1. Sorption processes in soil general term referring to the retention of material on solid surfaces - can include adsorption, surface precipitation, and polymerization

2. I. Adsorption - terminology Accumulation of a substance between a solid surface and the solution. Not including surface precipitation and/or polymerization. Different from absorption which refers to ingestion or uptake into a plant or solid body.

3. sorbent sorbate sorptive

4. Why study sorption? Important chemical process in soil affecting nutrients, contaminants,… http://www.btny.purdue.edu/Pubs/PPP/images/PPP-35.fatestransfer.jpg

5. www.montana.edu/wwwpb/pubs/mt200405.html Factors affecting the fate of soil-applied herbicides

6. Forces involved in Adsorption Physical forces (distance and valence) a.van der Waals (weak electrostatic forces between nonpolar molecules due to temporary dipole moment) b.Electrostatic complexes (e.g., ion exchange) Chemical forces (electron reconfiguration; breaking/making bonds) a. inner-sphere complexation (ligand exchange, covalent/ionic bonding, aka chemisorption or specific sorption)

7. http://www.columbia.edu/cu/biology/courses/c2005/images/vdw.gif

8. http://www.mpi-muelheim.mpg.de/kofo/ institut/arbeitsbereiche/schueth/grafik/z_ion_exchange.gif Ion Exchange (electrostatic complex)

9. Silica-based material being attacked by water. The process involves water physisorption (charge attraction) onto the surface, followed by chemical reactions with the surface (chemisorption) that break structural bonds. http://www.mri.psu.edu/faculty/pantano/group/leed/research.htm

10. II. Surface Functional Groups, (chemically reactive molecular unit on a solid surface) Organic: carboxyl, carbonyl, phenolic

11. Inorganic SFG’s O atoms of the silica tetrahedral layer (siloxane surface) in the interlayer region of phyllosilicates OH groups associated with edges of minerals http://surface.chem.uwm.edu/tysoe/research/Crown.gif

12. www.dartmouth.edu/~soilchem/uranium.htm Uranium Adsorption on Soils SFG’s

13. SFG's can be protonated or deprotonated by reaction in water to form exchange sites: S-OH + H + ↔ S-OH 2 + protonation (gains protons) S-OH ↔ S-O - + H + deprotonation (loses protons) S-OH + OH - ↔S-O - + H 2 Odeprotonation (loses protons)

14. www.humet.hu/141-vizsgalat-en.shtml Surface Functional Groups on Soil Organic Matter

15. III. Surface Complexes: SFG + ion or molecule in solution = stable molecular entity, called a surface complex. A. Outer-sphere complex - water molecule is present between the SFG and bound (adsorbed) ion or molecule. Also includes Diffuse Ion Swarms in solution. B. Inner-sphere complex - no water molecule present between the SFG and bound ion or molecule. C. Inner and outer-sphere complexation occurs simultaneously (i.e. not mutually exclusive).

16. Outer Sphere Complex weak (H-bonding) electrostatic interaction, thus surface must be charged rapid reversible (exchangeable) affected by ionic strength of the solution

17. Inner-Sphere Complex Strong (covalent and/or ionic bonding) Mono- or polydentate (held by one or more bonds) May be slower than outer sphere complexation Often irreversible or “fixed” depending upon environmental conditions Weakly affected by solution ionic strength Surface charge can be changed by complexation Charged surface is not required for complexation

19. Omoike A., J. Chorover, K. Kwon, and J.D. Kubicki (2004) Adhesion of bacterial exopolymers to FeOOH: Inner-sphere complexation of phosphodiester groups www.geosc.psu.edu/envchem/2.3.htm

20. IV. Adsorption Isotherms Conducting sorption experiments

21. Sorption experiments Equilibrate sorptive (chemical) with sorbent (soil) –Same Temperature and Pressure –Control or measure Ionic strength and pH Batch equilibrium experiments Column or flow-through experiments

22. Batch equilibration – unrealistic but easy, fast, common, maximum “q” Shake or stir soil with solution containing chemical of interest (sorptive) –Shaking or stirring too long may cause minerals to dissolve, weather, and/or precipitate new minerals –Insufficient mixing means that all surface functional groups may not be reached –Overly vigorous mixing may break minerals and expose new functional groups on edges

23. Batch sorption experiments 0 1 5 10 … 100 mM + Blanks Include a range of sorptive concentrations in a buffer. Keep as many variables the same to measure sorption. Solution + soil

24. 1.Equilibrate sorbent (soil) with sorptive (chemical in solution over reasonable range) 2.Measure solution composition and volume before and after equilibration 3.Control or measure I, pH, T, and P ALWAYS RUN BLANKS throughout experiment 4.Separate solution from soil by centrifugation, settling, or filtering; or collect leachate 5.Calculate sorption (q) by mass balance and plot Sorption experiments

25. Flow or column experiments Pass solution through soil and collect leachate. –Columns can be packed or collected directly from soil. No standard size or flow rate. Problems include macropores, cracks, inadequate exposure of sorptive to all functional groups. –Column size and packing affects results

26. http://www.clemson.edu/agbioeng/bio/images/sumint/fen3.jpg

27. http://www.hydrogeologie.tu-berlin.de/_data/images/sv2.jpg http://www.soilmeasurement.com/images/Tempe_cell.jpg http://www.sce.ait.ac.th/facilities/irrlab/images/Imagep30c.jpg