Recovered materials from spent lithium-ion batteries (LIBs) as adsorbents for dye removal: Equilibrium, kinetics and mechanism

Abstract

The present study focuses on the recovery of mixed metal oxide LiMn2O4 (MO) and graphite (GR) from cathode and anode of spent Li-ion batteries (LIBs) and their use as an adsorbent for the removal of anionic congo red (CR) and cationic methylene blue (MB) dye from aqueous solution. For better performance, recovered GR was converted to Graphite oxide (GO) by modified Hummer’s method and used as adsorbent for further studies. The recovered constituents of spent LIBs were characterized by PXRD, FT-IR, SEM, TEM, EDX, ICP-OES and Surface area analysis. The effects of operating variables such as adsorbent dosage, pH, initial dye concentration, contact time and temperature were studied. Equilibrium data were well fitted to the Freundlich and Sips for GO; Langmuir and Sips for MO. The adsorption kinetics fitted well with pseudo-second order and Elovich model for both dyes by both adsorbents. GO showed maximum adsorption capacity of 134.1mg/g for CR dye whereas MO showed adsorption capacity of 7.4mg/g and 4.2mg/g for CR and MB dyes respectively. In the case of GO, 100% of MB dye was adsorbed upto 1000mg/L due to electrostatic interaction of oppositely charged adsorbent-adsorbate species along with Π-Π interaction. Furthermore, thermodynamic parameters revealed that the adsorption is a physical process, spontaneous and endothermic in nature. The results demonstrated that the constituents of spent LIBs could be employed as effective adsorbents for the removal of CR and MB dyes from waste water.