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Pitzer and React

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From: Kirk J Cantrell

Subject: Pitzer and React

I am using React to calculate the solubility of a mineral at high ionic strength using the Phrqpitz thermo database. I modified the database to include a solubility constant for a mineral I am interested in, as well as some associated Pitzer parameters. Without giving you all the details, I have determined that the model is not using the new theta parameters for the interaction of two anionic species that I added to the Phrqpitz thermo database. The reason I know this is that at zero ionic strength, React is calculating the solubility correctly. When I go to 2 m NaCl, where the theta interaction parameters has a significant influence, the solubility calculated by React is less than half of what it should be (based on the model used to determine the solubility and Pitzer parameters for the mineral I am working with). If I go back and set the theta parameter in the thermo database to zero, I get the same solubility at 2 m NaCl. This suggests to me that for some reason, React is not including my newly added theta interaction parameter in the equilibrium calculation and that this is the reason the calculated solubility is too low. Do you have any clues as to why this could happen?

To make locating my additions to the thermo database easier to find, I have indicated them here:

In elements:

Uranium (U ) mole wt.= 238.0290

In basis species:

UO2(CO3)3----

charge= -4.0 ion size= 9.0 A mole wt.= 450.0554

3 elements in species

1.000 U 11.000 O 3.000 C

In aqueous species:

(UO2)3(CO3)6------

charge= -6.0 ion size= 20.0 A mole wt.= 1170.1386 g

3 species in reaction

3.000 H+ 3.000 UO2(CO3)3---- -3.000 HCO3-

-19.5000 -19.5000 -19.5000 -19.5000

-19.5000 -19.5000 -19.5000 -19.5000

In minerals:

Cejkaite type=

formula= Na4UO2(CO3)3

mole vol.= 150.000 cc mole wt.= 542.0146 g

2 species in reaction

4.000 Na+ 1.000 UO2(CO3)3----

-4.0800 -4.0800 -4.0800 -4.0800

-4.0800 -4.0800 -4.0800 -4.0800

In beta virial coefficients:

Na+ UO2(CO3)3----

beta0 = 0.61

beta1 = 18.2

beta2 = 0.0

cphi = 0.0

alpha1 = 2.0

alpha2 = 0.0

Na+ (UO2)3(CO3)6------

beta0 = 2.4

beta1 = 46.6

beta2 = 0.0

cphi = 0.0

alpha1 = 2.0

alpha2 = 0.0

In theta virial coefficients:

Cl- UO2(C03)3----

theta = -0.13

SO4-- UO2(C03)3----

theta = -0.37

Note that (UO2)3(CO3)6------ is not required for the current calculations. This species is required for very high carbonate conditions and I intended to put

estimates for its theta virial coefficients in the database later.

Attachments to this post:

http://gwb.eligeos.org/attachments/React-1...aiteSolPitz.rea

http://gwb.eligeos.org/attachments/React-1...hrqpitz_kjc.dat

From: Craig Bethke

Subject: Re: Pitzer and React

I think you will find that the cause of your trouble is that in entering theta values in the thermo dataset, you refer to species "UO2(CO3)3----" as

"UO2(C03)3----". In other words, for these entries you've typed in C-zero-3, not C-Oh-3.

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