talal almeelbi surface complexations of phosphate adsorption by iron oxide
TRANSCRIPT
Talal Almeelbi
Surface Complexations of Phosphate Adsorption by Iron Oxide
Outline
Introduction Surface Complexation Reactions Surface Complexation Model Principles Case Study Phosphate-NZVI Modeling Summary
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.
Introduction
Distribution Coefficient
Limitations : Fails to describe reactive transport Need for a new concept to describe the chemical
interaction between solid-liquid interface.
Surface Complexation Reactions
2+ 2+
2+ + +
2+ 0 +2
SOH + (M ) SOH(M )
SOH + (M ) SOM H
2 SOH + (M ) ( SO) M 2H
aq aq
aq
aq
outer-sphere complex
inner-sphere complex
bidentate inner-sphere complex
Pierre Glynn, USGS, March 2003
Surface Complexation Reactions
For all surface reactions:0 0 0 0
exp
total intrinsic coulombic intrinsic
app int
G G G G ZF
ZFK K
RT
is variable and represents the electrostatic work needed to transport
species through the interfacial potential gradient.
Kint strictly represents the chemical bonding reaction.
0coulombicG
Electrostatic or coulombic correction factor
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.
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
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
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
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
Case Study – Modeling
Total phosphorus
Total number of surface cites
Case Study- Modeling
Case Study – Result
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.
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.
The Model – Input
The Model- Output
Fe3(PO4)2:8H2OFe2O3
Summary
The concept of SCM was applied to Fe- PO4-3
reactions. PHREEQC modeling results: ERROR! Problem:
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. )
Thank you
Q&A