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pH effects in X1t and X2t


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Good day to you all,


I have been wrestling with a question of H+ production by anodes in stagnant water. I have been asked to look at whether the pH 10 cm from the anode will drop below 4. I decide to start with a simplified situation, disregarding OH- production at the kathode (some 1.2 m away).

The idea is that only diffusion will play a role in the distribution of H+ in this case

However, the tutorial showing the effect of diffusion only starts with a local spike in concentration which then diffuses into the fluid.

Is it possible to simulate a continuous addition of h+ ions to water?

I tried making an inlet fluid with the desired h+ concentration, however, in reality no water is actually flowing into the system. If I do this i need to have an inlet on both sides of the simulation as well, this is confusing to me (same as left).

Another thing I'm interested in is potential buffering by HCO3- in the fluid.

If you have any suggestions i'm eager to learn more about this!


I've added my feeble attempts at visualising the process in x1t and x2t.




pH situation.x2t

GWB pH prod x1t.x1t

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To simulate the continuous addition of ions into the fluid, you should use simple reactants. On the Reactants pane, click add > Simple > Aqueous… > H+. You’ll see a line that includes “React H+    +   0.0 mmol”. Click the “+” button to set a heterogeneous value for the rate of H+ addition. You might use the node-by-node editor or an equation to set the rate of H+ addition at the node containing the anode, and a rate of 0 everywhere else. The procedure is just like setting the spike in initial Pb concentration in the Diffusion tutorial. 

For more information, please see 3.1 Titration paths in the GWB Reaction Modeling Guide and the Heterogeneity Appendix to the GWB Reactive Transport Modeling Guide.


Brian Farrell
Aqueous Solutions LLC

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