blocking redox reactions for initial system?

[pandora]

If I understand correctly, Phreeqc will automatically calculate redox equilibria. So even if you start out with a small amount of ferrous ion, under the right conditions, some of it will in the solution end up as ferric ion. However, those redox reactions are often much slower than than speciation equilibria; and I'd like to calculate an initial equibrium assuming there are NO redox reactions taking place yet. Is that possible

[dlparkhurst]

The initial solution calculation, defined by SOLUTION, does not necessarily produce redox equilibrium. Any valence state of a redox element defined in the solution (such as Fe(2), O(0), S(6), S(-2)), will not convert to another redox state in the initial solution calculation. Any redox element defined as a total (Fe, S, C, etc) will be distributed among redox states dependent on  the choice of "-redox", pe by default, but can be set to a redox couple (O(-2)/O(0), for example).

All "reaction" calculations (calculations where a solution reacts with something, REACTION, MIX, or EQUILIBRIUM_PHASES, for example) will react to redox equilibrium.

If you want to disable redox equilbrium for a redox element, it is not particularly easy. There is an example of kinetic oxidation of ferrous iron in the manual.