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Protic amine/acid mixtures as solvents for the extraction of aqueous zinc salts: A mechanistic study
In this work, mixtures based on trihexylamine and cyclic carboxylic acids (aromatic and non-aromatic) were used as solvents for the extraction of zinc salts from aqueous phases via liquid–liquid extractions. The anions of the zinc salts were chosen to represent a range of kosmo-/chaotropic characters, and their influence on the extractions was observed. The extraction studies were supplemented by investigation of local liquid structure through small-angle x-ray scattering (SAXS). The results indicate that extraction is strongly influenced by the Hofmeister effect, but the local liquid structure appears insensitive to anion kosmo-/chaotropic character. In contrast to similar extraction studies, the strength of the Hofmeister effect did not change according to the composition of the mixtures.
Hydrophobic amine-based binary mixtures of active pharmaceutical and food grade ingredients: characterization and application in indium extraction from aqueous hydrochloric acid media
The wide spread use of hazardous and expensive solvents for the liquid-liquid extraction (LLE) of critical metals has been a growing source of waste in the metal refinement industry. We have developed and characterized room temperature liquid hydrophobic binary mixtures based on common pharmaceutical and food grade compounds as sustainable, cost effective alternatives to both ionic liquids and conventional solvents. Additionally, we introduce liquid mixtures with Proton Sponge® (1,8-bis(dimethylamino)naphthalene), one of the strongest known organic bases. These mixtures have been applied to the LLE of indium(III) ions from hydrochloric acid solutions, displaying an extraction efficiency greater than 99% in some systems. Here, a systematic approach to identifying the underlying mechanism of extraction, in particular relating to the charge, solubility, and complexation of the indium species in the organic phase has been developed.
Amphiphile Organization in Organic Solutions: An Alternative Explanation for Small-Angle X-ray Scattering Features in Malonamide/Alkane Mixtures
In this work, the role of different intermolecular interactions in the aggregation of amphiphiles in an organic solvent is studied for systems of relevance to liquid-liquid extraction (LLE), a chemical process used to selectively recover metals from complex mixtures. Of specific interest is the role, or lack thereof, of hydrogen bonding, which is often assumed to be a main driver of the organic phase structural organization that has been linked to separation efficacy. Toward that end, a series of malonamide extractants in n-dodecane have been studied in the absence of any extracted aqueous solutes, including water. The series of extractants includes N,N'-dimethyl-N,N'-dibutyltetradecylmalonamide (DMDBTDMA), two of its homologs, and N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA). This simplified model LLE system enables systematic investigation of the role of dipole-dipole and alkyl tail steric interactions in amphiphile aggregation. Small-angle X-ray scattering (SAXS) profiles computed from molecular dynamics trajectories are in good agreement with experimental SAXS data. Molecular dynamics simulations show that malonamide aggregation results from dipole-driven self-association and lacks characteristic aggregate sizes. Mid-q correlation peaks in the SAXS profiles emerge at high concentration for each malonamide. In those densely packed solutions, the correlation peaks are observed to result from alkyl tail-induced spacing between electron-rich polar head groups, with peak positions determined by the different alkyl tail lengths present in the malonamide molecule. This explanation of the SAXS correlation peaks contrasts with the prevailing literature, which attributes mesoscale features observed in small-angle scattering to the formation of microemulsions. Instead, this work finds that these features are present in the absence of water or any reverse micellar organization of the malonamides. As such, molecular-scale malonamide self-association and packing, rather than microemulsion-based colloidal-scale descriptions, is a more appropriate framework for these LLE systems.
