Mining Critical Metals and Elements from Seawater: Opportunities and Challenges

A new suggestion to marine gold extraction: Utilizing reduced graphene oxide membranes within seawater desalination processes

Traditional mining practices not only cause severe environmental issues, but also face the problem of insufficient production capacity of gold to meet its growing demand. The proposed alternative strategies for gold production, such as the extraction of gold from seawater, still keep a formidable challenge due to their strong dependence on adsorbent materials with high capacity, selectivity, and sensitivity, while also needing to meet the demands of being environmentally friendly and cost-effective. In practice, the direct extraction of gold from seawater is limited by its extremely low yield and high energy expenditure. However, if the combination of gold extraction techniques with seawater desalination can substantially reduce the energy consumption, the extraction of gold from seawater will become economical and feasible. In this paper, we evaluate the feasibility of marine gold extraction using reduced graphene oxide membranes (rGOM) during the seawater desalination process. The rGOM can adsorb almost all Au3+ from the solutions with trace concentrations of Au3+ ranging from 10 ppb to 200 ppb. The adsorption quantity is linearly related to the concentration, indicating that the adsorption capacity of rGOM is much higher than the total amount of Au3+ in the solution. Additionally, the rGOM can selectively adsorb 99 % of Au3+ in the mixed solution while hardly adsorbing other common elements in seawater. More importantly, the rGOM exhibits the long-term stability over 30 days when being immersed in the solution, making it directly compatible with the existing seawater desalination processes. These specific properties allow the rGOM to be an ideal candidate for combining the extraction of gold from seawater with seawater desalination processes. Our findings provide a methodology for enhancing the economic efficiency of the extraction of gold from seawater and hold promise for addressing the problem of gold scarcity.

Critical mineral source potential from oil & gas produced waters in the United States

The volume of produced water, a by-product of oil & gas operations and other energy processes, has been growing across the United States (U.S.) along with the need to manage or recycle this wastewater. Produced water contains many naturally occurring elements of varying concentrations, including critical minerals which are essential to the clean energy transition. However, the current understanding of critical mineral concentrations in produced water and the associated volumes across the U.S. is limited. This study has assessed available databases and literature to gain insight into the presence and concentration of five high priority critical minerals, namely cobalt, lithium, magnesium, manganese, and nickel. The U.S. Geological Survey's National Produced Waters Geochemical Database was the main data source used for determining average critical mineral concentrations in produced water from the major oil and gas reservoirs in the U.S. The volumes of produced water for these major reservoirs were coupled with these concentrations to provide insights into where critical minerals are likely to have high abundance and therefore more recovery options. The analysis indicated the highest recovery potential for lithium and magnesium from produced water in the Permian basin and the Marcellus shale region. However, these assessments should be considered conservative due to the limited availability of reliable concentration data. It is expected more critical mineral recovery options could emerge with comprehensive characterization data from more recent and representative sources of produced water.

Microbial Catalysis for CO2 Sequestration: A Geobiological Approach

One of the greatest threats facing the planet is the continued increase in excess greenhouse gasses, with CO2 being the primary driver due to its rapid increase in only a century. Excess CO2 is exacerbating known climate tipping points that will have cascading local and global effects including loss of biodiversity, global warming, and climate migration. However, global reduction of CO2 emissions is not enough. Carbon dioxide removal (CDR) will also be needed to avoid the catastrophic effects of global warming. Although the drawdown and storage of CO2 occur naturally via the coupling of the silicate and carbonate cycles, they operate over geological timescales (thousands of years). Here, we suggest that microbes can be used to accelerate this process, perhaps by orders of magnitude, while simultaneously producing potentially valuable by-products. This could provide both a sustainable pathway for global drawdown of CO2 and an environmentally benign biosynthesis of materials. We discuss several different approaches, all of which involve enhancing the rate of silicate weathering. We use the silicate mineral olivine as a case study because of its favorable weathering properties, global abundance, and growing interest in CDR applications. Extensive research is needed to determine both the upper limit of the rate of silicate dissolution and its potential to economically scale to draw down significant amounts (Mt/Gt) of CO2 Other industrial processes have successfully cultivated microbial consortia to provide valuable services at scale (e.g., wastewater treatment, anaerobic digestion, fermentation), and we argue that similar economies of scale could be achieved from this research.

All-Solid-State Supercapacitors Based on Cobalt Magnesium Telluride Microtubes Decorated with Tellurium Nanotubes

Magnesium (Mg) has received very little exploration on its importance in the realm of battery-type energy storage technologies. They are abundantly present in seawater, and if successfully extracted and utilized in energy storage systems, it could lead to the long-term advancement of human civilization. Here, we fabricated an all-solid-state supercapacitor (ASSSC) using tellurium nanotubes decorated cobalt magnesium telluride microtubes (Te NTs@CoMgTe MTs) clad on nickel foam (NF). Owing to the unique mixed phase hierarchical structure, Te NTs@CoMgTe MTs showcases some advancement in energy storage performance. When tested in a three-electrode system, multiphasic hybrid of elemental Te and metal tellurides, Te NTs@CoMgTe MTs outperforms the monometallic telluride owing to the strong synergistic interaction effect triggered from conductive three components and delivers a long-life span performance up to 15,000 cycles. The fabricated Te NT@CoMgTe MT//AC solid-state device exhibits a maximum areal capacity of 59.2 μAh cm-2 (56.3 mAh g-1) at a current density of 6 mA cm-2 with a maximum energy density of 42.2 Wh kg-1 (46.5 μWh cm-2) at a power density of 6857.1 W kg-1 (7574.6 μW cm-2). The performance of the device is rigid even at different bending angles (0 to 180°) which validates the extensibility of the process for future applications.

