Dolomitization in PHREEQC

[trungka]

Hi all, I'm newbie for PHREEQC. Can someone help me to simulate the dolomitization in PHREEQC. The reaction as follows:
2CaCO3 + Mg2+ = CaMg(CO3)2 + Ca2+
This reaction is substitution from calcite to dolomite instead of cation exchange. I don't know how to coding this reaction in PHREEQC. Need help from experts.
Thank you very much.
Jack

[dlparkhurst]

If not ion exchange, then there must be some other reaction driving dedolomitization. In Florida (see papers by LN Plummer), it is dissolution of anhydrite or gypsum. The following simulates the process up to approximately gypsum equilibrium. After that, sulfate reduction may cause additional anhydrite dissolution and continued dedolomitization. Plummer has also published on dedolomitization in North Dakota.

Code: [Select]

SOLUTION 1
EQUILIBRIUM_PHASES 1
    CO2(g)    -2 10
    Calcite   0 10
    Dolomite  0 10
SAVE solution 1
END
USE solution 1
EQUILIBRIUM_PHASES 1
    Calcite   0 10
    Dolomite  0 10
REACTION 1
CaSO4 1
0.015 mol in 10 steps
USER_GRAPH 1
    -headings               rxn delta_calcite delta_dolomite
    -axis_titles            "CaSO4 added, moles" "Delta Calcite and Dolomite, moles" ""
10 graph_x RXN
20 graph_y equi_delta("Calcite"), equi_delta("Dolomite")
END