Tungsten has long been treated as an environmentally benign metal, prized industrially for making tool steels harder and light bulb filaments glow. That reputation has eroded in recent years. Epidemiological studies have associated elevated tungsten exposure with cardiovascular and kidney effects, and laboratory work has raised questions about its toxicity and possible carcinogenicity. In the environment, tungsten typically travels as the tungstate oxyanion, a chemical form that behaves in some ways like chromate, arsenate, and molybdate, species well known for binding strongly to iron minerals. In acid mine drainage systems, where iron-rich, sulfate-laden waters create ideal conditions for schwertmannite precipitation, tungsten can be captured efficiently by this nanocrystalline mineral through a combination of surface adsorption and exchange with sulfate held in its tunnel-like structure.

The problem is that schwertmannite is metastable. Its poorly crystalline structure, rich in sulfate held in both outer-sphere and inner-sphere positions, represents a transient waypoint in iron geochemistry. Under natural conditions, particularly as temperatures rise, pH shifts, or microbial activity accelerates dissolution, schwertmannite gradually converts to goethite, a more thermodynamically stable iron oxyhydroxide. Earlier research has established that during this dissolution-reprecipitation process, contaminants formerly held by schwertmannite can be released into solution, incorporated into the growing goethite lattice, or redistributed between newly formed phases. What remained unclear, and what motivated the new investigation, is what happens specifically to tungsten when schwertmannite loaded with tungsten undergoes aging, and whether the tungsten itself influences the course of the mineral transformation.

To answer these questions, the team conducted controlled batch aging experiments at pH 3.5 and 60 degrees Celsius, conditions designed to accelerate the natural transformation of schwertmannite so that processes unfolding over years in the field could be observed within weeks. They compared two systems side by side: a tungsten-free schwertmannite suspension and an identical suspension in which the mineral had been loaded with tungsten. Over a month of monitoring, the researchers tracked sulfate release into solution, the development of iron mineral phases, and the partitioning of tungsten between the solid and dissolved pools. The accelerated design does not replicate every nuance of field chemistry, but it provides a geochemically grounded window into the trajectories that contaminated sediments in acid mine drainage environments may follow.

The headline finding is that tungsten loading altered the transformation in a distinctly stage-dependent manner. In the early stage of aging, the tungsten-bearing system released approximately 15 percent more sulfate into solution than the tungsten-free control, and goethite-related features developed noticeably earlier. This suggests that tungsten, held within or on the schwertmannite structure, promoted the initial destabilization of the host mineral, accelerating the sulfate-exchange and dissolution reactions that kick-start conversion to goethite. In effect, the contaminant acted as a chemical accomplice in its own mineral host’s restructuring during the opening phase of the transformation.

The story then reversed in the later stage. Rather than continuing to accelerate, the development of crystalline goethite in the tungsten-loaded system was attenuated, lagging behind what occurred in the tungsten-free suspension. The presence of tungsten appeared to interfere with the growth and crystallization of well-ordered goethite, consistent with a growing body of evidence that oxyanion surface complexes and structural incorporation can hinder nucleation and crystal growth of iron oxide phases. Tungsten’s strong affinity for iron oxide surfaces and its capacity to substitute into iron oxide structures appear to have imposed a drag on the recrystallization front, leaving the solid phase less crystalline than it would otherwise have been.

Meanwhile, the tungsten itself executed a striking round trip. During the early phase of transformation, as schwertmannite dissolved and sulfate flooded out, tungsten was released into solution, raising the prospect that aging sediments could temporarily export tungsten to downstream waters. But as the experiment progressed, dissolved tungsten was reassociated with the solid phase, migrating back onto and into the evolving iron minerals. Sequential extraction analysis showed that the residual tungsten fraction, the most strongly bound and least mobile pool, climbed to approximately 38 percent of the total tungsten by day 30. The later redistribution of tungsten coincided with the attenuated development of crystalline goethite, linking the contaminant’s immobilization to its own disruption of crystal growth, likely through incorporation into defect-rich, poorly crystalline iron phases and strong surface complexes.

