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Allowing No Precipitation of Minerals using Kinetics in React

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Guest lea512

Hello,

I am currently trying out new water chemistry and mineral data in REACT (compared to a previous forum discussion). I am using kinetic data in REACT and do not want any minerals to precipitate in the reaction. However, when I turn precipitation off, the reaction path says it is abandoned and only provides results for a couple of steps. How do I not allow mineral precipitation with kinetic data? Do I need to use only equilibrium data for no minerals to precipitate?

I have provided the file.

Thanks,

Lea

1755-1WaterChem_other SS.rea

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Hello,

I am currently trying out new water chemistry and mineral data in REACT (compared to a previous forum discussion). I am using kinetic data in REACT and do not want any minerals to precipitate in the reaction. However, when I turn precipitation off, the reaction path says it is abandoned and only provides results for a couple of steps. How do I not allow mineral precipitation with kinetic data? Do I need to use only equilibrium data for no minerals to precipitate?

I have provided the file.

Thanks,

Lea

Hi Lea:

Part of the problem is that your initial solution is highly supersaturated. Before React can begin the kinetic titration that you've set up, it needs to speciate the initial solution, and bring it to equilibrium. When you leave the precipitation setting in its default state, React swaps in a number of necessary mineral phases to allow the solution to precipitate minor mineral mass and come to equilibrium.

Have you considered using the Config - Suppress menu option? This allows you to remove from consideration mineral phases that might interfere with your kinetic titration, yet leave in other mineral phases necessary to allow your initial solution to come to equilibrium, and remain stable during the simulation.

Hope that helps,

Tom Meuzelaar

RockWare, Inc.

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Guest lea512

Thanks Tom.

I have tried to suppress minerals, but I have suppressed the minerals that are supersaturated or saturated in the last step of the reaction. When I do this, new minerals are then in the system. Am I using the wrong minerals, and if so, which minerals do you suggest that I suppress?

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Thanks Tom.

I have tried to suppress minerals, but I have suppressed the minerals that are supersaturated or saturated in the last step of the reaction. When I do this, new minerals are then in the system. Am I using the wrong minerals, and if so, which minerals do you suggest that I suppress?

Hi Lea:

There are no 'wrong' minerals - this often becomes more a matter of modeling approach. One strategy is to include just the minerals that you observe in the system you are modeling (or those that do not exist but could be reaction products), as well as those minerals that React needs for Basis swapping to maintain a stable solution matrix. All other minerals are suppressed.

Another modeling strategy is to include all minerals, and iteratively remove (Suppress) those that the model predicts which seem unrealistic to you.

Generally the decision to include/exclude a mineral is driven by the modeling time frame of interest and the dissolution/precipitation rates (kinetics) of the mineral. In other words, if you are modeling over a very short time scale, minerals that have very slow precipitation/dissolution rates can often be excluded.

Regards,

Tom

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Guest lea512

Tom,

Thank you for the information, it really helped me out. However, I think where I was getting confused was with the "Minerals in System" results. Are these minerals that the model has predicted have precipitated along with their amounts in grams and volume (cm3)? I notice that most of the minerals within the "Minerals in the system" heading are saturated in solution. Anyway, if you could clarify what exactly the "minerals in the system" heading provides results for, that would help me out tremendously.

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Tom,

Thank you for the information, it really helped me out. However, I think where I was getting confused was with the "Minerals in System" results. Are these minerals that the model has predicted have precipitated along with their amounts in grams and volume (cm3)? I notice that most of the minerals within the "Minerals in the system" heading are saturated in solution. Anyway, if you could clarify what exactly the "minerals in the system" heading provides results for, that would help me out tremendously.

Hi Lea:

The Minerals in System section lists minerals in equilibrium with the fluid only- that is, minerals that are defined in the initial Basis tab, or those that precipitate along the way. It does not list minerals that are precipitating or dissolving kinetically.

Regards,

Tom Meuzelaar

RockWare, Inc.

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Guest lea512

Hello again,

Ok, so if the minerals in the system are in equilibrium with the fluid, what do the grams and volume of each mineral represent?

In addition, I am adding CO2 into the system and sliding the fugacity which increases the acidity of the fluid, which means that I shouldn't have any minerals that are supersaturated (I am also adding in kinetic minerals and their dissolution rate). Quartz and kaolinite, however, are always supersaturated, but I have found that just adding these minerals in equilibrium eliminates this issue. Is there a better way kinetically to make it to where these two minerals are just in equilibrium or saturated in the fluid?

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Ok, so if the minerals in the system are in equilibrium with the fluid, what do the grams and volume of each mineral represent?

It represents the actual mass and volume of mineral in the system- remember that once a mineral is in equilibrium with a fluid, adding additional mineral mass will not change the concentrations of fluid components constrained by that mineral.

In addition, I am adding CO2 into the system and sliding the fugacity which increases the acidity of the fluid, which means that I shouldn't have any minerals that are supersaturated (I am also adding in kinetic minerals and their dissolution rate). Quartz and kaolinite, however, are always supersaturated, but I have found that just adding these minerals in equilibrium eliminates this issue. Is there a better way kinetically to make it to where these two minerals are just in equilibrium or saturated in the fluid?

I'm not sure I quite understand what your modeling object is- however, if you constrain a mineral mass in the Basis, you are ensuring that the fluid will initially be saturated with respect to that mineral. You could get there with kinetics, but kinetic reactions in GWB, by definition, move towards equilibrium. In other words, in order to model a kinetic mineral precipitation/dissolution reaction, you have to start with a fluid that is either undersaturated or supersaturated with respect to that mineral.

I hope that helps,

Tom

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Guest lea512

Ok, I think I may understand. What I was doing was running the model that contained about 9 minerals (with kinetics) for about 10 years and Quartz and Kaolinite were always supersaturated while everything else was either in equilibrium or undersaturated. So if I understand correctly, quartz and kaolinite just haven't reached equilibrium yet?

Thanks for the help!!

Lea

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Ok, I think I may understand. What I was doing was running the model that contained about 9 minerals (with kinetics) for about 10 years and Quartz and Kaolinite were always supersaturated while everything else was either in equilibrium or undersaturated. So if I understand correctly, quartz and kaolinite just haven't reached equilibrium yet?

Thanks for the help!!

Lea

Hi Lea:

Yes, if you are running the model with Quartz and Kaolonite as kinetic minerals, they likely will not have reached equilibrium in such a short timeframe. Of course, this depends on how far from equilibrium they were to begin with.

Regards,

Tom

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