Relevance of Intra-Particle Diffusion in Modelling ...
Transcript of Relevance of Intra-Particle Diffusion in Modelling ...
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Relevance of Intra-Particle Diffusion in
Modelling Hydrocarbon Transport
through Dual-Porosity Porous Media in
the Absence and Presence of Particles
Dr. Stephane Ngueleu, Prof. Peter Grathwohl, Prof. Olaf Cirpka
Kananaskis, April 22, 2015
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Outline
► Introduction
► Objectives
► Materials and Methods
► Results and Discussion
► Conclusions
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Introduction
(Citizen Journalist Exchange, 2013)
(The Canadian Press, 2012)
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Introduction
(Energy Resources Conservation Board, 2013)
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Introduction
(Energy Resources Conservation Board, 2013)
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Introduction
(Energy Resources Conservation Board, 2013)
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Introduction
Medium type
Flow rate
Oilmass
Processes
Oil
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Introduction
Sorption
and
intra-particle diffusion
Initial state Final state
Initial state
Advection
Diffusion
Dispersion
Compound
Followed path lines
Mean path line
Aquifer material
Final state
Initial state Final stateInitial state Final state
Sorption
Diffusion
Pollutant
Particle
Inter-particle pore
Intra-particle pore
Aquifer
particle/grain
Inter-pore
Intra-pore
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Introduction
Organic particles (size ≤ 10 µm) released from soils
and tailings ponds to aquifers.
!
(Figure from en.wikibooks.org)
Thin and mature fine tailings
(approx. size < 44 µm)
(Figure from www.gardguide.com)
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Objectives
Understand through model-based analysis:
Hydrocarbon transport in saturated dual-porosity
porous media
Organic particle transport and its influence on
hydrocarbon transport
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Materials and Methods
• Porous medium: natural soil with the structure of a
clayey sand, grain size up to 2 mm.
Laboratory experiments
Organic carbon content
[weight%]
Particle density
[g cm-3]
CaCO3
[weight%]
0.25 2.84 0.7
)( OCf
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Materials and Methods
• Organic particles: natural lignite (brown coal)
weight%.5.60OCf
Fine particlesd50 = 0.8 µm
Filtered particles
Based on the size: dissolved
organic carbon (DOC)
d50 ≤ 0.45 µm
d50 : median diameter based on the number of particles
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Materials and Methods
• Lindane (gamma-hexachlorocyclohexane):
very hydrophobic in water.
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Materials and Methods
Lindane
(contaminant)
Lignite
(Organic particle)
Clayey soil
(porous medium)
• Sorption behaviour of lindane through batch
sorption experiments
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Materials and Methods• Transport simulation through column experiments
Po
rou
s
med
ium
Length:
15 cm
Diameter:
2.4 cm
0.05 mL min-1
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Materials and Methods
Injection phase Elution phase
Lindane alone
in 0 to 60 mmol L-1 NaCl
0 to 60 mmol L-1 NaCl
Lindane and organic particles
in 0 to 60 mmol L-1 NaCl
0 to 60 mmol L-1 NaCl
!(Figure from en.wikibooks.org)
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Materials and Methods
• Transport of lindane alone:
One-dimensional transport modelling
- Model with kinetic sorption
- Model with equilibrium sorption and intra-particle diffusion
• Transport of lignite particles: Model with straining and
attachment
Attachment
Straining
Particles
Aquifer
matrix
• Simultaneous transport of lindane and lignite particles
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Results and Discussion
Equilibrium sorption of lindane
• Clayey soil:
- Linear distribution coefficient (Kd): 3.38 ± 0.16
- Low sorption!
1Lkg
Linear model
CKS d
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Results and Discussion
• Lignite:
- Freundlich distribution coefficient (KFr): 707 ± 18
- Freundlich exponent (1/nFr): 0.72 ± 0.02
- High sorption!
11/n1/n1kgLmg FrFr
Freundlich model
Frn
FrCKS1
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Results and Discussion Column experiments
1 pore volume4 pore volumes8 pore volumes12 pore volumes
Injection stopped
16 pore volumes20 pore volumes
• Spatial concentration profile of lindane alone
X [cm]
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Results and Discussion
Ionic strength reduction (60 to 6 mmol L-1 NaCl) did not cause soil particle
mobilization.
5.0n
Porosity
4.0 mn
1.0imn
Dual-
porosity
Kinetic sorption
Equilibrium
sorption and
intra-particle
diffusion
• Effluent chloride and lindane concentrations
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Results and Discussion
• Effluent lindane and organic particle concentrations
Travel time of lindane reduced by 25% with lignite particles < 0.45 µm.
Fine lignite particles were completely retained in the porous medium.
Lindane with
filtered particles or DOC
(d50 < 0.45 µm)
d50 < 0.45 µm
Lindane with
filtered particles or DOC
(d50 < 0.45 µm)
Lindane with
filtered particles or DOC
(d50 < 0.45 µm)
Lindane with
fine particles
(d50 = 0.8 µm)
Lindane without
particles
d50 < 0.45 µm
Lindane with
filtered particles or DOC
(d50 < 0.45 µm)
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Results and Discussion
• Hydraulic conductivity (K) and flow field
𝟏𝟎−𝟕
𝟏𝟎−𝟓
K [m s-1]
Extension to 2-D transport
Hydraulic gradient
𝛻ℎ ≈ 0.005
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Results and Discussion
• Separate transport of organic particles and
lindane (kinetic sorption)
Contamination time [day] ½
Concentration of organic particles [mg L-1] 12
Concentration of lindane [mg L-1] 5
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Results and Discussion
Particles, 5 days Particles, 1 month
Lindane, 5 days C/CinLindane, 1 month
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Results and Discussion
Particles, 6 months Particles, 1 year
Lindane, 6 months C/CinLindane, 1 year
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Results and Discussion
• Transport of lindane alone with equilibrium sorption
and intra-particle diffusion
Z [m
]
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Results and Discussion
Z [m
]
Z [m
]
Inter-particle porosity
Intra-particle porosity
X [m]
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Results and Discussion
Lindane, 5 days Lindane, 1 month
Lindane, 6 months Lindane, 1 year
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Conclusions
Organic particles < 0.45 µm (DOC) enhanced
contaminant transport.
Organic particles > 0.45 µm were strongly retained,
leading to retarded contaminant transport.
Lindane transport was represented best when accounting
for intra-particle diffusion.
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Conclusions
Long term contamination can be an indication of back
diffusion from intra-particle pores to inter-particle pores,
not an indication of new contamination.
Pollutant
Particle
Inter-particle pore
Intra-particle pore
Aquifer
particle/grain
Inter-pore
Intra-pore
Pollutant
Particle
Inter-particle pore
Intra-particle pore
Aquifer
particle/grain
Inter-pore
Intra-pore
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Supplementary Information
(Roy and Dzombak, 1997)
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