Predicting Ion Sequestration in Charged Polymers with the Steepest-Entropy-Ascent Quantum Thermodynamic Framework

The steepest-entropy-ascent quantum thermodynamic framework is used to investigate the effectiveness of multi-chain polyethyleneimine-methylenephosphonic acid in sequestering rare-earth ions (Eu3+) from aqueous solutions. The framework applies a thermodynamic equation of motion to a discrete energy eigenstructure to model the binding kinetics of europium ions to reactive sites of the polymer chains. The energy eigenstructure is generated using a non-Markovian Monte Carlo model that estimates energy level degeneracies. The equation of motion is used to determine the occupation probability of each energy level, describing the unique path through thermodynamic state space by which the polymer system sequesters rare-earth ions from solution. A second Monte Carlo simulation is conducted to relate the kinetic path in state space to physical descriptors associated with the polymer, including the radius of gyration, tortuosity, and Eu-neighbor distribution functions. These descriptors are used to visualize the evolution of the polymer during the sequestration process. The fraction of sequestered Eu3+ ions depends upon the total energy of the system, with lower energy resulting in greater sequestration. The kinetics of the overall sequestration are dependent on the steepest-entropy-ascent principle used by the equation of motion to generate a unique kinetic path from an initial non-equilibrium state.

Metal Recovery from Natural Saline Brines with an Electrochemical Ion Pumping Method Using Hexacyanoferrate Materials as Electrodes

The electrochemical ion pumping device is a promising alternative for the development of the industry of recovering metals from natural sources-such as seawater, geothermal water, well brine, or reverse osmosis brine-using electrochemical systems, which is considered a non-evaporative process. This technology is potentially used for metals like Li, Cu, Ca, Mg, Na, K, Sr, and others that are mostly obtained from natural brine sources through a combination of pumping, solar evaporation, and solvent extraction steps. As the future demand for metals for the electronic industry increases, new forms of marine mining processing alternatives are being implemented. Unfortunately, both land and marine mining, such as off-shore and deep sea types, have great potential for severe environmental disruption. In this context, a green alternative is the mixing entropy battery, which is a promising technique whereby the ions are captured from a saline natural source and released into a recovery solution with low ionic force using intercalation materials such as Prussian Blue Analogue (PBA) to store cations inside its crystal structure. This new technique, called "electrochemical ion pumping", has been proposed for water desalination, lithium concentration, and blue energy recovery using the difference in salt concentration. The raw material for this technology is a saline solution containing ions of interest, such as seawater, natural brines, or industrial waste. In particular, six main ions of interest-Na+, K+, Mg2+, Ca2+, Cl-, and SO42--are found in seawater, and they constitute 99.5% of the world's total dissolved salts. This manuscript provides relevant information about this new non-evaporative process for recovering metals from aqueous salty solutions using hexacianometals such as CuHCF, NiHCF, and CoHCF as electrodes, among others, for selective ion removal.

Material Design Strategies for Recovery of Critical Resources from Water

Population growth, urbanization, and decarbonization efforts are collectively straining the supply of limited resources that are necessary to produce batteries, electronics, chemicals, fertilizers, and other important products. Securing the supply chains of these critical resources via the development of separation technologies for their recovery represents a major global challenge to ensure stability and security. Surface water, groundwater, and wastewater are emerging as potential new sources to bolster these supply chains. Recently, a variety of material-based technologies have been developed and employed for separations and resource recovery in water. Judicious selection and design of these materials to tune their properties for targeting specific solutes is central to realizing the potential of water as a source for critical resources. Here, the materials that are developed for membranes, sorbents, catalysts, electrodes, and interfacial solar steam generators that demonstrate promise for applications in critical resource recovery are reviewed. In addition, a critical perspective is offered on the grand challenges and key research directions that need to be addressed to improve their practical viability.

Freeze desalination: Current research development and future prospects

Desalination is the solution for water security in regions with insufficient resources. This comes at high energy cost and hence improving desalination technologies translate into huge saving. Freeze desalination (FD) is emerging as an attractive low energy and less corrosion alternative to provide the needed fresh water. The maturity of the heat driven cooling technology and solar cooling have given freeze desalination an additional momentum. This paper summarizes the latest research progress done on FD that continues to push this technology towards deployment. It gives an overview of the FD configurations and highlighting its pros and cons, presents the recent experimental work that investigate the physics of the technology, and reviews the latest high-fidelity numerical modeling of brine freezing and salt diffusion away from crystal lattice which taps on the advanced development in computational power and multiphysics integration. This enables one to identify the challenges facing FD technology and stating the prospect and foreseeable research. The finding suggests that direct and indirect FD have been evolved well while the indirect is becoming the mainstream method for risk avoidance, while vacuum freezing and eutectic freezing are still facing large obstacles in their application. For direct FD, gas hydrate combined with liquefied natural gas (LNG) regasification has been popular topics to reduce their desalination cost. Simulation and modeling development in indirect FD continue to improve the knowledge of the mechanism of ice growth and salt entrapment which are key problems that need further experimental and numerical investigations. Nonetheless, the current successful application of LNG cold energy in freeze desalination, the hybridization of FD with conventional desalination technologies, as well as ultrasound assisted freezing are promising directions for FD commercialization.

