Noelia Muñoz García

This review presents the advances regarding the recovery and purification of zinc (Zn) and manganese (Mn) from alkaline batteries via hydrometallurgical processes. The characteristics of alkaline batteries are defined, and a comparison among leaching processes of spent batteries is presented, including the reactions that take place during the leaching process and the most influential operating parameters. Hydrometallurgical processes for recycling batteries arise as an advantageous alternative for spent batteries management. Data reported from the literature shows that alkaline and complexation‐assisted leaching are more focused on the selective extraction of Zn. To attain a high Mn dissolution, an acid‐reductive leaching is necessary, but this technique is not selective and simultaneously dissolves both Mn and Zn. To finish, metal separation and purification processes to recover high‐quality metals from the leachates are discussed. Precipitation, solvent extraction, ion exchange resins, and electrodeposition are the main operations presented in this work. It has been proven that more than one separation or purification techniques are required to obtain the separation of these metals with high purity.

Recycling the metals found in spent batteries offers both environmental and economic benefits, especially when extracted and purified using environmentally friendly processes. Two basic leaching agents were tested and compared: ammonium hydroxide (NH₄OH) and sodium hydroxide (NaOH). Using NH₄OH 4 M at 25 °C, 30.5 ± 0.7 wt. % of zinc (Zn) was dissolved for a solid/liquid (S/L) ratio of 1/10 (g of black mass (BM)/mL of solution); meanwhile, with NaOH 6 M at 70 °C, and an S/L ratio of 1/5 (g of BM/mL of solution), 69.9 ± 2.8 wt. % of the Zn initially present in the BM of alkaline batteries was leached. A virtual representation of the experimental data through digital twins of the alkaline leaching process of the BM was proposed. For this purpose, 90% of the experimental data were used for training a supervised learning procedure involving 600 different artificial neural networks (ANNs) and using up to 12 activation functions. The application was able to choose the most suitable ANN using an ANOVA analysis. After the training step, the network was tested by predicting the outputs of inputs that were not used in the training process, to avoid overfitting in a validating process with 10% of the data. The best model was employed for estimating the degree of leaching of different metals that can be obtained from BM, obtaining a data deviation of less than 10% for highly concentrated compounds such as Zn.

BACKGROUND: Batteries play a vital role in meeting global energy needs. When their life cycle concludes, improperly discarded spent batteries can pose environmental risks primarily due to their metal content. In this sense, the recycling of metals contained in spent batteries could mean a huge advantage if they are extracted and purified using environmentally friendly processes.RESULTS: In this study, the recovery of potassium (K), zinc (Zn) and manganese (Mn) from alkaline batteries was performed using a hydrometallurgical process consisting of neutral, acid and acid reductive leaching steps at room temperature and atmospheric pressure to extract K, Zn and Mn. In the neutral leaching step, 76.8 ± 3.4 (wt. %) of the K present in the spent batteries was extracted. Thus, in the acid leaching step, 90.9 ± 0.1 (wt. %) of the initial Zn and 36.7 ± 0.4 (wt. %) of the initial Mn was extracted using sulfuric acid (H₂SO₄) 2 M. In a subsequent acid reductive leaching step using H₂SO₄ 2 M and oxygen peroxide (H₂O₂) 0.8 M as reducing agent, 8.7 ± 0.1 (wt. %) of the initial Zn and up to 49.4 ± 0.2 (wt. %) of the initial Mn were extracted.CONCLUSION: The three‐unit process led to an overall extraction of 99.6 ± 0.3 (wt. %) of Zn and 86.1 ± 0.1 (wt. %) of Mn. Regarding the latter step, the extraction was not 100% because Mn complexes which are nearly insoluble were generated. This shows that extraction of valuable minerals from industrial residues is possible by hydrometallurgical processes. © 2024 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).