Novel bioleaching of waste lithium ion batteries by mixed moderate thermophilic microorganisms, using iron scrap as energy source and reducing agent

Abstract

Low kinetic is one of the most important disadvantages of bioleaching. The leaching rate can be increased by employing thermophilic microorganisms. In this research, the moderate thermophilic bioleaching of waste lithium ion batteries (LIBs) at 45 °C was investigated. The effects of sulfur (S0) and ferrous sulfate heptahydrate (FeSO4.7H2O) were investigated on cobalt, nickel and lithium bioleaching mechanisms. The results showed that increasing sulfur concentration improves lithium recovery; while it has no effect on cobalt and nickel dissolution. On the other hand, FeSO4.7H2O increased cobalt recovery and its leaching kinetic significantly. Fe2+ increased cobalt recovery by acting as reducing agent. Just within 2 days of bioleaching with 24.25 g/l FeSO4.7H2O, the Co, Ni and Li recoveries reached 99.9%, 99.7% and 84%. To reduce the process cost, iron sulfate heptahydrate was replaced with iron scrap. In bioleaching process, scrap was leached and produced Fe2+ which in turn acted as reducing agent and increased cobalt and nickel recoveries. The results showed that the final metals recoveries for tests with scrap and chemical FeSO4.7H2O are similar. Using iron scrap increased the bioleaching time from 2 days to 6 days. The formation of a jarosite layer on the surface of scrap particles limited the releasing ferrous ions. The microorganisms prefer to oxidize iron scrap particles before waste LIBs particles. Comparing the results of bioleaching and leaching tests shows that Li was dissolved due to acid leaching, Co was dissolved due to oxidation-reduction reactions and Ni dissolved due to direct bioleaching mechanism.