模拟铯废物钛硅酸盐玻璃的化学稳定性研究

熔制了模拟铯废物钛硅酸盐玻璃，用IR研究了玻璃的结构，用产品一致性试验法（PCT）研究了玻璃的化学稳定性，结果表明，所选组成的配料可以在1100℃熔制得玻璃，样品的密度在3．2703．35g/cm^3之间，玻璃中Ti^4 可能以[TiO4]进入玻璃网络，玻璃的结构主要由[SiO4]和[TiO4]组成，产品一致性试验法（PC）实验的浸出液中主要有R＋离子，当配料中n(TiO2):n(SiO2)为0．40－0．35时，浸出液中各种离子的浓度均较低，表明玻璃具有较好的化学稳定性。     

模拟锶铯废物铁磷酸盐玻璃固化及化学稳定性

研究了铁磷酸盐玻璃固化我国高放废液全分离流程中产出的锶废物及铯废物，熔制了相应的固化体。用XRD，IR测试了固化体的微观结构，用产品一致性试验方法(PCT)研究固化体的化学稳定性。研究表明：在所选的废物包容量范围内可熔制得均质模拟废物铁磷酸盐玻璃固化体，玻璃的主要结构基团为P2O7^4-，均质玻璃固化体有较好的化学稳定性。     

改性透辉石玻璃对Mo包容量的研究

高放废液中的钼在传统硼硅酸盐玻璃中的溶解度较低,超过溶解度的部分极易形成黄相,黄相的出现对固化体性能不利,并限制了固化体中废物的包容量。通过以改性透辉石玻璃为基体提高钼的溶解度,从而避免黄相的形成。采用X射线衍射、拉曼光谱、红外光谱、扫描电子显微镜、密度测量以及电感耦合等离子体发射光谱仪等现代分析测试技术对系列样品的成分、微观结构、理化性质和化学稳定性进行了表征。结果表明：用硼砂改性透辉石,可以有效地降低透辉石玻璃的烧制温度。改性透辉石玻璃对Mo的最大包容量为9%(质量分数),当MoO ₃的掺量为10%时,改性透辉石玻璃将析出CaMoO ₄晶体,表明改性透辉石对钼的包容量高于硼硅酸盐体系,此时固化体的密度为2.86 g/cm ³。经过浸出测试,改性透辉石玻璃固化体28天的浸出液Mo浸出率为1.8×10^-5 g/(m²·d),表明改性透辉石玻璃固化体具有良好的化学稳定性。     

模拟高钠高放废物铁硼磷酸盐玻璃固化体的结构和性能

以36Fe2O3--10B2O3--54P2O5为基础玻璃,制备了不同模拟高钠高放废物包容量的铁硼磷酸盐玻璃固化体,用Fourier变换红外光谱测试方法系统研究了由废物包容量引起的玻璃固化体结构变化,并用溶解速率法初步测试了固化体的化学性能。结果表明:随着废物包容量的增加,固化体试样结构中(PO4)3-四面体基团增加,[BO3]基团向[BO4]基团转变,磷酸盐基团彼此间的连接程度减小,Fe—O—P键在包容量为25%(质量分数)到30%时存在量较大。玻璃固化体网络结构以(PO4)3-四面体基团为主,易水化的(PO3)-磷酸盐基团的含量很小。但固化体结构中[BO3]基团的存在量还较大,该组分的基础玻璃网络形成体氧化物配比还可进一步优化。当废物包容量小于40%时,固化体不同浸泡周期的质量损失速率均在10--8 g/(cm2·min)数量级。     

不同氧化物对磷酸盐玻璃结构与性能的影响

在化学组成为40Na 2O·60P2 O 5的基础上,用CaO、MgO取代Na 2O或用Al2 O 3、B 2 O 3和SiO2取代P2 O 5制备5种磷酸盐玻璃体系,用X射线衍射(XRD)和傅立叶变换红外光谱(FTIR)对玻璃结构进行了表征,并测定了该玻璃体系样品的密度、化学稳定性等基本性质。研究发现,用CaO取代Na 2O和Al2 O 3取代P2 O5可以显著改善玻璃的化学稳定性;用SiO2取代P 2 O 5时,玻璃的化学稳定性下降;由于配位问题,B 2O 3和MgO对磷酸盐玻璃结构与性能的影响出现转折点。     

