Rare-Earth Metal Recovery for Green Technologies

Rare earths (REs) play an important and key role in human lives in the twenty-first century; REs have numerous applications in the high-tech industry (electrical or electronic fields). Hydrometallurgy, the aqueous processing of metal ion tool, is the cheapest and most convenient for RE recovery from primary resources (ores and minerals) and secondary resources (industrial wastes and scraps). South Korea has many high-tech industries in the fields of electrical and electronic item manufacturing, as well as supply to global needs. At the same time, this country has two major problems; one is the landfilling problem (generated manufacturing waste and after usage scraps), and the other is natural resources. And another major concern is the population densities. Sustainability leads the society in developing stages. It mainly is subject to society, environment, and economy. East Asian countries such as Korea have very limited natural resources of rare earths (REs); at the same time, Korea manufactures and supplies the electrical and electronic goods for global needs. The recycling subject concern is waste minimization, as well as environmental protection and economic incentives, energy considerations, and industrial ecology.

Demand for rare earth metals is increasing day by day in various high-tech applications such as super magnets, fluid cracking catalysts, nickel-metal-hydride (NiMH) batteries, and ordinance industries as well as in some defense applications. The rare earth metals are extracted from different REE-bearing minerals that occur in carbonatites, pegmatites, and placer deposits. About 95% of the world’s rare earth production comes from bastnaesite, monazite, and xenotime minerals. In many instances, rare earth minerals are found in association with various gangue minerals. The recovery of rare earth values from the lean-grade ores requires several stages of mineral beneficiation and hydrometallurgical unit operations. The mineral beneficiation techniques such as gravity concentration, magnetic separation, electrostatic separation, and flotation were employed for the recovery of rare earth minerals. The present chapter highlights the world distribution of rare earth deposits, occurrences, processing methodologies, and plant practices of few economic minerals.

Rare earth metals are one of the essential constituents of today’s evolving green technology materials. They are used in electric car, high-performance magnet-based miniaturized devices, wind mill turbines, advanced sensors and machinery used in space and nuclear energy sector, military navigation devices, communications, information and transportation systems, and many more. This book chapter discusses the basics of thermodynamic aspects for the extraction of rare earth metals from its oxides/minerals. Thermodynamic parameters for the feasibility of chemical reactions happening in the system under consideration using Gibbs free energy minimization tools. Thermodynamic steps involved in the processing of rare earth oxides/fluorides to produce rare earth metals by metallothermic reduction route are also studied.

The rare earth metals are high-tech elements of the periodic table and have extensive demand for their utilization on making high-end materials. Solvent extraction (SX) and supported liquid membrane (SLM) technology are key approaches in hydrometallurgical operation for effective extraction of rare earth metal(s) from numerous complex aqueous solutions. The major challenge and/or issue encountered is process selectivity especially on the separation of either of the rare earth metal(s) in the presence of others. The similar chemical property of the elements of lanthanides as well as actinides prevents effective and selective separation of individual rare earths, though high separation factor has been attained, while employing novel organic reagents through above techniques. Both in SX and SLM process, the extractant plays a vital role on achieving clean and effective separation of each of the RE metals. The most common reagents such as commercial organophosphorus reagents and oxidic reagents in general are applied for extraction of REEs; however, the noble green solvent like ionic liquids (ILs) appears to be more promising in these days. The basic principle, extraction chemistry, separation behaviour, loading ability of extractants and extraction isotherm (both in extraction and stripping) are discussed to ascertain the transportation behaviour of RE metals from one to other phase (aqueous to organic and vice versa). This book chapter is an attempt to give the insight about the adoption of SX and SLM methodologies in day by day progress in metallurgical extraction processes especially on separation of rare earth metals including lanthanides, actinides and other light rare earth metals (Scandium and Yttrium).

Due to the variety of applications of precious metals, platinum group metals (PGMs), the separation and recovery of PGMs are excellently worthy. In general, the restoration of these PGMs is associated with their high cost and other environmental impacts. In this chapter, the basic principles of adsorption-included adsorbent, adsorbate and isotherms, and kinetics and the factors that influenced adsorption process are briefly reviewed. Finally, a brief discussion is given on the adsorptive removal of precious metals such as Pd, Pt, Au, and Ag, by using low-cost adsorbents through adsorption phenomena. It also includes the strategies involved in the adsorptive extraction of rare earth elements (REEs). This chapter mainly looks at a perspective based on the applicability of certain low-cost magnetic-based metal oxides and biosorbents employed for the adsorptive removal of PGMs and REEs from aqueous solution, spent catalysts, and industrial wastes along with necessary information of adsorption process.

At present days the secondary solid wastes including e-wastes, catalyst waste, magnet waste, and scrap alloys have become important sources owing to claiming of a considerable amount of REE metals. Moreover, the global demand of the REE metals in recent days is extremely high for their extensive usages on making high-end materials. This certainly lured metallurgists for developing suitable processing technology for efficient and definite recovery of the REE metal values from the above sources as the existence of rare earth metals bearing minerals is limited. Various pyrometallurgical and hydrometallurgical approaches as well as the combination of both approaches have been adopted by different groups of researchers for effective recovery of REEs. The pyro-processing approach has a number of disadvantages and hence hydrometallurgical process accomplishing leaching-solvent extraction-precipitation route is being comprehensively adopted in most of the rare earth metallurgy. The adaptation of microwave (MW) assistance and ultrasound wave (UW) is becoming significant in chemical leaching processes. However in solvent extraction process in addition to the usage of commercial reagents, ionic liquids (ILs) have been reported to be very high process selective and promising. In terms of shortcomings, this chapter gives a detailed information about the sources of generation of each of these secondary solid wastes, issues and challenges, extraction strategies, prospective of hydrometallurgy, leaching process, assistance of MW and US and leaching mechanism, liquid-liquid extraction for separation of REE using commercial and noble IL reagents, SX mechanism study, and recovery of the REE metals through precipitation method.

The use of rare-earth element-based nanomaterials plays an essential role in biomedical applications due to their luminescent (upconversion, downconversion, and permanent luminescence), magnetic properties, and absorption ability of X-rays. Rare-earth elements have been widely used for the fabrication of nanomaterials that are shown attractive properties including absence of blinking, high photostability, large Stokes shifts, extremely narrow emission lines, and long lifetimes, respectively. This book chapter explores the recent applications of rare-earth element-based nanomaterials for the detection of various biomolecules in various biofluids.

In recent years, rare earth (RE)-based permanent magnets (PMs) have become a one of most valuable material due to its massive usage in many advanced green technological applications which include electric vehicles (bikes, cars, etc.), wind turbines, and many consumer goods (iPods, hard disc, speakers, etc.). Nd-Fe-B magnets have higher energy product [(BH)_max] among all RE-based PMs. Moreover, magnetic properties of Nd-Fe-B particles are key for high-performance Nd-Fe-B magnets and are estimated from phase purity, crystallinity, and structure which can be well controlled from fabrication process of Nd-Fe-B powders. Among the various processing techniques the spray drying-assisted reduction-diffusion (R-D) is favored to produce Nd-Fe-B powders with improved properties in larger yield. Optimization of R-D and washing process is essential to obtain the good magnetic properties. Optimization of these steps results in Nd-Fe-B powders with enhanced magnetic properties: Hc about 5.1 kOe and (BH)_max of 22.1 MGOe. The higher properties are attributed to the formation of single phase with high purity, good size distribution of particles, minor defects in the structure, and complete removal of by-products during the washing step. Therefore, the progresses in fabrication techniques and some important steps are discussed in this chapter.