Recent Advances in Lithium Extraction Using Electrode Materials of Li-Ion Battery from Brine/Seawater

With the rapid development of industry, the demand for lithium resources is increasing. Traditional methods such as precipitation usually take 1–2 years, and depend on weather conditions. In addition, electrochemical lithium recovery (ELR) as a green chemical method has attracted a great deal of attention. Herein, we summarize the systems of electrochemical lithium extraction and the electrode materials of the Li-ion battery from brine/seawater. Some representative work on electrochemical lithium extraction is then introduced. Finally, we prospect the future opportunities and challenges of electrochemical lithium extraction. In all, this review explores electrochemical lithium extraction from brine/seawater in depth, with special attention to the systems and electrode of electrochemical lithium extraction, which could provide a useful guidance for reasonable electrochemical-lithium-extraction.

Electrodialysis with Bipolar Membranes for the Generation of NaOH and HCl Solutions from Brines: An Inter-Laboratory Evaluation of Thin and Ultrathin Non-Woven Cloth-Based Ion-Exchange Membranes

The SEArcularMINE project aims to recover critical raw materials (CRMs) from brines from saltworks, thus facing a CRM shortage within Europe. To promote a fully circular scheme, the project valorises concentrated brines using electrodialysis with bipolar membranes (EDBM) to generate the required amounts of reactants (i.e., acids and bases). Regarding the performances of new non-woven cloth ion-exchange membranes (Suez): (i) an ultra-thin non-woven polyester cloth and (ii) a thin polypropylene cloth acting as the support structures were assessed. Additionally, the anion layer includes a catalyst to promote the water dissociation reaction. The effect of current density (100, 200, and 300 A m^-2) on the performance of two combinations of membranes in an inter-laboratory exercise using 2 M NaCl was evaluated. According to statistical analysis ANOVA, there was an agreement on the results obtained in both laboratories. NaOH/HCl solutions up to 0.8 M were generated working at 300 A m^-2 using both combinations of membranes. Regarding the performance parameters, stack set-ups incorporating thin polypropylene membranes showed lower specific energy consumption (SEC) and higher specific productivity (SP) than ultra-thin polypropylene ones. Hence, for ultra-thin polypropylene membranes, SEC was reported to be between 2.18 and 1.69 kWh kg^-1_NaOH and SP between 974 and 314 kg m^-2 y^-1.

Review: Brine Solution: Current Status, Future Management and Technology Development

Desalination brine is extremely concentrated saline water; it contains various salts, nutrients, heavy metals, organic contaminants, and microbial contaminants. Conventional disposal of desalination brine has negative impacts on natural and marine ecosystems that increase the levels of toxicity and salinity. These issues demand the development of brine management technologies that can lead to zero liquid discharge. Brine management can be productive by adopting economically feasible methodologies, which enables the recovery of valuable resources like freshwater, minerals, and energy. This review focuses on the recent advances in brine management using various membrane/thermal-based technologies and their applicability in water, mineral, and energy recoveries, considering their pros and cons. This review also exemplifies the hybrid processes for metal recovery and zero liquid discharge that may be adopted, so far, as an appropriate futuristic strategy. The data analyzed and outlook presented in this review could definitely contribute to the development of economically achievable future strategies for sustainable brine management.

Sequestering Rare Earth Elements and Precious Metals from Seawater Using a Highly Efficient Polymer Adsorbent Derived from Acrylic Fiber

An amidoxime and carboxylate containing polymer adsorbent derived from acrylic fiber has shown extremely high efficiencies for extracting critical materials and precious metals from seawater. Among 50 extractable elements, the lanthanides, cobalt, and palladium were ranked near the top with KD values in the order of 107, about an order of magnitude higher than that of uranium. The KD value of the lanthanides increased linearly with the atomic number indicating charge density is a factor controlling trivalent lanthanide extractability in seawater. The data given in this report provides crucial information regarding the strategies of ocean mining of critical materials and precious metals.

Mining Critical Metals from Seawater by Subnanostructured Membranes: Is It Viable?

The continuous demand for energy-critical elements such as lithium, cobalt, uranium and so on will soon exceed their availability increasing further their significance of geopolitical resources. Seawater is a relevant, not conventional source of critical metals. Synthetic membranes with subnanometer pores are the core of processes such as desalination for separating solutes from water. These membrane processes have achieved remarkable success at industrial level. However, state-of-the-art desalination membranes cannot selectively separate a single metal ion from a mixture of ions. In this review the challenges of membranes with subnanometer pores to selectivity discriminate among different metal ions are briefly discussed. The key points of the molecular-level mechanism that contribute to energy barrier for ions transport through subnanometer pores are highlighted to provide guidelines for the design of single-metal ion selective membranes.

From mine to mind and mobiles - Lithium contamination and its risk management

With the ever-increasing demand for lithium (Li) for portable energy storage devices, there is a global concern associated with environmental contamination of Li, via the production, use, and disposal of Li-containing products, including mobile phones and mood-stabilizing drugs. While geogenic Li is sparingly soluble, Li added to soil is one of the most mobile cations in soil, which can leach to groundwater and reach surface water through runoff. Lithium is readily taken up by plants and has relatively high plant accumulation coefficient, albeit the underlying mechanisms have not been well described. Therefore, soil contamination with Li could reach the food chain due to its mobility in surface- and ground-waters and uptake into plants. High environmental Li levels adversely affect the health of humans, animals, and plants. Lithium toxicity can be considerably managed through various remediation approaches such as immobilization using clay-like amendments and/or chelate-enhanced phytoremediation. This review integrates fundamental aspects of Li distribution and behaviour in terrestrial and aquatic environments in an effort to efficiently remediate Li-contaminated ecosystems. As research to date has not provided a clear picture of how the increased production and disposal of Li-based products adversely impact human and ecosystem health, there is an urgent need for further studies on this field.

