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

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: is variable and represents the electrostatic work needed to transport species through the interfacial potential gradient. K int strictly represents the chemical bonding reaction. Electrostatic or coulombic correction factor

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- PO 4 -3 Adsorption  PO 4 -3 Recovery using NZVI  99% removal of PO 4 -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- PO 4 -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), hydrous ferric oxide, 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 Cosmochimica Acta 72: 3431–3445  Pierre Glynn, (2003) USGS, Available online, http://www.ndsu.edu/pubweb/~sainieid/geochem/PHREEQCi -course-notes/phreeqci-sorption&kinetics/( accessed Dec. 2010. ) http://www.ndsu.edu/pubweb/~sainieid/geochem/PHREEQCi -course-notes/phreeqci-sorption&kinetics/

21. Thank you

22. Q&A