Dense pollucite ceramics obtained by hot-pressing as a potential matrix for the immobilization of cesium ions

A simple one-step method with direct thermal conversion at lower temperatures for removing Cs ions from water and incorporating them into a stable crystal structure that is ready for safe and permanent disposal was described. This stable structure is the one Cs-aluminosilicate phase known as pollucite. Cs-exchanged X zeolite was hot-pressed at temperatures ranging from 800 to 950 ºC to obtain dense pollucite ceramics. It was found that hot pressing decreases the temperature of pollucite synthesis and suppresses the possible volatilization of Cs ions. The influence of sintering temperature on density, phase composition, and mechanical properties was studied. The highest value of density (93 %TD) and compressive strength (79 MPa) was obtained in pollucite hot-pressed at 950 ºC for 3 h. Observation using SEM-BSE shows the heterogeneity of dense ceramics. The pollucite hot-pressed at 950 ºC had a low linear thermal expansion coefficient (4.67 × 10-6 K-1 ) and showed excellent resistance to Cs leaching. Based on these results one can conclude that hot pressing is the promising method for the permanent disposal of Cs radionuclides.X Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 26-27, 2022; Belgrad

Phase transformations of cesiumexchanged zeolites for obtaining stable cesium aluminosilicate crystalline structures, CsAlSi5O12 and CsAlSi2O6 potential matrices for the immobilization of cesium ions

Ispitan je mehanizam visoko temperaturskih faznih transformacija cezijum (Cs) izmenjenih zeolita tipa LTA i klinoptilolita (CLI). Analizirane su osobine dobijenih faza u pogledu termalne stabilnosti i otpornosti na luţenje jona cezijuma. Rezultati pokazuju da su dobijene stabilne kristalne alumosilikatne strukture polucita (CsAlSi2O6) i faze CAS (CsAlSi5O12) koje mogu biti matrice za imobilizaciju Cs jona...The mechanism of high-temperature phase transformation of cesium (Cs) exchanged zeolites such as LTA and clinoptilolite (CLI) was investigated. Thermal stability of obtained phases and their resistance to Cs ion leaching was also analysed. It was shown that the obtained stable, crystalline alumosilicate structures of pollucite (CsAlSi2O6) and CAS phase (CsAlSi5O12) can be used as matrices for Cs ion immobilisation..

Immobilization of nickel ions into stable crystal structures as a promising way for their removal from wastewater

Environmental pollution is increasing day by day due to industrial activities. Heavy metals are pollutants of special concern due to their toxicity, persistence, and bioaccumulation in nature. Nickel is a heavy metal that is mostly used in industries because of its anticorrosion behavior. As a consequence, nickel ions are present in the wastewater from mining, electroplating, battery manufacturing and metal finishing industries. Nickel ions are nonbiodegradable, and as such, they are present in surface water. Their high concentrations can have a dangerous impact on human health and aquatic life. In this work, a promising method for the removal of Ni ions from wastewater and their incorporation into a stable crystal structure was described. Ni-exchanged form of LTA zeolite was prepared by the standard procedure of ion exchange. After the ion exchange, powder samples were heated at temperatures of 900 to 1300 ºC in order to obtain a stable crystal structure of Ni-spinel, NiAl2O4. XRF analysis was used to study ion exchange efficiency. Characterization of raw as well as thermally treated powder samples of Ni-exchanged LTA zeolite was conducted by XRPD, DTA/TG, FT-IR and SEM analysisTwenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

Fabrication of Porous Anorthite Ceramic Insulation Using Solid Wastes

Porous anorthite (CaAl2Si2O8) ceramics, suitable for thermal insulation in buildings, were obtained using waste seashells as a source of CaO, kaolin as a source of Al2O3 and SiO2 and banana peel as a pore former. Changing the volume of banana peel as well as the processing temperature was found to be an effective approach to control the thermo-mechanical properties of the obtained anorthite ceramics. The sintering of powder compacts containing up to 30 wt% banana peel at temperatures ranging from 1100 to 1200 °C resulted in anorthite ceramics possessing up to 45% open porosity, a compressive strength between 13 and 92 MPa, a bulk density between 1.87 and 2.62 g/cm3 and thermal conductivity between 0.097 and 3.5 W/mK. It was shown that waste materials such as seashells and banana peel can be used to obtain cost-effective thermal insulation in buildings

