Surface Complexations of Phosphate Adsorption by Iron Oxide
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Transcript 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?
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
SO H + (M
2+
) aq SO H (M
SO H + (M
2+
) aq SO M H
2 SO H + (M
2+
+
2+
0
inner-sphere complex
+
) aq (SO ) 2 M 2 H
Pierre Glynn, USGS, March 2003
outer-sphere complex
) aq
+
bidentate inner-sphere complex
Surface Complexation Reactions
For all surface reactions:
G total G intrinsic G coulom bic G intrinsic Z F
0
K
app
0
K
G coulom bic
int
0
ZF
exp
RT
0
Electrostatic or coulombic
correction factor
0
is variable and represents the electrostatic work needed to transport
species through the interfacial potential gradient.
Kint strictly represents the chemical bonding reaction.
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
Initial Species
Hfo_sO6%
Hfo_sOH2+
1%
Hfo_sPO4H1%
Hfo_sOH
19%
Hfo_sOFe+
73%
The Model- Output
30
20
10
0
SI
Goethite
-10
-20
-30
-40
-50
Fe(OH)3(a)
H2(g)
H2O(g)
Hematite
Fe2O3
O2(g)
Vivianite
Fe3(PO4)2:8H2O
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