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

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

• Third Friday Seminar
• October 26, 2001

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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

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Introduction

• Sabbatical, one of four projects

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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

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General background

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

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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.

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General Background, cont.

• Other complexes
• Rates and
  equilibria
• Seawater
• pH
• Composition

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General Background, cont.

• Other complexes
• Rates and
  equilibria
• Seawater
• pH
• Composition

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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

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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

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Mercury Complexes
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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

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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-

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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

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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

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Literature Spectra
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Literature and Experimental Spectra
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pH Titration
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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

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Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6
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Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6 RhCl3(OH)
RhCl4(OH) RhCl5(OH)
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Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6 RhCl3(OH)
RhCl4(OH) RhCl5(OH) RhCl3(OH)2
RhCl4(OH)2
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Results and Conclusions, cont.
RhCl3 RhCl4
RhCl5 RhCl6 RhCl3(OH)
RhCl4(OH) RhCl5(OH) RhCl3(OH)2
RhCl4(OH)2 RhCl3(OH)3

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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)
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Acknowledgements

• Dr. Robert Byrne
• University of South Florida
• Roanoke College