Mixing Brine Water with groundwater

[rudolff16]

Hello Phreeqc experts,

A simple mixing Scenario was designed to check potential interaction or changes in chemical composition due to mixing of high salinity brine (Mine tailing water) with groundwater. For that mixing at 2 different ratios was tested (Brine Water: Groundwater ---> 0.5:0.5 and 0.75:0.25). Phreeqc input:

SOLUTION 1 Mining 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
    N(5)      11
    Br        911
    Hg        0.21
    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    1 # kg
END

SOLUTION 2 Groundwater
    temp      22.2
    pH        7.3
    units     ppm
    density   0.998
    Ca        133
    K         1.2
    Mg        29
    Cl        10
    Na        9.8
    S(6)      65 as SO4
    Alkalinity 458 as HCO3
    N(5)      0.43
    Br        0.25
    Hg        0.1
    Al        0.19
    As        0.0025
    Cd        0.0015
    Co        0.005
    Cr        0.005
    Cu        0.005
    Fe        0.02
    Mn        0.02
    Mo        0.005
    Ni        0.005
    Pb        0.005
    Zn        0.005
    -water    1 # kg
END
MIX 1 Mixing Brine:Groundwater 1:1
    1    0.5
    2    0.5

SAVE SOLUTION 3
END

MIX 2 Mixing Brine:Groundwater 1:1
    1    0.75
    2    0.25

SAVE SOLUTION 4
END

####
here is a simple comaprison between the lab results of mixing and phreeqc

Parameter            Lab                    Phreeqc
Ca                       100                      116
K                        12600                   20817
Mg                      25200                   41720
Cl                       92000                   151757
Na                      26000                    43193
SO4                    42500                   70966

As you see the results Show over estimated values calculated in PHREEQC! (by mising Ratio of 0.75:0.25 the Na concentration will even exceed the initial Na concentration of the solution 1!). How to solve that issue and optimize the results to be more resonable and match somehow the lab results?

thanks for any help or suggestion.

[dlparkhurst]

You have mixed two solutions that each have 1 kg of water. However, I suspect the lab mixed either equal masses of solution, or equal volumes of solution.

I would ignore the minor elements and use pitzer.dat to do the mixing. It allows calculation of density and volume of solution. From that information, you can mix either equal masses of solution or equal volumes.

[dlparkhurst]

Here is a simulation of mixing by mass of solution that matches your Na concentration for a 0.5:0.5 mix.

Only pitzer.dat, phreeqc.dat, and Amm.dat have the molar volume data necessary to calculate density and solution volume. I used density and volume to calculate mass of solution. However, volume and density are not required, only mass; it is possible to sum up the masses of species in solution using the SYS("aq", ...) function (and adding the mass of water) to calculate the mass of solution, in which case you can use other databases (with more elements) to do the calculation.

Code: [Select]

USER_PRINT
10 PRINT "Density, kg/L: ", rho
20 PRINT "Volume, L:     ", soln_vol
30 PRINT "Mass of soln:  ", rho*soln_vol
40 mass = rho*soln_vol
50 PRINT "Mix fraction for brine: ", 1 / mass
60 PRINT "Na, ppm: " TOT("Na")*TOT("water")*GFW("Na")/mass*1000
END
SOLUTION 1 Mining 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
    -water    1 # kg
END
MIX 1 # 1 kg of solution
1 6.0387e-01   
SAVE solution 1
END
SOLUTION 2 Groundwater
    temp      22.2
    pH        7.3
    units     ppm
    density   0.998
    Ca        133
    K         1.2
    Mg        29
    Cl        10
    Na        9.8
    S(6)      65 as SO4
    Alkalinity 458 as HCO3
    -water    1 # kg
END
USER_GRAPH 1
    -headings               Fraction Na_ppm
    -axis_titles            "Mass fraction groundwater" "Na, ppm" ""
    -axis_scale x_axis      0 1 auto auto
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 PRINT rho, soln_vol, rho*soln_vol
20 mass = rho*soln_vol
30 Na_ppm = TOT("Na")*TOT("water")*GFW("Na")/mass*1000
40 graph_x (sim_no - 5)/10
50 graph_y Na_ppm
  -end
    -active                 true
MIX 1 Mixing
    1    1
    2    0
END
MIX 1 Mixing
    1    0.9
    2    0.1
END
MIX 1 Mixing
    1    0.8
    2    0.2
END
MIX 1 Mixing
    1    0.7
    2    0.3
END
MIX 1 Mixing
    1    0.6
    2    0.4
END
MIX 1 Mixing
    1    0.5
    2    0.5
END
MIX 1 Mixing
    1    0.4
    2    0.6
END
MIX 1 Mixing
    1    0.3
    2    0.7
END
MIX 1 Mixing
    1    0.2
    2    0.8
END
MIX 1 Mixing
    1    0.1
    2    0.9
END
MIX 1 Mixing
    1    0
    2    1
END


[rudolff16]

