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Desorption mechanisms of cesium from illite and vermiculite
Applied Geochemistry ( IF 3.4 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.apgeochem.2020.104768
Kento Murota , Keitaro Tanoi , Asumi Ochiai , Satoshi Utsunomiya , Takumi Saito

Abstract It is known that cesium ion, Cs+, is strongly sorbed to micaceous minerals. However, the desorption of Cs+ at a trace sorption level with time in the presence of different salt ions is not well understood. In this study, we conducted long-term sorption and desorption experiments of Cs+ with illite and vermiculite at room temperature to study the effects of sorption time and co-existing cations on the desorption. A small amount of Cs+ (50 nM Cs+ spiked with 900 Bq 137Cs) was sorbed to illite and vermiculite in the presence of 1 mM K+ or Ca2+, or 1 mM K+ and 100 mM Ca2+ over 8 weeks, which was then desorbed in the presence of Prussian blue (PB) nanoparticles over 12 weeks. The PB nanoparticles were used to inhibit the re-sorption of desorbed Cs+. More than 90% of Cs+ was sorbed to the minerals in the presence of Ca2+; meanwhile, only 50 to 70% of Cs+ was in the presence of K+. For all samples other than the illite with Ca2+ (Ca-illite), more than 80% of Cs+ were desorbed within a few days, and almost all Cs+ was desorbed at the end of the experiment. The large and fast desorption of Cs+ indicated a large part of Cs+ sorbed to these minerals were indeed labile in the presence of a strong sorbent like PB nanoparticles. These desorption trends were hardly influenced by a change of the sorption time. The desorption of Cs+ from the Ca-illite was slow, taking more than one month before 80% desorption for the sample with 1-day sorption, and the desorption amount only reached less than 90%. This slow desorption of Cs+ from the Ca-illite became even slower with the sorption time from one day to two weeks, and only 70% of sorbed Cs+ was desorbed at the end of the experiment for the latter. The mechanisms of Cs+ desorption from the Ca-illite was quantitatively explained by fitting to a pseudo first-order desorption model, suggesting that 30 ∼ 40% of Cs+ was sorbed to the peripheral region of the interlayer of the Ca-illite and diffused into the interior part. The rest of sorbed Cs+ can be desorbed relatively fast. As these Cs+ was most likely sorbed to so-called frayed edge sites in the Ca-illite, these results suggested that a part of the sorbed Cs+ (70 ∼ 60%) was labile. Thus, the expansion and collapse of the peripheral regions of the interlayers induced by co-existing cations and interlayer migration of Cs+ are important processes constraining the sorption and desorption of Cs+ to/from the micaceous minerals. In addition, compared with the desorption from the pure minerals examined in this study, the desorption of Cs+ from real soils was slower likely due to weathering and/or the formation of aggregates.

中文翻译:

铯从伊利石和蛭石中的解吸机理

摘要 众所周知,铯离子 Cs+ 强烈吸附在云母矿物上。然而,在不同盐离子存在的情况下,Cs+ 在痕量吸附水平随时间的解吸尚不清楚。在本研究中,我们在室温下对 Cs+ 与伊利石和蛭石进行了长期吸附和解吸实验,以研究吸附时间和共存阳离子对解吸的影响。在 1 mM K+ 或 Ca2+ 或 1 mM K+ 和 100 mM Ca2+ 存在下,在 8 周内将少量 Cs+(掺入 900 Bq 137Cs 的 50 nM Cs+)吸附到伊利石和蛭石上,然后在存在下解吸普鲁士蓝 (PB) 纳米颗粒超过 12 周。PB纳米颗粒用于抑制解吸的Cs+的再吸附。在Ca2+的存在下,90%以上的Cs+被吸附到矿物质上;同时,只有 50% 到 70% 的 Cs+ 存在于 K+ 中。对于除含 Ca2+ 的伊利石(Ca-伊利石)以外的所有样品,80% 以上的 Cs+ 在几天内被解吸,并且在实验结束时几乎所有的 Cs+ 都被解吸。Cs+ 的大量快速解吸表明吸附到这些矿物质上的大部分 Cs+ 在强吸附剂(如 PB 纳米粒子)的存在下确实不稳定。这些解吸趋势几乎不受吸附时间变化的影响。Ca-伊利石对Cs+的解吸速度较慢,1天吸附的样品解吸80%需要1个多月的时间,解吸量仅达到90%以下。随着吸附时间从一天到两周,这种从 Ca-伊利石中缓慢解吸 Cs+ 的过程变得更加缓慢,对于后者,在实验结束时只有 70% 的吸附 Cs+ 被解吸。Ca-伊利石解吸Cs+的机制通过拟合伪一级解吸模型进行定量解释,表明30~40%的Cs+被吸附到Ca-伊利石夹层的外围区域并扩散到内饰部分。其余吸附的 Cs+ 可以相对较快地解吸。由于这些 Cs+ 最有可能吸附到 Ca-伊利石中所谓的磨损边缘位点,这些结果表明一部分吸附的 Cs+ (70 ∼ 60%) 是不稳定的。因此,共存阳离子引起的夹层外围区域的膨胀和塌陷以及 Cs+ 的层间迁移是限制 Cs+ 向/从云母矿物吸附和解吸的重要过程。此外,
更新日期:2020-12-01
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