Accounting for dissolution of pre-equilibrated SURFACE

[bschroth]

Hello:
I have a Fe(OH)3 surface that I establish in equilibrium with a starting water sample – I use the following block to do this:

SURFACE     1                 
  -equil solution 1                 
  Hfo_wOH   0.0012      600   0.65
SAVE SURFACE 1

In the next step of the simulation, this water mixes with another water, and results in partial dissolution of the Fe(OH)3, as defined in EQUILIBRIUM_PHASES of that next step.  How can I account for that loss of Fe(OH)3 in the surface calculations? In this case, SURFACE 1 is initially not linked to Fe(OH)3 in the first step, but my attempt to link it in the second step with the statements

USE SURFACE 1
SURFACE     1
      Hfo_wOH     Fe(OH)3     equilibrium_phase  0.2 6.4e4

results in the intial SURFACE 1 being erased and replaced with the surface linked to Fe(OH)3, which was not pre-equilibrated with the solution.

Thanks for looking
Brian

[dlparkhurst]

EQUILIBRIUM_PHASES 1
Fe(OH)3 0 0.0060
END
SURFACE     1                 
  -equil solution 1         
  Hfo_wOH     Fe(OH)3     equilibrium_phase  0.2 6.4e4
END
USE solution 2
USE surface 1
USE equilibrium_phases 1
END
END