The study, published in Archaeological and Anthropological Sciences, examined 59 fragments selected from documented production contexts at two sites about 150 metres apart in the city’s historic pottery district. The material dated mainly from the late eleventh to the mid-twelfth centuries, spanning the Taifa, Almoravid and early Almohad periods. One workshop contained a rod kiln that had been reused as a waste dump after abandonment; the other had a clay-setting pit and production debris. The researchers regarded these contexts as more securely documented than many assemblages of decorated medieval pottery found in residential areas.

Each fragment was mounted in resin and examined by optical microscopy, while all 59 were analysed with scanning electron microscopy and energy-dispersive X-ray spectroscopy, or SEM–EDS. Twenty specimens were prepared as 30-micrometre petrographic thin sections, 14 were tested by wavelength-dispersive X-ray fluorescence, and 18 underwent X-ray diffraction. The methods were chosen to connect visible vessel traits with microscopic fabric, elemental composition and mineral phases formed during firing. Because SEM–EDS can give broader readings across heterogeneous pastes, its results were combined with petrography and XRF rather than treated as a complete chemical map.

Petrography separated the assemblage into three principal fabric groups that broadly followed function. Kitchenware belonged to Fabric F1, whose dark, fine-grained matrix contained abundant phyllite, mica schist and granite inclusions. Its cooking pots were generally low in calcium and sodium but high in silicon, with average values of about 1.5 weight per cent CaO, 0.6 per cent Na₂O and 63.2 per cent SiO₂ in the SEM–EDS dataset. Quartz-rich particles and rock fragments would have increased resistance to thermal shock. Most cooking pots were handmade, although three of the analysed examples were wheel-thrown, documenting a technological transition within the same production setting.

Water jugs formed a distinct group, Fabric F2. Their bodies were poorer in silica and richer in calcium and magnesium than the cooking pots, with a CaO/MgO ratio near 1.25. The authors interpreted this composition as evidence that at least two clays were combined: a medium-grained, non-calcareous red material resembling that used for kitchenware and a lighter clay containing dolomitic inclusions. This blended paste was also chemically similar to that used for kiln rods, suggesting that available workshop clays were adapted according to the demands of different objects. The water vessels were wheel-thrown and decorated with painted red or black designs, while their handles were sometimes made by hand.

Tableware used a finer, calcareous fabric divided into two subgroups. Both had relatively low porosity and fewer inclusions than the kitchenware, but F3-S1 contained more potassium while F3-S2 contained more sodium. Their average K₂O concentrations were about 2.6 and 0.8 per cent, respectively, while Na₂O averaged approximately 1.1 and 2.4 per cent. Neither subgroup consistently belonged to one workshop, indicating that the chemical contrast was not a simple division between the two sites. Instead, the researchers proposed that it could reflect different local clay sources, clay mixing or paste-preparation practices. Geological sampling would be required to determine whether the workshops exploited the same deposits.

The glazes showed that shared clays did not imply a single firing recipe. SEM–EDS identified 26 glazed samples, including 11 kitchenware and 15 tableware examples, along with glaze droplets from workshop equipment. Many transparent glazes contained lead and were coloured honey-yellow by iron oxide. Transparent tableware glazes ranged from 27.1 to 56.2 per cent PbO. Comparison with the ceramic bodies indicated that lead compounds were combined with quartz sand rather than applied as a simple lead coating. The tableware glazes also showed evidence of a deliberately added potassium-bearing material, possibly derived from woody plant ash, while some recipes apparently included a sodium-rich component such as salt.

Colour was produced through a limited but technically varied palette. Copper oxide generated green transparent glazes, with some samples also containing zinc, possibly indicating the reuse of brass. Brown decoration on honey-coloured tableware contained iron and manganese oxides and may have been painted onto the biscuit-fired vessel before glazing. Opaque white glaze came from cassiterite crystals formed when tin oxide was added to lead glaze. Turquoise combined copper with tin, the latter dispersing fine cassiterite particles that increased opacity. A droplet adhering to a workshop handle contained partially dissolved quartz, cassiterite and lead glaze, consistent with preparation of tin “calx,” while its wider composition included substances associated with lustre pigments. The evidence demonstrates use of lustre-related materials, but the researchers stressed that it did not conclusively prove lustreware production at either workshop.

Principal component analysis reinforced the separation of the three fabric groups: the first three components accounted for 96 per cent of the total chemical variance, with 76.9 per cent contributed by the first component alone. Mineral phases also suggested varying firing temperatures. Kitchenware containing dehydrated muscovite was probably fired below 850 degrees Celsius, while some waterware and tableware indicated temperatures of about 850 degrees or higher; analcime in one tableware subgroup pointed to vitrification above 950 degrees Celsius. Workshop equipment showed repeated exposure to heat: kiln rods contained abundant glassy phases, and one tripod stilt appeared to have been fired more than once. Overall, the evidence points to a coherent but flexible craft system, with functional choices in clay selection and multiple glazing traditions rather than highly specialised production. The study’s principal limitation is that the two selected workshops and 59 fragments cannot establish the exact source of the clays or represent every medieval pottery tradition in Almería.

Subject of Research: Archaeometric characterization of medieval pottery production, clay fabrics, glazes and colorants in Almería, al-Andalus

Article Title: Materials and technological choices in ceramic production of Medieval Almería (al-Andalus): clays, glazes and colorants

Article References: Peregrina, M. J., Molera, J., Garcia-Porras, A., Pradell, T., & Salinas, E. (2026). Materials and technological choices in ceramic production of Medieval Almería (al-Andalus): clays, glazes and colorants. Archaeological and Anthropological Sciences, 18(11), Article 219. https://doi.org/10.1007/s12520-026-02575-6

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02575-6

Keywords: medieval pottery, archaeometry, Almería, al-Andalus, ceramic technology, clay fabrics, lead glazes, tin opacification, pottery workshops, X-ray diffraction, SEM–EDS, petrography

The stakes could hardly be higher. China’s total carbon dioxide emissions have surpassed 20 billion tons, roughly 30.65 percent of the global total, and the steel industry alone accounts for about 15 percent of the country’s emissions. Within ironmaking, blast furnaces are responsible for around 70 percent of the sector’s CO2 output. Coke is indispensable in these furnaces because it serves simultaneously as reducing agent, heat source, carburizing agent, and structural support for the burden column, but producing it releases CO2, CO, SO2, and nitrogen oxides along the way. Finding ways to stretch every kilogram of metallurgical coke has therefore become a central goal of low-carbon ironmaking research.

Nut coke is the fraction of screened coke smaller than 25 millimeters that has traditionally been burned as simple fuel rather than charged into the furnace. In every other respect it is virtually identical to the larger metallurgical coke, which is why steelmakers in China, the United States, France, and Japan already consume it at rates of 20 to 50 kilograms per ton of hot metal. Earlier plant trials by Murao and colleagues showed that controlled distribution of small coke during burden charging increased the blast furnace permeability index by about 5 percent while improving gas utilization by roughly 0.4 percent, and operating data analyzed by Logachov’s team indicated that nut coke consumption could be raised to 40 kilograms per ton of hot metal without hurting furnace productivity, with one kilogram of coke briquettes replacing approximately 0.67 kilograms of conventional coke.

What previous laboratory work had largely overlooked, however, was the effect of nut coke particle size itself. Most co-reduction studies employed nut coke of 10 to 12.5 millimeters, leaving the size question unexamined. Jiang’s team set out to close that gap by testing three size fractions—5 to 10 millimeters, 10 to 15 millimeters, and 15 to 20 millimeters—mixed with sinter of 10 to 12.5 millimeters at addition ratios of 0, 2, 4, 6, and 8 percent. The sinter, supplied by a commercial steel company, contained 59.28 percent total iron and 11.17 percent FeO, with hematite as its primary mineral phase, while the nut coke carried 87.07 percent fixed carbon, a coke reactivity index of 23.4, and a coke strength after reaction of 71.32.

The isothermal reduction experiments were conducted at 900, 950, and 1000 degrees Celsius under a gas atmosphere of 70 percent nitrogen and 30 percent CO, with the reducing gas switched on after a protective nitrogen hold and the sample mass tracked continuously by a balance system. The results were unambiguous: the reduction index of the sinter climbed steadily as the nut coke addition ratio rose from 0 to 8 percent, and it fell as the particle size increased. At 900 degrees Celsius, sinter alone reached a reduction index of 80.41 percent, but with 8 percent of 5 to 10 millimeter nut coke the index rose to 85.55 percent. The same 8 percent addition of 10 to 15 millimeter and 15 to 20 millimeter nut coke yielded only 83.95 percent and 82.57 percent, respectively. The pattern held at 950 and 1000 degrees Celsius, where the finest fraction pushed the reduction index to 88.52 and 90.56 percent, confirming that the optimum condition in this system is 8 percent nut coke of 5 to 10 millimeters.

