Calcite precipitation instability under openchannel flow

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Calcite precipitation instability under
open-channel flow
Øyvind Hammer Physics of Geological Processes,
University of Oslo Dag K. Dysthe, Bastien
Lelu PGP
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Travertine dams and rimstones
Troll Springs, Spitsbergen (80N)
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Troll Springs, Spitsbergen
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(No Transcript)
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We can explain these patterns by assuming a
linear correlation between flow rate and
precipitation rate
Inflow
Hammer et al., EPSL, 2007
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Mechanisms for precipitation localization

• (Turbulent) flow over a flat surface and no
  evolution
• in fluid chemistry
• Thinning of a laminar boundary layer at high
  flow rates
• Complex flow
• Advection normal to calcite surface, and
  deformation of
• concentration gradients
• Stagnant zones and eddies
• Degassing (depth, agitation, Bernoulli effect)
• (Particle sedimentation, erosion, biology)

Need for modelling!
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Hydrodynamics (Navier-Stokes) across an
obstruction
Gives a velocity vector field u
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Kinetic equations (slow reactions)
CO2 H2O ? H HCO3- CO2 OH- ? HCO3-
c HCO3- CO32-
Advection
Diffusion
Boundary conditions Degassing and precipitation
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Fast reactions and charge balance
HCO3- ? H CO32-
OH- KW / H
H2O ? H OH-
q 2Ca2 H HCO3- 2CO32- OH-
0
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Precipitation rate (PWP equation)
F ?1 (H) ?2 (H2CO3) ?3 ?4 (Ca2)(HCO3-)
CO2 degassing
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CO2
Precipitation mg/cm2/day
Precipitation
CO2
Precipitation mg/cm2/day
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Experimental validation
We tried this
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Experimental validation
Reaction chamber with limestone pebbles
We tried this
Water pump
CO2
Water in
But ended up with this
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Experiment
Precipitation mg/cm2/day
Model
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Conclusions

• Hydrodynamics are important for
• pattern formation
• Diffusion is important at low flow
• rates
• Mullins-Sekerka-type fingering
• growth
• (Degassing effects not locally
• important)

Thanks to Halvor Lund, Bjørn Jamtveit, Paul Meakin