This study reports on the capture of rare earth elements (REEs) from phosphate industry process streams, including phosphoric acid (PA) sludge and phosphogypsum (PG), using a membrane solvent extraction (MSX) process. While MSX has been proven effective for a relatively concentrated feed, its effectiveness for dilute REEs solutions remains unexplored. Investigated PA-sludge and PG particles contain total REEs concentrations of similar to 1100 and similar to 320 ppm, respectively. Acid leaching, implemented to dissolve the REEs, significantly dilutes the REEs concentration to similar to 210 ppm for PA-sludge leachate and similar to 60 ppm for PG leachate. These low concentrations, compounded by the higher levels of non-REE ions and radioactive species, uranium (U) and thorium (Th), poses challenges to the MSX process. Here, we demonstrated that N,N,N ',N '-tetraoctyl-diglycolamide (TODGA) selectively binds REEs from a >3 M nitric-acid leachate while effectively rejecting U and Th. Concentrations of light REEs in strip solution were doubled compared to the feed, while heavy REEs were preferentially extracted. Furthermore, >99% purity gypsum, free of U and Th, was precipitated during the acid leaching process, aiding separation by removing significant amounts of non-REEs species (e.g., calcium) prior to the MSX process. Molecular simulations support the experimental data, suggesting preferential separation of heavy over light REEs. Based on these results, a cost-effective integrated process including pretreatment, acid leaching, MSX, and wastewater treatment is proposed for the co-recovery of REEs, phosphoric acid, gypsum, and U. This work demonstrates MSX as a technically and economically feasible process for the recovery of REEs from low-concentration process streams, offering advantages over conventional solvent extraction.

Recent technological breakthroughs have paved the way for commercializing an innovative gravity separation device, the packed column jig (PCJ). This paper presents three case studies of PCJ use for processing tailings/byproducts from the phosphate industry. Pilot testing of PCJ on high-silica phosphate tailings recovered 87

Phosphorite, or phosphate rock, has garnered increasing attention in recent years as a promising unconventional resource for rare earth elements (REEs). This paper presents a processing scheme aimed at recovering both REEs and phosphate values from amine flotation tailings generated during phosphate beneficiation in Florida. In these tailings, REEs are primarily present as monazite and xenotime, often associated with heavy minerals. The proposed flowsheet includes gravity separation to pre-concentrate REE- and phosphate-bearing minerals, followed by flotation to further upgrade both REEs and phosphate, and finally sulfuric acid leaching to extract REEs and phosphate from the flotation concentrate. Gravity separation using a shaking table increased the total REE content from approximately 202 ppm to 657 ppm, with a concentrate yield of 12.51%, REE recovery of around 41%, and P2O5 recovery of 33%. Fatty acid flotation of the shaking table concentrate produced a final concentrate containing 1106 ppm REEs and 14.90% P2O5, with recoveries of approximately 86% for REEs and 90% for P2O5. Subsequent pyrolysis with concentrated sulfuric acid followed by water leaching achieved recoveries of about 85% for REEs and 93% for P2O5. While the process demonstrated effective concentration and leaching of REE minerals and apatite, the major challenge to further improving separation and extraction efficiency lies in the fine-grained nature of the valuable minerals and their interlocking with gangue minerals.

This study was conducted with different experimental conditions such as acids, temperatures, and reaction times for investigating leaching behavior for rare earth element (REE) leaching. In this study, phosphogypsum (PG) sample was obtained from a real PG plant in Florida and sample characteraziton was evaluated for REE, P2O5, 238U, and 232Th contents. Then preliminary leaching experiments were conducted as kinetic experiments with 9 different experimental conditions. These leaching tests showed that leaching yield was not so high. PG sample's leaching was so difficult, complex to get into solution also the REE concentration was small.

