Journal of Radioanalytical and Nuclear Chemistry, Vol. 265, No. 3 (2005) 419–421
0236–5731/USD 20.00 Akadémiai Kiadó, Budapest
© 2005 Akadémiai Kiadó, Budapest Springer, Dordrecht
Uranium(VI) extraction by Winsor II microemulsion systems
using trialkyl phosphine oxide
Zeng Shan, Yang Yan-zhao,* Zhu Tao, Han Jian, Luo Chang-Hong
School of Chemistry and Chemical Engineering, Shandong University, Jinan, P.R. China
(Received October 8, 2004)
The parameters affecting the formation of the microemulsion were investigated and the microemulsion region was determined. The extraction of
uranium(VI) from HNO
solution into a water in oil microemulsion was studied. The effects of the concentration of extractant (TRPO), the volume
ratio of oil to water and the acidity of outer water phase on the extraction equilibrium of uranium(VI) are discussed and the appropriate conditions
are obtained. The result showed the microemulsion has great efficiency for uranium(VI) extraction.
Solvent extraction is one of the most important
techniques in concentration and purification of solutions
containing uranium(VI). Liquid-liquid extraction has
been used for recovery of U(VI) from spent nuclear fuel
for several decades.
Compared with liquid-liquid
extraction, microemulsions have some advantages such
as faster extraction rate and improved extractability.
Microemulsion is an optically transparent and
thermodynamically stable system, which is formed
spontaneously by oil, water, surfactant and cosurfactant.
Its microstructure can be described as a dispersion of
microdroplets of two immiscible liquids, stabilized by
an interfacial membrane made up of surfactant and
cosurfactant. The interfacial tension between the two
phases is extremely low.
Microemulsions have been
used in the separation of metal ions, biological
substances, organic acids and contaminants in soil.
There are three types of microemulsion systems, called
Winsor I, Winsor II and Winsor III.
Winsor I is O/W
microemulsion coexisting with an oil phase, Winsor II is
W/O microemulsion coexisting with a water phase, and
Winsor III is a bicontinuous microemulsion coexisting
with oil and water phase. The microemulsion must be oil
continuous when utilized to separate material from
aqueous phase. Hence, Winsor II system is usually used
in metal ion extraction. In this paper, we report our
newest result on uranium(VI) removal from aqueous
phase using Winsor II systems.
Instruments and reagents
Vibrator (Yancheng Science Instrument Factory,
Jiangsu Province), with a vibration frequency of
, and a temperature controlling precision
1 K. UV grating spectrophotometer 752 Type
* E-mail: firstname.lastname@example.org
(Shanghai Third Analysis Instrument Factory). Magnetic
stirring apparatus (Yuhua Instrument Factory, Henan
Uranyl nitrate (AR, made in China), nitric acid (AR,
Shanghai First Reagent Factory), trialkyl phosphine
oxide (TRPO) (CP, average molecular weight is 346,
Jinan Phosphate Fertilizer Factory). N,N-
dimethyldodecylamine (purity 95%, Acros Organics,
USA), 1-hexanol (AR, Tianjin Bodi Reagent Factory),
n-heptane (AR, Tianjin Damao Reagent Factory).
Preparation of the microemulsion
Microemulsion must be made first. Oil phase was
mixed with surfactant/cosurfactant phase in certain
proportion under study. The oil phase is completely
miscible with surfactant and cosurfactant, so the mixture
is clear at the beginning. The mixture was titrated with
nitric acid solution until it turned turbid, and the mass of
the solubilized water was recorded. The ternary phase
diagram was constructed by plotting the percentages of
aqueous phase, oil phase and surfactant/cosurfactant
phase used in the experiment.
In the following studies, the temperature was
maintained at 298
1 K. Unless stated otherwise, the
acidity of the outer aqueous solution was controlled at
4.0 mol/l HNO
, the initial U(VI) concentration was
mol/l. The volume ratio of aqueous phase to
microemulsion was expressed as R, the percentage of
TRPO in microemulsion was expressed as X (wt.%), the
extraction rate percentage was expressed as E%. The
C/S is the mass ratio of cosurfactant to surfactant.
U(VI) extraction rates were determined by shaking
the two phases mechanically for 5 minutes (the
equilibrium reached in 1 minutes). After extraction, the
U(VI) concentration in the aqueous solution was