Hello Dr. Parkhurst:
I am currently doing some solubility studies of
clay minerals and I want to use the phrqeeqc code to simulate what is occurring
in the reactions. problem is I have tried several different ways to describe the
system to phrqeeqc and have collected the resulting outputs but I am not sure if
the method I am using is best suited for what I am looking for since
none of the test cases threats this problem directly. in addition, comparison
with other speciation codes is a little difficult because of my
uncertainty.
I am therefore hoping that you can give me some
insight.
a typical run involves adding:
~2.0g Solid A + ~2.0g Solid B to 30ml of
equil. solution (1.0 M MgCl2 + 0.001 M HCl; initial pH = 3.412) and seal in a
LDPE bottle and allowed to equilibrate for several days.
1) What is the best approach you would
suggest in defining this system to Phrqeeqc?
2) Which pH sould I be using? the initial pH
or the final pH (pH at the end of run)
Secondly,
What is the best approach for multiple runs, each
having a different quantity of starting solid, or a different volume of solution
with a different initial pH (and subsequently different final pH). I have tried
SOLUTION_SPREAD keyword but to handled all the variations in the runs I would
have to use multiples.
e.g. in the above run: Solid A =
2.0g, 2.3g, 1.6g, 1.8g and 2.5g
Solid B = 2.0g, 1.2g, 1.7g, 2.3g, and 2.2g
Vol. = 10ml, 15ml, 20ml, and 30 ml.
initial pH = 3.412,
7.800, 10.235
from my understanding, I would have to
describe three solutions, two phases for each quantity, or am I wrong. I am
having a problem with the treatment of a fixed amt. of a solids in a fixed vol.
of solution at a specific starting pH vs.
describing the ending solution.
any suggestions would be helpful, thanks in
advance.
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