Closed-vessel microwave leaching of valuable metals from spent lithium-ion batteries (LIBs) using dual-function leaching agent: Ascorbic acid

A novel closed-vessel microwave system for leaching of valuable metals from spent LIBs was examined using ascorbic acid. Important parameters and energy requirement were assessed. Leaching efficiency of Li, Co, and Mn and total energy requirement decreased as microwave heating rate increased from 5 degrees C/min to 90 degrees C/min. Leaching efficiency increased significantly with increasing acid concentration. Leaching rate of Li, Co, and Mn increased as temperature increased from 75 degrees C to 125 degrees C and data fitted well with pseudo second order model. Complete leaching of Li, Co, and Mn from spent LIBs was obtained at 0.5 M of ascorbic acid, 40 degrees C/min heating rate, 10 g/L of solid to liquid ratio, 125 degrees C within 10 min. Using 0.1 M of ascorbic acid could induce reduction of Co (III) in spent LIBs Co (II), as evidenced by XPS analysis. Total of 97.66% of Co and 58.99% of Mn in leaching solution were recovered on the addition of oxalic acid. Compared with conventional leaching, the closed-vessel microwave system provides an effective and energy-efficient leaching process since the heat loss is lessened and the high pressure and temperature of ascorbic acid solution intensified leaching reactions.

Automated summary

The novel closed-vessel microwave system utilizing ascorbic acid showed efficient leaching of valuable metals from spent LIBs, with leaching efficiency depending on acid concentration, heating rate, and temperature. Optimal conditions for complete leaching were determined as 0.5 M ascorbic acid, 40 degrees C/min heating rate, 10 g/L solid to liquid ratio, and 125 degrees C within 10 min. Although using 0.1 M ascorbic acid could facilitate the reduction of Co (III) to Co (II), additional oxalic acid was required for higher recovery of Co and Mn in the leaching solution.