Environmental Engineering Reference
In-Depth Information
9.5.3.3 Recovery Studies
In this study, the 0.1 g Cr(VI)-adsorbed modified MnFe
2
O
4
was desorbed by 5
mL of 0.01 M NaOH and the final concentration of Cr(VI) in NaOH solution was 620
mg/L. Therefore, the desorption efficiency was calculated to be 98.9%, indicating that
most of Cr(VI) ions could be desorbed. By comparison, Sharma and Forster (1993)
reported that exhausted peat can hardly be recovered due to the strong peat-Cr(VI) bond,
and thus, requires disposal through incineration. Aoyama and Tsuda (2001) showed that
only 17.5% of Cr(VI) adsorbed could be desorbed using 0.1 M HNO
3
, but completely
recovered by burning the Cr-laden bark. It is clear that the regeneration of adsorbents for
reuse purposes has not been widely studied, especially in considering economical and
technical issues. In this study, to achieve the complete desorption of the adsorbed-Cr(VI)
from the adsorbent, another 2 mL of 0.01 M NaOH was used for continuous desorption
until equilibrium was reached when the nanoparticles were thoroughly washed with
ultrapure water and freeze-dried for XPD investigation. There is no chromium peak
present in the XPS spectra, indicating that the remaining chromium was entirely
removed from the nanoparticles.
Figure 9.31
Desorption efficiency of Cr from Cr-sorbed MeFe
2
O
4
.
The modified MnFe
2
O
4
nanoparticles are superparamagnetic; that is, they do not
become permanently magnetized after aggregate formation. Hence, these nanoparticles
may be reused without sacrificing adsorption capacity. Studies pertaining to the
regeneration of modified MnFe
2
O
4
nanoparticles and readsorption of Cr(VI) were
conducted in six consecutive cycles. The results are shown in Figure 9.32. As can be
seen, at the first cycle, the adsorption capacity is 31.4 mg Cr/g nanoparticles. At the
sixth cycle, the adsorption capacity is 31.3 mg/g. By comparison, the adsorption
capacity almost kept unchanged undergoing at least six cycles, indicating that there were
Search WWH ::
Custom Search