Characteristics of Oxidation Reaction of Rare-earth Chlorides for Precipitation in LiCl-KCl Molten Salt by Oxygen Sparging

Abstract

The precipitation reaction of some rare earth chlorides (La/Ce/Nd/GdCl 3 ) in a LiCl-KCl molten salt has been carried out by using the oxygen sparging method. In this study, regardless of the oxygen sparging time and the molten salt temperature, oxychlorides (REOCl) for LaCl 3 , NdCl 3 and GdCl 3 , and an oxide (REO 2 ) for CeCl 3 are formed as a precipitate. The conversion of rare-earth chlorides into insoluble precipitates was described by using a conversion ratio. The conversion ratio increased exponentially with the oxygen sparging time and finally showed asymptotic value at 1,023 K of the molten salt temperature condition. The conversion ratios of LaCl 3 , NdCl 3 and GdCl 3 were increased with the molten salt temperature, however, even though the conversion ratio was increased from 0.660 to 0.995 with increasing molten salt temperature from 823 to 923 K at 60 min of a sparging time, the values of the conversion ratio of CeCl 3 were nearly constant (over 0.999) with the molten salt temperature. As a result of the thermogravimetric analysis of the precipitates (oxychlorides), about 11-13% of a weight loss happened in the case of LaOCl, NdOCl and GdOCl, and all the oxychlorides were converted to their oxides i.e. La 2 O 3 , Nd 2 O 3 and Gd 2 O 3 at a high temperature and oxygen atmosphere.

Methanation of CO2 over Cobalt-Lanthanide Aerogels: Effect of Calcination Temperature

“…It is known that lanthanides, particularly those from the beginning of the series, tend to form oxychlorides when chlorine salts are used as starting reagents [22]. The formation of lanthanide oxychlorides is thermodynamically favorable at low temperatures, while the formation of perovskites or sesquioxides becomes preponderant at higher temperatures (>650 • C), except for the cerium chloride system since the formation of CeO 2 is thermodynamically favored at lower temperatures (T > 200 • C) [23].…”

Vacuum distillation of a mixture of LiCl–KCl eutectic salts and RE oxidative precipitates and a dechlorination and oxidation of RE oxychlorides

“…7, the oxides (CeO 2 /Eu 2 O 3 /PrO 2 ) were maintained during the dechlroination and oxidation, however, the oxychlorides (NdOCl/PrOCl) were converted to stable oxides (Nd 2 O 3 /PrO 2 ). Based on the above results, it is postulated that the dechlorination and oxidation of the rare-earth oxychlorides happens simultaneously at a high temperature of more than 1200 • C under an oxidative atmosphere [5]. The reaction of the dechlorination and oxidation of them can be expressed by the following equations; Fig.…”

“…An oxidation method can be used to achieve that because it converts the rare-earth chlorides to rare-earth oxychlorides or oxides precipitated as insoluble compounds. Among the various oxidation methods, a promising and potential alternative method is by sparging O 2 gas [4,5]. The rare-earth chlorides in the waste salts are precipitated by sparging O 2 gas and during this process, pure LiCl-KCl eutectic salts can be recovered from the waste salts.…”

“…Therefore, a separation of the LiCl-KCl eutectic salts from this mixture and a stabilization of the rare-earth oxychlorides are essential to reuse these salts, to reduce the high level waste volume and to stabilize a final waste form. A distillation process can be used for a salt recovery from the mixture [9][10][11], and a dechlorination and oxidation of the rare-earth oxychlorides can convert them to stable oxide forms at a high temperature of more than 1200 • C [5].…”

Electrochemical Salt Wasteform Development: A Review of Salt Treatment and Immobilization Options

“…Separation processes include selective reaction and/or removal of different salt components such as halides, alkalis, alkaline earths, or rare earths (REs). Salt separation techniques discussed herein include vacuum distillation, melt crystallization, reactive precipitation, oxidative precipitation, zone freezing, and dehalogenation. , The ideal scenario for salt recycle would be a technique for removing the base salt from the fission products, such as distillation or selective crystallization so that (1) the base salt could be recycled for future fuel dissolution batches and (2) only the remaining fission products would need to be immobilized in a wasteform. If this were the case, the wasteform volumes could be significantly reduced compared to waste processing strategies that require the entire salt to be immobilized.…”