Compute the chemical equilibria of single chemical systems (SysEq)

Transcription

1 MODULE 2: REACTION PATH MODELING In this tutorial, you will learn to model the reaction path of K-feldspar in contact with a NaCl-bearing aqueous solution and calculate the evolution of the fluid and the minerals formed as a function of increased fluid-rock interaction. We will use the GEMS project file Module2 located in the Module2/Examples folder. Installation instructions for GEMS can be found at html Compute the chemical equilibria of single chemical systems (SysEq) 1. Copy the folder Module2 to your project folder located in Library\Gems3\projects. 2. Open GEMS and choose the project in the Equilibria Calculation Mode. The user interface is shown in Figure 1. Panel 1 permits to create new records and run the program for calculations. Panel 2 gives you different calculation options. 3. Choose the Create New Record System from the menu in Panel 1 and fill the parameters listed in Figure 2 4. In the Open recipe dialog, which can also be found in Panel 1, add phases, quantity and units as shown in Figure 3; Aqua (1000 g), HCl (0.1 M), NaCl (50 g), O 2(g) (1e-7) and K-feldspar (10 g). Fig. 1: GEMS user interface 1

2 Fig. 2: New record window 5. Model the chemical equilibrium between 10 g of K-feldspar (microcline) and H 2 O at 150 C by pressing Calculate BCC followed by Calculate Equilibrium in Panel 1. Inspect the pop up window with ph, redox and phase proportions, then accept. (a) Determine the ph of this system as shown in the lower right of the main window (Figure 4). (b) What is the ph of this system with 10, 20, 50 and 100 g K-feldspar? Change the amount of feldspar by clicking the Open recipe dialog (Figure 3) followed by Calculate BCC and by Calculate Equilibrium. (c) What minerals are stable with increasing ph? 6. Clone your existing Rct path 1 chemical system by selecting it and choosing Clone a new record in Panel 1. Change the temperature to 300 C in the pop up window. (a) Determine the ph of this system as shown in the lower right of the main window. (b) What is the ph of this system with 10, 20, 50 and 100 g K-feldspar? 2

3 (c) What minerals are stable with increasing ph? (d) Are there differences between the modeled system at 150 and 300 C Fig. 3: System Recipe dialog moles minerals ph Fig. 4: Results of the calculations, i.e. with 10 g K-feldspar added to the fluid. 3

4 Compute processes using a titration model (Process) 1. Select the Process option in Panel 2 (Figure 1). 2. Click Creat a record from scratch in Panel 1 and select your system (SysEq) calculated at 150 C (Figure 5). 3. Name this process simulation titration model and use the Process simulation code (S) as shown in Figure In the next window, choose a model ( titration cnu linear), a mineral ( Compos, Min K-feldspar) and select the temperature (150 C), pressure (0 for water vapor saturation P) and amount of mineral to be added (inu: g in 10 g steps) as shown in Figure Select items to be plotted (Scalars: ph; Xa: Kaolinite, Pyrophyllite, Microcline, Muscovite, Albite and Quartz) as shown in Figure Accept all the following dialogues and click on Save this record to database in Panel 1 (Figure 1). Then click on the calculator icon Re-calculate and check record data. 7. There is a tab menu with 3 important selections: Controls, Sampling and Results. In the Controls tab add a description of the modeling project (Figure 9). In the Sampling tab change the script as shown in Figure 10 to choose as x-variable the amount of K-feldspar added (the process extent: cnu). Click Save this record to database and the calculator icon (Re-calculate and check record data) in Panel 1. Toggle to the Results tab to inspect your modeling results. (a) How many grams of K-feldspar need to be added to get a constant ph and what is the value? (b) Which mineral assemblages buffer the fluid ph, are there different ranges? 8. Clone your existing Rct path 1 chemical system by selecting it and choosing Clone a new record in Panel 1 (Figure 1). Select your system (SysEq) calculated at 300 C (Figure 11). Accept all the following dialogues. In the Controls tab (Figure 9) change the description of the modeling project and change the temperature to 300 C to replace the starting and ending values of 150 C. Click Save this record to database. 4

5 9. Switch the tab to Results and click the calculator icon (Re-calculate and check record data) in Panel 1 (Figure 1) to see how ph and mineralogy is changed by varying the system temperature. 10. Toggle between both calculated process simulations at 150 and 300 C on the left pane and inspect the results. (a) How many grams of K-feldspar need to be added to get a constant ph and what is the value? (b) Which mineral assemblages buffer the fluid ph, are there different ranges? (c) What are the main difference for the simulations at 150 and 300 C? 11. Finally, we are going to fine tune the model and plot it! Choose the process simulation at 150 C and in the Controls tab change the amount of K-feldspar to be added (Figure 9) using 2 to 50 g in 2 g steps and save. Choose the Results tab and click the calculator icon (Re-calculate and check record data). Click on the small Plot data on Graph dialog in Panel 1 (Figure 1). The resulting graph should look similar to Figure 12. The plots indicate different mineral assemblage buffer the fluid at different ph values. You can inspect which minerals by choosing the Customize button with values shown in Figure The resulting reaction path at 150 C is shown in Figure The resulting reaction path at 300 C is shown in Figure 15 5

6 Fig. 5: Select a chemical system (SysEq) for modeling a Process Fig. 6: Name the Process and indicate the type (note: the process type code names are described and changeable on the next screen as well) 6

7 P at psat (1) titration model T at 150 ºC (2) choose mineral add g of min in 10 g steps Fig. 7: Set the parameters for the Process simulation 7

8 Fig. 8: Choose the results to be plotted description amount of min pressure temperature added modeling script Fig. 9: The Controls dialog for defining the model conditions 8

9 choose x-variable choose y-variables Fig. 10: The Sampling dialog for selecting the output data to plot. single chemical systems from SysEq Results from Process simulation Fig. 11: Choosing a SysEq record when cloning a Process simulation 9

10 Fig. 12: Results using the Plot data on Graph dialog (1) (2) Fig. 13: Customize x- and y- axis in the plots (1). Note: the Fragment option (2) permits to select an inset view in the graph by toggling the Fragment button in the graph (see Figure 12) 10

11 Fig. 14: The resulting reaction path at 150 C Fig. 15: The resulting reaction path at 300 C 11