A new study from RMIT University, published in Environmental Science and Pollution Research, has put five Australian natural waste clays through one of the most rigorous environmental audits yet attempted for cement alternatives. Led by Ishan Basnayaka and Chamila Gunasekara, the team did something that earlier studies rarely bothered to do: they normalized every environmental impact to the actual compressive strength each binder achieved, measuring impacts per megapascal rather than simply per kilogram of material. This performance-normalized life cycle assessment matters because a green binder that crumbles under load is not green at all. A cement substitute must deliver both lower emissions and adequate mechanical performance, and only by dividing environmental burden by strength can researchers make a genuinely fair comparison between materials that behave very differently in a testing machine.

The five clays were chosen to represent the messy reality of geology outside the laboratory. Rather than relying on pristine, high-grade kaolin, which is increasingly contested by the ceramics and paper industries, the researchers sourced two kaolinite-dominant natural mixed clays known as Red Sealing Clay and Blended Sealing Clay, an illite-dominant clay, a kaolinite-illite blend called Hanson White Clay, and a montmorillonite-and-carbonate bentonite. Each clay was dried, crushed, and sieved to 75 micrometers, then activated by one of two competing routes. The first was calcination, heating the clay to between 600 and 900 degrees Celsius to drive off structural hydroxyl groups and unlock pozzolanic reactivity. The second was mechanochemical activation, an entirely different philosophy: instead of heat, high-shear grinding in a ball mill mechanically fractures the clay particles, dramatically increasing their surface area and reactivity without ever lighting a flame.

The activated clays then replaced 30 percent of general-purpose cement by mass in paste mixes with a water-to-binder ratio of 0.4, cured for 28 days and crushed in a universal testing machine according to Australian standards. The results revealed a clear hierarchy. The calcined Red Sealing Clay binder reached 58.6 megapascals, the only mix to beat the reference cement’s 57.5 megapascals. At the other end of the scale, the mechanochemically activated bentonite managed just 36.1 megapascals, a mere 63 percent of the reference strength. Across the board, every calcined clay outperformed its mechanically activated counterpart, a pattern that would prove decisive once the environmental accounting began.

That accounting, performed in SimaPro using the Ecoinvent and AusLCI databases within a cradle-to-gate boundary, produced a headline finding with real significance for the construction industry. The calcined binders achieved up to 18.6 percent lower global warming potential than general-purpose cement, with the calcined Red Sealing Clay blend delivering the lowest carbon footprint of just 0.0129 kilograms of CO2 equivalent per functional unit. This figure aligns closely with previous studies of calcined clays worldwide, which reported reductions of roughly 15 to 18 percent at similar replacement levels. The mechanism is straightforward: replacing cement directly avoids the emissions from limestone decomposition, and the lower temperatures required for clay dehydroxylation, theoretically just 1145 kilojoules per kilogram for pure kaolinite, cut the energy bill compared with clinker production.

But here is where the story takes a twist worthy of attention. When the researchers examined abiotic depletion potential, a measure of non-renewable mineral resource consumption, the picture inverted dramatically. Mechanochemically activated clays showed up to 255 percent higher resource depletion than ordinary cement, driven primarily by the electricity consumed during grinding and the manufacture and wear of steel grinding media. Because more than 80 percent of Australia’s electricity grid is still powered by fossil fuels, the mechanically activated binders also exhibited fossil fuel depletion up to 59.4 percent above the cement baseline, despite using no direct fossil fuel combustion in the activation step itself. This is a textbook case of what environmental scientists call burden shifting: solving one problem, carbon emissions, while quietly creating another, in this case resource exhaustion and upstream pollution from the grid.

The endpoint analysis, conducted with the ReCiPe 2016 method, extended the pattern to human health, ecosystems, and resource scarcity. All calcined clay binders performed better than cement on human health, measured in disability-adjusted life years, and on ecosystem damage, measured in species-years, with calcined Red Sealing Clay again leading. Yet the mechanochemically activated bentonite increased human health burdens by 39 percent over the cement baseline. In the resource scarcity category, expressed in dollars of future extraction cost, nearly every clay binder exceeded cement, with mechanochemically activated mixes showing increases above 55 percent. Only the calcined bentonite binder achieved a 13 percent reduction in resource scarcity, thanks to its relatively high strength and short transport distance.

Sensitivity analysis added crucial nuance about the levers available to engineers. Cutting clay transport distances to 100 kilometers reduced resource depletion by 3.0 percent, human health impacts by 0.7 percent, and ecosystem damage by 0.5 percent for every 100-kilometer saving, a reminder that road freight, which emits far more CO2 per tonne-kilometer than rail or shipping, matters enormously for bulk materials. More striking were the energy scenarios. Switching mechanochemical activation to Australia’s projected 2050 electricity mix reduced impacts by up to 8.5 percent, and a fully decarbonized grid of hydropower and wind cut endpoint impacts by up to 17.4 percent. On the calcination side, replacing coal with natural gas improved human health and ecosystem scores but inflated resource impacts by up to 50.9 percent, while biomass fuel delivered reductions of up to 6 percent across categories without the resource penalty.

