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[OLD] GWB & X2t - Kds


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From: Criscenti, Louise J

Subject: GWB & X2t - Kds

I have a question regarding the calculating local Kds after using a surface complexation model to distribute a contaminant (e.g., Uranium) between the solid and aqueous phases. The “Uranium in Sorbate� can be plotted in “mg/kg�. The “Uranium in Fluid� can also be plotted as “mg/kg�. A Kd is strictly defined as the (mass of solute sorbed per dry unit weight of solid in mg/kg) divided by (concentration of solute in solution in equilibrium with the mass of solute sorbed onto the solid (mg/L). Is the Uranium in Sorbate plotted in mg/kg, plotted in mg per kg of fluid? mg/(kg of dry solid)? mg/(kg of solid+fluid?)?


From: Craig Bethke

Subject: Re: GWB & X2t - Kds

In Gtplot and Xtplot, you are plotting concentrations, not KDs, so the unit conversion options (molal, mg/kg, ...) all refer to mass per unit solution or solvent mass. You can check yourself, of course: just take the component mass and divide it by solution mass, and rock mass. The answer should match the former.

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