Rare earth elements (REE) include the lanthanide series elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) plus Sc and Y. Currently these metals have become very critical to several modern technologies ranging from cell phones and televisions to LED light bulbs and wind turbines. This article summarizes the occurrence of these metals in the Earth's crust, their mineralogy, different types of deposits both on land and oceans from the standpoint of the new data with more examples from the Indian subcontinent. In addition to their utility to understand the formation of the major Earth reservoirs, multi-faceted updates on the applications of REE in agriculture and medicine including new emerging ones are presented. Environmental hazards including human health issues due to REE mining and large-scale dumping of e-waste containing significant concentrations of REE are summarized. New strategies for the future supply of REE including recent developments in the extraction of REE from coal fired ash and recycling from e-waste are presented. Recent developments in individual REE separation technologies in both metallurgical and recycling operations have been highlighted. An outline of the analytical methods for their precise and accurate determinations required in all these studies, such as, X-ray fluorescence spectrometry (XRF), laser induced breakdown spectroscopy (LIBS), instrumental neutron activation analysis (INAA), inductively coupled plasma optical emission spectrometry (ICP-OES), glow discharge mass spectrometry (GD-MS), inductively coupled plasma mass spectrometry (including ICP-MS, ICP-TOF-MS, HR-ICP-MS with laser ablation as well as solution nebulization) and other instrumental techniques, in different types of materials are presented.

Rare earth elements:A review of applications, occurrence, exploration, analysis, recycling, and environmental impact

Clean solid biofuel production from high moisture content waste biomass employing hydrothermal treatment.

This Review focuses on whether the emerging industry of deep-seabed mining aligns with the sustainable development agenda. We cover motivations for deep-seabed mining, including to source metals for technology that assists with decarbonization, as well as governance issues surrounding the extraction of minerals. Questions of sustainability and ethics, including environmental, legal, social and rights-based challenges, are considered. Slowing the transition from exploration to exploitation and promoting a circular economy may have regulatory, technological and environmental benefits. This Review covers the sustainability of deep-seabed mining, suggesting a slower transition from exploration to exploitation may be beneficial.

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Challenges to the sustainability of deep-seabed mining

Recovery potential of rare earth elements from mining and industrial residues: A review and cases studies

In recent years, recovery of rare earth elements (REEs) from coal fly ashes (CFAs) has been considered as a promising resource recovery option. Yet, quantitative information on REE speciation in CFAs and its correlation with REE extractability are not well established. This study systematically investigated the REE speciation-extractability relationship in four representative CFA samples by employing multiple analytical and spectroscopic techniques across the micro to bulk scale and in combination with thermodynamic calculations. A range of REE-bearing phases are identified, such as REE oxides, REE phosphates, apatite, zircon, and REE-bearing glass phase. REEs can occur as discrete particles, as particles encapsulated in the glass phase, or distribute throughout the glass phase. Although certain discrepancies exist on the REE speciation quantified by X-ray adsorption spectroscopy and acid leaching due to intrinsic limitations of each method, both approaches show significant fractions of REE oxides, REE phosphates, apatite, and REE-bearing Fe oxides. This study contributes to an in-depth understanding of the REE speciation-distribution-extractability relationship in CFAs and can help identify uncertainties associated with the quantification of REE speciation. It also provides a general methodology for future studies on REE speciation in complex environmental samples and a knowledge basis for the development of effective REE recovery techniques.

Comprehensive Understandings of Rare Earth Element (REE) Speciation in Coal Fly Ashes and Implication for REE Extractability

Potential risks of supply shortages for critical metals including rare-earth elements and yttrium (REY) have spurred great interest in commercial mining of deep-sea mineral resources. Deep-sea mud containing over 5,000 ppm total REY content was discovered in the western North Pacific Ocean near Minamitorishima Island, Japan, in 2013. This REY-rich mud has great potential as a rare-earth metal resource because of the enormous amount available and its advantageous mineralogical features. Here, we estimated the resource amount in REY-rich mud with Geographical Information System software and established a mineral processing procedure to greatly enhance its economic value. The resource amount was estimated to be 1.2 Mt of rare-earth oxide for the most promising area (105 km2 × 0–10 mbsf), which accounts for 62, 47, 32, and 56 years of annual global demand for Y, Eu, Tb, and Dy, respectively. Moreover, using a hydrocyclone separator enabled us to recover selectively biogenic calcium phosphate grains, which have high REY content (up to 22,000 ppm) and constitute the coarser domain in the grain-size distribution. The enormous resource amount and the effectiveness of the mineral processing are strong indicators that this new REY resource could be exploited in the near future.

