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Modeling Competitive Arsenate-Phosphate Retention and Transport in Soils: A Multi-Component Multi-Reaction Approach

Sturgis Hall, School of Plant, Environmental and Soil Sci., Louisiana State Univ., Baton Rouge, LA 70803

View larger version (11K): [in this window] [in a new window]   Fig. 1. A schematic diagram of the multireaction model (MRM) with equilibrium, kinetic, and irreversible adsorption sites. Here C is concentration in solution, Se is the amount sorbed on equilibrium sites, S1 is the amount sorbed on kinetic sites, S2 is the amount retained on consecutive irreversible sites, and Ss is amount retained on concurrent irreversible sites. The parameters Ke, k1, k2, k3, and ks are the respective rates of reactions.

View larger version (16K): [in this window] [in a new window]   Fig. 2. Tritium breakthrough curves (BTCs) for Olivier (column 3) and Windsor (column 6) soils. Solid curves depict results from curve-fitting using the advective-dispersive equation (ADE) for non-reactive solutes.

View larger version (16K): [in this window] [in a new window]   Fig. 3. Single component As(V) and P adsorption isotherms for Windsor and Olivier soils after 24 h of reaction time. Solid and dashed curves are simulations using the Freundlich equation (Eq. [1]).

View larger version (24K): [in this window] [in a new window]   Fig. 4. Arsenate concentrations versus reaction time for Olivier and Windsor soils. Symbols are for different initial As(V) concentrations of 0.067, 0.13, 0.27, 0.53, 1.07, and 1.33 mmol L–1. Solid and dashed curves are single component multireaction model (MRM) simulations.

View larger version (19K): [in this window] [in a new window]   Fig. 5. Phosphate concentrations versus reaction time for Olivier and Windsor soils. Symbols are for different initial P concentrations of 0.32, 1.29, and 3.23 mmol L–1. Solid and dashed curves are single component multireaction model (MRM) simulations.

View larger version (23K): [in this window] [in a new window]   Fig. 6. Arsenate concentrations versus reaction time with the presence of various concentrations of phosphate for Olivier and Windsor soils. The initial As(V) concentrations were 0.13 mmol L–1. Symbols are for different initial P concentrations of 0, 0.32, 1.29, and 3.23 mmol L–1. Solid and dashed curves are multi-component multi-reaction model (MCMRM) simulations.

View larger version (21K): [in this window] [in a new window]   Fig. 7. Phosphate concentrations versus reaction time with the presence of various concentrations of arsenate for Olivier and Windsor soils. The initial P concentration was 0.32 mmol L–1. Symbols are for different initial As(V) concentrations of 0, 0.13, and 1.29 mmol L–1. Solid and dashed curves are multi-component multi-reaction model (MCMRM) simulations.

View larger version (23K): [in this window] [in a new window]   Fig. 8. Competitive sorption kinetics of As(V) and P on Windsor soils. Top: The initial As(V) concentrations was 0.13 mmol L–1. Symbols are for different initial P concentrations of 0, 0.32, 1.29, and 3.23 mmol L–1. Bottom: The initial P concentration was 0.32 mmol L–1. Symbols are for different initial As(V) concentrations of 0, 0.13, and 1.33 mmol L–1. Solid and dashed curves are multi-component multi-reaction model (MCMRM) simulations.

View larger version (28K): [in this window] [in a new window]   Fig. 9. Experimental As(V) breakthrough curves (BTCs) in Olivier (Column 1) and Windsor (Column 4) soil without addition of P. Solid curves are single-component multi-reaction model (MRM) predictions using batch kinetic parameters. The dashed curves depict MRM results based on nonlinear optimization. Arrows indicate pore volumes when flow interruptions occurred.

View larger version (28K): [in this window] [in a new window]   Fig. 10. Experimental As(V) and P breakthrough curves (BTCs) in Olivier (Column 2) and Windsor (Column 5) soil. Solid curves are multi-component multi-reaction model (MCMRM) predictions using batch kinetic parameters. The dashed curves are MCMRM simulations using kinetic parameters obtained from single component As(V) transport experiment. Arrows indicate pore volumes when flow interruptions occurred.

View larger version (24K): [in this window] [in a new window]   Fig. 11. Experimental As(V) and P breakthrough curves (BTCs) in Olivier soil (Column 3). Solid curves are multi-component multi-reaction model (MCMRM) predictions using batch kinetic parameters. The dashed curves are MCMRM simulations using kinetic parameters obtained from single component As(V) transport experiment. Arrows indicate pore volumes when flow interruptions occurred.

View larger version (26K): [in this window] [in a new window]   Fig. 12. Experimental As(V) and P breakthrough curves (BTCs) in Windsor soil (Column 6). Solid curves are multi-component multi-reaction model (MCMRM) predictions using batch kinetic parameters. The dashed curves are MCMRM simulations using kinetic parameters obtained from single component As(V) transport experiment. Arrows indicate pore volumes when flow interruptions occurred.