Thematic Articles

Applications of Zeolites in Environmental Remediation

Thematic Articles, Zeolites / Hossein Kazemian

The use of natural zeolites and their modified forms in environmental remediation reflects their effectiveness, abundance, and relatively low production cost. By combining innovative technologies with research on natural zeolites, several important environmental applications have been developed. These include the separation, binding, and chemical stabilization of hazardous and/or radioactive species, such as Cs and Sr, in soils and waters impacted by nuclear operations and accidents. In the case of hazardous waste, zeolites can be used to transform pollutants into stable materials suitable for final disposal. They can also remove naturally occurring pollutants from drinking water, which is crucial in a world where many people still lack access to safe water, and they can improve soils to support sustainable agriculture.

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Natural Zeolites: Pathways to Green and Durable Cement and Concrete

Thematic Articles, Zeolites / Ruben Snellings

Rocks containing natural zeolites have been used since antiquity as components of concrete and mortars. As pozzolans, natural zeolites react with slaked lime (Ca(OH)₂) or Portland cement and water to form sparingly soluble calcium silicate and calcium aluminate hydrates. This pozzolanic reaction improves the long-term strength and durability of the mortar and concrete. Moreover, natural zeolites may replace Portland cement, reducing CO₂ emissions from cement production, thereby making them an interesting decarbonization solution. Ongoing mineralogical investigations have revealed the influence of zeolitic framework topology, Si/Al ratio, and cation-exchange capacity on the pozzolanic reactivity of natural zeolites within cementitious matrices. This research paves the way to better utilization of this natural resource and leveraging its CO₂-saving potential in construction.

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New and Innovative Applications of Natural Zeolites

Thematic Articles, Zeolites / Aleksandra Daković

The unique properties of natural zeolites have been exploited for decades in a myriad of applications. Recent innovative applications of natural zeolites have applied surfactants to modify their surfaces, augmenting their normal cation-exchange property with an ability to interact with non-polar and anionic species. These surfactant-modified zeolites have been studied for removal of viruses, bacteria, pharmaceuticals, organic compounds, and oxyanions (including AsO₄^3-) from waters and of mycotoxins from animal feed. They have also been applied as active ingredients in medical devices, drug carriers, and wound-healing accelerators. Natural zeolites have been evaluated in wine and beer making, often producing superior results when combined with bentonite. Applications for natural zeolites continue to grow, but the polymineralic nature of most deposits must be considered.

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Zeolites as Tools for Interpreting Geological and Geochemical Conditions

Thematic Articles, Zeolites / Tobias B. Weisenberger

Natural zeolites typically form in low-temperature (<200 °C) environments under alkaline conditions (pH > 8). Their formation generally follows a thermal–chemical gradient, which often results in a zonation pattern of zeolites and other alteration minerals that can be linked to the physicochemical conditions existing during formation. Careful investigation of mineral compositions, sequences, and patterns at different scales facilitates unraveling past fluid–rock interactions. Investigations of the time-dependent alteration and formation of zeolites in young volcanic tephra deposits allow for a better understanding of the variability of zeolite mineralogy with respect to the effects of temperature, fluid chemistry, hydrological conditions, and time.

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Natural Zeolite Crystal Chemistry: Structural Diversity and Behavior Under Non-ambient Conditions

Thematic Articles, Zeolites / Paolo Lotti

Zeolites have remarkable structural and chemical versatility, arising from their wide range of framework configurations, the variable populations of extra-framework species occupying their structural voids, and their ability to adsorb molecular species. These characteristics underpin unique properties like cation exchange, molecular sieving, selective adsorption, and catalytic behavior. Their framework flexibility allows dynamic responses to environmental stimuli, including temperature, pressure, and relative humidity, leading to phenomena such as negative thermal expansion (contraction), amorphization, and dehydration. Under pressure, zeolites can undergo pressure-induced incorporation of ions and molecules from surrounding fluids, modifying their structure and properties. Understanding these responses opens new pathways for tailoring zeolite behavior for technological applications and deepening our comprehension of their role in geological processes.