Recovery of Critical Metals from Aqueous Sources

Critical metals, identified from supply, demand, imports, and market factors, include rare earth elements (REE), platinum group metals, precious metals, and other valuable metals such as lithium, cobalt, nickel, and uranium. Extraction of metals from U.S. saline aqueous, emphasizing saline, sources is explored as an alternative to hardrock ore mining. Potential aqueous sources include seawater, desalination brines, oil-and-gas produced waters, geothermal aquifers, and acid mine drainage, among others. A feasibility assessment reveals opportunities for recovery of lithium, strontium, magnesium, and several REE from select sources, in quantities significant for U.S. manufacturing and for reduction of U.S. reliance on international supply chains. This is a conservative assessment given that water quality data are lacking for a significant number of critical metals in certain sources. The technology landscape for extraction and recovery of critical metals from aqueous sources is explored, identifying relevant processes along with knowledge gaps. Our analysis indicates that aqueous mining would result in much lower environmental impacts on water, air, and land than ore mining. Preliminary assessments of the economics and energy consumption of recovery show potential for recovery of critical metals.

Selective Adsorption of Potassium in Seawater by CoHCF Thin Film Electrode and Its Electrochemical Desorption/Regeneration

Cobalt Hexacyanoferrate (CoHCF) was tested for the selective uptake of K from seawater and the electrochemical method was adopted for the desorption and regeneration of the material. Powder form CoHCF could adsorb about 6.5 mmol/g of K from the seawater. For the ease of the electrochemical desorption and regeneration, CoHCF thin film was coated onto the Indium Tin Oxide (ITO) glass to obtain a CoHCF electrode. K adsorption kinetics on CoHCF thin film was found to be well fitted with the intraparticle diffusion model, which was a two-step process. Five consecutive adsorption-desorption-regeneration cycles were carried out to know the gradual decrease in the adsorption capacity owing to changes in the redox states of two metals, Co and Fe, in the material. Fourier Transform Infrared Spectroscopy (FT-IR) and Ultraviolet-Visible (UV-Vis) measurement results corresponded to the color change of CoHCF thin film, indicating the valence change of transition metals and the exchange of alkali metal cations happened on the CoHCF at different operation stages. In order to elucidate the reaction mechanism, composition of the material was analysis in the following steps: adsorption, desorption, and regeneration. It was proved that the system based on CoHCF thin film modified electrode had the potential of recovering potassium from seawater.

Removal of lithium and uranium from seawater using fly ash and slag generated in the CFBC technology

Fly ash and slag were produced as a result of the incineration of municipal sewage sludge using the circulating fluidized bed combustion (CFBC) technology and were examined for the simultaneous recovery of lithium and uranium from seawater in batch adsorption experiments. These waste materials have been characterized in terms of their physicochemical properties using several research methods including particle size distribution, bulk density, SEM-EDS analysis, thermogravimetry, SEM and TEM morphology, BET, specific surface area, pore volume distribution by the BJH method, ATR FT-IR, and zeta potential. The fly ash and slag waste materials showed the following research results for Li-ion recovery: adsorption efficiency 12.1% and 6.8%, adsorption capacity 0.55 mg g^-1 and 0.15 mg g^-1, respectively. Better results were reported for U ion recovery: adsorption efficiency 98.4% and 99.9%, adsorption capacity 21.3 mg g^-1 and 56.7 mg g^-1 for fly ash and slag, respectively. In conclusion, the conducted research revealed that CFBC fly ash and slag are promising low-cost adsorbents for the effective recovery of Li and U ions from seawater.

An overview of brine management: Emerging desalination technologies, life cycle assessment, and metal recovery methodologies

This study examines which management methods are the most recent and advanced in managing rejected brine generated from desalination plants. It also provides up-to-date information regarding the most adequate technologies that generate a minimum quantity of rejected brine via the use of minimization techniques and analyzes the method of direct disposal that has lately received noticeable improvements. It further discusses the reuse of discarded brine to recover valuable goods and sequestration of carbon dioxide. Sustainability is an important parameter that needs consideration to achieve uninterrupted operation of the discarded brine management to achieve the least environmental, social, and economic aftermath. To properly deal with any environmental issues related to brine disposal, different methods are implemented so that, in the end, higher water recovery is achievable from the desalination processes, namely brine minimization and rejection technologies (pressure retarded osmosis, microbial desalination cell technology), membrane-based technologies (vibratory shear enhanced processing, forward osmosis, electrodialysis, electrodialysis reverse, and electrodialysis metathesis, pervaporation method, thermal-based technologies (wind-aided intensified evaporation, brine concentrators, ohmic evaporator, membrane distillation, multi-stage flash distillation. This review also critically examined the two conventional approaches commonly used in life cycle assessment (LCA), when evaluating the ecotoxic effect of discarded brine. It intends to discuss the currently available methods and propose an improved method for evaluating the toxicity potential of brine on the aquatic ecosystem originated from seawater desalination plants. The Group-by-Group method takes into consideration the demerits of the two methods of the traditional method of LCA or chemical-specific approach as it provides a more holistic coverage for complicated brine to be disposed of. Recently, attention has been focused on recovering valuable metals from the discharged concentrated brine waste. Certainly, attaining marketable products from the discharged concentrated brine would offer an economic benefit and reducing the whole desalination costs. Ion imprinting polymers have potential applications in metal recovery from brine. Finding selective, more efficient, and less expensive imprinted polymers for extraction/pre-concentration of valuable ions is a vital and challenging task. Lastly, the brine should be seen as a resource and not as a waste to attain sustainability in its management approaches. Hybrid processes would be highly recommended to get the absolute transformation of the discarded brine from desalination processes to more valuable constituents.

