Point of zero charge

[Ihor]

Hi, I'm Kovalenko Ihor, PhD Student from Ukraine.

I'm trying to find out how can I calculate Point of zero charge. Is it possible with GWB?

I'm have an GSS file with data of full chemical analysis of water sample including pH, 90Sr activity. In GSS I calculated the Ionic strength, SrCO3, SrOH+, SrNO3+. Is it possible to calculate Pzc for example with SpecE8?

Thank you.

[Jia Wang]

Hello Kovalenko,

SpecE8 solves the chemical mass distribution of species at equilibrium given a complete chemical analysis of a fluid. If you are using a two-layer surface complexation model, you can plot the pH vs the surface charge after the calculation is finished. To find the point of zero charge, you can recalculate at different pH values until you get to a surface charge of 0 in SpecE8.

If you have access to the Standard and Professional Edition, you can use React to set a sliding pH path to scan across a range of pH values. This way, you can view a range of surface charge values corresponding to the pH values.

Best regards,
Jia Wang
Aqueous Solutions LLC

[Ihor]

Can you please tell where can i find "surface charge" parameter to plot it with pH?

[Jia Wang]

Hello,

In Gtplot configuration, you would select the Variable type "Surface parmeters" and see the option for "HFO surface charge). You can select this for one of the axes and pH value (under Variable type "Chemical parameters) on the other axis. Please note that this variable type would only appear if you have loaded a surface complexation reaction dataset for your run. For more information on configuring XY plots in Gtplot, please see sections 6.2 in the GWB Reaction Modeling User Guide.

Hope this helps,
Jia

[Ihor]

Thank you for help.

Could you please explain how can i find out what type of sorbing surcace should i choose?

And as I understood in SpecE8 I can work only with one water sample at once, right?

[Jia Wang]

Hello,

The software is capable of modeling both two-layer and triple-layer surface complexation reactions in addition to a wide range of more simple sorption processes (e.g. distribution coefficient approach, freundlich isotherm, langmuir isotherm). You can chose the surface model that's best suited for your problem based on the details provided for each type in section 7.7 Sorption onto mineral surfaces in the GWB Essentials User Guide. Once you determine the type that is most suitable for your work, you can use the surface reaction datasets provided (Gtdata folder where GWB is installed) as templates for customizing a reaction datasets you can use for your calculations.

Only one water sample can be loaded in a SpecE8 instance at a time. You can, however, launch multiple SpecE8 samples at the same time in GSS. Please refer to section 3.5 Launching SpecE8 and React.

Hope this helps,
Jia