Phosphogypsum (PG), a byproduct of wet-process phosphoric acid production, has accumulated in vast quantities worldwide. Most of this material is stacked in open areas, raising significant environmental concerns due to its residual radioactivity and chemical impurities, which limit its reuse. This research found that the majority of radioactivity in a Florida PG sample was concentrated in the micro-fine fraction (− 400 mesh) and the coarse fraction (+ 35 mesh). In contrast, the intermediate size fractions (20 to 400 mesh) exhibited lower radioactivity levels, meeting the U.S. Environmental Protection Agency (EPA) civil use threshold of less than 10 pCi/g. Moreover, a clear inverse relationship was observed between gypsum content and radioactivity—the higher the gypsum purity, the lower the radiation level. Conventional flotation methods for gypsum separation, which operate in neutral or weakly alkaline conditions, require large amounts of alkalis to neutralize the acidic pulp, resulting in prohibitively high costs. In this study, an alternative flotation process was developed that operates directly in acidic pulp, using sulfuric acid to adjust pH and an amine as the collector. At an optimized pulp pH of approximately 1.44, the flotation concentrate achieved a gypsum grade of 93

Different types of and huge amount of wastes, residue and by-products are generated in worldwide. These wastes could be considered as flotation tails, concentrate, end-of-life products, phosphogypsum (PG), bauxite residue (red mud), mine tailings, metallurgical slags and industrial process residues from thermal treatment facilities. These kinds of different wastes may become inherently complex, heterogeneous and contain different kinds of metals, rare earth elements (REEs), radioactive elements and impurities. Recovery of these wastes, which are harmful to the environment and those with economic benefits, is very important in terms of both sustainability and protecting the environment and obtaining economic benefits. Therefore it could increase resource efficiency in the sense of a sustainable circular economy. In this paper, it was evaluated reviews studies about radionuclides contents of PGs, typical REE contents and recovery efficiencies with different experimental conditions.

Under this project and in collaboration with Pacific Northwest National Laboratory (PNNL), Oak Ridge National Laboratory (ORNL), Florida International University (FIU), and Mosaic, the FIPR Institute successfully developed and demonstrated on laboratory batch scale a complete processing technology for production of high-purity rare earth elements (REE) in the form of mixed rare earth oxides (MREO) and rare earth metals (REM) using phosphoric acid sludge (a byproduct from phosphate mining) as the REE feedstock. Based on the research results, a technical research plan has been developed with expanded team members to elevate the technology readiness level (TRL) of the subject technology from 4 to 6 by conducting continuous testing of the processing flowsheet with the ultimate goal of producing about 900 tons per year of REM using the phosphate mining byproduct. Those 900 tons of REM would contain approximately 180 tons of Y, 120 tons of Nd, 50 tons of Gd, 37 tons of Dy, 33 tons of Sm, and 31 tons of Pr, meeting the US demand of roughly 39%, 6%, 42%, 48%, 101% and 7% for these elements, respectively. The advanced technologies for REE separation and purification involves three technology companies: K-Technologies, Inc. would test their continuous-ion-exchange/continuous-ion chromatography technologies on both the REE leachate and solvent extraction concentrate for 4 production of high-purity individual or binary REM. Rare Earth Salts would test their innovative electrochemical technology on the REE leachate or re-dissolved MREO in dilute acid for production of high-purity individual or binary REM. Rare Earth Technologies, Inc. would evaluate their advanced chromatographic separation technology on the dissolved MREO product for production of high-purity individual or binary REM.

Sustainability faces many challenges, including the availability of materials necessary for technological advancement. Rare earth elements (REEs), for example, are key materials for several manufacturing industries that can unlock renewable energy and sustainable development. In this study, a decanter centrifuge has been employed to successfully separated phosphoric acid and REE-containing particles from phosphoric acid sludge with concentrations ranging from 1000 to 2200 ppm REEs. Operating efficiently with up to 35 wt.% solids, the centrifuge was demonstrated to achieve approximately 95% phosphoric acid recovery and 90% REE recovery in a single pass, eliminating the need for additional processing steps. This breakthrough supports a proposed rare earth oxide (REO) recovery process integrating phosphoric acid (PA), elemental phosphorus (P4), and REO into two potential pathways: PA-REO and PA-P4-REO. These processes aim to reintroduce recovered phosphoric acid into the main product to significantly increase output and revenue. Post-separation, phosphorus-rich particles can be converted to P4, while REE-containing solids undergo further treatment including acid leaching, extraction/stripping, precipitation, and calcination to produce a marketable REO material. Technoeconomic analysis indicates promising profitability, with the PA-REO process showing a delta net present value (∆NPV) of USD 441.8 million over a 12-year period and expected return within a year of construction, while the PA-P4-REO process yields a ∆NPV of USD 178.7 million over a 12-year return period. Both pathways offer robust financial prospects and demonstrate the feasibility of commercial-scale REO recovery from phosphoric acid sludge, offering an economically feasible approach to produce REEs for future sustainable development challenges related to sustainability.

