Supercritical Extraction of Lanthanide Tributyl Phosphate Complexes: Current Status and Future Directions

A review of greener approaches for rare earth elements recovery from mineral wastes

The use of rare earth elements (REE) in many various fields, including high-tech products, increases the demand for these materials day by day. The production of REE from primary sources has expanded in response to increasing demand; however, due to its limited, a more sustainable supply is also started to offer for the REE demand by using secondary sources. The most commonly used metallurgical method for REE recovery is hydrometallurgical processes. However, it has some disadvantages, like pyrometallurgical methods. In the review, studies of the environmental impacts of REE production from primary sources and life cycle assessments of products containing REE were investigated. According to the results, it has been seen that those studies in the literature in which hydrometallurgical methods have changed to more environmentally friendly approaches have begun to increase. In this review, mine wastes, which are secondary sources, were defined, conventional methods of recovery of rare earth elements were discussed, greener approaches to the recovery of REE from these sources were comprehensively examined and studies in the literature were evaluated. Furthermore, it was stated that there are limited studies on green approaches and REE recovery from mineral wastes and that this field is developing with an emphasis on the current outlook and future perspectives.

Modeling Lanthanide Ions in Solution: A Versatile Force Field in Aqueous and Organic Solvents

In this paper, we propose a new nonpolarizable force field for describing the Ln3+ (Ln = lanthanide) series based on a 12-6-4 Lennard-Jones potential. The development of the force field was performed in pure water by adjusting both the ion-oxygen distance and the hydration free energy. This force field accurately reproduces the Ln3+ hydration properties through the series, especially the coordination number that is hardly accessible using a nonpolarizable force field. Then, the validity and the transferability of the current force field were evaluated for two different systems containing Ln3+ in various solvents, namely, 0.1 mol L-1 La(NO3)3 salts in methanol and Eu(NO3)3 salts in solvent organic phases composed of DMDOHEMA molecules in n-heptane. The good agreement between our simulations and the data available in the literature confirms the accuracy of the force field for describing the lanthanide cations in both aqueous and nonaqueous media.

N-oxide ligands for selective separations of lanthanides: insights from computation

Preorganized ligands such as bis-lactam-1,10-phenanthroline (BLPhen) show unique selectivity trends across the lanthanide series, indicating the synergistic effects of both N and O donors in complexing with lanthanides. We hypothesize that by replacing amide functional groups with an N-oxide functionality would open the door to new ligand architectures with improved selectivities. To test this idea, we computationally examined mixed N,O-donor ligands containing pyridinic N and N-oxide groups and evaluated their relative aqueous La(iii)/Ln(iii) selectivity by computing free energy changes for the exchange reaction between the designed ligands and a reference ligand. Three novel ligands show promise as excellent extractant agents in selectively separating trivalent lanthanides. The extent of conjugation (and hyperconjugation), the complex geometry, and the electron accumulations on the two O-donors of the N-oxide groups are found to be important factors in dictating the selectivity trends.

Future of industry 5.0 in society: human-centric solutions, challenges and prospective research areas

Industry 4.0 has been provided for the last 10 years to benefit the industry and the shortcomings; finally, the time for industry 5.0 has arrived. Smart factories are increasing the business productivity; therefore, industry 4.0 has limitations. In this paper, there is a discussion of the industry 5.0 opportunities as well as limitations and the future research prospects. Industry 5.0 is changing paradigm and brings the resolution since it will decrease emphasis on the technology and assume that the potential for progress is based on collaboration among the humans and machines. The industrial revolution is improving customer satisfaction by utilizing personalized products. In modern business with the paid technological developments, industry 5.0 is required for gaining competitive advantages as well as economic growth for the factory. The paper is aimed to analyze the potential applications of industry 5.0. At first, there is a discussion of the definitions of industry 5.0 and advanced technologies required in this industry revolution. There is also discussion of the applications enabled in industry 5.0 like healthcare, supply chain, production in manufacturing, cloud manufacturing, etc. The technologies discussed in this paper are big data analytics, Internet of Things, collaborative robots, Blockchain, digital twins and future 6G systems. The study also included difficulties and issues examined in this paper head to comprehend the issues caused by organizations among the robots and people in the assembly line.

