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SOIL PHYSICS

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

^* Corresponding author (mselim{at}agctr.lsu.edu).

This study was conducted to investigate the kinetics of arsenate [As(V)]-phosphate [P] competitive retention during transport in soils. Time-dependent batch experiments were performed to describe competitive As(V)-P sorption kinetics in Olivier (fine-silty, mixed, active, thermic Aquic Fraglossudalfs) and Windsor (mixed, mesic Typic Udipsamments) soils. Miscible-displacement experiments were also performed to quantify As(V)-P competition when anion pulses were introduced simultaneously or consecutively into water-saturated soil columns. The results demonstrated that the rates and amounts of As(V) sorption are significantly reduced by increasing addition of P. Due to competitive sorption, the presence of P resulted in increased mobility of As(V) in the soil columns. Flow interruptions indicated the dominance of time-dependent sorption during As(V) and P transport in soils. We extended the equilibrium-kinetic multireaction model (MRM) to simulate competitive retention kinetics of multiple chemical species in soils. Competitive coefficients from Sheindorf–Rebhun–Sheintuch (SRS) equation were adopted to describe the extent of As(V)-P competition. A multi-component multireaction model (MCMRM) was coupled with the advection-dispersion equation (ADE) to describe breakthrough curves (BTCs) of As(V) and P simultaneously. Model predictions of measured BTCs for competitive As(V)-P transport were achieved using rate coefficients based on inverse modeling.

Abbreviations: ADE, advection-dispersion equation • As(V), arsenate • BTC, breakthrough curve • MCMRM, multi-component multi-reaction transport model • MRM, multireaction model • P, phosphate • SRS, Sheindorf–Rebhun–Sheintuch