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Equation syntax for surface area.

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I want to use the equation feature of surface area of a reactant. What could be syntax for the attached equation (SSA - specific surface area, d = particle diameter)? Also how can we do the same in case we have time in our equation? I looked in the guides but couldn't find any examples for this.


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You can set the specific surface area to vary with time and many other properties, like volume or mineral mass using a custom equation, script, script file, or even a compiled C++ function . The custom method and accepted syntax for each is the same as that of setting a custom kinetic rate law, which you can find detailed information and examples of in Chapter 5 Custom Rate Laws in the GWB Reaction Modeling Guide. Table 5.1 and 5.2 shows the list of internal parameters and helper functions that can be used in your customized input.

The GWB does not keep track of particle size of minerals but it does keep track of mineral volume as precipitation and dissolution occurs. You won't be able to use the particle size minerals directly in the equation. The program takes in a mineral mass or volume and a total surface area is calculated based on the specific surface area (area/g). If you have a measurement of particle size, you can plug it in the equation and set the SSA as a constant value for the simulation. If you also have a correlation between the particle size and one of the other properties (e.g. mineral volume), you can use one of the custom options mentioned above.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

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