钙钛锆石玻璃陶瓷体的晶化和抗浸出性能

以SiO2、A12O3、B2O3、CaO、TiO2和ZrO2为原料,加入3％CeO2（质量分数,下同）作为模拟核素,利用熔融法制备钙钛锆石基玻璃陶瓷体,对含锕系元素的放射性废物进行固化处置。通过X射线衍射仪和场发射扫描电子显微镜等对热处理后玻璃陶瓷体进行表征。以电感耦合等离子体质谱测试玻璃陶瓷体抗浸出性能。结果表明：在晶化温度为1050℃,B203掺量为12．5％时,玻璃陶瓷体中低质量分数的TiO2和ZrO2更易参与生成钙钛锆石晶体,但固化体中仍有其他晶相存在;在同样晶化温度下,B203掺量为8．33％时对玻璃陶瓷体形成钙钛锆石单一晶相较为有利,且具有较好的抗浸出性能,其中Ce在产品一致性测试法下元素标准化浸出率7d后维持在10^-6数量级,固化效果明显。     

BaO-TiO2-SiO2系统结构、玻璃形成能力及析晶性能

BaO-TiO2-SiO2系统玻璃具有高折射率和好红外透过性等优异性能特点.在选定组成范围内,采用传统熔融法制备玻璃,通过平板淬冷法进行成形.采用XRD,DSC,RAMAN光谱和SEM,探讨了BaO-TiO2-SiO2系统的玻璃形成能力、析晶性能及玻璃结构变化规律.研究结果表明:随着SiO2从5mol%~20mol%逐渐增加,成玻能力逐渐增强,SiO2≥20mol%开始得到完全非晶态玻璃.等SiO2含量下,随TiO2含量的增加,玻璃转变温度逐渐升高.SiO2含量等于15mol%时,随着TiO2含量的增加,[TiO6]先增加后减少,TiO2含量为45mol%时,[TiO6]的Ti-O振动峰出现,60mol%时,[TiO6]的Ti-O振动峰消失,[TiO4]在TiO2的含量为40mol%~50mol%时存在,Ba2+对Si-O骨架具有破坏作用.     

Na-Ti-Si氧化物Ti元素的化学状态分析

利用熔融方法制备了Na2O-TiO2-SiO2系统玻璃样品，用IR以及XPS等测试手段对系统玻璃样品结构进行了分析。结果表明：Na2O-SiO2-SiO2系统玻璃中Ti^4 离子可以部分地取代Si^4 离子的位置而以网络形成体的形式参与成玻。此外，通过对该系统玻璃的XPS钛元素的化学状态分析，认为该系统玻璃中Ti^4 离子存在[TiO4],[TiO6]等几种不同的微结构单元，并且随着玻璃中TiO2含量的增加，该系统玻璃中四方双锥结构的[TiO6]与正四面体结构的[TiO4]之比增大。     

CaO含量对镧硼硅酸盐玻璃陶瓷晶相和化学稳定性的影响

采用熔融冷却法制备了Na₂O-CaO-La₂O₃-B₂O₃-SiO₂玻璃,经热处理获得了硅酸盐氧基磷灰石硼硅酸盐玻璃陶瓷,并采用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、差示扫描量热法(DSC)、产品一致性试验(PCT)法等方法探究了CaO取代SiO₂对该硼硅酸盐玻璃陶瓷物相、微观结构和化学稳定性的影响规律。结果显示:随着CaO含量增加,硅酸盐氧基磷灰石晶相衍射峰增强,其他晶相的衍射峰减弱直至消失,当CaO摩尔分数为15%时获得只含CaLa₄(SiO₄)₃O晶相的玻璃陶瓷样品;CaO含量会对玻璃陶瓷的晶相种类和晶体形状、大小、分布产生影响,CaO含量变化会造成陶瓷相晶体发生团簇和长大;采用PCT法浸泡28 d后,所有样品关于Si、Ca、La三种元素的归一化浸出率(g·m^-2·d^-1)均保持在10^-3数量级以下,表明其具有优异的化学稳定性,且CaO摩尔分数为15%的玻璃陶瓷样品化学稳定性最优异。研究结果表明,硅酸盐氧基磷灰石硼硅酸盐玻璃陶瓷是固化富La和某些锕系元素高放废物的潜在基材。     

