Kinetic dissolution models

[michael.lawson]

I am struggling developing a model for barite dissolution and was wondering whether I have something wrong in a unit conversion that someone could help with? I have found a activation energy in the literature of 32 kJ/mol (32000 J/mol) and a pre-exponential factor (Ln A) of -2.41. I convert this to a pre-exponential value of 0.0898 mol/m2s. The input in the kinetic mineral section of GWB requires the input in mol/cm2sec - which I am assuming I should convert to give 898 mol/cm2s (multiply by 10000). This is then in a consistent format with the surface area I have of 107 cm2/g. The issue I have is this gives a very rapid equilibration to high concentrations of aqueous Ba and SO4 within 30 mins which doesn't appear reasonable to me. Have I made in error in converting something that does not require converting?

 

Appreciate any advice and support.

[Brian Farrell]

Hi Michael,

 

Your conversion seems fine, as far as I can tell. I think an important question to ask yourself is whether the conditions of your model are similar to the experiment(s) from which the kinetic parameters were derived.

 

Since you're using the Arrhenius equation, the rate constant is going to increase with temperature - is your temperature too high? Perhaps you've specified a very large initial mass for Barite, which means it has a very high surface area, and thus a very high dissolution rate.

 

Were pH or headspace gases controlled in the experiment, but not fixed in your model? Are there any differences between the promoting or inhibiting species used in your model and those used in the original reference?

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC