Model Apatite Systems for the Stabilization of Toxic Metals: I, Calcium Lead Vanadate

Apatites of composition (Ca_{10− x} Pb _x )(VO₄)₆F₂ with 0 ≤ x ≤ 9 were synthesized by sintering in air at 800°C the oxides of calcium, lead, and vanadium that were mixed with calcium fluoride. Variations in lattice parameters, grain size, and durability were monitored as a function of composition. The expected dilation in unit cell edges with increasing replacement of calcium (IR = 1.26 Å) by lead (IR = 1.45 Å) was observed. The a cell edge (in angstroms) varied linearly (0.0458 x + 9.7068) with x , while c followed the binomial function 0.0018 x ²+ 0.0279 x + 7.0118. Average grain sizes increased from approximately 5 μm ( x = 0) to 25 μm ( x = 9) as grain growth was enhanced due to incipient melting of the lead-rich compositions. For x < 5 the materials were biphasic. Overall dissolution, as determined by the toxicity characteristic leaching procedure (TCLP), was faster in calcium-rich apatites. Etching of well-crystallized apatite grains occurred preferentially on {10 1 0} faces. These leach losses were augmented through the more rapid removal of cryptocrystalline regions and intergranular thin films.     

Model Apatite Systems for the Stabilization of Toxic Metals: II, Cation and Metalloid Substitutions in Chlorapatites

Environmental chlorapatites, of the form A₁₀(B _x C_{1− x} O₄)₆Cl₂, where A=Ca, Cd, or Pb; B/C=P, V, or Cr and 0≤ x ≤1, were synthesized by solid-state reactions. Crystal structure variations, primarily lattice parameters, were examined through powder X-ray diffraction methods, while performance and long-term durability of these waste form apatites were assessed by a combination of the toxicity characteristic leaching procedure (TCLP) and the American Nuclear Society (ANS) method. As expected, an overall dilation of unit cell edges was observed with increasing ionic substitutions. However, a discontinuity in linearity was often observed, generally for x ≥0.5. The correlation of microstructural changes and leach testing shows that lead chlorapatite is found to be more suitable for waste stabilization than calcium and cadmium analogues.     

Selective Transport of Histamine from a Mixture of Histidine and Histamine by the Use of Organic Liquid Membrane Systems

Abstract

The transport behaviors of histidine (His) and its related compounds through organic liquid membranes were examined. The organic liquid membranes system was composed of two aqueous phases (Phases I and II) which were put on both sides of an organic layer containing a carrier. Chloroform and sodium di-2-ethylhcxyl sulfosuccinate (AOT) were used as the organic layer and the carrier, respectively. No transport reaction occurred without the carrier. The amounts of removal into the organic layer increased with an increase in the concentration of AOT up to 5 mM and maintained at higher concentrations. His and carnocine, which possess the carboxyl group, could be removed into the organic layer from Phase I at pH 4–5 but could not be removed at pH values higher than 5. On the other hand, histamine (Hm) and histidinol, which lack the carboxyl group, could be removed into the organic layer from Phase I at pH 7. Also, the compounds in the organic layer could be removed into Phase II at pH 10. On the basis of these results, the separation of Hm from the Hm-His mixture occurred with pH 7 in Phase I and pH 10 in Phase II through the organic layer containing 5 mM of AOT. Hm was effectively transported from Phase I to Phase II through an organic layer using some molar ratios (1, 50, and 100) of mixtures (molar ratio = concentration of His/concentration of Hm).     

Effective and Selective Recovery of Precious Metals by Thiourea Modified Magnetic Nanoparticles

Adsorption of precious metals in acidic aqueous solutions using thiourea modified magnetic magnetite nanoparticle (MNP-Tu) was examined. The MNP-Tu was synthesized, characterized and examined as a reusable adsorbent for the recovery of precious metals. The adsorption kinetics were well fitted with pseudo second-order equation while the adsorption isotherms were fitted with both Langmuir and Freundlich equations. The maximum adsorption capacity of precious metals for MNP-Tu determined by Langmuir model was 43.34, 118.46 and 111.58 mg/g for Pt(IV), Au(III) and Pd(II), respectively at pH 2 and 25 °C. MNP-Tu has high adsorption selectivity towards precious metals even in the presence of competing ions (Cu(II)) at high concentrations. In addition, the MNP-Tu can be regenerated using an aqueous solution containing 0.7 M thiourea and 2% HCl where precious metals can be recovered in a concentrated form. It was found that the MNP-Tu undergoing seven consecutive adsorption-desorption cycles still retained the original adsorption capacity of precious metals. A reductive adsorption resulting in the formation of elemental gold and palladium at the surface of MNP-Tu was observed.     

Cermets: I, Fundamental Concepts Related to Micro-structure and Physical Properties of Cermet Systems

The microstructure of tungsten carbide and titanium carbide base cermets has been evaluated on the basis of wettability of the carbide phase. Incomplete wetting was found to result in a coalescence of the carbide phase leading to an apparent increase in the carbide particle size. Improvement in the wettability of the nickel-titanium carbide systems by the addition of molybdenum was found to promote the dispersion of the carbide phase and to lead to improved hardness and impact resistance.     