Extracted Water Induces Concentration Fluctuations in Model Ternary Liquid–Liquid Extraction System
Organic phase aggregation and phase splitting are two important (and connected) phenomena in liquid–liquid extraction of metal ions. Previously, we demonstrated how structure in binary mixtures of extractant and diluent originates from concentration fluctuations associated with the so-called “third-phase formation” liquid–liquid phase instability. For more complex systems, we sought to understand how extracted aqueous components affect these concentration fluctuations. Here, in this study, we use small-angle X-ray scattering and molecular dynamics simulations to investigate organic phase structural changes upon contact with water in a model ternary system of water/alkane/extractant. Critical exponents were determined from scattering with temperature variation and were consistent with mean field values. Then, by controlling the water content in the organic phase through direct dissolution of fixed quantities at constant temperature, we relate the observed increase in the fluctuation length scale to changes to the spinodal temperature of the third-phase formation phase boundary. We find a roughly linear relationship between water concentration and the spinodal temperature and a similar slope in that relationship for different linear alkane diluents. This suggests that the mechanism by which water extraction impacts the organic phase structure is to enhance concentration fluctuations through the introduction of additional polar extractant-water complexes, which increases the spinodal temperature and thereby decreases the reduced temperature, i.e., the distance to the instability. This explanation for how solutes induce aggregation in liquid–liquid extraction organic phases may extend to more complex systems, explaining the large increases in correlation lengths reported under high acid and metal loading.
Analyzing the upscaling potential and geospatial siting of calcination-free calcium hydroxide production in the United States
This study evaluates the techno-economic feasibility and the embodied carbon dioxide intensity (eCI) of a novel process for producing nominally pure (>95 mass %) calcium hydroxide without the need for the thermal calcination of limestone. The process relies on the aqueous extraction of calcium from alkaline industrial wastes following which portlandite (Ca(OH) 2 : CH, a.k.a. slaked lime or hydrated lime) is precipitated by application of a waste-heat based thermal swing. This approach takes advantage of the temperature dependent solubility of CH at ambient pressure. We evaluated the feasibility of implementing this process in the U.S. based on the geospatial availability of waste heat and slags as a Ca-source. For the base case, the cost of production of “Low-Temperature Portlandite (LTP)” is 2-to-3 times that of traditional portlandite (~$180/tonne). The main driver of cost is the electricity demand for reverse osmosis (RO) which is used to concentrate Ca-ions in solution, and the costs of membrane replacement. Our sensitivity analysis showed that parity with the cost of production of traditional portlandite is readily achievable by selecting membranes with better durability (i.e., better pH resistance) and flux (i.e., higher permeability) without sacrificing selectivity. Significantly, LTP features an eCI that is between 40%- and - 80 % lower than its traditional counterpart when electricity is sourced from natural gas combustion or wind power, respectively. Finally, our geospatial analysis reveals that there are three areas in the U.S. with the potential for implementation of industrial-scale facilities that could produce at least 50 tonnes of pure Ca(OH) 2 per day, while achieving a production cost of ~$270 per tonne of Ca(OH) 2 , owing to the proximity between slag feedstocks and waste heat sources.
U(VI) binding onto electrospun polymers functionalized with phosphonate surfactants
We previously observed that phosphonate functionalized electrospun nanofibers can uptake U(VI), making them promising materials for sensing and water treatment applications. Here, we investigate the optimal fabrication of these materials and their mechanism of U(VI) binding under the influence of environmentally relevant ions (e.g., Ca 2+ and CO 3 2- ). We found that U(VI) uptake was greatest on polyacrylonitrile (PAN) functionalized with longer-chain phosphonate surfactants (e.g., hexa- and octadecyl phosphonate; HDPA and ODPA, respectively), which were better retained in the nanofiber after surface segregation. Subsequent uptake experiments to better understand specific solid-liquid interfacial interactions were carried out using 5 mg of HDPA-functionalized PAN mats with 10 μM U at pH 6.8 in four systems with different combinations of solutions containing 5 mM calcium (Ca 2+ ) and 5 mM bicarbonate (HCO 3 -). U uptake was similar in control solutions containing no Ca 2+ and HCO 3 - (resulting in 19 ± 3% U uptake), and in those containing only 5 mM Ca2+ (resulting in 20 ± 3% U uptake). A decrease in U uptake (10 ± 4% U uptake) was observed in experiments with HCO 3 -, indicating that UO 2 -CO 3 complexes may increase uranium solubility. Results from shell-by-shell EXAFS fitting, aqueous extractions, and surface-enhanced Raman scattering (SERS) indicate that U is bound to phosphonate as a monodentate inner sphere surface complex to one of the hydroxyls in the phosphonate functional groups. New knowledge derived from this study on material fabrication and solid-liquid interfacial interactions will help to advance technologies for use in the in-situ detection and treatment of U in water.
