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Re: Mn species

> I`d like to introduce MnS-Species to the database, but cannot find log_k
values and delta_h values for the complex MnS(HS)- and the preciptitation
of MnS2. Well, I do find a log_K for MnS(HS)- of +37.25 in
Landing, W.M. and Lewis, B.L., 1991. Thermodynamic modelling of trace metal

speciation in the Black Sea. In: E. Izdar and J.W. Murray (Editors), Black
Sea Oceanography. NATO ASI Series C. Kluwer Academic Publishers, Dordrecht,

pp. 125-160.

> But this value seems rather high to me. Putting this in the database, all

the solute Mn is in this MnS(HS)- species, and all others are negligible,
which seems not to be right to me.

I've had that problem with sulfide and polysulfide species too. The
literature values appear to apply to specific systems and are not generally
usable. The polysulfides can cause some strange physical results (inability
to reach mineral saturation because the complexes are so strong) or cause
the numerical method to fail.

As you probably know, none of the databases distributed with phreeqc have
Mn-sulfide complexes. I think only wateq4f.dat even has iron bisulfide
complexes. None have a phase MnS2.

> Do you have any idea how to find the log_k and delta_h values?
I would be greatful for any hint.

I'm afraid I don't know of any thermodynamic data. Other than searching the
literature for more, the only suggestion I could make is to use iron as an
analog and include Mn-bisulfide complexes with the same K's as
Fe-bisulfide. I don't know if there really is an MnS2 phase, but you could
copy pyrite or marcasite for Mn.


David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

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