The Metals in the Biological Periodic System of the Elements: Concepts and Conjectures

A significant number of chemical elements are either essential for life with known functions, or present in organisms with poorly defined functional outcomes. We do not know all the essential elements with certainty and we know even less about the functions of apparently non-essential elements. In this article, I discuss a basis for a biological periodic system of the elements and that biochemistry should include the elements that are traditionally part of inorganic chemistry and not only those that are in the purview of organic chemistry. A biological periodic system of the elements needs to specify what “essential” means and to which biological species it refers. It represents a snapshot of our present knowledge and is expected to undergo further modifications in the future. An integrated approach of biometal sciences called metallomics is required to understand the interactions of metal ions, the biological functions that their chemical structures acquire in the biological system, and how their usage is fine-tuned in biological species and in populations of species with genetic variations (the variome).     

采用双线性变换的线性离散系统模型降阶

针对线性定常离散系统,提出一种新的不受稳定性限制的降阶方法,即利用双线性反变换,将离散系统转化为连续系统,利用已知的连续系统的降阶方法进行降阶,之后再经双线性变换为离散系统,得到了原离散系统的降阶模型,给出并证明了误差上界.数值算例说明了此方法的有效性.     

Selective Separation of Metals from Deep-Sea Ferromanganese Nodules by Sulfur Dioxide Reduction

Abstract

An investigation of the reaction of deep-sea ferromanganese nodules with SO₂ has been carried out in the temperature range 300 and 600 [ddot]C. Maximum sulfation occurs with dehydrated nodules after treatment with a SO₂-O₂ gas mixture at 400 [ddot]C. X-ray photoelectron spectroscopy and x-ray diffraction techniques indicate that the oxides of manganese, which are major components in the nodules, are sulfated. The oxides of Cu, Ni, and Co are also converted into their sulfates when reacted with SO₂ and O₂, and Mn, Cu, Ni, and Co can be nearly quantitatively extracted by leaching the sulfated nodules. Iron, which is also a major component and present as goethite, a-FeO(OH), is not sulfated but transformed into hematite, α-Fe₂O₃. Thus it can be separated from other metals which form water-soluble sulfates during the high-temperature sulfation process.     

An Improved Model for the Extraction of Multivalent Metals in Winsor II Microemulsion Systems

Abstract

Our earlier paper described a liquid-liquid extraction process for metal ions using a Winsor I1 microemulsion system (I). A Winsor I1 system is a biphasic system in which a water-in-oil microemulsion exists in equilibrium with a lower predominately aqueous phase (2). Complete details of the system, the experiments, and the modeling efforts have been given in our earlier work (1). Hence, to avoid redundancy, only the salient features are discussed here as a prelude to dealing with the extension of the model.     

Simulating the Complexities of Heterogeneous Catalysis with Model Systems: Case studies of SiO2 Supported Pt-Group Metals

Model catalyst surfaces, consisting of vapor-deposited metal nanoparticles supported on a planar oxide support, can help to link reactivity studies on well-defined single crystal surfaces with those conducted on high-surface area supported catalysts. When coupled with near atmospheric pressure kinetic and spectroscopic techniques, these well-defined model catalyst surfaces represent a useful approach to combine the power of surface analytical techniques with reactivity studies under relevant reaction conditions. Here, we review recent results of our investigations characterizing the physical and catalytic properties of Pt/SiO₂ and Rh/SiO₂ model catalyst surfaces. As will be discussed, the model catalyst approach can help simulate the complexities of catalytic reactions on supported catalysts, helping to provide insights into the role of particle size, particle morphology, and surface adsorbates in dictating the observed structure-sensitivity (activity and selectivity) during reactions at near atmospheric pressures.     

有机凝胶先躯体转化法制备六角铁氧体中空纤维

以柠檬酸和金属盐为原料,采用有机凝胶先驱体转化法制备了直径在0.5-3 μmM型钡锶铁氧体(Ba0.5Sr0.5Fe12O9)中空纤维.通过TG/DSC、FTIR、XRD、SEM和VSM等技术对所得纤维进行了表征.结果表明,凝胶的可纺性与pH值有关,当pH值在4.5左右时,凝胶的可纺性最好.经700℃焙烧后,制备的M型钡锶铁氧体纤维具有较大的长径比和明显的中空结构,组成纤维的晶粒形貌为六角片状.随着温度的升高,晶粒片状结构越来越明显.经800℃焙烧后制备的M型钡锶铁氧体纤维在室温下的饱和磁化强度为59.5A·m2·kg-1,矫顽力为330.1 kA·m-1.     