The Era of Nanomaterials: A Safe Solution or a Risk for Marine Environmental Pollution?

In recent years, the application of engineered nanomaterials (ENMs) in environmental remediation gained increasing attention. Due to their large surface area and high reactivity, ENMs offer the potential for the efficient removal of pollutants from environmental matrices with better performances compared to conventional techniques. However, their fate and safety upon environmental application, which can be associated with their release into the environment, are largely unknown. It is essential to develop systems that can predict ENM interactions with biological systems, their overall environmental and human health impact. Until now, Life-Cycle Assessment (LCA) tools have been employed to investigate ENMs potential environmental impact, from raw material production, design and to their final disposal. However, LCA studies focused on the environmental impact of the production phase lacking information on their environmental impact deriving from in situ employment. A recently developed eco-design framework aimed to fill this knowledge gap by using ecotoxicological tools that allow the assessment of potential hazards posed by ENMs to natural ecosystems and wildlife. In the present review, we illustrate the development of the eco-design framework and review the application of ecotoxicology as a valuable strategy to develop ecosafe ENMs for environmental remediation. Furthermore, we critically describe the currently available ENMs for marine environment remediation and discuss their pros and cons in safe environmental applications together with the need to balance benefits and risks promoting an environmentally safe nanoremediation (ecosafe) for the future.

Extraction of lithium and aluminium from bauxite mine tailings by mixed acid treatment without roasting

Bauxite mine tailings can be used as the reserve resources of aluminium and lithium. In this study, a less energy consumption treatment method for extracting aluminium and lithium from bauxite mine tailings has been proposed, which used mixed acid to leach aluminium and lithium from tailings directly, avoided roasting for reducing energy consumption, and obtained effective results.The minerals in the tailings are kaolinite, diaspore, boehmite, anatase and illite, among others. The minerals have fine dissemination sizes and low liberation. Under the leaching conditions of Al and Li of an acid concentration of 60%, a liquid-solid ratio of 4 mL/g, a reaction temperature of 100 °C and a reaction time of 3 h, the highest leaching rates of Al and Li are 88.64% and 96.35%, respectively. In the leaching process, phosphoric acid reacts with Al and Li in the strong acidic environment provided by sulphuric acid to produce heteropoly acids or heteropoly acid salts that dissolve in the solution.

Enrichment of marine manganese-oxidizing microorganisms using polycaprolactone as a solid organic substrate

OBJECTIVE

Heterotrophic manganese (Mn)-oxidizing microorganisms responsible for biogenic manganese oxide (Bio-MnOx) production are fastidious. Their enrichment is not easily accomplished by merely adding a soluble organic substrate to non-sterile mixed cultures. The objective of this study was to evaluate polycaprolactone (PCL), an aliphatic polyester, as an effective solid organic substrate for the enrichment of marine Mn-oxidizing microorganisms.

RESULTS

We successfully obtained marine microbial enrichment with the capacity for dissolved Mn removal and MnOx production using PCL as a solid organic substrate. The removal of dissolved Mn by the Mn-oxidizing enrichment culture followed first-order kinetics with a rate constant of 0.014 h^-1. 16S rRNA gene amplicon sequencing analysis revealed that the Mn-oxidizing enrichment culture was highly dominated by operational taxonomic units related to the bacterial phyla Cyanobacteria, Planctomycetes, and Proteobacteria.

CONCLUSIONS

Our data demonstrate that PCL can serve as a potential substrate to enrich Mn-oxidizing microorganisms with the ability to produce MnOx under marine conditions.

Integrating biometallurgical recovery of metals with biogenic synthesis of nanoparticles

Industrial activities, such as mining, electroplating, cement production, and metallurgical operations, as well as manufacturing of plastics, fertilizers, pesticides, batteries, dyes or anticorrosive agents, can cause metal contamination in the surrounding environment. This is an acute problem due to the non-biodegradable nature of metal pollutants, their transformation into toxic and carcinogenic compounds, and bioaccumulation through the food chain. At the same time, platinum group metals and rare earth elements are of strong economic interest and their recovery is incentivized. Microbial interaction with metals or metals-bearing minerals can facilitate metals recovery in the form of nanoparticles. Metal nanoparticles are gaining increasing attention due to their unique characteristics and application as antimicrobial and antibiofilm agents, biocatalysts, in targeted drug delivery, for wastewater treatment, and in water electrolysis. Ideally, metal nanoparticles should be homogenous in shape and size, and not toxic to humans or the environment. Microbial synthesis of nanoparticles represents a safe, and environmentally friendly alternative to chemical and physical methods. In this review article, we mainly focus on metal and metal salts nanoparticles synthesized by various microorganisms, such as bacteria, fungi, microalgae, and yeasts, as well as their advantages in biomedical, health, and environmental applications.

