I'm attempting to reproduce in GWB 8.0.12, program React, the results of a paper (Zerai et. al., 2005) that used GWB 3.2.2. In the paper, a particular Na-Cl (Ca) brine of ionic strength ~7, initially at a pH of 6.4, is brought into contact with CO2(g) at a fugacity of 100 bars, at 54 degrees C. It absorbs 0.7 mol of CO2(aq) and reaches a pH of approximately 4.25.
I get the same molality of CO2(aq), but a pH of 2.9 - 3.0. Having tried everything I know of within the software to reconcile the two pHs, I'm here to ask for help.
Setup details: Initial brine composition and pH is input as the basis. CO2(g) is added as a reactant, fugacity sliding to 100 bars. Using the B-dot model and thermo.dat. Model limit on ionic strength (by default, 3) removed. Diameter of CO2(g) set to -0.5 A, as per instructions on simulating the salting-out effect. All other variables reset to default values.
Any suggestions on where to look for differences?