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Kaizen

Evaporation

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Hi,

 

I am a new user, so please be gentle. I am evaporating an acidic, saline water from mineral processing, >200 g/L TDS. I want to maintain an oxidising Eh of +600 mV throughout but I am getting errors in React related to e-/Eh, O2 (e.g. don't know species Eh). Is there a way to set this up reaction using hmw or pitzer (or other) databases so I can (i) evaporate to various points evaluate SI's, and (ii) using this new brine composition to examine Cu or Zn speciation at each point in for instance Eh-pH diagrams?

 

A sample .gss file is attached if that is of help. Many thanks to any/all for any assistance.

 

Kaizen

Brine chemistry.gss

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Hi Kaizen,

 

The availability, accuracy, and comprehensiveness of thermodynamic datasets will affect how you set up your simulations. Depending on the extent of evaporation, there is a potential to reach very high ionic strengths which might necessitate use of the Pitzer/HMW/virial methods instead of the standard B-dot variation of the Debye-Huckel equation. The thermo_hmw and thermo_phrqpitz are the two datasets distributed with the GWB recommended for use. These datasets do not contain data for many elements, including Cu and Zn. Unless you have access to alternate datasets, you'll need to assess what is most important in your model. If you're interested in those metals, you may need to use a standard dataset like thermo.dat and live with the likelihood of error in estimating activity coefficients.

 

If you'd like to fix oxidation state, that are a few options available. You can add O2(aq)to the Basis (assuming it's in the thermo dataset) and then swap it out for e-. Set Eh to 600 mV, then go to the Reactants pane to "fix Eh." Alternatively, if your water is exposed to the atmosphere, you might swap in O2(g) for O2(aq) and set a fugacity (like a partial pressure) of 0.2, or whatever it may be in your system. You can then fix this gas buffer over the course of your run. Depending on your situation, oxygen gas may be a better constraint than Eh, since there are well-known issues with Eh electrodes.

 

Once your simulation is up and running, you can view how SI, aqueous species, mineral mass, etc. vary as the reaction path proceeds. This may be more useful than a simple Eh-pH diagram, especially since you want the oxidation state to remain fixed.

 

If you post your React script (and thermo dataset if its not from GWB) I can take a look at your specific error.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

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Hi,

 

I am a new user, so please be gentle. I am evaporating an acidic, saline water from mineral processing, >200 g/L TDS. I want to maintain an oxidising Eh of +600 mV throughout but I am getting errors in React related to e-/Eh, O2 (e.g. don't know species Eh). Is there a way to set this up reaction using hmw or pitzer (or other) databases so I can (i) evaporate to various points evaluate SI's, and (ii) using this new brine composition to examine Cu or Zn speciation at each point in for instance Eh-pH diagrams?

 

A sample .gss file is attached if that is of help. Many thanks to any/all for any assistance.

 

Kaizen

 

 

Hi Brian,

 

I probably need to use hmw given the high ionic strength and my need to further evaporate the solution. The challenge I have is that the Fe and Al dissolved into a pH 1.48 solution constitute quite a bit of the cation suite so it is hard to get a satisfactory ion balance with removing these as I will also have to remove anions. I guess my only option is to stick with thermo (with its limitations at very high ionic strength) as you suggest and go from there.

 

Thanks

 

Kaizen

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Hello Kaizen,

 

I would probably not remove anions to achieve charge balance when Fe and Al are excluded. You can just turn charge balance off.

 

The lack of Fe and Al species may be the bigger problem here. If you can't find more datasets/ data in the literature, I would recommend creating separate runs using the Debye-Huckel and virial datasets distributed with GWB. Try to compare your results, keeping in mind that with a D-H dataset you'll probably have more coverage of all the components in your system, but with the virial datasets you'll likely have a better handle on the solubility of the minerals that are included.

 

Regards,

Brian

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