Csaba Szabó

CO ₂ degassing from the deep Earth provides important insights into the global carbon cycle. CO ₂ ‐rich fluid inclusions in mantle xenoliths record fluid sources and migrations in the deep lithosphere, while the contribution of mantle components in groundwater can be traced via dissolved gas geochemistry. Here, we integrate basin‐scale geochemical observations with thermo‐kinematic modeling to reconstruct CO ₂ release in the Neogene Carpathian–Pannonian continental back‐arc system. He‐Ne isotope ratios were determined from mantle xenoliths studied in detail by fluid inclusion analyses, collected from the Styrian Basin ( R _c / R _a = 5.8–6.8), Bakony–Balaton Highland ( R _c / R _a = 6.1–7.3) and Perşani Mountains Volcanic Fields ( R _c / R _a = 2.3–5.3). This was compared with groundwater data from the same areas using previous studies and new data from the Bakony–Balaton Highland ( R _c / R _a = 1.0–2.1 and δ ¹³ C = −9.60‰ to −6.24‰). Considering the inferred genetic connection of deep fluids and groundwater, the results on mantle degassing can be extrapolated and modeled to recent times owing to the same geodynamic setting prevailed during xenolith transport to the surface. Continuous crystallization of CO ₂ ‐bearing, non‐extractable melts within the asthenosphere results in gradual release of CO ₂ during post‐rift lithospheric thickening. This mechanism is supported by numerical analysis of melting, melt extraction and mantle degassing over time, demonstrating that persistent post‐rift CO ₂ release until today is physically plausible. This mechanism provides a reasonable explanation for the widespread occurrence and longevity of non‐volcanic CO ₂ emissions far from areas of active volcanism in the Carpathian–Pannonian region and in analogous post‐rift tectonic environments worldwide.

The Laleaua Albă (White Tulip) magmatic complex (LA) consists of small-scale composite andesitic–dacitic dikes representing the third volcanic phase (8.5–8.0 Ma) of the Gutâi Volcanic Zone (GVZ) within the Neogene–Quaternary volcanic chain of the East Carpathians (Romania). The LA comprises two composite dikes that crosscut older volcanic units. The outcrop, at the sampling site exhibit a tulip-shaped light-colored dacitic core – containing abundant mafic microgranular enclaves (MME) – surrounded by a dark gray andesitic envelope. Volcanic rocks from the GVZ and LA display typical post-collisional (calc-alkaline) geochemical signatures. Based on their major element compositions, the studied clinopyroxenes are primitive (Mg#: 73–85) and represent the earliest crystallization phases. Clinopyroxene geothermobarometry indicates crystallization pressures of ~5.5–8.5 kbar, suggesting a deep magma storage system in the lower crust at depths of 22–30 km, proximal to the regional Moho (33–35 km). Micro-Fourier Transform Infrared (FTIR) spectrometry was used to determine the structurally bound hydroxyl contents of nominally anhydrous minerals (NAMs) across the three lithologies to reconstruct the volatile evolution of the dike system. Measured structurally bound hydroxyl concentrations in clinopyroxene (80–610 ppm), plagioclase (11–37 ppm), and quartz (2.5–9.5 ppm) indicate moderate to high values. The equilibrium water contents calculated from clinopyroxene range between 0.6 and 4.7 wt.% H2O. These values are consistent with subduction-related calc-alkaline magmatism, though evidence of re-equilibration with the dacitic melt is observed, aligning with previous quartz-hosted melt inclusion studies. Variations in hydroxyl content between the dacitic host and MMEs record the history of magma mixing. The preservation of high hydroxyl concentrations indicates that the dike did not undergo significant post-emplacement degassing, maintaining high water activity during cooling. This study demonstrates that subvolcanic rocks can effectively preserve primary magmatic water signatures, serving as essential benchmarks for the volatile budgets of post-collisional volcanic systems.

Boric acid enriched in 10B (EBA) is a novel neutron absorber that can be used in reduced quantities in nuclear power plants compared with boric acid with natural isotopic abundance (natural boric acid, NBA). Consequently, the amount of waste requiring solidification prior to disposal can also be reduced. However, our previous study demonstrated that, due to isotopic, elemental, and molecular differences of boron, the leachability of B—and thus the chemical stability—of cementitious waste forms produced from NBA and EBA liquid wastes differ significantly. In the present study, the leachability of the other major elements constituting the cementitious matrices, including Ca, Si, S, Al, and Na, was also investigated. Analytical techniques such as ICP-MS/OES, and XRD or SEM-EDX were applied to examine the effects of varying boric acid concentration and isotopic enrichment. The results showed that the leachability of non-structural elements (i.e., B and Na) is lower in EBA-containing specimens—by up to 29%—compared with NBA-based materials. In contrast, the leachability of the structural elements of the cementitious matrix (Ca, Si, S, and Al) increased, in some cases by up to 120%. These contrasting trends highlight the need for a comprehensive evaluation of the leaching behaviour of all major elements present in cementitious matrices when assessing the long-term durability of simulated final waste forms, rather than relying solely on boron leachability, as is commonly done.

