Synthesis and characterization of TENORM-free nano zirconia from zircon sand

To avoid radiation exposure in the use of nano zirconia in the ceramics and dentistry industries, a Technologically Enhanced Natural Radioactive Materials (TENORM)-free nano zirconia was required. The purpose of this research was to obtain an environmentally friendly TENORM-free nano zirconia prototype. TENORM-free nano zirconia synthesis consists of processing zircon sand into sodium zirconate, leaching of sodium zirconate to form zirconyl chloride solution, separation of impurities (silica, ThO₂, U₃O₈, etc.), crystallization of zirconyl chloride, zirconyl-oxalate sol-gel formation, and calcination. The quality test of nano zirconia products was characterized by XRD, FT-IR, SEM, and Surveymeter, while the composition test was carried out by the XRF method. The results of this research obtained an environmentally friendly TENORM-free nano zirconia prototype, that has the chemical compound of ZrO₂, the crystal size was 15.09 nm, the average particle size was 91.33 nm, free of radiation exposure, and its composition includes ZrO₂: 96.599%, HfO₂: 2.899%, and CaO: 0.303%. This synthesis can process zircon sand containing TENORM (ThO₂: 0.070% and U₃O₈: 0.047%) into TENORM-free nano zirconia and increase the added value by increasing the zirconia content from 40.493% to 96.599%.     

Theoretical study of the polarized electronic absorption spectra of vanadium-doped zircon

The polarized electronic absorption spectra of a blue vanadium-doped zircon single crystal, grown by the flux method, has been studied by quantum chemical (CI) calculations in order to determine the position of the V⁴⁺ dopant in the zircon host structure. Particularly, the excitation energies and polarizations of V⁴⁺ occupying alternate positions, either the zirconium or silicon position or the interstitial site 16g, have been considered. It is concluded that the observed electronic absorption spectra and the color of zirconblue can only be explained if the V⁴⁺ chromophore is placed on the respective interstitial position.     

进口锆英砂放射性γ能谱分析

利用γ能谱分析技术对2个产地共17个进口锆英砂样品中的放射性核素226Ra、232Th和40K进行了定量分析,并提出了一种新的样品自吸收修正方法。结果:产地1样品中226Ra的比活度均值为2399.75Bq/kg,232Th的比活度均值为422.72Bq/kg;产地2样品中226Ra的比活度均值为1852.91Bq/kg,232Th的比活度均值为455.45Bq/kg;2个产地样品中40K的比活度均很低。研究表明,锆英砂样品中放射性主要来源是226Ra、232Th。两产地样品中232Th的放射性比活度相差较小,而226Ra的放射性比活度差别明显。同一产地样品中放射性核素比活度也存在较大差异。样品自吸收对分析结果的影响可达10%—30%,须进行自吸收修正。     

Mineral zircon: A novel thermoluminescence geochronometer

Mineral zircon contains trace amounts (typically 10-1000 v ppm) of the f -emitters uranium and thorium, which irradiate this mineral internally. This outstanding feature of zircon turns out to be extremely useful when this mineral is applied as a thermoluminescence (TL) dating medium, because the build-up of the age-dependent luminescence is dominated by the presence of well-defined internal radioactive sources and the contributions to the dose from external radiation sources are two orders of magnitude smaller. The results presented in this paper have led us to the conclusion that for zircon dating it is necessary to carefully select the best and homogeneous zircon grains of the highest optical quality. For successful dating experiments on very young and historically well-defined coastal dune sands, selection of the most stable luminescence component by means of narrow band interference filters is needed. Our results suggest that ultimately optical zircon dating will allow us to determine the age of extremely young samples ( e.g. 12 months!).     

Spectroscopic Characterization of Metamictization and Recrystallization in Zircon and Titanite

Recent applications of infrared and Raman spectroscopy in the study of the metamict (or "amorphized") state, high-temperature recrystallization and radiation-induced OH species in natural zircon (ZrSiO₄) and titanite (CaTiSiO₅) are reviewed.     

