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Metal Speciation In Seawater or What Is the Actual Form Of The Metal Ion When In Seawater

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... different chemical entities and have different chemical and physical properties. Hg0 , Hg2 , CH3Hg , HgCl42- , organically bound Hg ... – PowerPoint PPT presentation

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Title: Metal Speciation In Seawater or What Is the Actual Form Of The Metal Ion When In Seawater


1
Metal Speciation In Seawater or
What Is the Actual Form Of The Metal Ion When In
Seawater?
  • Third Friday Seminar
  • October 26, 2001

2
Outline
Available on Web at http//www.roanoke.edu/Chemist
ry/Miller/speciation.ppt
  • Introduction
  • Why interested
  • General background
  • Other types of complexes
  • Rates and equilibria
  • Seawater
  • Mercury complexes
  • Rhodium complexes
  • Approach
  • Results
  • Conclusions

3
Introduction
  • Sabbatical, one of four projects

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10
Why Interested in Speciation?
  • Different chemical species are different chemical
    entities and have different chemical and physical
    properties
  • Hg0 , Hg2 , CH3Hg , HgCl42- , organically bound
    Hg
  • Reactivity, toxicity, adsorb to negatively or
    positively charged particles

11
General background
  • First understanding of NaCl
  • Ionic
  • Separated ions in aqueous solution
  • Bare Na ion?
  • No, hydration
  • Valid for all metal ions?

12
More Complete Understanding
  • NaCl
  • Still valid
  • HgCl2
  • Still have Hg2 and Cl- in aqueous solution
  • But also have HgCl and HgCl20
  • RhCl3
  • Rh3 with well-defined hydration sphere, and with
    Cl- ligands
  • Rh(H2O)63, Rh(H2O)5Cl2, Rh(H2O)4Cl2 , etc.

13
General Background, cont.
  • Other complexes
  • Rates and
    equilibria
  • Seawater
  • pH
  • Composition

14
General Background, cont.
  • Other complexes
  • Rates and
    equilibria
  • Seawater
  • pH
  • Composition

15
Interest in Mercury
  • Toxicity
  • Neurological damage, chromosome breakage, birth
    defects, in very low concentrations
  • Sources
  • Past industrial wastes
  • Today - coal-fired power plants are becoming more
    important
  • Environmentally recycled

16
Interest in Rhodium
  • Toxicity
  • Not much known about low level effects
  • But, . . . a heavy metal and a good catalyst
  • Sources
  • Industrial wastes but too valuable
  • Catalytic converters in automobiles

17
Mercury Complexes
18
Mercury Complexes
  • Chloro complexes
  • Hg2 Cl- HgCl
  • HgCl Cl- HgCl2
  • HgCl2 Cl- HgCl3-
  • HgCl3- Cl- HgCl42-
  • Hydroxy complexes
  • Hg2 OH- HgOH
  • HgOH OH- Hg(OH)2(s)
  • Mixed complexes

19
Rhodium Complexes
  • Chloro complexes
  • Rh(H2O)63 Cl- Rh(H2O)5Cl2
  • Rh(H2O)5Cl2 Cl- Rh(H2O)4Cl2
  • Rh(H2O)4Cl2 Cl- Rh(H2O)3Cl3
  • Rh(H2O)3Cl3 Cl- Rh(H2O)2Cl4-
  • Rh(H2O)2Cl4- Cl- Rh(H2O)Cl52-
  • Rh(H2O)Cl52- Cl- RhCl63-

20
Rhodium Complexes, cont.
  • Hydroxy complexes
  • Rh(H2O)63 OH- Rh(H2O)5(OH)2
  • Rh(H2O)5(OH)2 OH- Rh(H2O)4(OH)2
  • Rh(H2O)4(OH)2 OH- Rh(OH)3(s)
  • Mixed complexes
  • Polynuclear complexes

21
Approach
  • Concentrations in seawater
  • Hg 15 pM, 3 ppt
  • Rh 1 pM, 0.1 ppt
  • Measure at high concentrations, calculate
    (extrapolate) to low concentrations
  • Reliability of extrapolations?
  • Experimental
  • Spectrophotometry, pH titration

22
Literature Spectra
23
Literature and Experimental Spectra
24
pH Titration
25
Results and Conclusions
  • Mercury
  • Reactions are fast, less than second
  • Tentative HgCl3- and HgOH , although
    HgCl2(OH)- cannot be ruled out
  • Rhodium
  • Reactions are slower, taking minutes to days
  • Some kind of mixture of Rh3-containing ions with
    four or five Cl- and one or two OH- ions attached

26
Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6
27
Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6 RhCl3(OH)
RhCl4(OH) RhCl5(OH)
28
Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6 RhCl3(OH)
RhCl4(OH) RhCl5(OH) RhCl3(OH)2
RhCl4(OH)2
29
Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6 RhCl3(OH)
RhCl4(OH) RhCl5(OH) RhCl3(OH)2
RhCl4(OH)2 RhCl3(OH)3

30
Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6 RhCl3(OH)
RhCl4(OH) RhCl5(OH) RhCl3(OH)2
RhCl4(OH)2 RhCl3(OH)3
RhCl3(s)
31
Acknowledgements
  • Dr. Robert Byrne
  • University of South Florida
  • Roanoke College
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