# PhreeqcUsers Discussion Forum

## Processes => Oxidation and reduction equilibria => Topic started by: Charlie on March 12, 2014, 10:02:09 AM

Title: Redox calculation example
Post by: Charlie on March 12, 2014, 10:02:09 AM
#Simulation of redox reactions with the stepwise addition of organic carbon. (Based on example in Appelo and Postma, 2005)

TITLE Redox calculations

SOLUTION 1
units mmol/kgw
pH   6.5
Na   1.2
Cl   1.5
O(0)   0.12
N(5)   0.06
Mg   0.12
S(6)   0.09
Ca   0.07
Alkalinity   0.3

EQUILIBRIUM_PHASES 1
Goethite   0   2.5e-3
FeS(ppt)   0   0
Pyrolusite   0   4e-5

REACTION 1
C
0.6E-3 in 25 steps
INCREMENTAL_REACTIONS true

USER_GRAPH
headings C   O2   NO3   Mn   Fe   SO4   S(-2)   C(-4)
axis_titles   "Carbon added (mmol/L)" "Concentration (mol/L)"
-start
10 graph_x step_no * 0.6/25       #converted from mol/L to mmol/L
20 graph_y tot("O(0)")/2, tot("N(5)"), tot("Mn(2)"), tot("Fe(2)"), tot("S(6)"), tot("S(-2)"), tot("C(-4)")
-end

END
Title: Re: Redox calculation example
Post by: JG on May 11, 2015, 03:41:34 PM
Hi. I ran this.

(there is a missing parenthesis in Basic line 20: => ... tot("N(5)"), ... )

Not much is happening. Not enough C added?
Title: Re: Redox calculation example
Post by: dlparkhurst on May 11, 2015, 04:02:34 PM
Your solution is defined as mol/kgw. So, you have 112 mmol of O(0) and add only a fraction of a millimole of C, which makes only a small dent in the O2(aq) concentration. You probably mean mmol/kgw for your solution; then, mmol of C will make a difference.
Title: Re: Redox calculation example
Post by: Charlie on July 03, 2015, 02:20:13 PM
Thanks - have amended the script above