Tom Meuzelaar Posted May 13, 2008 Share Posted May 13, 2008 [admin notice: the below is from the former GWB users group email distribution list. This message was originally posted 6/13/2006] Posted by: Rachana Agar Hi all: I am a new user to Geochemist Workbench and trying to work with adsorption of arsenic as a function of pH using "FeOH.dat" data file (Input file is enclosed). I wanted to maintain background electrolyte as 0.01M NaCl. Now in React (basis) when i entered these species (Na+= 10mmol, Cl-= 10mmol, As(OH)3= 10mmol) it is showing charge imbalance. In order to balance that i added K+ species and it started working, but the problem is it is changing the ionic strength of the solution. So can you please guide me how can i fix the ionic strength and charge balance together for this type of situation. The second problem is I want to work with Aluminum hydroxide instead of FeOH sorbing surface. Is there any data file for AlOH also in geochemist or if not where can I get log K values for AlOH and arsenic related surface species? And if I am modifying the data file (FeOH.dat) for aluminum hydroxide, do I need to change the thermo file (thermo.dat) also and how can I do that. Here are specifications for this problem: - Software version: Geochemist's Workbench Standard 6.0 - The program in question- React - Platform- Window XP - Dataset- FeOH.dat - File: Attached Thanks a lot in advance for your help and guidance. Rachana Posted by: Craig Bethke Hi Rachana, There are several issues with this input. First, I'm pretty sure you want to set the free mass of Fe(OH)3 to 4 mg, not the total mass. Second, you set the As concentration to 20 mmolal, not 10. If you make these two changes, the program converges. The underlying issue, however, is that you have set a background electrolyte concentration as NaCl and specified an acidic pH as the starting point. But you can't get to pH 3 simply by adding H+; you must also enter a counterbalancing anion like Cl-. So your initial Cl- concentration should reflect not only the background electrolyte but the acid needed to attain the initial pH. Hope this helps, Craig Quote Link to comment Share on other sites More sharing options...
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