Intrapore energy barriers govern ion transport and selectivity of desalination membranes

State-of-the-art desalination membranes exhibit high water-salt selectivity, but their ability to discriminate between ions is limited. Elucidating the fundamental mechanisms underlying ion transport and selectivity in subnanometer pores is therefore imperative for the development of ion-selective membranes. Here, we compare the overall energy barrier for salt transport and energy barriers for individual ion transport, showing that cations and anions traverse the membrane pore in an independent manner. Supported by density functional theory simulations, we demonstrate that electrostatic interactions between permeating counterion and fixed charges on the membrane substantially hinder intrapore diffusion. Furthermore, using quartz crystal microbalance, we break down the contributions of partitioning at the pore mouth and intrapore diffusion to the overall energy barrier for salt transport. Overall, our results indicate that intrapore diffusion governs salt transport through subnanometer pores due to ion-pore wall interactions, providing the scientific base for the design of membranes with high ion-ion selectivity.

Forward Osmosis as Concentration Process: Review of Opportunities and Challenges

In the past few years, osmotic membrane systems, such as forward osmosis (FO), have gained popularity as "soft" concentration processes. FO has unique properties by combining high rejection rate and low fouling propensity and can be operated without significant pressure or temperature gradient, and therefore can be considered as a potential candidate for a broad range of concentration applications where current technologies still suffer from critical limitations. This review extensively compiles and critically assesses recent considerations of FO as a concentration process for applications, including food and beverages, organics value added compounds, water reuse and nutrients recovery, treatment of waste streams and brine management. Specific requirements for the concentration process regarding the evaluation of concentration factor, modules and design and process operation, draw selection and fouling aspects are also described. Encouraging potential is demonstrated to concentrate streams more than 20-fold with high rejection rate of most compounds and preservation of added value products. For applications dealing with highly concentrated or complex streams, FO still features lower propensity to fouling compared to other membranes technologies along with good versatility and robustness. However, further assessments on lab and pilot scales are expected to better define the achievable concentration factor, rejection and effective concentration of valuable compounds and to clearly demonstrate process limitations (such as fouling or clogging) when reaching high concentration rate. Another important consideration is the draw solution selection and its recovery that should be in line with application needs (i.e., food compatible draw for food and beverage applications, high osmotic pressure for brine management, etc.) and be economically competitive.

Can seawater desalination be a win-win fix to our water cycle?

While we increasingly turn to desalination as a secure water supply, it is still perceived as an expensive and environmentally damaging solution, affordable only for affluent societies. In this contribution, we recast desalination from one of a last resort to a far-reaching, climate change mitigating, water security solution. First, we argue that the benefits of desalination go beyond the single-use value of the water produced. If coupled with water reuse for irrigation, desalination reduces groundwater abstraction and augments the water cycle. As such, it may support both adaptation to, and mitigation of climate change impacts by deploying plentiful water for human use, with all the benefits that entails, while helping preserve and restore ecosystems. Second, we counter two arguments commonly raised against desalination, namely its environmental impact and high cost. The environmental impact can be fully controlled so as not to pose long-term threats, if driven by renewable energy. Desalination may then have a zero carbon footprint. Moreover, appropriately designed outfalls make the disposal of brine at sea compatible with marine ecosystems.. Recovery of energy, minerals and more water from brine reject (particularly in the form of vapour for cooling to enable more crops and vegetation to grow), while possible, is often hardly economically justified. However, resource recovery may become more attractive in the future, and help reduce the brine volumes to dispose of. When fresh water becomes scarce, its cost tends to go up, making desalination increasingly economic. Moreover, desalination can have virtually no environmental costs. Considering the environmental costs of over-abstraction of freshwater, desalination tilts the balance in its favour.

Rapid Room-Temperature Preparation of Hierarchically Porous Metal-Organic Frameworks for Efficient Uranium Removal from Aqueous Solutions

The effective removal of uranium from an aqueous solution is a highly valuable process for the environment and health. In this study, we developed a facile and rapid method to synthesize hierarchically porous Cu-BTC (RT-Cu-BTC) using a cooperative template strategy. The as-synthesized RT-Cu-BTC exhibited hierarchically porous structure and excellent thermostability, as revealed by X-ray powder diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Compared with conventional metal-organic frameworks (MOFs) and zeolites, the obtained RT-Cu-BTC exhibited enhanced adsorption capacity (839.7 mg·g-1) and high removal efficiency (99.8%) in the capture of uranium (VI) from aqueous solutions. Furthermore, the conditions such as adsorbent dose, contact time, and temperature in adsorption of uranium (VI) by RT-Cu-BTC were investigated in detail. The thermodynamics data demonstrated the spontaneous and endothermic nature of the uranium (VI) adsorption process. The Langmuir isotherm and pseudo-second-order models could better reflect the adsorption process of uranium (VI) onto RT-Cu-BTC. In addition, the as-synthesized RT-Cu-BTC showed excellent stability in removing uranium (VI) from an aqueous solution. This work provides a facile and rapid approach for fabricating hierarchically porous MOFs to realize a highly efficient removal of uranium (VI) from aqueous systems.

A low-cost anodic catalyst of transition metal oxides for lithium extraction from seawater

Lithium reserves in seawater are tens of thousands of times higher than on land, making it a promising candidate for lithium resources. A lithium extraction method based on a solar-powered electrolysis technique with a solid-state electrolyte, Li1.5Al0.5Ge1.5(PO4)3 (LAGP), as the selective membrane has been reported to obtain metallic lithium from seawater. Herein, the electrolytic cell is optimised by replacing the anode catalyst materials. The NiO@SP anode shows excellent electrochemical performance, relatively high energy utilization efficiency and low cost among the anode materials investigated. An electrolytic cell adopting NiO@SP achieves a lithium production efficiency of 57.2 mg W h-1 with a potential of 4.5 V at a current density of 333 μA cm-2. Based on the investigation by in situ mass spectroscopy the oxygen evolution reaction (OER) and chlorine evolution reaction (CER) occur together on the anode with the production of oxygen and hypochlorite.

