Calcite Disolution

[pia said]

Hi, i'm modeling calcite disolution in acidic water. i'm confused. i dont know if use EQUILIBRIUM_PHASES or REACTION, i don't understant the differece between both KEYWORDS.

[dlparkhurst]

EQUILIBRIUM_PHASES will dissolve or precipitate the mineral to the point of equilibrium (assuming a target saturation index zero is specified). If there is not enough mineral (moles of mineral is part of the EQUILIBRIUM_PHASE definition) to reach equilibrium, the mineral will dissolve completely and the saturation index of the resulting solution will be negative.

If you define REACTION to be the same mineral, it will dissolve in the increment(s) that you define, regardless of the saturation state of the solution. Thus, the resulting solution may be undersaturated, saturated, or supersaturated with respect to the mineral.

Look carefully at the output from these examples, especially at the saturation index for calcite.

Code: [Select]

SOLUTION 1
pH 0
Cl 1 charge
END
USE solution 1
EQUILIBRIUM_PHASES
Calcite 0 10
END
USE solution 1
REACTION 1
Calcite 1
1 moles in 5 steps
END