Welcome,
Guest
. Please
login
or
register
.
Did you miss your
activation email
?
1 Hour
1 Day
1 Week
1 Month
Forever
Login with username, password and session length
Forum Home
Login
Register
PhreeqcUsers Discussion Forum
»
Processes
»
Oxidation and reduction equilibria
»
Laboratory vs PHREEQC Redox States
« previous
next »
Print
Pages: [
1
]
Go Down
Author
Topic: Laboratory vs PHREEQC Redox States (Read 1590 times)
awillou4
Frequent Contributor
Posts: 16
Laboratory vs PHREEQC Redox States
«
on:
June 25, 2017, 12:16:58 AM »
I'm dealing with a situation where lab redox & pH imply a particular redox state; however PHREEQC concentration outputs only match lab data when using a different redox state. In my case my lab solution chemistry implies As(5); however PHREEQC isotherms only fit when As(3) is dominant (As(3) has a much smaller affinity for HFO). I've included a basic version of my input with complete water chemistry below.
I'm wondering if its possible that the dominant species in my lab isotherms is actually As(3), even though redox and pH suggest otherwise. If not, perhaps the native soil I used could have introduced competing ions which allowed As(5) to sorb far less during my batch runs?
SURFACE 1
Hfo_wOH 6.71E-06 600 0.00504
SOLUTION 1
temp 25
pH 6.27
pe 4
redox pe
units ppm
density 1
As(3) 0.403
B 0.397
Ca 20
Cd 0.446
Cr 0.516
Mg 5
Mo 0.389
S(6) 25
Se 0.636
Tl 0.624
V 0.245
Na 10
C(4) 10
-water 0.2 # kg
USE solution 1
USE surface 1
Logged
dlparkhurst
Top Contributor
Posts: 2483
Re: Laboratory vs PHREEQC Redox States
«
Reply #1 on:
June 25, 2017, 12:59:48 AM »
If you measured A(5) then I would tend to believe it is A(5), in which case, you could consider whether the characteristics and log Ks of Hfo are adequate, or whether the sorption characteristics of your soil may be different.
If you measured redox with a platinum electrode, I would not put too much faith in it. What the electrode responds to is in question, but it probably is not responding to As. So, I think you would need other evidence to try to estimate the state of the As in your system.
Logged
Print
Pages: [
1
]
Go Up
« previous
next »
PhreeqcUsers Discussion Forum
»
Processes
»
Oxidation and reduction equilibria
»
Laboratory vs PHREEQC Redox States