Electrochemical Methods for Lithium Recovery: A Comprehensive and Critical Review

Due to the ubiquitous presence of lithium-ion batteries in portable applications, and their implementation in the transportation and large-scale energy sectors, the future cost and availability of lithium is currently under debate. Lithium demand is expected to grow in the near future, up to 900 ktons per year in 2025. Lithium utilization would depend on a strong increase in production. However, the currently most extended lithium extraction method, the lime-soda evaporation process, requires a period of time in the range of 1-2 years and depends on weather conditions. The actual global production of lithium by this technology will soon be far exceeded by market demand. Alternative production methods have recently attracted great attention. Among them, electrochemical lithium recovery, based on electrochemical ion-pumping technology, offers higher capacity production, it does not require the use of chemicals for the regeneration of the materials, reduces the consumption of water and the production of chemical wastes, and allows the production rate to be controlled, attending to the market demand. Here, this technology is analyzed with a special focus on the methodology, materials employed, and reactor designs. The state-of-the-art is reevaluated from a critical perspective and the viability of the different proposed methodologies analyzed.

Design Strategies to Enhance Amidoxime Chelators for Uranium Recovery

To move nuclear as a primary energy source, uranium resources must be secured beyond what terrestrial reserves can provide. Given the vast quantity of uranium naturally found in the ocean, adsorbent materials have been investigated to recover this vital fuel source. Amidoxime (AO) has been found to be the state-of-the-art functional group for this purpose, however, improvements must still be made to overcome the issues with selectively capturing uranium at such a low concentration found in the ocean. Herein, we report PAF-1 as a platform to study the effects of two amidoxime ligands. The synthesized adsorbents, PAF-1-CH₂NHAO and PAF-1-NH(CH₂)₂AO, with varying chain lengths and grafting degrees, were investigated for their uranium uptakes and kinetic efficiency. PAF-1-NH(CH₂)₂AO was found to outperform PAF-1-CH₂NHAO, with a maximum uptake capacity of 385 mg/g and able to reduce a uranium-spiked solution to ppb level within 10 min. Further studies with PAF-1-NH(CH₂)₂AO demonstrated effective elution for multiple adsorption cycles and showed promising results for uranium recovery in the diverse composition of a spiked seawater solution. The work presented here moves forward design principles for amidoxime-functionalized ligands and provides scope for strategies to enhance the capture of uranium as a sustainable nuclear fuel source.

Rapid and selective lithium recovery from desalination brine using an electrochemical system

Due to the steep increase in the use of mobile electronics and electric vehicles, there has been a dramatic rise in the global lithium consumption. Although seawater is considered as an ideal future source of lithium, technological advances are necessary to ensure the economic feasibility of lithium recovery from seawater because the concentration and portion of Li+ are extremely low in seawater. Especially, battery-based electrochemical systems for lithium recovery have been considered as promising lithium recovery methods, though they have not been considered for seawater applications due to the extremely low concentration of Li+. In this study, we demonstrate that an electrochemical system based on a battery electrode material (λ-MnO2) can be used for efficient lithium recovery from desalination brine (2-3 times concentrated seawater). Our approach was able to capture Li+ within a substantially short period of time compared to conventional processes at a rate that was at least 3 times faster than that of adsorption processes, and our approach did not require acid or toxic chemicals unlike the other recovery technologies. Moreover, by consecutive operation of the system, a lithium recovery solution containing 190 mM of Li+ was obtained with only a small consumption of energy (3.07 Wh gLi-1), and the purity of Li+ was increased to 99.0%.

Selective Recovery of Rare Earth Elements from Coal Fly Ash Leachates Using Liquid Membrane Processes

Coal combustion residues and other geological waste materials have been proposed as a resource for rare earth elements (REEs, herein defined as the 14 stable lanthanides, yttrium, and scandium). The extraction of REEs from residues often generate acidified leachates that require highly selective separation methods to recover the REEs from other major soluble ions in the leachates. Here, we studied two liquid membrane processes (liquid emulsion membranes, LEM, and supported liquid membranes, SLM) and compared them to standard solvent extraction techniques for selective recovery and concentration of REEs from a leachate of coal fly ash. All separation methods involved an organic solution of di(2-ethylhexyl)phosphoric acid dissolved in kerosene or mineral oil and an acid strippant solution of 5 M nitric acid for the liquid-based separations. The LEM configuration, which separated REEs by immersing an acid-in-oil emulsion in the ash leachate, resulted in similar recovery percentages of individual REEs as the conventional solvent extraction approach. The recovery of REEs in the SLM configuration, which involved the impregnation of the solvent in a hydrophobic membrane, was slower than the LEM process. However, the SLM process was notably more selective for the heavy (and higher value) REEs, while the conventional extraction and LEM processes were more selective for the light REEs. A flux-based model of the extraction processes suggested that recovery rates were limited by REE affinity for the solvent chelator in the SLM, while the rates of REEs separation via LEM were limited by diffusive mass transfer across the liquid membrane. Altogether, these results help to identify specific steps in the recovery process that future work should target in the development of scalable liquid membrane separations for REE recovery.

