the many solid phases that can remove Hg from solution.

Prediction of contaminant retention and transport in soils using kinetic multireaction models.

Mathematical models that describe the retention reactions of contaminants in the soil system are presented. Single and multireaction-type models for simultaneous retention and transport in the soil profile are discussed. Single retention models are classified into two types: equilibrium and kinetic models. Emphasis is given to the nonlinearity and kinetic behavior of solute retention processes in soils. Two-site models that include the equilibrium-kinetic types as well as the fully kinetic type are also examined. A multireaction-type model is also presented, which includes reversible and irreversible retention processes of the equilibrium and kinetic types. Advantages of the multireaction approach over the single or two-site models are discussed. The predictive capability of the two-site model and the multireaction model for their description of experimental results for phosphorus and two heavy metals (Cd and Cr) are examined.

Prediction of Contaminant Retention and Transport in Soils Using Kinetic Multireaction Models

Mathematical models that describe the retention reactions of contaminants in the soil system are presented. Single and multireaction-type models for simultaneous retention and transport in the soil profile are discussed. Single retention models are classified into two types: equilibrium and kinetic models. Emphasis is given to the nonlinearity and kinetic behavior of solute retention processes in soils. Two-site models that include the equilibrium-kinetic types as well as the fully kinetic type are also examined. A multireaction-type model is also presented, which includes reversible and irreversible retention processes of the equilibrium and kinetic types. Advantages of the multireaction approach over the single or two-site models are discussed. The predictive capability of the two-site model and the multireaction model for their description of experimental results for phosphorus and two heavy metals (Cd and Cr) are examined.

Kinetics of Chromium(VI) and Cadmium Retention in Soils; a Nonlinear Multireaction Model

Kinetics of Chromium(VI) and Cadmium Retention in Soils; a Nonlinear Multireaction Model

Retention and release of metals by soils — Evaluation of several models

Several kinetic models, including irreversible and reversible 1st, 2nd, and nth order models, and several equilibrium models, including the linear, Langmuir, two-surface Langmuir, and Freundlich models, were evaluated for their ability to describe the retention/release of Cr, Cd, and Hg by various soils. The retention/release data were obtained using a batch reaction method. In general, no single-reaction kinetic model fit the data over the entire time and concentration ranges studied for any of the metals or soils. The relationship between the amount of metal retained by the soil and the concentration of metal in solution was described by either the two-surface Langmuir or Freundlich models. A significiant fraction of the metals retained by the soil was not released to solution and was not exchangeable, indicating that some irreversible retention of the metals occurred. The results suggest that a multi-reaction model consisting of irreversible and reversible kinetic models is needed to fit all the data.