Arsenic Sorption error

[tsnmaster]

Hi guys.

I have a problem with this code:

SOLUTION_SPREAD
    -units    mg/l
   pH    pe    Alkalinity     Al       B     Br     Ca     Cl    Fe(3)    Fe(2)       K       Mg    Mn(3)    Mn(2)    N(5)     Na     Pb    S(6)     Zn     Si    Description    Temperature    As(5)
                   meq/l                                                                                                                                                                           
 2.24     9             0    156    19.7    3.3    233    920     46.9      2.1    87.7    159.2        9        1     0.1    333    0.6    2450    9.8    200         Azufre             10      2.1
  8.7     9             2    0.7     3.3    0.5    120    190     0.57      0.3    20.0     55.0      0.1        0     0.4    170      0     477    0.1     15                            10     0.05

end


PHASES
   Schwertmannite
      Fe8O8(OH)6(SO4)+ 22 H+ = 8 Fe+3 + SO4-2 + 14 H2O
      log_k 10


SURFACE_MASTER_SPECIES 1
    Alunite_           Alunite_OH

SURFACE_SPECIES 1
AsO4-3 + 3H+ + Alunite_OH = Alunite_H2AsO4 + H2O
   log_k     26.94
AsO4-3 + 2H+ + Alunite_OH = Alunite_HAsO4- + H2O
   log_k     21.79
AsO4-3 + Alunite_OH = Alunite_OHAsO4-3
   log_k     6.39
Alunite_OH = Alunite_OH
   log_k     0
Alunite_OH + H+ = Alunite_OH2+
   log_k     7.17
Alunite_OH = Alunite_O- + H+
   log_k     -11.18



Hfo_wOH + AsO4-3 + 3H+ = Hfo_wH2AsO4 + H2O
   -log_k   31.29

Hfo_wOH +  AsO4-3 + 2H+ = Hfo_wHAsO4- + H2O
   -log_k   25.39

Hfo_wOH +  AsO4-3 + H+ = Hfo_wAsO4-2 + H2O
   -log_k   17.72

USE SOLUTION 1
USE SOLUTION 2

MIX

1    0.090
2   0.910

SAVE SOLUTION 3

EQUILIBRIUM_PHASES 1
    Alunite   0 0
    Basaluminite 0 0
    CO2(g)    -3.6373 10
    Gibbsite  0 0
    O2(g)     -0.8833 10
    Schwertmannite 0 0

USE EQUILIBRIUM PHASES 1
   
SURFACE 1
    Alunite_OH Alunite      equilibrium_phase 0.0115 2495
    Hfo_sOH Schwertmannite  equilibrium_phase 0.2    21690
    Hfo_wOH Schwertmannite  equilibrium_phase 0.05
    -donnan 1e-08

end

The problem surge after adding


Hfo_wOH +  AsO4-3 + 2H+ = Hfo_wHAsO4- + H2O
   -log_k   25.39

Hfo_wOH +  AsO4-3 + H+ = Hfo_wAsO4-2 + H2O
   -log_k   17.72


The warning is:

* mass of water is less than 1e-10 kilograms
* numerical method failed with this set of convergence parameters
*trying smaller step size


I hope u can help me, because i don't know if this code it is ok.

Thanks

[dlparkhurst]

This file runs for me. The messages are "WARNING"s, which do not mean the overall calculation failed. If the calculation fails, there should be one or more "ERROR" messages.

I have revised your input file in a way that I hope makes the calculation sequence clearer. The new thermodynamic definitions are first. SOLUTION_SPREAD, EQUILIBRIUM_PHASES, and SURFACE are defined separately by adding END after each definition. The reaction is then defined with MIX and USE statements. I assumed that the reaction was actually the MIX reaction. You can only USE one solution or one MIX in a reaction calculation (actually only one of any numbered entity).

[tsnmaster]

I really appreciate your help.
Thank you very much ;)