Juan Posted February 9, 2012 Share Posted February 9, 2012 Hi Brian: I am trying to equilibrate a real water sample and react it with uraninite. Testing with different mass(g)of uraninite and running the simulation several times produces a singular matrix on 1-th iteration. I expected to view results in tabular form and output plot results as the K-feldspar example. Should I send you some water analysis to have more information of the simulation?. The analysis include Eh, temperature, pH, U, TDS and trace and mayor elements. Thanks a lot. Juan Carlos Burillo Quote Link to comment Share on other sites More sharing options...
Brian Farrell Posted February 14, 2012 Share Posted February 14, 2012 Hi Juan, Please attach your React script (.rea file) and whatever water sample analysis you are using so I can try to figure out your problem. Thanks, Brian Farrell Aqueous Solutions LLC Quote Link to comment Share on other sites More sharing options...
Juan Posted February 14, 2012 Author Share Posted February 14, 2012 Hi Brian, I am sending you two files. Apr10_sample 15 doesn´t run so I can´t see plot results. However Nov09_sample 11 runs perfectly, React let me visualize a minerals (grams) vs. uraninite reacted (mg) gtplot. Can you explain me a reason why it sometimes run and other times don´t? I mean, I just change the chemical analysis in both tests. Thanks Juan Apr10_sample 15.rea Nov09_ sample 11.rea Quote Link to comment Share on other sites More sharing options...
Brian Farrell Posted February 15, 2012 Share Posted February 15, 2012 Hi Juan, A few things. When choosing the ion to use for charge balance, it often helps to have one at a high concentration. In this example, Cl- is present at much lower concentrations than many of the other ions, like HCO3-. I noticed that the concentration of O2(aq) in the nonworking script is 1.0e23 mg/kg. That is awfully high. Dissolved oxygen in equilibrium with the atmosphere is approximately 8 mg/kg. If you set a more reasonable concentration, and swap out U++++ for UO2++ (a more oxidized U species) the simulation will run. Basis swapping is important for constraining your initial system, and providing an initial guess for the solver. To constrain the carbonate system, for example, use CO2(aq) at low pH and CO3-- at high pH. Similarly, in a reducing environment, you might use HS-, but SO4-- would work better in a more oxidized environment. Please take these suggestions into consideration and see if you can get your script running. Cheers, Brian Quote Link to comment Share on other sites More sharing options...
Juan Posted February 16, 2012 Author Share Posted February 16, 2012 Hi Brian, As you suggest, choosing the correct ion in charge balace, using reasonable concentrations, swaping and constraining systems are very important aspects of modeling. Both samples run now, so that plot results are obtained correctly. One Question: I swapped U++++ for UO2++ but I didn´t change the concentration value (for this line) in the Basis pane, Is there any problem with that?. I am trying to estimate the concentration of uranium in one nonsampling well base on other uranium concentrations deep-well results. Toposecuence is composed of volcanic and alluvial profiles developed on a riolite basement. Basalts and clay lens are present also.Distance between wells is 20m approximately. Thanks a lot. Juan Quote Link to comment Share on other sites More sharing options...
Brian Farrell Posted February 17, 2012 Share Posted February 17, 2012 Hi Juan, When you specify the analytical concentration of U++++ or UO2++, you specify the total amount of dissolved Uranium, otherwise known as the Uranium component. The sum of all U species, including U++++, UO2++, etc. will add up to the analytical concentration that you specified, so you should not change this concentration. The program will solve for the distribution of mass between the various Uranium species. It is best to choose (swap in) a Uranium species which is likely to be dominant in your system in order to make the numerical solution easier. Hence, choose UO2++ (U(VI)) in an oxidizing environment, and U++++ (U(IV)) in a reducing environment. As for using GWB to predict the concentration of Uranium in nonsampling wells, that's a little more difficult. Do you have reason to believe your formation water is in equilibrium with some uranium mineral? Do you believe that some reaction is controlling uranium concentration, and you can set up some sort of reaction path/ reactive transport model? Do you have the concentration of other analytes in these other wells? You might try plotting U concentration vs. other analytes and looking for some sort of correlation, or you might try some sort of spatial interpolator. Quote Link to comment Share on other sites More sharing options...
Juan Posted February 17, 2012 Author Share Posted February 17, 2012 Hi Brian, Estimate uranium concentrations on nonsampling wells is more difficult than I thought. Thanks for your hints and sharing your knowledge on GWB but specially on geochemistry. I really appreciate it! Thank you ver much Juan Quote Link to comment Share on other sites More sharing options...
Brian Farrell Posted February 27, 2012 Share Posted February 27, 2012 You're welcome Juan. Glad I can help out. Cheers, Brian Quote Link to comment Share on other sites More sharing options...
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