Hierarchical Ag-SiO2@Fe3O4 magnetic composites for elemental mercury removal from non-ferrous metal smelting flue gas

Hierarchical Ag-SiO_2@Fe_3O_4 magnetic composites were selected for elemental mercury(Hg~0) removal from non-ferrous metal smelting flue gas in this study. Results showed that the hierarchical Ag-SiO_2@Fe_3O_4 magnetic composites had favorable Hg~0 removal ability at low temperature. Moreover, the adsorption capacity of hierarchical magnetic composite is much larger than that of pure Fe_3O_4 and SiO_2@Fe_3O_4. The Hg~0 removal efficiency reached the highest value as approximately 92% under the reaction temperature of 150°C, while the removal efficiency sharply reduced in the absence of O_2. The characterization results indicated that Ag nanoparticles grew on the surface of SiO_2@Fe_3O_4 support. The large surface area of SiO_2 supplied efficient reaction room for Hg and Ag atoms. Ag–Hg amalgam is generated on the surface of the composites. In addition, this magnetic material could be easily separated from fly ashes when adopted for treating real flue gas, and the spent materials could be regenerated using a simple thermal-desorption method.     

Optimising yield and resource utilisation of summer maize under the conditions of increasing density and reducing nitrogen fertilization

The inefficient use of resources always poses risks of maize (Zea mays L.) yield reduction in China. We performed this research to monitor the effects of increasing plant density and reducing nitrogen (N) rate on radiation-use efficiency (RUE), N efficiency traits, grain yield (GY) and their inter-relationships. Besides, whether GY and resource-use efficiency can both be maximized was examined. Hence, a 2-year field experiment was conducted using a widely grown variety “Denghai 618” in Shandong, China. Treatments contained two different plant densities [67,500 (D₁) and 97,500 (D₂) plant ha^?1] and three N levels [0 (N_?2), 180 (N_?1), 360 (N_ck) kg ha^?1], set D₁N_ck as control. Significant increases in grain yield, biomass, RUE, above-ground N uptake (AGN) and N efficiency were observed when density increased from D₁ to D₂. Declining N application was accompanied by reductions in yield, RUE and AGN especially under high density, yet an obvious improvement in N recovery efficiency (NRE), agronomic N efficiency and N partial factor productivity. The increased GY was positive related with population biomass (r = 0.895**), RUE (r = 0.769**) and AGN (r = 0.923**), whereas it has no significant correlation with N efficiency. In this study, D₂N_ck obtained 18.8, 17.9, 24.8 and 29.7% higher grain yield, RUE, AGN and NRE respectively, compared to control, optimizing both yield and the efficiencies of radiation and N use. Furthermore, higher yield and RUE with more desirable N efficiency may be possible via optimizing density and N rate combination.     

基于复合软电离源飞行时间质谱的小型化大气非甲烷烃在线快速监测系统的设计与应用

针对大气非甲烷烃(NMHCs)的时空分布监测需求,并弥补现有监测技术时间分辨率低、体积和功耗较大的不足,本研究自主研发出一套高性能、小型化的大气非甲烷烃在线快速测量系统.该方法基于串联吸附剂在特定温度下对目标物质的富集与解吸,采用单光子/化学复合软电离源飞行时间质谱(SPI/CI-TOFMS)作为分离和检测手段,实现对C_2～C_(10)挥发性有机物的快速分离和检测.通过对标准样品的测量表明:在SPI/CI模式下,C_2～C_(10)物种工作曲线(0～10×10~(-9))拟合优度R~20.99,大部分物种方法检出限为1×10~(-12)～80×10~(-12),仪器检出限为1×10~(-12)～35×10~(-12),RSD(n≥10)小于10%.将仪器初步应用于北京大学站点进行定点观测,测量结果与商业化仪器TH-300B离线分析结果吻合.本系统样品分析时间5～12 min可调,整机重量低于40 kg,整机尺寸小于50 cm×50 cm×80 cm,功率低于500 W,可满足大气非甲烷烃的快速监测需求,为提供高分辨率大气NMHCs时空分布数据提供技术支持.     

