Inverse modeling really only requires the correct total concentrations of the elements. The speciation may be entirely erroneous and the saturation indices unreliable, but it should not matter. You are looking for mole transfers that account for the changes in concentrations between two solution compositions that have been (mostly) measured. There may be problems with total carbon if pH and alkalinity are used to determine total carbon; this would be model dependent. Also, if you perform any mineral equilibrium calculations in the course of defining the solution composition of any of your inverse modeling solutions, you could have problems. However, if you can feel confident about the total concentrations in the solutions, then you should be able to proceed with INVERSE_MODELING. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Michael Zilberbrand To: 'David L Parkhurst' <dlpark@xxxxxxxx> <w_mzilberbrand@x cc: In-Reply-To: <01C1CD9A.8141DF00@xxxxxxxxxx> ail.gov.il> Subject: Inverse modeling of brine formation 03/17/02 02:59 AM Dear David, Could you please help me? I have a question. Is it possible to use the inverse modeling with PHREEQC for explanation of formation of brines with very high ion strength (through evaporation, mixing and reactions)? What may be the arguments? For studying the influence of complexes at low ion strengths, I tried to model addition of Na2CO3 to concentrated Gypsum solution (formed in equilibrium with Gypsum). At Na2CO3 amount required for the complete CaCO3 precipitation (without taking into consideration complexes), (CaSO4)0 concentration in the final solution was not nil. It became very small only at strong Na2CO3 excess. Does it mean that inverse modeling is impossible without taking into consideration complexes? I"ll very appreciate your help. Sincerely, Michael ------------------------------------------ Dr. Michael Zilberbrand Hydrological Service of Israel Research Division P.O.B. 36118, Jerusalem 91360 Israel TITLE Complexes and Calcite precipitation SELECTED_OUTPUT -reset false -file Complexes-Calcite_prec_res.prn -molalities Ca+2 CaSO4 SOLUTION 1 Temp 20 pH 7.0 EQUILIBRIUM_PHASES 1 Gypsum 0.0 SAVE SOLUTION 2 END USE SOLUTION 2 REACTION 1 Na2CO3 1.0 0.01532 moles SAVE SOLUTION 3 END USE SOLUTION 3 EQUILIBRIUM_PHASES 1 Calcite 0.0 END # RESULTS at Na2CO3 1 mol # m_Ca+2 m_CaSO4 # 0.0104 0.0049 After equilibration with CaSO4 # 0.0011 4.53E-05 After addition of Na2CO3 # 2.89E-07 1.21E-08 After equilibration with Calcite # RESULTS at Na2CO3 0.01532 moles (0.0104+0.0049) # 1.0365e-02 4.9486e-03 # 4.9106e-03 2.2413e-03 # 1.4375e-04 9.0900e-05
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