Complexities of Hydrometallurgical Recycling of Spent NiMH and Li-ion Batteries

Nickel metal hydride (NiMH) and lithium ion (Li-ion) batteries are the keystone for many devices in our everyday lives. Their unique chemistry, the very thing that enables them to function as batteries, makes their recycling a complex metallurgical challenge. Improving the understandingof chemical behavior of spent batteries in metallurgical recycling is at the core of this thesis. In this thesis, the recycling, or metallurgical processing, of these two battery types was investigated. Particular emphasis was placed on observing the phenomena associated with the leaching of industrially processed spent batteries. In the case of Li-ion batteries, the resultsobtained from treating industrially processed spent batteries was contrasted to more controlled conditions where synthetic active cathode materials, along with synthetic impurities, were dissolved and studied. Leaching-related chemistry was investigated with both battery types inH2SO4. HCl was briefly investigated with Li-ion batteries. Data was obtained on Fe catalyzed leaching of LiCoO2 in the presence of Cu. The choice of impurities was based on understanding of the composition of spent batteries and industrially processed spent battery scrap. It was shown that under synthetic conditions, dissolved Fe catalyzes the dissolution of Cu and LiCoO2, resulting in extraction rates ranging between 95% - 100% under relatively mild (T = 30 °C, [H2SO4] = 2 M, no H2O2) leaching conditions. In the case of NiMH batteries, the treatment of REEs found in these batteries was investigated by the means of experimentation and process modeling. Their precipitation and removal from the leachate were achieved with the traditional double salt precipitation. Mixed-element crystals were observed in the charcaterization, containing both Na and K in the lattice along with REEs. Their further processing was investigated by NaOH conversion and in-situ Ce oxidation. Ce oxidation degree of 93% was achieved, however limited conversion was observed which was hypothesized of being due to formation of hydroxysulfates resulting from the dissociation of the double salt. Process sidestreams resulting from the REE processing were investigated by the methods of modelling (HSC Chemistry), metamodeling (Regression), and laboratory experiments in order to help understand the relation of process parameters to observed process behaviour. As an overarching theme of the dissertation, the compendium contains suggestions related to methodology through which the spent batteries could be studied more effectively in the future: for instance, thorough the characterization and flexible combinatorial use in research of simulated conditions, manually opened spent batteries, and industrial spent battery streams would be desirable. Forming a comprehensive understanding of the leaching behavior in industrial wastes requires several approaches. The use of flowsheet modeling and a combination of synthetic and industrial material experiments have been shown to be beneficial tools in understanding the planned process system as a whole.