Solubility > Dissolution/precipitation

what is the difference between FeCO3, Siderite(d), Siderite in phreeqc database?

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Penny:
I want to precipitate FeCO3  formed in the solution, but there are there possible phases in phreeqc database, which are showed below. Could anyone help explain these phases? Thank you very much.


#FeCO3               559
        Fe+2 + CO3-2 = FeCO3
        log_k           4.38

Siderite(d)(3)      9
        FeCO3 = Fe+2 + CO3-2
        log_k           -10.45

Siderite            94
        FeCO3 = Fe+2 + CO3-2
        log_k           -10.89
        delta_h -2.48 kcal

dlparkhurst:
The first is an aqueous ion pair, which is defined in a SOLUTION_SPECIES data block.

The second two are defined in PHASES and are minerals that you might use in EQUILIBRIUM_PHASES. The two siderites represent different crystallinities and have different log Ks. The "d" probably represents "disordered", and is more soluble than the phase designated simply "Siderite". Note that both minerals will not be in equilibrium simultaneously; thermodynamically, the disordered version should convert to the more stable siderite.

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