[OLD] Perchlorate

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From: Henry Kerfoot

Subject: Perchlorate

I am trying to assess the reduction of perchlorate by addition of organic compounds. However, GWB wants an initial chloride concentration. It seems as if decoupling ClO4- and inputing both initial chloride and Initial perchlorate concentrations results in a lack of reduction of perchlorate, even when elemental Carbon is being formed. Even kilogram amounts of Ethanol do not reduce 225 mg/l perchlorate (but make methane) ... My script for reaction with 0.3 mole Ethanol is attached ......

If I swap ClO4- for Cl- with the two coupled, the Step 0 concentrations in the output show Cl- but no ClO4-. Sometimes I get two sets of Step 0 outputs, and I always thoughtv that the first was the input data and the second showed the results of initial equilibration of the system .... In Step 0 (the first Step 0, where the initial equilibration has not yet occurred, with reactants not consumed at all) I find chloride but no ClO4-. (.. So, it seems as equilibration has taken place ... ??) What is the appropriate method to evaluate the reduction of perchlorate by Ethanol, if there is one? Am I missing a command that would allow me to do this?

 

From: Craig Bethke

Subject: Re: Perchlorate

Try this: first decouple chlorine compounds (since you don't want to set a redox equilibrium between perc and chloride) and carbon compounds (since you want your reductant to be in redox disequilibrium w/ carbonate). Then set a kinetic rate law for the reaction you want to model.

E.g., 3 ClO4- + 2 Ethanol -3 Cl- + 4 HCO3- + 4 H+ + 2 H2O

 

From: Henry Kerfoot

Subject: Re: Perchlorate

I am getting a message that says the kinetic law is applicable only to Minerals.....? I seem to get that message when I try to input first-order perchlorate decay ..... With the perchlorate and ethanol decoupled, the O2(aq) (approximately 5 mg/l) does not seem to react with the Ethanol either ......

My objective is to model the reaction of Ethanol with the stoichiometric amount of perchlorate (including O2(aq) and nitrate electron demands) and to observe what happens to the dissolved manganese concentration with and without addition of CO2(g) for pH control. For 225 mg perchlorate (and 5 mg O2(aq) and 10.5 mg NO3-) I am adding 75.15 mg Ethanol.

 

From: Craig Bethke

Subject: RE: Perchlorate

You need to set a kinetic redox, not mineral reaction. There are examples in the User's Guide, under “Kinetics of Redox Reactions�.