An electrochemical study of stainless steels and a nickel alloy in a decontamination agent using the potentiodynamic method

Chemical decontamination is accepted as one of the effective methods for decreasing radioactivity from radioactive materials existing in the systems of the nuclear power plants. In chemical decontamination processes, metal oxides dissolve in chelating agents such as oxalic acid and EDTA (Ethylenediaminetetraacetic acid) in the dissolution step for the chemical decontamination process. It is important to investigate corrosion behaviors with respect to decontaminating agents in the development of decontamination process. In this study, the potentiodynamic method was considered among electrochemical methods in order to investigate corrosion behaviors of stainless steels (SS 316, SS 304) and a nickel alloy (Inconel 600). The corrosion behaviors observed in the potentiodynamic results agreed with those of corrosion behaviors observed in the weight loss method, showing that the electrochemical study is a very useful method for estimating corrosion behavior.     

Uptake of decontaminating agent from aqueous solution: a study on adsorption behaviour of oxalic acid over Al-MCM-41 adsorbents

Hydrothermal method was followed to synthesis the mesoporous Al-MCM-41 (Si/Al = 25, 50, 75 and 100) and Si-MCM-41 molecular sieves using a cetyltrimethylammonium bromide as a surfactant and the materials were unambiguously characterized by XRD, N₂ sorption studies, ²⁷Al MAS-NMR and TEM. The removal of oxalic acid from aqueous solution was studied through an adsorption process because oxalic acid may cause complexes with radioactive cations during decontamination operation in nuclear industry, which resulting in interferences in their removal by conventional treatment. Adsorption of oxalic acid over Al-MCM-41 shows the applicability of Langmuir isotherm and follows first order kinetics. The effects of parameters such as contact time, concentration of oxalic acid, adsorbents (various Si/Al ratios of Al-MCM-41, Si-MCM-41 and activated charcoal) and pH have been investigated to yield higher removal of oxalic acid. The percentage of oxalic acid adsorbed per unit gram of adsorbent for Al-MCM-41 at Si/Al = 100, 75, 50 and 25, Si-MCM-41, and activated charcoal are 34.6, 40.9, 51.4, 61.3, 16.1 and 60, respectively. Retainment of crystallinity and absence of structural collapse of Al-MCM-41 after desorption and adsorption of oxalic acid, respectively has been achieved in this study.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

电解废渣中重金属的提取及分离

为了充分回收利用电解废渣中的镍,该文运用酸溶及化学沉淀的方法,通过试验确定了酸溶和多种金属沉淀分离的最佳条件。试验表明采用5%的酸及2%的酸分别溶解两次、每次溶解时间为1 h、过滤后在加碱的最佳条件下,浸出液中镍离子的保留率可达90%以上,其他金属离子去除率达到99%以上,最终得到高纯度含镍提取液。     

Application of flyash instead of activated carbon for oxalic acid removal

Flyash, a waste product from thermal power plants, has been used as an adsorbent for the removal of oxalic acid. The adsorption process follows first-order kinetics and the equilibrium is attained within 30 min in the concentration range studied (0.01-0.1M). The adsorption obeys both the Freundlich and Langmuir isotherms and the constants have also been reported for flyash and activated carbon. At low concentrations, the increase in pH with flyash is comparatively more than for activated carbon. There seems to be a good scope for the use of flyash in place of activated carbon as an adsorbent for oxalic acid removal.     

Chemical behavior of conductive carbon blacks in Leclanche type batteries

Chemical behavior of conductive carbon blacks has been studied during storage and discharge of Leclanché type batteries. Carbon is collected from cathodic mixture by dissolution of MnO₂ in a solution of oxalic acid. Contents of surface chemical groups have been determined by alcalimetric titration.Results point out a very limited reactivity of carbon insufficient to be a controlling step in the process involved.     

Catalytic Ozonation of Oxalic Acid Using SrTiO3 Catalyst

A new catalyst, strontium titanate (SrTiO₃), has been successfully employed to degrade oxalic acid in catalytic ozonation process. About 4.5%, 9.3% and 45.8% of oxalic acid removal efficiencies were noted in adsorption, ozonation, and catalytic ozonation processes, respectively, which demonstrates the catalytic activity of SrTiO₃ towards ozone_. The optimum amount of catalyst loading on decomposing oxalic acid was found to be 1.25 g/L. The catalytic stability was investigated up to four successive cycles and found that the catalyst was still stable and efficient.     

