The mass-balance results look ok to me. I'm guessing that you are not accounting for the stoichiometric coefficient of uranium in the species. In the output, the molality applies to the molality of the species. You must multiply by the stoichiometric coefficient of uranium in the species and sum the results to obtain the total molality of uranium. In the following example: 4.2e-4 = 5.078e-005*3 + 3.882e-005*3 + 3.467e-005*4 + 8.014e-006 + 3.630e-006 + 5.466e-007 + ... David U(6) 4.200e-004 (UO2)3(OH)7- 5.078e-005 4.854e-005 -4.294 -4.314 -0.020 (UO2)3(OH)5+ 3.882e-005 3.711e-005 -4.411 -4.431 -0.020 (UO2)4(OH)7+ 3.467e-005 3.314e-005 -4.460 -4.480 -0.020 UO2(OH)3- 8.014e-006 7.661e-006 -5.096 -5.116 -0.020 UO2(CO3)2-2 3.630e-006 3.030e-006 -5.440 -5.519 -0.078 UO2CO3 5.466e-007 5.468e-007 -6.262 -6.262 0.000 UO2OH+ 2.174e-007 2.078e-007 -6.663 -6.682 -0.020 UO2(CO3)3-4 6.291e-008 3.055e-008 -7.201 -7.515 -0.314 (UO2)3(OH)4+2 3.270e-009 2.730e-009 -8.485 -8.564 -0.078 (UO2)2(OH)2+2 3.116e-009 2.601e-009 -8.506 -8.585 -0.078 UO2+2 6.496e-010 5.423e-010 -9.187 -9.266 -0.078 UO2SO4 9.341e-011 9.344e-011 -10.030 -10.029 0.000 UO2(OH)4-2 8.831e-012 7.372e-012 -11.054 -11.132 -0.078 UO2NO3+ 9.089e-013 8.688e-013 -12.041 -12.061 -0.020 (UO2)3(CO3)6-6 1.413e-013 2.781e-014 -12.850 -13.556 -0.706 UO2(SO4)2-2 1.334e-013 1.114e-013 -12.875 -12.953 -0.078 (UO2)2OH+3 5.349e-014 3.563e-014 -13.272 -13.448 -0.176 UO2Cl+ 4.302e-014 4.112e-014 -13.366 -13.386 -0.020 UO2Cl2 1.132e-019 1.132e-019 -18.946 -18.946 0.000 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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