Rapid synthesis of Gd2Zr2O7 ceramics by flash sintering and its aqueous durability

The high radiation resistance and long time stability of Gd₂Zr₂O₇ ceramics make it a promising candidate for high level waste (HLW) immobilization materials. In this study, single phase nanocrystalline Gd₂Zr₂O₇ was successfully synthesized and consolidated at temperatures around 1050 °C for only 1 min by flash sintering for the first time. The phase evolution and microstructural development during flash sintering were systematically studied and compared with the conventionally sintered samples. The flash sintered Gd₂Zr₂O₇ exhibit defect fluorite structure, and a following heat treatment at 1400 °C could transform the Gd₂Zr₂O₇ ceramics from defect fluorite phase into pyrochlore phase. The MCC-1 leaching test shows that the flash sintered Gd₂Zr₂O₇ samples exhibit good aqueous durability.     

Immobilization of simulated waste into pure Gd2Zr2O7 pyrochlore without space occupancy design

In this study, different molar ratios of Nd:Ce were directly mixed with prepared pure Gd₂Zr₂O₇ powders without space occupancy design. Samples were obtained by performing sparking plasma sintering (SPS) at 1750°C for 5 minutes. X-ray diffraction (XRD) results show that maximum solid solubility of simulated radionuclides can reach 50 mol%. In addition, all samples with the maximum solid solubility have high compactness, and all elements are evenly distributed on the surface of the samples. The samples show a better crystallization effect as the molar ratio of Nd:Ce increases. The maximum solid solubility increases from 42 mol% to 50 mol% when the amount of Nd₂O₃ reaches 66 mol%.     

Thermal properties of sodium borosilicate glasses as a function of sulfur content

Sulfur trioxide (SO₃) additions, up to 3.0 mass%, were systematically investigated for effects on the physical properties of sodium borosilicate glass melted in air, with a sulfur-free composition of 50SiO₂–10Al₂O₃–12B₂O₃–21Na₂O–7CaO (mass%). Solubility measurements, using electron microscopy chemical analysis, determined the maximum loading to be ~1.2 mass% SO₃. It was found that measured sulfur (here as sulfate) additions up to 1.18 mass% increased the glass transition temperature by 3%, thermal diffusivity by 11%, heat capacity by 10%, and thermal conductivity by 20%, and decreased the mass density by 1%. Structural analysis, performed with Raman spectroscopy, indicated that the borosilicate network polymerized with sulfur additions up to 3.0 mass%, presumably due to Na₂O being required to charge compensate the ionic additions, thus becoming unavailable to form non-bridging oxygen in the silicate network. It is postulated that this increased cross-linking of the borosilicate backbone led to a structure with higher dimensionality and average bond energy. This increased the mean free paths and vibration frequency of the phonons, which resulted in the observed increase in thermal properties.     

Viscosity of glass-forming melt at the bottom of high-level waste melter-feed cold caps: Effects of temperature and incorporation of solid components

During the final stages of conversion of melter feed (glass batch) to molten glass, the glass-forming melt becomes a continuous liquid phase that encapsulates dissolving solid particles and gas bubbles that produce primary foam at the bottom of the cold cap (the reacting melter feed in an electric glass-melting furnace). The glass-forming melt viscosity plays a dominant role in primary foam formation, stability, and eventual collapse, thus affecting the rate of melting (the glass production rate per cold-cap area). We have traced the glass-forming melt viscosity during the final stages of feed-to-glass conversion as it changes in response to changing temperature and composition (resulting from dissolving solid particles). For this study, we used high-level waste melter feeds—taking advantage of the large amount of data available to us—and a variety of experimental techniques (feed expansion test, evolved gas analysis, thermogravimetric analyzer-differential scanning calorimetry, X-ray diffraction, and viscometer). Starting with a relatively low value at the moment when the melt connects, melt viscosity reached maximum within the primary foam layer and then decreased to its final melter operating temperature value. At the cold-cap bottom—the boundary between the primary foam layer and the thermal boundary layer—where physicochemical reactions of a melter feed influence the driving force of the heat transfer from the melt to the cold cap, the melt viscosity affects the rate of melting predominantly through its effect on the temperature at which primary foam is collapsing.     

Quantitative analysis of fuel-saving potential for waste heat recovery system integrated with hybrid electric vehicle