The broader lesson from this study is that there is no single greenest cement substitute, only the right substitute for the right place. Calcination emerges as the more environmentally favorable activation route for Australian natural mixed clays under the current coal-heavy grid, offering superior strength and the largest carbon reductions. Yet mechanochemical activation could become genuinely competitive as the electricity grid decarbonizes, since its environmental fate is tethered almost entirely to the carbon intensity of the electrons feeding the mill. For builders, cement manufacturers, and policymakers, the message is clear: the sustainability of low-carbon binders depends not just on the percentage of cement replaced, but on clay mineralogy, activation method, energy source, and transport logistics, all of which must be optimized together. As the world searches for ways to decarbonize the most consumed industrial product on Earth, this Australian study shows that the humblest materials, dug from waste deposits and activated by fire or friction, could carry a substantial share of that transition, provided we count every burden, not just the carbon.

Subject of Research: Performance-normalized life cycle assessment of calcined and mechanochemically activated Australian waste clays as low-carbon cement substitutes

Article Title: Performance-normalized life cycle assessment of calcined and mechanochemically activated clays in Australia as cement substitutes

Article References: Basnayaka, I., Gunasekara, C., Law, D., Jayathilakage, R., & Setunge, S. (2026). Performance-normalized life cycle assessment of calcined and mechanochemically activated clays in Australia as cement substitutes. Environmental Science and Pollution Research, 33(28), 14408-14423. https://doi.org/10.1007/s11356-026-38183-z

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38183-z

Keywords: cement, clay, life cycle assessment, calcination, mechanochemical activation, supplementary cementitious materials, global warming potential, burden shifting, sustainable construction, Australia, decarbonization, compressive strength

The research, published in the journal Construction and Building Materials, examined whether red mud, a highly alkaline residue generated in enormous quantities by aluminum refining, could be combined with dredged sediment to replace a substantial portion of conventional Portland cement in concrete formulations. The team, led by Faber Chaparro and Mohamed Osman, both MSc and PhD graduates of 2026 respectively, along with their colleague Mohammad Almakhadmeh and supervised by Ahmed Soliman, associate professor in Concordia’s Department of Building, Civil and Environmental Engineering, estimated that the substitution could reduce greenhouse-gas emissions by anywhere from 25 to 50 per cent, depending on how the mixture is formulated. That range is significant because it suggests the approach is not a marginal improvement but a potentially transformative one for an industry under intense pressure to shrink its environmental impact.

The logic behind the study rests on a class of materials known as limestone calcined clay cements, often abbreviated as LC3, which have emerged in recent years as one of the most promising routes to lower-carbon concrete. Rather than relying almost entirely on clinker, LC3 blends combine clinker with calcined clay and limestone powder, allowing a large fraction of the traditional binder to be replaced while retaining most of the mechanical performance. The catch is that the clay must be of reasonable quality, rich in the reactive minerals that participate in the pozzolanic reactions responsible for strength development. Low-grade clays and dredged sediments, which are abundant and cheap, often fall short of that standard because they contain impurities and lack the reactive phases that make calcined clays useful binders.

This is where red mud enters the picture. Red mud is the caustic slurry left behind when bauxite ore is processed with sodium hydroxide to extract alumina, the feedstock for aluminum metal. It is produced at a rate of well over 150 million tonnes per year worldwide, and it accumulates in vast holding ponds that pose both environmental hazards and disposal costs for the aluminum industry. Chemically, however, red mud contains oxides of iron, aluminum, and silicon, along with residual alkaline compounds, several of which are precisely the kinds of constituents that can contribute to cementitious reactions if the material is properly activated. The Concordia researchers hypothesized that red mud could compensate for the deficiencies of low-quality dredged sediment, supplying the reactive components that the sediment lacks.

To test that hypothesis, the team first subjected both the red mud and the dredged sediment to a thermal treatment, heating them at 800 degrees Celsius. Calcination at this temperature drives off bound water and restructures the mineral phases, breaking down crystalline structures and creating amorphous, chemically hungry material that can dissolve and react in the alkaline environment of a hydrating cement paste. The researchers varied the duration of the heating and found that one hour produced the best overall results, maximizing the reactivity of the two materials without wasting energy on longer treatment. That finding matters for practical deployment, because the energy cost of the calcination step directly affects both the economics and the carbon accounting of the final cement.

With the activated materials in hand, the team prepared a series of blended cement formulations in which the treated red mud and dredged sediment replaced varying proportions of Portland cement. The mixtures were then evaluated for their physico-chemical performance, including the formation of hydration products and the mechanical strength of the resulting pastes and mortars. The results revealed a clear synergistic effect: red mud could offset some of the inherent limitations of the dredged sediment, promoting the formation of the compounds that give cement its strength. In several formulations, the combination of the two waste materials produced stronger products than mixtures containing the dredged sediment on its own, demonstrating that the pairing is more than the sum of its parts.

