Environmental Engineering Reference
In-Depth Information
adsorption applications include decolorizing and drying of petroleum fractions,
recovering organic solvent vapors, dehydrating gases, removing carbon dioxide and
sulfur compounds from natural gas, and removing dissolved organic/inorganic pollutants
from drinking water supplies (Tien, 1994). Solid adsorbents commonly used for these
applications include powdered and granular activated carbon (PAC, GAC), polymeric
ion-exchange and chelating resins, and silica gel (Faust and Aly, 1987). These
adsorbents may be effective in the removal of heavy metal species as well.
Table 6.2
Separation processes for removal of heavy metal species.
Properties of
Heavy Metals
Processes
Separating Agents
Aqueous-Phase
Solubility
Biologically mediated
precipitation
Sulfate-reducing
microorganisms
Chemical precipitation
Hydroxides, carbonates, sulfides
Physical
Dimensions
Reverse osmosis/nanofiltration
Membranes
Redox Potentials
Electroplating/reduction
Electricity
Ionic Charges and
Diffusivity
Donnan dialysis
Acid and membranes
Electrodialysis
Electricity and membranes
Ion Charges
and/or Lewis
Acidity/Basicity
Biosorption
Dead biomass
Ion-exchange/chelation process
Activated carbons, polymeric
ion-exchange resins and
chelating resins, zeolites
Liquid/liquid extraction
Organic solvent and
hydrophobic extractants
Micelle or polyelectrolyte
enhanced ultrafiltration
Surfactants, hydrophilic
polymeric extractants and
membranes
Others
Phytoremediation
via
rhizofiltration and
phytoextraction
Plant roots
One of the major mechanisms applied in adsorption removal of metal cations or
anions is ion-exchange process based on Coulombic electrostatic attraction between
oppositely charged species. For instance, ion-exchange resins possessed ionizable
functional groups such as the sulfonic acid group or quaternary ammonium groups could
remove cations or anions respectively. However, selective sequestration of specific
Search WWH ::
Custom Search