No abstract

The consumption of lithium has increased dramatically in recent years. This can be primarily attributed to its use in lithium-ion batteries for the operation of hybrid and electric vehicles. Due to its specific properties, lithium will also continue to be an indispensable key component for rechargeable batteries in the next decades. An average lithium-ion battery contains 5–7% of lithium. These values indicate that used rechargeable batteries are a high-quality raw material for lithium recovery. Currently, the feasibility and reasonability of the hydrometallurgical recycling of lithium from spent lithium-ion batteries is still a field of research. This work is intended to compare the classic method of the precipitation of lithium from synthetic and real pregnant leaching liquors gained from spent lithium-ion batteries with sodium carbonate (state of the art) with alternative precipitation agents such as sodium phosphate and potassium phosphate. Furthermore, the correlation of the obtained product to the used type of phosphate is comprised. In addition, the influence of the process temperature (room temperature to boiling point), as well as the stoichiometric factor of the precipitant, is investigated in order to finally enable a statement about an efficient process, its parameter and the main dependencies.

Organic acids, such as gluconic acid, have been widely studied for their potential in the hydrometallurgical recycling of lithium-ion batteries. These organic alternative leachants offer several environmental and recycling-related benefits, including a high selectivity in terms of dissolving valuable metals, as well as a reduced environmental impact due to the application of non-toxic and biodegradable organic acids. Gluconic acid has previously been demonstrated in the oxidative degradation of glucose, either as an alternative reducing agent or in biometallurgical approaches, and has been described as an efficiency-supporting reagent. The results of this study demonstrate the effectiveness of using gluconic acid for the recovery of metals such as lithium, cobalt, nickel, and manganese from spent lithium-ion batteries. Recovery rates of above 98% for lithium, cobalt, and manganese, and a recovery rate of more than 80% for nickel could be reached by optimizing the leaching parameters, including an acid concentration of 1.2 M, the addition of hydrogen peroxide of 1.6 vol %, a solid-to-liquid ratio of 25 g/L, a leaching temperature of 75 °C, and a leaching time of 192 min. These results show that gluconic acid has the potential to become a viable and sustainable option for the hydrometallurgical recycling of lithium-ion batteries, as well as for opening a possible biohydrometallurgical route. Further investigations are required into the results obtained, to verify the existence of a new hydrometallurgical and sustainable process route involving gluconic acid.

The need to recover critical elements from lithium-ion batteries is undisputed. The further development of cathode materials and the move towards cheaper alternatives make it necessary to adapt the corresponding hydrometallurgical recycling processes. In the best case, however, a process is so flexibly structured and designed that it can be used for a variety of cathode materials with different compositions. The leaching of nickel manganese cobalt oxide with sulfuric acid and a reducing agent has already been demonstrated and optimized in previous research work. Based on these data, an evaluation of the process as well as a parameter study for lithium iron phosphate cathode material, which has recently been used with increasing frequency but has a significantly lower valuable metal content, was carried out within the scope of this publication. By using the synergy effects that occur, an optimized parameter combination for the leaching of the critical element lithium could be found and further critical factors identified.

The need to recover valuable metals from spent lithium-ion batteries (LIBs) is undisputed. However, the environment and the climate are also affected by emissions from the recycling processes. Therefore, the call for environmentally friendly recycling methods is currently louder than ever. In the field of hydrometallurgical recovery of metals from spent LIBs, inorganic acids have so far proved to be an effective, but environmentally problematic, leaching agent, since the pollution of wastewater by high salt loads and the emission of toxic gases cannot be avoided. This has recently led to a trend towards the application of organic acids, as these have significantly more environmentally friendly properties. In order to continue this approach, and to improve it even further from an environmental point of view, this work focuses on the utilization of low leaching temperatures in combination with organic acids for the recovery of valuable metals from spent lithium-ion batteries. This can drastically reduce the required energy demand. Furthermore, attention is paid to higher (50–100 g·L−1) solid-liquid ratios, which are indispensable, especially with regard to the economic establishment of the tested process. The experimental verification of the feasibility using citric, oxalic, and formic acid showed the possibility of an efficient recovery of cobalt, nickel, and lithium. In particular, citric acid in combination with hydrogen peroxide as a reducing agent appears to be a suitable and environmentally friendly alternative to classical inorganic acids, even at low process temperatures, for the hydrometallurgical recycling of lithium-ion batteries.