The implications cut in two directions. On one hand, the initial pulse of tungsten release during early aging is a warning sign: sediments rich in schwertmannite in acid mine drainage streams, mine tailings impoundments, and mining lakes could episodically deliver tungsten to overlying waters as environmental conditions drive mineral transformation, threatening water quality in the same systems where the metal had been sequestered. On the other hand, the substantial long-term reassociation of tungsten with the solid phase, and its growing sequestration in residual pools, indicates that aging iron mineral assemblages can ultimately retain much of the tungsten they capture. The net outcome for tungsten mobility therefore depends critically on where in the transformation sequence a given sediment sits, a nuance that simple equilibrium models of adsorption would miss entirely.

For environmental managers and risk assessors, the study supplies a geochemical basis for evaluating tungsten retention and mobility in acid mine drainage related systems. It suggests that monitoring programs should track not only dissolved tungsten but also the mineralogical state of iron precipitates, since the transition from schwertmannite to goethite marks periods of elevated release risk followed by renewed immobilization. The work also adds tungsten to the list of contaminants, alongside arsenic, chromium, and antimony, whose fates are governed by the dynamic transformation behavior of schwertmannite rather than by static adsorption constants. As global demand for tungsten continues to grow, along with the mining and industrial exposures that accompany it, understanding how this metal interacts with the ephemeral minerals of acidic mine waters becomes an increasingly urgent piece of the environmental puzzle. The researchers note that the findings define a stage-dependent relationship between mineral transformation and tungsten partitioning under accelerated aging conditions, a framework that can now be tested and refined across the wide range of temperatures, pH values, and competing ions that characterize real acid mine drainage environments.

Subject of Research: Tungsten redistribution during the aging and transformation of schwertmannite in acid mine drainage

Article Title: Tungsten-induced alteration of schwertmannite transformation and its implications for tungsten mobility in acid mine drainage

Article References: Yang, C., Huang, R., & Du, H. (2026). Tungsten-induced alteration of schwertmannite transformation and its implications for tungsten mobility in acid mine drainage. Environmental Geochemistry and Health, 48(15), Article 593. https://doi.org/10.1007/s10653-026-03496-y

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03496-y

Keywords: tungsten, schwertmannite, goethite, acid mine drainage, mineral transformation, sulfate release, iron oxyhydroxides, oxyanion adsorption, trace metal mobility, geochemistry, environmental contamination, batch aging experiments

The investigation, published in Environmental Geochemistry and Health, monitored bottom sediments at four strategic sites between March 2019 and July 2024: the Aimorés and Mascarenhas reservoirs upstream, and two estuarine stations near the river mouth, one of which is directly influenced by saltwater wedge intrusion. Researchers collected twenty-four mud-fraction samples covering both wet and dry seasonal cycles, using a sterile Van Veen grab sampler to retrieve the uppermost centimeters of sediment. This spatiotemporal design allowed the team to separate the slow mineralogical fingerprint inherited from the tailings from the faster changes driven by present-day environmental forcing.

To dissect the iron chemistry, the team combined selective dissolution procedures with X-ray diffraction, diffuse reflectance spectroscopy, magnetic susceptibility measurements, and multivariate statistics. Acid ammonium oxalate extraction targeted poorly crystalline iron forms such as ferrihydrite and lepidocrocite, while citrate–bicarbonate–dithionite extraction captured more crystalline phases like goethite and hematite. Alkali fusion provided total elemental inventories for iron, manganese, and the trace-element suite of arsenic, cadmium, cobalt, chromium, molybdenum, nickel, lead, vanadium, and zinc, quantified by ICP-MS with certified reference materials confirming recoveries between 93 and 109 percent.

The results reveal a sediment system dominated by crystalline iron oxyhydroxides. Dithionite-extractable iron ranged from roughly 15 to 70 grams per kilogram, while oxalate-extractable iron stayed below 20 grams per kilogram. Yet the ratio between the two fractions varied dramatically, from 0.14 to 0.82, with the strongest fluctuations at the estuarine stations. This temporal decoupling, the authors argue, is evidence of ongoing post-depositional transformation: crystalline phases are periodically destabilized by reducing conditions, and subsequent oxidation events generate short-range-order phases with high sorptive capacity, resetting the geochemical clock again and again.

