Calcite Dissolution Kinetic Help

[mems]

Hi All,
First of all, I'd like to say that I have very limited knowledge on PHREEQC simulation and that I'm still a learner. So if the following question seems dumb, please bear with me.
I'd like to simulate calcite dissolution with kinetic data block, but I've ran into some confusions. Based on the "wateq4f" database, parameter 1 is the specific surface area of calcite in cm^2/mol calcite, but based on the reference given in the database (Appelo et al. 1998. Applied Geochemistry, Vol 13 pp257-268) and and the text box Geochemistry groundwater and pollution (2nd ed) pg 213, the parameter 1 is  A/V (area of calcite divided by the solution volume in unit in dm-1).
My questions are 1) which one is correct? and 2) how to get the specific area in cm^2/mol? (as the sample calculation given in the text book p163 was done in per kg bases).
Thank you very much for your help in advance

[dlparkhurst]

With the release of PHAST version 3, the rates that depend on surface area (heterogeneous reactions) were revised to have a parameter in KINETICS that is specific area (L^2/mol). PHAST 3 uses a representative volume of 1 L, so usually, the volume of solution is equal to the porosity. If a fixed surface area for one liter of water (commonly in PHREEQC) is defined in KINETICS, then the rates would not scale properly for PHAST. Thus, the RATES definitions were revised to consider potential solution volumes that were not equal to one. These changes are in the PHREEQC databases, so that PHREEQC calculations are also affected.

Look at your database and use parameters as defined in the database. Old databases will be consistent with Appelo and Postma, new databases will be modified as I just described.

The reactive surface area is not very well defined, and often it is a fitting parameter. You can use BET measurements, or a geometric argument based on particle size, or some other rationale for the surface area parameters.