Effect of roasting pretreatment on micro-nanobubble-assisted flotation of spent lithium-ion batteries

Abstract

In this research study, a novel process of roasting-assisted flotation was developed for the separation of spent vehicle lithium-ion batteries (LIBs) in the presence of micro-nanobubbles (MNBs). For this purpose, roasting technology along with MNBs was applied to overcome the challenge of poor efficiency of electrode active materials flotation. The roasting properties (temperature: 300–500 °C and time: 1 h) and corresponding surface alterations of the electrode active materials (zeta potential, contact angle, and X-ray photoelectron spectroscopy (XPS)) were analyzed to explore the surface properties of roasting materials in the presence of MNBs. MNB-assisted flotation was employed to effectively separate the cathode active materials (CMs) from anode active materials (AMs). Results showed that the efficiency of electrode materials flotation without the roasting process was low due to the existence of residual organic binders and electrolytes. Scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS), XPS and zeta potential analyses showed that the electrolyte residuals and organic binders were eliminated following roasting at 400 °C for 1 h. After roasting, the zeta potential of the CMs and AMs increased from −55 ± 2 to −26 ± 1 mV and −46 ± 1 to −30 ± 1 mV, respectively. These improvements indicated that CM surfaces were more hydrophilic, while the AM surfaces were more hydrophobic. In the presence of MNBs, contact angle measurements showed the highest and lowest values of 91 ± 1° and 29 ± 1° for the AMs and CMs, respectively at 400 °C. It was found that the flotation performance was improved after the roasting process and in the presence of MNBs and relatively lower reagent consumption (50%) was required to obtain higher recovery. Two-stage flotation processes in the presence of MNBs could further upgrade the grade of CMs from 65 ± 2% to 93 ± 3%.