Siderophore-inspired chelator hijacks uranium from aqueous medium

Over millennia, nature has evolved an ability to selectively recognize and sequester specific metal ions by employing a wide variety of supramolecular chelators. Iron-specific molecular carriers—siderophores—are noteworthy for their structural elegance, while exhibiting some of the strongest and most selective binding towards a specific metal ion. Development of simple uranyl (UO₂²⁺) recognition motifs possessing siderophore-like selectivity, however, presents a challenge. Herein we report a comprehensive theoretical, crystallographic and spectroscopic studies on the UO₂²⁺ binding with a non-toxic siderophore-inspired chelator, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H₂BHT). The optimal pK_a values and structural preorganization endow H₂BHT with one of the highest uranyl binding affinity and selectivity among molecular chelators. The results of small-molecule standards are validated by a proof-of-principle development of the H₂BHT-functionalized polymeric adsorbent material that affords high uranium uptake capacity even in the presence of competing vanadium (V) ions in aqueous medium.

Development of simple uranyl recognition motifs possessing siderophore-like binding strength and selectivity presents a challenge. Here the authors show a comprehensive theoretical and experimental study on uranyl binding with a polymeric adsorbent material decorated with a non-toxic siderophore inspired small molecule chelator.

High-Affinity Detection and Capture of Heavy Metal Contaminants using Block Polymer Composite Membranes

Adsorptive membranes offer one possible solution to the challenge of removing and recovering heavy metal ion contaminants and resources from water supplies. However, current membrane-based sorbents suffer from low binding affinities, leading to issues when contaminants are present at trace concentrations or when the source waters have a high concentration of background electrolytes that compete for open binding sites. Here, these challenges are addressed in the design of a highly permeable (i.e., permeability of ∼2.8 × 104 L m-2 h-1 bar-1) sorbent platform based on polysulfone and polystyrene-b-poly(acrylic acid) composite membranes. The membranes possess a fully interconnected network of poly(acrylic acid)-lined pores, which enables the surface chemistry to be tailored through sequential attachment of polyethylenimine brushes and metal-binding terpyridine ligands. The polyethylenimine brushes increase the saturation capacity, while the addition of terpyridine enables high-affinity binding to a diversity of transition metal ions (i.e., Pd2+, Cd2+, Hg2+, Pb2+, Zn2+, Co2+, Ni2+, Fe2+, Nd3+, and Sm3+). This platform removes these metal contaminants from solution with a sorbent capacity of 1.2 mmol g-1 [based on Cu2+ uptake]. The metal capture performance of the functionalized membranes persists in spite of high concentrations of competitive ions, with >99% removal of Pb2+ and Cd2+ ions from artificial groundwater and seawater solutions. Breakthrough experiments demonstrate the efficient purification of feed solutions containing multiple heavy metal ions under dynamic flow conditions. Finally, fluorescence quenching of the terpyridine moiety upon metal ion complexation offers an in situ probe to monitor the extent of sorbent saturation with a Stern-Volmer association constant of 2.9 × 104 L mol-1. The permeability, capacity, and affinity of these membranes, with high-density display of a metal-binding ligand, offer a chemically tailored platform to address the challenges that arise in ensuring clean water.

Diagnosis and ecotoxicological risk assessment of 49 elements in sludge from wastewater treatment plants of Chongqing and Xiamen cities, China

Limited information about the sludge quality is a major constraint for its usage and proper disposal. This study investigated the occurrence of 49 elements in sludge from 11 wastewater treatment plants (WWTPs) in Chongqing and Xiamen cities of China. The concentration of 46-detected elements ranged from 16.2 μg kg^-1 (Pt) to 55.0 g kg^-1 (Al) on dry solid basis in the sludge. The enrichment factor of most of the elements was > 1.5, indicating their possible anthropogenic origin. The precious metals had considerably higher enrichment factor ranging from 56.3 to 200,000. Principal component analysis clustered the samples from Chongqing and Xiamen separately to suggest strong spatial variations. Contamination factor, pollution loading index, and integrated pollution degree were calculated to evaluate the elemental pollution risk. The pollution loading index indicated unpolluted to highly polluted levels of the elements in the sludge. In addition, results from the ecotoxicological risk index showed an individual low to very high ecotoxicological risk posed by eight metal(loid)s (As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) in the WWTPs.

Rubidium extraction from seawater brine by an integrated membrane distillation-selective sorption system

The ultimate goal of seawater reverse osmosis (SWRO) brine management is to achieve minimal liquid discharge while recovering valuable resources. The suitability of an integrated system of membrane distillation (MD) with sorption for the recovery of rubidium (Rb⁺) and simultaneous SWRO brine volume reduction has been evaluated for the first time. Polymer encapsulated potassium copper hexacyanoferrate (KCuFC(PAN)) sorbent exhibited a good selectivity for Rb⁺ sorption with 10-15% increment at 55 °C (Langmuir Q_max = 125.11 ± 0.20 mg/g) compared to at 25 °C (Langmuir Q_max = 108.71 ± 0.20 mg/g). The integrated MD-KCuFC(PAN) system with periodic membrane cleaning, enabled concentration of SWRO brine to a volume concentration factor (VCF) of 2.9 (65% water recovery). A stable MD permeate flux was achieved with good quality permeate (conductivity of 15-20 μS/cm). Repeated cycles of MD-KCuFC(PAN) sorption with SWRO brine enabled the extraction of 2.26 mg Rb⁺ from 12 L of brine (equivalent to 1.9 kg of Rb/day, or 0.7 tonne/yr from a plant producing 10,000 m³/day brine). KCuFC(PAN) showed a high regeneration and reuse capacity. NH₄Cl air stripping followed by resorcinol formaldehyde (RF) resin filtration enabled to recover Rb⁺ from the desorbed solution.