Electrochemical behaviour and corrosion of lead in some carboxylic acid solutions

The electrochemical behaviour and corrosion of lead in various concentrations of acetic, lactic (0·01 M –1·0 M ), oxalic and tartaric (0·01 M –0·15 M ) acid solutions were studied at 25°C by a potentiodynamic method. The lead anode is readily soluble both in acetic and lactic acid solutions up to 2000 mV. In these two acid solutions, the anodic dissolution of lead increases with increases in the acid concentration and the dissolution process is under charge transfer control. Lactic acid is more corrosive than acetic acid. However, in oxalic and tartaric acid solutions, the E/i profiles depend on the acid concentration. Above a certain specific concentration, the profiles exhibit an anodic current peak associated with a dissolution of the metal and the formation of a passivating lead salt film and a cathodic peak which is related to the reduction of the film. The active dissolution of the lead increases with the acid concentration, the scan rate and stirring of the solution. The passivation of lead in these two acid solutions occurs by a dissolution–precipitation mechanism and the process is controlled by diffusion. X-ray diffraction analysis confirmed the presence of a passivating salt film (either lead oxalate or lead tartrate) on the electrode surface. © 1998 SCI     

Evaluation of reaction variables in the dissolution of serpentine for mineral carbonation

The sequestration of CO₂ through the employment of magnesium silicates, olivine and serpentine, is beyond the proof of concept stage. Serpentine has been chosen as the feedstock mineral due to its abundance and availability. Although the reactivity of olivine is greater than that of serpentine, physical and chemical treatments have been shown to greatly increase the reactivity of serpentine. A sulfuric acid leaching stage has been shown to alleviate the rate limiting step of magnesium removal, thereby accelerating the overall carbonation process. Varying reaction conditions can significantly influence the results for the dissolution process with an extreme reaction environment providing desirable results. However, a more careful assessment of the reaction variables under milder conditions is needed for a better understanding of the reaction processes and potential pathways for high extraction yields under more modest conditions. Accordingly in this work, a statistical design of experiments was conducted to ascertain the effect of acid concentration, particle size and reaction time and temperature on the leaching of magnesium from serpentine using sulfuric acid. Results demonstrated that acid concentration provided primary control on the dissolution via the removal of water, which is closely correlated with the extraction of magnesium from serpentine. Particle comminution to a median size less than 163 μm remained an important consideration in increasing reactivity and liberating magnetite. Single variable experimentation demonstrated dissolution enhancements with increased reaction time and temperature. An increase in magnesium dissolution of 46% and 70%, over a baseline test, occurred for increased reaction time and temperature, respectively.     

Scale-up studies of the electrolytic reduction of oxalic to glyoxylic acid

The work examines a possible process for the electrolytic reduction of oxalic acid to glyoxylic acid. The reaction is investigated in filter press type cells varying from small bench scale to pilot plant size and it is shown that the product can be produced with current efficiencies better than 70% and chemical yields better than 90%. It is demonstrated that the cell product containing 8–10 wt% of glyoxylic acid can be concentrated to the commercial specification of a 50 wt% aqueous solution.     

高硅铝比B-NaY分子筛合成及催化二乙苯烷基转移性能

为了得到性能良好的B-NaY分子筛,采用直接水热合成法合成杂原子B-NaY分子筛,研究了未处理硅源以及分别用草酸、硫酸、硫酸铝预处理硅源方法所合成B-NaY分子筛物化性能。结果表明,当采用草酸对硅源进行预处理时,可以得到相对结晶度为97%,骨架硅铝比为6.3的高硅B-NaY分子筛,且晶化速率较快。采用草酸对硅源进行预处理,不仅可以增大硅源中硅酸根离子的聚合度,而且在晶化过程中草酸作为一种络合剂能通过与OH-一起和Al3+配位形成四配位活性铝物种,促进凝胶溶解,使得溶液中活性铝物种含量增加,有利于加速晶化。考察了所合成分子筛在二乙苯与苯烷基转移制备乙苯的反应中的催化性能,在反应温度175℃、反应压力3 MPa、苯与二乙苯质量比2、质量空速为3.3 h-1条件下,二乙苯转化率达50%以上,乙苯选择性达99.3%。草酸预处理硅源合成B-NaY分子筛的方法操作简单、快捷,所合成B-NaY分子筛性能优异,有良好的工业应用前景。     

