> I have computed a value (EQUILIBRIUM_PHASES 1; Gibbsite 0 10) for a single sample but, would like to know if there a way to repeat this command for each sample (in the SOL_SPREAD)? Or do I have to SAVE each 'initial solution 1-20'? It is possible to estimate the Al concentration that would give equilibrium with gibbsite within the SOLUTION_SPREAD definition. However, it is not identical to the calculation you performed for solution 1. By adding a column for Al and a subheading of "Gibbsite", the program will adjust the aluminum concentration until the saturation index for gibbsite for the solution is 0.0. Note that the pH and all other concentrations are not affected in this calculation. When you use equilibrium_phases, a different calculation is performed: Al(OH)3 is added to the solution until the saturation index for gibbsite is 0.0. Thus, OH is added in addition to Al and the pH will consequently change. The first method with SOLUTION_SPREAD is probably what you want to do, keeping everything in the solution unchanged, except estimating an aluminum concentration. Note that even using gibbsite in solution_spread, and including the equilibrium_phases calculation, the reaction calculation with equilibrium phases dissolves some more gibbsite. This is because of redox reactions with nitrogen. The reaction calculation forces redox equilibrium, which causes adjustments among N(-3), N(0), and N(5). These reactions affect the pH, which in turn causes gibbsite to adjust. David Not sure the units are correct in this file, the tabs didn't come through in the email. (See attached file: Phrqc3.pqi) David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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