If you’ve ever swum in the ocean and been touched by seaweed, there’s a good chance it was Sargassum! This free-floating seaweed can have population explosions in coastal waters, degrading water quality, ecosystems, fisheries, and tourism. However, despite its drawbacks, scientists think that Sargassum could be useful for extracting valuable metals, known as rare earth elements (REEs). 

REEs are classified by their average masses and atomic weights. Light REEs include cerium, praseodymium, and neodymium, middle REEs include gadolinium, terbium, and dysprosium, and heavy REEs include erbium, thulium, and ytterbium. These metals are used in magnets, electronic motors, wind turbines, spacecraft, and more. Our current methods of extracting REEs, open-pit mining and chemical processing, are invasive, causing habitat loss and producing toxic waste. Additionally, REEs are difficult to import due to restricted access worldwide. But what if these metals could be extracted using natural methods? 

Scientists from Woods Hole and UCLA recently tested whether Sargassum could accumulate REEs, creating a sustainable solution to these problems. They harvested Sargassum at Waterfront Park in Woods Hole, rinsed the wet samples, and stored them in sterilized, filtered seawater, which they aerated with 12-hour cycles of light and dark to keep the Sargassum alive. They dried another set of samples in the sun under controlled outdoor conditions, stored them in sealed containers, and later rehydrated them in seawater for 3 hours before the experiments.

For each experiment, they added 5 grams (about 0.2 ounces) of Sargassum to solutions containing a mixture of 9 REEs – cerium, praseodymium, neodymium, gadolinium, terbium, dysprosium, erbium, thulium, and ytterbium – in concentrations totalling 0.1 micromolar (μM) REEs, 11μM REEs, 100 to 110μM REEs, and 575 to 600μM REEs. They performed each experiment 4 times: twice with fresh seaweed and twice with rehydrated seaweed. 

The researchers removed 1 gram (about 0.04 ounces) of seaweed from each solution after 1, 3, and 7 days, and dissolved it in acid to release the REEs it had absorbed. They analyzed the concentrations of REEs in each seaweed sample and the leftover solutions using 2 different plasma-based methods. They used these REE concentrations to calculate the ratio of REEs in the Sargassum versus in the solution, known as the bioconcentration factor, to determine how effectively the seaweed absorbed REEs. 

They found that after 7 days at lower REE concentrations (0.1μM), the fresh seaweed had bioconcentration factors of over 1,000. At higher REE concentrations (11μM), their bioconcentration factors ranged from about 400 to 700. However, these levels of REEs were eventually toxic to the fresh Sargassum, so they died after 2 weeks. In addition, the higher REE concentrations of 100 to 600μM were immediately toxic to the fresh Sargassum, which died within 1 day in solution. 

The researchers determined that once the seaweed died, it could no longer actively take up REEs into its tissues but could only accumulate them on its surface or adsorb them. Adsorption can be thought of as a powdered donut – when the surface is covered with powdered sugar, no more powder fits on the donut. Similarly, there was a limit to how many REEs could stick to the Sargassum. Due to this limit, the fresh seaweed samples had bioconcentration factors below 250 in the highest REE concentrations. In contrast, the rehydrated Sargassum consumed less REEs at lower concentrations, but didn’t experience toxicity and continued to accumulate REEs at higher concentrations.

Finally, the team compared Sargassum to a common industrial method of accumulating REEs, known as activated carbon. REEs bond easily to activated carbon because of its abundant surface area and high porosity. Both materials accumulated a similar amount of REEs in solutions of 0.1μM REEs. However, at 575 to 600μM REEs, Sargassum accumulated about twice as many REEs as activated carbon, especially the heavier REEs. 

​The researchers concluded that Sargassum is a natural hyper-accumulator, meaning it successfully concentrates REEs. However, they recommended that future researchers test whether Sargassum performs the same in the natural environment as it does in the lab. If so, Sargassum could be used to accumulate REEs from wastewater, like mine drainage, or other water sources with higher concentrations of REEs. Regardless, they suggested that using Sargassum to obtain REEs could simultaneously expand global access to these metals and mitigate toxic blooms.

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In a groundbreaking study published in Scientific Reports, a team of researchers led by Liu, D., Li, X., and Zhang, Z. has unveiled pivotal insights into the intricate mechanisms dictating how particle size influences the migration and deposition behaviors of weathered crust elution-deposited rare earth ores. This investigation probes deeply into the physicochemical principles and dynamic environmental interactions responsible for the distribution patterns of these valuable mineral resources, providing an unprecedented lens on their geochemical mobility.

The research tackles the challenge of understanding the migration pathways of rare earth elements (REEs) within the weathered crust, a layer significantly dictating ore generation. Central to their inquiry is the particle size of these ore constituents, which affects not only sediment transport dynamics but also the ore’s eventual deposition patterns through complex physicochemical interactions with surrounding media. The work bridges gaps between mineralogy, sedimentology, and geochemistry, offering a holistic view important for both scientific and industrial applications.

