(372g) Co1-X[Fe(III)(CN)6]/Ag for Electrochemical Recovery of Cobalt Ion from Spent Nickel Metal Hydride Batteries

Cobalt is utilized as a core element in rechargeable batteries, catalysts, magnets, inks and pigments. The rapidly growing use of rechargeable batteries in electric vehicles increases the demand for cobalt at a fast pace. Thus, exploration of feasible cobalt recovery and recycling technologies are essential to meet the global demand. In addition, cobalt is a toxic element that causes adverse effect on human health, thus recycling this element can reduce environmental pollution as well as minimize the wastage of such valuable element. Because of the uncertainty surrounding the supply of primary cobalt and its status as a critical raw material, improving the recycling and recovery of cobalt is becoming more vital. The secondary sources of cobalt include waste catalysts, magnets, super alloys, cemented carbides, rechargeable batteries, and other metallurgical waste/byproducts. The techniques used for the recovery of cobalt from these secondary sources are mainly pyrometallurgy and hydrometallurgy, which are characterized by high energy consumption, emission of pollutants, and involvement of complicated steps such as acid leaching. Thus, alternative cobalt recycling practices should be explored.

Electrochemical techniques for metal ion recovery are known to have advantages over the conventional adsorption and precipitation techniques such as high performance, easy operation, low cost, easy separation, and high rate of ion capture. Herein, cobalt hexacyanoferrate (Co_1-x[Fe(III)(CN)₆]) was utilized to recover cobalt ions from a simulated leachate of spent nickel metal hydride batteries (NiMH) batteries through electrochemical approach. Co_1.5[Fe(III)(CN)₆] electrode delivers a high reversible capacity and a high capacity retention after several cycles. The high capacity and excellent cyclic stability of the material makes it ideal for electrochemical applications. Thus, a three-electrode assembly consisting of Co²⁺ selectiveintercalating electrode (Co_1-x[Fe(III)(CN)₆]), a chloride-capturing silver electrode, and Ag/AgCl reference electrode were utilized for Co²⁺ capture. The structural and morphological properties of the electrodes were thoroughly characterized. The cyclic stability of the electrodes was examined through cyclic galvanostatic charge and discharge tests. The selective Co²⁺ intercalation and de-intercalation were tested by cyclic voltammetry test and galvanostatic charge and discharge tests at different operating conditions. The overall performance of CoHCF/Ag system was examined by the Co²⁺ intercalation and de-intercalation capacity, selectivity and energy requirement.

In this study, the potential of the Co_1-x[Fe(III)(CN)₆]/Ag electrode pair for the electrochemical Co²⁺ from a simulated spent NiMH batteries aqueous source was successfully demonstrated. The stability of the electrode pair in aqueous environment was confirmed by the material and electrochemical characterizations. Cyclic galvanostatic discharge and charge tests confirmed the stability of the material over 50 cycles. The increase in applied current and time facilitated the Co²⁺ capture. Co_1-x [Fe^(III)(CN)₆] selectively captured Co²⁺ in the presence of other cations such as Ni²⁺, Ce³⁺, La³⁺, Nd³⁺, and Pr³⁺ in the simulated spent NiMH feed solution. Overall, the proposed electrochemical system is eco-friendly, effective, selective, and recyclable for Co²⁺ recovery from spent NiMH battery source.

This work was supported by NRF funded by The Ministry of Science and ICT (2021R1H1A2008284, 2020R1A2C1003560, 2021R1A2C2093746), Basic Science Research Program through the Ministry of Education (2020R1A6A1A03038817).