Leaching of exhausted LNCM cathode batteries in ascorbic acid lixiviant: a green recycling approach, reaction kinetics and process mechanism

Abstract

BACKGROUND Critical metals (lithium, cobalt and nickel) used in Li-ion batteries have been estimated to face a supply crunch by the end of 2020 due to their limited natural reserves and complex metallurgy. A green recycling approach to treat the exhausted batteries may potentially mitigate supply risks of metals and environmental burden of metal toxicity. RESULTS The maiden application of bio-producible/degradable ascorbic acid for the leaching of LiNi Co-x Mn-y O-z(2) (LNCM) cathode batteries was investigated while performing parametric variations. Inhibited leaching at high temperature and long contact time showed the adversity caused by the possible decomposition of ascorbic acid. The low leaching of cobalt as a function of acid concentration indicated the hindrance in dissolution of Co(III) compound. A quantitative leaching of metals (>= 96%) could be achieved under the following optimal conditions: agitation speed, 500 rpm; acid concentration, 2.0 mol L-1; temperature, 75 degrees C; time, 90 min; and pulp density, 6%. The apparent activation energy of metals was calculated to be more than 40 kJ mol(-1). CONCLUSION Ascorbic acid could potentially dissolve the cathode material without introducing any additional reducing agent into the system. The leaching kinetics fitted with an empirical model {-ln(1 - x)}(2) versus t could reveal that the overall dissolution process follows a chemically controlled mechanism. The present study leads towards sustainable metallurgy using a biodegradable reagent instead of applying harsh and hazardous mineral acids.