Simple mix without pe value

[rfembilejr]

Hi,

I know this may be a simple one. I have worked with MIX before but this time I have no pe value. Is it okay to just use the default of 4 and redox of pe? Also, I have both S and S(6) but no Cl. I would like to mix the following two solutions but then I would have a problem with percent error in the results. It seems that putting charge balance on S(6) and ignoring S is the only one that works. Does this make sense?

Thanks in advance,
RFE

SOLUTION 1
    temp      10
    pH        8
    pe        4
    redox     pe
    units     ug/l
    density   1
    Ca        20.3 mg/L
    Fe        0.08 mg/L
    K         42.5 mg/L
    Mg        13.7 mg/L
    Na        61.9 mg/L
    #S         62.7 mg/L
    Si        2.56 mg/L
    Al        173
    As        45.3
    Ba        361
    Cd        1.31
    Co        0.2
    Cr        0.9
    Cu        1.2
    Hg        0.02
    Mn        0.96
    Mo        1980
    Ni        1.52
    Pb        7.41
    Sb        784
    Sr        365
    U         0.03
    V         2.81
    Zn        5.14
    S(6)      198 mg/L charge
    -water    1 # kg

SAVE Solution 1


SOLUTION 2
    temp      10
    pH        8
    pe        4
    redox     pe
    units     ug/l
    density   1
    Ca        59.6 mg/L
    Fe        2.02 mg/L
    K         28.9 mg/L
    Mg        3.3 mg/L
    Na        67.6 mg/L
    #S         24.8 mg/L
    Si        3.96 mg/L
    Al        1590
    As        52.6
    Ba        362
    Cd        0.34
    Co        1.37
    Cr        4.72
    Cu        217
    Hg        0.45
    Mn        123
    Mo        203
    Ni        21.2
    Pb        101
    Sb        53.8
    Sr        2070
    U         0.09
    V         3.98
    Zn        298
    S(6)      68.3 mg/L charge
    -water    1 # kg
SAVE Solution 2
END

MIX 1
   1   0.7
   2   0.3
SAVE Solution 3
END

[dlparkhurst]

First, unless you have some reason to believe that the sulfate analysis is the only cause of the charge balance error, I would simply do the calculations with your original analyses.

Second, your redox state of your system is going to be uncertain regardless of what you do. The pes that you choose will affect the redox elements that are specified as totals (As, V, Mo, U, Cr, others). You need some additional information to at least get in the right ballpark. Do you know if you have dissolved oxygen, nirate, ammonia, sulfide, or methane? But really, I would ignore resolts for trace redox elements unless they are really important to your study.

[rfembilejr]

Thanks David,

This list of elements including SO4 are what I have so far. I have no data for dissolved oxygen, ammonia, sulfide, or methane. When you say "ignore the results for trace redox elements", these  trace redox elements are As, V, Mo, U, Cr, others? But for the metals e.g. Cu, Pb, Zn, Sb, etc., the resulting concentrations should be usable?

Lastly, what's the maximum number of solutions can I mix?

Thanks,
RFE

[dlparkhurst]

The pe is used to distribute redox elements for which total concentrations are defined among the redox states of the element.  Cu actually can have a couple of redox states (+1 and +2), so it depends on the database that you use whether elements are defined with multiple redox states.

There is no limit on the number of solutions that can be included, but it is unlikely that you will have enough knowledge of mixing fractions to include very many.

[rfembilejr]

Got it. :)
But just to get a quick idea of the resulting solution after mixing, the default pe of 4 should work? Assuming the solution has few oxidized species (since I have no idea of, e.g. Fe(3) or Fe(2) concentrations).
I'm using Minteq.