1. Solid-Water Interface
Mineralogical transformation
biomineralization
dissolution
precipitation
Mn+
Oxidation
Reduction
Mn+x
release
Bacteria
deposition
Organic
Matter
Mineral
adsorption
Organic ligand
desorption
Soil Profile
complexation
Aqueous Metal Ion
degradation
Metal-Organic Complex
Surface complex

2. Surface Charge Permanent Charge (so) Variable Charge (sH)
>Al-OH-1/2 + H+  >Al-OH2+1/2
>Al=O H+  >Al=OHo + H+  >Al=OH2+

3. Ion Retention
sorption
desorption
Aqueous Metal Ion

4. Types of Ion Retention Adsorption Absorption
Precipitation (homogeneous)
Surface (heterogeneous) Precipitation
Terms
Sorption
Adsorption
Absorption
Surface precipitation
Precipitation
Sorptive
Sorbate
Sorbent

5. Types of Ion Retention c b a Surface precipitation Absorption
Adsorption a

6. Adsorption: Chemical versus Electrostatic

7. Chemical Adsorption: Requirements
1. Chemically Reactive Ion
2. Chemically Reactive Surface

8. Chemical Reactivity of Ions
Ion Reactive (with oxide surfaces)
Cl- no
SO42- partially
NO3- no
F- yes
PO43- yes
SeO32- yes
SeO42- partially
AsO43- yes
AsO33- yes (but conditionally)
CrO42- partially

9. Lewis Acids and Bases
Hard Lewis Acids: H+, Na+, K+, Cs+, Ca2+, Mg2+, Cr3+, Fe3+, Al3+, Si4+
Intermediate Lewis Acids: Fe2+, Co2+, Ni2+, Cu2+, Zn2+
Soft Lewis Acids: Ag+, Au+, Cd2+, Hg2+
Hard Lewis Bases: H2O, OH-, O2-, CO32-, NO3-, PO43-, SO42-, F-
Intermediate Lewis Bases: Br-, Cl-
Soft Lewis Bases: R-SH, S2-, I-

10. Electrostatic Interactions+
Electrostatic Interactions + +
Diffuse
Swarm + + + + +
Outer-sphere complex

11. Ion Selectivity 1 Dehydrated radius (inverse to hydrated radius)
Radius (nm)1
Desorption (%)2
Li+
0.068 68
Na+
0.097 67 K+
0.133 49
NH4+
0.143 50
Cs+
0.167 37
Mg2+
0.066 31
Ca2+
0.099 29
Al3+
0.051 15
Th4+
0.102 2
1 Dehydrated radius (inverse to hydrated radius)
2 Reacted with 1 M KCl or NH4Cl

12. Electrostatic Interactions: Exchange Reactions

13. Eisenman Model rs
Ca2+
ra,b

14. Salt Affected Soils

15. Acid Soils