北京市春季交通干道移动源非甲烷总烃的在线跟踪观测与特征分析

机动车排放(Vehicular Emission,VE)是地面非甲烷烃(Non-methane hydrocarbon,NMHCs)的重要人为源之一.为获得北京市交通主干道NMHCs的实际排放情况,本研究以自主研发的吸附/热解吸前处理-单光子/化学复合软电离源飞行时间质谱(SPI/CI-TOFMS)为检测手段,于2018年3月14日在北京四环、五环主干道,对C_2～C_(10)挥发性有机物进行了车载在线跟踪观测.结果表明,C_2、C_3高挥发性物质浓度较高,其次是苯系物和丁烷;从空间分布来看,NMHCs浓度在离市中心较近的四环主干道相对较高,且车流量较大的南五环公路和西四环处NMHCs污染也较为严重;从NMHCs的结构组成来看,烷烃(63%、52%)占比最多,芳香烃(23%、32%)次之,烯烃(14%、16%)最少;对NMHCs特征物质之间的线性关系和比值关系进行分析,确定机动车排放对此次观测中NMHCs的生成贡献较大;通过计算各物种臭氧生成潜势(OFP),评估出C_3、C_4烯烃类物质和苯系物为北京四、五环地区优先控制物种.     

Distinct element modeling of laser assisted milling of silicon nitride ceramics

Laser assisted milling (LAMill) of ceramics shows some complicated characteristics such as discontinuous chips, crack formation, propagation and coalescence. In this paper, numerical simulation is conducted to explore the machining mechanism of LAMill. The distinct element method (or discrete element method, DEM) is applied to model the microstructure of a β-type silicon nitride ceramic. Clusters are used to simulate the real grain shape of the silicon nitride ceramic and parallel bonds are employed to represent the connections between intergranular glass phase and grains. Numerical tests (compression, bending and fracture toughness tests) are performed to evaluate the macroproperties of the synthetic material, thus matching the corresponding physical properties of the real silicon nitride. Moreover, a temperature-dependent synthetic DEM specimen is created and then used in simulations of LAMill. The DEM model is validated through comparing the simulation results with the experimental ones in terms of the cutting forces and subsurface damage under different depths of cut. It is shown that the model can successfully predict the subsurface damage in LAMill.     

零价汞在MnOx/α-Al2O3-氯气体系中的催化氧化

为强化烟气中零价汞向二价汞的转化,利用模拟含汞烟气研究了以MnOx/α-Al2O3作为催化剂、利用氯气作为氧化剂催化氧化零价汞的方法.着重考察了氯气浓度、温度、空速和SO2对催化氧化零价汞性能的影响,并与HCl作为氧化剂的结果进行了对比.同时,对催化剂进行表征,探讨了催化剂表面吸附态汞的形态.研究结果表明,Cl2较HCl更易活化且活性温度区间更广,在100～300℃范围内,Cl2体积分数为2.0×10-6时的催化氧化效率即可达80%以上;在1.6×104-6.4×104 h-1空速范围内,零价汞氧化率保持在90%以上.空速继续提高到1.92×105h-1时,零价汞氧化率呈现线性下降趋势;烟气中的SO2与Cl2:反应会消耗Cl2,Cl2体积分数低时对催化氧化反应抑制作用显著,但Cl2体积分数增至5.0×10-6时对催化氧化反应的抑制效果较弱,仅为10%左右.     

