Acetic acid leaching of neodymium magnets and iron separation by simple oxidative precipitation
Joni Niskanen, Manu Lahtinen, Siiri Perämäki
Abstract
Neodymium-iron-boron (NdFeB) has become the most prominent permanent magnet alloy, with a wide variety of applications and an ever-increasing demand. Their recycling is important for securing the supply of critical raw materials used in their manufacturing. The use of organic acids such as acetic acid has been of recent interest for the recycling of waste NdFeB magnets. Despite achieving good leaching efficiencies, the published literature has not properly investigated the effects of key factors influencing the acetic acid leaching process and their respective interactions, which has led to conflicting findings as to what conditions are optimal. The present work goes to show that no such optimum exists by taking a look at the major factors (concentration, solid-to-liquid ratio, time, and temperature) and their interactions. The results show that leaching efficiencies >95% and even up to 100% can be achieved using a variety of different conditions showing that the leaching reaction is quite flexible, which is helpful for a potential upscaling of the process. The separation of the leached elements presents another problem in NdFeB magnet processing. As a novel application, this work investigated iron separation from the acetic acid leachate by the means of simple and inexpensive aeration. It was found that up to 99% of iron could be precipitated as FeO(OH) (goethite) within 2 h at pH 5 and 80 °C, while only minor neodymium co-precipitation was observed (5%). Separation of iron from the leachate can help obtain purer REE products in further processing.