Equally important was the finding that dosage matters. The researchers observed that excessive amounts of red mud could reduce strength in some mixtures, a consequence likely tied to the material’s iron-rich composition and its residual alkalinity, which can interfere with normal hydration chemistry when present in high concentrations. At moderate levels, however, the red mud improved the structure and performance of the blended binder, refining the microstructure and supporting the development of strength-giving phases. This dose-response behaviour underscores a recurring theme in cement chemistry: supplementary cementitious materials are not interchangeable fillers but reactive components whose optimal proportions must be carefully calibrated for each combination of source materials.

The implications extend beyond the laboratory. Dredged sediment is generated continuously by ports, waterways, and harbours around the world, and disposing of it is a persistent logistical and environmental challenge, since contaminated sediments cannot simply be dumped back into ecosystems. Red mud, meanwhile, sits in accumulating stockpiles that occupy land and carry risks of alkaline leaching. If even a fraction of these two streams could be diverted into cement production, the construction industry would gain a low-cost, locally available source of binder materials while two waste-management problems would be partially solved at once. The emissions benefit compounds the appeal: because the waste materials displace both clinker and virgin raw materials, the approach attacks the carbon problem from two directions simultaneously, reducing the need for limestone calcination and for quarrying fresh clay.

The study, titled “Physico-chemical performance of red mud/dredged-based LC3,” was published on 12 September 2026 and received funding from the Natural Sciences and Engineering Research Council of Canada, the Fonds de Recherche du Québec – Nature et Technologies, and the Canadian Standards Association. The authors declared no known competing financial interests. As with any experimental cement research, the path from laboratory formulations to structural concrete will require further validation, including long-term durability testing, work on workability and setting behaviour, and assessment of how variability in waste-stream composition affects performance at industrial scale. But the core result stands: materials that industries currently pay to dispose of can be transformed, with a modest input of heat, into ingredients that make cement both stronger and substantially cleaner. In a sector where even single-digit percentage reductions in emissions are celebrated, a formulation capable of cutting greenhouse gases by up to half represents the kind of advance that could reshape how the world builds.

Subject of Research: Using red mud and dredged sediment as supplementary materials in low-carbon limestone calcined clay cement

Article Title: Research: Industrial waste can be a key ingredient in low-carbon cement, new Concordia study shows

Article References: Research: Industrial waste can be a key ingredient in low-carbon cement, new Concordia study shows. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: cement, red mud, dredged sediment, LC3, clinker, carbon emissions, Concordia University, construction materials, aluminum industry, waste valorization, calcination, sustainable building

The starting point of the study is a familiar frustration in surface science. Superhydrophobic coatings, which repel water so thoroughly that droplets bead up and roll away, typically demand elaborate multi-stage synthesis, energy-hungry processing and, very often, fluorinated compounds that raise environmental and regulatory concerns. Long-chain per- and polyfluoroalkyl substances have come under increasing scrutiny for their persistence, so materials researchers have been searching for fluorine-free routes that do not sacrifice performance. The Chinese team’s answer is to let a single thermal treatment do the chemical heavy lifting, converting a blended precursor into a functional hierarchical surface in one pass through the furnace.

The chemistry behind the transformation is where the elegance lies. UiO-66 is a zirconium-based metal-organic framework, a crystalline lattice of zirconium clusters linked by organic struts, prized for its chemical robustness and thermal stability. When a UiO-66@PDMS composite is calcined, the framework’s organic components burn away and the zirconium nodes are converted into zirconium dioxide, or ZrO2, while the PDMS does not simply vanish. Instead, it partially decomposes, leaving behind oligomeric silicone fragments. The result is a composite microstructure in which inorganic ZrO2 particles derived from the framework are married to residual PDMS-derived oligomers, and it is precisely this combination that endows the coating with its slippery superhydrophobic character.

That dual character matters because superhydrophobicity and slipperiness address different aspects of how water interacts with a surface. A water contact angle exceeding 150 degrees signals that droplets sit atop trapped air pockets with minimal solid contact, so they bead and roll. Slipperiness adds a dynamic dimension: droplets that do make contact slide off easily rather than pinning to the texture. Surfaces that combine both traits resist the accumulation of condensed moisture far better than conventional superhydrophobic materials, which can fail when water vapor infiltrates the texture and condenses inside it, flooding the air pockets and collapsing the water-repellent effect. The USS coating’s composite structure appears to sidestep that failure mode.

The anti-condensation performance is one of the study’s headline results. In humid environments, the coating effectively inhibits water vapor from condensing on treated surfaces, and under low-temperature conditions it extends the freezing-thawing cycle time of water droplets while maintaining stable superhydrophobic properties. That combination is directly relevant to real infrastructure. Condensation on cooled surfaces plagues power transmission equipment, optical lenses, refrigeration systems and building envelopes, and ice formation on aircraft wings, wind turbine blades and power lines remains a costly and hazardous problem. A coating that delays both condensation and freezing, without fluorine, could find wide application in cold and humid climates.