MoO3对玄武岩玻璃结构及性能的影响

三氧化钼在硼硅酸盐玻璃系统中的溶解度非常低,其在核废料玻璃中的过量存在可导致易溶“黄相”的形成。本实验以天然玄武岩制备的玄武岩玻璃为基体,掺入不同含量的MoO₃制备玻璃固化体。采用X射线衍射分析、场发射扫描电子显微镜等测试手段对不同条件制备的玻璃固化体进行表征,研究了MoO₃添加量对玻璃固化体微观形貌、理化性能、化学稳定性的影响。结果表明:MoO₃的大量引入将使玄武岩玻璃析出CaMoO₄。随着MoO₃添加量增加,玻璃固化体Tg下降,密度上升。其钼酸盐最大溶解度为5.5%(质量分数),高于硼硅酸盐玻璃系统,此时玻璃化转变温度、密度分别为619℃、2.70 g/cm²。玄武岩玻璃富含铝,通过对硼硅酸盐玻璃和玄武岩玻璃成分的对比分析,这是其具有优异钼酸盐溶解度的主要原因,玄武岩玻璃固化体28天的浸出液Mo浸出率为8.5×10^-6 g/(m²·d),与广泛使用的硼硅酸盐玻璃相当。     

Thermodynamic assessment of the pseudoternary Na2O–Al2O3–SiO2 system

Vitrified high‐level radioactive waste that contains high concentrations of Na₂O and Al₂O₃, such as the waste stored at the Hanford site, can cause nepheline to precipitate in the glass upon cooling in the canisters. Nepheline formation removes oxides such as Al₂O₃ and SiO₂ from the host glass, which can reduce its chemical durability. Uncertainty in the extent of precipitated nepheline necessitates operating at an enhanced waste loading margin, which increases operational costs by extending the vitrification mission as well as increasing waste storage requirements. A thermodynamic evaluation of the Na₂O–Al₂O₃–SiO₂ system that forms nepheline was conducted by utilizing the compound energy formalism and ionic liquid model to represent the solid solution and liquid phases, respectively. These were optimized with experimental data and used to extrapolate phase boundaries into regions of temperature and composition where measurements are unavailable. The intent is to import the determined Gibbs energies into a phase field model to more accurately predict nepheline phase formation and morphology evolution in waste glasses to allow for the design of formulations with maximum loading.     

Surface Analysis of Cr2O3‐, CoO‐, and Al2O3‐Doped Iron–Phosphate Glasses at High Temperature

Surface structures of iron–phosphate glasses were examined using X‐ray photoelectron spectroscopy (XPS). Cr₂O₃, CoO, and Al₂O₃ were introduced to the glass by the replacement of a part of Fe₂O₃, and the simulated fission products are also added. The obtained glasses showed high chemical durabilities by MCC‐1 test. In situ high‐temperature and room‐temperature XPS measurements were conducted on the polished sample surfaces and also those after 1‐week chemical durability test. Unique trends were observed in XPS spectra on heating and after the chemical durability test, respectively. Nature of the glass surface of iron–phosphate glasses was explained from the point of view of surface energy, and the origin of high chemical durability and the effect of chromium ions were discussed based on the changes on surface composition and valence states of transition‐metal ions.     

Vitrification of a waste water flocculate from a petroleum catalyst manufacturer

Chemical and mineral compositions of a waste water flocculate generated in a manufacturer producing fluidized-bed catalytic cracking catalysts were analyzed. The flocculate was then calcined at 1200–1350 °C. X-ray diffraction analysis results indicate that the flocculate can be directly vitrified at 1350 °C without the addition of any other ingredients. The density and chemical durability of the directly vitrified product are comparable with commercial soda-lime-silicate glasses. However, the viscosity of directly vitrified glass melt was very high. Thus, the refining and shaping of the glass melt were difficult. With the addition of minerals such as limestone, dolomite and fluorite, workable glasses could be formed. The influence of MgO on the structure and properties of the obtained glasses is discussed. Results show that the density and hardness of the glass increase with the increase of MgO, whereas the chemical durability, transition and crystallization temperatures decrease. The present study provides a general way to utilize waste water flocculates in glass production.     

