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

金沢大学理工研究域地球社会基盤学系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. © 2018 The Author(s)

Trends in Extraction of Rare Earth Elements from Coal Ashes: A Review

The demand for novel, cost-effective, and environmentally friendly rare earth element and yttrium (REY) sources is essential. The recovery of REY and other valuable components from coal fly ash (CFA) may result in securing alternative resources, decreased disposal costs, and environmental protection, all of which may have positive effects. However, research on the recovery of REY from CFA is underway, and it is still necessary to assess its viability from an economic and environmental standpoint. The authors have reviewed some of the most recent advances in extracting rare earth elements from CFA. However, most techniques reported for the treatment of CFA are still at the laboratory scale. Nevertheless, there are several pathways for industrial-scale applications. Therefore, CFA treatment and the extraction of valuable products from it have considerable potential for reducing both its carbon footprint and environmental burden

Two-Liquid Flotation for Separating Mixtures of Ultra-Fine Rare Earth Fluorescent Powders for Material Recycling—A Review

This paper reviews two separation methods applying two-step two-liquid flotation for recovering ultra-fine rare earth fluorescent powders (i.e., red, green, and blue). The paper aims to extract the science behind separation by two-liquid flotation, and to provide resulting engineering tips for material recycling. Two-liquid flotation, also called liquid-liquid extraction, involves two solvents (i.e., non-polar and polar solvents) to capture hydrophobic/hydrophobized particles at their interface, and a surfactant to selectively modify the surface property of the target powder(s). For separating a three powder mixture, two different developed flowsheets, composed of two-step separation are discussed. The major difference found was the polar solvents used. The first flowsheet (called the aqueous-organic system) employed water as a polar solvent while the second flowsheet (called the organic-organic system) utilized N,N-dimethylformamide, DMF as a polar solvent. The organic-organic system at the optimized conditions achieved both the grade and recovery of all the separated fluorescent powders at greater than 90% while the aqueous-organic system did not satisfy these criteria. This paper also reviews the mechanism behind the separation, as well as performing a cost comparison between the two methods. The cost comparison indicates that the organic-organic system is a more cost effective method for recovering rare earth fluorescent powders than the aqueous-organic system. Since the size of powders (i.e., several µm) is too small for the application of conventional separation technologies (e.g., froth flotation), two-liquid flotation is a unique pathway for the material recycling of ultra-fine rare earth fluorescent powders

Particle size measurement of TiO2 nanoparticles in non-aqueous solvent by interactive force apparatus under and electric field

This paper describes the measurement of particle size distribution of TiO2 nano-particles in non-aquesous solvent by interactive force apparatus (IFA) under electric field in order to suggest the application of the apparatus to the measurement of particle size distribution. The results were compared with results obtained from size measurement by SEM. The results show that the distribution measured by IFA at 0.03 and 0.06 V was larger (D 50 = 430 - 480 nm) and at 0.12 - 0.48 V was smaller (D50 = 200 - 270 nm) than the one measured by SEM (D50 = 340 nm). The difference is mainly because small size fraction increased with increasing supply voltage. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The electric breakdown was explained by curve fitting of two different particle size distribution functions with particle size distribution functions with particle size distribution obtained from IFA measurement.

Measurement of particle size distribution of silica nanoparticles by interactive force apparatus under an electric field

This paper describes the measurement of particle size distribution of silica nanoparticles by interactive force apparatus (IFA) under an electric field in order to suggest the application of the apparatus to the measurement of particle size distribution. The results were compared with results obtained from size measurement by dynamic light scattering. D50 measured by IFA was closer to the average particle size determined by TEM (5 nm). Also, when compared the results under three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The distribution measured by IFA (D50 = 5–7 nm) was larger than the one measured by DLS (D50 = 1 nm). The electric breakdown was explained by curve fitting of three different particle size distribution functions with particle size distribution obtained from IFA measurement. Crown Copyright 2010 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan.

Assessing Different Treatment Options for Plastic Wastes from Discarded Television Sets in the Context of LCA

In the present work, the energy recovery and the mechanical recycling, i.e. two treatment options for plastic wastes from the discarded TV sets have been assessed and compared in the context of the life cycle assessment methodology (LCA). The environmental impact of each option was assessed by calculating the following impact indicators: energy depletion (ED), depletion of abiotic resources (ADP), and global warming potential (GWP). Then, the indicators were compared and the option with the smaller environmental impact was selected. The main finding of this study was that mechanical recycling of plasticsis more attractive treatment option in environmental terms than incineration for energy recovery

Mitigation of arsenic accumulation in rice (Oryza sativa L.) seedlings by oxygen nanobubbles in hydroponic cultures

Arsenic (As) is a toxic non-essential metal. Its accumulation in rice has not only seriously affected the growth of rice, but also poses a significant threat to human health. Many reports have been published to decrease the arsenic accumulation in the rice plant by various additives such as chemicals, fertilizers, adsorbents, microorganisms and analyzing the mechanism. Nanobubble is a new technology widely used in agriculture because of its long existence time and high mass transfer efficiency. However, a few studies have investigated the effect of nanobubbles on arsenic uptake in rice. This study investigated the effect of oxygen nanobubbles on the growth and uptake of As in rice. The oxygen nanobubbles could rupture the salinity of nutrients and produce the hydroxyl radical. The hydroxyl radical caused the oxidation of arsenic As(III) to As (V) and the oxidation of ferrous ions. At the same time, the oxidized iron adsorbing As (V) created the iron plaque on the rice roots to stop arsenic introduction into the rice plant. The results indicated that the treatment of oxygen nanobubbles increased rice biomass under As stress, while they increased the chlorophyll content and promoted plant photosynthesis. Oxygen nanobubbles reduced the As content in rice roots to 12.5% and shoots to 46.4%. In other words, it significantly decreased As accumulation in rice. Overall, oxygen nanobubbles mitigated the toxic effects of arsenic on rice and had the potential to reduce the accumulation of arsenic in rice

Measurement of metal grade of ore particles in slurry using laser-induced breakdown spectroscopy

This paper describes experimental works to apply Laser-Induced Breakdown Spectroscopy (LIBS) for in-situ measurement of the metal grade of ore particles handled in seafloor mineral processing system for seafloor massive sulfides. LIBS measurements of ore particles containing metallic elements in slurry were performed, where ore slurry was circulated through a chamber mounted on the optical probe of a LIBS device. The chamber was positioned to set the focal point of laser from the LIBS device at the center of the tubular space in the chamber, where the slurry runs. Analytically useful LIBS spectra were obtained from the slurry with enough slurry concentration. While relatively strong LIBS signals assigned to major elements appeared in many spectra, sharp LIBS signals assigned to minor elements appeared in a spectrum. Individual ore particles are not homogeneous even though they are prepared from single ore. The results suggest that multiple measurements are required to assess the metal grade in the seafloor mineral processing system