过氧化氢催化活化体系及其在危化品消毒中的应用

随着我国化工行业的飞速发展,危险化学品事故时有发生,洗消成为化学应急处置的关键技术环节之一。本文综合考虑化学品的毒性、产销量、洗消的必要性等因素,初步建立了潜在危化品洗消污染物谱系;同时,在论述洗消原理及洗消剂的基础上,重点探讨了无机催化剂和有机活化剂对过氧化氢的催化活化原理。无机催化体系主要包含金属离子、金属盐和金属配位体,活性成分为·OH、¹O₂等;有机活化剂主要有酯类、酰胺类、脒类、胍类和腈类等,活性成分为过氧酸或过氧亚酰胺酸。各类体系在危化品消毒处置和漂白印染等领域都有研究和应用,有望成为未来危化品消毒剂的发展主体。本文可为过氧化物类消毒剂产品的研发提供一定的理论依据,为应对危化品事故应急救援洗消需求奠定技术基础。     

A new method of amine solvent recovery with acid addition for energy reduction in the CO2 absorption process

Chemical absorption/stripping technologies using an amine-based solvent have a lot of advantages for capturing carbon dioxide in post-combustion capture system. However, the higher energy demand for the solvent recovery makes the technology difficult to retrofit to existing plants. To overcome this obstacle, an alternative stripping process using an organic acid was studied to decrease the solubility of carbon dioxide and save the energy demand, but further research is necessary to recover the amine solvent and an organic acid effectively. In this study, a new amine recovery method using an organic acid is proposed and the method suggests a two-step of reaction crystallization process to separate the amine and the acid. This study demonstrates that an amine solvent (monoethanolamine, MEA) and an organic acid (oxalic acid) could be recycled effectively by reaction crystallization experiment. MEA and oxalic acid recovery efficiencies were also obtained using the experimental data in this study. The percentages of MEA recovery and the acid losses were estimated through these data. In addition, the energy demands for two recovery processes were estimated.     

活化稻壳纯化废液及再利用去除石英砂中的铁杂质

采用活化稻壳作为吸附剂纯化废液,再利用其去除石英砂中铁杂质。吸附剂的制备是在110℃下,质量分数1%的KOH溶液活化稻壳1 h,然后于600℃热处理2 h。研究了KOH的浓度、吸附剂的量、吸附时间、吸附液初始浓度和温度参数对去除废液中铁和铝的影响。结果表明,在最优试验条件下,铁和铝的去除率分别为97.2%和94.2%。研究发现纯化的废液对石英砂中铁的去除率远高于未纯化废液;在额外添加3.6%的磷酸时,纯化废液对铁的去除率达到77.1%,这项技术不仅可以节省大量的水(966 kg/m3)和磷酸(57.8 kg/m3)还可以避免环境污染。     

常温精脱硫新工艺工业应用初探

介绍了我国开发的ＨＬ－１、ＩＴＬ－４常温精脱硫剂新工艺在联（甲）醇厂、双甲流程、中低变一甲烷化流程、食品级ＣＯ２气体、双氧水、甲酸钠、ＤＭＦ等生产工艺中的应用，以保护甲醇、甲烷化、氨合成等化肥催化剂、高效吸附剂、贵金属催化剂及产品质量。     

Decontamination of radioactive concrete using electrokinetic technology

The experimental results of the electrokinetic decontamination with 0.01 M of nitric acid were that the cesium ions were removed by up to 52% from the concrete after 15 days, also the cobalt ions were only removed by up to 0.7%. The concrete should be washed with H₂SO₄ as a pretreatment before electrokintic decontamination to lower its pH below 4.0. The removal efficiencies of ⁶⁰Co and ¹³⁷Cs by nitric acid were increased by 3.1 and 2.5% more than those by acetic acid. The larger the particle size of the concrete, the more the removal efficiencies of ⁶⁰Co and ¹³⁷Cs were increased. Also, the removal efficiencies of ⁶⁰Co and ¹³⁷Cs by the application of an electric current of 20 mA/cm² were increased by 1.6 and 3.9% more than those by the application of 10 mA/cm². The removal efficiencies of ⁶⁰Co and ¹³⁷Cs from the radioactive concrete of 1,940 Bq/kg were 99.8 and 92.3% by electrokinetic decontamination after pretreatment by the application of an electric current of 20 mA/cm² for 25 days.     

