Enhancing Uranium Uptake by Amidoxime Adsorbent in Seawater: An Investigation for Optimum Alkaline Conditioning Parameters
Enhancing Uranium Uptake by Amidoxime Adsorbent in Seawater: An Investigation for Optimum Alkaline Conditioning Parameters
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DOI：
10.1021/acs.iecr.5b02735
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发表时间：
2016-04-20
影响因子：
4.2
通讯作者：
Dai, S.
中科院分区：
文献类型：
--
作者：
Das, S.;Tsouris, C.;Dai, S.
橡树岭国家实验室研制了一种高比表面积聚乙烯纤维吸附剂(AF160-2)，它是由丙烯腈和衣康酸辐射引发接枝聚合而成。通过羟胺处理，将接枝腈转化为胺基。然后，通过改变不同的反应参数，如氢氧化钾浓度(0.2、0.44和0.6M)、时间(1、2和3h)和温度(60、70和80℃)，对胺肟化的吸附剂进行处理。然后用含有氯化钠和碳酸氢钠的模拟海水溶液以及铀浓度为7-8ppm和pH 8的硝酸铀模拟海水溶液进行吸附剂筛选。傅立叶变换红外光谱和固体核磁共振分析表明，在KOH调节过程中，一小部分胺肟基被水解为羧酸盐。在所有KOH浓度下，模拟海水筛分溶液对铀的吸附容量随处理时间和温度的升高而逐渐增加。还观察到，在所有的处理时间和温度下，随着KOH浓度的增加，吸附容量都会增加。AF160-2吸附剂样品还与天然海水进行了流动实验，以确定不同的KOH处理时间和温度对铀的吸附能力。根据几个AF160-2样品的铀承载能力值，观察到在60、70和80℃下将KOH处理时间从3小时改变到1小时会导致海水中铀承载能力的增加，这与实验室用模拟溶液筛选时发现的趋势不同。较长的KOH调节时间会显著提高二价金属离子(如钙和镁)的摄取率，这是由于胺肟转化为选择性较差的羧酸盐所致。扫描电子显微镜显示，长时间的处理也可能导致吸附剂的降解。
A high-surface-area polyethylene-fiber adsorbent (AF160-2) has been developed at the Oak Ridge National Laboratory by radiation-induced graft polymerization of acrylonitrile and itaconic acid. The grafted nitriles were converted to amidoxime groups by treating with hydroxylamine. The amidoximated adsorbents were then conditioned with potassium hydroxide (KOH) by varying different reaction parameters such as KOH concentration (0.2, 0.44, and 0.6 M), duration (1, 2, and 3 h), and temperature (60, 70, and 80 degrees C). Adsorbent screening was then performed with simulated seawater solutions containing sodium chloride and sodium bicarbonate, at concentrations found in seawater, and uranium nitrate at a uranium concentration of similar to 7-8 ppm and pH 8. Fourier transform infrared spectroscopy and solid-state NMR analyses indicated that a fraction of amidoxime groups was hydrolyzed to carboxylate during KOH conditioning. The uranium adsorption capacity in the simulated seawater screening solution gradually increased with conditioning time and temperature for all KOH concentrations. It was also observed that the adsorption capacity increased with an increase in concentration of KOH for all the conditioning times and temperatures. AF160-2 adsorbent samples were also tested with natural seawater using flow-through experiments to determine uranium adsorption capacity with varying KOH conditioning time and temperature. Based on uranium loading capacity values of several AF160-2 samples, it was observed that changing KOH conditioning time from 3 to 1 h at 60, 70, and 80 degrees C resulted in an increase of the uranium loading capacity in seawater, which did not follow the trend found in laboratory screening with stimulated solutions. Longer KOH conditioning times lead to significantly higher uptake of divalent metal ions, such as calcium and magnesium, which is a result of amidoxime conversion into less selective carboxylate. Scanning electron microscopy showed that long conditioning times may also lead to adsorbent degradation.