1. TRACE METAL TRANSFER FROM ROCKS TO THE PEDO- AND HYDRO- SPHERES

2. ROCK WEATHERING 1 Physical weathering 2 Biological weathering 3 Chemical weathering: Acid dissolution of minerals Congruent and incongruent dissolution Primary and secondary minerals Balancing weathering chemical reactions DEFINITIONS

3. Rain Water as Weathering Agent  Solubility of CO 2 in water  pH of natural rain and pristine waters  Example determination of pH of pristine rain water  Determine the pH of rain water if the following is given:  T =25 0 C, P CO2 =10 -3.5 bar  The chemical equilibria applicable to the problem are:  CO 2 + H 2 O  H 2 CO 3 k 1 = 10 -1.47 (1)  H 2 CO 3  H + + HCO 3 - k 2 = 10 -6.35 (2) Answer: pH ~ 5.7

4. Balancing Weathering Rxns  Select the mineral that undergoes weathering and on the left side of the weathering equation place  Selected mineral + CO 2 + H 2 O  Example: CaAl 2 Si 2 O 8 (anorthite) + CO 2 + H 2 O  Select/identify the secondary mineral formed as result of chemical weathering and place on the right side of the equation  CaAl 2 Si 2 O 8 + CO 2 + H 2 O  Al 2 Si 2 O 5 (OH) 4 (kaolinite)  Balance aluminum atoms (Al)  CaAl 2 Si 2 O 8 + CO 2 + H 2 O  Al 2 Si 2 O 5 (OH) 4 In this case, Al already balanced (2 on each side)  Release and balance cations  CaAl 2 Si 2 O 8 + CO 2 + H 2 O  Al 2 Si 2 O 5 (OH) 4 + Ca 2+  Set bicarbonate (HCO 3 - ) to balance electrical charges  CaAl 2 Si 2 O 8 + CO 2 + H 2 O  Al 2 Si 2 O 5 (OH) 4 + Ca 2+ + 2HCO 3 -  Balance Si with H 4 SiO 4  CaAl 2 Si 2 O 8 + CO 2 + H 2 O  Al 2 Si 2 O 5 (OH) 4 + Ca 2+ + 2HCO 3 - (Si is already balanced in this case)  Set the number of CO 2 molecules to balance carbon atoms in HCO 3 -  CaAl 2 Si 2 O 8 + 2CO 2 + H 2 O  Al 2 Si 2 O 5 (OH) 4 + Ca 2+ + 2HCO 3 -  Use water molecule(s) on the left to balance hydrogen (H)  CaAl 2 Si 2 O 8 + 2CO 2 + 3H 2 O  Al 2 Si 2 O 5 (OH) 4 + Ca 2+ + 2HCO 3 -  Count oxygen atoms (O) on both sides of the equation to check balance  [O] left = 15and [O] right = 15

5. Example Weathering Rxns  Write and balance the weathering equations of the following conversions:  Ca 2 Mg 4 AlSi 7 AlO 22 (OH) 2 to Al 2 Si 2 O 5 (OH) 4  CaMg(CO 3 ) 2 to Al 2 Si 2 O 5 (OH) 4

6. 4 Tracer: –Element or compound that is or can be assumed nearly inert during weathering –Examples include: Al 2 O 3, ZrO 2, and TiO 2 5 Enrichment factor (EF) –The EF of an element “X” in the environmental compartment receiving the product of weathering can be determined as follows: DEFINITIONS (Cont’d)

7. Illustration of Atmospheric EF vs. Physicochemical Parameters 1.Predictive approaches for metal enrichment in the atmosphere (see handout) 2.Trace metal atmospheric EF vs. boiling point of oxides (see handout)

8. Weathering Control on Surface Water Major Element Chemistry  Mechanisms controlling world water chemistry (see Handout)  Weathering  Precipitation  Evaporation/Crystallization

9. A WEATHERING EXAMPLE Composition of a granitic-type rock and of its weathering products  Determines chemical and biological properties of water

10. Weathering and Control on water Chemistry Weathering – Precipitation- Evaporation/Crystallization