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<p>Valorizing solid leach residues rich in critical metals, as the rare earth elements (REEs), while reducing reactant and water consumption, is a major challenge in hydrometallurgical processing. In the case of spent nickel–metal hydride (NiMH) battery processing, the most direct way to recover light REEs (La, Ce, Nd, Pr) from the pregnant leach solution (PLS) is by selective precipitation of REE sodium double sulfate salts (REE-DSS), NaREE(SO<sub>4</sub>)<sub>2</sub>.H<sub>2</sub>O. These salts then have to be post-treated to remove the elements Na and S. In primary REEs production processes, the main option is to convert REE-DSS to hydroxides. However, for NiMH batteries, the presence in the PLS of other metals, particularly nickel (~ 46&#xa0;g/L), and potassium, raises the question of alternative routes for REE-DSS conversion to avoid the co-precipitation of these elements. In this work, a thermodynamic and experimental study was carried out on industrially prepared NiMH leachates to compare the conversion of REE-DSS into hydroxides, carbonates, or oxalates, focusing for the precipitation reactions on the yields, kinetics, selectivity, and water consumption. While the high yields and fast kinetics are similar for all three routes, it appears that precipitation as REE oxalate (REE<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>.10H<sub>2</sub>O) avoids co-precipitation of nickel, thus reducing by a factor of 5 the amount of water required during the initial washing of the REE-DSS to remove the impurities. However, REE oxalate salts are limited in further aqueous processing compared to hydroxide and carbonate salts because of their poor solubility, while they are suitable to thermal decomposition ways.</p> Graphical Abstract <p></p>

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Conversion of Sodium-Rare Earth Double Sulfate Salts Prepared from Spent NiMH Batteries: Comparison of Precipitation Pathways as Oxalate, Hydroxide, and Carbonate

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年7月7日

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  • C. Laskar,
  • B. Guzhov,
  • A. Barnabé,
  • M. Josse,
  • B. Biscans,
  • L. Cassayre

摘要

Valorizing solid leach residues rich in critical metals, as the rare earth elements (REEs), while reducing reactant and water consumption, is a major challenge in hydrometallurgical processing. In the case of spent nickel–metal hydride (NiMH) battery processing, the most direct way to recover light REEs (La, Ce, Nd, Pr) from the pregnant leach solution (PLS) is by selective precipitation of REE sodium double sulfate salts (REE-DSS), NaREE(SO4)2.H2O. These salts then have to be post-treated to remove the elements Na and S. In primary REEs production processes, the main option is to convert REE-DSS to hydroxides. However, for NiMH batteries, the presence in the PLS of other metals, particularly nickel (~ 46 g/L), and potassium, raises the question of alternative routes for REE-DSS conversion to avoid the co-precipitation of these elements. In this work, a thermodynamic and experimental study was carried out on industrially prepared NiMH leachates to compare the conversion of REE-DSS into hydroxides, carbonates, or oxalates, focusing for the precipitation reactions on the yields, kinetics, selectivity, and water consumption. While the high yields and fast kinetics are similar for all three routes, it appears that precipitation as REE oxalate (REE2(C2O4)3.10H2O) avoids co-precipitation of nickel, thus reducing by a factor of 5 the amount of water required during the initial washing of the REE-DSS to remove the impurities. However, REE oxalate salts are limited in further aqueous processing compared to hydroxide and carbonate salts because of their poor solubility, while they are suitable to thermal decomposition ways.

Graphical Abstract