Key Takeaways & Executive Findings
- •• • Sulfonated covalent organic frameworks (S-COF) achieved a uranium sorption capacity of 31.5 mg/(g·day) from seawater, the highest reported to date, attributed to uranyl-recognition pockets and –SO3H units that form strong coordination with uranyl ions, demonstrating the potential of designed porous materials for selective uranium capture. • • Amidoxime-based organic cages exhibited a sorption capacity of 11.97 mg/g after 30 days in seawater, highlighting the effectiveness of amidoxime groups in binding uranium, though the capacity is lower than S-COF, indicating trade-offs between capacity and kinetics. • • A 'micro-redox reactor' strategy using copper-ion-mediated reactions (UO2²⁺ + Cu⁺ → UO2⁺ + Cu²⁺; 2UO2⁺ → UO2²⁺ + UO2(s)) enables continuous regeneration of binding sites by reducing adsorbed uranium to insoluble precipitates, thereby enhancing material reusability and long-term performance. • • Electrochemical techniques can catalytically convert soluble U(VI) species into UO2 or bimetallic U(IV)-containing oxides via a two-electron transfer process, offering a new paradigm for uranium capture in complex wastewater systems, but their application in real seawater remains unproven.
Abstract
Nuclear energy is critical for sustainable economic development and achieving carbon neutrality. With only about 6.14 million tons of terrestrial uranium, sufficient for ~70 years of global nuclear power plant operation, the recovery of uranium from seawater and spent fuel is essential for long-term nuclear fuel supply. The ocean contains approximately 4.5 billion tons of uranium, which could sustain nuclear power for ~2000 years if efficiently extracted. However, seawater uranium extraction faces significant challenges due to the extremely low uranium concentration (~3.3 ppb), high concentrations of competing ions, natural organic matter, and marine biofouling. This perspective reviews representative laboratory advances, including sulfonated covalent organic frameworks (S-COF) achieving a sorption capacity of 31.5 mg/(g·day) with high selectivity, amidoxime-based organic cages with a capacity of 11.97 mg/g over 30 days, and a micro-redox reactor strategy that continuously regenerates binding sites. Electrochemical methods have also shown promise for converting soluble U(VI) to insoluble U(IV) oxides. Despite these advances, the transition from laboratory powders to durable marine materials remains problematic. Key gaps include the need for antibacterial properties, mechanical stability under wave action, cost competitiveness with terrestrial mining, and environmental safety of nanomaterials. Artificial intelligence (AI) is proposed to accelerate the design of high-performance, stable materials. This perspective emphasizes the necessity for interdisciplinary research to bridge the gap between bench-scale innovations and practical ocean deployment.
1. Introduction
Seawater uranium extraction is a critical technological frontier for ensuring the long-term sustainability of nuclear energy. Terrestrial uranium reserves are finite, with only ~6.14 million tons available, sufficient for ~70 years at current consumption rates. The ocean, however, contains ~4.5 billion tons of uranium, representing a virtually inexhaustible resource that could power nuclear reactors for millennia. Despite this potential, commercial deployment has been stymied by the extreme technical challenges of selectively extracting uranium from seawater, where it exists at a concentration of ~3.3 parts per billion, amidst a complex matrix of competing ions, organic matter, and biological activity. Traditional mining and hydrometallurgical processes are ineffective at such dilute concentrations, and existing adsorbent materials suffer from low capacity, poor selectivity, and rapid fouling in marine environments.
Recent laboratory innovations have demonstrated remarkable progress in overcoming these barriers. For instance, sulfonated covalent organic frameworks (S-COF) have achieved uranium sorption capacities of 31.5 mg/(g·day) with high selectivity, while amidoxime-based organic cages have shown promise with 11.97 mg/g over 30 days. Electrochemical and micro-redox strategies have also been developed to enhance uranium reduction and recovery. However, these materials are typically tested as powders under idealized conditions, and their performance in real seawater—characterized by wave action, biofouling, and variable salinity—remains largely unvalidated. The transition from bench-scale successes to buoy-deployed systems requires addressing critical issues such as material durability, antibacterial properties, cost-effectiveness, and environmental impact. This perspective critically evaluates the state-of-the-art and identifies the key scientific and engineering bottlenecks that must be overcome to realize the dream of harvesting uranium from the sea.
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SUN Zhenli, WANG Hanyang, CHEN Zhongshan, TAI Xishi, LEI Jiehong, HU Baowei, WANG Suhua, WANG Xiangke (2026). From Bench to Buoy: Challenges in Seawater Uranium Extraction. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3919-0
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Frequently Asked Questions
What is the current state-of-the-art sorption capacity for uranium extraction from seawater, and how does it compare to the theoretical maximum?
The highest reported sorption capacity is 31.5 mg/(g·day) for sulfonated covalent organic frameworks (S-COF), as reported by Guo et al. This is a significant improvement over previous materials, but it is still far below the theoretical capacity of uranium in seawater, which is estimated at ~3.3 ppb. The practical capacity is limited by factors such as competing ions, biofouling, and the kinetics of uranium binding. For comparison, amidoxime-based organic cages achieved 11.97 mg/g over 30 days, indicating that different materials offer trade-offs between capacity and rate.
How do the materials perform in real seawater conditions, particularly regarding biofouling and mechanical stability?
Most laboratory studies use synthetic seawater or spiked solutions, which do not replicate the complex biological and physical conditions of the ocean. Biofouling is a major concern because bacteria and other microorganisms can occupy active sites, reducing sorption capacity. For example, the presence of bacteria can significantly decrease uranium uptake. Mechanical stability under wave action is also a challenge, as many materials are in powder form and would need to be fabricated into robust membranes or fibers. The durability of these materials over extended periods (months to years) in marine environments has not been adequately tested.
What is the cost of seawater uranium extraction compared to terrestrial mining, and what factors influence economic viability?
The cost of seawater uranium extraction is currently estimated to be several times higher than terrestrial mining (which is around $50-100 per kg U3O8). The cost is influenced by the synthesis of adsorbent materials, their reusability, and their sorption capacity. For example, materials with high capacity and good reusability can reduce the overall cost. Additionally, the energy and infrastructure required for ocean deployment (e.g., mooring systems, pumps) add to the cost. To be competitive, the extraction process must achieve a cost of less than $100-200 per kg U, which requires significant improvements in material performance and process engineering.
What are the main challenges in scaling up from laboratory powder materials to practical marine deployment?
Scaling up involves several challenges: (1) Fabricating materials into forms suitable for ocean deployment, such as membranes, fibers, or beads, without losing their active sites or sorption kinetics. (2) Ensuring long-term stability in seawater, including resistance to hydrolysis, oxidation, and biofouling. (3) Developing methods for efficient uranium recovery and material regeneration. (4) Minimizing environmental impact, such as the release of nanoparticles. For example, the micro-redox reactor strategy shows promise for continuous operation, but its scalability and performance in real seawater are unknown.
How can artificial intelligence (AI) accelerate the development of seawater uranium extraction materials?
AI can be used to screen and design materials with optimal properties, such as high uranium affinity, selectivity, and stability. By training machine learning models on existing data, researchers can predict the performance of novel materials and narrow down the design space. This reduces trial-and-error cycles and accelerates the identification of candidates that can withstand marine conditions. For instance, AI could help optimize the pore structure and functional groups of covalent organic frameworks to enhance uranium binding while maintaining mechanical integrity. However, the success of AI-driven design depends on the availability of high-quality experimental data and the ability to model complex interactions in seawater.
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