Reaching Max Residual with Calcite

[al3xwall3r]

I was wondering if I could get some help with one of my models. I am recreating a soil profile with various minerals and measuring the rate of carbon consumption. The model works and runs perfectly until I add "Kinetic Calcite" into my reactants and then the simulation only gets a minute in before coming up with the message "Newton-Raphson didn't converge after 999 iterations, max residual =    4.27e-07, Xi = 0.0031  / Newton failed at node 0". I was wondering if one of your team could get a better understanding about why I run into this problem. I have attached my input file below.

Weathering Soil Test Broken.x1t

[Jia Wang]

Hello Alex,

I took a quick look at your script and noticed that you have set a really high rate constant for kinetic calcite relative to all the other minerals in your system. To investigate error, I shortened the run time on your simulation to 1 day and looked at mineral dissolution rates during the simulation. Because of the high rate constant for calcite, you have high reaction rates adjacent to zero rates, in a moving front as the model progresses. To see this, plot the x-position on the x-axis and dissolution rate of calcite on the y-axis. Since the rate constant for calcite is many orders of magnitude higher than other minerals, it might be better to consider calcite using the equilibrium approach. If you want to continue using a kinetic rate law for calcite precipitation/dissolution, you should reconsider the rate constant that you are using. 

 

I also noticed that you have set a nucleus density for tridymite, kaolinite, and illite. This is only necessary if the mineral you are setting up a kinetic rate law for does not exist in the system. In your case, you do not need them. 

 

Hope this helps,

Jia Wang

[al3xwall3r]

Great, thank you so much for your help! The model is now running perfectly!