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This keyword data block is used to define the correspondence between surface binding-site names and surface master species. Normally, this data block is included in the database file and only additions and modifications are included in the input file. The default databases contain master species for Hfo_s and Hfo_w, which represent the weak and strong binding sites of hydrous ferric oxides (Dzombak and Morel, 1990).

Example data block

Line 1a:      Surf_s      Surf_sOH
Line 1b:      Surf_w      Surf_wOH



Keyword for the data block. No other data are input on the keyword line.

Line 1: surface binding-site name, surface master species

surface binding-site name --Name of a surface binding site. It must begin with a capital letter, followed by zero or more lower case letters. Underscores ("_") plus one or more lower case letters are used to differentiate types of binding sites on a single surface. Multiple binding sites can be defined for each surface.

surface master species --Formula for the surface master species, usually the OH-form of the binding site.


In this example data block, a surface named "Surf" has a strong and a weak binding site. Association reactions must be defined with SURFACE_SPECIES for the master species associated with each binding site and for any additional surface complexation species. All reactions for the binding sites of a surface (Surf_s and Surf_w, in this example data block) must be written in terms of the surface master species (Surf_sOH and Surf_wOH in this example data block). Each surface master species must be defined by an identity reaction with log K of 0.0 in SURFACE_SPECIES input. The number of sites, in moles, for each binding site must be defined in the SURFACE data block. Information defining the surface area is also specified with the SURFACE data block. In setting up the equations for a simulation that includes multiple binding sites, one mole-balance equation is included for each binding site for each surface and one charge-balance equation is included for each surface (including all of its binding sites).

Example problems

The keyword SURFACE_MASTER_SPECIES is not used in the example problems. See the listing of the default database file in Attachment B for examples.

Related keywords


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