Water-Clay Interaction

[rudolff16]

Hello Phreeqc members,

A lab experiment was conducted by centrifuging clay sample with high mineralized water to check the final water chemical composition. To simulate that Experiment a Simulation in Phreeqc is needed with Output matches or Close to the patch results. I started the Simulation as follows: (after centrifuging pH changed to 6 and Temp = 22.7):

SOLUTION 1 # High mineralized water
    temp      22.6
    pH        6.2 
    units     ppm
    density   1.34
    Ca        60
    K         25100
    Mg        50300
    Cl        183000   
    Na        52100
    S(6)      85500 as SO4
    Alkalinity 104 as HCO3
    Br        911
    Hg        0.00021
    Al        0.59
    As        0.005
    Cd        0.0015
    Co        0.03
    Cr        0.005
    Cu        0.74
    Fe        0.71
    Mn        2.7
    Mo        0.04
    Ni        0.05
    Pb        0.01
    Zn        1.7
    -water    0.134 # kg

EXCHANGE 1
    X                 0.5  # 0,5 mmol exchanger
    -equilibrate with solution 1 #
    -pitzer_exchange_gammas true
SAVE SOLUTION 2

REACTION_TEMPERATURE 1
    22.7 22.6 in 1 steps

EQUILIBRIUM_PHASES 2
    Muscovite 0 1
    Calcite   1 10     
END

### comparison ####
   Lab            Phreeqc
Ca   120           93,652
K   22500   11659,62
Mg   48200   77380,92
Cl   181000   303501,63
Na   49800   41136,498
SO4   79600   102673,2
Br   942           1510,909
Hg   0,0034   0,000348304
Al   1,6           0,76374984
As   0,003   0,008292895
Cd   0,003   0,002487858
Co   0,41           0,049755778
Cr   0,005   0,003717129
Cu   0,11           1,2272751
Fe   0,75           1,1606344
Mn   16           4,3328727
Mo   0,005   0,066344429
Ni   0,19           0,08292897
Pb   0,12           0,012376263
Zn   2,1           2,1375991

Unfortunately,  the Phreeqc simulated concentrations Mg, K, Cl, SO4 are much higher than Lab-results.
Please I need your help.. what must be changed to decrese the simulated concentrations above?

[dlparkhurst]

First, you are specifying the exchange composition to be in equilibrium with solution 1. This calculation has no effect on solution 1. So, most of the reaction you are specifying is EQUILIBRIUM_PHASES. Calcite is undersaturated in your initial solution, so you are assuming that calcite is present to react. Is that reasonable? I would ignore muscovite for now.

Second, Cl and SO4 have nothing to do with ion exchange anyway. They should be relatively unchanged in an equlibration with an exchanger. Your initial solution is a very concentrated brine and is supersaturated with several evaporite minerals. It is possible that one or more of these minerals precipitated, but I'm not a brine specialist, so I would not hazard a guess as to the reactions that may occur.

Finally, I think you need to consider what you are trying to learn from this modeling.