The tremendous potential of deep-sea mud as a source of rare-earth elements

PROBLEM TO BE SOLVED: To obtain a fuel for cement production from a waste such as a municipal refuse and effectively utilize the fuel while reducing equipment cost and operation cost.SOLUTION: Waste treatment equipment 1 comprises breaking and sorting means 2 which sorting a waste W1 after breaking thereof or sorting the waste while breaking the same, secondary breaking means 3 for further breaking a combustible material W2 which is obtained by the breaking and sorting means and is not suitable for fermentation, and blowing means 79 which blows a broken material (fuel) F3 broken by the secondary breaking means into a cement kiln 75 as a cement fuel. The breaking and sorting means is equipped with: a makeup port 2a; a rotary vane 2c which is mounted to a revolving shaft 2j horizontally disposed in a cylindrical body 2b and breaks the waste introduced into the body through the makeup port; a discharge rotor 2h which is mounted to the revolving shaft and discharges the waste broken by the rotary vane through an exhaust port 2k; and a screening device 2e which is disposed below the rotary vane. The waste W2 discharged through the exhaust port is secondarily broken by the secondary breaking means.

Waste treatment equipment and treatment method

PROBLEM TO BE SOLVED: To provide a method of supplying cement raw fuel by which raw fuel originating in biomass having low bulk density and large water content is granulated to obtain the cement raw fuel and the granulated cement raw fuel is efficiently transported to a cement plant.SOLUTION: The raw fuel originating in the biomass is granulated by a volume reducing container capable of dehydrating the raw fuel originating in the biomass on site and the granulated raw fuel originating in the biomass is transported by a mobile vehicle and the transported raw fuel originating in the biomass is charged into a cement kiln or a boiler as the cement raw fuel.

Method of supplying cement raw fuel

PROBLEM TO BE SOLVED: To provide a treatment method of waste materials containing chlorine with an easy method.SOLUTION: In this waste material treatment method, waste materials containing chlorine is decomposed and desalinated, and then dried under a high temperature. Along with introducing the waste material into a reaction vessel, superheated steam is supplied and exhausted to the reaction vessel, and organic chlorine in the waste materials is thermally decomposed in the reaction vessel. Then the solid materials remaining in the reaction vessel is led to the outside of the reaction vessel as regenerated solid fuel.

Treatment method of waste materials

PROBLEM TO BE SOLVED: To treat the exhaust gas of a chlorine bypass system without using a large amount of water.SOLUTION: An apparatus 1 for treating a cement kiln combustion exhaust gas includes a probe 3 which extracts a part G of combustion exhaust gas while cooling it from a kiln exhaust gas passage ranging from the kiln bottom of a cement kiln 2 to a lowest step cyclone of a preheater, a heat reclaimer 6 which makes extraction gas G2 subjected to heat exchange and temperature decrease, a spray tower 7 which sprays extraction gas G3 with water, allows slaked lime produced from quick lime in extraction gas and water react with SOin the extraction gas, and removes SOin the extraction gas, and a dust collector 8 which recovers dust D2 contained in the exhaust gas G4 of the spray tower. The apparatus may includes a thickener 9 which separates slurry containing the dust recovered by the dust collector into slaked lime slurry S produced from quick lime contained in the dust, gypsum G, and salt water SW, wherein the slaked lime slurry separated by the thickener is sprayed on the extraction gas by the probe in the spray tower.

Ishida Yasuyuki

Papers

The tremendous potential of deep-sea mud as a source of rare-earth elements

Waste treatment equipment and treatment method

Method of supplying cement raw fuel

Treatment method of waste materials

Apparatus and method for treating cement kiln combustion exhaust gas