The second major demonstration involves oil-water separation, a technology with urgent environmental stakes given the frequency of oil spills and the volume of oily industrial wastewater. The researchers applied the USS coating to stainless-steel mesh, turning it into a superhydrophobic, oleophilic filter that lets oil pass while blocking water. The numbers are striking: the modified mesh achieved a separation flux of up to 40,000 liters per hour per square meter for trichloromethane, a dense chlorinated solvent that passes through under gravity alone. Flux at that scale means large volumes of oil-water mixture can be processed quickly, which is essential for any practical spill-response or wastewater-treatment deployment.

Equally important is durability, the Achilles heel of many laboratory superhydrophobic surfaces that lose their magic after a few uses. The coated mesh retained a separation efficiency above 90 percent and a water contact angle still exceeding 150 degrees even after 15 separation cycles. Sustained performance across repeated use suggests that the calcined composite structure is mechanically and chemically robust enough to survive continuous contact with liquids, a prerequisite for commercial membranes and filters. The result also aligns with a broader trend in the field, where metal-organic frameworks and their derivatives are increasingly being harnessed as building blocks for superwettable separation materials.

The third function, flame retardancy, is perhaps the most unexpected for a coating that also repels water. When USS-coated cotton fabric was exposed to flame, the coating absorbed flame heat and generated a dense char layer, a carbonaceous barrier that inhibits combustion by shielding the underlying fibers from heat and oxygen. The coating also cut down black smoke emission, addressing a major hazard in textile fires, since smoke inhalation is a leading cause of fire fatalities. Critically, the treated fabric kept its structural integrity and its superhydrophobicity intact through the process, meaning the water repellency does not have to be sacrificed to gain fire protection.

Multifunctionality of this kind is increasingly the benchmark for advanced coatings, because real-world surfaces rarely face a single threat. A tent fabric, a worker’s protective garment or an industrial filter might simultaneously encounter rain, oil contamination and fire risk. Previous efforts have combined such properties by stacking multiple layers or blending numerous additives, often at the cost of complexity and performance trade-offs. The UiO-66@PDMS route achieves the combination from a single precursor and a single thermal step, which simplifies manufacturing and reduces the energy footprint compared with conventional multi-step superhydrophobic coating preparation.

The work, conducted at the College of Materials Science and Engineering at South China University of Technology and supported by the Key-Area Research and Development Program of Guangdong Province and the Natural Science Foundation of Guangdong Province, offers a template that other laboratories can adapt. Because UiO-66 is one of the most studied and chemically tunable metal-organic frameworks, and PDMS is cheap, widely available and easy to process, the strategy could in principle be extended to other substrates and other framework chemistries. For now, the study stands as a demonstration that a furnace, a framework and a silicone can together produce a surface that repels water, resists ice, filters oil and fights fire, all without a single fluorine atom.

Subject of Research: Fluorine-free ultra-slippery superhydrophobic multifunctional coatings fabricated by one-step calcination of UiO-66@polydimethylsiloxane

Article Title: Fabricating ultra-slippery superhydrophobic multifunctional coatings by one-step calcination of UiO-66@polydimethylsiloxane

Article References: Lai, D., Wang, H., Kong, G., Che, C., & Miao, X. (2026). Fabricating ultra-slippery superhydrophobic multifunctional coatings by one-step calcination of UiO-66@polydimethylsiloxane. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13895-2

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13895-2

Keywords: superhydrophobic coating, UiO-66, metal-organic framework, polydimethylsiloxane, calcination, oil-water separation, flame retardancy, anti-condensation, anti-icing, ZrO2, fluorine-free, surface wettability

The review’s central finding is that thermal exposure produces a recognizable progression of macroscopic and microscopic changes. As heat intensifies, bone shifts in color from brownish and blackened hues toward gray, then chalky white as organic components burn away and the mineral phase calcines. Alongside this chromatic journey come shrinkage, warping, and a characteristic suite of fractures. These changes are not governed by peak temperature alone. The authors emphasize that oxygen availability, the duration of combustion, and the overall burning conditions all shape the final appearance of the remains, which helps explain why two bodies exposed to the same nominal fire can emerge with markedly different skeletal damage.

That multi-factorial picture matters because forensic anthropologists routinely try to reconstruct fire circumstances from burned remains. Color, for instance, has long been treated as a rough thermometer, and the review highlights work using spectrophotometric and colourimetric analysis to make that assessment more objective. Studies cited in the review measured bone color quantitatively to estimate the temperature of exposure in cortical and medullary bone, while other research examined how prolonged heating affects both color and crystallinity. The mineral crystals of bone grow and reorganize as heat destroys the collagen scaffold, and techniques such as FTIR-ATR spectroscopy and X-ray diffraction can track those crystal-size changes, offering a chemical complement to visual inspection.