The mechanism behind these numbers is a two-part story of chemistry and physics. Chemically, CO strips oxygen from hematite in a stepwise cascade—Fe2O3 first becomes Fe3O4, then FeO, and finally metallic Fe—generating CO2 in the process. Nut coke counteracts the resulting loss of reducing potential through the Boudouard reaction, in which solid carbon reacts with CO2 to regenerate CO, sustaining the atmosphere needed to keep the iron oxides shrinking. Physically, sinter particles tend to adhere and agglomerate at elevated temperatures, choking the burden bed and creating stagnant zones where the reducing gas never reaches the ore. The mixed nut coke alleviates this agglomeration, improves bed permeability, and ensures more complete contact between gas and sinter. Intriguingly, the study suggests that larger nut coke improves permeability so well that the reducing gases flow through faster, shortening their residence time and actually limiting reduction—which may explain why coarser fractions underperform the finest ones.

To probe the kinetics, the researchers applied the classical unreacted core model to their thermogravimetric data, testing whether the reaction was limited by interfacial chemistry, by gas diffusion through the solid product layer, or by a mixture of both. External diffusion was ruled out because the gas velocity of 0.26 meters per second far exceeds the critical velocity of 0.05 meters per second for diffusion-controlled reactions. The interfacial chemical reaction model produced excellent linear fits, with coefficients of determination above 0.95, while the diffusion and mixed-control models performed poorly—demonstrating that the rate-limiting step is the chemical reaction at the oxide interface itself. The fitted rate constants also showed that sinter mixed with 5 to 10 millimeter nut coke reacted fastest, consistent with the reduction index measurements.

From the Arrhenius relationship between the rate constants and temperature, the team calculated apparent activation energies of 10.81, 10.48, and 10.89 kilojoules per mole for the three nut coke fractions at 8 percent addition, compared with 12.39 kilojoules per mole for sinter alone. These values are strikingly low next to previous reports: Jin and colleagues found 28.88 kilojoules per mole for sinter-coke systems, Mousa’s team reported 24 to 40 kilojoules per mole, and Bao’s work on iron carbon agglomerates reached 72.58 to 97.41 kilojoules per mole. The authors attribute the low values to the sinter’s superior reducibility, the narrow 900 to 1000 degree Celsius window used for the Arrhenius fit, and the extra CO regenerated by the Boudouard reaction, while noting that activation energy is strongly influenced by ore type, particle size, gangue composition, reducing atmosphere, and raw material properties.

Microstructural analysis backed up the macroscopic picture. X-ray diffraction of the reduced products showed Fe, FeO, and SiO2 as the dominant phases, while scanning electron microscopy with energy-dispersive spectroscopy revealed FeO progressively transforming into Fe, with iron phases crystallizing and growing into a dense network structure that coarsened as the temperature rose from 900 to 1000 degrees Celsius. The SEM images also confirmed the ranking of the mixtures, with the 5 to 10 millimeter fraction showing the most advanced reduction at every temperature.

For an industry under pressure to decarbonize, the message is practical and precise: when charging nut coke mixed with sinter, favor the smaller end of the size spectrum and push the addition ratio toward 8 percent. Doing so promotes efficient utilization of a coke fraction that would otherwise be wasted as fuel, partially replaces premium metallurgical coke, lowers ironmaking costs, and trims the carbon footprint of the most emissions-intensive step in steel production. As hydrogen metallurgy advances and blast furnaces evolve, understanding these coupled reduction behaviors at the particle scale will be essential groundwork for the furnaces of a low-carbon future.

Subject of Research: Isothermal reduction behavior and kinetics of sinter mixed with nut coke of varying particle sizes and addition amounts

Article Title: Reduction behaviors between sinter and nut coke with varying particle sizes and addition amounts

Article References: Jiang, X., Fan, K., Jiang, Y., He, L., Ai, M., Zheng, H., & Shen, F. (2026). Reduction behaviors between sinter and nut coke with varying particle sizes and addition amounts. Results in Engineering, 32, Article 113546. https://doi.org/10.1016/j.rineng.2026.113546

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113546

Keywords: blast furnace, nut coke, sinter, ironmaking, reduction kinetics, Boudouard reaction, carbon emissions, activation energy, XRD, SEM-EDS, Reduction, behaviors

The research team, led by Xinyi Zhao of Shaanxi University of Science and Technology together with colleagues in China and France, including Philippe Sciau of the French National Centre for Scientific Research, assembled a suite of complementary analytical techniques to interrogate the sherds. Colorimetry quantified the visual appearance of the black and white regions. Optical microscopy revealed the layered structure of the ceramics at magnification. X-ray fluorescence spectroscopy mapped the elemental composition, while X-ray diffraction and Raman spectroscopy identified the crystalline phases present. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, or SEM-EDS, provided the crucial cross-sectional views that showed exactly where the iron-rich pigment sat within the glaze. Finally, and perhaps most tellingly, the team conducted replication experiments, making controlled ceramic samples using both underglaze and overglaze application methods to see which technique reproduced the microscopic signatures found in the ancient sherds.

The analytical findings converge on a clear identification of the pigment itself. Hematite, the iron oxide mineral responsible for the deep red of rust and the rich black of many historical ceramics, emerged as the main crystalline phase in the black-painted regions of the sherds. This confirms that Cizhou potters were working with iron-rich pigments, a choice consistent with the geology of northern China and with the long tradition of iron-based decoration in Chinese stoneware. But identifying hematite was only the beginning. The deeper question concerned the distribution of iron within the glaze structure, because the vertical position of the iron-rich material turns out to be a diagnostic fingerprint of when the pigment was applied relative to glazing.

That fingerprint revealed a striking contrast within the sample set. In sherds where the pigment had been applied under the glaze, the iron-rich material was concentrated near the interface between the engobe, the white slip layer coating the body, and the glaze above it. In other words, the painter had decorated the slip-covered vessel first, and the glaze had then been applied over the dried design, sealing the pigment deep within the structure. In sherds where the pigment had been applied after glazing, a completely different profile appeared: the iron formed a shallow band positioned just beneath a thin glassy cover near the glaze surface. This near-surface distribution arises because pigment applied on top of a glazed surface only partially dissolves and diffuses into the glass during firing, leaving most of the iron close to where it was painted.

The replication experiments provided the decisive confirmation. When the researchers made controlled replicas using underglaze application, the resulting samples showed iron concentrated at the engobe-glaze interface, matching the deep-pigment sherds. When they applied pigment over the glaze, the replicas developed the shallow, near-surface iron band seen in the other sherds. The correspondence between ancient artifacts and modern reproductions means that the pigment position in the Ming and Qing sherds can be interpreted with confidence as a record of the original workshop sequence. Application order, the study concludes, is the primary factor controlling where the pigment ends up in the finished ceramic, although the firing process itself can modify the detailed profile, smoothing boundaries and driving some diffusion of iron into the surrounding glass.

The black appearance of the painted decoration, the team found, is not simply a matter of pigment chemistry alone. It is associated both with the iron-rich layers and with the microstructure of the glaze surrounding them. The density and distribution of hematite particles, together with the way light interacts with the glassy matrix, jointly determine whether a painted area reads as jet black, brownish, or something in between. This interplay between composition and microstructure helps explain why Cizhou wares achieve their characteristic tonal depth, and why subtle variations in firing conditions could produce visible differences in the final appearance of pieces made in the same workshop with the same pigment.

The significance of this work extends well beyond the nine sherds examined. Cizhou kilns, centered in northern China and active over many centuries, produced some of the most influential painted ceramics in Chinese history, and their black-and-white wares were widely imitated across Asia. Attribution of undated or unprovenanced pieces to particular kiln sites, periods, or production methods often rests on stylistic judgment alone, which can be subjective and contested. A physical, measurable criterion, such as the depth profile of iron within the glaze, offers an independent line of evidence. Museums and collectors could in principle use similar analytical protocols to distinguish underglaze from overglaze decoration in pieces where the working sequence is unknown, adding a scientific dimension to connoisseurship.

