Solubilities and solubility products of thorium hydroxide under moderate temperature conditions
Solubilities and solubility products of thorium hydroxide under moderate temperature conditions
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DOI：
10.1515/ract-2017-2917
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发表时间：
2018-08-01
影响因子：
1.8
通讯作者：
Takagi, Ikuji
中科院分区：
文献类型：
--
作者：
Nishikawa, Shogo;Kobayashi, Taishi;Takagi, Ikuji
本研究对在高氯酸钠和高氯酸的0.5 M离子强度溶液中，通过欠饱和及过饱和方法制备的初始含氢氧化钍（无定形）的样品溶液在pH（c）为2.0 - 8.0范围内、在298、313和333 K的老化温度（T - a）下储存后的钍溶解度进行了研究。根据T - a的不同，经过长达40周的一定时间后，在298、313和333 K的测量温度（T - m）下，样品溶液的上清液通过3 kDa的膜进行超滤。通过使用孔径从3到100 kDa不同的膜进行超滤来研究胶体物种的尺寸分布，并通过X射线衍射（XRD）对固相进行检测。在T - a = 298 K下使用连续振荡的欠饱和方法老化后获得的样品溶液的溶解度与干燥的氢氧化钍沉淀的溶解度相似。在T - a = 313和333 K下老化后获得的溶解度低于在T - a = 298 K下的溶解度。XRD光谱表明在这些升高的温度下固相发生了结晶。在T - a = 333 K下使用过饱和技术老化后获得的样品溶液的溶解度与使用欠饱和方法制备并在相同T - a下老化的样品溶液的溶解度相似。在两种方法制备的样品溶液中都观察到表观溶解度对T - m有轻微的温度依赖性。通过溶解度分析确定了不同T - a和T - m后的溶度积（K - sp，(Ta)(T - m)）。随着T - m的增加，观察到Th⁴⁺ + (4 + x)H₂O(l) ⇌ Th(OH)₄·xH₂O(s，T - a) + 4H⁺的形成常数（K - s，(Ta)(T - m)）增加，这表明该反应是吸热的。Th(OH)₄·xH₂O(s，T - a)和ThO₂（晶态）固相之间的焓变（ΔH - r°(m_Ta → cr)）表明从Th(OH)₄·xH₂O(s，T - a)到ThO₂（晶态）的固相转变包含一个吸热过程。
The Th solubilities of the sample solutions that initially contained Th(OH)(4)(am) prepared by undersaturation and oversaturation methods in the pH(c )range of 2.0-8.0 in a 0.5 M ionic strength solution of NaClO4 and HClO4 and stored at aging temperatures (T-a) of 298,313 and 333 K were investigated in this study. After a certain period of time up to 40 weeks depending on T-a, supernatants of the sample solutions were ultrafiltrated through 3 kDa membranes under the measurement temperature (T-m) of 298, 313 and 333 K. Size distributions of the colloidal species were investigated by ultrafiltration using membranes with different pore sizes ranging from 3 to 100 kDa, and the solid phases were examined by X-ray diffraction (XRD). The solubility of the sample solutions obtained after aging at T-a = 298 K using undersaturation method with continuous shaking was similar to those of dried precipitate of Th hydroxide. The solubilities obtained after aging at T-a = 313 and 333 K were lower than those at T-a = 298 K. The XRD spectra suggested that the crystallization of the solid phase proceeded under these elevated temperatures. The solubility of the sample solutions obtained after aging at T-a = 333 K using the oversaturation technique were similar to those prepared by undersaturation method and aged at the same T-a. A slight temperature dependence of the apparent solubilities on the T-m was observed in the sample solutions prepared by both methods. The solubility products (K-sp,(Ta) (T-m)) after different T-a and T-m were determined from the solubility analysis. The observed increase in the formation constant (K-s,(Ta) (T-m)) of Th4+ + (4 + x) H2O(1) reversible arrow Th(OH)(4 )center dot xH(2)O(s,T-a) + 4H(+) with increasing T-m indicated that the reaction was endothermic. The enthalpy change (Delta H-r degrees(m_Ta -> cr)) between the solid phases of Th(OH)(4) center dot xH(2)O(S,T-a) and ThO2(cr) suggested that the solid phase transformation from Th(OH)(4 )center dot xH(2)O(s,T-a) to ThO2(cr) contains an endothermic process.