The microscopic scale tells an equally important story. Histological studies of heated compact bone, including work on human rib tissue, show that the microstructure of bone degrades in ways that can interfere with established methods of age estimation, which often rely on examining bone remodeling features under the microscope. The review notes that research has tested whether histological age estimation remains viable in burned ribs, and that the survival of age-at-death diagnostic features under heat is a genuine concern. One cited study found that heat-induced changes affect the skeletal features used for age-at-death estimation, underscoring that fire does not merely damage bone superficially but can erase or distort the very markers anthropologists depend upon.

Warped and shrunken bone poses a parallel problem for the biological profile, the set of estimates covering age, sex, ancestry, and stature that anchors identification efforts. The review draws on experimental work showing that heat-induced dimensional changes in bone have direct consequences for metric analysis, since measurements taken after burning no longer match the pre-burning skeleton. Yet the news is not uniformly grim. Studies on osteometric sex determination of burned remains and performance tests of stature estimation methods in burned skeletal material, including a Portuguese population sample, suggest that metric approaches can still perform usefully when their limitations are understood. Research into the pre-burning condition of remains aims to correct for shrinkage and distortion, effectively reconstructing what the skeleton looked like before the fire.

Perhaps the most forensically charged question the review addresses is trauma analysis: can investigators still distinguish a perimortem fracture, inflicted around the time of death, from a fracture caused by the fire itself? The literature assembled here says it is sometimes possible, though never straightforward. Classic work on differentiating traumatic from heat-related fractures established diagnostic criteria, and more recent studies have tested the differentiation of mechanical versus thermal damage as causes of bone fractures. Researchers have examined whether cranial perimortem fractures remain identifiable in cremated remains, whether perimortem traits survive on burnt long bones, and even whether dismemberment-related toolmarks and pre-existing ballistic trauma can be detected after burning. The review’s verdict is that trauma examination remains feasible in some cases, but fragmentation and calcination may obscure the diagnostic features on which such determinations depend.

Underlying all of these applications is the basic material science of bone as a composite. Bone combines a flexible organic phase, dominated by collagen, with a stiff mineral phase of hydroxyapatite. Heat attacks both. Vibrational spectroscopy studies cited in the review explored how the collagen content of human bone influences heat-induced warping, capturing the idea that bone with more surviving collagen tends to deform by yielding rather than shattering. As temperatures rise, water and organic matter are driven off, the mineral recrystallizes, and the bone becomes brittle and calcined. Scanning electron microscope observations of incinerated human femoral bone documented these microstructural transformations in detail, and comparative work on burning under oxidizing versus reducing conditions showed that the chemical atmosphere of the fire itself leaves detectable signatures in the bone.

The review also situates burned-bone analysis within the broader operational world of fatal fire investigation. Forensic anthropologists are increasingly involved in the search and recovery of victims from structure fires and wildland fires, and in disaster victim identification, where burned and fragmented remains are common. Studies on the degree of bodily destruction relative to the duration of the fire, and postmortem computed tomography findings of thermal bone injuries in actual cases, illustrate how anthropological interpretation now intersects with imaging and fire-science expertise. Classification systems that categorize thermal damage by body segment aim to standardize how investigators document and communicate burn patterns, and experimental work on accidental versus deliberate burning scenarios explores whether bone can reveal whether a fire was intentional.

What emerges from the systematic review is a discipline maturing toward methodological self-awareness. The authors conclude that the effects of thermal alteration vary according to the component of the biological profile being assessed, the methods employed, and the degree of skeletal preservation, a formulation that effectively warns against one-size-fits-all interpretation of burned remains. Understanding the mechanisms of heat-induced skeletal change, they argue, improves the examination of burned human remains and supports more reliable forensic anthropological analysis in fire-related investigations. For a field whose conclusions can shape criminal prosecutions and identification of fire victims, that mechanistic grounding is not academic luxury. It is the difference between reading the skeleton’s fiery testimony accurately and mistaking the fire’s own handiwork for evidence of violence.

Subject of Research: Heat-induced structural and chemical alterations of human skeletal remains and their implications for forensic anthropological analysis

Article Title: Thermal alteration of skeletal remains in forensic anthropology: a systematic review

Article References: Cevahiroglu, N., & Buyuksungur, A. (2026). Thermal alteration of skeletal remains in forensic anthropology: a systematic review. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-03995-8

Image Credits: AI Generated

DOI: 10.1007/s00414-026-03995-8

Keywords: forensic anthropology, burned bone, thermal alteration, calcination, biological profile, trauma analysis, heat-induced fractures, bone color, systematic review, fire investigation, age estimation, shrinkage

For decades, engineers and researchers have optimized the Pidgeon process by studying heat transfer, reaction kinetics, furnace configuration, and thermal field distribution. Yet nearly all of this work shares a hidden assumption: that calcined dolomite behaves as an ideal binary mixture of magnesium oxide and calcium oxide, produced by the complete decomposition of the mineral dolomite, CaMg(CO3)2. Under that ideal framework, the silicothermic reaction requires a one-to-one molar ratio between the two oxides, and the maximum magnesium producible is set by whichever oxide is the limiting reagent. The calcium silicate larnite, Ca2SiO4, is understood as the thermodynamic sink that forms during reduction itself, driving the equilibrium toward metallic magnesium release.

