Characterization and Mechanical Treatment of Spent Nickel Metal Hydride Batteries

Abstract

The present master’s thesis has been realized in Agen (Lot-et-Garonne, France) inside the research and development department of Fonroche Lighting, company specialized in solar lighting. Indeed, the company offers a lighting street with a solar panel, a nickel-metal hydride battery and a lighting lantern. In order to integrate the circularity of their product, Fonroche Lighting aims to recycle these batteries that contain valuable materials. This study is then composed of a state of the art including historic and development of the batteries, composition and chemical reactions involved in the functional system of nickel-metal hydride batteries, a contextualization about scarcity and depletion of raw materials that European Union and the world have to face, and bibliography about recycling of the nickel-metal hydride batteries focusing in majority on recovery of metals by mechanical treatments. A study of the product to be recycled has been realized including manual dismantling in order to identify the different components followed by a characterization of the electrodes by elemental analyses. This characterization permitted to know in what the batteries are made of, and which metals should be targeted for recovery during the recycling process. After that, milling tests were performed on batteries and the outputs have been size classified by sieving. In order to concentrate as much as possible the metals in the sieved outputs obtained, magnetic separations have been made for each size fractions, and three others outputs recovered for each of them. These outputs were then analyzed by elemental analyses to know their content in elements and see in which fractions they are concentrated. To go further in the recycling process and metals recovery, two leaching tests have been realized to confirm the potential and the possible perspectives of recovery of these metals by hydrometallurgy route and start a prelude of what could be a research and creation of a recycling process using this technology. Finally to finish this study, a business case and an economic study are proposed in order to estimate the viability of the recycling project for nickel-metal hydride batteries by the company.