PrintHomework Question 1: extension of example 3.1 (total 90 points):
If instead we have two types of surface sites on illite surface with the reactions and parameters shown in Tables 5. All other conditions remain the same as in example 3.1.
- (10 points) At the pH of 8.0, calculate the concentrations of surface complexes on the surface sites; what is the pH at equilibrium?
- (10 points) At the pH = 4.0, calculate the concentrations of surface complexes on the surface sites; what is the pH value at equilibrium?
- (30 points) Change pH also to 2.0, 6.0, and 10.0 and run simulations. Combining simulation results from 1) – 3), plot total sorbed Cr(VI) and Na(I) as a function of pH. How does pH change the sorbed concentration for Na(I) and Cr(VI)?
- (40 points) At the pH of 8.0, run the simulation using the specific surface area of 1, 5, 25, 50 m2/g. Combining simulation results from 1), plot total sorbed Cr(VI) and Na(I) as a function of specific surface area. How does specific surface area change the sorbed concentration for Na(I) and Cr(VI)?
| Initial conditions | Value |
|---|---|
| Temperature | 25oC |
| Solution volume | 250 mL |
| pH | 8.0 |
| Total CrO4-- | $9.61 \times 10^{-5} \mathrm{~mol} / \mathrm{L}$ |
| Na+ | 0.01 mol/L |
| Cl- | 0.01 mol/L |
| K+ | $18.5 \times 10^{-5} \mathrm{~mol} / \mathrm{L}$ |
| Site density $\equiv \mathrm{SiOH}$ | $1.0 \times 10^{-6} \mathrm{~mol} / \mathrm{m}^{2}$ |
| Site density $\equiv A l O H$ | 0.1 10-6 mol/m2 |
| Illite specific surface area | 15.36 m2/g |
| Illite volume fraction | 0.003 |
| Reactions | Log K |
|---|---|
| $\equiv\mathrm{SiOH}+\mathrm{H}^+\Leftrightarrow\ \equiv\mathrm{SiOH}_2^+$ | 0.95 |
| $\equiv\mathrm{SiOH}\quad\Leftrightarrow\ \equiv\mathrm{SiO}^-+\mathrm{H}^+$ | -6.59 |
| $\equiv\mathrm{SiOH}+\mathrm{Na}^+\Leftrightarrow\ \equiv\mathrm{SiONa}+\mathrm{H}^+$ | -6.60 |
| $\equiv \mathrm{SiOH}+\mathrm{CrO}_{4}^{2-}+2 \mathrm{H}^{+} \Leftrightarrow\left(\equiv \mathrm{SiOH}^{0}-\mathrm{H}_{2} \mathrm{CrO}_{4}^{0}\right)^{0}$ | 14.50 |
| $\equiv\mathrm{AlOH}+\mathrm{H}^+\Leftrightarrow\ \equiv\mathrm{AlOH}_2^+$ | 5.70 |
| $\equiv AlOH\quad\Leftrightarrow\ \equiv AlO^-+H^+$ | -11.40 |
| $\equiv AlOH+Na^+\Leftrightarrow\ \equiv AlONa+H^+$ | -9.15 |
| $\equiv\mathrm{AlOH}+\mathrm{Cl}^-+\mathrm{H}^+\Leftrightarrow\ \equiv\mathrm{AlOH}_2\mathrm{Cl}$ | 7.90 |
| $\equiv \mathrm{AlOH}+\mathrm{CrO}_{4}^{2-}+\mathrm{H}^{+} \Leftrightarrow\left(\equiv \mathrm{AlOH}_{2}^{+}-\mathrm{CrO}_{4}^{2-}\right)^{-}$ | 9.42 |
| $\equiv \mathrm{AlOH}+\mathrm{CrO}_{4}^{2-}+2 \mathrm{H}^{+} \Leftrightarrow\left(\equiv \mathrm{AlOH}_{2}^{+}-\mathrm{HCrO}_{4}^{-}\right)^{0}$ | 16.30 |