Ammonia-free recovery of rare earth elements from ion-adsorption clays using sodium citrate

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

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.

Recovery of rare earth elements (REEs) with trace amount in environmental applications and nuclear energy is becoming an increasingly urgent issue due to their genotoxicity and important role in society. Here, highly efficient recovery of low-concentration REEs from aqueous solutions by an enhanced chemisorption and electrosorption process of oxygen-doped molybdenum disulfide (O-doped MoS2) electrodes is performed. All REEs could be extremely recovered through a chemisorption and electrosorption coupling (CEC) method, and sorption behaviors were related with their outer-shell electrons. Light, medium, and heavy ((La(III), Gd(III), and Y(III)) rare earth elements were chosen for further investigating the adsorption and recovery performances under low-concentration conditions. Recovery of REEs could approach 100% under a low initial concentration condition where different recovery behaviors occurred with variable chemisorption interactions between REEs and O-doped MoS2. Experimental and theoretical results proved that doping O in MoS2 not only reduced the transfer resistance and improved the electrical double layer thickness of ion storage but also enhanced the chemical interaction of REEs and MoS2. Various outer-shell electrons of REEs performed different surficial chemisorption interactions with exposed sulfur and oxygen atoms of O-doped MoS2. Effects of variants including environmental conditions and operating parameters, such as applied voltage, initial concentration, pH condition, and electrode distance on adsorption capacity and recovery of REEs were examined to optimize the recovery process in order to achieve an ideal selective recovery of REEs. The total desorption of REEs from the O-doped MoS2 electrode was realized within 120 min while the electrode demonstrated a good cycling performance. This work presented a prospective way in establishing a CEC process with a two-dimensional metal sulfide electrode through structure engineering for efficient recovery of REEs within a low concentration range.

Acid leaching recovery and occurrence modes of rare earth elements (REEs) from natural kaolinites

ABSTRACTThe rapid use of electrical and electronic devices due to their wide applications in various fields produces a large amount of e‐waste (electronic waste) in the modern world. To overcome this problem, there is a need to recycle the used product into useful products from e‐waste. Therefore, this approach is essential for the development of advanced technologies for the recovery and separation of REEs (rare earth elements) from e‐waste. Here, REEs are sometimes referred to as the “vitamins” of the modern industry. E‐waste can contribute significantly to REE pollution since it is frequently handled hazardously and contains high amounts of REEs. Apart from the harmful effects on the environment, these wastes also destroy precious materials such as gold, silver, copper, platinum, palladium, and rare earth elements. Every year, 50 million tons of e‐waste is generated worldwide. A large amount of e‐waste goes to waste as only 20% of it is handled properly worldwide. The various approaches, including bioleaching, biosorption, siderophores, pyrometallurgical, and hydrometallurgical processes, have been reported in numerous studies on the recovery and separation of rare earth elements (REEs) from electronic waste. This review paper provides an overview of the introduction, characteristics, sources, and applications of clean and green energy technologies. The current pathways for REEs production and recovery point out significant deficiencies in methods currently in use and emphasise areas where multidisciplinary research may lead to more practical solutions. A summary also provides the impact of e‐waste on health and the environment. The challenges, research gap, and future directions and suggestions are reported at the end of this review paper.

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.

The recovery of rare earth elements (REEs) through heap leach/in situ techniques from so-called ion adsorption clays (IACs) is attractive due to their inherent simplicity. However, the underlying mechanisms of these processes are poorly understood. In this study, the deportment of REEs in a typical IAC material has been investigated and was found to concentrate in the phyllo-layers of the clays, especially hallyosite, and was readily desorbed by various ion-exchange reagents indicating various potential routes to liberate them. Here we are reporting the use of seawater (0.5 M NaCl), spiked with various amounts of (NH4)2SO4, and found better extraction using a reagent mixture than NaCl on its own. Further, the leaching of REEs from a bed of clay material was investigated over time to understand the rate of transport through the stagnant material. Results indicate that REE release is likely to be controlled by diffusion through the clay material, while desorption in agitated systems is rapid. A degree of fractionation between different REEs can be observed during diffusion. Nonetheless, the successful operation of in situ leach operations for this type of material would depend primarily on how easily solution cocktails can be made to flow through the bed material.

The establishment of a mathematical model for the ion exchange leaching process is key to creating a theoretical basis for the recovery of rare earth elements (REEs) from ion adsorption clay. Given the complexity of the process and limitations of experimental methods, modelling and simulation provide a promising, cost-effective approach to understanding ion exchange leaching mechanisms for REE extraction. Therefore, this study aims to develop a such a model, employing the Shrinking Core Model and utilizing MgSO4 as the leaching solution. A kinetic model was successfully developed based on the rate-determining step equation which belonged to the internal diffusion control. The calculated k value was 0.005, and the initial n value of 1.53 was later modified to 1.33 due to a deviation exceeding 10% in the Normalized Root Mean Square Error (NRMSE) value. The statistical model validation demonstrated a high level of agreement with the index values of d = 0.978, indicating an excellent agreement with experimental data, and a low value of NRMSE = 7.9 %, indicating an excellent performance model. The model consistently exhibits exponential growth in REE leaching efficiency, eventually reaching a maximum of 100% as leaching time progresses, demonstrating the leaching behaviour of REE extraction observed in this model follow the patterns observed in the leaching experiment. In conclusion, the developed kinetic model has the potential to provide reliable data on REE leaching efficiency at different leaching times across various concentrations of MgSO4solution.