污泥干化过程氨的释放与控制

通过模拟试验,深入研究了污泥氨在自然状态和不同温度下的释放特征及其影响因素,并结合污泥低温干化工艺的特点,建立了污泥氨释放的收集与处理系统.结果表明,污泥在储存的四天时间内,氨在空气条件下自然释放的日平均释放量为0.11μg/(g·d),在污泥干化过程中,氨的主要释放量集中在0~30min的早期阶段,氨的释放与水的蒸发同步发生,干化温度决定了污泥氨的释放强度,控制污泥在低温下完成干化过程,是抑制污泥氨释放强度的有效措施.通过多级湿式除尘除气不但可以去除污泥干化时释放的绝大部分氨和其他有害气体(如硫化氢),而且几乎可以去除全部烟尘.     

Plant species coexistence alleviates the impacts of lead on Zea mays L.

Whether plant coexistence can reduce the impacts of lead (Pb) on crops in agroecosystems has not been well understood. We conducted a factorial experiment to investigate the effects of weeds coexisting with maize (Zea mays L.) on Pb accumulation in maize and soil microbes at two Pb levels (ambient and 300 mg/kg). Elevated Pb tended to increase the Pb concentration in maize and decreased soil microbial activity (indicated by the average well color development, AWCD), functional group diversity, as well as arbuscular mycorrhizal (AM) colonization and vesicle number of maize. Compared to the monoculture, weeds coexisting with maize reduced the Pb concentrations in the root, leaf, sheath and stem of maize at both seedling and mature stages. In maize-weed mixtures, soil microbial activity and functional group diversity tended to increase for both Pb treatments relative to the monoculture. Furthermore, principal component analysis revealed that the soil microbial community structure changed with the introduction of weeds. The highest Pb accumulation in weeds occurred for the elevated Pb treatment in a three species mixture. The results suggest that multiple plant species coexistence could reduce lead accumulation in crop plants and alleviate the negative impacts on soil microbes in polluted land, thereby highlighting the significance of plant diversity in agroecosystems.     

Utilization of aluminum hydroxide waste generated in fluoride adsorption and coagulation processes for adsorptive removal of cadmium ion

Although Al-based coagulation and adsorption processes have been proved highly efficient for fluoride (F) removal, the two processes both generate large amount of Al(OH)₃ solid waste containing F (Al(OH)₃-F). This study aimed to investigate the feasibility of utilizing Al(OH)₃-F generated in Al(OH)₃ adsorption (Al(OH)₃-F_ads) and coagulation (Al(OH)₃-F_coag) for the adsorption of cadmium ion (Cd(II)). The adsorption capacity of Al(OH)₃-F_ads and Al(OH)₃-F_coag for Cd(II) was similar as that of pristine aluminum hydroxide (Al(OH)₃), being of 24.39 and 19.90 mg·g^–1, respectively. The adsorption of Cd(II) onto Al(OH)₃-F_ads and Al(OH)₃-F_coag was identified to be dominated by ion-exchange with sodium ion (Na⁺) or hydrogen ion (H⁺), surface microprecitation, and electrostatic attraction. The maximum concentration of the leached fluoride from Al(OH)₃-F_ads and Al(OH)₃-F_coag is below the Chinese Class-I IndustrialWastewater Discharge Standard for fluoride (<10 mg·L^–1). This study demonstrates that the Al(OH)₃ solid wastes generated in fluoride removal process could be potentially utilized as a adsorbent for Cd(II) removal.     

深圳福田红树林无瓣海桑与海桑群落的重金属累积和循环

研究了深圳福田红树林无瓣海桑与海桑群落对重金属Cu、Pb、Zn、Cr、Ni元素的吸收、累积、分布和循环.结果表明,该林地表层土壤(0～30cm)Cu、Pb、Zn、Cr、Ni元素的储量关系为Zn＞Pb＞Ni＞Cr＞Cu;群落中3种植物对土壤中5种重金属元素富集能力的大小依次为海桑＞无瓣海桑＞秋茄.该群落Cu、Pb、Zn、Cr、Ni的现存累积量分别为:23019.61、23429.65、117870.41、6835.79、12995.08μg/m²;年吸收量分别为:6592.20、266