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

[Display omitted] •Recovery of valuable and hazardous metals from spent Ni-Cd batteries was investigated.•Formic acid was used as both leaching and precipitating reagent.•About 99.70 % Ni, 98.50 % Cd, and 100 % Co were simultaneously leached out at 90 °C for 4 h.•Nickel and cadmium were recovered as Ni(COOH)2 and Cd(COOH)2 with purity of 98.9%.•This process does not produce any toxic gas and avoids corrosion. 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