Asymmetric alumina membranes electrochemically formed in oxalic acid solution

Alumina membranes were fabricated by anodizing aluminium metal in 0.15 M oxalic acid. The growth kinetics of the porous layer were investigated in the temperature range –1 to 16 °C using linear potential scans up to 70 V. The faradaic efficiencies of metal oxidation and of porous layer formation, determined by applying Faraday's law, were found to be independent of both temperature and electrical charge. SEM analysis of the metal-side and solution-side surfaces revealed different morphologies. After dissolution of the barrier layer in phosphoric acid, the metal-side surface showed circular pores whose size of about 90 nm was found to be uniform and independent of temperature. The pore population was also practically independent of temperature and a value of about 4 × 10¹³ pores m^–2 was determined. On the solution-side surface the presence of a deposit partially occluding the mouths of pores was observed. This coating could be removed by chemical etching in NaOH or thermal treatment at 870 °C, where decomposition of oxalate occurs. This supports the hypothesis that the deposit consists of an aluminium salt containing oxalate anions precipitated from the solution. The results show that it is possible to control the morphological characteristics of the anodic alumina membranes by careful choice of experimental conditions.     

Restoring Solvent for Nuclear Separation Processes

Abstract

Solvent extraction separation processes are used to recover usable nuclear materials from spent fuels. These processes involve the use of an extractant/diluent (solvent) for separation of the reusable actinides from unwanted fission products. The most widely used processes employ tributyl phosphate as an extractant diluted with a normal-paraffin hydrocarbon. During use, the solvent is altered due to hydrolysis and radiolysis, forming materials that influence product losses, product decontamination, and separation efficiencies. In most processes, the solvent is recycled after cleaning. Solvent cleaning generally involves scrubbing with a sodium carbonate solution. Studies at the Savannah River Laboratory have shown that carbonate washing, although removing residual solvent activity, does not remove more solvent-soluble binding ligands (formed by solvent degradation), which hold fission products in the solvent. Treatment of the solvent with a solid adsorbent after carbonate washing removes binding ligands and significantly improves recycled solvent performance. Laboratory work to establish the advantage of adsorbent cleaning and the development of a full-scale adsorption process will be described The application of this process for cleaning the first cycle solvent of a Savannah River Plant production process will be discussed.     

Mechanically activated starch magnetic microspheres for Cd(Ⅱ) adsorption from aqueous solution

Magnetic starch microspheres(AAM-MSM) were synthesized via an inverse emulsion graft copolymerization by using mechanically activated cassava starch(MS) as a crude material, acrylic acid(AA) and acrylamide(AM) as graft copolymer monomers, and methyl methacrylate(MMA) as the dispersing agent and used as an adsorbent for the removal of Cd(II) ions from aqueous solution. Fourier-transform infrared spectroscopy(FT-IR), X-ray photoelectron spectroscopy(XPS), scanning electron microscopy(SEM), and vibrating sample magnetometry(VSM) were used to characterize the AAM-MSM adsorbent. The results indicated that AA, AM, and MMA were grafted to the MS, and the Fe_3 O_4 nanoparticles were encapsulated in the AAM-MSM adsorbent microspheres.The adsorbent exhibited a smooth surface, uniform size, and good sphericity because of the addition of the MMA and provided more adsorption sites for the Cd(II) ions. The maximum adsorption capacity of Cd(II) on the AAM-MSM was 39.98 mg·g~(-1). The adsorbents were superparamagnetic, and the saturation magnetization was 16.7 A·m~2·kg~(-1). Additionally, the adsorption isotherms and kinetics of the adsorption process were further investigated. The process of Cd(II) ions adsorbed onto the AAM-MSM could be described more favorably by the pseudo-second-order kinetic and Langmuir isothermal adsorption models, which suggested that the chemical reaction process dominated the adsorption process for the Cd(II) and chemisorption was the rate-controlling step during the Cd(II) removal process.