Selective leaching of Ni from Cd-depleted spent Ni-Cd batteries by glycine-citrate solution

Abstract

In the present study, the selective leaching of Ni over Fe from Cd-depleted spent Ni-Cd batteries has been presented using a glycine-citrate solution. These findings can be considered experimental proof of our concept of developing an eco-friendly protocol for the green recycling of both Cd and Ni. In the present study, the pertinent factors affecting Ni leaching, including glycine concentration (0.5–1.5 M), citrate concentration (17–51 mM), temperature (25–55 °C), and time (1–36 h), were investigated. It was found that nearly 95% of Ni can be dissolved when glycine concentration = 1.5 M, citrate concentration = 34 mM, and solid-to-liquid ratio = 2.5% at T = 55 °C after 36 h; noticeably, the amount of Fe entered to solution is only 920 (mg/L). The thermodynamics of the leaching system were comprehensively evaluated and the reactions, responsible for the dissolution of Ni, were predicted. Finally, based on semiempirical kinetic modeling, it was found that the Ni dissolution process is governed by the surface chemical reaction with an activation energy of ∼105 (kJ/mol).