Modeling the Electrokinetic Decontamination of Concrete

Abstract

The decontamination of concrete is a major concern in many Department of Energy (DOE) facilities. Numerous techniques (abrasive methods, manual methods, ultrasonics, concrete surface layer removal, chemical extraction methods, etc.) have been used to remove radioactive contamination from the surface of concrete. Recently, processes that are based on electrokinetic phenomena have been developed to decontaminate concrete. Electrokinetic decontamination has been shown to remove from 70 to over 90% of the surface radioactivity. To evaluate and improve the electrokinetic processes, a model has been developed to simulate the transport of ionic radionuclei constituents through the pores of concrete and into the anolyte and catholyte. The model takes into account the adsorption and desorption kinetics of the radionuclei from the pore walls, and ion transport by electro-osmosis, electromigration, and diffusion. A numerical technique, orthogonal collocation, is used to simultaneously solve the governing convective diffusion equations for a porous concrete slab and the current density equation.

This paper presents the theoretical framework of the model and the results from the computation of the dynamics of ion transport during electrokinetic treatment of concrete. The simulation results are in good agreement with experimental data.

     

影响复合酶去污力的因素

为研究复合酶对无磷洗衣粉去污力的影响,针对加酶浓度、洗涤温度、洗涤时间、水质硬度和pH值等不同条件进行了反复实验,不但得出了酶制剂对洗衣粉去污力具有明显影响的结论,还确定了影响复合酶去污力的几个具体因素,以用于指导加酶洗衣粉的生产实践.     

混凝土中的爆坑实验研究

利用爆炸相似理论讨论了固体介质中的相同装药量在不同埋深爆炸情况时的爆坑、炸深与埋深的关系，将传统理论的1／3比例因子修正为1／3．4或1／3．6比例因子。据此设计了混凝土中的炸坑效应缩比实验，并利用某原型实验进行了验证。将实验结果与修正后的比例因子计算值进行了对比，符合较好，其精度可用于工程设计计算。     

硬化混凝土中胶凝材料测定方法探讨

胶凝材料(水泥、粉煤灰和矿粉)是影响混凝土质量的重要因素,基于混凝土中胶凝材料化学反应的机理,以及硬化混凝土中测定胶凝材料的不同方法,探讨了这些方法在不同胶凝材料共存时的适应性,认为相对于有机溶剂溶解法,可溶性SiO_2法适应性更强;提出可以用粉碎试样测可溶性SiO_2法或分离试样测CaO法判断硬化混凝土是否按原配合比施工。     

Decontamination of Nitrate Polluted Water

Abstract

Nitrate can be extracted from water at any pH below 10 by a water-insoluble quaternary ammonium 2, 4, 6-tri-methylphenate or N-benzyl-H-methylbenzenesulfonamidate dissolved in trioctylphosphate (TOP). Membranes were prepared by taking up TOP solutions of the quaternary ammonium bases in porous polypropylene (Celgard^R-2400). These membranes were used in a modified dialysis cell to transfer N0₃ ^? from near-neutral water to stripping solutions of pH, 12–14. Specific rate constants, k, in excess of 10^?4 cm s^?1 were observed for nitrate removal under a wide variety of loading and stripping conditions. This is sufficient to project a practical device for the decontamination of nitrate-polluted water.

When the hydrodynamic resistances in both the feed and the strip are removed by pumping these solutions through static mixers adjacent to the membrane, K is reduced by making the stripping solution less basic or by increasing its nitrate concentration. These observations suggest that the disassembly of the carrier of the N0₃ ^? and H⁺ at the stripping interface is a step-wise process, involving energetically unfavorable, charge-separated species.     

用废砼作粗骨料配制再生混凝土的试验研究

采用正交试验方法分析了水胶比、砂率、粉煤灰掺量及减水剂掺量对混凝土再生性的影响,并根据综合平衡法得出所用原材料体系中各因素的最佳取值范围。在此基础上,采用42.5R普通硅酸盐水泥与人工破碎所得的砼再生骨料成功配制出强度达50MPa的混凝土,给出了不同水胶比下的再生混凝土推荐配合比。     