The authors are careful to frame the scope of their conclusions. The findings apply to the investigated samples and do not, by themselves, establish that any particular application sequence was prevalent across Cizhou production as a whole. Nine sherds, however well analyzed, cannot capture the full diversity of a tradition that spanned multiple kiln sites, dynasties, and workshop practices. The Ming and Qing periods saw considerable evolution in Cizhou techniques, and it remains possible that different workshops, or the same workshops at different times, employed both underglaze and overglaze methods depending on the piece, the design, or the intended market. Broader sampling across more sites and date ranges will be needed to map how decoration practices changed over time and geography.

Methodologically, the study demonstrates the power of combining multiple techniques with experimental replication, an approach increasingly favored in heritage science. Spectroscopy alone can identify what a material is, but only cross-sectional imaging can show where it sits, and only replication can test whether a proposed manufacturing sequence actually produces the observed result. By closing that loop, the researchers transformed a set of analytical observations into a functional reconstruction of craft practice. The work also benefited from an international collaboration between Shaanxi University of Science and Technology and the CNRS laboratory CEMES in Toulouse, supported by funding from the National Natural Science Foundation of China and partner institutions, reflecting the growing globalization of research into ceramic technology.

For anyone who has held a Cizhou pillow or vase and wondered at the confident brushwork of its painted flowers and figures, the study offers a quiet revelation: the pigment’s position within the glaze is a fossilized record of the painter’s hand and the workshop’s order of operations. Each sherd carries within it a microscopic stratigraphy that, once decoded, tells whether the artist worked on raw slip awaiting glaze or on an already glassy surface. As analytical instruments become more accessible and databases of reference profiles grow, such reconstructions of ancient craft sequences are likely to become routine tools in ceramic studies, illuminating not just what historical potters made, but how, step by step, they made it.

Subject of Research: Decoration sequence and pigment position in Ming and Qing Cizhou kiln black-and-white ceramics

Article Title: Decoration sequence and pigment position in Ming Qing Cizhou kiln black and white ceramics

Article References: Zhao, X., Luo, H., Wang, F., Ren, Z., Zhu, J., Wang, T., Shi, P., & Sciau, P. (2026). Decoration sequence and pigment position in Ming Qing Cizhou kiln black and white ceramics. npj Heritage Science. https://doi.org/10.1038/s40494-026-03046-w

Image Credits: AI Generated

DOI: 10.1038/s40494-026-03046-w

Keywords: Cizhou kilns, Ming dynasty, Qing dynasty, hematite pigment, underglaze decoration, ceramic glaze, heritage science, Raman spectroscopy, SEM-EDS, X-ray diffraction, replication experiments, Chinese ceramics

Iron gall ink was the writing medium of Europe from the 12th through the 19th centuries, and its recipe sounds almost alchemical. Scribes mixed iron(II) sulfate with tannin-rich extracts from plant galls and organic binders such as gum arabic. The polyphenols in the tannins react with iron to form dark complexes that deepen to a rich brown-black on exposure to oxygen. The chemistry that made the ink so legible, however, also made it corrosively acidic, and the same reactivity has been slowly eating away at parchment and paper for centuries. In some ancient documents, conservators noticed something stranger still: crystals forming within the ink itself, causing the written text to fade rather than simply darken.

Those crystals turned out to be jarosite, a potassium iron sulfate hydroxide mineral that also occurs in sodium and hydronium varieties. Jarosite precipitation requires a very specific combination of conditions: abundant sulfate, ferric iron, and a strongly acidic environment. Previous attempts to reproduce its formation in laboratory-made inks reached no conclusive explanation, though repeated wetting and drying cycles have long been considered the main trigger. The new study offers a more complete picture, showing that the mineral’s appearance in the manuscript reflects interconnected inorganic and organic processes, including iron redox cycling, organic-iron complexation, and a drop in pH below 3.0, with most of the precipitation chemistry being essentially non-biological.

Under the microscope, the jarosite in the faded manuscript appeared in two telling forms. Dendritic precipitates, branching like miniature frost patterns, marked areas where the mineral had crystallized rapidly from supersaturated solutions. Elsewhere, pseudo-rhombohedral crystals displayed clear evidence of dissolution, their edges etched and corroded. This combination of fresh precipitation and active dissolution is the mineralogical signature of a system in flux, where jarosite forms, breaks down, and re-forms as chemical conditions shift within the ink layer. Crucially, both crystal types were closely associated with fungi and bacteria, placing the microorganisms at the heart of the mineral’s life cycle.

Metagenomic analysis of the ink identified acidophilic fungi belonging to the genera Geotrichum and Coniochaeta as key players. These organisms are extremophiles in a quiet sense, thriving in an environment that would dissolve most organic life. The researchers found that these fungi mobilized elements both inside and outside the inked areas of the manuscript, effectively transporting iron, sulfur, and other components across the document’s surface. In other words, the microbes were not merely passive residents of an acidic niche; they were actively redistributing the ink’s chemistry, driving the dissolution of jarosite crystals and enabling their reprecipitation in new locations.

The mechanism the authors propose is a feedback loop between biology and geochemistry. The ink’s inherent acidity, maintained by residual iron sulfate and the oxidation of iron-tannin complexes, selects for acid-tolerant microorganisms. As fungi and bacteria metabolize the organic binders and interact with the inorganic components, they alter local pH and redox conditions, releasing iron from organic complexes and supplying it to solution. When evaporation concentrates the pore solutions during drying cycles, jarosite precipitates. When humidity rises and conditions shift, the same microbes help dissolve the mineral again, translocating its elements. Each cycle leaves the ink paler and the document more fragile.

This finding reframes a long-standing conservation problem. Ink corrosion has traditionally been treated as a purely chemical threat, managed through deacidification, phytate treatments to complex free iron ions, and strict humidity control. The demonstration that living communities of extremophilic microorganisms participate in the mobilization of iron and sulfate means that microbial management may need to become part of the conservation toolkit. It also explains why laboratory reconstructions of jarosite formation in inks have been inconclusive: without the microbial actors, the full sequence of dissolution, translocation, and reprecipitation cannot be reproduced.

The analytical approach itself is a model for modern heritage science. Micro-Raman spectroscopy allowed the team to identify jarosite and distinguish its potassium, sodium, and hydronium varieties directly on the manuscript without sampling. Scanning electron microscopy paired with energy-dispersive X-ray spectroscopy revealed the crystal morphologies and their elemental signatures, while metagenomics uncovered the taxonomic composition of the microbial community without the need for cultivation, which is essential when the organisms in question are adapted to conditions nearly impossible to replicate on a petri dish. Together, these techniques connected the mineralogical evidence to its biological drivers.

Beyond the archive, the study resonates with research far from the library stacks. Jarosite is a hallmark of acid sulfate environments on Earth, from mine tailings to volcanic hot springs, and its detection on Mars has been interpreted as evidence of ancient acidic water. The Italian manuscript demonstrates that jarosite can form in a human-made, organic-rich microenvironment over historical timescales, provided acidity, iron, and sulfate are available and wetting-drying cycles concentrate the solutions. That a 17th-century scribe’s ink became a natural laboratory for the same geochemistry seen in planetary science is a striking reminder of how universal these processes are.

For the curators and conservators who steward Europe’s documentary heritage, the message is both sobering and actionable. The fading of iron gall ink is not a single chemical event but an ongoing ecological and mineralogical process, one in which acid-loving fungi such as Geotrichum and Coniochaeta and their bacterial companions continuously reshape the ink’s mineralogy. Understanding jarosite precipitation, dissolution, and translocation as coupled biological and inorganic phenomena offers a path toward interventions that address the microbial community as well as the chemistry, potentially slowing the disappearance of texts that have survived centuries of war, humidity, and neglect, only to be threatened by organisms small enough to live inside a single stroke of a pen.

