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Modeling ARD


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Can GWB be used to model the biotic and abiotic reactions of acid generation from pyrite? I'd like to use the program to model Acid Rock Drainage (ARD) and, more or less, duplicate lab results from humidity cells and kinetic cells.

There would need to be two reactions: pyrite to ferrous iron reaction and then the ferrous to ferric iron react reaction.



If not, can GWB be used for ARD prediction in other ways?

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There are various ways that you can set up a model of ARD with the GWB. You’ll probably want to decouple ferric iron from ferrous iron (Config - Redox couples...). In this way, you prescribe a state of redox disequilibrium in your model. When you do this and set up pyrite as a kinetic reactant (add – Kinetic – Mineral… - Pyrite) the mineral will add ferrous iron to solution as it dissolves. You could then set up a kinetic redox transformation (add – Kinetic – Redox) for the ferrous iron oxidation. In fact, you can set parallel rate laws for the iron oxidation. One could be abiotic, while the other could be microbially mediated (add – Kinetic – Microbial reaction). For more information, please see section 7.3, Redox disequilibrium, in the GWB Essentials Guide and section 4, Kinetic Reaction Paths, in the GWB Reaction Modeling Guide. There’s also a useful chapter on Acid drainage in Craig Bethke’s Geochemical and Biogeochemical Reaction Modeling text.

Hope this helps,

Brian Farrell

Aqueous Solutions LLC
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