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Re: bernd 15-01-02


- Do I have access on pH in the BASIC? If not -
    how can I realize this, I need this examination of pH-value.
    I think it would be very important to implement
    the access of pH in RATES.

In Basic, you can calculate pH with the following statement: pH = -LA("H+")

- How often will carry out the loop in RATES?
    I build a little inputfile to test this but the
    results shown after, don't give any hint.
    Is it controled by TIME ?

For a specified time step, defined in one of the following, TRANSPORT,
ADVECTION, or KINETICS, the RATES data block will be evaluated 1 to many
times. The program automatically adjusts subtime steps to achieve a
tolerance (either default or defined in KINETICS) in the rate integration.
Normally, RATES are evaluated 6 times per time step. If the error estimate
from the integration from these 6 evaluations is not smaller than the
tolerance, a smaller subtime step is set and the integration begins again
and will require at least 2 6-evaluation integrations (but likely more) to
integrate over the original time step. If the moles calculated by all RATE
equations are 0, then the RATE program is only evaluated once.

- If I use the parameter ALK with the command
    If ALK < 0.0 Then ....
    the value of ALK itself was changed

The value of ALK can not be changed within the Basic program, but it may be
changed by the reaction that the KINETICS data block adds as a result of
the evaluation of the RATE program.

- see input-files above: LoII_MIX129_RATES2 gives pH=5.52
                                LoII_MIX129_RATES gives pH=6.52
- with the same input!?

Your Basic programs are pretty jumbled. The two programs probably do not
calculate the same amounts of Ca(OH)2.

- Your proposal (email 14/11/01) to rate
    with M=-ALK*0.5 doesn't work in Phreeqci 2.5;
    in Phreeqci RC1 I'm not sure.

PhreeqcI RC1 uses Phreeqc 2.5 to do the calculations, so the two programs
will give the same result. I don't remember what I proposed, but I'd say
you must find suitable rate equations for your problem.

In general:

- In a very great MIX-file I've print out all values of N and see that
    the values of N = N(5), what is N in

N NO3- 0.0 N 14.0067
N(+5) NO3- 0.0 N
N(+3) NO2- 0.0 N
N(0) N2 0.0 N
N(-3) NH4+ 0.0 N

N is the element nitrogen, which can exist as NO3- [N(5)], NO2- [N(3)],
dissolved N2 [N(0)], or ammonia species NH3 and NH4+ [N(-3)].

- If one set the Redox-condition:
    redox Fe(2)/Fe(3)
    in the solutions and then call up many MIX commands in the kind:

MIX 121
1 0.00208268
2 0.00000000
3 0.01971970
1120 0.97819763
USE equilibrium_phases 2
SAVE solution 1121

    will then the Redox-condition be current/valid for all the
    following MIXings?

"redox Fe(2)/Fe(3" only affects the initial solution calculation for a
solution. A pe calculated from Fe(2) and Fe(3) will be calculated and used
to speciate any redox elements for which a total concentration is given (so
unless you define total Mn, As, or some other redox element, it has no
effect). During batch reaction calculations like the one above (MIX 121),
the redox definition no longer has any effect.

- If I use the same MIX - number several times, does it have any
    consequences ?

The latest definition will overwrite the previous definition. The only
effect is that you can no longer "USE" the previous definition.


David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

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