 Liquid-liquid extraction (LLE):
Liquid-liquid extraction, also known as solvent extraction and partitioning, is a
method to separate compounds based on their relative solubilities in two different
immiscible liquids, usually water and an organic solvent. It is an extraction of a
substance from one liquid phase into another liquid phase. Liquid-liquid
extraction is a basic technique in chemical laboratories, where it is performed
using a separatory funnel. This type of process is commonly performed after a
chemical reaction as part of the work-up.
In other words, this is the separation of a substance from a mixture by
preferentially dissolving that substance in a suitable solvent. By this process, a
soluble compound is usually separated from an insoluble compound. Solvent
extraction is used in nuclear reprocessing, ore processing, the production of fine
organic compounds, the processing of perfumes, and other industries.
Liquid-liquid extraction is possible in non-aqueous systems: In a system
consisting of a molten metal in contact with molten salt, metals can be extracted
from one phase to the other. This is related to a mercury electrode where a metal
can be reduced, the metal will often then dissolve in the mercury to form an
amalgam that modifies its electrochemistry greatly. For example, it is possible for
sodium cations to be reduced at a mercury cathode to form sodium amalgam,
while at an inert electrode (such as platinum) the sodium cations are not reduced.
Instead, water is reduced to hydrogen. A detergent or fine solid can be used to
stabilize an emulsion, or third phase.
is an important unit operation that allows one to separate fluids based on
different solutes being soluble to different degrees in different solvents. In
the this experiment, acetone is extracted by contact with water from a feed
stream containing an unknown concentration of acetone in butyl acetate
(BA).
 Purpose:
The goal of this laboratory exercise is to study the performance of a liquidliquid extraction column.
 Learning Objectives
The main learning objective of this laboratory exercise is to gain
experience in characterizing the behavior of a liquid-liquid extraction
column. To do this, one must examine such parameters as the
composition of the top and bottom products at various feed rates and
compositions. These parameters should be calculated theoretically
using available computer programs and determined experimentally
from the column.
 Distribution ratio:
In solvent extraction, a distribution ratio is often quoted as a measure
of how well-extracted a species is. The distribution ratio (D) is equal
to the concentration of a solute in the organic phase divided by its
concentration in the aqueous phase. Depending on the system, the
distribution ratio can be a function of temperature, the concentration
of chemical species in the system, and a large number of other
parameters.
Note: that D is related to the ΔG of the extraction process.
Sometimes, the distribution ratio is referred to as the partition
coefficient, which is often expressed as the logarithm. See partition
coefficient for more details. Note that a distribution ratio for uranium
and neptunium between two inorganic solids (zirconolite and
perovskite) has been reported.[1] In solvent extraction, two
immiscible liquids are shaken together. The more polar solutes
dissolve preferentially in the more polar solvent, and the less polar
solutes in the less polar solvent. In this experiment, the nonpolar
halogens preferentially dissolve in the nonpolar mineral oil.
 Separation factors:
The separation factor is one distribution ratio divided by another; it is
a measure of the ability of the system to separate two solutes. For
instance, if the distribution ratio for nickel (DNi) is 10 and the
distribution ratio for silver (DAg) is 100, then the silver/nickel
separation factor (SFAg/Ni) is equal to DAg/DNi = SFAg/Ni = 10.
 Extraction in the organic chemistry teaching
labs:
Liquid-liquid extractions using a reparatory funnel are essentially the
only kind of extraction performed in the organic teaching labs. The
"liquid-liquid" phrase means that two liquids are mixed in the
extraction procedure. The liquids must be immiscible: this means
that they will form two layers when mixed together, like oil and
vinegar do in dressing. Some compounds are more soluble in the
organic layer (the "oil") and some compounds are more soluble in the
aqueous layer (the "vinegar").
Extractions use two immiscible phases to separate a solute from one
phase into the other. The distribution of a solute between two phases
is an equilibrium condition described by partition theory. Boiling tea
leaves in water extracts the tannins, the bromine, and caffeine (the
good stuff) out of the leaves and into the water. More typical lab
extractions are of organic compounds out of an aqueous phase and
into an organic phase.
 Illustration of an extraction in a reparatory funnel:
Analytical Extractions
Elemental analysis generally requires fairly simple (not necessarily
easy) sample preparation. Solids are usually dissolved or digested in
caustic solution and liquids are sometimes extracted to separate the
analyte from interferences.
Organic analysis is often much more complicated. Real-world
samples can be very complicated matrices that require careful
extraction procedures to obtain the analyte(s) in a form that can be
analyzed.
 Techniques:
 Salvation mechanism:
Using solvent extraction it is possible to extract uranium, plutonium,
or thorium from acid solutions. One solvent used for this purpose is
the organophosphate tri-n-butyl phosphate. The PUREX process that
is commonly used in nuclear reprocessing uses a mixture of tri-nbutyl phosphate and an inert hydrocarbon (kerosene), the
uranium(VI) are extracted from strong nitric acid and are backextracted (stripped) using weak nitric acid. An organic soluble
uranium complex [UO2(TBP)2(NO3)2] is formed, then the organic
layer bearing the uranium is brought into contact with a dilute nitric
acid solution; the equilibrium is shifted away from the organic
soluble uranium complex and towards the free TBP and uranyl nitrate
in dilute nitric acid. The plutonium(IV) forms a similar complex to the
uranium(VI), but it is possible to strip the plutonium in more than one
way; a reducing agent that converts the plutonium to the trivalent
oxidation state can be added. This oxidation state does not form a
stable complex with TBP and nitrate unless the nitrate concentration
is very high (circa 10 mol/L nitrate is required in the aqueous phase).
