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Initial values (Rxn progress = 0 ) are different from input values


Teng Deng
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Hello

I try to use React to model the water-rock interaction, but I ran in to a problem.

First of all, I use SpecE 8 to balance the fluids, and the fluid was produced for Reaction.

In React, I use the fluid to react with Abite, Anorthite, Phlogopite, Annite, Muscovite, Quartz, Maxium_Microline, pyrite and Daphinite-14.

 

In the initial fluid (processed by SpecE 8):

pH = 4.5,  UO2++ = 15.2 mg/kg (component)

 

However, in the Gtplot file produced by React, the initial values are (Rxn progress = 0 )

pH = 4.032,  UO2++ = 0.0001326 mg/kg (component in fluid)

 

My question is: Why aren’t they the same (pH and UO2++)?

 

The SpecE 8, React and Gtplot file are seen attached.

Best wishes

Teng Deng

Fluid composition-V2-output to input.sp8 Reaction V10.rea UO2++.gtc pH.gtc

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Hello Teng,

With your React_output.txt file, you should see two Xi = 0 text blocks any time an initial system contains supersaturated minerals and precipitation is not disabled. The first block shows you the metastable equilibrium state of your aqueous speciation after you have initialized your run, where no supersaturated minerals have been precipitated. You can see in this first block of text, under section of Original basis, you have 15.2 mg/kg for the component UO2++ and the pH is 4.5.

In the next Xi = 0 block, React reports the calculations for a true equilibrium state after allowing supersaturated fluids to precipitate. You can see that a small amount of uraninite precipitated out which removes some uranium from fluid. Section 2.3 Initial system in the GWB Reaction Modeling Guide describes the difference between the two output block in detail and provides a comparison between SpecE8 and React using the seawater.sp8 example. 

Hope this helps,
Jia Wang

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