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Surface Complexations of Phosphate Adsorption by Iron Oxide

Surface Complexations of Phosphate Adsorption by Iron Oxide . Talal Almeelbi . Outline . Introduction Surface Complexation Reactions Surface Complexation Model Principles Case Study Phosphate-NZVI Modeling Summary. Why P and Fe?.

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Surface Complexations of Phosphate Adsorption by Iron Oxide

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  1. Surface Complexations of Phosphate Adsorption by Iron Oxide Talal Almeelbi

  2. Outline • Introduction • Surface Complexation Reactions • Surface Complexation Model Principles • Case Study • Phosphate-NZVI Modeling • Summary

  3. Why P and Fe? • Iron Oxides present in soils, Sediments, aquatic systems, and minerals. • Phosphate resources are rapidly depleting • Excess phosphate in water is undesirable • Need statement: An efficient method for phosphate removal and recovery.

  4. Introduction • Distribution Coefficient • Limitations : Fails to describe reactive transport • Need for a new concept to describe the chemical interaction between solid-liquid interface.

  5. Surface Complexation Reactions outer-sphere complex inner-sphere complex bidentate inner-sphere complex Pierre Glynn, USGS, March 2003

  6. Surface Complexation Reactions For all surface reactions: Electrostatic or coulombic correction factor is variable and represents the electrostatic work needed to transport species through the interfacial potential gradient. Kint strictly represents the chemical bonding reaction.

  7. Surface Complexation Model Principles • Sorption on oxides takes place at specific sites. • Sorption reactions on oxides can be described quantitatively via mass law equations. • Surface charge results from the sorption reaction themselves. • The effect of surface charge on sorption can be taken into account by applying a correction factor derived from EDL theory to mass law constants for surface reactions. David A. Dzombak, François Morel,(1990), Surface complexation modeling: hydrous ferric oxide, Wiley-Interscience.

  8. Why SCM? • To determine the chemical and electrostatic forces involved in ion retention • To provide a framework that allows such processes to be modeled • To improve problem solving

  9. Case Study • Spiteri et al., (2008), Surface complexation effects on phosphate adsorption to ferric iron oxyhydroxides along pH and salinity gradients in estuaries and coastal aquifers, Geochimica et Cosmochimica Acta 72: 3431–3445

  10. Case Study • SCM - to describe the adsorption of phosphate on the iron oxide goethite, along the transition from freshwater to seawater in surface and subterranean mixing regimes. • The SCM is coupled with a 2D groundwater flow model to explore the effect of saltwater intrusion on phosphate mobilization in a coastal aquifer setting

  11. Case Study – Modeling • The SCM describes the adsorption of phosphate on goethite (FeO(OH)), the most common and stable crystalline iron (hydr)oxide in soils and sediments

  12. Case Study – Modeling Total phosphorus Total number of surface cites

  13. Case Study- Modeling

  14. Case Study – Result

  15. Conclusion • Phosphate adsorption on minerals in aquatic environments reflects the interaction the mineral surfaces and in solution, and the chemical interactions leading to the formation of aqueous and surface complexes. • (SCM) describing phosphate binding to goethite is the first step in unraveling how this interplay controls the dissolved phosphate levels in surface and subsurface estuaries • Phosphate adsorption and desorption behavior in surface and subterranean estuaries is different, due to difference in salinity-pH relationships in both settings, but also because the sorbing phase, which is transported with the flow in surface estuaries, is part of the solid matrix in a groundwater system.

  16. SCM for Fe- PO4-3 Adsorption • PO4-3 Recovery using NZVI • 99% removal of PO4-3 • 80% recovery • Idea: to use SCM to describe NZVI-phosphate sorption reactions n aqueous solutions using data from my research.

  17. The Model – Input

  18. The Model- Output Fe3(PO4)2:8H2O Fe2O3

  19. Summary • The concept of SCM was applied to Fe- PO4-3 reactions. • PHREEQC modeling results: ERROR! • Problem:

  20. References • Arai and Sparks, (2001), Journal of Colloid and Interface Science 241: 317–326 • Elzinga and Sparks, (2007), Journal of Colloid and Interface Science 308: 53–70 • David A. Dzombak, François Morel,(1990),hydrousferricoxide, Wiley-Interscience. • Spiteri et al., (2008), Surface complexation effects on phosphate adsorption to ferric iron oxyhydroxides along pH and salinity gradients in estuaries and coastal aquifers, Geochimica et CosmochimicaActa72: 3431–3445 • Pierre Glynn, (2003) USGS, Available online, http://www.ndsu.edu/pubweb/~sainieid/geochem/PHREEQCi-course-notes/phreeqci-sorption&kinetics/( accessed Dec. 2010. )

  21. Thank you

  22. Q&A

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