海泡石对废水中有机物和重金属的吸附

简述了海泡石的结构特点,及其改性方法,总结了海泡石对废水中有机物和重金属的吸附效果,分析了改性方法、pH、温度、污染物性质与浓度、海泡石用量和吸附时间等因素对吸附效果的影响．探讨了海泡石的吸附机理与等温式,展望了海泡石在废水处理中的应用前景。     

溶解性有机质对土壤中有机污染物迁移转化的影响因素

溶解性有机质(DOM)对土壤中有机物的迁移转化有重要作用,也受众多因素影响。介绍了DOM的基本概念、分类和环境作用;讨论了DOM的来源、DOM的分子量大小、DOM的浓度和p H值等影响因素对DOM与有机物的作用并分析了原因;提出了研究的走向。     

Selective Recovery of Platinum Group Metals from Spent Automobile Catalyst by Integrated Ion Exchange Methods

Selective recovery of platinum group metals (PGMs), such as Pd, Pt, and Rh, from spent automobile catalyst has been investigated by integrated ion exchange method using dihexyl sulfide (DHS) impregnated resin and commercial weak anion exchange resin (Diaion WA-21) as adsorbents. Batchwise adsorption revealed that the DHS impregnated resin possesses the selective adsorption ability for Pd and WA-21 possesses selectivity for all PGMs, especially Rh. Chromatographic separation of Pd with column packed with DHS impregnated resin can be selectively achieved. The chromatographic separation of Pd and Pt with a column packed with WA-21 is effectively progressed, while that of Rh is insufficient yield due to a slow adsorption rate. Separation of Rh from other two PGMs can therefore be achieved by switching the eluent. Both adsorbents show almost no adsorption abilities for other heavy metals containing in the spent automobile catalyst. Sequential chromatographic operation of the column packed with DHS impregnated resin followed by the column packed with WA-21 can be finally achieved to recover mutual PGM from leaching solution of spent automobile catalyst.     

Brain Plasticity in Humans and Model Systems: Advances,Challenges, and Future Directions

Plasticity, and in particular, neurogenesis, is a promising target to treat and prevent a wide variety of diseases (e.g., epilepsy, stroke, dementia). There are different types of plasticity, which vary with age, brain region, and species. These observations stress the importance of defining plasticity along temporal and spatial dimensions. We review recent studies focused on brain plasticity across the lifespan and in different species. One main theme to emerge from this work is that plasticity declines with age but that we have yet to map these different forms of plasticity across species. As part of this effort, we discuss our recent progress aimed to identify corresponding ages across species, and how this information can be used to map temporal variation in plasticity from model systems to humans.     

A Quantitative Approach to the Ensemble Model of Catalysis by Metals

The concept of ensembles is based on the idea that adsorbed species and intermediates in catalytic reactions require more than one surface atom. This model can probably be traced to the mul-tiplet theory of Balandin [1], who, as early as 1929, made the assumption that a reacting molecule can be simultaneously adsorbed on several atoms.     

A Quantitative Approach to the Ensemble Model of Catalysis by Metals

The concept of ensembles is based on the idea that adsorbed species and intermediates in catalytic reactions require more than one surface atom. This model can probably be traced to the mul-tiplet theory of Balandin [1], who, as early as 1929, made the assumption that a reacting molecule can be simultaneously adsorbed on several atoms.     

Selective Hydrogenation of Citral in an Organic Solvent,in a Ionic Liquid,and in Substance

It is investigated whether the catalyst system Ag‐In/SiO₂ can be applied in the selective hydrogenation of citral, with the aim of synthesizing the acyclic, allylic terpene alcohols geraniol/nerol with high selectivity and space‐time yield. In addition, as liquid‐phase hydrogenations are often also influenced by the choice of solvent, it is of interest to know how the solvent, in particular in terms of its polarity and hydrogen solubility, affects the activity and the selectivity of catalysts during hydrogenation of the α,β‐unsaturated aldehyde citral.     

碳酸钠促进选择性非催化还原脱硝的动力学模型与模拟

Abstract The detailed kinetic model of selective non-catalytic reduction （SNCR） of nitric oxide, including so-dium species reactions, was deyeloped on the basis of recent studies on thermal DeNOx mechanism, NOxOUTmechanism and promotion mechanism of Na2CO3. The model was validated by comparison with several experi-mental findings, thus providing an effective tool for the primary and promoted SNCR process simulation. Experimental and simulated results show part-per-million level of sodium carbonate enhances NO removal efficiency andextend the effective SNCR temperature range in comparison with use of a nitrogen agent alone. The kinetic modeling, sensitivity and rate-of-production analysis suggest that the performance improvement can be explained as ho-mogeneous sodium species reactions producing more reactive OH radicals. The net result of sodium species reac-tions is conversion of H2O and inactive HO2 radicals into reactive OH radicals, i.e. H2O＋HO2=3OH, which enhances the SNCR performance of nitrogen agents by mainly increasing the production rate of NH2 radicals. More-over, N2O and CO are eliminated diversely via the reactions Na＋N20=NaO＋N2, NaO＋CO=Na＋CO2 andNaO2＋CO =NaO＋CO2, in.the pro.moted SNCR process, especially in the NOxOUT process.