Reduction of UO2 and ThO2 content in zircon mineral from Bangka Region using calcium borate and hydrochloric acid

In an effort to reduce radiation exposure in the use of zircon minerals as opacity for the ceramic industry, it is required that the concentrations of UO₂ and ThO₂ contained in zircon must be less than 500 ppm. The purpose of this study was to reduce the concentration of UO₂ and ThO₂ in zircon minerals. The experimental investigation was initiated by synthesizing of calcium borate (CB), roasting of zircon concentrate with CB at various temperatures, and leaching with hydrochloric acid. The product quality of zircon minerals before and after roasting and leaching was characterized by Fourier Transform Infrared Spectrometer, X-Ray Diffractometer, and X-ray Fluorescence Spectrometer. The experimental results show that roasting zircon concentrate with CB at a zircon/CB ratio of 5/5 (weight/weight), a temperature of 1200 °C, a contact time of 3 h, and the leaching of the roasted results with 6 M HCl can reduce the total concentration of UO₂ and ThO₂ in zircon from 2008,1 ppm to 498.4 ppm. It can be concluded that the prototype zircon product from the experimental results has fulfilled the premium grade zircon with UO₂ and ThO₂ content of less than 500 ppm.     

Imaging of growth banding of minerals using 2-stage sectioning: application to accessory zircon

In the past, investigations of mineral growth were routinely carried out by the application of light-microscopic methods and, later on, by the production of single crystal sections and their documentation using specific imaging techniques (CL, BSEI, etc.). In the present work, a method is described which enables the precise sectioning of elongate crystals parallel and perpendicular to their longest axis. By examining backscattered electron images of parallel and perpendicular sections of the same grain, growth of all faces may be evaluated without major geometric correction. The new technique is applied to zircon crystals of a granitoid exposed in the southwestern Bohemian Batholith, Austria. For the studied zircon population, pyramidal and prism development during crystal growth is worked out very clearly by the imaging procedure. Besides its significance in crystal studies, the introduced method could also find a use in material science for the growth study of synthetic mineral phases.     

Mesozoic cooling history of the “Bachu Uplift” in the Tarim Basin,China: Constraints from zircon fission-track thermochronology

We applied zircon fission-track analysis to outcrop and borehole samples to study the Mesozoic cooling history of the Bachu Uplift, the Central Uplift of the Tarim Basin. Zircon fission-track (ZFT) ages of 182 Ma – 249 Ma are younger than the sample depositional ages indicating substantial post burial thermal annealing and can effectively reveal cooling events in the Bachu Uplift. The strong correlation between single grain ZFT age and U content indicates that most of the zircon grains represent ages that have been partially annealed and so the age is not directly indicative of the time of cooling. The youngest ZFT age populations with modal peak ages of 151 ± 8 Ma (Well HT1 samples), 126 ± 6 Ma (Well T1 samples) and 192 ± 10 Ma (Xiaohaizi Reservoir profile samples) from the decomposition of the ZFT single-grain ages represent the onset of cooling events in the Bachu Uplift, which were related to the collisions of the Qiangtang Terrane and Lhasa Block with the southern margin of the Eurasia continent, respectively. This study provides new insights into the tectonic and sedimentary evolution of the Tarim Basin and even Central Asia by constraining the higher temperature (c. 250–180 °C) part of the basin thermal history.     

Time-resolved OSL of natural zircon: A preliminary study

Time-resolved OSL (TR-OSL) from natural zircon (ZrSiO₄) minerals was investigated using 445 nm blue laser light for stimulation. Analyses of the TR-OSL spectra have showed that the decay is composed of two exponential components with lifetimes varying around ∼17 μs and around ∼110 μs respectively. The behaviour of these signal components, was examined under various sample treatments and experimental conditions. Preheating experiments showed that the OSL signal is stable up to temperatures ∼250 °C then becomes unstable. The dose response of the TR-OSL signal from zircon was determined in the range from 1 Gy to 1 kGy and observed to be increasing linearly. Practically, no effect of radiation dose on the lifetimes of signal components was observed. In addition, the effect of measurement temperature on the TR-OSL decay lifetimes was also investigated. Thermal quenching energies of the “fast” and the “slow” components were found to be very close to each other i.e. 0.18 and 0.24 eV respectively.     

Kinetic model for the annealing of fission tracks in zircon

A model for the annealing kinetics of fission tracks is proposed based on a simplified track. The principal hypothesis is that the atoms displaced during the passage of the fission fragment have to transmit through a potential barrier to occupy the vacant sites left. The resulting model equation is applied to zircon data both from laboratory and geological sources. The model succeeded in fitting the data and the addition of the geological data during the fitting procedure improved the extrapolation of the model to the timescale of millions of years, which is the timescale of interest in geology applications.