X-ray diffraction confirmed goethite as the dominant iron oxyhydroxide across every environment and campaign, with hematite appearing as a subordinate but highly variable phase, particularly in estuarine sediments and at the Mascarenhas reservoir. Diffuse reflectance spectroscopy, interpreted through the Kubelka–Munk function, tracked the relative abundance of the two minerals and showed goethite-dominated assemblages giving way episodically to hematite-rich intervals, especially at the saltwater-influenced station during 2023. Magnetic susceptibility remained consistently low, indicating that antiferromagnetic oxyhydroxides, not ferrimagnetic magnetite, control the magnetic signal of these sediments.

Perhaps most striking are the crystallographic details. Goethite mean crystal dimensions ranged from about 20 to 40 nanometers along the 110 direction, with crystals preferentially elongated along that axis, a morphology consistent with assemblages inherited from the Fundão tailings. Specific surface areas of goethite spanned 57 to nearly 120 square meters per gram, and aluminum substitution in its structure varied from 0.097 to 0.199 mol per mol. Because aluminum substitution inhibits crystal growth, shrinks crystallite size, and boosts surface area, these variations translate directly into differences in the density and accessibility of sorption sites where trace elements bind through inner-sphere complexation, adsorption, and co-precipitation.

The geochemical data show that estuarine stations consistently carry the highest contaminant loads. Nickel reached 448 milligrams per kilogram at the saltwater-influenced station in March 2024, chromium peaked at 321 milligrams per kilogram, and arsenic concentrations climbed steadily between 2019 and 2024 at the neighboring estuarine site. Dithionite-extractable arsenic at that site surged nearly sixfold over the monitoring period, and wet-period campaigns brought marked increases in cobalt, chromium, molybdenum, nickel, and zinc. Reservoir sediments, by contrast, showed lower concentrations and less temporal volatility, behaving as relatively stable retention zones.

Principal component analysis tied the story together. The first two components explained 56 percent of total variance and cleanly separated reservoir from estuarine samples. Most potentially toxic elements loaded strongly alongside dithionite-extractable iron, total iron, and hematite crystallographic parameters, while the upstream Aimorés reservoir clustered instead with goethite surface area and aluminum substitution. Hierarchical clustering confirmed four distinct sample groups, demonstrating that spatial differences in contaminant partitioning are governed by iron mineralogy and crystallography rather than by total elemental abundance alone.

Why does this matter beyond the Doce River? Estuaries are often treated as terminal sinks where contaminated sediments come to rest. This study shows they are better understood as reactive biogeochemical reactors. Salinity fluctuations alter colloidal stability and surface reactivity, organic matter degradation drives suboxic conditions that partially dissolve iron phases, and resuspension during floods exposes fresh mineral surfaces. Each cycle can release a pulse of trace elements and then re-sequester them into newly formed, highly reactive phases. The contaminated pool is therefore dynamic, capable of responding to environmental perturbations rather than remaining permanently immobilized.

The findings also carry a clear message for environmental monitoring: total concentration measurements alone miss the story. Two sediments with identical arsenic totals may behave entirely differently depending on whether the element is locked inside well-crystallized goethite or loosely held on freshly precipitated ferrihydrite. The authors argue that mineralogical indicators and selective extraction procedures deserve a permanent place in long-term monitoring frameworks, not just in the aftermath of disasters. As climate variability reshapes hydrological regimes and saltwater intrusion pushes further inland, the mineral-scale processes documented here will increasingly determine whether legacy contaminants stay buried or re-enter the food web. A decade on, the Doce River’s iron minerals are still writing the disaster’s next chapter.

