Reviews (Parhi 2013; Dzygiel and Wieczorek 2010) on the supported liquid membrane indicate a variety of laboratory studies including the separation of radioisotopes such as plutonium, cesium-137, europium-154, and ruthenium-106. The
liquid–liquid extraction with supported liquid membrane has been shown to have a
good potential by a number of studies related to the extraction of metal ions in
hydrometallurgical separations as well as from wastewater (Zhang et al. 2010; Ren
et al. 2010). Recoveries of copper and uranium from sulfate leach liquors, uranium
from wet phosphoric acid, and zinc from the waste liquors were demonstrated on
pilot scale (Smith et al. 2014). Many solvents have been used including chelating or
acidic extractants for the extraction of various metal ions such as copper, zinc,
cobalt, nickel, iron, manganese, and molybdenum (VI). Extractants such as
Alamine-336, Aliquat-336, and Alamine-304 based on amines have been used for
molybdenum, chromium, and vanadium in the chloride solutions and crown ethers
for alkali or alkaline earth metals (Padwal et al. 2018). In spite of all the potentialities
including high selectivity, supported liquid membrane is not a commercially viable
proposition because of the instability of the immobilized solvent which acts as a
membrane and its high cost.
Membrane Solvent Extraction
In membrane solvent extraction, the feed and the solvent are independently circulated through the hollow fiber membrane element, one through the shell side and the
other through tube side, depending on the design. Mass transfer occurs between the
two streams in contact across the membrane pores. Unlike supported liquid membrane, extraction and stripping are carried out in two independent steps. However,
when two sets of membrane elements are assembled together in a loop such that the
extracting solvent passes through both the units, extraction and stripping occur
continuously. The first unit extracts the species from the feed, while in the second
unit, stripping takes place, thus enabling the simultaneous extraction and stripping
resulting in the recycling of solvent and recovery of the species (Hemmati et al.
2015).
A number of investigations have been reported on the wastewater treatment for
the removal and recovery of contaminants such as acetic acid (Sofiya et al. 2019),
phenol (Shen et al. 2009), metal ions such as plutonium (Gupta et al. 2005), and
cadmium (Fouad and Bart 2007). The advantage of using membranes includes large
interfacial contact area without mixing of the phases and freedom to choose the
solvent without density considerations. As the two phases are distinct, the flow rates
can be varied independently, and problems of flooding and emulsification do not
arise.
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271
liquid–liquid extraction with supported liquid membrane has been shown to have a
good potential by a number of studies related to the extraction of metal ions in
hydrometallurgical separations as well as from wastewater (Zhang et al. 2010; Ren
et al. 2010). Recoveries of copper and uranium from sulfate leach liquors, uranium
from wet phosphoric acid, and zinc from the waste liquors were demonstrated on
pilot scale (Smith et al. 2014). Many solvents have been used including chelating or
acidic extractants for the extraction of various metal ions such as copper, zinc,
cobalt, nickel, iron, manganese, and molybdenum (VI). Extractants such as
Alamine-336, Aliquat-336, and Alamine-304 based on amines have been used for
molybdenum, chromium, and vanadium in the chloride solutions and crown ethers
for alkali or alkaline earth metals (Padwal et al. 2018). In spite of all the potentialities
including high selectivity, supported liquid membrane is not a commercially viable
proposition because of the instability of the immobilized solvent which acts as a
membrane and its high cost.
Membrane Solvent Extraction
In membrane solvent extraction, the feed and the solvent are independently circulated through the hollow fiber membrane element, one through the shell side and the
other through tube side, depending on the design. Mass transfer occurs between the
two streams in contact across the membrane pores. Unlike supported liquid membrane, extraction and stripping are carried out in two independent steps. However,
when two sets of membrane elements are assembled together in a loop such that the
extracting solvent passes through both the units, extraction and stripping occur
continuously. The first unit extracts the species from the feed, while in the second
unit, stripping takes place, thus enabling the simultaneous extraction and stripping
resulting in the recycling of solvent and recovery of the species (Hemmati et al.
2015).
A number of investigations have been reported on the wastewater treatment for
the removal and recovery of contaminants such as acetic acid (Sofiya et al. 2019),
phenol (Shen et al. 2009), metal ions such as plutonium (Gupta et al. 2005), and
cadmium (Fouad and Bart 2007). The advantage of using membranes includes large
interfacial contact area without mixing of the phases and freedom to choose the
solvent without density considerations. As the two phases are distinct, the flow rates
can be varied independently, and problems of flooding and emulsification do not
arise.
8 Role of Membranes in Wastewater Treatment
271