Processes > Inverse modelling

Mix end precipitation

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INZILLO:
Hi everyone,
I have a brine that I would like to mix with NaHCO3 to understand which phase or mineral will it precipitates.
it's possible to do it?
if yes, how?

dlparkhurst:
If you have a NaHCO3 solution, you can define it as a SOLUTION and then use MIX to mix the two solutions in the appropriate proportions.

--- Code: ---SOLUTION 1
...
END
SOLUtION 2
pH 7 charge
Na 1
C   1
END
MIX
1 0.9
2 0.1

--- End code ---

Alternatively, you can add NaHCO3 to your solution with REACTION. Note that REACTION adds moles of reactants, so you would have to convert any mass amounts to moles.

--- Code: ---SOLUTION 1
...
END
REACTION 1
NaHCO3 1
0.001 moles
END
USE solution 1
USE reaction 1
END

--- End code ---

INZILLO:
Great as always, thank you very much.
One further question,
can I simulate the introduction of NaHCO3 into solution at different time instants?
and also quantify how many "mg" of CaCO3 or other solid phases precipitate, for example?
to then be able to make a "precipitation over time" graph.

dlparkhurst:
This is more or less what you describe. NaHCO3 is added in increments and the amount of calcite precipitated is plotted against amount added. Although possible, it gets a little trickier to plot calcite vs time when using REACTION, but amount of reaction is probably more relevant anyway.

--- Code: ---SOLUTION 1
pH  7.3
Ca 3
C  1 Calcite 0 10
END
USE solution 1
EQUILIBRIUM_PHASES 1
Calcite 0 10
REACTION
NaHCO3 1
0.001 0.003 0.004 0.006
USER_GRAPH 1
-axis_titles            "NaHCO3 added, moles" "Calcite precipitated, moles" ""
-initial_solutions      false
-connect_simulations    true
-plot_concentration_vs  x
-start
10 GRAPH_X RXN
20 GRAPH_Y EQUI_DELTA("Calcite")
-end
-active                 true
END
--- End code ---

If NaHCO3 is added continuously, you could use KINETICS with a RATES expression, in which case it is simpler to plot calcite precipitated vs time.