In general, the phosphatic rock contains around 0.05 wt% rare earth elements (REEs). The global commercial phosphatic rock output is anticipated to obtain 250 million tons per year, making phosphate rocks a significant source of REEs. The review discusses the geological aspects of phosphate rocks, their availability, and methodologies to convert them to phosphoric acid and ultimately to phosphogypsum. Phosphogypsum (PG) is a high-volume by-product of phosphate-based chemical industries that produce phosphoric acid. Because of the low radioactivity of radionuclide contaminants, roughly 85% of PG is stored in open fields. These PG stacks require enormous land areas, cause substantial upkeep expenses, and may create major environmental damage. Apart from the detailed analysis of metal worth in phosphogypsum, the efforts put forth by researchers in recovering valuable rare earth elements from PG have been discussed. Additionally, the processes for metal separation and purification are also discussed in vogue.

A decanter centrifuge has been employed to successfully separated phosphoric acid and rare-earth-element (REE)-containing particles from phosphoric acid sludge with concentrations ranging from 1,000 to 2,200 ppm REEs. Operating efficiently with up to 35 wt.% solids, the centrifuge was demonstrated to achieve approximately 95% phosphoric acid recovery and 90% REEs recovery in a single pass, eliminating the need for additional processing steps. This breakthrough supports a proposed REEs oxide recovery process integrating phosphoric acid (PA), elemental phosphorus (P4), and REEs into two potential pathways: PA-REO and PA-P4-REO. These processes aim to reintroduce recovered phosphoric acid into the main product to significantly increase output and revenue. Post-separation, phosphorus-rich particles can be converted to P4, while REEs-containing solids undergo further treatment including acid leaching, extraction/stripping, precipitation, and calcination to produce a marketable rare-earth oxide (REO) material. Techno-economic analysis indicates promising profitability, with the PA-REO process showing a delta net present value (∆NPV) of $441.8 million and an expected return within a year of construction, while the PA-P4-REO process yields a ∆NPV of $178.7 million over a 12-year return period. Both pathways offer robust financial prospects and demonstrate the feasibility of commercial-scale REEs recovery from phosphoric acid sludge.

We analyzed a novel cationic collector using chemical plant byproducts, such as cetyltrimethylammonium bromide (CTAB) and dibutyl phthalate (DBP). Our aim is to establish a highly effective and economical process for the removal of quartz from collophane. A microflotation test with a 25 mg·L−1 collector at pH value of 6–10 demonstrates a considerable difference in the floatability of pure quartz and fluorapatite. Flotation tests for a collophane sample subjected to the first reverse flotation for magnesium removal demonstrates that a rough flotation process (using a 0.4 kg·t−1 new collector at pH = 6) results in a collophane concentrate with 29.33wt% P2O5 grade and 12.66wt% SiO2 at a 79.69wt% P2O5 recovery, providing desirable results. Mechanism studies using Fourier transform infrared spectroscopy, zeta potential, and contact angle measurements show that the adsorption capacity of the new collector for quartz is higher than that for fluorapatite. The synergistic effect of DBP increases the difference in hydrophobicity between quartz and fluorapatite. The maximum defoaming rate of the novel cationic collector reaches 142.8 mL·min−1. This is considerably higher than that of a conventional cationic collector.

