An alternative approach to reclaim spent nickel–metal hydride batteries

Spent nickel-metal hydride (NiMH) batteries contained some valuable metals which are worthy of recovery. This study focuses on the reclamation of spent NiMH batteries using an alternative approach, thermal separation process (TSP). Spent NiMH batteries were mixed with cullet, limestone, and dolomite. The mixture was heated to 1,450°C and cooled to room temperature without forced convection. During the TSP, the output-materials were divided into slag, ingot, and flue gas according to the boiling points and densities of metals. Results show that metals having a relatively low boiling points, such as Cd, Hg, Pb, and Zn, were mostly vaporized into flue gas. Among the metals retained in molten materials, Co, Cu, Fe, and Ni predominately went into the bottom layer and formed the ingot; on the contrary, Al, Ca, Mg, and Si stayed in the upper layer and formed slag. Therefore, the main components of slag were Si (316,000 mg/kg), Ca (289,000 mg/kg), and Mg (32,400 mg/kg) and the major crystalline phases were CaSiO₃, CaMgSi₂O₆, and Ca₂MgSi₂O₇. The slag was pended as non-hazardous materials and could be reused as road pavement or building materials. The ingot had high levels of Ni (408,000 mg/kg), Fe (349,000 mg/kg), and Co (55,400 mg/kg) and could act as an additive in stainless steel manufacturing process.