Surface-Complexation modelling for describing adsorption of phosphate on hydrous ferric oxide surface

Abstract

Adsorption of dissolved phosphate onto synthetic hydrous ferric oxide (HFO) was measured in the laboratory as a function of pH, ionic strength, and phosphate relative concentration. Experimental data were used to constrain optimal values of surface complexation reactions using a geochemical modeling code JCHESS according to the diffuse layer model. Te results provide a consistent set of model equilibrium constant (log K) values at 25° C and 100 KPa for the following reactions: (Formula Presented) These results differ significantly from previously-published estimates of log (Formula Presented) and log (Formula Presented) [1–3], and provide a more accurate ft to experimental measurements over a broad range of pH (3–12), ionic strength (0.001–0.1 mol/ℓ) and total relative phosphate concentration (12–500 µmol phosphate/g HFO). Te results provide a close ft to the experimental data within a wide range of conditions, and should be adopted in modelling the chemical speciation of phosphate in natural systems containing HFO as a predominant adsorbing material.