Recovery of rare earth elements (REEs) from various industrial and natural streams currently draws significant attention in efforts to meet the demands of the manufacturing industry. Among many industrial byproducts and waste streams, phosphoric acid sludge could be one of the most economically feasible resources for the recovery of REEs because solid particles in the sludge contain relatively concentrated REEs, up to 3,000 ppm, while the liquid component of the sludge is valuable phosphoric acid (P2O5) that can be recovered and returned to the main product. Due to high viscosity and large solids content (e.g., 30-40 %), however, this byproduct stream requires multistep separation and purification processes. In this study, a single-step process involving a continuous-flow decanter centrifuge (CFDC) was employed to investigate its feasibility for continuous solid/ liquid separation from real phosphoric acid sludge. High centrifugal forces generated from up to 1500 G gravity acceleration separate solid particles from the sludge, generating a liquid-rich stream and a solids-rich stream at the exit of the CFDC. A single pass of phosphoric-acid sludge through the CFDC yielded 95 % liquid recovery and 90 % recovery of REEs-containing solids from 20 to 34 wt% solids-containing sludge. A reduced order model developed for the CFDC operation showed good agreement with experimental data, and preliminary tech-noeconomic analysis revealed potential process feasibility.

Patrick Zhang, Haijun Liang, Zhen Jin FIPR Institute, Florida Polytechnic University David DePaoli, Oak Ridge National Lab Jan Miller and Chen-Luh Lin, University of Utah Raquel Crossman, Freeport McMoRan

Froth flotation is often used for fine-particle separation, but its process efficiency rapidly decreases with decreasing particle size. The efficient separation of ultrafine particles (UFPs) has been a major challenge in the mineral processing field for many years. In recent years, the use of surface nanobubbles in the flotation process has been recognized as an effective approach for enhancing the recovery of UFPs. Compared with traditional macrobubbles, nanobubbles possess unique surface and bulk characteristics, and their effects on the UFP flotation behavior have been a topic of intensive research. This review article is focused on the studies on various unique characteristics of nanobubbles and their mechanisms of enhancing the UFP flotation. The purpose of this article is to summarize the major achievements on the two topics and pinpoint future research needs for a better understanding of the fundamentals of surface nanobubble flotation and developing more feasible and efficient processes for fine and UFPs.

Collophane is difficult to upgrade by reverse flotation of quartz with amine collector alone due to its low grade, complex structure, fine dissemination grain size, etc. This investigation was conducted to explore the synergistic effect of dibutyl phthalate (DBP) as a surfactant with cetyltrimethyl ammonium bromide (CTAB) as the collector on the separation of quartz from collophane by means of micro-flotation tests, surface tension and aggregate size measurements, and froth water mass fraction/recovery characterization. It was found that DBP reduced the surface tension of the reagent solution and enhanced the collision probability between bubbles and quartz particles by increasing the size of aggregates through increased hydrophobic interaction between the quartz particles and DBP droplets. The addition of DBP reduced the entrainment of fine collophane particles as a result of improved defoaming and increased the flotation recovery of quartz without resulting in any flotation of collophane at dosages lower than 200 mg/L. Flotation test results with the binary artificial mineral mixture showed that DBP improved the P2O5 recovery, SiO2 rejection, and P2O5 grade by up to 7%, 12%, and 1%, respectively.

Reprocessing and valorization of secondary resources is a possible solution to alleviate the supply-demand disparity for critical materials. The current study investigated the recovery of P and enrichment of REEs from Florida waste clay (WC). Clays, dolomite, and quartz are the main associated gangue minerals, while apatite is the predominant P-bearing mineral, and monazite and xenotime are the rare earth minerals in this WC. A 1.5-in. diam. hydro-cyclone unit was initially employed for the removal of clays. Froth flotation was then examined for the separation of values from the cyclone underflow. Various depressants and surface modifying agents were assessed for both direct and reverse flotation separations. Results showed that the direct flotation does not offer a solution for the selective recovery of P from WC. Despite their documented affinity for apatite and rare earths, hydmxamic acid collectors do not produce a selective separation. A single-stage reverse cationic process provides a more economically viable route due to its capability to avoid the loss of REEs. Test results of the single-stage reverse cationic process indicated that the P2O5 grade was increased to 21 wt.% from an initial grade of similar to 8 wt.% with a corresponding recovery of approximately 80%. The REE content was elevated from an initial value of 307.1 ppm to 800 ppm, with an 80% recovery resulting from the same process. The removal of clays, silicates, and carbonates up to a point to meet the medium-grade phosphate ore specifications also facilitates the subsequent recovery of REEs using chemical separation.

