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Clarification on SA/V parameter in Kinetics
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Topic: Clarification on SA/V parameter in Kinetics (Read 295 times)
rfembilejr
Top Contributor
Posts: 60
Clarification on SA/V parameter in Kinetics
«
on:
July 23, 2017, 03:29:16 PM »
Hi,
Another clarification I wanted to ask is the use of the SA area parameter for a rate expression.
I come upon an article by Eary and Willimason (2006), which made me think about which should I use. Although in the user manual, for pyrite oxidation, the following is shown (this is what I am following as a format):
Basic: 1 rem PARM(1) = log10(A/V, 1/dm)
Q: In this case, the surface area A has a unit of m2 while V has a unit of dm3? I guess I am just confused on how to come up with 1/dm. Do I just convert the m2 to dm2 to obtain the 1/dm unit?
In Eary and Williamson (2006), they showed that Phreeqc may use the general equation adapted from Palandri and Kharaka (2004):
Rate(mole/kg/H2O) = (A/M) (k_H(H+)^a + k_w + k_OH(OH)^b)
In this case, they were saying that the surface area parameter has the unit of m2 per kg H2O, thus the A/M and not A/V term.
They were saying that the surface area (m2/g) is multiplied by the mineral contents per kg H2O to give the surface area per kg H2O. Now, I am not quite sure how to get the mineral contents per kg H2O.
Q: If I am to use this rate expression, is the mineral content just the mineral fraction in a kg of material? But it says kg of H2O. I'm confused.
Thanks in advance for shedding some light on this.
Rodrigo
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dlparkhurst
Top Contributor
Posts: 1073
Re: Clarification on SA/V parameter in Kinetics
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Reply #1 on:
July 23, 2017, 07:34:17 PM »
When you use the SAVE function in a rates expression, the units are moles. Note that this is not necessarily mol/kgw or mol/L, if the solution does not contain 1 kg or 1 L. (In particular, for PHAST version 3, the volume of water in the representative volume of a saturated system is generally equal to the porosity.)
Use whatever units are necessary to arrive at the moles of reactant that enter/leave the solution of volume SOLN_VOL over the time period given by TIME, while accounting for surface area if necessary. Note that SOLN_VOL is well defined only for phreeqc.dat, amm.dat, and pitzer.dat.
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rfembilejr
Top Contributor
Posts: 60
Re: Clarification on SA/V parameter in Kinetics
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Reply #2 on:
July 24, 2017, 11:50:48 AM »
I guess I will have to make adjustments since I have 2 kg in my columns.
Thanks, it much clearer now.
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Clarification on SA/V parameter in Kinetics