Another method is to simply use dilute nitric acid as a stripping agent
for the plutonium. This PUREX chemistry is a classic example of a
salvation extraction.
Here in this case DU = k TBP2[[NO3]]2.
 Ion exchange mechanism:
Another extraction mechanism is known as the ion exchange
mechanism. Here, when an ion is transferred from the aqueous phase
to the organic phase, another ion is transferred in the other direction
to maintain the charge balance. This additional ion is often a
hydrogen ion; for ion exchange mechanisms, the distribution ratio is
often a function of pH. An example of an ion exchange extraction
would be the extraction of americium by a combination of terpyridine
and a carboxylic acid in tert-butyl benzene. In this case
DAm = k terpyridine1carboxylic acid3H+−3
Another example is the extraction of zinc, cadmium, or lead by a
dialkyl phosphoric acid (R2PO2H) into a no polar diluents such as an
alkane. A non-polar diluents favors the formation of uncharged nonpolar metal complexes.
Some extraction systems are able to extract metals by both the
salvation and ion exchange mechanisms; an example of such a
system is the americium (and lanthanide) extraction from nitric acid
by a combination of 6,6'-bis-(5,6-dipentyl-1,2,4-triazin-3-yl)-2,2'bipyridine and 2-bromohexanoic acid in tert-butyl benzene. At both
high- and low-nitric acid concentrations, the metal distribution ratio is
higher than it is for an intermidate nitric acid concentration.
 The Physical Basis of Extractions:
Let's go back to our example of the chemical dissolved in water that
makes its way into methylene chloride through a liquid-liquid
extraction. While the procedure is successful in our hypothetical
case, this laboratory trick does not always work. The following
conditions must be satisfied for our liquid-liquid extraction example
to be successful:



The compound (solute) that is initially dissolved in water must
also be soluble in methylene chloride.
The compound must be more soluble in methylene chloride
than it is in water (which is the case for many organic
compounds).
Water and methylene chloride must be immiscible (incapable of
forming a homogeneous mixture).
We can extend our example to illustrate another useful property of
extraction. Assume that the compound being transferred into
methylene chloride from water is initially mixed with another solute in
water. If the other solute in water is not soluble in methylene chloride,
then the extraction separates the two solutes: one moves into
methylene chloride, and the other stays behind in water. Here we see
extraction being used for its most common purpose: purification.
Liquid-liquid extractions work because solutes preferentially migrate
to or remain in the solvent in which they are most soluble. By
requiring that the solvents used be immiscible (e.g. water and
methylene chloride), physical separation of the solutions becomes
easy: the less dense solution floats on top of the more dense one
without mixing. The separatory funnels used in extractions are
specially designed to facilitate separations of liquid layers.
 References:
1. ^ Scholz, F.; S. Komorsky-Lovric, M. Lovric (February 2000). "A
new access to Gibbs energies of transfer of ions across liquid".
Electrochemistry Communications (Elsevier) 2 (2): 112–118.
doi:10.1016/S1388-2481(99)00156-3.
2. ^ Danil de Namor, A.F.; T. Hill (1983). Journal of the Chemical
Society, Faraday Transactions: 2713.
3. ^ Mackenzie, Murdoch. "The Solvent Extraction of Some Major
Metals". Cognis GmbH.
http://www.cognis.com/NR/rdonlyres/62A4BDA0-2B5F-45799761-968114B57A2A/0/thesolve.pdf. Retrieved 2008-11-18.
4. ^ M. Filiz, N.A. Sayar and A.A. Sayar, Hydrometallurgy, 2006, 81,
167-173.
5. ^ Yoshinari Baba, Minako Iwakuma and Hideto Nagami, Ind.
Eng. Chem. Res, 2002, 41, 5835-5841.
6. ^ J. M. Sánchez, M. Hidalgo, M. Valiente and V. Salvadó, Solvent
Extraction and Ion Exchange, 1999, 17, 455-474.
7. ^ Lee W. John. "A Potential Nickel / Cobalt Recovery Process".
BioMetallurgical Pty Ltd.
http://www.biomet.com.au/Extract/NiCoFS.htm.
8. ^ "Precious Metals Refining By Solvent Extraction". Halwachs
Edelmetallchemie und Verfahrenstechnik.
http://www.halwachs.de/solvent-extraction.htm. Retrieved 200811-18.
9. ^ P. Giridhar, K.A. Venkatesan, T.G. Srinivasan and P.R.
Vasudeva Rao, Hydrometallurgy, 2006, 81, 30-39.
^ K. Takeshita, K. Watanabe, Y. Nakano, M. Watanabe (2003). "Solvent
extraction separation of Cd(II) and Zn(II) with the organophosphorus
extractant D2EHPA and the aqueous nitrogen-donor ligand TPEN".
Hydrometallurgy 70: 63–71.