Understanding the Influence of Water-Soluble Compounds from Unpretreated Corn Stover Pellets on Enzymatic Hydrolysis of Cellulose
Aqueous extractives are minor and non-structural compounds in biomass that can be extracted using solvents, while contributing significantly to lignocellulose characteristics. Yet their roles in enzyme-mediated processing of lignocellulosic biomass remain elusive. Here, we examine the composition and features of extractives derived from untreated pelleted corn stover as well as their effects on enzymatic hydrolysis. Unlike the observations described in previous reports, we find that water extractable material improves the enzymatic hydrolysis of extractive-free stover by 67% with a glucose yield increase from 12% to 20% with 6 FPU cellulase per g glucan, whereas the enzyme activities are diminished when using microcrystalline cellulose as a substrate. The different behavior of corn stover and microcrystalline cellulose is likely attributed to the presence of lignin, which may interact with inhibitory compounds such as phenolics, mitigating the detrimental impacts of soluble inhibitors or insoluble lignin or both. These findings advance our fundamental understanding of the intrinsic behavior of extractives and help to optimize the schemes for efficient and cost-competitive enzymatic conversion of lignocellulose.
Nanoscale Critical Phenomena in a Complex Fluid Studied by X-ray Photon Correlation Spectroscopy.
The advent of high-speed x-ray photon correlation spectroscopy now allows the study of critical phenomena in fluids to much smaller length scales and over a wider range of temperatures than is possible with dynamic light scattering. We present an x-ray photon correlation spectroscopy study of critical fluctuation dynamics in a complex fluid typical of those used in liquid-liquid extraction (LLE) of ions,dodecane-DMDBTDMA with extracted aqueous Ce(NO 3 ) 3 . We observe good agreement with both staticand dynamic scaling without the need for significant noncritical background corrections. Critical exponents agree with 3D Ising values, and the fluctuation dynamics are described by simple exponential relaxation.The form of the dynamic master curve deviates somewhat from the Kawasaki result, with a more abrupt transition between the critical and noncritical asymptotic behavior. The concepts of critical phenomena thus provide a quantitative framework for understanding the structure and dynamics of LLE systems and a path forward to new LLE processes.
Lipophilic diglycolamide compounds for extraction of rare earth metals from aqueous solutions
A method for extracting rare earth metals (e.g., lanthanides and/or actinides) from aqueous solution, the method comprising: (i) acidifying an aqueous solution containing said rare earth metals with sulfuric acid to result in an acidified aqueous solution containing 1-12 M concentration of sulfuric acid; and (ii) contacting the acidified aqueous solution with an aqueous-insoluble hydrophobic solution comprising a rare earth extractant molecule dissolved in an aqueous-insoluble hydrophobic solvent to result in extraction of one or more of the rare earth metals into the aqueous hydrophobic solution, wherein the rare earth extractant molecule has the following structure: wherein R1, R2, R3, and R4 are independently selected from hydrocarbon groups containing 1-20 carbon atoms, provided that the total carbon atoms in R1, R2, R3, and R4 is at least 12; and R5 and R6 are independently selected from hydrogen atom and hydrocarbon groups containing 1-3 carbon atoms.
Fast extraction of nickel from aqueous media by using ionic metal-organic frameworks
As global demand for stainless steel rapidly increases, supply for minerals such as nickel, manganese, and chromium become more critical. To shift mineral peak production and delay scarcity of alloying minerals, recycling rate of the mineral needs to increase. Development of simple and cost-effective techniques for critical mineral production and recovery from industrial wastewater will lead to enhance the current recycling rate of the mineral and reduce potential hazards of industrial wastewater bearing high concentrations of minerals. Here, in this study, ionic metal-organic framework (iMOF)-based sorbents are successfully designed for critical metal ion extraction from aqueous solution. The iMOFs are highly stable in aqueous solution over wide pH ranges, indicating that they are suitable for use in industrial wastewater with harsh chemical environments. The sorption capacity of iMOFs towards Ni reaches 34.1 mg/g with a removal efficiency of >99.9%. Notably, complete extraction of Ni takes place within 5 min, which is much faster compared to other sorbents. Moreover, the iMOFs can simultaneously coextract multiple minerals, proving their effectiveness as general sorbents for critical mineral recovery.
