Green and sustainable route for the efficient leaching and recovery of valuable metals from spent Ni−Cd batteries

Abstract

Recycling of Ni, Cd and Co from spent Ni−Cd batteries is significant for preventing nickel and cobalt deficiency and protecting the environment. Although several studies have developed methods for recycling these metals from spent Ni−Cd batteries, the simultaneous leaching (extraction) and recovery of Ni, Cd and Co via an environmentally benign and economical manner is still challenging. Herein, a formic acid-assisted method for leaching and recovering valuable metals from the cathode and anode materials of spent Ni−Cd batteries is proposed. The effects of temperature, time, and liquid/solid ratio on Ni, Cd, and Co leaching were also extensively investigated. The single factor experimental results and statistical analysis revealed that more than 95 % leaching efficiencies of Cd and Co could be achieved from the cathode and anode materials at 80 °C and 2.5 h, while a maximum of 81 % Ni leaching was attained in formic acid at 90 °C, 4 h and a 30 mL/g liquid/solid ratio. Moreover, the statistical analysis results revealed that the temperature and time had significant effect (ρ < 0.0001) on Ni and Cd leaching. It was difficult to leach metallic Ni present in the cathode material because of its high inertness property; however, a conversion of 99.70 % Ni was achieved at 60 °C for 2 h when H2O2 (15 %, v/v) was used as an oxidizing agent. The findings of this study suggest that the formic acid-assisted recycling process could be a sustainable alternative for the efficient leaching and recovery of valuable metals from spent Ni−Cd batteries because it features a reduced highly corrosive acid consumption, mild leaching conditions, and less environmental footprints.