Bi(Ⅲ)在NaCl-KC1熔盐体系中的电化学行为

为开发环境友好型铋提取技术，在700℃下采用循环伏安、方波伏安和计时电位等方法研究了NaCl?KCl熔盐体系中Bi(III)在玻碳电极上的电化学行为。在–0.3 V (vs. Ag/AgCl)电位下以玻碳电极为工作电极对NaCl?KCl?BiCl3进行恒电位电解。结果表明，Bi(III)在NaCl?KCl熔盐体系中的还原反应是一步得到3个电子的准可逆反应Bi3++3e?=Bi，起始还原电位为0.05 V (vs. Ag/AgCl)，该反应受扩散控制。Berzins-Delahay方程和Sand方程计算的700℃下Bi(III)在熔盐中的扩散系数分别为0.83×10–5和1.0×10–5 cm2/s。阴极产物为致密纯金属Bi，不含杂质。

Electrochemical behavior of Bi(III) in molten NaCl-KCl

Bismuth has a wide range of applications such as in metallurgy, chemical engineering, electronic industry, medical service, aeronautics, astronautics, and nuclear industry, etc., owing to its excellent properties including large density, low melting point, nontoxicity as well as the abnormal nature of expansion in cooling down and contraction in heating up. As one of the nonrenewable and scarce metal resources, the extraction and recycling of bismuth has received increasing attention in recent years. Molten salt electrolysis is one of the most widely used methods for metal extraction. Therefore, extraction of bismuth from BiCl3 directly by molten salt electrolysis was evaluated in the present work in order to develop an environmentally friendly technology for bismuth recovery. Firstly, the electrochemical behavior of Bi(III) ions in molten NaCl?KCl at 700℃ was investigated by cyclic voltammetry, square wavevoltammetry, and chronopotentiometry on a glassy carbon working electrode. The results indicated that the reduction of Bi(III) in the NaCl?KCl molten salt was a one-step process with three electrons exchanged Bi3++3e?=Bi, and the initial reduction potential of Bi(III) ions was detected at 0.05 V (vs. Ag/AgCl), approximately. Meanwhile, the reduction of Bi(III) ions in the melts was a quasi-reversible diffusion-controlled process, and the diffusion coefficient of Bi(III) in molten salt at 700℃ were determined to be 0.83×10–5 and 1.0×10–5 cm2/s, respectively, based on the results of cyclic voltammetry and chronopotentiometry using the Berzins-Delahay equation and the Sand equation. Then, potentiostatic electrolysis at –0.3 V (vs. Ag/AgCl) was carried out in molten NaCl?KCl?BiCl3 under 700℃ and spherical metal granules were obtained around cathode. The cathodic products were compact in microstructure and confirmed to be pure bismuth with no other impurities detected by XRD and SEM?EDS analyses. The present results confirmed that it was an effective method for extraction of bismuth by direct electrolysis of bismuth chloride in molten NaCl?KCl, which could be subsequently used to recycling of bismuth from bismuth-bearing materials.