Subject of Research: Long-term evolution of iron oxyhydroxide mineralogy and potentially toxic element partitioning in mining-impacted sediments of the Lower Doce River fluvial–estuarine system, Brazil

Article Title: Long-term evolution of Fe oxyhydroxide mineralogy and potentially toxic element partitioning in mining-impacted sediments of the Lower Doce River fluvial–estuarine system

Article References: Long-term evolution of Fe oxyhydroxide mineralogy and potentially toxic element partitioning in mining-impacted sediments of the Lower Doce River fluvial–estuarine system. (n.d.). https://doi.org/10.1007/s10653-026-03495-z

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03495-z

Keywords: Fundão dam collapse, Doce River, iron oxyhydroxides, goethite, hematite, potentially toxic elements, sediment geochemistry, selective dissolution, X-ray diffraction, estuarine biogeochemistry, trace-element partitioning, mining disaster legacy

The study, led by Hongsheng Yuan of the Center for High Pressure Science and Technology Advanced Research in Shanghai, together with Lianjie Man and Leonid Dubrovinsky of the Bayerisches Geoinstitut at the University of Bayreuth and an international team of collaborators, is published in Nature Geoscience. Using laser-heated diamond anvil cells—devices that squeeze samples between two gem-quality diamond tips while laser beams raise temperatures to thousands of degrees—the researchers created conditions rivaling those near the core–mantle boundary, where pressures exceed one hundred gigapascals and temperatures climb above several thousand kelvin.

What emerged from these experiments were two hexagonal iron oxyhydroxides with the nominal compositions Fe5O12Hx and Fe7O12Hx, where x denotes a variable hydrogen content. These are not exotic compounds dreamed up in a computer simulation; they are crystalline phases whose structures were determined directly from in situ single-crystal X-ray diffraction measurements at synchrotron facilities, including the European Synchrotron Radiation Facility, PETRA III at DESY in Hamburg, and the Shanghai Synchrotron Radiation Facility. The crystallographic data underpinning the structure determinations have been deposited in the Cambridge Structural Database, and the broader experimental datasets are openly available through figshare, giving other researchers the means to scrutinize and extend the findings.

The significance of these phases lies in two properties highlighted by the team. First, they can form under water-undersaturated conditions, meaning they do not require an abundant free water reservoir to crystallize. This is crucial because the deep mantle is generally thought to be far drier than the shallow regions from which volcanic gases escape. Second, the new oxyhydroxides are remarkably dense. Density matters enormously in a planet whose interior is sorted by gravity: materials less dense than their surroundings tend to rise, while denser ones sink. The high densities of Fe5O12Hx and Fe7O12Hx mean that once formed, they would gravitationally settle and remain stably parked near the base of the mantle rather than escaping upward.

That combination of stability and density provides what the authors describe as a plausible mineralogical basis for the seismically observed ultralow-velocity zones. These zones, which can stretch for hundreds of kilometers horizontally but are only a few to tens of kilometers thick, reduce seismic shear and compressional wave speeds so severely that ordinary mantle minerals alone struggle to explain them. Hydrogen-bearing iron-rich phases, with their altered elastic properties and potentially partial molten character, have been increasingly invoked as candidates. Earlier work had identified a hydrogen-bearing iron peroxide and pyrite-type FeOOH as possible deep water hosts; the new hexagonal oxyhydroxides extend that family of compounds and demonstrate that iron, oxygen, and hydrogen can combine into dense crystalline architectures at the pressures and temperatures of the lowermost mantle.

The context for why water might be down there in the first place reaches back to the planet’s earliest history. Isotopic anomalies in helium and hydrogen recorded in deep-sourced volcanic rocks have long hinted that some primordial water—water inherited from the materials that accreted to form Earth—survives in isolated reservoirs deep in the mantle rather than having been lost entirely to space or mixed into the surface water cycle. A leading scenario involves a basal magma ocean: a dense, iron-rich melt that ponded at the base of the mantle during planetary differentiation and crystallized slowly over geological time. The question that has frustrated researchers is which minerals, if any, could have sequestered hydrogen during that crystallization. Most candidate hydrous silicates decompose at the relevant temperatures, and common mantle minerals such as bridgmanite hold very little water at depth. The new oxyhydroxides fill that gap, offering mineral hosts capable of locking hydrogen into the deep interior both from primordial sources and from water recycled downward by subducting slabs.

