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Reaction paths for fluid-fluid mixing and mineral precipitation


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Hi to all,

 

I would like to ask you for some advices in choosing the right reaction paths models in REACT.

 

I'd like to calculate a mixing model of (1) hot metal-bearing fluid (small volume, low pH, supersaturated with some mineral phase) with a (2) cold, almost pure fluid (high pH, high volume).

I want to find out the amount of metals that can be removed and precipitated as minerals from hot fluids (should be mainly due to changes in T and pH) when it starts to mix with the cold fluid. I want neglect any supersaturated minerals that might be present in the initial fluids.

 

Once the minerals precipitated as a result of the mixing of the fluids, they should be prevented from re-dissolving into the liquida at any further step of the fluid mixing.

 

In REACT I played around with the "flow-through" and "flash" models (with "dump" option on). The results of both look quite different.

Could you please give a recommendation, which model might be the best in order to describe the mineral precipitation from one fluid as a result of the 2-fluid mixing.

 

Many thanks in advance,

 

Sebastian

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  • 3 weeks later...
Hi Sebastian,


The “flow-through” configuration might be used to follow a packet of fluid as it migrates through an aquifer, or to trace the evaporation of seawater. In either case, the program isolates minerals that form over the reaction path and prevents them from back reacting. With the “flush” configuration, the program tracks the evolution of a water-rock system (a volume of porous media) through which a fluid migrates. An even simpler model, the “titration” path, is like pouring one fluid into a bucket of another. Section 2.2.5, Local equilibrium models, in the Geochemical and Biogeochemical Reaction Modeling text contains a more complete description and diagrams of these and other conceptual models. Please see as well Section 3, Tracing Reaction Paths, in the GWB Reaction Modeling Guide.


You’ll have to think about your conceptual model and which would be the best choice. Does the second fluid displace the original fluid, or does it all pool together? It may be helpful to set up very simple examples of each (perhaps just Na+, Cl-, and Temperature for your fluid(s)). Gtplot can be very helpful here. Pay attention to how water mass changes (or doesn’t change) in each configuration, for example, or use temperature or Na+ and Cl- as tracers as you mix one fluid into another.


Another way to prevent minerals from re-dissolving into the fluid is to implement dissolution/ precipitation kinetics using a custom rate law. Your rate law would depend on the saturation state of the mineral. There’s an example in section 5.2, Rate law scripts, in the GWB Reaction Modeling Guide that should be useful.


By the way, there’s an example of fluid mixing at hydrothermal vents in section 22.2, Black smokers, in the GBRM text. This sounds pretty similar to what you’re trying to do.


Hope this helps,


Brian Farrell

Aqueous Solutions LLC

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