Shoshan T. Abrahami

Rare-earth elements recovery from post-consumer hard-disc drives

Abstract The recovery of neodymium from post-consumer products is gaining significant interest. To study the recycling feasibility of neodymium in end-of-life (EOL) computer hard disc drives (HDDs), NdFeB magnets were collected using a steel grate during commercial shredding, followed by thermal demagnetisation, grinding and screening to yield an upgraded scrap. Two metallurgical extraction routes were investigated. The first is a high temperature molten slag extraction followed by H2SO4 leaching at room temperature. Both CaO–SiO2–Al2O3 and CaO–CaF2 slag systems were tested with more than 99% rare earths recovery, but with incomplete leaching. In the second route, the upgraded scrap was directly leached to dissolve 97% rare earth content. In both cases, 98% of the rare earths in the leach solution were subsequently converted into a high purity (98·4%) rare earths double salt (NaNd(SO4)2·H2O) that can be converted to either RF3 or R2O3, the two common raw materials in the production of rare earth metals.

Interface strength and degradation of adhesively bonded porous aluminum oxides

For more than six decades, chromic acid anodizing has been the main step in the surface treatment of aluminum for adhesively bonded aircraft structures. Soon this process, known for producing a readily adherent oxide with an excellent corrosion resistance, will be banned by strict international environmental and health regulations. Replacing this traditional process in a high-demanding and high-risk industry such as aircraft construction requires an in-depth understanding of the underlying adhesion and degradation mechanisms at the oxide/resin interface resulting from alternative processes. The relationship between the anodizing conditions in sulfuric and mixtures of sulfuric and phosphoric acid electrolytes and the formation and durability of bonding under various environmental conditions was investigated. Scanning electron microscopy was used to characterize the oxide features. Selected specimens were studied with transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy to measure resin concentration within structurally different porous anodic oxide layers as a function of depth. Results show that there are two critical morphological aspects for strong and durable bonding. First, a minimum pore size is pivotal for the formation of a stable interface, as reflected by the initial peel strengths. Second, the increased surface roughness of the oxide/resin interface caused by extended chemical dissolution at higher temperature and higher phosphoric acid concentration is crucial to assure bond durability under water ingress. There is, however, an upper limit to the beneficial amount of anodic dissolution above which bonds are prone for corrosive degradation. Morphology is, however, not the only prerequisite for good bonding and bond performance also depends on the oxides’ chemical composition.Surface coating: interface strength and degradationChromic acid anodizing has been the dominant electrochemical process used to create a thin aluminum oxide layer upon aluminum alloys. Such thin layers are critical to the corrosion protection of alloys that enable many of our daily expectations, including aerospace applications. However, such a chromic acid treatment is being forced to be soon phased out as a result of the associated environmental and health concerns. Now a team led by Arjan Mol from Delft University of Technology in the Netherlands, with co-workers from Denmark and Belgium, are working on alternative treatment processes and reveal the fundamental adhesion and degradation mechanism at the interface between the surface oxide and an accompanying resin. Aided by both imaging and spectroscopic characterization, this study provides fresh insights into the interplay between the anodizing conditions and the formation and durability of bond strength, showing that the morphology and chemistry of the surface oxide are the two factors that should be considered in the selection of chromium-free surface treatments.

Towards Cr(VI)-free anodization of aluminum alloys for aerospace adhesive bonding applications: A review

For more than six decades, chromic acid anodizing (CAA) has been the central process in the surface pre-treatment of aluminum for adhesively bonded aircraft structures. Unfortunately, this electrolyte contains hexavalent chromium (Cr(VI)), a compound known for its toxicity and carcinogenic properties. To comply with the new strict international regulations, the Cr(VI)-era will soon have to come to an end. Anodizing aluminum in acid electrolytes produces a self-ordered porous oxide layer. Although different acids can be used to create this type of structure, the excellent adhesion and corrosion resistance that is currently achieved by the complete Cr(VI)-based process is not easily matched. This paper provides a critical overview and appraisal of proposed alternatives to CAA, including combinations of multiple anodizing steps, preand post anodizing treatments. The work is presented in terms of the modifications to the oxide properties, such as morphological features (e.g., pore size, barrier layer thickness) and surface chemistry, in order to evaluate the link between fundamental principles of adhesion and bond performance.

Adhesive Bonding and Corrosion Performance Investigated as a Function of Aluminum Oxide Chemistry and Adhesives

The long-term strength and durability of an adhesive bond is dependent on the stability of the oxide-adhesive interface. As such, changes in the chemistry of the oxide and/or the adhesive are expected to modify the interfacial properties and affect the joint performance in practice. The upcoming transition to Cr(VI)-free surface pretreatments makes it crucial to evaluate how the incorporation of electrolyte-derived sulfate and phosphate anions from, respectively, phosphoric acid anodizing and sulfuric acid anodizing affect the interfacial chemical properties. Hence, different types of featureless aluminum oxides with well-defined surface chemistries were prepared in this study. The relative amounts of O2−, OH−, , and surface species were quantified using x-ray photoelectron spectroscopy. Next, bonding with two types of commercial aerospace adhesive films was assessed by peel and bondline corrosion tests. The presented results indicate that the durability of the oxide-adhesive interface depends on the inte...

Recovery of REEs from End-of-Life Permanent Magnet Scrap Generated in WEEE Recycling Plants

NdFeB permanent magnets are the best available magnets used in many technology applications. However, at their end-of-life (EoL) most of magnets and the contained REEs are lost during the recycling of the bulk metals. The REEs are classified as the most critical raw materials in the European Union, and recycling of REEs from EoL products will reduce their criticality and contribute to the sustainability of REE. Various technological routes have been reported, but most of the methods are effective for highly concentrated magnets or magnet scrap, which is greatly dependent on expensive pre-dismantling processes. This paper presents various innovative metallurgical solutions to the effective REE recovery from current industrial practice for WEEE recycling, including the ferrous scrap from WEEE shredder products and shredder residues from computer hard disk drives. Both hydrometallurgical and combined hydro- and pyrometallurgical REE recovery routes are developed after demagnetization and physical upgrading.