PHREEQC APPLICATION EXAMPLES
Most of these examples stem from Appelo and Postma, 2005. Geochemistry, groundwater
and pollution, 2nd ed.
The examples have been rewritten for PHREEQC version 3.
- Equilibrium Reactions
- Ca2+ / F- in equilibrium with
fluorite ( CaF2 )
explains high F- concentration in African Rift Valley waters.
- Dissolution of calcite ( CaCO3 )
depends on the CO2 pressure.
Mixing causes subsaturation which explains cave formation in karst areas and coastal zones.
- The Al concentration in water depends on Gibbsite
( Al(OH)3 ) equilibrium.
- Both at low and high pH, the Al concentration may exceed
the drinking water limit.
- Ca and SO4 concentrations diverge when
gypsum (CaSO4.2H2O) precipitates
from an evaporating brine.
- The series of salts that precipitate from
evaporating seawater can be computed using Pitzer equations for calculating activities.
- Ion exchange
- Surface complexation
- Zn sorption edge, % Zn sorbed as function of pH and the Zn concentration.
- CO2 sorption on oxy-hydroxides
is important in natural systems and must be included in the Dzombak and Morel database.
- Kinetic reactions
- Pressure effects on reactions
- Application examples
- Modeling isotope fractionation
- Multicomponent diffusion
- Multicomponent diffusion can be upgradient, contrary to Fick's laws,
as explained in a column example.
- PHREEQC's multicomponent module can be checked by calculating CaCl2 diffusion profiles:
- Compare with the Nernst equation which gives the diffusion
coefficent of a salt from its constituent ions. Charge on the tracer, or diffusion in a concentrated solution
give different results!
- Compare with classic PHREEQC, which calculates with one and
the same diffusion coefficient for all species.
- Multicomponent diffusion of seawater in a fresh water sediment is
different for cations and anions.
- Multicomponent diffusion of tracers in clays is a function of the
tracer diffusion coefficient and diffuse double layer effects such as anion exclusion and enhancement of cation transport.
- Surface or interlayer diffusion can be significant for strongly sorbed cations such as Cs+.
- Electro-migration: principles explains the effects of applying an electric potential gradient over a column.
- Diffuse Double Layer calculations
- The membrane properties of clays depend on the extent of the diffuse double layer.
- Colloid transport
- Ferrihydrite, with sorbed Uranium, can be transported as colloid through a column.
- Specific Conductance
- Solution density calculations
- Utilities