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Natural Zeolites: Understated Minerals with Remarkable Versatility

Thematic Articles, Zeolites / G. Diego Gatta

Zeolites commonly occur as microscopic crystals and are often overlooked. However, we benefit from these minerals in many unrecognized ways. Their distinctive crystal structures result in their ability to hydrate/dehydrate reversibly, to exchange cations with aqueous solutions, and to act as molecular sieves. These structure-related physicochemical properties make zeolites an important group of industrial minerals. In nature, they form as one of the first alteration products of continental and oceanic crust under low-temperature conditions. The distribution and occurrence of zeolites can provide important constraints on the spatial and temporal evolution of geological systems within the shallow crust.

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Stromatolites as Recorders of Major Oxygenation Events and Biogeochemical Metal Cycling through Earth’s History

Thematic Articles, Stromatolites and Other Microbialites / Sylvie Bruggmann

Microbial carbonates are found throughout most of the geological record and have formed under varying atmospheric and hydrospheric conditions. Recent advancements in analytical techniques have enabled the use of novel, highly promising geochemical proxies, such as metals and their isotopes, to reconstruct ancient microbial habitats. Here, we review recent discoveries and the benefits of applying redox-sensitive and bioessential metal proxies in microbialites, aiming to reconstruct Earth’s oxygenation and determine the availability of dissolved metals in past microbial habitats. These findings contribute to a better understanding of the evolution of microbial life and its ecological niches on Earth through time. Moreover, they offer a potential blueprint for the search for extra-terrestrial life, thereby informing ongoing and future planetary studies.

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Exploring the Stable Isotope Record of Stromatolites

Thematic Articles, Quartz, Stromatolites and Other Microbialites / Christophe Thomazo

Stromatolites rank among the most productive ecosystems on Earth, with extremely high rates of element cycling, especially carbon, oxygen, nitrogen, iron, and sulfur. Their study provides critical insights into early microbial life evolution, environmental conditions, and associated biogeochemical cycling. Specifically, carbon, nitrogen, and sulfur isotopes can be used to assess metabolic activities of microbial communities, including those that may regulate the formation and preservation of modern and ancient stromatolites, such as photosynthesis, nitrogen fixation, and sulfate reduction. Moreover, while Precambrian stromatolites’ isotopic signals can record microbial communities that both influence and adapt to changing major redox conditions such as the Great Oxidation Event, local and secondary processes can open a window onto microbial evolution such as the early evolution of bacterial sulfate reduction.

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Stromatolites Through Earth’s Early History

Thematic Articles, Stromatolites and Other Microbialites / Axel Hofmann

Stromatolites are widespread in Precambrian sedimentary successions and provide important insights into life, environmental processes, and surface conditions on the young Earth. Shaped by interactions among microbial processes, sediment deposition, and mineral precipitation, stromatolites have a record spanning most of Earth’s history and are sensitive indicators for past hydrodynamic conditions and water chemistry. Significant variations in the composition, texture, and structure of stromatolites and associated sedimentary facies occur throughout the geological record, constraining the evolution of surface conditions. The ability of microbial communities to build large carbonate platforms in turn actively influenced the Precambrian hydrosphere and atmosphere. Stromatolites are direct, visible evidence of microbial ecological success that shaped the Precambrian Earth’s surface.

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Microbialite-Associated Microbial Communities, Present and Past

Thematic Articles, Stromatolites and Other Microbialites / Miguel Iniesto

This chapter describes the biological composition of modern microbialites, aiming at identifying the major microbial actors that may contribute to their mineralization and growth. Despite the vast diversity in community composition, environmental conditions, and dominant mineral phases, certain key components emerge as critical drivers of these processes. Additionally, the dominance of specific microbial populations can serve as a proxy for identifying key metabolisms involved in mineralization, such as oxygenic and anoxygenic photosynthesis, sulfate reduction, and methanogenesis. Finally, we discuss how these insights enhance our understanding of ancient microbialites, bridging the gap between modern observations and the geological record.

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December 2025 --The Variscan Orogeny in Europe – Understanding Supercontinent Formation