A new study published in Results in Engineering by Aldemir de Melo Sotero and colleagues at the Universidade Federal do Pará in Brazil challenges that assumption in a way that could reshape how magnesium producers evaluate their raw materials. The team investigated two natural dolostones from Brazil with sharply contrasting clay contents: the Alcântara Dolostone, drawn from a Cretaceous coastal formation in the state of Maranhão, which contains the hydrated magnesium-aluminum clay mineral palygorskite at levels of 2.7 and 11.1 weight percent in two variants, and a Silurian dolostone more than 400 million years old that is essentially pure dolomite at 99.8 weight percent. The pure sample served as a mineralogical reference, while the clay-bearing rocks exposed a yield-destroying chemistry that bulk analysis cannot see.

The problem begins with what palygorskite does when heated. This phyllosilicate loses adsorbed and channel water below about 300 degrees Celsius, dehydroxylates between roughly 400 and 500 degrees Celsius, and then undergoes structural collapse above approximately 800 degrees Celsius, releasing poorly ordered, chemically reactive silica. That temperature range overlaps almost exactly with the calcination stage of the Pidgeon process, in which dolomite decomposes into lime and periclase. The freshly released reactive silica does not wait for the reduction stage. It reacts immediately with free calcium oxide, and to a lesser extent magnesium oxide, forming calcium and magnesium silicate phases before any reducing agent is introduced. The same silicate chemistry that is productive and mechanistically necessary during reduction becomes a yield-limiting constraint when it occurs during calcination, because it permanently removes oxides from the pool available for reduction.

To quantify this sequestration, the researchers designed a full 2³ factorial experiment varying charge mass from 1 to 10 grams, calcination temperature from 900 to 1100 degrees Celsius, and residence time from 1 to 8 hours, with center-point replicates, for a total of 12 runs per sample. They characterized the raw materials and calcined products using wavelength-dispersive X-ray fluorescence, simultaneous differential scanning calorimetry and thermogravimetry, and powder X-ray diffraction coupled with Rietveld quantitative phase analysis. The Rietveld method, a full-pattern fitting approach that iteratively refines a calculated diffraction profile against the measured pattern, delivered weight fractions for every crystalline phase with refinement agreement indices showing weighted profile R-factors between 5.4 and 9.0 percent and goodness-of-fit values close to unity.

The phase assemblages revealed a far more complex silicate chemistry than previously reported for clay-bearing dolostones. In the moderately clay-rich sample, larnite formed under every experimental condition, reaching weight fractions up to 43.8 percent, while diopside, MgCaSi2O6, gehlenite, Ca2Al2SiO7, and a magnesium silicate with Mg3Si2O9 stoichiometry appeared at higher temperatures and longer residence times. The gehlenite confirmed that aluminum released from palygorskite structural collapse also partitions into silicate phases. The Mg3Si2O9 phase, which is thermodynamically unstable at calcination temperatures, was interpreted as a retrogressive product crystallizing during cooling, when freshly calcined periclase reacts with residual amorphous silica. In the pure Silurian reference sample, by contrast, the calcined products consisted exclusively of periclase and lime, with no silicate phases detected in any run, establishing a clean baseline.

The team then built a Rietveld-based stoichiometric model that converts crystalline phase weight fractions into molar quantities per 100 grams of calcined material, performs elemental balances to separate reducible from sequestered oxide fractions, and simulates the silicothermic reduction with commercial 75-grade ferrosilicon. The results were striking. In the pure dolostone, available calcium oxide and magnesium oxide appeared in nearly equimolar proportions, matching the ideal Pidgeon stoichiometry. In the low-clay sample, available calcium oxide ranged from 22.5 to 35.5 weight percent, and theoretical magnesium yield ranged from 0.401 to 0.626 moles per 100 grams. In the high-clay sample, available calcium oxide collapsed to as little as 3.0 weight percent under severe conditions, leaving more than 90 percent of the periclase without its calcium counterpart and driving theoretical magnesium yield down to 0.053 moles per 100 grams, nearly an order of magnitude below the pure reference. Bulk oxide chemistry would have overestimated recoverable magnesium by about 42 percent for the low-clay sample and by up to roughly 1200 percent for the clay-rich sample under the harshest conditions.

