Efficient and green recovery of rare-earth elements from coal gangue via electric field-assisted leaching in a sulfamic-ascorbic acid system

Recovery of light and heavy rare earth elements from apatite ore using sulphuric acid leaching, solvent extraction and precipitation

A biosorption-based approach for selective extraction of rare earth elements from coal byproducts

An acid baking approach to enhance heavy rare earth recovery from bituminous coal-based sources

Different separation techniques such as solvent extraction, ion exchange, and precipitation are often used for recovery of rare earth elements (REEs) from pregnant leach solutions obtained from acid leaching. Solvent extraction is generally accepted as the most appropriate commercial technology for separating REEs due to the need to be able to handle larger volumes of diluted pregnant solutions. This study focused on the development of selective separation of light and heavy REEs from the pregnant leach solution obtained from leaching of apatite ore in 1 M sulfuric acid (H2SO4) using solvent extraction. Three different commercial organophosphorus extractants (di-(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) and tributyl phosphate (TBP)), and the influences of experimental parameters such as extractant concentration, organic/aqueous phase ratio, diluent type, pH, extraction time and stripping agent concentration were examined. Results showed that light REEs (LREEs) and heavy REEs (HREEs) in the pregnant leach solution were selectively separated with D2EHPA via a two-stage extraction process. In the first-stage of solvent extraction, >90% of (0.05 g/L) HREEs was extracted with 1.8 M D2EHPA in kerosene while the vast majority (>95%) of LREEs was remained in raffinate. In the second-stage, >93% (1.01 g/L) of LREEs was extracted from the raffinate with 1.8 M D2EHPA dissolved in kerosene at pH 1.6. HREEs (>95%) and LREEs (>90%) loaded with D2EHPA after the first and second-stage of extraction were stripped by 4 M H2SO4 and 1 M H2SO4 solutions, respectively. Distribution of middle rare earth elements (MREEs) was discussed through the extraction processes in this study.

A Two-Dimensional Metal-Organic framework for efficient recovery of heavy and light rare earth elements from electronic wastes

The recovery of rare earth elements (REEs) from the Western Kentucky No. 13 and Fire Clay coal wastes was enhanced by alkali pretreatment with concentrated NaOH solutions. The enhancements in the recovery of light REEs (LREEs) are more significant than those of heavy REEs (HREEs). For example, after treating with 5 M NaOH at 90 °C, the recovery of LREEs from the Western Kentucky No. 13 coal waste increased from 26% to 71%, while the recovery of HREEs only increased from 29% to 41%. Based on mineralogical studies through scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray diffraction analyses, two mechanisms were proposed to explain the positive effect of alkali pretreatment: (1) decomposition of rare earth minerals (primarily crandallite-group minerals) during the alkali pretreatment, and (2) liberation of encapsulated REE-bearing particles due to the enhanced dissolution of clay minerals. The more significant enhancements in the recovery of LREEs were explained by the fact that the REEs comprised in the crandallite-group minerals were mainly LREEs. Compared with zircon, monazite, and xenotime, alkali pretreatment with 5 M NaOH led to a more significant decomposition of crandallite-group minerals. In order to further increase the recovery of REEs, particularly HREEs, harsher alkali treatment conditions are required.

Silica-chitosan hybrid beads were synthesized via three different methods to investigate the selective recovery of REE from AMD. The influence of amino/non-amino silanes, high molecular weight/high viscous chitosan and N-/O- based ligands were studied and their effects on REE removal efficiencies were analyzed. The adsorption efficiencies of three various groups of modified beads were inspected with respect to feed pH, in a single and a multi-component system, and their affinities towards the light and heavy rare earth elements (LREE/ HREEs) were interpreted to understand the intra-series REE separation behavior. The focus of the study was mainly directed towards utilizing these fabricated beads for the recovery of valuable REEs from the real AMD obtained at three different sampling depths which was found rich in iron, sulfur and aluminum. Moreover, the selectivity of the beads towards REEs improved with silanized and ligand immobilized gels and their impacts on REE recovery in the presence of competing ions were successfully presented in this paper. Also, the synthesized beads showed rapid REE adsorption and recovery within a process time of 5 min. Group II adsorbents, synthesized by forming silica-chitosan hybrid beads followed by PAN/acac modifications, showed superiority over the other groups of adsorbents.

Selective separation of light and heavy rare earth elements from acidic mine waters by integration of chelating ion exchange and ligand impregnated resin

Leaching recovery of rare earth elements from the calcination product of a coal coarse refuse using organic acids

Rare earth elements in tea garden soils and their bioavailability to tea buds in Taiwan

This paper presents results on the characterization and hydrometallurgical studies for the recovery of Rare Earth Elements (REE) from micro-granite type hard rock REE deposit of Bhatikheda, Siwana Ring Complex, Rajasthan, India. The total REE (TREE) content of the ore is 0.36%. Heavy REE (HREE) constitutes about 40% of the TREE by weight. Allanite, zircon and gittinsite were identified as the major REE bearing phases. The nature of occurrence of REE phases in the ore is widely varying with the presence of fully liberated grains to those which occur very finely disseminated in lighter gangue minerals. Physical beneficiation using gravity-based separation techniques gave suboptimal performance. Agitation leaching of ground ore with different mineral acids gave good solubilisation of light REE (LREE), about 75%, but the leach recovery of HREE was only 40%. However, sulfation roasting followed by aqueous leaching (SRAL) yielded leach recovery of 85% of total REE under optimised conditions. The lean tenor of TREE in the leachate coupled with its complex solution chemistry necessitated use of ion exchange (IX) process with strong cationic resin in lieu of conventional solvent extraction based separation and purification. The dissolved REE values from the purified liquor were quantitatively precipitated in the form of TREE fluoride using HF as the precipitant. The final product was about 90% pure on dry weight basis. An integrated process scheme for the recovery of TREE values from the Bhatikhera hard rock deposit is designed-

The extraction of rare earth elements (REEs) from red mud, a by-product of alumina production from bauxite, poses considerable environmental and economic challenges. This study investigates the viability of bioleaching as a sustainable and environmentally friendly approach for REE recovery from red mud. Bioleaching employs microorganisms to extract valuable metals from ores and offers a potentially less harmful alternative to traditional chemical extraction techniques. Specifically, the objective of this study is to recover REEs from Indonesian red mud using the mixotrophic bacterium Priestia aryabhattai , which is capable of oxidizing both iron and sulfur and producing biosurfactants. The bioleaching experiments were carried out over a period of three days under aerobic conditions, with the introduction of a 10% v/v inoculum of P. aryabhattai . The experiments varied the concentrations of red mud in the bioleaching medium to 1.5, 3, and 6 g/L. The results indicated that the maximum recovery of heavy rare earth elements (HREEs) was approximately 70% for terbium (Tb), whereas the highest recovery of light rare earth elements (LREEs) was about 60% for gadolinium (Gd). Most notably, increasing the concentration of red mud resulted in lower REE recovery levels. In conclusion, this study demonstrates the effectiveness of biohydrometallurgical methods for REE recovery from Indonesian red mud. The findings support sustainable metallurgical practices and present a promising pathway for more environmentally responsible REE recovery.

Rare earth elements recovery using staged precipitation from a leachate generated from coarse coal refuse

Effects of acid concentration on the recovery of rare earth elements from coal fly ash

Electrodialytic recovery of rare earth elements from coal ashes