A question about SURFACE_MASTER_SPECIES

[omarchaabi]

Hello,

I am new to CD-MUSIC and I have a question that might be trivial. I was reading the manual and looking at the examples and I was wondering why do we usually use the OH form of the binding site for the surface master species? any elaboration on this would be appreciated. Thanks in advance.

Regards,
Omar

[dlparkhurst]

It is not required to use the OH form, but the usage can be traced to the surface complexation monograph by Dzombak and Morel. The surface of hydrous ferric oxide HFO is represented as S=OH, which allows protonation and deprotonation reactions.

For CD_MUSIC the master species you can use a charged "master" species, but there are a couple places where you need to be careful (for both CD_MUSIC and nonCD_MUSIC). The formula you use in SURFACE when not using -equil or when a surface is related to a mineral or kinetic reaction should be charge balanced.  The attached file uses a charge balanced master species for CD_MUSIC, but the concentration of the master species is forced to be small. The moles of surface are related to the mineral Goethite.