Dear dlparkhurst,
thank you for the valuable hints. I am using modified Phreeqc database which can considere small concentrations of heavy Metalls during mixing of high salinity solution. It was configured based on sit.dat.
here I would share you the Input file. The output has confirmed the lab's results:


TITLE Mixing Brine & Groundwater
SOLUTION 1 # Brine
    temp      17.2
    pH        6.3
    units     ppm
    density   1.336
    Ca        50
    K         24500
    Mg        49000
    Cl        181000
    Na        50300
    S(6)      82100 as SO4
    Alkalinity 104 as HCO3
    #N(5)      11
    Br        941
    Hg        0.0001
    Al        0.63
    As        0.006
    Cd        0.0015
    Co        0.03
    Cr        0.005
    Cu        0.72
    Fe        0.94
    Mn        2.5
    Mo        0.04
    Ni        0.05
    Pb        0.02
    Zn        1.8
    -water    0.015
END

SOLUTION 2 # Groundwater
    temp      17.1
    pH        7.9
    units     ppm
    density   0.999
    Ca        133
    K         1.3
    Mg        30
    Cl        10
    Na        11
    S(6)      66 as SO4
    Alkalinity 437 as HCO3
    #N(5)      0.43
    Br        0.25
    Hg        0.0001
    Al        0.005
    As        0.0025
    Cd        0.0015
    Co        0.005
    Cr        0.005
    Cu        0.005
    Fe        0.01
    Mn        0.005
    Mo        0.005
    Ni        0.005
    Pb        0.005
    Zn        0.005
    -water    0.0345
END

MIX 1 # Mixing Brine: Groundwater M 1:1
    1    0.5
    2    0.5
EQUILIBRIUM_PHASES 1
    Fix_pH    -6.7 HCl
SAVE SOLUTION 3
SELECTED_OUTPUT 2
    -file                 C:\....
    -pH                   true
    -temperature          true
    -totals               Ca  K  Mg  Cl  Na  S(6)  Alkalinity
                          Br  Hg  Al  As  Cd  Co  Cr
                          Cu  Fe  Mn  Mo  Ni  Pb  Zn
END

##
As subsequent Simulation I will check the mixture chemical composition in contact with clay Sediment (Illite) and compare the simulated results to our lab expirement. For that I have to considere the Cation Exchange and Equilibrium processes as follows:
TITLE Mixing Brine with Clay Sediments
SOLUTION 1 # Brine
    temp      22.7
    pH        6.3
    units     ppm
    density   1.336
    Ca        50
    K         24500
    Mg        49000
    Cl        181000
    Na        50300
    S(6)      82100 as SO4
    Alkalinity 104 as HCO3
    #N(5)      11
    Br        941
    Hg        0.0001
    Al        0.63
    As        0.006
    Cd        0.0015
    Co        0.03
    Cr        0.005
    Cu        0.72
    Fe        0.94
    Mn        2.5
    Mo        0.04
    Ni        0.05
    Pb        0.02
    Zn        1.8
    -water    0.001
EQUILIBRIUM_PHASES 1   
    Illite-Al 0 5
    Illite-FeII 0 5
    Illite-Mg 0 5
    Calcite   0 1
SAVE SOLUTION 2
END
EXCHANGE 1
    AlX3    0.00999
    CaX2    0.22176
    FeX2    0.003915
    KX      0.04392
    MgX2    0.039735
    MnX2    9e-005
    NaX     0.00567
    -equilibrate with solution 2
    -pitzer_exchange_gammas true

SELECTED_OUTPUT 1
    -file                 C:xx
    -pH                   true
    -temperature          true
    -totals               Ca  K  Mg  Cl  Na  S(6)  Alkalinity
                          Br  Hg  Al  As  Cd  Co  Cr
                          Cu  Fe  Mn  Mo  Ni  Pb  Zn
END

Am I doing it in right way?
thanks for any Suggestion

[rudolff16]

here are the lab's result:
Parameter   Brine+Clay
pH   6
T °C   22.7
Ca   120
K   22500
Mg   48200
Cl   181000
Na   49800
SO4   79600
HCO3   NA
Br   942
Hg   0.0034
Al   1.6
As   0.003
Cd   0.003
Co   0.41
Cr   0.005
Cu   0.11
Fe   0.75
Mn   16
Mo   0.005
Ni   0.19
Pb   0.12
Zn   2.1

[dlparkhurst]

Rather than equilibrating with the minerals, I would simply look at saturation indices in your brine/clay solution to see whether equilibrium is reasonable.

Similarly, I would start by assuming no mineral reaction and equilibrating exchange with solution 1 to see how much the composition changes.

[rudolff16]

Dear dlparkhurst,
after simple run without Equilibrium or Exchange reactions, the results Show Minerals at Equilibrium: Alunite, and supersaturated: Goethite, Hematite. Where the Minerals: Calcite, Gypsum, Al(OH)3a, Fe(OH)3a were undersaturated.
I may considere the Alunite during Equilibrium Phase.