Improved recovery of valuable metals from spent lithium-ion batteries by efficient reduction roasting and facile acid leaching.

A combined process was investigated to recover valuable metals from LiNixCoyMnzO2 cathode materials of spent lithium-ion batteries. In this approach, the cathode materials were first roasted with graphite which recycled from anode materials, and then conducted to a reductant-free sulfuric acid leaching for efficient recovery of valuable metals. The reduction roasting was meticulously investigated to control the composition of roasted products, and the physicochemical changes of the cathode materials in the reduction thermal treatment was studied by XRD, TGA, XPS, SEM and EDS analyses. The experimental results show that under the optimum processing conditions of 600 °C, 3 h, and mass ratio of cathode materials to anode graphite of 6:1, the mixed electrode materials can be transformed into the desired phase of CoO, NiO, MnO and Li2CO3 primarily. Being different from obtaining Co and Ni metallic phase in reduction roasting, producing CoO and NiO benefit to a lower energy consumption, no H2 emission in the leaching process, and more facile conditions for complete leaching. More than 99% of Ni, Co and Li were extracted, and more than 97% of Mn was leached without adding reductant under the optimum conditions: 1.05 times of theoretical H2SO4 consumption, and L/S = 6 ml·g-1 at 85 °C for 1 h. This promising process can not only make efficient use of waste anode graphite, save energy consumption, but also avoid generation of massive H2 in the subsequent facile leaching of valuable metals.