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Comparison of Alkali Metal Cation Extraction by new AzaCalixarene Crown Derivatives

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Calix[4]arene crowns have been shown to selectively extract cesium through ... Calix[4]arenes containing aza-crowns have been ... Org: 10mM Calix. Conclusions ... – PowerPoint PPT presentation

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Title: Comparison of Alkali Metal Cation Extraction by new AzaCalixarene Crown Derivatives


1
Comparison of Alkali Metal Cation Extraction by
new Aza-Calixarene Crown Derivatives
  • Cara Johnston, Colorado College
  • GCLA/ACM ORSS
  • CSD, Chemical Separations Group
  • ORNL

2
Motivation
  • 137Cs comprises a significant portion of
    radioactivity in nuclear waste
  • Calix4arene crowns have been shown to
    selectively extract cesium through liquid/liquid
    extraction
  • This selectivity is due to the matching of size
    between the calixarene cavity and the cesium as
    well as ?-bonding interactions with the arene
    groups, and structural preorganization of
  • the molecule
  • Calix4arenes containing aza-crowns have been
    proposed so as to functionalize the crown and
    increase potential anion selectivity

Cs
3
Compounds to be Studied
Monobenzo-crown-6
Monocrown-6
Dibenzo-crown-6
VP-3,4-NH
VP-2,5-NH
VP-3,4-NNHTs
4
Method
  • Cs and Na extraction experiments
  • Cs and Na extractability determined using
    radiotracer isotopes 137Cs and 22Na, respectively
  • Small scale extractions with a 11
    (organicaqueous) contacting ratio were performed
  • Competitive Cation Experiments
  • Extraction of all other cations was determined by
    ICP
  • The distribution coefficient is used to measure
    extraction efficiency
  • Dion Ionorg/Ionaq

5
Competitive Cation Effects
Extraction of Alkali Metal Cations
Selectivity of Calixarene for Cs
T 25ºC Contact ratio 11 1M LiNO3 1M
NaNO3 0.1M KClO4 2mM RbNO3 1mM CsNO3 For pH
12, add 0.01M NaOH
Log D
Log D
?Na ?K ?Rb ? Cs
? Cs/Li ? Cs/Na ? Cs/K ? Cs/Rb
  • Li and Na concentrations below detection limit,
    which was used to calculate selectivity.
  • The trend is found that the further down Group
    IA, the higher the extraction of the ion.
  • Mg, Ca, Sr, and Ba were analyzed and were not
    found extracted to any extent, concentrations
    being below detection limit.

6
pH Dependence of Compounds
pH Dependence of Cs and Na Extraction
  • Both aza containing compounds are highly pH
    sensitive
  • Precipitation at pH 1
  • By pH 14, the pH threshold for VP-2,5-NH was not
    yet reached
  • High selectivity for Cs over Na
  • pH 14 used for subsequent stoichiometric
    experiments based on these results

T 25ºC, Contact ratio 11 Aq 1.9M NaNO3,
0.1M NaClO4, 1mM CsNO3 Varying NaOH
concentration Org 10mM Calixarene
7
Simple Thermodynamics
  • Extraction Equation
  • B Calixarene
  • nCsaq nNO3-aq mBorg Bm(CsNO3)n org
    Keq Bm(CsNO3)norg
    CsnaqNO3-naqBmorg
  • Using logarithms and knowing that DCs
    Csorg/Csaq, the equation becomes
  • Log D nLog NO3- mLogB (n-1)Log Cs
    Log Keq
  • Thus by changing the concentration of one species
    and holding the others constant, the
    stoichiometry can be determined.
  • Actual slopes will deviate from expected integer
    values due to activity effects.

8
Stoichiometry Variation of Calixarene
  • Each Calixarene gives a slope close to 1.
  • The stoichiometry of monocrown-6 has been
    determined previously, showing a 11
    stoichiometric ratio of calixarene.
  • nCsaq nNO3-aq mBorg Bm(CsNO3)n org
  • (m1)
  • VP-3,4-NH must have same stoichiometry by
    comparison

Log D vs. Log Calixarene
m 1
D
Calixarene
T 25ºC, Contact ratio 11 Aq 1M NaOH,1M
NaNO3, 3x10-4 M CsNO3
9
Stoichiometry Variation of Cs
Log Csorg vs Log Csaq
  • Each calixarene gives a slope close to 1.
  • A slope of 1 shows a 11 stoichiometric ratio
  • nCsaq nNO3-aq mBorg Bm(CsNO3)n org
    (n1)
  • The highest possible calixarene concentration is
    1x10-2M, thus the leveling of the curves at this
    value can be explained by loading effects. The
    organic phase can only accommodate as much cesium
    as calixarene present.

Highest Calixorg
Cs org
m1
Csaq
T 25ºC, Contact ratio 11 Aq 1M NaOH, 1M
NaNO3, varying CsNO3 Org 10mM Calix
10
Conclusions
  • Both compounds are highly pH sensitive, so all
    experiments must take place in a basic
    environment.
  • VP-3,4-NH is comparable to previously studied
    calixarene crowns, while VP-2,5-NH is a poor
    extractant.
  • The stoichiometry of all compounds was
    determined to be 1 1 1 (Cs NO3 B).

Acknowledgments
  • Laetitia Delmau - supervision of work, Tamara
    Haverlock - supervision of ICP use, and Viktor
    Pastushok - compound synthesis
  • This research is sponsored by the Division of
    Chemical Sciences, Geosciences, and Biosciences,
    Office of Basic Energy Sciences, and by the
    Environmental Management Science Program of the
    Offices of Science and Environmental Management,
    U.S. Department of Energy, under contract
    DE-AC05-00OR22725 with Oak Ridge National
    Laboratory, managed and operated by UT-Battelle,
    LLC.
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