Query regarding molar volume of Montmorillonite in the database.

[Aditya-Puru]

Hello,
Montmorillonite in the database of GWB has a default molar volume of 0. Is there a reason behind it and is there the possibility that this factor might cause errors in complex modelling problems. If yes what is the most probable volume that should be used?

Thanks.

[Jia Wang]

Hello,

This means that no information regarding the molar volume was provided in the original dataset. Note that The GWB does not maintain reactions in databases. You can find more information regarding the origin of the database under the Header pane if you are looking at the dataset in the TEdit application. 

The program uses a default density of 2.65 g/cm3 and the molar mass of a mineral to calculate a molar volume if one is not provided. You can see the molar volume for the mineral of interest in the run if you go to the Config menu -> Show.. Configuration for sorption sites are specified in the surface dataset. Please see the Reference Manual for chapter on Surface Datasets for more information. If you are referring to other issues, please specify so we can better assist you.

You can search literature to obtain a molar volume measured by others for Montmorillonite. There are various end members of Montmorillonite that do have a molar volume in databases installed with The GWB. They might be a good starting point for you. Note that molar volume will depend on the stoichiometry assumed for a montmorillonite mineral; different databases or literature sources might use very different stoichiometries.

Hope this helps,
Jia Wang
Aqueous Solutions LLC