Electrokinetic properties of polyformaldehyde fibers

Electrokinetic properties, namely, zeta potential (ζ), surface charge density (σ), and surface conductivity (K_s) of polyformaldehyde fibers [poly(oxymethylene) fibers] have been studied in the presence of direct dyes, with or without surfactants and an electrolyte. The anionic dyes increased the negative zeta potential of fibers. The increase in ζ was found to be a function of concentration and basicity of the dye in the streaming solution. Thus, the tetrabasic dye gave higher value of negative ζ than the equivalent concentration of the dibasic dye. The cationic surfactant brought about a decrease in negative ζ, giving a point of inflection, while the anionic surfactant increased it. The nonionic surfactant brought about a certain reduction in negative ζ, but failed to give a point of inflection. In the presence of a direct dye, the cationic surfactant brought about considerable reduction in negative ζ, to give a point of inflection. The presence of an electrolyte in the streaming dye solution progressively lowered the negative ζ. In general, σ increased with the increase in the concentration of either a dye or an electrolyte in the presence of a given concentration of the dye in the streaming solution. Results on K_s indicated that the surface conductivity of the fibers is a function of concentration of dye, surfactant, and electrolyte. It was, however, observed to be independent of the nature of the surfactant. Although both the dibasic and tetrabasic direct dyes brought about an increase in K_s, the extent of increase was dependent upon the basicity of the molecules.     

Electrokinetic properties of textile fabrics

This paper reports electrokinetic phenomena concerning the properties of textile fabrics that are crucial for dyeing and finishing processes. These interface phenomena influence the adsorption of surfactants, optical brighteners, dyes and finishing agents due to interaction forces between the fibre surface and solution. Zeta potential, isoelectric point, point of zero charge and the amount of surface charge of standard adjacent fabrics (cotton, wool, viscose rayon, polyamide, polyester and acrylic) have been determined. Electrokinetic potential was measured by a method involving streaming potential/current using an electrokinetic analyser. The specific amount of surface charge was calculated by a back-titration method.     

放化厂退役去污

阐述了放化厂的退役去污,介绍了去污的目的、主要污染核素及其来源和污染的机理,并论述了系统去污和拆卸去污工艺的选择等。     

氯气泄漏洗消技术研究

采用碱液进行中和洗消,是目前基层消防部队处置氯气泄漏事故最常用的洗消方法。本文通过对常见氯气洗消剂的用量、性价、性能等方面进行综合比较,提出了如何选择洗消剂的合理化意见和建议,同时对氯气洗消技术的应用进行了简要归纳,重点提出了利用排吸器比例配制碱液进行喷雾洗消的新方法,并对此方法的实战应用特点及优势进行了分析。本文的研究结果,对广大基层消防指挥员提高科学施救的能力,正确、有效处置氯气泄漏事故将起到一定的帮助作用。     

一种环保型混凝土路面修补材料的试验研究

利用正交试验方法,研究了矿渣细度、水泥熟料掺量、水泥熟料细度和水玻璃掺量各因素对凝结时间、砂浆强度的影响规律,确定出环保型混凝土修补材料的初步配方.通过调整水玻璃的模数和水灰比对配方进行优化,研制出一种凝结时间短、抗折强度高、干缩小、粘结强度高的性能优良的环保型混凝土修补材料.     

再生骨料混凝土耐久性能的试验研究

在实验室浇筑C20普通混凝土,经28d养护后用破碎机将其破碎、筛选调配制成再生粗骨料与细骨料,以此再生骨料100%替代天然碎石和砂子制备出再生骨料混凝土,探讨了再生骨料混凝土的耐久性能之一,抵抗冻融循环的能力以及抗碳化(中性化)能力.结果表明,100%再生骨料混凝土(简称RR混凝土)试件的冻融循环抵抗性与粗,细骨料置换率为0%的普通混凝土(简称NN混凝土)试件相比,水灰比分别为0.45、0.55时耐久性指数分别降低6%和9%,而且抵抗碳化能力差,碳化速度几乎快三倍.     

Electrokinetic properties of iron-containing microporous glasses

The electrokinetic properties of the particles of microporous borosilicate glass powder containing the magnetite phase in its composition on the background of an indifferent electrolyte (NaCl) have been studied. It is found that the modification of two-phase sodium borosilicate glass with iron oxide leads to a shift in the position of the isoelectric point from pH 0.5 for alkali borosilicate (ABS) porous glass (PG) to pH 4.1 ± 0.1 for iron-containing ABS PG. The observed changes in the behavior of modified PG open up new prospects for their practical application.     

Electrokinetic desalination of glazed ceramic tiles

Electrokinetic desalination is a method where an applied electric DC field is the driving force for removal of salts from porous building materials. In the present paper, the method is tested in laboratory scale for desalination of single ceramic tiles. In a model system, where a tile was contaminated with NaCl during submersion and subsequently desalinated by the method, the desalination was completed in that the high and problematic initial Cl⁻ concentration was reduced to an unproblematic concentration. Further conductivity measurements showed a very low conductivity in the tile after treatment, indicating that supply of ions from the poultice at the electrodes into the tile was limited. Electroosmotic transport of water was seen when low ionic content was reached. Experiments were also conducted with XVIII-century tiles, which had been removed from Palacio Centeno (Lisbon) during renovation due to damage of the glazing from the presence of salts. These tiles were severely contaminated with both chlorides and nitrates, and one of the tiles also contained sulphates though at a low concentration. The charge transfer was too low in the experiments to obtain full desalination, but promising results were obtained as significant decreases (>81% Cl⁻, ~59% NO₃ ⁻ and ~22% SO₄ ²⁻) were seen.     

