Rare Earth Elements: A Review of Production, Processing ...

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Rare Earth Elements Review Section 5 – Rare Earth Element Recovery/Alternative Material Use Figure 5-2. Left: Dismantling table with pneumatic tools used for manual dismantling of hard disks. Right: Components resulting from the process and including REE-containing magnets (upper right corner) (Schluep et al., 2009). Advances to manual separation methods are being investigated as a way to reduce costs, increase speed, and reduce potential worker exposures. Two examples of successes in this area are the following: � A process developed by Hitachi for disassembling hard disk drives that involves placing the drives in a rotating drum where forces such as shock and vibration are employed. This process is reported to be eight times faster than manual separation and, therefore, more cost-effective (Clengfield et al., 2010). � A process developed by NIMS that includes a small-scale electronic crushing device that, in a few seconds, is able to reduce cell phones and small home appliances to small pieces. This step is followed by placing the pieces in a three-dimensional ball mill that degrades the parts recovered from the crushing device to a powdered form. Because of the short treatment time in the ball mill, the remaining pieces of plastics and other materials remain intact and therefore can be recovered in a condition that allows for plastic recycling. The powder can then be further processed to recover metals of concern (NIMS, 2009). During the dismantling and preprocessing steps, hazardous or other unwanted substances have to be removed and then either stored or treated safely while valuable materials are removed for reuse or recycling. For devices containing ozone-depleting substances, such as refrigerators and air-conditioners, the degassing step is crucial in the preprocessing stage because the refrigerants used (e.g. chlorofluorocarbon or hydrochlorofluorocarbon, in older models) need to be removed carefully to avoid air emissions of ozone-depleting substances, which have a large global warming potential. LCD monitors containing mercury or other toxic metals need to be dismantled with care to ensure worker and environmental protection. Circuit boards present in electronic equipment can contain lead in solder and flame retardants containing resins (Schluep et al., 2009). After removal of the hazardous and other special components, the remainder of the item being recycled can be further separated by manual dismantling or mechanical shredding and (automated) sorting techniques. Some shredding technologies have the potential to generate dust or other particulate matter that can impact worker health. Additionally, all mechanical processing equipment requires energy inputs that have additional associated environmental impacts. 5-6
Rare Earth Elements Review Section 5 – Rare Earth Element Recovery/Alternative Material Use 5.2.3 Processing After completion of the preprocessing steps, the components of interest are ready for the processing step. Processing technologies that are currently used, or are in the research stage, for the recovery of REEs are discussed in several references (Schuler et al, 2011; Ellis et al., 1994; Schluep et al., 2009; ICF International, 2011; Meyer and Bras, 2011) and can be grouped into the following general categories: � Pyrometallurgy processes are energy intensive, using high temperatures to chemically convert feed materials and separate them so that the valuable metals can be recovered. It should be noted that rare earths can oxidize easily in these types of processes, making recovery difficult. While one recycling facility in Japan reportedly is recovering REEs using this type of process (Tabuki, 2010), others companies such as Umicore and Alcoa are conducting research that will enable wider use of this type of technology for REE recycling. During smelting, volatile organic compounds (VOCs) and dioxins could be generated and would need to be managed. � Hydrometallurgy processes use strong acidic or basic solutions to selectively dissolve and then precipitate metals of interest from a preprocessed powder form. The specific process used will vary depending on the metal to be recovered, but options could include solvent extraction, leaching, and selective precipitation, among others. Variations of this type of technology are frequently reported in the literature, and a recent summary is provided by Schuler et al. (2011). The fundamental processes used for recycling REEs are the same as those utilized for raw ore. Accordingly, the waste streams and pollutants of concern are the same as those presented in Section 4. In short, chemical and particulate air emissions, as well as slag material from the smelting process are all potential pollutant sources. � Electrometallurgy processes such as electrowinning (where a current is passed from an inert anode through a liquid leach solution containing the metal; the metal is extracted by an electroplating process, which deposits the rare earths onto the cathode), and electrorefining (where the anode is composed of the recycled material--when the current passes from the anode to the cathode through the acidic electrolyte, the anode corrodes, releasing the rare earth ions into the solution, then electrowinning occurs). No specific information was located on environmental impacts from these processes when they are used to recycle REEs; however, they are expected to be similar to those identified in Section 4 for primary processing operations. � Dry processes (research stage) use hydrogen gas at atmospheric pressure to turn neodymiumcontaining magnets to a powder that can then be re-formed into new magnets under heat and pressure. This research is being conducted at the University of Birmingham in the United Kingdom, and while the newly produced magnets are not of the same quality as the originals, they are suitable for use in motors (Davies, 2011). � Tailings recycling involves reprocessing of existing tailings to recover the remaining amounts of REEs they contain. Recycling of tailings generally will occur at the same location as the mining operation using existing processes and equipment and resulting in the same contaminants as when processing the original ore. As reported by Xiaozhi (2011), the economic benefit, energy savings, and environmental benefits can be significant. � Microbe-filled capsule technology (research stage) has been recently reported in the literature as being developed jointly by Morishita Jintan Co. and Osaka Prefecture University. With this technology, capsules are reportedly placed in a medium containing rare metals, and the microbes then absorb the metals. While the research to date has focused on rare metals (not specifically rare earths), it is thought to be transferable. If this is in fact proven to be true, an official at the Japan Society of Newer Metals has indicated that it could help to make REE recycling more costeffective (Alibaba.com, 2010). � Titanium dioxide process (research stage): While evaluating a process to develop methods for extracting higher yields of titanium dioxide, researchers from the University of Leeds, Faculty of 5-7
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Rare Earth Elements Review Table of
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Foreword The U.S. Environmental Pro
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Abstract Rare earth elements (REEs)
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Table of Contents List of Acronyms
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List of Tables 2-1. Abundance of El
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Rare Earth Elements Review Appendix
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