Hybrid electric vehicles (HEVs) with low fuel consumption, low emissions, and long driving range are the ideal transition models between conventional fuel vehicles and pure electric vehicles. The growing demand for increased vehicle efficiency has motivated the introduction of waste heat recovery (WHR) technology in the automotive industry, with the organic Rankine cycle (ORC) as the most promising measure for recycling waste energy. Currently, only a few studies have been conducted to couple HEV and WHR systems. These studies have mainly focused on the hybrid powertrain control strategy, but lack quantitative methods to comprehensively analyze the fuel-saving potential due to the WHR system. In this study, an HEV-WHR integrated system that includes a mechanism-based dynamic model of ORC and a hybrid diesel-electric truck model is established. Further, a quantitative evaluation method that simultaneously considers the negative integrated effects (increased vehicle weight and increased exhaust back pressure) and the positive impact values of the engine, motor, and WHR system on the fuel-saving potential is proposed. Finally, the influence of two environmental factors (wind speed and ambient temperature) on the fuel-saving performance is analyzed. The results reveal that under the standard highway driving cycle (HWY), the negative integrated effects reduce the ideal fuel-saving potential of the HEV-WHR system from 6.10% to 5.42%. However, the optimized performances of the engine, motor, and WHR system improve the fuel-saving rate by 0.39%, 1.81%, and 3.22%, respectively. The results also indicate that the fuel-saving potential increases from 1.62% to 8.60% with increasing wind speed and decreases from 6.70% to 4.25% with increasing ambient temperature.     

基于遗传算法的汽油机朗肯循环余热回收系统的优化

为了更加高效利用汽油机排气余热,分析了某款汽油机排气余热回收潜力,建立了基于蒸发器和活塞式膨胀机的汽油机-朗肯循环联合余热回收系统模型。利用遗传算法,同时考虑膨胀机输出功、排气利用率、蒸发器效率和膨胀机绝热效率,以膨胀机输出功和系统总效率为优化目标,以蒸发压力和膨胀机转速为优化变量,对汽油机4个工况下朗肯循环系统的最佳运行参数进行了研究。结果表明,在整个发动机转速范围内,排气最大可利用效率均高于46%,转速越高则排气品质越高。在不同工况下存在最优的膨胀机转速和蒸发压力。经过优化,在选取的4个工况下,功率提高率均在6%以上,最高达到7.08%。     

Assessment of supercritical water gasification of food waste under the background of waste sorting: Influences of plastic waste contents

Waste sorting is being gradually implemented as a key measure for circular and sustainable development in China, food waste will be separately collected and separated from municipal solid waste (MSW), thus the plastic content in food waste also will be reduced. In this study, supercritical water gasification (SCWG) of food waste with different contents of plastic (0–3.5 wt%) was experimentally investigated to simulate the influence of waste sorting on the food waste treatment. The results showed that lower plastic content in food waste favored higher gas yield and gasification efficiencies. The highest H₂ yield and total gas yield were 3.11 mol/kg and 8.41 mol/kg in the plastic-free case, respectively. When the plastic content decreased from 3.5 wt% to 0 wt%, the cold gas efficiency (CGE), carbon conversion efficiency (CE) and hydrogen gasification efficiency (HE) increased by 125.97%, 173.48% and 94.09%, respectively. However, lower plastic content negatively affected the quality of produced syngas through decreasing H₂ mole fraction and LHV. The solid residues from SCWG of food waste with lower plastic content had higher ratio of fixed carbon to volatile matter (FC/VM). Based on the analysis of pyrolysis properties and combustion behavior, decreasing the plastic content in food waste helped to improve the thermal stability of solid residues. Moreover, lower plastic content resulted in a decrease of total organic carbon (TOC) concentration in liquid effluent, which is favorable for further treatment of liquid effluent.     

Fast removal of Pb(II) and Cu(II) from contaminated water by groundwater treatment waste: impact of sorbent composition

ABSTRACT

A non-hazardous groundwater treatment waste (GWTW) was examined as a low-cost sorbent for Pb(II) and Cu(II) ions. The content of the dominant elements in GWTW was as follows: 78% Fe₂O₃, 7.4% P₂O₅, 7.4% CaO and 5.2% SiO₂. The removal of Pb(II) and Cu(II) was fast, and more than 67–95% of ions were accumulated by GWTW during the first 3 min. The sorption capacity of GWTW depends on solution pH, concentration and temperature. Equilibrium data fitted well with Langmuir–Freundlich and Langmuir-partition models. The inherently formed nano-adsorbent could be utilized for the treatment of water contaminated with Pb(II) and Cu(II) ions.     

滴定-凝胶法制备球形水凝胶吸附材料及其在废水处理中的应用

滴定-凝胶法制备球形水凝胶吸附材料具有3D倒漏斗状微观形貌结构，孔径分布宽泛，对水体中重金属、染料等污染物具有快速响应机制，已被广泛用于水处理过程研究。综述了滴制法制备球形水凝胶吸附材料的主要过程机理、水凝胶具有的特殊形貌结构及其在水处理过程中的应用，分析了球形水凝胶吸附材料在水处理应用过程中存在的问题和局限，并指出了其在水处理领域的应用前景及发展方向。     

生活垃圾焚烧烟气脱硝超低排放技术经济比较

介绍了生活垃圾焚烧烟气成分及特点,针对垃圾焚烧烟气温度偏低及二噁英类、重金属、HCl、Hg、H2O等杂质含量偏高、SO2浓度低等特点,提出垃圾焚烧烟气脱硝超低排放的4种技术方案,并进行技术经济比较。分析结果表明:固体脱硝剂SNCR脱硝技术投资及运行成本最低,脱硝效率可达90%以上,是一种生活垃圾焚烧烟气处理优选的脱硝技术。