Subduction supplies the second pathway. Oceanic plates carry hydrated minerals down into the mantle, and laboratory studies in recent years have shown that some hydrous phases can survive transit to the lowermost mantle, potentially delivering water to the core–mantle boundary billions of years after Earth formed. If that arriving water reacts with iron-bearing mantle material—or with metallic iron from the core itself—the dense oxyhydroxides identified in this study could crystallize and accumulate. The result would be chemically distinct, hydrogen-rich lumps at the base of the mantle, exactly the kind of heterogeneity that seismic imaging keeps revealing.

The implications ripple outward from mineralogy into planetary evolution. The authors note that the stability of these phases provides a mechanism for transporting volatiles into Earth’s core, where hydrogen and oxygen could act as light elements dissolved in liquid iron alloy, or conversely for their episodic release back into the mantle. Mantle plumes—hot, buoyant upwellings that rise from the core–mantle boundary and feed surface hotspots such as Hawaii and Iceland—appear to be rooted in some of the same deep regions. If dense oxyhydroxide accumulations are destabilized or partially melted at the edges of plumes, the water they carry could be injected into the upwelling flow, eventually influencing the melting behavior, chemistry, and gas emissions of hotspot volcanoes at the surface. In this way, minerals formed nearly three thousand kilometers down could modulate the volatile budget of the planet across geological time.

The experimental achievement behind these conclusions should not be understated. Diamond anvil cell experiments at lowermost mantle conditions are notoriously difficult: samples are measured in volumes smaller than the width of a human hair, laser heating must be controlled with precision to avoid catastrophically melting the diamond anvils, and extracting single-crystal diffraction data from polycrystalline samples squeezed to megabar pressures demands sophisticated analysis software and high-brightness synchrotron beams. The team combined these techniques with electron microscopy and chemical analysis of recovered samples to characterize the new phases from multiple angles, including constraints on their hydrogen contents and densities at high pressure. Extended data on unit-cell parameters and refined atomic positions support the structural assignments, and the authors report that chemical analysis of recovered material found no evidence of contamination from the rhenium gasket or other experimental artifacts that might otherwise mimic the observed compositions.

Much remains to be tested. Whether the new oxyhydroxides can account quantitatively for the seismic properties of ultralow-velocity zones, how much water the deep mantle could realistically store in them, and how they interact with surrounding mantle minerals at the atomic scale are questions for future experiments and modeling. But the study reframes a long-standing problem in Earth science: the search for the planet’s missing deep water no longer needs to rely on sparse hydrous silicates that barely survive at depth. Iron, the most abundant element in Earth’s core and a major component of the deep mantle, combined with oxygen and hydrogen, may instead form its own family of dense reservoir minerals. If those reservoirs exist at the core–mantle boundary today, they could be simultaneously a vault preserving water from the planet’s birth, a sink for water recycled from its surface, and a chemical trigger for the plumes that reshape its surface—tying together, in a single crystal structure, processes that span the whole depth and history of our planet.

Subject of Research: Dense iron oxyhydroxide phases as potential water reservoirs in the deep lower mantle

Article Title: Dense iron oxyhydroxides as possible reservoirs of water under deep mantle conditions

Article References: Yuan, H., Man, L., Kupenko, I., Yin, Y., Aprilis, G., Pantousas, A., Pakhomova, A., Zhou, W., Pierru, R., Yang, K., Glazyrin, K., Rodrigues, J. E., Garbarino, G., Ball, J. A. D., Bykova, E., Hu, Q., Sossi, P. A., Frost, D. J., & Dubrovinsky, L. (2026). Dense iron oxyhydroxides as possible reservoirs of water under deep mantle conditions. Nature Geoscience. https://doi.org/10.1038/s41561-026-02067-1

Image Credits: AI Generated

DOI: 10.1038/s41561-026-02067-1

Keywords: iron oxyhydroxides, deep mantle water, core–mantle boundary, ultralow-velocity zones, diamond anvil cell, high-pressure experiments, basal magma ocean, mantle plumes, subduction, hydrogen storage, volatile cycles, Nature Geoscience