Abstract
In this research, the recycling of industrially collected and crushed nickel metal hydride battery waste, rich in valuable metals such as Ni and rare earth elements (REE), was investigated. The crushed waste was characterized based on elemental distribution per particle size class and density. Although issues with sieving, such as agglomeration of shredded separator fibers, were observed, a good separation of Fe and plastics could be achieved by using a 1-mm sieve size. It was observed that, as the waste battery particles were washed with water, some organic compounds were dissolved. Acid consumption of 14 mol H+ ions per 1 kg of battery sample (sieve fraction—1 mm) was determined to be sufficient to achieve the desired final pH of < 1. Selectivity of the leaching at higher equilibrium pH was also investigated by using dilute H2SO4. Pregnant leach solution rich in Ni (46 g/L) and REEs (La: 9 g/L, Ce: 7.5 g/L, Pr: 1.4 g/L, Sm: 0.29 g/L, Y: 0.17 g/L) was obtained and REE precipitation was investigated as a function of dilute Na2SO4 solution concentration (0.01–0.5 M) at a temperature of 50 °C. The best precipitation efficiency was achieved with a Na:REE ratio of 9.1, which resulted in a > 99% precipitation efficiency for the REEs.
Highlights
Nickel metal hydride (NiMH) batteries are a battery class that has recently been overtaken by lithium-ion batteries (LIBs), these types of batteries still find extensive use in certain applications like hybrid electrical vehicles (HEV), consumer electronics, and tools [1, 2]
The findings detailed here show that if the washing of the NiMH waste raw material is undertaken prior to direct NiMH battery waste leaching, several aspects need to be taken into account: (i) the washing step results in a basic washing water rich in Na (500–1000 mg/L) and K (1500–4000 mg/L) and a variety of other elements, which would need a separate unit process for water purification to be considered
NiMH batteries were obtained from an industrial operator in a crushed state
Summary
Nickel metal hydride (NiMH) batteries are a battery class that has recently been overtaken by lithium-ion batteries (LIBs), these types of batteries still find extensive use in certain applications like hybrid electrical vehicles (HEV), consumer electronics, and tools [1, 2]. The crushing process ensures that complete oxidation of the battery waste does not occur, a claim which is supported by a previous study that detected gas evolution during the sulfuric acid leaching of NiMH waste [19] as a result of H+ ion reduction during the oxidation of the metal alloys Taken together, these observations suggest that La2O3 and La(OH) are most likely present only in small quantities as thin passivation layers. The findings detailed here show that if the washing of the NiMH waste raw material is undertaken prior to direct NiMH battery waste leaching, several aspects need to be taken into account: (i) the washing step results in a basic washing water rich in Na (500–1000 mg/L) and K (1500–4000 mg/L) and a variety of other elements, which would need a separate unit process for water purification to be considered Were it not for the unknown exact composition of the precipitating mass, the wash water itself could potentially be used as a precipitating agent in REE double sulfate precipitation. The PLS and REE double sulfates produced here can be further treated such that it can be accommodated into current state-of-the-art industrial processes [30, 31]
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