Subject of Research: Microbial colonization of acidic historic iron gall ink and the precipitation, dissolution, and translocation of jarosite

Article Title: Extremophilic microorganisms colonization of acidic historic ink with precipitation, dissolution and translocation of jarosite

Article References: Maisto, F., Pin, L., Pavlović, J., Biocca, P., Bicchieri, M., Cuadros, J., Pangallo, D., & Pinzari, F. (2026). Extremophilic microorganisms colonization of acidic historic ink with precipitation, dissolution and translocation of jarosite. npj Heritage Science. https://doi.org/10.1038/s40494-026-02969-8

Image Credits: AI Generated

DOI: 10.1038/s40494-026-02969-8

Keywords: iron gall ink, jarosite, extremophiles, acidophilic fungi, Geotrichum, Coniochaeta, heritage science, manuscript conservation, micro-Raman spectroscopy, metagenomics, SEM-EDS, mineral dissolution

The numbers behind the finding are remarkable. Microplastic concentrations in Plum Run ranged from 1.2 to 23.0 particles per liter, averaging 7.6 particles per liter with a standard deviation of 4.9, meaning the stream’s plastic burden swung wildly from one sampling trip to the next. When the researchers split the year into warm and cool seasons, the pattern was unmistakable: mean concentrations were approximately 4.7 particles per liter between May and September, but 10.6 particles per liter from November through March, roughly a twofold difference. A statistical comparison using Welch’s unequal-variances t test confirmed that winter concentrations were significantly higher than summer values, with a difference of 6.8 particles per liter and a 95 percent confidence interval of 3.1 to 10.5.

What makes this study unusual is not just the seasonal signal but the statistical machinery used to detect it. Rather than relying on a single regression approach, the team built three separate multiple linear regression models: a stepwise selection model guided by the Akaike information criterion, a LASSO regression that shrinks weak predictors to zero, and an elastic net model that balances variable selection with the retention of correlated predictors. All three approaches converged on the same answer. Higher wind gusts were positively associated with microplastic counts, with a coefficient of 0.14 and a p-value of 0.037, while higher temperatures were negatively associated, with a coefficient of -0.34 and a p-value below 0.0002. The stepwise model alone explained roughly 60 percent of the variation in concentrations, with an adjusted R-squared of 0.60.

To guard against overfitting in a dataset of only 49 samples, the researchers subjected their models to repeated tenfold cross-validation, repeating the process 100 times so that every subset of the data served as both training and validation material. The results were strikingly consistent. The stepwise model achieved a cross-validated R-squared of 0.75 with a root mean squared error of 3.1 particles per liter, while the LASSO and elastic net models both reached cross-validated R-squared values of 0.79 with root mean squared errors of 2.9 particles per liter. Taken together, the models explained approximately 80 percent of the variability in microplastic concentrations, an unusually high figure for environmental field data and a strong indication that temperature and wind gusts are the dominant environmental controls on plastic abundance in this stream.

The physical story the researchers propose is one of wind-driven atmospheric delivery. Fibrous microplastics, which made up 96 percent of the particles identified in Plum Run, have high aspect ratios and low effective settling velocities, allowing them to remain suspended in air far longer than fragments or films of equivalent mass. Laboratory and field studies have shown that small fibrous particles are more readily entrained into the atmosphere as wind speeds increase, and short-lived gusts may exceed the threshold velocities needed to lift fibers that stay put under average conditions. Once aloft, these particles can travel considerable distances before turbulence subsides and they settle back to Earth, potentially landing directly on the stream surface or on the riparian corridor beside it. The mean aspect ratio of fibers measured in this study was 14, squarely within the range that model simulations identify as having enhanced atmospheric transport potential.

Two mechanisms may explain why cold weather amplifies the effect. First, vegetation acts as a seasonal filter: deciduous trees trap airborne particulates on their leaves, and the epidermal waxes that enable this trapping peak during spring and summer before declining sharply in autumn and winter. Forested zones in metropolitan areas are estimated to capture roughly 2.2 billion airborne microplastic particles per year, so when leaves fall, the pathway from air to stream becomes far less obstructed. Second, and perhaps more provocatively, cold weather changes human behavior. People wear heavier, more densely woven synthetic garments in winter, wash them more often, and run their tumble dryers more frequently, and mechanical agitation of synthetic textiles in dryers is a known source of airborne microfibers. A single dryer cycle can release more than 500,000 synthetic microfibers into the environment.

The polymer chemistry points in the same direction. Using scanning electron microscopy with energy-dispersive X-ray spectroscopy, the team screened 75 individual particles and found that 93.3 percent were polyester, with the remainder identified as polyvinyl chloride and polyolefins. Because EDS cannot definitively distinguish among carbon-rich polymers, the researchers confirmed a subset of 30 particles with Fourier transform infrared spectroscopy coupled to a diamond attenuated total reflection crystal. Every fiber that had shown oxygen peaks in its EDS spectrum, 28 particles in all, was confirmed as polyester by FTIR, while the two remaining carbon-dominated particles proved to be polypropylene. Polyester fibers are the signature morphotype of synthetic textiles, and with residential land use covering roughly half of the Plum Run watershed, the authors argue that laundering and drying of synthetic clothing is the most plausible dominant source.

To test whether wind-driven delivery is physically plausible rather than merely statistically suggestive, the team regressed wind gust data against daily plastic flux in the stream, obtaining a relationship with an R-squared of 0.42. The wind-sensitive component predicted by this regression averaged 1.28 times ten to the seventh particles per day, closely matching the mean observed stream flux of 1.38 times ten to the seventh particles per day. Scaling this wind-associated export over a 50-meter riparian buffer along the stream’s 19.3-kilometer length, and assuming a conservative one percent same-day delivery ratio, yields an implied atmospheric deposition rate of 663 particles per square meter per day. A sensitivity analysis spanning riparian widths of 10 to 150 meters and delivery ratios of 1 to 10 percent produced deposition rates from 22 to 3,161 particles per square meter per day, all of which fall within the range of atmospheric microplastic deposition previously measured in urban, suburban, and rural settings worldwide.

The authors are careful to frame these results as an indirect inference rather than a proven mechanism. The wind connection rests on statistical association, not on direct measurements of atmospheric deposition, and polymer identification by FTIR was limited to particles larger than 250 micrometers, leaving the smallest fibers characterized only by EDS screening. Still, the study carries a pointed message for anyone who assumes that rain and runoff are the whole story of riverine plastic pollution. In temperate, non-monsoonal catchments like Plum Run, the atmosphere itself may be a major conveyor of microplastics, and the rhythm of pollution may follow the calendar of human comfort: when the wind picks up and the temperature drops, the fibers of our winter wardrobes may be riding the gusts straight into the water.

Subject of Research: Environmental and meteorological controls on microplastic concentrations in a freshwater stream

Article Title: Seasonality and maximum wind gusts correlate with microplastic concentrations in a freshwater stream system

Article References: Mattie, C., Ashman, I., Fork, M., & Arnold, T. E. (2026). Seasonality and maximum wind gusts correlate with microplastic concentrations in a freshwater stream system. Environmental Monitoring and Assessment, 198(11), Article 1173. https://doi.org/10.1007/s10661-026-15985-9

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15985-9

Keywords: microplastics, freshwater streams, atmospheric deposition, wind gusts, polyester fibers, synthetic textiles, seasonality, regression modeling, FTIR spectroscopy, SEM-EDS, urban watershed, Pennsylvania

The research focused on one of the most diagnostic classes of material that an ancient metalworking site can yield: slag, the stony waste product left behind when iron is produced or worked. Slag is far more than debris. Its mineralogy and chemical composition encode the temperature of the furnace, the type of ore and fuel used, and the fundamental nature of the smelting or melting process. Because different ironmaking traditions leave chemically distinct residues, slag can act as a fingerprint for reconstructing ancient technology even when the furnaces themselves have not survived.

The team applied three complementary techniques to the Zhujiazui assemblage. Macroscopic classification allowed researchers to sort slag fragments and iron artifacts into groups based on shape, texture, color, and other visible features, providing a first-pass typology of the material. Metallographic analysis, in which samples are polished, etched, and examined under a microscope, reveals the internal microstructure of the metal and slag, including phases that form only under specific thermal and chemical conditions. Finally, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, known as SEM-EDS, delivered precise elemental compositions at the microscopic scale, identifying the distribution of elements such as iron, silicon, calcium, and magnesium within individual slag phases.

The results pointed decisively in one direction. The analytical signature of the slags indicated operations within a cast iron technological system, rather than bloomery smelting or a fining process. This distinction is fundamental to the history of metallurgy. In bloomery smelting, the dominant early technology in much of the ancient world, iron ore is reduced in a solid state below the melting point of iron, producing a spongy mass of metallic iron mixed with slag that must be repeatedly hammered to expel impurities. Cast iron, by contrast, contains enough carbon to melt at a much lower temperature, allowing liquid iron to be tapped from a furnace and poured directly into molds. Ancient China was remarkable for developing and widely deploying cast iron technology centuries before it became common elsewhere, and the Zhujiazui evidence adds a late Tang data point to that long trajectory.