Effect of hydrophobic ionic liquids aqueous solubility on metal extraction from hydrochloric acid media: Mathematical modelling and trivalent thallium behavior
A mathematical model to explain cations’ solubility of both protic and aprotic ionic liquids in a wide range of hydrochloric acid solutions has been developed. The concept of this model is based on an assumption of the mineral acid extraction into the organic phase, formation of a salt there between an ionic liquid cation and chloride-anion due to ions recombination and partial salt back-extraction. The proposed approach allows estimating corresponding extraction constants. Comparison of calculated and experimentally measured solubility product constants shows that they are in good agreement. It has been determined also that the more the hydrophilicity of the ionic liquids’ cation the more hydrochloric acid is extracted. Furthermore, this model has been utilized to facilitate analysis of thallium transfer into hydrophobic ionic liquids providing insights into the mechanism of metal extraction.
Aryl Diazonium-Assisted Amidoximation of MXene for Boosting Water Stability and Uranyl Sequestration via Electrochemical Sorption
Despite that two-dimensional transition metal carbides and carbonitrides (MXenes) are burgeoning candidates for remediation of environmental pollutants, the construction of robust functionalized MXene nanosheets with a high affinity for target heavy metal ions and radionuclides remains a challenge. Here we report the successful placement of amidoxime chelating groups on Ti 3 C 2 T x MXene surface by diazonium salt grafting. The introduction of amidoxime functional groups significantly enhances the selectivity of Ti 3 C 2 T x nanosheets for uranyl ions and also greatly improves their stability in aqueous solution, enabling efficient, rapid, and recyclable uranium extraction from aqueous solutions containing competitive metal ions. Benefiting from the excellent conductivity of MXenes, the amidoxime functionalized Ti 3 C 2 T x nanosheets show outstanding electrochemical performance such that when loaded on carbon cloth the application of an electric field increases the uranium adsorption capacity from 294 to 626 mg/g, outperforming all organic electrochemical sorption materials reported previously. Finally, the present work provides an effective strategy to functionalize MXene nanosheets with fundamental implications for the design of MXene-based selective electrosorption electrode materials.
Sorption of rare-earth elements onto a ligand-associated media for pH-dependent extraction and recovery of critical materials
Toward recovering rare-earth elements, we prepared a solid-phase media that binds and elutes metals for extraction and enrichment. We report the synthesis and methodology for a solid-phase media that exhibits pH-dependent binding of aqueous rare-earth elements. The media shows pH-dependent binding of Nd III and retains efficiency over at least six cycles of binding and elution. Mixed solutions of rare-earth elements demonstrated a preference for mid and heavy rare-earth elements based on thermodynamic binding preferences of the ligand, and selectivity for rare-earth elements over iron and aluminum were observed with coal fly ash leachate. In conclusion, we expect this new recovery method to be a significant step towards aqueous-based extraction and enrichment of critically important rare-earth elements.
Recovery of High Purity Rare Earth Elements (REE) from Coal Ash via a Novel Electrowinning Process (Final Report)
The goal of this project was to produce a high purity, separated (>90%) rare earth oxide (REO) product from coal-based sources. This product was achieved using the following three steps: 1. Battelle’s ADP: The ADP process involves pretreatment of ash (milling and caustic leaching), leaching of pretreated ash with nitric acid, roasting of loaded acid solution containing REE, and water leaching of residual from roasting step, resulting in a REE pregnant solution. 2. Solvent Extraction (SX) Upgrading: The SX involves the extraction of REE from a pregnant REE solution using an organic extractant (note after extraction, the aqueous phase was a residual solution and the organic phase contained REE), and stripping of REE from the organic phase product obtained from the extraction using an acid solution (the stripped solution was the final purified product containing REE, organic traces, and traces of other metals for further separation in the electrowinning process). 3. Rare Earth Salts’ (RES) Electrochemical Separation and Purification Process: The staged electrochemical process was separated REO products from the mixed REE solution. Testing by RES was also included in the investigation of options to minimize the solvent extraction steps. This report covers laboratory testing, production of a high purity coal-based REO, process design of the overall REE recovery and purification process, technoeconomic assessment (TEA), and a commercialization plan discussing the overall REE recovery and purification process.