Determination of the Fe2+/Fe3+ Ratio in Nuclear Waste Glasses

The Fe²⁺/Fe³⁺ ratios of 47 simulated nuclear waste glass samples with ratios varying from 0.01 (oxidized) to 1.6 (reduced) were determined by wet-chemical and Mössbauer spectral analyses. The wet-chemical method involved the spectrophotometric determination of Fe²⁺ and total iron using remote spectroscopy with fiber optic chemical sensing. Interferences from other species present in these glasses were examined and alternative analytical techniques were investigated. Results of wet-chemical and Mössbauer spectral analysis were comparable; however, the wet-chemical method is probably preferable for the analysis of highly radioactive glasses until such glasses have been shown to have satisfactory Mössbauer spectra.     

Current advances on titanate glass-ceramic composite materials as waste forms for actinide immobilization: A technical review

As the emerging versatile waste forms for immobilizing actinide-rich radioactive wastes, glass-ceramic composite materials based on some durable ceramic phases are being developed. They have apparent advantages over the conventional borosilicate glasses and multi- or single- phase ceramics as they essentially combine the chemical and processing flexibilities of glasses to accommodate processing impurities and excellent chemical durability of ceramic phases to host actinides. More recently, some new advances have been made on scientific and technological aspects including new glass-ceramic systems; improved understanding of ceramic phase evolution in glass; actinide validation studies and simplified processing techniques. This review is intended to cover the current advances on the development of glass-ceramic composite waste forms focusing on titanate ceramic phases (zirconolite, pyrochlore and brannerite) for immobilizing various actinide-rich radioactive wastes arising from the nuclear fuel cycle.     

Derivation of the Structural Integrity of Residual (SIR) glass model for the enhancement of waste loading

A new model based on glass structure to allow for enhanced waste loading in nuclear waste glass while maintaining chemical durability is proposed. The model is derived by splitting the molar concentrations of the targeted starting glass composition into theoretical crystalline phases anticipated to be observed during devitrification and a residual glass. An empirically derived relationship based on maintaining the residual glass structure, determined from a calculated non-bridging oxygen content, was demonstrated to successfully screen glasses for acceptable durability. The proposed model can successfully identify durable glass compositions containing 20–35 wt% Al₂O₃, a concentration that would significantly increase the projected waste loading in glasses processed at the Hanford Tank Waste Treatment and Immobilization Plant.     

Phosphate-based glasses and glass ceramics for immobilization of lanthanides and actinides

Borosilicate glasses used to be a choice to vitrify nuclear wastes in most of the countries. However, Russian HLW vitrification plant at the Mayak Production Association (Chelyabinsk Region, Urals) uses phosphate-based glasses. Initially, Russian HLW glasses were based on sodium-aluminophosphate with the following approximate composition (mol.%): 40 Na₂O_, 20 Al₂O₃, 40 P₂O₅. Recently we have modified this composition by replacing of up to 50% Al₂O₃ with Fe₂O₃. Such replacement increases chemical durability and resistance to devitrification and radiation of the glasses. The phase composition and structure of these glasses containing ~ 10?wt% RE oxides and ~ 10, ~ 50, and ~ 100?wt% UO₃ (over 100?wt%) were studied in details using XRD and FTIR. Glasses and glass-ceramics have high chemical durability. Thus, the glasses and glass ceramics on sodium-aluminum-iron-phosphate basis are good waste forms for lanthanide fraction of HLW generated at spent nuclear fuel pyroprocessing and minor actinides.     

Chemical Durability of Savannah River Plant Waste Glass as a Function of Waste Loading

The leachability of Savannah River Plant (SRP) waste forms was assessed for glass containing up to 50 wt% simulated waste oxides. Leach tests included standard MCC-1 static tests and pH-buffered solution experiments. An integrated approach combining leachate solution analysis with both bulk and surface analyses was used to study waste-glass corrosion as a function of waste loading. Scouting tests on key processing and product parameters, such as viscosity, electrical resistivity, and density were also performed. Results of this study show that the durability of SRP waste glass improves due to the presence of the waste, for waste loadings up to 50 wt% because of the formation of protective surface layers. In addition, the data indicate that the practical limit of waste loading will be determined not by chemical durability of the product, but by processing considerations.