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Basic Chemical Principals of Mercury

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Presentation on theme: "Basic Chemical Principals of Mercury"— Presentation transcript:

1 Basic Chemical Principals of Mercury

2 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

3

4 Morel et al., 2002

5 Air Water Hg(II) (s) Hgo (g) Hg(II) Hgo (aq) Hgo (l) deposition
volatilization Water reduction Hg(II) Hgo (aq) Hgo (l) oxidation dissolution Natural concentrations: 5 to 100 pM (1 – 20 ng /L)

6 Air Water Hg(II) (s) Hgo (g) Hg(II) Hgo (aq) Hgo (l)
deposition Air volatilization Water reduction Hg(II) Hgo (aq) Hgo (l) oxidation dissolution Hgo (l)  Hgo (aq) K = (mol/L) Hgo (g)  Hg (aq) K = 2.56 x (mol / L · atm)

7 Hg(II) (s) Hgo (g) Air Water reduction Hg(II) Hgo (aq) oxidation

8 Oxidation-Reduction Reactions
Hg(II) Hgo (aq) Microbially mediated (dominant) Photoreduction oxidation Hgo (aq) Hg(II) Limited in freshwater Particle surfaces catalyze O2 oxidation of Hg-halides (HgCl2, for example)

9 Air Water Hg(II) (s) Hgo (g) Hg(II) Hgo (aq) reduction oxidation
Natural concentrations: 5 to 100 pM (1 – 20 ng /L)

10 Ion Coordination: Hg(II)

11 Solutions Speciation: Differences in molecular configuration
Hg2+, HgCl2o, Hg(OH)2o, Hg(SH)2o, HgS(SH)-, CH3Hg(SH)o

12 Ion Complexes Cation + Anion (termed ligand) => Complex
Hg Cl-  HgCl- Keq = 107.2 (association reaction) Hg(SH)2o  Hg HS- log K = -36.6 (dissociation reaction) Kdiss = (Hg2+) (HS-)2 / (Hg(SH)2o) DG = -RT ln K

13 Oxic (Aerated) Waters Morel et al. (2002)

14 Air Water Interaction with Solids Sediment Hg(II) (s) Hgo (g) Hg(II)
deposition volatilization Water reduction Hg(II) Hgo (aq) Hgo (l) oxidation Dissolution/precipitation HgS Sediment

15 Solubility Products HgS = Hg S log Ksp = -53

16 Guadalupe River Watershed

17 San Francisco Bay, ‘Stinky Mud’

18 Energy Electron Donor Electron Acceptor Yield (food) (breathing)
CH2O  CO2 DGdonor - DGdonor SO42-  H2S NH4+  NO3- Fe3+  Fe2+ Fe2+  Fe3+ NO3-  NH4+ H2S  SO42- O2  H2O Energy Energy

19 Sulfide Complexes of Hg
Hg(SH)2o HgS(SH)- Hg(Sn)SH- Hg HS-

20 Methyl Mercury (MeHg) Hg(HS)2 SRB HgS(HS)- MeHg MeHg: CH3HgS- CH3HgCl
CH3HgOH

21 Methylated Species of Hg

22 Solubility Products HgS = Hg2+ + S2- log Ksp = -53
What about other Hg(II) species?

23 Role of Sulfide with So

24 Interaction with Solids

25 Ion Retention adsorption desorption Aqueous Metal Ion

26 Adsorption: Chemical versus Electrostatic
(strong) (weak) Hg2+

27 Cylcing of Mercury

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