Equally telling was what the excavated area lacked. The researchers found no iron ore and no ore-processing debris, the materials that would be expected if smelting, the initial reduction of ore to metal, had taken place on site. Instead, the excavation yielded ceramic molds and cast iron artifacts. Taken together, the absence of ore and the presence of molds indicate that the excavated area was primarily used for the melting and casting of cast iron. In other words, Zhujiazui was not a place where rock was turned into metal for the first time, but a foundry where already-produced cast iron was reheated, liquefied, and shaped into finished objects. This division of labor, with smelting at ore sources and casting at separate workshops, reflects an organized industrial chain rather than a single self-contained production site.

The chemistry of the slags offered further clues about workshop practice. Some of the analyzed samples showed elevated levels of calcium oxide and magnesium oxide, which the authors suggest may indicate the use of dolomitic flux. Fluxes are added to furnaces to lower the melting point of gangue, the unwanted mineral components of the charge, and to promote the formation of fluid slag that can be easily separated from the metal. Dolomite, a calcium magnesium carbonate mineral, would have served this purpose effectively. Identifying a possible dolomitic flux through slag chemistry provides a rare glimpse into the deliberate choices made by Tang dynasty metallurgists, who understood through accumulated craft knowledge which additives improved furnace performance, even without a modern theory of silicate chemistry to guide them.

Fuel evidence came in a more direct and visually striking form. The slags preserved charcoal impressions, providing direct evidence that charcoal was the fuel used in the ironworking operations. Charcoal, produced by burning wood in low-oxygen conditions, was the standard metallurgical fuel of the premodern world because it burns hot and introduces relatively few contaminants into the charge. Impressions of charcoal fragments frozen into slag record the fuel in situ, anchoring the reconstruction of furnace conditions in physical evidence rather than inference alone. For a site of this period, the confirmation of charcoal fuel also connects the foundry to the broader environmental and logistical demands of large-scale iron production, which consumed substantial quantities of wood resources.

The chronological placement of the site is significant in its own right. The late eighth to early tenth century corresponds to the late Tang dynasty and its turbulent aftermath, a period when China’s economic center of gravity was shifting southward and when iron production supported agriculture, weaponry, coinage, and daily implements on an enormous scale. Ezhou’s location on the Yangtze River places it within a region long associated with metalworking, and the authors note that the site’s location and regional context raise the possibility that it participated in wider systems of metal supply and product circulation. A casting workshop positioned within such networks would have depended on pig iron delivered from smelting sites and would have distributed its cast products through riverine trade routes, embedding Zhujiazui in an economy of raw materials and finished goods that stretched beyond the immediate locality.

Methodologically, the study demonstrates the value of reassessing archaeological contexts alongside laboratory analysis. Macroscopic classification, metallography, and SEM-EDS each answer different questions, and only by integrating them with a careful re-reading of the excavation record could the team distinguish a casting workshop from a smelting site, a difference that surface finds alone might not reveal. The work was supported by the National Social Science Fund of China and the Shaanxi Provincial Natural Science foundation, and it was carried out with the assistance of the Hubei Provincial Institute of Cultural Relics and Archaeology, whose excavation made the assemblage available for study.

For the archaeology of Chinese metallurgy, Zhujiazui contributes a clearly characterized example of late Tang cast iron melting and casting, complete with evidence for flux use and charcoal fuel, and a persuasive argument that the site operated as one node in a larger industrial landscape. As analytical techniques continue to be applied to slag assemblages across China, studies of this kind are transforming fragmentary industrial debris into readable records of ancient technology, revealing not only how iron was made but how production was organized, supplied, and connected across the Tang world.

Subject of Research: Late Tang dynasty cast iron melting and casting technology at the Zhujiazui site in Ezhou, China

Article Title: Iron production at the Zhujiazui site of the late Tang dynasty in Ezhou, South China

Article References: Zhang, M., Gao, Y., Su, J., Ma, B., & Li, X. (2026). Iron production at the Zhujiazui site of the late Tang dynasty in Ezhou, South China. npj Heritage Science. https://doi.org/10.1038/s40494-026-03010-8

Image Credits: AI Generated

DOI: 10.1038/s40494-026-03010-8

Keywords: iron production, cast iron, Zhujiazui site, Tang dynasty, archaeometallurgy, slag analysis, SEM-EDS, metallography, dolomitic flux, charcoal fuel, Ezhou, ancient foundry

Vivianite, chemically a hydrated iron phosphate, is well known to mineralogists for its striking coloration, which shifts from nearly colorless when freshly formed to deep blue or green as iron in its structure oxidizes. The mineral forms in waterlogged, oxygen-poor settings where dissolved iron and phosphate are abundant, conditions typical of lake bottoms, bogs, and saturated soils. In archaeological contexts, vivianite has been found adhering to bones, textiles, and even human remains, with famous occurrences including the Neolithic Iceman recovered from the Tyrolean Alps and the waterlogged Roman deposits at Vindolanda in northern England. Its presence has long been treated as a sign of anaerobic burial, but the Mengxihe study goes further by linking the mineral’s occurrence to measurable contrasts in soil chemistry across the same cultural layer.

The researchers analyzed vivianite associated with three distinct kinds of substrates at the site: acorn shells, fragments of bone, and the surfaces of soil aggregates known as peds. This association is itself significant, because it ties the mineral directly to the decomposition of organic matter. When plant or animal material degrades in an anoxic environment, it releases phosphate into the surrounding pore water. At the same time, the decay of organic matter consumes oxygen and drives the chemical reduction of iron oxides in the sediment, releasing ferrous iron. When these two ingredients meet in sufficient concentrations, and when competing anions such as sulfate are scarce, vivianite crystallizes. In other words, every speck of vivianite at Mengxihe marks a microenvironment where organic material once decayed under waterlogged, reducing conditions.

To identify and characterize the mineral, the team employed a trio of complementary analytical techniques. Scanning electron microscopy coupled with energy-dispersive spectroscopy, or SEM-EDS, revealed that the vivianite occurs as fine microcrystalline aggregates built from irregular short prismatic to pseudocubic crystallites. The elemental composition is dominated by iron and phosphorus, the defining constituents of the mineral, with minor amounts of manganese ranging from 0.3 to 1.4 weight percent. Raman spectroscopy provided molecular-level confirmation, detecting the characteristic vibrational modes of the phosphate groups. Notably, the Raman peaks showed shifts and broadening compared with those of well-crystallized reference vivianite, a signature of structural disorder at the nanoscale.

X-ray diffraction corroborated this picture. The diffraction patterns matched vivianite but displayed the broadened reflections characteristic of nanocrystalline material, meaning the crystals are extremely small and imperfectly ordered. This degree of crystallinity carries information in itself. Rapid precipitation from supersaturated pore waters, or formation in the presence of organic molecules that interfere with crystal growth, tends to produce such poorly ordered phases. The authors interpret the nanocrystalline character as evidence that the vivianite formed under specific local geochemical conditions rather than through slow, equilibrated diagenesis. The manganese substitution in the structure further suggests that the pore waters carried a modest dissolved manganese load, consistent with strongly reducing conditions in which manganese oxides, like iron oxides, dissolve.

The most consequential part of the study is the geochemical comparison between sediments that contain vivianite and those that do not. The researchers collected soil samples from zones proximal to and distal from the vivianite occurrences and analyzed a suite of chemical parameters. The results revealed systematic contrasts. Sediments near the vivianite showed higher concentrations of water-soluble phosphate, substantially reduced sulfate levels, near-neutral pH, and elevated organic carbon content. Crucially, the grain-size distributions of the two sediment groups remained comparable, which rules out simple sedimentological differences as the cause of the chemical contrasts. The differences must instead reflect localized geochemical processes operating within the deposit.

Each of these chemical signals fits the known requirements for vivianite precipitation. Elevated water-soluble phosphate indicates an abundant supply of dissolved phosphorus, liberated from decaying organic matter such as the acorns and bones with which the mineral is associated. Low sulfate is critical because in sulfate-rich settings, bacterial sulfate reduction generates sulfide ions that bind iron into iron sulfide minerals, effectively starving vivianite of its iron supply. Where sulfate is scarce, iron remains available to combine with phosphate instead. Near-neutral pH favors the stability of ferrous iron in solution, and high organic carbon both fuels the microbial respiration that maintains anoxic conditions and supplies the phosphate itself. Together, these parameters describe a self-reinforcing chemical niche in which organic decay, iron reduction, and phosphate precipitation proceed hand in hand.

