利用含HNO3-TBP錯合物之冷媒HFC-134a於固相基質中萃取鈾金屬

Abstract

於核能發電工業中，廢燃料棒中鈾及鈽金屬之回收再利用，是核能工業上最主要研究項目之一。處理核燃料棒一般需要大量之有機溶劑以及硝酸，因而會產生大量之廢液。目前，已有研究利用超臨界二氧化碳（SF-CO2）來取代傳統有機溶劑來進行萃取，萃取完成後，二氧化碳洩壓即可氣化而與萃取物分離，達到濃縮效果而且無需處理有機廢溶劑；文獻指出為了減少大量濃硝酸使用以及避免硝酸直接接觸到燃料棒樣品，於前處理時先將螯合劑TBP（Tributylphosphate）與硝酸結合形成錯合物，並溶解於SF-CO2直接進行固相基質鈾金屬萃取。 本實驗嘗試利用液態冷媒HFC-134a（1,1,1,2-tetrafluoroethane）來取代SF-CO2，其所需壓力比使用SF-CO2降低約100個大氣壓以上，且其有類似SF-CO2經壓縮之後具有溶解度之性質，於操作安全考量上優於SF-CO2。前處理時亦先將螯合劑TBP與硝酸結合形成錯合物，並溶解於HFC-134a直接進行固相基質鈾金屬萃取，藉由此法亦可避免直接使用濃硝酸進行鈾金屬萃取，安全性也可以被大幅提升，能夠達到經濟且高效率的回收。

In nuclear power industry, the recycling of uranium and plutonium metal in the form of used nuclear fuel rod is often an important subject. The nuclear fuel rod is usually dissolved in concentrated nitric acid and extracted using chelate - containing organic solvent. Uranium and plutonium can be recovered efficiently in this process. However, a large amount of waste organic solvent must be reprocessed. Supercritical fluid carbon dioxide(SF-CO2) has been introduced recently to replace the organic solvent. SF-CO2 evaporates after the extraction process and then separates from the extracts. Thus, it can be used to save the endeavor to reprocess the extraction solvent. Researchers also tried to synthesize a complex using TBP with nitric acid first. The complex-containing SF-CO2 was found to be able to extraction uranium metal from solid waste samples. This technique can prevent the overuse of nitric acid and avoid direct contant between nitric acid and the fuel samples. In this Study, we attempted to replace SF-CO2 with liquid HFC-134a (1,1,1,2-tetrafluoroethane) as the extraction solvent due to its much operational pressure, and the similar salvation power compared with SF-CO2. We followed the same way to synthesize the complex of TBP and nitric acid. This complex-containing HFC-134a showed great capability in extracting uranium. In addition, we did extractions for a number of metals that would be produced during the nuclear fission process. Except for La(III)、Gd(III) and Lu(III), recoveries of other metals were negligible. Therefore, using of HFC-134a may provide a more economical and safer way to recover uranium from used nuclear fuel rods.