Voltage imaging with fluorescent dyes affords the opportunity to map neuronal activity in both time and space. One limitation to imaging is the inability to image complete neuronal networks: some fraction of cells remains outside of the observation window. Here, we combine voltage imaging, post hoc immunocytochemistry, and patterned microisland hippocampal culture to provide imaging of complete neuronal ensembles. The patterned microislands completely fill the field of view of our high-speed (500 Hz) camera, enabling reconstruction of the spiking patterns of every single neuron in the network. Cultures raised on microislands are similar to neurons grown on coverslips, with parallel developmental trajectories and composition of inhibitory and excitatory cell types (CA1, CA3, and dentate granule cells, or DGC). We calculate the likelihood that action potential firing in one neuron triggers action potential firing in a downstream neuron in a spontaneously active network to construct a functional connection map of these neuronal ensembles. Importantly, this functional map indicates preferential connectivity between DGC and CA3 neurons and between CA3 and CA1 neurons, mimicking the neuronal circuitry of the intact hippocampus. We envision that patterned microislands, in combination with voltage imaging and methods to classify cell types, will be a powerful method for exploring neuronal function in both healthy and disease states. Additionally, because the entire neuronal network is sampled simultaneously, this strategy has the power to go further, revealing all functional connections between all cell types.

The ability to optically record dynamics of neuronal membrane potential promises to revolutionize our understanding of neurobiology. In this study, we show that the far-red voltage sensitive fluorophore, Berkeley Red Sensor of Transmembrane potential-1, or BeRST 1, can be used to monitor neuronal membrane potential changes across dozens of neurons at a sampling rate of 500 Hz. Notably, voltage imaging with BeRST 1 can be implemented with affordable, commercially available illumination sources, optics, and detectors. BeRST 1 is well-tolerated in cultures of rat hippocampal neurons and provides exceptional optical recording fidelity, as judged by dual fluorescence imaging and patch-clamp electrophysiology. We developed a semi-automated spike-picking program to reduce user bias when calling action potentials and used this in conjunction with BeRST 1 to develop an optical spike and connectivity analysis (OSCA) for high-throughput dissection of neuronal activity dynamics. The high temporal resolution of BeRST 1 enables dissection of firing rate changes in response to acute, pharmacological interventions with commonly used inhibitors like gabazine and picrotoxin. Over longer periods of time, BeRST 1 also tracks chronic perturbations to neurons exposed to amyloid beta 1–42 (Aβ 1–42 ), revealing modest changes to spiking frequency but profound changes to overall network connectivity. Finally, we use OSCA to track changes in neuronal connectivity during maturation in culture, providing a functional readout of network assembly. We envision that use of BeRST 1 and OSCA described here will be of use to the broad neuroscience community.

This study level process design represents an economically viable method for extracting thorium dioxide and other rare earth elements from monazite ore. This paper incorporates results from the 2019 capstone project from the honors Design Internship in Green Engineering in Chemical and Biomolecular Engineering. In this activity, senior students in Chemical Engineering at the University of Tennessee (UT) focused on the development and study of a process for the recovery of thorium dioxide and P2O5 from monazite. While not mandated, the process offers rare earth oxides as attractive byproducts. The project focused on recovery of byproducts rather than the creation or addition to waste streams. Additionally, (1) the process economics relied heavily on recovery of rare earth byproducts, (2) thorium handling portions of the process could be effectively segregated from rare earth and phosphate handling portions of the process, and (3) thorium and uranium content of waste streams should be carefully managed and eliminated where possible.