Electrokinetic Properties of Acid-Activated Montmorillonite Dispersions

In this study, the influence of pH, electrolyte concentration, and type of ionic species on the electrokinetic properties (zeta potential and electrokinetic charge density) of the acid-activated montmorillonite mineral have been investigated using the microelectrophoresis method. The electrokinetic properties of acid-activated montmorillonite dispersions have been determined in aqueous solutions of mono-, di-, and trivalent salts and divalent heavy metal salts. Zeta potential experiments have been performed to determine the point of zero charge (pzc) and potential determining ions (pdi). The zeta potential values of the acid-activated montmorillonite particles were negative and did not vary significantly within the pH range studied. Acid-activated montmorillonite dispersions do not have point of zero charge (pzc). The valence of the electrolytes has a great influence on the electrokinetic behavior of the suspension. A gradual decrease in the zeta potential (from ?25 mV to ?5 mV) occurs with the monovalent electrolytes when concentration increased. Divalent and heavy metal electrolytes have less negative z-potentials due to the higher valence of ions. A sign reversal of z-potential has been observed at AlCl₃, FeCl₃, and CrCl₃ electrolytes (potential determining ions) and zeta potential values have had a positive sign at high electrolyte concentrations.

The electrokinetic charge density of acid-activated montmorillonite has shown similar trends for variation in mono- and divalent electrolyte solutions. Up to concentrations of ca. 10^?3 M, it has remained practically constant at approximately 0.5 × 10^?3 C m^?2 For higher concentrations of monovalent electrolytes more negative values (?16 × 10^?3 C m^?2) were observed. It has less negative values in divalent electrolyte concentrations according to monovalent electrolytes (?5 × 10^?3 C m^?2). For low concentrations of trivalent electrolytes, the electrokinetic charge density of montmorillonite particles is constant, but at certain concentrations it rapidly increased and changed its sign to positive.     

Electrokinetic behaviour of coal particles suspensions

Measurements of the zeta potential of coal suspensions have been carried out by micro-electrophoresis. The influence of colloidal particles concentration, temperature, pH and ionic strength on two types of Spanish coals have been studied. Experimental results are discussed in terms of the adsorptive properties of coal surface and with regard to the formation of aggregates by coagulation.     

Electrokinetic restoration of saline agricultural lands

Salinization of greenhouse soils has become a serious problem in Korea because of the extensive use of chemical fertilizers to improve crop yield. This study investigated the feasibility of electrokinetic (EK) treatment for reclamation of saline soil. Experiments were conducted using voltage gradients of 1, 2, and 3 V/cm applied for 48 and 96 h. Anions such as chloride, sulfate, and nitrate were transported toward the anode and accumulated there, whereas cations were transferred toward the cathode by electromigration. Among the various ions, the highest removal efficiency was achieved for nitrate: >80% at 48 h and >99% at 96 h. Chloride removal after 96 h was substantially higher than that after 48 h because the longer period of time allowed more electrical transport via electromigration and electro-osmosis. However, the removal efficiency for sulfate and calcium did not change significantly between 48 and 96 h. Soil EC was lower than the initial value in all soil sections at 96 h. The lowest value, 1.8 dS/m, was seen in the experiment employing a gradient of 3 V/cm for 48 h. This study demonstrated that nitrate can be readily removed from soil by electromigration. Further, other ions can also be removed by EK treatment; therefore, it could be successfully used for reclamation of saline soils.     

Electrokinetic properties of modified polyester fibers

Electrokinetic properties of normal polyester flat filament, texturized polyester and cationic dyeable polyester were studied when solutions of different pH and cationic dye concentrations were run through them. The textured polyester exhibited maximum negative zeta potential whereas cationic dyeable polyester showed minimum. The negative zeta potential was found to be maximum near neutral pH. The effect of heat-setting at extreme conditions (220°C, 90 s) on electrokinetic properties was also studied. Such heat-setting was found to lower negative zeta potential, attributed to a decrease in surface area. Cationic dyeable, “easy” dyeable, and normal flat filament type polyester were also investigated. Results with respect to negative zeta potential, surface charge density, and surface conductivity, are discussed. © 1993 John Wiley & Sons, Inc.     

微乳液电动色谱的研究进展

微乳液电动色谱在胶束电动色谱基础上发展起来的一种色谱技术。由于操作中可调节的因素众多,它的应用范围广泛。对其与胶束电动色谱比较、手性拆分、在线富集技术连用、离子液体连用等方面进行了综述。