Mixing and evaporation prior to infiltration

[Merche]

Dear Phreeqc users:

I would be very grateful if you could advise me with a script:

I want to develop a single-cell model of the salt balance of an aquifer in an agricultural area. As a first step, I need to simulate the input of rainwater mixed with irrigation water that recharge the aquifer in proportions 0.8:0.2 respectively. This recharge water undergoes evaporation before infiltrating (concentration factor 5.0 and 44.4 moles of water lost). I want to verify if the recharge water generates calcite, dolomite and aragonite precipitation and to calculate the amounts of precipitate.

To do so, I have used the script that I indicate below. First I mixed the two types of water, then I used the equilibrium phases function for the calcite, aragonite and dolomite and finally, I simulated the evaporation of 44.4 moles of water. I would really appreciate if you could tell me if the procedure and steps indicated in the script are correct.

TITLE Mezcla lluvia y riego
SOLUTION 1  Agua lluvia
    temp      19
    pH        6.2
    units     mg/l
    density   1.00
    Ca        22
    Mg        0.6
    Na        2.1
    K         0.1
    Alkalinity 5. as HCO3
    S(6)      1.4
    Cl        3.2
SAVE solution 1
END
SOLUTION 2  Agua riego
    temp    23.61
     pH      7.50
    units    mg/l
    density   1.00
    Ca       187.6
    Mg       56.14
    Na       293.2
    K         21.54
    Cl        415.5
    Alkalinity      236.1 as HCO3
    S(6)            324.6
SAVE solution 2
END
TITLE Mezcla de las aguas
MIX 1
    1      0.8
    2      0.2
SAVE solution 3
END
Use solution 3
EQUILIBRIUM_PHASES 1
Calcite 0 0
Dolomite 0 0
Aragonite 0 0
SAVE SOLUTION 4
END
TITLE Proceso evaporacion 5fc
USE solution 4
REACTION 1
    H2O     1
    -44.4 moles in 1 step
SAVE solution 5
END


On the other hand, the resulting saturation indices indicate slight supersaturation of calcite and aragonite (0.16 and 0.01 respectively), but do not indicate the amount of moles precipitated. How could I calculate them with Phreeqc?

Thank you very much in advance!

Kind regards

[dlparkhurst]

On principle, I do not deem scripts to be correct. It is up to you to decide if it is doing the calculation that you expect.

Your final simulation is as follows:

Code: [Select]

TITLE Proceso evaporacion 5fc
USE solution 4
REACTION 1
    H2O     1
    -44.4 moles in 1 step
SAVE solution 5
END
If you want to equilibrate with minerals, you need to add EQUILIBRIUM_PHASES. Note that calcite and aragonite will not coexist in equilibrium except under very rare circumstances. The calculation will only form one of the two minerals. In most low-temperature, natural environments, calcite is more stable than aragonite.