Environmental Engineering Reference
In-Depth Information
surface area and high cation-exchange properties. Modiication of natural zeolites with
quaternary amines, such as the cationic surfactant hexadecyltrimethylammonium, results
in sorbent material that has anion-exchange properties. This sorbent was found to be effec-
tive in selectively removing (
ClO
4
−
) from water in the presence of competing ions. The
sorbed (
ClO
4
−
) was stable against leaching by a variety of luids over a wide pH range.
The sorbent media can be regenerated by leaching with concentrated nitrate solution. The
anions in the leachate can then be biodegraded. The capacity of the media was reported to
about 40-47 mmol/kg
(Zhang et al., 2007).
32.2.8.3 Surfactant-Modiied Nanostructured Porous Media
MetaMateria Technologies has developed a nanostructured highly porous ceramic media
for perchlorate removal. The approach relies on a proprietary technology to produce a
high-surface-area ceramic with hierarchical porosity whose sizes range from millimeter
to nanometer scale. The larger pores allow for high low rates of water into the structure
without developing back pressure. The iner meso/nano pore structure provides surfaces
that can be engineered to bind targeted contaminants. The material can be economically
produced in various shapes and sizes.
A novel liquid slurry method is used to prepare the porous ceramic substrate. Slurries of
reactive materials are prepared containing aggregate materials and surfactants/gas-forming
agents. These slurries are mixed together and the liquid is poured into molds to make
desired shapes or into a mix chamber to make aggregates. What results is an alumino-
silicate bonded matrix with interconnected porosity that is formed during gas expansion
of liquid (about three times expansion) followed by solidiication due to chemical reac-
tions. This approach produces open porosity materials that are then taken through a cur-
ing step and other postforming procedures. This approach was used to prepare materials
for the removal of perchlorate. A highly porous media, with surface area 100-300 m
2
/g ,
was prepared that contained nanopores (~10 nm) at the cell wall surface of the substrate.
This provides active surface surfaces that are then modiied to develop hydrophobicity
and then the resulting surfaces are functionalized with ammonium cation surfactants.
The surfactants are adsorbed onto the surfaces of the adsorbent through lipophilic afinity
between their hydrophobic tail and porous surface. The nanostructure permits a high con-
centration of these surfactants. The cation heads of the surfactant then provide for adsorp-
tion of perchlorate from water through ion pair bonding.
This approach was used to successfully remove perchlorate. Test samples were pre-
pared under different processing conditions and with varying compositions. Batch tests
were conducted to evaluate the potential for each to remove perchlorate. The results are
shown in Figure 32.1 for 200 ppb and Figure 32.2 for 4000 ppb concentrations of perchlo-
rate. Testing was done using challenge water containing 50 ppb of Cl
−
and
SO
2−
and 5 ppb
of
NO
3
−
. Perchlorate was tested at 200 and 4000 ppb. Each media (2 g) was shaken with
100 mL of test solution for 24 h. The concentration of perchlorate was then analyzed after
iltration.
These results showed that perchlorate could be completely removed by three of the
surfactant-modiied high-surface-area, nanostructured porous media. The other media
removed 60%-90% of the perchlorate at 4000 ppb, and two of the media were found to
lower the concentration to below 200 ppb.
Testing was also done with granular material in columns having a 3.8 cm diameter and a
height of 13.3 cm. Efluent samples were collected periodically and analyzed for perchlorate
removal. Perchlorate concentration was reduced from 4000 to 1500 ppb during the irst 10 days