Their methodology encompassed a series of meticulously designed experiments and computational models to simulate natural conditions accurately. By varying particle sizes in controlled settings, the research team could monitor kinetic behaviors, adhesive interactions, and sedimentation rates of particles subjected to elution and migration processes. This allowed them to unravel size-dependent mechanisms underlying the spatial distribution and aggregation tendencies of REE particles within lateritic profiles.

In particular, the findings underscore the critical role of smaller particle fractions, which exhibited enhanced mobility due to lower gravitational settling but showed a propensity to adsorb onto mineral surfaces, thus influencing local concentration hotspots. Conversely, larger particles demonstrated reduced migration, primarily influenced by mechanical transport limits and gravitational forces, leading to more stable deposition zones. These differential behaviors directly affect the ore-forming processes and the quality of recoverable deposits.

Chemically, weathered crust environments present dynamic pH and redox conditions, which modulate particle surface charge, coagulation tendencies, and dissolution rates. The research elaborates how particle size accentuates these processes, with fine particles showing increased surface area promoting more extensive ion exchange and adsorption phenomena. Such micro-scale interactions substantially dictate macro-scale deposition patterns, impacting exploration strategies targeting rare earth mineralizations.

Moreover, the research extends its implications to understanding the environmental fate of rare earth elements beyond mining contexts. Rare earth particles, when mobilized through weathering, can traverse soil and water systems, posing ecological and human health risks. The particle size-dependent migration insights unveiled serve as crucial input for predictive environmental risk assessments and remediation planning around mining sites.

One of the most compelling aspects of the study is its integration of field data with laboratory results, ensuring real-world relevance. Samples collected across multiple deposit sites demonstrated consistent size-dependent migration tendencies, validating laboratory conclusions and revealing nuanced local variations driven by topographical and hydrological factors. Such data synthesis enhances the predictive power of their proposed migration and deposition models.

Their study also contributes to refining current geochemical theories related to elution-deposited ores, challenging prior assumptions that often overlooked particle size as a key variable. By pinpointing size-specific migration thresholds, the researchers clarify ore genesis mechanisms in weathered crusts, a region crucial for the global rare earth supply chains. This knowledge can revolutionize resource estimation practices, allowing for improved accuracy in reserve quantification.

Technologically, the researchers leveraged state-of-the-art microscopy and spectroscopic techniques to characterize particle morphologies, mineral compositions, and surface chemistry details. These sophisticated analytical methods provided high-resolution data necessary to comprehend how particle physical attributes interact with chemical environments, culminating in comprehensive migration and deposition profiles. This multidimensional approach epitomizes modern Earth sciences research.

The implications for mining engineering and metallurgy are profound. Understanding particle size effects on ore distribution allows for optimized beneficiation processes, enhancing the efficiency and economic viability of rare earth extraction. Tailored grinding, sorting, and sedimentation techniques can be developed based on specific ore particle sizes, reducing waste and environmental footprints. This research lays the foundation for such industry advances.

Further, the research opens avenues for innovative environmental management practices. By predicting rare earth particle transport pathways, stakeholders can implement targeted monitoring and control strategies to minimize ecological disturbances. This is particularly relevant in the context of expanding rare earth mining activities fueled by the global demand for clean energy technologies, where sustainable practices are paramount.

The interdisciplinary essence of the research, combining geology, chemistry, physics, and engineering, sets a benchmark for future studies addressing complex natural and anthropogenic processes influencing critical mineral resources. The clarity gained about particle size’s role in migration and deposition elucidates broader Earth system processes, benefiting multiple scientific domains and policy frameworks concerning resource stewardship.

In conclusion, Liu and colleagues’ study represents a significant advancement in our understanding of the fundamental processes underlying rare earth ore formation within weathered crust environments. Their comprehensive focus on particle size effects offers vital scientific and practical insights, opening new research horizons and contributing to the sustainable development of an indispensable resource underpinning modern technologies.

Subject of Research: Influence mechanism of particle size on the migration and deposition of weathered crust elution-deposited rare earth ores

Article Title: Research on the influence mechanism of particle size on the migration and deposition law of weathered crust elution-deposited rare earth ores

Article References:
Liu, D., Li, X., Zhang, Z. et al. Research on the influence mechanism of particle size on the migration and deposition law of weathered crust elution-deposited rare earth ores. Sci Rep (2026). https://doi.org/10.1038/s41598-026-56907-6

Image Credits: AI Generated

What if a waste product from coal-fired power plants could become a valuable source of materials needed for electric vehicles, smartphones, and renewable energy technologies? Researchers at the Georgia Institute of Technology have developed a new method to recover rare earth elements from coal fly ash, a powdery waste left behind after coal is burned. […]

The post Scientists turn coal ash waste into a valuable source of rare earth elements appeared first on Knowridge Science Report.