Immobilization of nickel ions into stable crystal structures as a promising way for their removal from wastewater

Environmental pollution is increasing day by day due to industrial activities. Heavy metals are pollutants of special concern due to their toxicity, persistence, and bioaccumulation in nature. Nickel is a heavy metal that is mostly used in industries because of its anticorrosion behavior. As a consequence, nickel ions are present in the wastewater from mining, electroplating, battery manufacturing and metal finishing industries. Nickel ions are nonbiodegradable, and as such, they are present in surface water. Their high concentrations can have a dangerous impact on human health and aquatic life. In this work, a promising method for the removal of Ni ions from wastewater and their incorporation into a stable crystal structure was described. Ni-exchanged form of LTA zeolite was prepared by the standard procedure of ion exchange. After the ion exchange, powder samples were heated at temperatures of 900 to 1300 ºC in order to obtain a stable crystal structure of Ni-spinel, NiAl2O4. XRF analysis was used to study ion exchange efficiency. Characterization of raw as well as thermally treated powder samples of Ni-exchanged LTA zeolite was conducted by XRPD, DTA/TG, FT-IR and SEM analysis

Effect of Milling Time on Mechanical Properties of Anorthite Obtained by Thermal Transformation of Ca-LTA Zeolite

Anorthite ceramics was fabricated from calcium exchanged Na-LTA zeolite. The powder compacts of Ca-LTA zeolite were sintered at different temperatures ranging between 1100 and 1400°C. It was found that the temperature of 1100°C was sufficiently high to trigger formation of anorthite which stayed stable even at temperature as high as 1400°C. The highest relative density and the lowest open porosity were measured in samples sintered at 1200°C for 3 h. The effect of milling time of Ca-LTA zeolite precursor on density, microstructure and mechanical properties of samples sintered at 1200°C for 3 h was investigated. The particle size refinement appeared to be beneficial in accelerating densification process and improving mechanical properties. The density, compressive strength and hardness of anorthite ceramics obtained from non-milled precursor were measured to be 70.5 %TD, 64 MPa and 1.45 GPa, respectively. On the other side the anorthite ceramics obtained from 24-hour-long milled zeolite precursor had density of 83.9 %TD, compressive strength of 101 MPa and hardness of 3.44 GPa

Permanent disposal of Cs ions in the form of dense pollucite ceramics having low thermal expansion coefficient

A promising method for removal of Cs ions from water and their incorporation into stable crystal structure ready for safe and permanent disposal was described. Cs-exchanged X zeolite was hot-pressed at temperature ranging from 800 to 950 °C to fabricate dense pollucite ceramics. It was found that the application of external pressure reduced the pollucite formation temperature. The effect of sintering temperature on density, phase composition and mechanical properties was investigated. The highest density of 92.5 %TD and the highest compressive strength of 79 MPa were measured in pollucite hot-pressed at 950 °C for 3 h. Heterogeneity of samples obtained at 950 °C was determined using scanning electron microscopy. The pollucite hot-pressed at 950 °C had low linear thermal expansion coefficient of ∼4.67 × 10−6 K−1 in the temperature range from 100 to 1000 °C. © 201

Characterization of BiFeO3 Nanopowder Obtained by Hydrothermal Synthesis

Cesium aluminosilicate phases are of great interest as possible hosts for 137Cs immobilization in radioactive waste management. Cs+ exchanged forms of two synthetic zeolites (4A and 3A) were prepared by standard procedure, and content of exchanged ions was determined by ion chromatography. Obtained samples were investigated by differential thermal gravimetry TG/(DTG) and SEM/EDS analysis. All samples were annealed in the range of 600–1500 °C. High temperature phase transformations of Cs+ exchanged zeolites (LTA) were investigated. Based on data obtained by XRD analysis of the samples, it was concluded that above 1000 °C Cs-LTA (4A and 3A) frameworks recrystallized in a pollucite phase