Re: Phreeqci questions

["Cory Dalton" <c_dalton@xxxxxxxxxxx>]

David--

Thanks for your rapid response, and you seem to have cleared up most of  the problems we were having.  We have run through the data set to perform the evaporations.  In the output file we only get one of the evaporations to show up.  Is this the nature of the beast or are we missing something?  I have attached a copy of a sample of one our files we are processing.

Thanks again,

Cory

Center for Environmental Studies

Geology Department

University of Akron

Akron, OH

(330)972-8348

 

----Original Message Follows----

From: "David L Parkhurst"

To: "Cory Dalton"

Subject: Re: Phreeqci questions

Date: Tue, 15 Jul 2003 09:21:53 -0600

> First, most of the data we are using gives alkalinity in the form of

bicarbonate. The question that we have is should this data be entered

under the heading of "Alkalinity", "C", or "C(IV)" to produce the best

results.

You should enter the data as "Alkalinity" and add a field to show that it

is as HCO3, default is as CaCO3. I am assuming the units are mg/L. The

input file looks like this:

-units mg/L

Alkalinity 73 as HCO3

> We were also wondering if there was a straight forward way to essentially

simulate evaporation on our samples and see what mineral phases precipitate

out and at what concentrations. We have tried to do this via the steps

outlined in Example 4 (p.209) of the PHREEQC user's guide but were met with

little success, and we're unsure if it was due to differences between the

programs or whether we were not fully grasping the concept of how to do

this type of reaction in PhreeqcI.

I can't tell what problem you were having. Evaporation is accomplished by

removing water. The initial solution normally has 1 kg water after the

initial solution calculation. That is about 55.5 moles of water. If you

want to evaporate 90 percent of the water, you must remove about 50 moles

of water. Example 2 removes 52.73 moles or 95 percent of the water.

For precipitation of solids, you should probably first simulate the

evaporation and then look at the saturation indices for minerals that you

think might precipitate. Minerals that have positive saturation indices

could precipitate.

One further complication is that you probably want to stay in equilibrium

with atmospheric CO2 during the simulations. You need to add an

EQUILIBRIUM_PHASES data block including CO2(g).

Once you decide which minerals you want to let precipitate, add them to the

EQUILIBRIUM_PHASES data block with 0 moles present initially. PHREEQC will

precipitate them when they reach saturation by evaporation.

David

Any help or suggestions you may be able to offer us would be greatly

appreciated.David Parkhurst (dlpark@xxxxxxxx)

U.S. Geological Survey

Box 25046, MS 413

Denver Federal Center

Denver, CO 80225

Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled

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