Structural analyses of amorphous calcium carbonate before and after removing strontium ions from an aqueous solution
Amorphous calcium carbonate (ACC) is a precursor of crystalline calcium carbonate; hence, its structural information at the atomic level is very important for controlling the morphology of crystalline calcium carbonate. In this study, we attempted to elucidate the process of Sr extraction from aqueous solution by using ACC for the purpose of removal of radioactive Sr from the contaminated water leaked after the Fukushima Daiichi nuclear accident. Here, the pair distribution functions, g(r) obtained by X-ray and neutron diffraction (ND) measurements show that ACC has a structure partially similar to that of monohydrocalcite, suggesting that ACC is transferred to the crystalline calcium carbonate starting from its crystal nucleus. Rietveld analysis of the ND data showed that the ACC that removed Sr was crystallized to calcite. However, the Sr–O coordination analyzed using extended X-ray absorption fine structure (EXAFS) implies that the local environment of O around Sr is similar to that in crystalline calcium carbonate aragonite.
Toward Lithium Recovery Using Modular (and Membraneless) Phase Separation and Extraction (MPSE) Technology with Ionic Liquid (IL) Solvents: Effect of Coatings
In this work, a single-channel slope-plate Modular and Membrane-less Phase Separation and Extraction (MPSE) device was fabricated using 3D printing. The slope-plate was designed with an insertable glass slide to enable surface modification with coatings. Self-assembled monolayers (SAMs) and perfluoropolyether (Zdol) coatings were applied to tailor surface wettability and enhance phase separation. Using a model biphasic system of water and hexadecane, both coatings significantly improved the separation efficiency compared to the uncoated device by promoting selective wetting. Building on these results, lithium extraction from a simulated saline solution was investigated using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf₂]) as the ionic liquid (IL) extractant. The IL effectively extracted Li⁺ from the aqueous phase in bulk extraction, demonstrating its potential for lithium recovery. However, the low interfacial tension between the IL and aqueous phases posed challenges for phase separation. The application of SAM and Zdol coatings effectively mitigated this issue. Overall, integrating tailored surface chemistry with the slope-plate MPSE design shows great promise as an efficient and scalable platform for studying liquid–liquid separation and optimizing ionic liquid–based extraction processes for lithium recovery from saline sources.
New directions and principles for solvent extraction for recovery of lithium from aqueous brines and mineral leachates: A brief review
Increasing demand for lithium for manufacturing of batteries is fueling the unprecedented search for improved recovery and alternative sources. Wider source distribution, lower energy consumption, and greater sustainability make extraction of lithium from brines, both natural and process-derived, an attractive alternative to mineral ores. Solvent extraction, used industrially for production of metals, salts, and pharmaceuticals, has been investigated as a methodology for lithium recovery for several decades. However, industrial application of solvent extraction for lithium recovery has so far been limited. In contrast, direct lithium extraction using adsorbents based on inorganic minerals has rapidly advanced from research to commercialization. A comparison of solvent extraction processes to adsorption highlights these issues and explains the preference for adsorbents. Although the application of solvent extraction has been criticized for use of large amounts of acid, alkali, and organic solvents, steady progress has been made to improve its potential for industrial lithium production, spurred on generally by the advantages of solvent extraction in selectivity and throughput. Previously developed beta-diketone, organophosphate, and crown ether ligands are being adapted and improved. Their novel use with ionic liquids, deep eutectic solvents, and membrane technologies promises to expand capabilities for extraction of lithium from dilute aqueous sources while improving sustainability. Possibilities for further discovery and innovation abound. In this review, we provide a unique perspective from the field of solvent extraction starting with fundamentals such as ion-transfer theory and apply them to understanding lithium selectivity and extraction behavior. In conclusion, the results are cast in the light of the practical realities of developing economical solvent extraction processes.