The immobilization of radioactive liquid waste through cementitious encapsulation remains a cornerstone strategy in nuclear waste management. This study examines the microstructural impacts of increasing gamma irradiation doses on a PC-SAC-zeolite-bearing composite for boric acid RLW immobilization. The PC-SAC-zeolite-bearing composite specimens were exposed to varying doses of gamma radiation, i.e. to 10 Gy, 500 Gy, and 1000 Gy, respectively. After exposure to gamma radiation, the specimens were then studied using a combination of visual analyses using Stereo Microscopy and Scanning Electron Microscopy (SEM) and microstructural analyses using a combination of Transmission Electron Microscope (i.e. Bright-Field BF, Selected Area Electron Diffraction SAED, and Energy Dispersive Spectroscopy EDS), Fourier Transform Infrared Spectroscopy FTIR, and Raman Spectroscopy) analysis to investigate observable changes in the PC-SAC-zeolite-bearing composite specimens after exposure to gamma radiation. Visual alterations and changes in the microstructure of the specimen were observed at a gamma irradiation of 1000 Gy.

The relationship between microbial communities and mineralogical/mechanical changes was studied regarding the biodeterioration of Portland cement (PC) and calcium sulfoaluminate cement (CSAC) in a wastewater treatment plant. An in situ experiment was conducted by submerging 12 independent PC and CSAC specimens in a sand-trap structure for 10, 30, 75, 150, and 240 days. The microbiological analyses of the 16S rRNA genes of bacteria and Archaea from the biofilms and the geochemical analysis were performed on the studied specimens. The results showed that while there were characteristic changes in PC specimens over time, CSAC specimens showed few biodeterioration effects. The dominant bacteria identified from the biofilms of specimens belonged to the classes of Gammaproteobacteria (8.4–32.4%), Bacilli (1.6–21.6%), Clostridia (4–15.4%), Bacteroidia (2–18.8%), Desulfovibronia (0.5–19%), Campylobacteria (0.4–26.8%), and Actinobacteria (1.8–12.8%). The overall relative abundance of the bacteria linked to biodeterioration processes increased to more than 50% of the total bacterial communities after 75 days of sewage exposure and was found to be strongly correlated with several PC deterioration parameters (e.g., mass loss, calcite and ettringite minerals), whereas no significant correlation was revealed between these genera and CSAC characteristics.

Wastewater treatment plants (WWTPs) are critical environmental solutions for sanitation management in many cities and municipalities. The construction of these facilities uses cementitious materials (e.g., concretes) due to their low cost, high strength and excellent watertightness properties. However, the long-term performance of these materials in WWTPs is affected by deterioration influenced by the formation of new (secondary) cement minerals. These secondary minerals are formed as a result of biogeochemical interactions between cementitious materials and wastewater microbial communities. The literature shows a lack of consensus on the mechanisms involved in the biogeochemical mechanism of sewage and cementitious materials in WWTP facilities. As a result, many civil and water engineers are unaware of its adverse effects on the sustainability of WWTP facilities, and as a consequence, the operation of many WWTP facilities costs billions of dollars in repair and maintenance due to concrete failure. This study studies the possible processes of biogeochemical interactions between sewage and cementitious materials in WWTPs and their subsequent mineral alteration and formation.An in-situ experiment exposed 48 cement specimens of ordinary Portland cement and calcium sulfoaluminate cement to the sewage pumping station and sand-trap structures. The research involves: (1) geochemical analysis (SEM and XRD) to study the change of cement materials, (2) engineering analysis to study their mechanical change and (3) microbiological investigations to explore the microbial communities involved in the biogeochemical interaction.The preliminary results of the study: (a) change of color from light grey to a mixture of yellow and brown for cement pastes exposed in the sewage pumping station, whereas the samples from the sand-trap maintained their original grey color. (b) the appearance of secondary minerals such as gypsum (CaSO4.2H2O), ettringite (Ca6Al2(OH)12(SO4)3·26H2O), and thaumasite (Ca3Si(OH)6 (CO3) (SO4)12.H2O) which are characterized as expansive process causing several cracks in the concrete structures. (c) the main mechanism for the formation of these sulfur-related minerals (i.e., gypsum, ettringite, and thaumasite) involves sulfide adsorption and its subsequent oxidation to form biogenic H2SO4 which eventually attack the cement alkaline mineral phases such as portlandite (Ca(OH)2 and calcium silicate hydrate (C-S-H). Another biogeochemical mechanism for sewage-cement interaction observed in this work was the carbonation process, which resulted in the formation of calcite mineral in hydrated cement.

Wastewater treatment plants (WWTPs) are critical infrastructures for wastewater management, and their durability is crucial. Due to their excellent water tightness and strength, cementitious materials are used to build WWTPs. However, the performance of these materials is affected by aggressive environments. There are few in situ experiments in the literature regarding the deterioration of cementitious materials in WWTPs. This paper investigates their deterioration mechanisms in a sewage pumping station and a sand-trap structure of a WWTP. In situ experiment was conducted by exposing cement specimens in both locations for 1, 2, 3 and 7 months. The physical and morphological changes of the specimens were examined using stereo microscopy and scanning electron microscopy, whereas the mineralogical/solid phase changes were examined using X-ray diffraction. The results showed that the specimens from the pumping station formed colored surface products, which were confirmed to be secondary minerals (i.e., gypsum and ettringite), whereas there were no colored surface products in the sand-trap structure. The results demonstrated that cementitious materials subjected to wastewater vapors (in a pumping station) had higher deterioration effects than those subjected to wastewater liquid (in a sand-trap structure), suggesting that the wastewater vapors are more aggressive toward cementitious materials than wastewater liquids.