Tantalum (Ta) has garnered significant attention due to its exceptional physicochemical properties and mechanical performance, enabling its widespread use in electronics, energy, metallurgy, and chemical industries. It is particularly strategic for high-temperature alloys, electronic components, and chemical processing equipment. Currently, the main methods for tantalum production include thermal reduction and molten salt electrolysis. Among them, molten salt electrolysis has emerged as a promising approach for the extraction and purification of refractory metals, owing to its advantages of low energy consumption, high product purity, and minimal environmental impact [1].

Several molten salt electrolysis methods have been developed for tantalum, including the FFC process (molten salt electro-deoxidation method), SOM process (solid oxygen-permeable membrane method), and the USTB process. The USTB method, pioneered by the University of Science and Technology Beijing, integrates carbothermal reduction with molten salt electrolysis. This two-step process employs metal carbon–oxygen solid solutions as soluble anodes to enable the efficient reduction and extraction of metals in a NaCl–KCl electrolyte. In 2006, Prof. Hongmin Zhu’s team first reported the successful electrolytic production of titanium metal using TiC_xO_y solid solutions as anode materials, laying a foundation for the advancement of soluble anode electrolysis technology [2].

In this approach, conductive compounds containing the target metal serve as soluble anodes, releasing metal ions into the molten salt under controlled potentials or current densities, followed by cathodic reduction and deposition [3]. Compared to traditional oxide anodes, soluble anodes offer advantages including higher energy efficiency, lower emissions, and sustained anodic dissolution. The core requirement lies in developing anode materials with excellent electrical conductivity and controllable electrochemical dissolution behavior. Carbon–oxygen solid solutions release C and O in the form of CO or CO₂ gas during electrolysis, thus avoiding electrode passivation caused by carbon buildup—a common issue in conventional anodes—making them a topic of current research interest. Given the similar thermodynamic and electrochemical properties of tantalum and titanium, it is reasonable to anticipate that TaC_xO_y solid solutions also hold promise as anode materials for molten salt electrolysis. However, research in this area is still in its infancy, with limited studies on material design, electrochemical behavior, and process optimization.

Additionally, the electrolyte composition plays a critical role in determining current efficiency, electrode stability, and product quality. Existing molten salt systems are primarily categorized into chlorides, fluorides, and mixed fluoride–chloride salts. The nature of the ionic species significantly affects the coordination environment and electrochemical behavior of metal ions [4]. Studies have shown that introducing an appropriate amount of fluoride ions (F^-) into NaCl–KCl molten salts can form more stable coordination structures with metal ions, enhancing their solubility and electrochemical stability. This facilitates continuous cathodic reduction, thereby improving current efficiency and process controllability [5].

Building upon previous research and the urgent demand for green, efficient tantalum extraction, this study proposes two innovative strategies: (1) Development of a molten salt electrolysis system based on TaC_xO_y solid solution anodes: This aims to assess the feasibility and advantages of using TaC_xO_y as a soluble anode for tantalum extraction. (2) Fluoride ion regulation in the electrolyte: To address the low Ta ion concentration and poor reduction efficiency, we propose modulating the F^- content in the molten salt to precisely control the solubility and coordination environment of Ta ions, enhancing the anodic dissolution–cathodic deposition equilibrium and improving extraction efficiency.

Finally, TaC_xO_y solid solutions with excellent electrical conductivity and structural stability were successfully synthesized and validated as effective soluble anode materials for the efficient electrolytic extraction of metallic tantalum in a NaCl–KCl molten salt system. Experimental results revealed that in the absence of fluoride ions, tantalum ions exhibited high volatility, significant current fluctuations, and low electrolysis efficiency. Conversely, the introduction of KF significantly reduced tantalum volatilization, simplified the reduction pathway from a two-step to a one-step process, and substantially enhanced both deposition efficiency and current stability. The obtained electrolytic products consisted primarily of spherical tantalum clusters with fine particle size, uniform morphology, and high purity, further confirming the effectiveness of the proposed approach. Overall, the “soluble anode + fluoride ion regulation” strategy developed in this study presents a promising and sustainable route for the green and efficient extraction of tantalum.