1. Alkali-activated materials from diverse solid precursors : structural, mechanical and radiological propertiesNataša Mladenović Nikolić, Marija Ivanović, Snežana B. Nenadović, Jelena Potočnik, Sabina Dolenec, Dušan Bučevac, Aleksandar Kandić, Ljiljana Kljajević, 2026, izvirni znanstveni članek Povzetek: This study investigates the gel characteristics of alkali-activated materials (AAMs) synthesized using wood ash (WA), and metakaolin (MK) as solid precursors. The research explores the influence of precursor type and sodium hydroxide (NaOH) concentrations in the alkali activator solution on the resulting physicochemical, microstructural, mechanical, and radiological properties of gels. The alkaline activators were prepared by mixing sodium hydroxide solutions (6 M and 12 M) with a sodium silicate (water glass) solution at a volume ratio of 1.5. The physicochemical characteristics of raw materials and AAMs were thoroughly analyzed using X-ray fluorescence (XRF), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with EDS elemental mapping. FTIR analysis confirmed the formation of an amorphous gels geopolymer network. XRD revealed the presence of characteristic crystalline phases (quartz, calcite) within an amorphous matrix. Mechanical properties, such as compressive strength, depended on precursor type and alkali molarity: metakaolin (12 M) reached ~14 MPa, while wood ash showed ~4 MPa (6 M) and ~0.5 MPa (12 M) due to high CaO, low Si and Al, and unfavorable SiO2/Al2O3 (5.71) and Na2O/Al2O3 (3.19) ratios. Furthermore, this research estimates radiological doses by quantifying radionuclide content via gamma-spectrometry. Alkali activation significantly reduced radiological haz- ard parameters, with radium equivalent activity (Raeq) decreasing to 238.0 Bq/kg and the external hazard index (Hex) to 0.643 for A12MK, while the annual effective dose rate for A12WA was only 0.265 nSv/y-all values remaining well below the recommended safety limit of 370 Bq/kg (≤1 mSv/y). The decrease in activity concentration index (Iγ), Raeq, and Hex with increasing NaOH concentration indicates effective radionuclide immobilization within the geopolymer matrix, confirming the suitability of these alkali-activated materials for safe use in construction from a radiation protection perspective.
Ključne besede: wood ash, metakaolin, alkali-activated materials, radionuclides
Objavljeno v DiRROS: 24.03.2026; Ogledov: 195; Prenosov: 157
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2. Radiological characterization of alkali-activated material doped with Sm[sub]2O[sub]3 and its polymerization productsSanja Knežević, Marija M. Ivanović, Snežana S. Nenadović, Milica Rajačić, Marijan Nečemer, Jelena Potočnik, Miloš Nenadović, 2024, izvirni znanstveni članek Povzetek: The aim of this study was determination of radiological characterization of alkali-activated material with Sm2O3 and its polymerization products. Alkali-activated materials with 1 wt.% and 5 wt.% addition of Sm2O3 were synthesized and their natural radioactivity was determined. Energy dispersive X-ray fluorescence showed changes in the phase composition, or the formation of stable compounds, at higher temperatures. All samples demonstrated good pozzolanic activity, while the percentage of Sm2O3 was slightly changed. The X-ray photoelectron spectroscopy confirmed that the obtained material has a very low carbon content making it environmentally friendly, due to its low carbon content. A detailed analysis of the oxygen peak indicates variations in the stoichiometry of the oxides, which may affect the changes of natural radioactivity. Scanning electron microscopy confirmed that with the increase in the temperature of the thermal treatment, the opening of the pores in the alkali-activated material occurs, as well as further propagation of reaction that increased porosity and crystallization. Radiological measurement confirmed that examined alkali-activated material is safe for usage and exploitation. It should be emphasized that the presence of artificial radionuclide cesium 137Cs was not detected.
Ključne besede: alkali-activated material, energy dispersive X-ray fluorescence, X-ray photoelectron spectroscopy, samarium oxide
Objavljeno v DiRROS: 15.01.2026; Ogledov: 334; Prenosov: 208
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3. Adsorption efficiency of cadmium (II) by different alkali-activated materialsNataša Mladenović Nikolić, Ljiljana Kljajević, Snežana B. Nenadović, Jelena Potočnik, Sanja Knežević, Sabina Dolenec, Katarina Trivunac, 2024, izvirni znanstveni članek Povzetek: The objective of this study was to demonstrate the potential utilization of fly ash (FA), wood ash (WA), and metakaolin (MK) in developing new alkali-activated materials (AAMs) for the removal of cadmium ions from waste water. The synthesis of AAMs involved the dissolution of solid precursors, FA, WA, and MK, by a liquid activator (Na2SiO3 and NaOH). In concentrated solutions of the activator, the formation of an aluminosilicate gel structure occurred. DRIFT spectroscopy of the AAMs indicated main vibration bands between 1036 cm−1 and 996 cm−1, corresponding to Si-O-Si/Si-O-Al bands. Shifting vibration bands were seen at 1028 cm−1 to 1021 cm−1, indicating that the Si-O-Si/Si-O-Al bond is elongating, and the bond angle is decreasing. Based on the X-ray diffraction results, alkali-activated samples consist of an amorphous phase and residual mineral phases. The characteristic “hump” of an amorphous phase in the range from 20 to 40◦ 2θ was observed in FA and in all AWAFA samples. By the XRD patterns of the AAMs obtained by the activation of a solid three-component system, a new crystalline phase, gehlenite, was identified. The efficiency of AAMs in removing cadmium ions from aqueous solutions was tested under various conditions. The highest values of adsorption capacity, 64.76 mg/g (AWAFA6), 67.02 mg/g (AWAFAMK6), and 72.84 mg/gmg/g (AWAMK6), were obtained for materials activated with a 6 M NaOH solution in the alkali activator. The Langmuir adsorption isotherm and pseudo-second kinetic order provided the best fit for all investigated AAMs.
Ključne besede: fly ash, metakaolin, wood ash, adsorption kinetics, cadmium (II)
Objavljeno v DiRROS: 23.05.2024; Ogledov: 2602; Prenosov: 1038
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