Title: Comparison of Alkali Metal Cation Extraction by new AzaCalixarene Crown Derivatives
1Comparison of Alkali Metal Cation Extraction by
new Aza-Calixarene Crown Derivatives
- Cara Johnston, Colorado College
- GCLA/ACM ORSS
- CSD, Chemical Separations Group
- ORNL
2Motivation
- 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
3Compounds to be Studied
Monobenzo-crown-6
Monocrown-6
Dibenzo-crown-6
VP-3,4-NH
VP-2,5-NH
VP-3,4-NNHTs
4Method
- 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
5Competitive 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.
6pH 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
7Simple 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.
8Stoichiometry 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
9Stoichiometry 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
10Conclusions
- 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.