Kinetics and mechanism of Eu(III) transfer in tributyl phosphate microdroplet/HNO3 aqueous solution system revealed by fluorescence microspectroscopy

In this study, we reveal an Eu(III) extraction mechanism at the interface between HNO₃ and tributyl phosphate (TBP) solutions using fluorescence microspectroscopy. The mass transfer rate constant at the interface is obtained from the analysis of fluorescence intensity changes during the forward and backward extractions at various HNO₃ and TBP concentrations to investigate the reaction mechanism. This result indicates that one nitrate ion reacts with Eu(III) at the interface, whereas TBP molecules are not involved in the interfacial reaction, which is different from the results obtained using the NaNO₃ solution in our previous study. We demonstrate that the chemical species of Eu(III) complex with nitrate ion and TBP in the aqueous solution play an important role for the extraction mechanism. The rate constants of the interfacial reactions in the forward and backward extractions are (4.0-5.0) × 10^-7 m M^-1 s^-1 and (3.2-3.3) × 10^-6 m s^-1, respectively. We expect that our revealed mechanism provides useful and fundamental knowledge for actual solvent extraction.

P-Chloride-Free Synthesis of Phosphoric Esters: Microwave-Assisted Esterification of Alkyl- and Dialkyl Phosphoric Ester-Acids Obtained from Phosphorus Pentoxide

It is a reasonable endeavour to replace P-chloride starting materials (e.g., POCl3) with greener and cheaper reagents. Our purpose was to start from phosphorus pentoxide, i.e. to utilize its reaction with alcohols in the preparation of (HO)2P(O)(OR) and HOP(O)(OR)2, and to convert the mixtures of the corresponding monoester and diester, so obtained, into the target trialkyl esters. Separate experiments showed that the monobutylphosphate undergo microwave (MW)-assisted esterification with butanol in the presence of [bmim][BF4] catalyst at 200 °C to afford dibutylphosphate in a selective manner (ca. 95%) that, in turn, may be converted into tributylphosphate by alkylation under MW irradiation. In this way, the mixtures of (HO)2P(O)(OR) and HOP(O)(OR)2 obtained by the practical reaction of phosphorus pentoxide and alcohol (ROH) could also be converted in two additional steps into the corresponding trialkyl esters. The three-step synthesis of trialkylphosphates starting from phosphorus pentoxide was also transformed in a one-pot (step 1: preparation of the monoester diester mixture, step 2: diesterification) and telescoping (step 3: triesterification) variation, avoiding the isolation and purification of the intermediates, and affording the triesters­ in 86–93% yields. The three- and two-step P-chloride-free methods developed are ‘green’ and of more general value.

Application of Green Solvents for Rare Earth Element Recovery from Aluminate Phosphors

Two processes applying green solvents for recovering rare earth elements (REEs) from different types of aluminate phosphors are demonstrated in this report. For magnesium aluminate-type phosphors, a pretreatment with peroxide calcination was implemented first, and then followed by a supercritical fluid extraction (SFE) process. Supercritical carbon dioxide (sc-CO2) provides an effective and green medium for extracting REEs from dry materials. With the addition of a complex agent, tri-n-butyl phosphate-nitric acid complex, highly efficient and selective extraction of REEs using supercritical carbon dioxide can be achieved. The highest extraction efficiency was 92% for europium from the europium doped barium magnesium aluminate phosphor (BAM), whereas the highest extraction selectivity was more than 99% for the REEs combined from the trichromatic phosphor. On the other hand, for strontium aluminate type phosphors, a direct acid leaching process is suggested. It was found out that acetic acid, which is considerably green, could have high recovery rate for dysprosium (>99%) and europium (~83%) from this strontium aluminate phosphor materials. Nevertheless, both green processes showed promising results and could have high potential for industrial applications.

Enhanced Separation of Neodymium and Dysprosium by Nonaqueous Solvent Extraction from a Polyethylene Glycol 200 Phase Using the Neutral Extractant Cyanex 923

Neodymium and dysprosium can be efficiently separated by solvent extraction, using the neutral extractant Cyanex 923, if the conventional aqueous feed phase is largely replaced by the green polar organic solvent polyethylene glycol 200 (PEG 200). While pure aqueous and pure PEG 200 solutions in the presence of LiCl or HCl were not able to separate the two rare earth elements, high separation factors were observed when extraction was performed from PEG 200 chloride solutions with addition of small amounts of water. This addition of water bridges the gap between traditional hydrometallurgy and novel solvometallurgy and overcomes the challenges faced in both methods. The effect of different variables was investigated: water content, chloride concentration, type of chloride salt, Cyanex 923 concentration, scrubbing agent. A Job plot revealed the extraction stoichiometry is DyCl3·4L, where L is Cyanex 923. The McCabe-Thiele diagram for dysprosium extraction showed that complete extraction of this metal can be achieved by a 3-stage counter-current solvent extraction process, leaving neodymium behind in the raffinate. Finally, a conceptual flow sheet for the separation of neodymium and dysprosium including extraction, scrubbing, stripping, and regeneration steps was presented. The nonaqueous solvent extraction process presented in this paper can contribute to efficient recycling of rare earths from end-of-life neodymium-iron-boron (NdFeB) magnets.