Amount of Exchange sites in the porous media?

[JW]

Hi,

Let's suppose the Na occupancy on a soil porous media is 1 mol/kg which is calculated from the experiment, and the porosity and dry bulk density of the soil are 0.4 and 1,500 kg/m^3, respectively. And, the soil is fully saturated.
For the reactive transport using SOLUTION_MODIFY, I realized that maintaining a volume of SOLUTION at 1 liter would be advantageous for later use of SOLUTION_MODIFY, since the chemicals are defined as mol instead of molarity in SOLUTION_MODIFY. Am I right?
For this reason, if I want to keep water volume as 1 L (= 1e-3 m^3) or 1 kgw in SOLUTION, do I have to use 2.25 mol (= 1 mol/kg * 1,500 kg/m^3 * (1-0.4)/0.4 * 1e-3 m^3) for the exchange site as follows?

SOLUTION
   Na ***
   *** ***
   -water 1  # kg

EXCHANGE
   NaX  2.25  # mol


Thank you in advance.

[dlparkhurst]

Sorry, I may have misunderstood when I read your email.

You are correct that you are correct that the units for SOLUTION_MODIFY and EXCHANGE are moles.

I think your calculation is correct for for -water 1.

If you are simulating reactive transport, PhreeqcRM is a reaction module intended to be used with multicomponent transport. By default, it uses a representative volume of 1 L, and there are various options to convert PHREEQC input to the appropriate moles of reactants in the  cell representative volume.

[JW]

Thank you for the reply.

I couldn't find where I can post at first, so that I sent a message to you by mistake. Sorry.

By the way, dose PhreeqcRM work in the Linux system as well? Since IPhreeqc, which is COM object, doesn't work in the Linux system, I am in trouble.

[dlparkhurst]

There is an IPhreeqc, as opposed to IPhreeqcCOM, that can be compiled for Linux (or Windows). When compiled, it is a library that can be linked to C, C++, or Fortran programs.

PhreeqcRM is similar to IPhreeqc, in that it can be compiled on Windows or Linux to make a library that can be linked to C, C++, or Fortran.