• Resources Recycling
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• v.28 no.6
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• pp.18-25
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• 2019

In order to recover the cerium contained in the spent nickel metal hydride batteries (NiMH battery), the recovered rare earth complex precipitates from NIMH were converted into rare earth hydroxides through ion exchange reaction to react with NaOH aqueous solution at a reaction temperature of 70 ℃, for 4 hours. Rare earth hydroxides were oxidized by injecting air at 80 ℃ for 4 hours to oxidize Ce³⁺ to Ce⁴⁺. The oxidation rate of cerium was confirmed to be about 25 % through XPS, and the oxidized powder was separated from the rest of the rare earth using the difference in solubility in dilute sulfuric acid. The finally recovered powder has a crystal phase of cerium hydroxide (Ce(OH)₄). The cerium purity of the final product was about 94.6 %, and the recovery rate was 97.3 %.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.2
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• pp.85-90
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• 2018

For the recovering rare earths in the spent nickel-metal hydride batteries, 10 M NaOH is added to the solution leached with sulfuric acid. The rare earth powders were precipitated at rate of 98 % at the condition of pH 2.0 or less. The recovered rare earth complex precipitate increased the leaching rate to nitric acid by heat treatment at $800^{\circ}C$ for 4 hours. Subsequently secondary precipitation was performed by adding oxalic acid to the solution in which the rare earth complex precipitate was dissolved. The re-precipitated rare earth powders were converted into oxide form through heat treatment at $800^{\circ}C$ for 4 hours with purity of 99.5 %.