For the archaeology of Mengxihe, these findings have direct interpretive value. The site is unusual among Palaeolithic localities in preserving botanical remains at all, since seeds, nuts, and wood normally decay rapidly after burial. The study shows that the heterogeneous preservation of organic material within the cultural layer is not random but is governed by the distribution of the geochemical conditions that favor vivianite formation. Where those conditions held, organic matter was incorporated into a chemical environment that slowed its destruction; where they did not, decay proceeded to completion. Vivianite thus serves as a map marker, pointing archaeologists to the pockets of enhanced preservation within an otherwise ordinary deposit.

The broader implications extend well beyond a single site in Sichuan. If vivianite and its associated geochemical signatures can be used as proxies, archaeologists could screen sediments for phosphate, sulfate, organic carbon, and pH to identify zones of organic preservation before committing resources to fine-grained excavation or fragile-material conservation. This would be especially valuable at waterlogged Palaeolithic sites, where organic artifacts and ecofacts are the most informative and the most perishable classes of evidence. The approach also contributes to reconstructing ancient burial environments in general terms, since the redox conditions recorded by vivianite speak to water tables, sedimentation rates, and the original character of the landscape in which early humans lived and deposited their refuse.

The Mengxihe study also connects archaeology to a much wider scientific conversation. Vivianite has become a subject of intense interest in environmental engineering, where it is studied as a means of recovering phosphorus from wastewater, and in limnology, where its formation in lake sediments controls the cycling of nutrients. Research on the mineral’s oxidation to metavivianite, its stability fields, and the influence of organic ligands on its growth continues to refine the framework that archaeologists can borrow. What the Mengxihe work demonstrates is that this body of knowledge can be turned back onto the archaeological record with real effect. A mineral once noted merely as a blue stain on old bones now offers a quantitative, testable window into the chemistry of burial, and with it, a better chance of understanding and protecting the fragile traces of the deep human past.

Subject of Research: Vivianite formation and soil geochemistry as indicators of burial environments at the Mengxihe Palaeolithic site, China

Article Title: Soil chemistry and vivianite formation in archaeological contexts: evidence from the Mengxihe Palaeolithic site, China

Article References: Wang, F., Wang, Y., & Mou, L. (2026). Soil chemistry and vivianite formation in archaeological contexts: evidence from the Mengxihe Palaeolithic site, China. Archaeological and Anthropological Sciences, 18(11), Article 212. https://doi.org/10.1007/s12520-026-02577-4

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02577-4

Keywords: vivianite, Mengxihe site, Palaeolithic archaeology, soil chemistry, geochemistry, burial diagenesis, iron phosphate mineral, organic preservation, Raman spectroscopy, X-ray diffraction, SEM-EDS, Sichuan China

The researchers, led by Bernadetta Kaźmierczak, began with dried used coffee grounds sieved to a particle size of 600 to 400 micrometers. They pyrolyzed 120-gram batches in a chamber furnace at 600 degrees Celsius under a carbon dioxide protective gas flowing at 5 liters per minute, following a carefully staged temperature program with holding periods at 200, 550 and 600 degrees Celsius. This produced an unactivated reference biochar, designated BFK_600, with a yield of about 20 percent of the starting mass. For the activated variants, the team cut off the carbon dioxide supply once 600 degrees Celsius was reached and introduced water vapor instead, at flow rates of either 2 or 4 milliliters per minute, for activation times of 15, 30 or 45 minutes. Six activated biochars resulted, each named for its exact activation recipe.

Chemical characterization began with Fourier-transform infrared spectroscopy, which tracks the vibrational fingerprints of functional groups on the biochar surface. The spectra revealed a dramatic transformation during pyrolysis itself. The raw coffee grounds displayed broad hydroxyl bands between 3530 and 3300 inverse centimeters, aliphatic C-H bands at 2923 and 2856 inverse centimeters, and a suite of carbonyl, amide and ether signals. After pyrolysis at 600 degrees Celsius, most of these bands vanished, reflecting the dehydration, decarboxylation and decarbonylation reactions that strip oxygen from the carbon matrix at high temperature. In other words, the very process that creates the carbon skeleton also destroys many of the oxygen-containing groups that make a sorbent chemically active.

The striking finding was that water vapor activation partially reversed this loss. Activated biochars developed new hydroxyl bands in the 3800 to 3000 inverse centimeter region that were absent from the unactivated material, along with shifted C-O, C-N and C-O-C signals near 1144 to 1146 inverse centimeters and new bands attributed to C=C, N-H and N-COO structures. The effect depended on the steam dose. At a flow of 4 milliliters per minute, the biochars gained additional hydroxyl bands at 3619, 3608, 3361 and 3331 inverse centimeters, plus a band at 1240 inverse centimeters corresponding to C-O, C-OH and N-COO groups that appeared only in the 15-minute sample. Notably, the longest and most intense activation, 4 milliliters per minute for 45 minutes, produced no hydroxyl bands at all, suggesting that excessive steam exposure can push the surface chemistry past a useful point.

Surface area measurements told an equally nuanced story. The unactivated biochar had a BET specific surface area of just 7.4 square meters per gram, typical of a poorly developed pyrolysis char. Steam activation increased this figure in every case, but not linearly. At the 2 milliliter per minute flow, the best result was 37.9 square meters per gram after 15 minutes, falling to 17.4 after 45 minutes. At 4 milliliters per minute, the optimum shifted to 30 minutes, yielding 62.6 square meters per gram, roughly a ninefold expansion over the unactivated char, while the 15-minute sample at that flow reached only 12.9. The team concluded that steam first carves open new pores, but prolonged or overly intense treatment begins to destroy the porous framework it created. Nitrogen adsorption isotherms classified all the materials as mesoporous, with dominant pore diameters between 2 and 2.5 nanometers.

Scanning electron microscopy coupled with energy-dispersive X-ray analysis added morphological and elemental detail. Raw coffee grounds showed a flat, fibrous structure with no visible porosity. After pyrolysis, the material fragmented into a heterogeneous network resembling broken fibers, with recesses hinting at pores. Activated samples retained this rough, folded texture, with cavities confirming porosity. The elemental analysis was particularly revealing: pyrolysis raised the relative carbon content from 49.7 to 65.7 percent while oxygen fell from 32.7 to 9.7 percent, as volatile oxygen compounds escaped. Steam activation then pushed oxygen back up, by factors of 1.3 to 1.7 depending on the recipe, and nitrogen also rose relative to the unactivated char, likely because the water vapor blanket on the particle surface limits the volatilization of nitrogen species while oxidation-reduction reactions rebuild organooxygen groups.

With the surface chemistry mapped, the researchers turned to the practical question: could these biochars remove chromium(III) from water? They selected the biochar with the richest oxygen functionality, BFK_600_4ml_15min, and the one with the largest surface area, BFK_600_4ml_30min, and compared them against the unactivated reference. Adsorption tests used a chromium(III) solution of 120 milligrams per liter at pH 4 and 20 degrees Celsius, conditions chosen to keep the metal dissolved while mimicking the mildly acidic character of real tannery wastewater streams. Chromium concentrations were tracked by inductively coupled plasma mass spectrometry.

The results showed that surface chemistry mattered more than raw surface area. The biochar activated at 4 milliliters per minute for 15 minutes, despite its modest BET area, achieved the best performance: 51 percent chromium removal with a 0.5-gram sorbent dose and 56 percent with 1.0 gram, compared with 44 and 47 percent for the unactivated char. The high-surface-area 30-minute biochar reached 47 and 55 percent respectively. The team attributes the advantage of the 15-minute material to its hydroxyl bands and the distinctive 1240 inverse centimeter C-OH signal, which provide active binding sites for trivalent chromium ions. Kinetics followed a familiar pattern: adsorption was fastest in the first ten minutes and approached equilibrium by 210 minutes for activated samples, versus 150 minutes for the unactivated char. Statistical analysis confirmed a significant effect of contact time, with Pearson correlation coefficients between 0.87 and 0.99 linking contact time to removal efficiency.

