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

Authors

  • Haile A Mengistu Wayne County Community College District, 801 W Fort St., Detroit MI 48226, USA
  • Abera Tessema Department of Geology, University of Limpopo, Turfloop Campus, Sovenga 0727, Private Bag X1106, South Africa
  • Molla B Demlie 1. School of Geological Sciences, University of Kwazulu-Natal, Private Bag X54001, Durban, South Africa; 2. GNS Science, Private Bag 2000, Taupo, New Zealand
  • Tamiru A Abiye School of Geosciences, University of the Witwatersrand, Private Bag X3, PO Wits 2050, Johannesburg, South Africa
  • Oddvar Roeyset Norwegian Institute for Water Research (NIVA), Gaustadalléen 21, N-0349 OSLO, Norway

DOI:

https://doi.org/10.4314/wsa.v41i1.19

Keywords:

phosphate, adsorption, hydrous ferric oxide, surface complexes, equilibrium constants

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. The results provide a consistent set of model equilibrium constant (log K) values at 25° C and 100 KPa for the following reactions:

>FeOH + PO43- + 3H+ = >FeO-H2PO4 + H2O (log K1int = 19.0)

>FeOH + PO43- + 2H+ = >FeO-HPO4- + H2O (log K2int = 14.3 ± 0.17)

>FeOH + PO43- + H+ = >FeO-PO42- + H2O (log K3int = 8.32 ± 0.27)

These results differ significantly from previously-published estimates of log K2int and log K3int [1–3], and provide a more accurate fit 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). The results provide a close fit 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

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Published

2015-01-28

How to Cite

Haile A Mengistu, Abera Tessema, Molla B Demlie, Tamiru A Abiye, & Oddvar Roeyset. (2015). Surface-complexation modelling for describing adsorption of phosphate on hydrous ferric oxide surface. Water SA, 41(1 January). https://doi.org/10.4314/wsa.v41i1.19

Issue

Vol. 41 No. 1 January (2015): Water SA

Section

Research paper

License

Copyright (c) 2022 Haile A Mengistu, Abera Tessema, Molla B Demlie, Tamiru A Abiye, Oddvar Roeyset

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