Abstract
This manuscript investigates an improvised gasification process for capturing and recycling rare earth metals (REMs) from consumer and industrial electronic wastes, often termed “e-waste”. The proposed procedure is based on the formation of coalesced and aggregated metal nodules on biochar surfaces through the gasification of e-waste mixed with gasifier feedstocks. A preliminary understanding of metal nodule formation based on different atmospheric conditions (inert, oxidizing, and oxidizing followed by reducing atmospheres) was examined in both pilot-scale gasifier and tube furnace experiments using iron powder mixed with corn. Iron powder is representative of the REM in the e-waste. Metal nodule sizes, morphology, and composition are analyzed and compared via scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray fluorescence spectroscopy (XRF) techniques. We conclude that sintering is the key mechanism responsible for metal nodule growth through metal particle coalescence and aggregation by migration and diffusion of metal particles on biochar surfaces at elevated temperatures. Oxidizing atmosphere followed by a reducing atmosphere facilitates larger metal nodule growth compared to only an inert or oxidizing atmosphere. Additionally, the effect of adding NaCl salt is investigated on lowering the metal nodules’ surface energy and enhancing both metal particle and metal nodule agglomeration characteristics. Salt addition facilitates spherical metal nodule formation without any significant effect on the nodule composition and localized formation of nodules.