The broader significance lies in the process itself. Physical activation with steam avoids the corrosive reagents such as potassium hydroxide or phosphoric acid used in chemical activation, which can generate surface areas above 3000 square meters per gram but leave behind liquid waste streams requiring careful disposal. Steam activation produces no such by-products, and the new study demonstrates that at 600 degrees Celsius it does something chemical activation often cannot: it regenerates the oxygen-bearing functional groups that high-temperature pyrolysis destroys, even if the resulting surface areas remain modest. Earlier work by the same group showed that at 700 degrees Celsius steam activation instead wipes out organooxygen groups and boosts surface area far more dramatically, so the activation temperature emerges as a dial for choosing between a chemically rich surface and a geometrically extensive one.

For a waste stream generated at a scale of millions of tons annually, the prospect of turning espresso dregs into a green sorbent for heavy-metal-laden wastewater is compelling, and the study’s careful dissection of steam flow and activation time gives future work a clear parameter map. The removal percentages reported here, in the 44 to 56 percent range under conservative single-pass conditions, are lower than the 90 to 99 percent figures reported in the literature for lead, cadmium and manganese on coffee biochars, and the authors are explicit that their experiments were comparative rather than optimized. Even so, the message is clear: the humble used coffee ground, activated with nothing but water vapor, can be engineered into a functional water-cleaning material, and the recipe that best restores its chemical appetite for chromium is a short, gentle blast of steam rather than a long, aggressive one.

Subject of Research: Water vapor activation of biochars produced from used coffee grounds for chromium(III) adsorption from water

Article Title: Water vapor activated biochars made from used coffee grounds

Article References: Kaźmierczak, B., Radulski, P., Osuch-Słomka, E., & Zięba, E. (2026). Water vapor activated biochars made from used coffee grounds. Results in Chemistry, 31, Article 103908. https://doi.org/10.1016/j.rechem.2026.103908

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103908

Keywords: used coffee grounds, biochar, water vapor activation, pyrolysis, chromium(III), adsorption, FTIR spectroscopy, BET surface area, SEM/EDS, wastewater treatment, circular economy, functional groups

The research team, led by Cynthia C. Nwaeju and Francis O. Edoziuno, collected raw crab shells from the seashore of the Kurutie River in the Gbaramatu Kingdom of Delta State. After separating the shells from the crabs, they brushed away flakes, washed the material thoroughly with distilled water to remove sand and mud, and sun-dried it for 48 hours. The shells were then oven-dried at 100 degrees Celsius and crushed in a planetary ball mill running at 200 revolutions per minute for one hour and 45 minutes. Sieving produced a uniform powder of 75 micrometer particles, a size the authors selected because it balances surface area against homogeneity: finer particles tend to agglomerate and weaken composites, while coarser ones create stress concentration points under mechanical loading.

Half of the powder was then carbonized in a muffle furnace, ramping from ambient temperature to 800 degrees Celsius at 5.5 degrees per minute and holding there for one hour under a high-purity nitrogen atmosphere. The uncarbonized particles, which the team labels UCSP, appeared off-white, reflecting their natural content of chitin and calcium carbonate. After carbonization, the particles, dubbed CCSP, turned a dark greyish-brown, a visible signature of thermal decomposition and the loss of volatile organic compounds. The measured moisture content of the raw shells was 9.78 percent and the ash content 16.25 percent, values the authors note are lower than those reported in related studies and within the range considered suitable for industrial use.

The heart of the study lies in a battery of characterization techniques. X-ray fluorescence revealed that calcium and oxygen dominate both particle types, with significant amounts of silicon, aluminum, phosphorus, iron, and trace elements including sulfur, chlorine, potassium, manganese, and magnesium. The dominant oxides were calcium oxide, silicon dioxide, aluminum oxide, and phosphorus pentoxide. Calcium content fell from 61.781 percent in the raw particles to 59.462 percent after carbonization, a decrease the researchers attribute to the decomposition of calcium carbonate into calcium oxide and carbon dioxide, along with the removal of volatile matter, which raised the relative concentrations of other elements.

Fourier-transform infrared spectroscopy mapped the functional groups on the particle surfaces. The uncarbonized shells showed absorption peaks at 3265.1, 2113.4, 1789.1, 1654.9, 1405.2, 1066.0, 1028.7, 872.2, and 711.9 inverse centimeters, corresponding to amine stretching, alkyne stretching, carbonyl groups, alkene and aromatic stretches, and the characteristic bands of calcite, the crystalline form of calcium carbonate. The presence of a carboxylic group signals an organic matrix within the raw particles, which earlier work suggests could act as a lubricant during sliding wear and improve corrosion resistance, both valuable traits in a reinforcement material. In the carbonized particles, the spectrum shifted: peaks at 2512.0, 2844.0, and 1790.6 inverse centimeters indicated overlapping hydroxyl vibrations, carbon-hydrogen bending, and carbonyl stretching, while bands at 1401.5 and 1043.7 confirmed aromatic and carboxylic acid groups. The team also observed evidence of interaction between calcite and magnesium in the carbonized material, meaning the calcite there is not entirely pure, unlike in the raw shells.

X-ray diffraction told perhaps the most dramatic story. In the uncarbonized particles, the dominant diffraction peak at 29.7426 degrees two-theta, with a d-spacing of 3.001 angstroms and full relative intensity, matched calcite, with additional reflections corresponding to aragonite, brushite, graphite, periclase, lime, quartz, and sylvine. Quantitative analysis confirmed calcite and brushite as the dominant phases. After carbonization at 800 degrees Celsius, the pattern transformed: peaks at 29.7160 and 29.8551 degrees two-theta confirmed calcium oxide, the product of the classic decomposition reaction in which calcium carbonate breaks down into calcium oxide and carbon dioxide. Residual calcium phosphate peaks survived the heat, and a major peak indexed as magnesium calcite, in which magnesium substitutes into the carbonate lattice, replaced the pure calcite of the raw material. The sylvine phase vanished entirely, having volatilized, while new low-angle peaks signaled the formation of graphitic or amorphous carbon from the partial decomposition of organic matter.

Scanning electron microscopy added the morphological dimension. The raw particles displayed a nodular crystalline structure with rough surfaces and uneven distribution, while the carbonized particles revealed large rod-like crystalline formations, likely corresponding to calcium-magnesium carbonate precipitates that grew in situ as volatile matter burned away. Rod-like calcium carbonate crystals are associated with orthorhombic calcite phases, corroborating the diffraction results. Energy-dispersive X-ray spectroscopy on both particle types showed strong peaks for calcium, carbon, oxygen, and magnesium, with calcium by far the most intense, confirming that crab shells are naturally calcium-rich materials. The team notes that this heterogeneous, nodular-and-rod morphology is conducive to mechanical interlocking, the physical gripping between reinforcement and matrix that underpins load transfer in particulate composites.

Why does any of this matter for engineering? In metal matrix composites, particularly aluminum matrix composites prized for their strength-to-weight ratio and corrosion resistance, the choice of reinforcement determines both performance and cost. Synthetic ceramics such as silicon carbide, alumina, and boron carbide work well but are expensive and energy-intensive to produce. Researchers have therefore turned to waste-derived fillers: palm kernel shell ash, rice husk ash, eggshells, coconut shell ash, fly ash, and glass powder have all been shown to boost the hardness, tensile strength, or wear resistance of aluminum alloys. Crab shells had largely been overlooked, with prior research focused on extracting chitin and calcium carbonate for biomedical devices and water purification rather than using the particles directly. The new study shows that the oxide chemistry of crab shell particles, dominated by calcium oxide with contributions from silica, alumina, and magnesia, closely resembles that of established agro-waste reinforcements. Calcium oxide is known to impede dislocation movement in metal matrices, enhancing strength and rigidity, while magnesium oxide acts as a grain boundary stabilizer that restricts grain growth, improves interfacial bonding, and enhances wettability between reinforcement and matrix.

The carbonized form emerges as the more promising candidate. Its conversion of calcium carbonate to calcium oxide enhances thermal stability and reactivity, and the presence of magnesium calcite has been linked in earlier literature to improved corrosion resistance. The authors conclude that carbonized crab shell particles, with their enhanced stability and mineral composition, are a viable eco-friendly reinforcement for composite applications. They also caution, implicitly, that this is a characterization study: the mechanical performance of actual aluminum composites containing these particles remains to be tested in follow-up work, as does the scalability of shell collection and processing.

