WASTE MANAGEMENT | CAESIUM REMOVAL
Reusability of KCaSnS To study the behaviour of the structural Ca2+
on the
recyclability of KCaSnS under acidic conditions, a series of adsorption-desorption experiments using different eluents were conducted. When Ca2+
remained in the structure because Cs+ than Ca2+
. This resulted in a lower adsorption capacity of
KCaSnS-Ca than that of the pristine KCaSnS. With K+ eluent, most of the Cs+ were replaced with K+
is rather high (1 mol/L), some structural Ca2+ be further replaced with K+ test, the replaced K+ high Cs+
hardness and ionic radius to Cs+ K+
capacity. For the eluent containing both K+ the structural Ca2+
as an
in both the interlayer and structure because K+
has similar chemical
. As the concentration of ions might
. In the successive adsorption was readily exchangeable with Cs+
concentrations, resulting in higher adsorption and Ca2+
replaced most of the adsorbed Cs+ at , most of
the structure because of the high concentration of Ca2+ the solution. As K+
Above: Acidic water contaminated with caesium can be a challenging waste treatment issue for ion exchange adsorbents
in the Cs-KCaSnS-acidic might remain in in
, the
adsorption capacity of KCaSnS-K&Ca was similar to that of pristine KCaSnS. Finally, the two-step elution with Ca2+ K+
and in succession produced a product with approximately the
same elemental composition as the regenerated KCaSnS-K. This indicated that the intermediate regeneration step with Ca2+
did not influence the second K+ initial pH range of 4–8, the adsorption experiments
resulted in an increase in the final solution pH, implying competitive adsorption of protons in the lower Cs+ concentrations at the end stage. In acidic solutions, KCaSnS shows higher values of Kd than AgSnSe-1, KAlSnS-3, InSnOS, KTS-3, KMS-2, and PATiW (polyaniline titanotungstate), except for hf-TiFC. It is worth noting that the Kd of KCaSnS under acidic conditions is also higher than that of FJSM-SnS-4, NVPC, and MIL-101-SO3H, all of which have higher adsorption capacities than KCaSnS in neutral conditions.
Effect of interfering ions on the Cs+ , Mg2+ , and Ca2+ selective adsorption of Cs+ in radioactive wastewaters interfere with Cs+
High concentrations of nonradioactive ions such as Na+ K+
adsorption ,
in the radioactive wastewater inhibit the . Furthermore, protons contained adsorption via
two routes: the breakdown of the adsorbent structure and the competition for adsorptive sites with Cs+
. Accordingly,
the adsorption performance of KCaSnS in acidic solutions with various concentrations of competing ions was investigated. When the concentrations of competing ions ranged from 0.1 to 1 mmol/L, the Kd for Cs+ 1.27 × 10⁴ mL/g. The effects of divalent Mg2+ more prominent than those of monovalent Na+
were and K+
range because of stronger electrostatic interaction. To simulate a more practical case, the adsorption performance of KCaSnS toward Cs+
was investigated in
different water environments, including TW, ASW, and acid-spiked TW and ASW. KCaSnS showed high distribution coefficients for Cs+
in TW (4.30 × 10⁴ mL/g) and ASW (3.29
× 10³ mL/g) (Fig. 4d). Notably, the high Kd values can be maintained even in the acid-spiked water systems, i.e., 1.33 × 10⁴ mL/g in acidic TW and 2.95 × 10³ mL/g in acidic ASW. The values of Kd in neutral conditions are comparable to previous works such as KAlSnS-3 [30] and SbS-1 K. One might consider the acidic TW and ASW impractical; in this study, they are just simulated acidic water based on real water resources.
32 | July 2023 |
www.neimagazine.com regeneration step. Thus,
KCaSnS-Ca-K showed the same trend of an increase in the adsorption capacity as KCaSnS-K. To further evaluate the reusability, regeneration tests with an eluent solution of KCl were performed three times successively. The first, second, and third regenerated adsorbents were named KCaSnS-K-1, KCaSnS-K-2, and KCaSnS-K-3, respectively. As mentioned earlier, KCaSnS-K-1 showed a higher adsorption capacity than the pristine KCaSnS; whereas the capacity gradually decreased in the second and third regeneration tests, finally reaching that of the pristine KCaSnS. The reason for the capacity reduction might be attributed to the remaining K during adsorption. In summary, the regenerated adsorbents indicate that KCaSnS is highly reusable in acidic conditions.
Cs+ removal mechanism The removal of Cs+ was found to occur via ion exchange
under both neutral and acidic conditions. Ion exchange was shown between K+
/Ca2+ and Cs+ .
was higher than and Ca2+
in this
The adsorption capacity of KCaSnS was shown to be higher in the acidic condition than in the neutral condition, which opposes the common behaviour of most adsorbents. In the neutral condition, the molar ratio of the adsorbed Cs+ to the released K+ Ca2+
was 1.11, indicating that the interlayered also participated in the ion exchange. Clearly, this
molar ratio value is greater than that of prior research in which only K+
interlayered Ca2+
may operate as an exchangeable ion. The in addition to K+
was replaced with Cs+
under neutral conditions. The acidic condition enhanced the Cs+ facilitating the leaching of the structural Ca2+ Radioactive Cs+
adsorption by .
-rich wastewater with high acidity and
salinity is difficult to treat with conventional adsorbents. It was recently reported that a new metal sulphide adsorbent InSnS-1 exhibited excellent acid resistance even at pH 0. On the contrary, this study aimed to improve the adsorption efficiency at pH conditions that most adsorption studies have employed, at high acidity conditions in particular. Hence, a layered KCaSnS was synthesised incorporating
was used as an eluent, some Cs+ is chemically softer
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