Are clay-based materials promising tools in CRM recovery?

Due to the growth of global population, digitalisation, and the number of innovative technologies, OECD forecasted that global materials demand will roughly increase in the next decades, leading to a high dependence on them. In 2023 the list of critical raw materials candidates increased up to 70 candidates. In this perspective electric and electronic waste (WEEE) represents an enormous resource due to their wide metal composition. WEEE can be treated in different ways to recover the critical raw materials in it contained: from pyrometallurgical to hydrometallurgical plants. Of great relevance is the adsorption step used as separation technique into hydrometallurgical plants after a leaching step. One of the key points of this step is the exploitation of solid sorbent materials thanks to their possible selectivity, large surface area (porosity), chemical stability, and potential reusability. Clays are natural materials which can be suggested as green alternative. The target of this work is to recover valuable materials that can be found in WEEE components, such as disposed NdFeB magnets of hard disks. It has been exploited the composition of a real leached solution, and the adsorption capability behaviour of Ca-rich clays in both Nd-simulated and real solutions. A nitric acid solution has been used as leaching agent in which the magnets have been dissolved. After the leaching step, the most important metal composition found by ICP-OES analysis is Nd of 8.2% (w/w), and of Fe of 88.6%(w/w) among a wide variety of metals. Simulated mono-ionic Neodymium solutions have been obtained by dissolution of Nd nitrate into deionized water. The adsorption occurred in solid/liquid ratio of 0.04 g/mL, under vigorous stirring, for 90 minutes of time at room temperature. Also release experiments have been carried out in both simulated and real leached solution. Both the uptake and release experiments of Neodymium show some interesting results regarding the different behaviour of the clay in simulated mono-ionic solutions and real complex matrixes. This preliminary work is of upmost importance for the possible industrial application of valuable materials recovery by means of natural and recoverable materials such as clays.