Leaching of crushed NiMH batteries

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Antti Porvali, Mari Lundström

Rare earth elements (REE) are critical to several key technologies, finding applications in military, green energy technology, batteries, optics, and electronics. As they are hard to directly replace due to their unique chemical properties, their recycling is seen as of increasing importance. For Europe, the problem is the lack of primary production of REEs and the supply risk caused by the fact. Secondary production of REEs is considered as a way to reduce the risks of global supply issues.

Nickel-metal hydride batteries (NiMH) are, after the lithium ion (Li-ion) batteries, the most used batteries in the consumer markets. Specifically, NiMH batteries find applications in domestic applications, power tools and hybrid electric vehicles. NiMH batteries contain hydride forming materials of variety of alloys. The most commonly used NiMH batteries are of type containing AB5 anode electrode materials. The hydride forming metal alloy, AB5, typically contains A = La or A = LaCePrNd and B = NiCoMnAl. NiMH batteries contain, depending on the size of the battery, from one gram to kilograms of REEs. The recycling of NiMH batteries, and especially the recovery of REEs from the battery waste, has been investigated by several researchers. Several processes have been proposed for the recycling of NiMH batteries. Apart from the processes operated by Umicore and Solvay (Rhodia), few have gone forward to be implemented in industrial scale to recycle variable sizes of NiMH batteries. Losing the REEs to slag as nickel is recovered can be considered as unsustainable.

In this paper, the hydrometallurgical treatment of NiMH battery scrap was investigated. Prior to the leaching the scrap was subjected to crushing. The experimental setup consisted of 7 experiments. Sulfuric acid was chosen as the leaching agent. The investigated parameters in leaching were solid to liquid ratio, temperature and acid concentration as these variables are important to the cost of industrial processes.

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