Statistical analysis of the factorial design added a second layer of insight. For the low-clay sample, residence time was the only significant factor for both magnesium yield and total silicate formation, with opposing effects that confirmed the mineralogical trade-off: longer heating simultaneously increases silicate formation and decreases magnesium availability. For the clay-rich sample, temperature became the dominant factor by a wide margin, with residence time second and a significant temperature-by-time interaction reflecting the self-limiting nature of silicate growth once available calcium oxide is exhausted. Composite desirability optimization identified low temperature, short residence time, and low charge mass as the optimal calcination window for both samples, but the operating window was far narrower for the clay-rich rock. Even at their respective optima, the clay-rich sample yielded about 12 percent less theoretical magnesium and generated about 24 percent more slag than the low-clay sample, a penalty attributable to raw material mineralogy that process adjustment can mitigate but never eliminate.

The practical implications reach directly into industrial operations. The authors argue that ferrosilicon dosage should be calculated on the basis of effectively available calcium oxide rather than total periclase content, since dosing against total magnesium oxide in a clay-bearing feedstock would produce a substantial and costly excess of reducing agent. They also recommend routine X-ray diffraction characterization of dolomite raw materials as an integral component of quality control, replacing reliance on bulk oxide chemistry alone, because two feedstocks with identical bulk compositions can differ dramatically in reducible magnesium depending on how much of their oxide inventory is already locked into silicates. The mechanistic framework extends beyond palygorskite to other phyllosilicate impurities such as kaolinite, smectites, chlorites, and illite, each of which releases reactive silica at calcination temperatures. The theoretical yields reported here represent a mineralogical ceiling on recoverable magnesium, and the authors note that experimental validation through representative silicothermic reduction trials is planned as a dedicated follow-up study. For an industry that produces nearly a million tonnes of magnesium a year under thin margins, the message is clear: the clay hidden in the rock can quietly consume the metal before the furnace ever gets its chance to make it.

Subject of Research: Quantitative assessment of clay-derived reactive silica sequestration of CaO and MgO during dolostone calcination and its impact on theoretical magnesium yield in the Pidgeon silicothermic reduction process

Article Title: Magnesium yield estimation based on Rietveld refinement of clay-bearing dolostone: implications for silicothermic reduction

Article References: Sotero, A. D. M., Oliveira, R. L. R., Brito, C. E. C., Albuquerque, A. R. L., Paz, S. P. A., & Angélica, R. S. (2026). Magnesium yield estimation based on Rietveld refinement of clay-bearing dolostone: implications for silicothermic reduction. Results in Engineering, 32, Article 113155. https://doi.org/10.1016/j.rineng.2026.113155

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113155

Keywords: magnesium, Pidgeon process, silicothermic reduction, dolostone, palygorskite, Rietveld refinement, calcination, larnite, reactive silica, X-ray diffraction, ferrosilicon, mineralogy

K. S. Swathi and K. Gopalakrishna Naik synthesized titanium dioxide nanoparticles using the sol–gel method, a low-cost wet-chemistry route in which titanium tetra(iv) isopropoxide, a common liquid precursor, is added dropwise to ethanol under constant stirring. Hydrochloric acid was used to set the pH of the solution to 1.4, ensuring that hydrolysis proceeded under acidic conditions. After two hours of stirring at room temperature, the solution was heated to 125 degrees Celsius for an hour, and the resulting gel was pre-heated at 300 degrees Celsius for two hours to drive off reaction by-products and begin crystallizing the material. The white powder was then divided into batches and calcined for two hours in a tubular furnace at temperatures ranging from 300 to 900 degrees Celsius.

The team then subjected each batch to a battery of characterization techniques, including powder X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, high-resolution TEM, selected area electron diffraction and UV–visible absorption spectroscopy. The X-ray diffraction results told a clear story. Samples calcined at 300 degrees Celsius showed broad, low-intensity diffraction peaks characteristic of the tetragonal anatase phase, a signature of nanoscale crystallites with a large fraction of atoms at surfaces, along with surface defects and amorphous grain boundaries. Samples calcined at 400 and 500 degrees Celsius remained purely anatase, but their diffraction peaks sharpened as crystallinity improved.

The first hint of change came at 600 degrees Celsius, where a very low-intensity peak at around 27.5 degrees in 2-theta, corresponding to the (110) lattice planes of rutile, appeared alongside the dominant anatase reflections. This marked the onset of the anatase-to-rutile transformation. By 700 degrees Celsius the diffraction patterns matched the tetragonal rutile phase, and samples calcined at 800 and 900 degrees Celsius were overwhelmingly rutile. Notably, a faint anatase (101) peak persisted even at 900 degrees Celsius, indicating that the applied temperature and two-hour duration were not sufficient to achieve complete transformation to pure rutile, a phase that in many studies only forms above 1000 degrees Celsius.

Using the Scherrer equation on the most intense diffraction peaks, the researchers estimated that crystallite size grew from about 3.39 nanometers at 300 degrees Celsius to 61.5 nanometers at 900 degrees Celsius. Microstrain and dislocation density, both indicators of crystal defects and distortion, decreased steadily with increasing calcination temperature, confirming that heat treatment suppresses surface defects and amorphous grain boundaries while allowing crystallites to grow. The relative amounts of anatase and rutile were quantified with the Spurr–Myers method, which showed that the rutile weight fraction increased monotonically between 600 and 900 degrees Celsius as enhanced atomic diffusion and grain growth drove the transformation forward.

