Print1. Carbonate Dissolution (Example 1 extension) (Total 70 points, each sub question is 10 points):
Thermodynamics and kinetic parameters that affect mineral dissolution include specific surface area (SSA), kinetic rate constants (k), and equilibrium constants. In addition, geochemical conditions can also have a large impact on mineral dissolution rates, including salinity (e.g. NaCl) and pH. With the provided CrunchFlow template files in example 1 as a starting point, please do the following analysis comparing Ca(II) concentration evolution under different parameters and geochemical conditions. In each question, please only change the parameter that is discussed and keep all other parameters the same as those in Example 1.
1) Calcite specific surface area (SSA). In three different simulations, run the code using SSA being 0.024, 0.24, and 2.4 m2/g. Plot the total Ca(II) as a function of time under these surface area values in one figure. Discuss how SSA affects calcite dissolution kinetics.
2) Kinetic rate constant: increase and decrease the original three rate constant values in Example 1 by an order of magnitude. Compare the Ca(II) concentration evolution under the three k values in one figure. Also compare this figure here with the figure in 1) with the SSA of 0.24 m2/g. Do changing k and A have the same impact on dissolution rates?
3) Equilibrium constant Keq quantifies how much a mineral can dissolve in aqueous phase. Increase and decrease the equilibrium constant by an order of magnitude. Please plot the three curves (total Ca(II) ~ t) with different Keq values in one figure. What do the rate kinetics change with the total Ca(II) evolution figure?
4) Initial pH condition. Compare the base case with two more cases where you have the initial pH being 4.0 and 6.0.
5) The role of speciation. In this question you remove all secondary species such as CaOH+, CaCO3(aq), and CaHCO3+. Draw the same figures as those in Example 1 and solution from this question if the same figure. Compare and describe your observations. Does the reaction system evolve in the same way in these two systems? What do you think are the effects of speciation?
6) Salinity: in the base case scenario there is no NaCl in the solution. Simulate two more cases with NaCl at concentrations of 0.01 and 0.1 mol/kgw, respectively. Please compare total Ca(II) evolution under these three salinity conditions.
7) Go back to your answer to each question 1)-6). Summarize your observations in these questions. Which factors have the most significant control on calcite dissolution?
2. Feldspar Dissolution (optional, bonus points: 30, for students who develop clear solution and reasoning):
Feldspars dissolve following the TST rate law and have very different dissolution rates depending on their composition (figure 7 in [Blum and Stillings, 1995]). Pick a feldspar mineral from the paper and/or the cited reference that has a complete TST rate law from acidic to alkaline conditions. Set it up in CrunchFlow to simulate its dissolution with initial pH conditions varying from acidic (for example, pH =4.0), to neutral (pH = 7), and to alkaline condition (pH = 10.0). Compare the reaction production evolution under these three conditions. Please make sure that you use reasonable rate constant and specific surface area values from literature.