SED & PREDOM / SED

A solubility diagram shows total dissolved concentrations (on a logarithmic scale) usually plotted against a free concentration. It is convenient to set the activity = 1 for the solid phase of interest. This can be done by exchanging a component for a reaction, for example exchanging Ca²⁺ with CaCO₃(s).

The following diagram shows the solubility of calcite in the system H⁺, CaCO₃(s), and CO₂(g) at log P_CO2 = −3.5:

In this case the component CO₃⁻ has also been exchanged with CO₂(g). The diagram was obtained with the following input file:

 3 9 3 1
H+,  CO2(g),  CaCO3(cr)
CaCO3     , -5.139   0  0  1  CaHCO3+        ,  2.959   1  0  1
CaOH+     , -3.156   1 -1  1  CO2            , -1.472   0  1  0
H2CO3     , -4.247   0  1  0  HCO3-          , -7.825  -1  1  0
OH-       , -14.002 -1  0  0  Ca 2+          ,  9.674   2 -1  1
CO3 2-    , -18.152 -2  1  0  Ca(OH)2(cr)    , -12.941  0 -1  1
CaCO3(am) , -2.088   0  0  1  CaO(cr)   , -23.026  0 -1  1
LS,-9, 1, H+,
LAV, -5 -11  LA, -3.5  LA, 0