Even so, the implications extend beyond one laboratory. Crab shells are generated in enormous quantities by seafood consumption, and their slow degradation and improper disposal contribute to genuine pollution problems in coastal communities. Redirecting even a fraction of that stream into composite manufacturing would exemplify circular economy thinking, converting a disposal liability into a raw material. The Nigerian study, funded through the Tertiary Education Trust Fund, demonstrates that a suite of standard characterization tools can rapidly vet a novel waste stream before any expensive composite synthesis begins. If subsequent mechanical testing confirms what the microstructure and chemistry promise, the humble crab shell, today ground into fishmeal or dumped on beaches, could one day find itself embedded in automotive components, structural panels, or lightweight machinery, a quiet transformation of marine waste into engineering value.

Subject of Research: Characterization of crab shell waste particles as sustainable reinforcement materials for composite applications

Article Title: Transforming marine waste into valuable resources: morphological and structural characterization of crab shell particles for composite applications

Article References: Nwaeju, C. C., Edoziuno, F. O., Okuma, S. O., & Tuaweri, T. J. (2025). Transforming marine waste into valuable resources: morphological and structural characterization of crab shell particles for composite applications. BMC Environmental Science, 2(1), Article 7. https://doi.org/10.1186/s44329-025-00023-9

Image Credits: AI Generated

DOI: 10.1186/s44329-025-00023-9

Keywords: crab shells, marine waste, composites, aluminum matrix composites, calcium carbonate, calcium oxide, X-ray diffraction, FTIR spectroscopy, SEM-EDS, carbonization, circular economy, sustainable materials

The answer, published in the journal Discover Soil, is a qualified but emphatic yes. Twenty soil samples were excavated from four sites around Dir, Borwarra, Jolie-soir, Lamido and Yayouwé, using a systematic diamond-mesh pattern of twenty pits roughly 1.3 meters deep, deep enough to reach the construction-relevant lateritic horizon beneath the organic-rich topsoil. The samples were then analyzed across three specialized laboratories in Yaoundé, covering everything from moisture content and density to X-ray diffraction, infrared spectroscopy, X-ray fluorescence and scanning electron microscopy.

The physical results were encouraging from the outset. Natural moisture contents ranged from about 12 to 33 percent, mostly moderate values consistent with sandy, freely draining textures. Absolute densities between 2.48 and 2.75 grams per cubic centimeter sat close to the optimal range for earth bricks, and plasticity indices of roughly 8 to 12 percent fell squarely within the window recommended by Cameroonian standard NC 102-115 for compressed earth block production. That combination matters: enough clay fines to give cohesion and workability during molding, but not so much that blocks crack and shrink as they dry. Most particle-size curves from the four sites landed inside the recommended grading envelope, although a few gravel-rich samples from Lamido and elsewhere exceeded the 40 percent gravel threshold and would need sieving, crushing or corrective blending before use.

Mineralogical and chemical analysis revealed why these soils behave the way they do. X-ray diffraction showed a composition dominated by quartz, with the characteristic doublet peaks of kaolinite, residual micas such as muscovite, biotite and illite, and hematite, the iron oxide responsible for the soils’ red color. The coexistence of illite and kaolinite points to an intermediate stage of tropical weathering, in which the underlying granito-gneissic bedrock is gradually breaking down under humid conditions. The chemistry told the same story in a more dramatic way: silica between 40 and 53 percent, alumina up to 27 percent, iron oxides around 16 to 17 percent, and base cations like sodium, potassium and magnesium almost entirely leached away, averaging below 0.2 percent. The Chemical Index of Alteration exceeded 96 percent across all samples, meaning these soils are among the most chemically mature weathering products possible, essentially quartz and kaolinite skeletons stripped of nearly everything soluble.

That extreme maturity is good news for builders. Quartz provides dimensional stability and mechanical strength; kaolinite, a low-activity clay, offers plasticity without the swelling behavior that destroys earthen buildings; hematite adds cohesion and the desired coloration. The main caution is residual illite, which can raise water absorption, so the researchers recommend moderate stabilization, typically 4 to 6 percent cement or lime, along with careful moisture control during construction.

The mechanical testing program produced 64 block specimens, 16 unstabilized and 48 stabilized with varying cement contents, cured for up to 28 days. Unstabilized blocks showed moderate compressive strengths between 1.47 and 3.91 megapascals, and only the Borwarra samples cleared the 2.4 megapascal minimum set by Cameroonian standards. Cement changed the picture dramatically. With stabilization, 28-day compressive strengths climbed as high as 9.79 megapascals and flexural strengths reached 4.38 megapascals, values that comfortably exceed international durability benchmarks. Hydric properties remained favorable throughout: bulk densities of 1.79 to 1.99 tonnes per cubic meter, porosity of 25 to 30 percent, and water absorption mostly between 11 and 15 percent, within normative limits.

What elevates the study beyond routine characterization is its statistical machinery. A Principal Component Analysis on eleven geotechnical parameters revealed that soil behavior is governed by four independent factors: texture and compaction, plasticity and clay activity, the organic-mineral balance of the fines, and natural moisture content. Together these four axes explain 85.47 percent of the total variance, an unusually high figure for geotechnical data, and they provide a rational framework for formulating blocks by function rather than by trial and error. The researchers then went further, building nonlinear regression models that predict compressive and flexural strength from a handful of measurable soil properties plus cement dosage. The compressive model explained nearly 90 percent of the variance with a prediction error of about 0.34 megapascals, and the flexural model performed even better, with an R-squared of 0.966.

Those models uncovered some genuinely surprising physics. The relationship between cement content and strength turned out to be parabolic, with a minimum effective threshold near 2 percent. Below that dose, cement appears to disrupt the soil’s natural cohesive structure without forming a coherent binding network, actually weakening the material; above it, strength accelerates rapidly. Even more counterintuitive, organic matter proved harmful to compressive strength, acting as a lubricant and creating voids as it decomposes, yet beneficial to flexural strength, where moderate amounts seem to act as a natural plasticizer that toughens the block and helps it redistribute stress before cracking. Plasticity index, by contrast, was consistently detrimental, promoting shrinkage microcracks. The practical implication is that block formulation should be tailored to the expected load: elements under bending need low plasticity and moderate organic content, while compression-dominated walls demand organic matter be minimized.

Microscopy tied the macroscopic story to the nanoscale. Backscattered electron images of blocks with 0, 4, 8 and 12 percent cement showed a progressive transformation from loose grain assemblies held together by point contacts to a dense, continuous matrix. Energy-dispersive spectroscopy mapped the chemistry behind that change: calcium, nearly absent in the unstabilized soil, rose steadily with cement content as calcium-rich zones co-localized with silicon and aluminum, the signature of calcium silicate hydrate gels forming intergranular bridges. Meanwhile the relative iron signal declined as ferruginous grains became encapsulated within the growing hydration network. This is the microscopic mechanism behind the strength gains and the falling water absorption, captured directly for the first time in Dir’s soils.

The broader significance extends well one locality. Earthen materials cover roughly 70 percent of Cameroon’s territory, yet earthen construction has been held back by modest strength and vulnerability to rain. By demonstrating that Dir’s laterites can produce load-bearing, standard-compliant blocks with modest cement additions, and by supplying validated predictive tools that reduce reliance on costly laboratory iteration, the study offers a template that can be replicated for other under-characterized regions. The authors frame the work as a contribution to Sustainable Development Goals 9, 11 and 13, industry and innovation, sustainable cities, and climate action, since locally sourced stabilized earth carries a far lower carbon footprint than fired brick or concrete. They also acknowledge limits: long-term durability under wet-dry cycling and accelerated aging remains to be tested, and the predictive models are valid only within the measured ranges of gravel, organic matter, plasticity and cement dosage. Still, the message is clear. The red earth of Adamawa is not a poor substitute for modern materials; with the right science behind it, it is a modern material in its own right.

Subject of Research: Multi-scale characterization of lateritic soils in Cameroon for sustainable compressed earth block production

Article Title: Multi-scale characterization of lateritic soils from the Adamawa region of Cameroon and their suitability for sustainable compressed earth block production

Article References: Pierre, S. A. E., Hermann, K. T. J., François, N. N. G., Japhet, T. D., Bienvenu, M. O. A., Yannick, T. L., & Houivet, D. (2026). Multi-scale characterization of lateritic soils from the Adamawa region of Cameroon and their suitability for sustainable compressed earth block production. Discover Soil, 3(1), Article 134. https://doi.org/10.1007/s44378-026-00284-z

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00284-z

Keywords: lateritic soils, compressed earth blocks, Cameroon, soil stabilization, cement stabilization, geotechnical characterization, kaolinite, quartz, predictive modeling, sustainable construction, SEM-EDS, Principal Component Analysis