One of the electrochemical properties of a liquid metal electrode is lowering the reduction potential of elements by forming the intermetallic compounds. Therefore, the liquid metal electrode is utilized in the electrowinning process of pyroprocessing, which is one of the reprocessing options with strength in light of nuclear non-proliferation. Cadmium metal has been considered as the candidate of liquid metal electrodes, but attempts to find other surrogate metals have been conducted because of its harmfulness and low vapor pressure. Hence, bismuth, tin, and zinc are selected as the surrogate liquid metal electrode to investigate the electrochemical properties of cerium on liquid metal electrodes in this study. First, the cerium-metal binary system on the solid tungsten electrode was utilized to investigate the cerium-metal intermetallic compounds, which are formed during the electrowinning process. The number of intermetallic compounds was confirmed from the oxidation peaks of cyclic voltammetry and the plateaus of open-circuit chronopotentiometry. The Gibbs free energy of formation of each intermetallic compound was used to determine the composition of each intermetallic compound. Subsequently, the electrochemical behaviors of cerium were investigated on the liquid metal electrodes. The high blank current was observed on the liquid bismuth electrode and the liquid tin electrode compared to the liquid zinc electrode from cyclic voltammetry results. The activity coefficient of cerium on the liquid bismuth, tin, and zinc electrodes was revealed to be lower than one on the liquid cadmium electrode. It was also found that the calculation of the exchange current density on the liquid metal electrode is feasible in the system with a low blank current, such as cerium on the liquid zinc electrode. This study provides a basic understanding of the liquid metal electrode system for the efficient electrowinning process.
액체 금속 전극은 금속간 화합물의 형성을 통해 원소의 환원 전위를 낮추는 특성을 지니고 있어 파이로프로세싱의 전해 제련 과정에서 활용된다. 현재까지 액체 금속 전극 물질로 고려되어 온 카드뮴 금속의 유해성과 낮은 증기압으로 인해, 대체 물질로서 다른 금속에 대한 연구가 진행되어 오고 있다. 이에 본 연구에서는 대체 액체 금속 물질로 비스무스, 주석, 아연을 선정하여 액체 금속 전극 상에서의 세륨의 특성을 확인하였다. 먼저, 고체 텅스텐 전극 상에서의 세륨-금속 이성분계를 활용하여 세륨과 형성된 금속간 화합물의 개수를 확인하고 각각의 깁스 형성 자유에너지를 계산하였다. 또한, 액체 금속 전극을 작업 전극으로 활용하여 세륨의 전기화학적 거동을 확인하고 교환전류밀도를 계산하였다. 본 연구는 액체 금속 전극에 대한 이해도를 높이고 효율적인 전해 제련 공정에 필요한 정보를 제공할 수 있을 것으로 기대된다.