Raman spectroscopy independently confirmed the phase evolution. Samples calcined up to 600 degrees Celsius displayed only anatase features, dominated by the intense E_g vibrational mode near 144 inverse centimeters, together with the B1g band near 397 inverse centimeters and the combined A1g plus B1g and E_g modes near 513 and 635 inverse centimeters. The 700-degree sample was a hybrid, showing both the anatase E_g band and strong rutile E_g and A1g modes, along with a multi-phonon scattering feature near 230 inverse centimeters. At 800 and 900 degrees Celsius, only rutile bands remained. The team also tracked a gradual red shift of the E_g modes with increasing temperature, attributing it to phonon softening caused by lattice expansion, anharmonic vibrational effects and partial relaxation of residual strain. The phonon confinement model, rooted in the Heisenberg uncertainty principle, explains how smaller particles broaden the phonon momentum distribution and produce asymmetric broadening of Raman bands.

Electron microscopy added a subtle twist. Field-emission SEM images of samples calcined at 400, 600 and 800 degrees Celsius showed micrometre-sized agglomerates of fine, roughly spherical nanoparticles, with no dramatic morphological change across the temperature range. Energy-dispersive X-ray spectra confirmed the presence of only titanium and oxygen. Transmission electron microscopy, however, revealed that average particle size rose from roughly 8.6 nanometers at 400 degrees Celsius to 25.5 nanometers at 600 degrees Celsius, then unexpectedly fell to about 12 nanometers at 800 degrees Celsius before jumping to around 202 nanometers at 900 degrees Celsius. The authors attribute the dip at 800 degrees Celsius to the breaking and rearranging of titanium–oxygen bonds during the anatase-to-rutile transformation, in which distorted anatase octahedra break apart and reassemble into the denser rutile structure, collapsing loosely bound agglomerates into more compact grains.

High-resolution TEM lattice fringes and selected area electron diffraction patterns corroborated the diffraction results. The d-spacing measured at 400 and 600 degrees Celsius was about 0.35 nanometers, matching the (101) planes of anatase, while the 800-degree sample contained grains with d-spacings of both 0.35 and 0.32 nanometers, corresponding to anatase (101) and rutile (110) planes respectively. At 900 degrees Celsius the d-spacing of about 0.25 nanometers confirmed the rutile (101) plane. Inverse fast Fourier transforms of the 800-degree sample revealed structural distortion from edge dislocations, direct visual evidence of the strain involved in the phase transformation. The SAED ring patterns confirmed that all calcined samples were polycrystalline.

Optical measurements revealed perhaps the most intriguing finding. Using Tauc analysis of UV–visible absorption data, the researchers found that the nanoparticles exhibited apparent direct-transition-like band gap behavior, even though bulk anatase is classically an indirect band gap semiconductor. The direct-transition fits produced more linear absorption edges and better near-band-edge fitting than indirect models, which the authors attribute to quantum confinement, structural disorder and defect-induced localized states that modify the electronic band structure at the nanoscale. The sharp absorption edges, without pronounced tails, suggested low densities of localized defect states and improving crystallinity with temperature. The band gap decreased from about 3.51 electron volts at 300 degrees Celsius to 3.34 electron volts at 700 degrees Celsius as anatase crystallites grew, then settled at 3.33 and 3.25 electron volts for the 800 and 900-degree rutile-dominated samples, consistent with the known band gaps of the two phases.

The study’s significance lies in its integrated view of how a single processing variable, calcination temperature, simultaneously governs phase composition, crystallite size, vibrational response and optical behavior in titanium dioxide. By clarifying why nano-anatase appears to behave like a direct band gap semiconductor and by mapping the gradual, incomplete anatase-to-rutile transformation between 600 and 900 degrees Celsius, the work offers practical guidance for researchers tailoring titanium dioxide nanoparticles for photocatalysis, solar energy conversion and optoelectronic devices, where the balance between anatase and rutile often determines performance.

Subject of Research: Calcination temperature effects on the structural, vibrational and optical properties of sol–gel synthesized TiO2 nanoparticles

Article Title: Calcination effect on the properties of sol–gel synthesized TiO2 nanomaterials

Article References: Swathi, K. S., & Naik, K. G. (2026). Calcination effect on the properties of sol–gel synthesized TiO2 nanomaterials. Discover Industrial Chemistry and Materials, 1(1), Article 3. https://doi.org/10.1007/s44508-026-00003-0

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00003-0

Keywords: titanium dioxide, TiO2 nanoparticles, sol–gel synthesis, calcination, anatase, rutile, phase transformation, X-ray diffraction, Raman spectroscopy, optical band gap, photocatalysis, nanomaterials