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| Removal of Heavy Metal Ions from Groundwater using Porous-Magnetic Biopolymer Beads |
| Project Description: Aqueous waste streams from manufacturing processes
are often contaminated with dilute concentrations of toxic heavy metal ions.
Chitosan, a glucosamine
biopolymer, selectively adsorbs transition metal ions but does not adsorb
alkali and alkaline earth metal ions. In this project, we are developing methods to
make highly-porous beads of chemically crosslinked
chitosan. A representative
SEM image is shown below. |
| Chitosan beads are prepared by dropwise addition
of an aqueous solution containing chitosan and
acetic acid into a bath of aqueous NaOH. The NaOH neutralizes
the acetic acid and precipitates the chitosan
as a gel, which assumes the form of a bead.
Linear glucosamine chains within the gel
bead are chemically crosslinked with glutaraldehyde
dissolved in water. Crosslinked
gel beads are freeze dried to remove water in a way that makes the material
highly porous. |
|
| Crosslinked chitosan beads are engineered
for high metal ion adsorption capacity and chemical stability needed for
surface water and subsurface groundwater treatment applications. Chitosan beads crosslinked with glutaraldehyde
possess internal surface areas exceeding 200 m2 / g and are insoluble
in acid solution (see figure below). The chitosan
beads also contain magnetite. Therefore,
porous-magnetic chitosan beads can retrieved from
the site of clean up by devices such as a magnetic field gradient separator. |
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[pictures to add: surface area vs. extent of crosslinking, SEM of porous bead]