Surface Complexation

[sharmilan]

Dear Phreeqc experts,

for my surface complexation, I am defining the surface through the site density, specific_area_per_gram and mass of phase in grams (see script below).

SURFACE 1
   equilibrate with solution 1
   sites_units density
   Surf_s 4.878    5.774461414796E+02     8.923883160678E+02
   donnan 7.182757128035E-10
   only_counter_ions true

The Phreeqc calculation shows that the total mol of the surface site is 4.174e+00 moles  (Surf_s). Could you explain how this total mol of the surface site is calculated from input data?

Note: I am attaching the output file also.

Thank you
S.Sharmilan

[dlparkhurst]

As my high school chemistry teacher taught me, "Follow the units".

4.878 sites/nm2 * 1e18 nm2/m2 = 4.878e18 sites/m2

577 m2/g * 892 g = 5.15e5 m2

5.15e5 m2 * 4.878e18 sites/m2 = 2.51e24 sites

2.51e24 sites / 6.02e23 sites/mol = 4.17 moles of sites