Chemistry Reference
In-Depth Information
TP
R
EC
CP
HPP
CS
Oven
CF
S E
Figure 3.4
Schematic diagram of the extraction system (S - oil sample; E - extractant; TP - triphasic pump;
HPP - high pressure pump; CP - confluence point; EC - extraction coil; CS - cooling system; R - restrictor;
CF - collection flask). Reproduced from [10] with permission from Elsevier, © 2004.
the extractant were continuously pumped at the pressure needed to maintain the liquid state at preset
temperature by the dosifer piston pump and the high pressure pump, respectively. The oil and extractant
streams reached at the confluence point and then, the segments of the immiscible phases led to the extraction
coil in the oven at the working temperature. The segments of oil and extractant circulated through the
extraction coil at high temperature and pressure allowed the analytes to be transferred from the oil into the
aqueous phase. After extraction, the oil-water segments were cooled at the end of the oven by passage through
another coil located in a waterbath at 25°C. Both phases were spontaneously separated after collection in a
vessel. The analytes were determined in treated and untreated oil by flame atomic absorption spectrometry.
Comments
This experiment is highly significant with respect to solution of a solid waste disposal problem.
The uncontrolled dumping of used tires is of great environmental concern. The solution to this problem
comes from an innovative technology based on the recycle of this solid waste. A liquid-liquid extraction
method using modified superheated steam as an extractant for removal of various metals from oil resulting
from recycled tires has been effective. The study provides useful data for the cheapest working conditions to
be used in order to obtain a given demetalization level.
3.2.2
Green separation using liquid-liquid, solid-phase and solventless extractions
The most widespread techniques for separation and preconcentration are liquid-liquid and solid-liquid
extractions. Typically, preconcentration is achieved by addition of a suitable reagent to the sample solution and
extraction of the resulting product to an organic phase or a hydrophobic solid phase. Various greener alternatives
have been developed by minimizing both the use of organic solvents and the extraction times in comparison to
traditional liquid-liquid extractions [11]. Solid-phase extraction offers a number of important benefits when
compared with liquid-liquid extraction, such as elimination of solvents, higher enrichment factors, high
recoveries, rapid phase separation, lower cost and the facility for coupling to different detection techniques.
3.2.2.1
Environmentally clean extraction of mercury species
Aqueous biphasic extraction system (ABS) offers a clean approach for extracting metal ions in an eco-
friendly way. ABS may be thought of as relatively green separation medium since they are made of water and
rather harmless polymer such as polyethylene glycol (PEG). The phase separation in an ABS occurs due to
water structuring and the partial dehydration of the polymer chain within the two phases. Applications of the
polymer-salt ABS in the separation of organic molecules, metal ions, radiochemicals, and the recovery of
nanoparticles and minerals have been demonstrated. Thus the use of ABS instead of traditional solvent
