251
Reverse Osmosis
In reverse osmosis, when hydrostatic pressure is higher than osmotic pressure, solvent passes through semipermeable membrane in direction opposite to that of
osmosis process. Heavy metals like zinc and copper removal using low pressure
below 690 kPa with a reverse osmosis membrane has been studied by researchers
which showed that Zn
2+
and Cu
2+
removal was improved in the presence of polysulfone reverse osmosis membrane (Ujang and Anderson 1996). The major disadvantage of this technique is it is not cheap (Kurniawan et al. 2006).
Electrodialysis
Electrodialysis is a process in which separation of metal ions across charged membranes from one solution to another in the presence of an electric field which acts as
driving force. Membranes applied in this process are of two types: anion exchange
membrane and cation exchange membrane. This technique is generally used for
making drinking water from seawater and brackish water, for recovery of valuable
materials from effluents, and for salt production. Limitations of this process are
such that organic matter and colloids cannot be removed by electrodialysis and
stack selection is necessary for compatibility guarantee with the feed stream.
10.2.4 Electrocoagulation
Electrocoagulation is an electrochemical approach which utilizes electrical current
for not only removal of heavy metals from aqueous solution but also capable of
removing suspended solids, dissolved metals, tannins, and dyes from wastewater.
The metal ions become destabilized and precipitate in a stable form when they are
neutralized with ions of opposite electrical charges provided by coagulates such as
ferrous sulfate, aluminum, and ferric chloride. Heavy metals like cadmium, copper,
and nickel removal from an artificial wastewater was performed with an efficiency
of 99.78%, 98.90%, and 99.98%, respectively, using electrocoagulation method at
neutral pH 7. The formation of metal hydroxides leads to clogging of the membranes which is the main limitation of this method (Pedersen 2003).
10.2.5 Flotation
Flotation is used to separate heavy metals from a liquid phase by bubble-metal
attachment process. The common flotation processes for the removal of metal ions
from solution are dissolved air flotation, ion flotation, and precipitation flotation.
Among these, dissolved air flotation process is mostly used than any other flotation
10 Heavy Metal Removal by Low-Cost Adsorbents
Reverse Osmosis
In reverse osmosis, when hydrostatic pressure is higher than osmotic pressure, solvent passes through semipermeable membrane in direction opposite to that of
osmosis process. Heavy metals like zinc and copper removal using low pressure
below 690 kPa with a reverse osmosis membrane has been studied by researchers
which showed that Zn
2+
and Cu
2+
removal was improved in the presence of polysulfone reverse osmosis membrane (Ujang and Anderson 1996). The major disadvantage of this technique is it is not cheap (Kurniawan et al. 2006).
Electrodialysis
Electrodialysis is a process in which separation of metal ions across charged membranes from one solution to another in the presence of an electric field which acts as
driving force. Membranes applied in this process are of two types: anion exchange
membrane and cation exchange membrane. This technique is generally used for
making drinking water from seawater and brackish water, for recovery of valuable
materials from effluents, and for salt production. Limitations of this process are
such that organic matter and colloids cannot be removed by electrodialysis and
stack selection is necessary for compatibility guarantee with the feed stream.
10.2.4 Electrocoagulation
Electrocoagulation is an electrochemical approach which utilizes electrical current
for not only removal of heavy metals from aqueous solution but also capable of
removing suspended solids, dissolved metals, tannins, and dyes from wastewater.
The metal ions become destabilized and precipitate in a stable form when they are
neutralized with ions of opposite electrical charges provided by coagulates such as
ferrous sulfate, aluminum, and ferric chloride. Heavy metals like cadmium, copper,
and nickel removal from an artificial wastewater was performed with an efficiency
of 99.78%, 98.90%, and 99.98%, respectively, using electrocoagulation method at
neutral pH 7. The formation of metal hydroxides leads to clogging of the membranes which is the main limitation of this method (Pedersen 2003).
10.2.5 Flotation
Flotation is used to separate heavy metals from a liquid phase by bubble-metal
attachment process. The common flotation processes for the removal of metal ions
from solution are dissolved air flotation, ion flotation, and precipitation flotation.
Among these, dissolved air flotation process is mostly used than any other flotation
10 Heavy Metal Removal by Low-Cost Adsorbents