Rare earth elements recovery and mechanisms from coal fly ash by column leaching using citric acid

The article covers the issues related to the characteristics, application, and some methods of rare earth elements (REEs) recovery from coal fly ashes. REEs are elements with growing demand and a very wide range of application, especially when it comes to modern technologies. The conducted analysis and price forecast proved the existing upward tendency, and this confirmed the need to search for new REE sources, among industrial waste (proecological effect). The development of the REE recovery technology would involve solving several problems related to REE speciation, optimization of factors controlling their extractivity and selection of the REE separation method from obtained extraction solutions with a very extreme pH and complicated composition. The paper presented advantages and disadvantages of usually used methods of REE separation from coal fly ashes, like physical and acid–base leaching. It was also presented alternative REE recovery techniques in the form of membrane and biological methods and based on ion liquids (ILs) or chelating agents. The directions of further modifications, which will allow the efficient REE recovery were presented. The aim of this article was to propose specific solutions based on the creation of appropriate multistage method of REE recovery. It will be a combination of magnetic and size separation, acid–base leaching (including roasting in justified cases), removal of matrix elements with ILs (Al, Si, and Fe), and finally REE membrane separation, allowing one to obtain the appropriate process efficiency.

According to the European Commission’s Report on Critical Raw Materials and the Circular Economy, the raw materials, such as rare earths, have a high economic importance for the EU, and are essential for the production of a broad range of goods and applications used in everyday life, as well as they are crucial for a strong European industrial base. Uncertainty plays an important role in the real world used Life Cycle Assessment (LCA) approach. The validity of LCA depends strongly on the significance of the input data. Data uncertainty is often mentioned as a crucial limitation for a clear interpretation of LCA results. The stochastic modelling used for Monte Carlo (MC) analysis simulation was reported in order to assess uncertainty in life cycle inventory (LCI) of rare earth elements (REEs) recovery. The purpose of this study was REEs recovery from secondary sources analysed in the ENVIREE ERA-NET ERA-MIN-funded research project. The software Crystal Ball® (CB) program, associated with Microsoft® Excel, was used for the uncertainties analysis. Uncertainty of data can be expressed through a definition of probability distribution of those data. The output report provided by CB, after 10000 runs is reflected in the frequency charts and summary statistics. The analysed parameters were assigned with lognormal distribution. The uncertainty analysis offers a well-defined procedure for LCI studies, and provides the basis for defining the data needs for full LCA of the REEs beneficiation process. Results can improve current procedures in the REEs beneficiation process management and bring closer to industrial application through the involvement of end users.

Acid baking treatment is widely used to extract rare earth elements (REEs) from refractory rare earth bearing minerals such as monazite and xenotime. Since these REE minerals have been identified in coal-based sources, a parametric study was conducted to evaluate the impact and optimize the parametric values associated with the acid-baking process when treating a bituminous coal source. The parameters studied using a three-level statistical experimental program were acid baking time, acid solution concentration, baking temperature, and acid solution-to-solids ratio and each were found to significantly impact REE and contaminant element recovery. An increase in baking temperature up to around 250°C improved the light and heavy REE recovery values by more than 50 absolute percentage points relative to performances achieved when direct leaching. Acid baking was needed to dehydroxylate the clays and liberate the REE minerals, which allowed access for the acid to solubilize the REEs. Acid concentration of the solution used for acid baking was studied as a means of minimizing the amount of acid needed to achieve a target REE recovery. However, thermo-gravimetric and differential scanning calorimetry analysis (TGA-DSC) of sulfuric acid under oxidizing atmosphere revealed that the addition of water decreased the evaporation temperature, which explains the lower REE recovery values obtained when using lower acid concentrations. Using pure sulfuric acid at an acid-to-solid ratio of 0.8:1 resulted in recovery values of around 70% for both LREEs and HREEs. The decomposition reaction time was relatively quick with 65% of the TREEs recovered within the first 10 minutes. Water leaching experiments performed on the acid-baked products under a temperature of 25°C instead of 75°C revealed an increase in REE recovery by 10 absolute percentage points, which was likely due to the high solubility of REE-sulfates at room temperatures.

Recovery of rare earth elements from mine wastewater using alginate microspheres encapsulated with zeolitic imidazolate framework-8

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

Recovery of rare-earth and radioactive elements from contaminated water through precipitation: A review