Decontamination of radioactive soil wastes using an agglomeration-leaching process

An agglomeration-leaching process was evaluated to decontaminate Co-60 and Cs-137 from radioactive soils. Radioactive soils were screened based on the particle size of 0.075 mm. The soils with particle size of less than 0.075 mm were agglomerated by using a 2 wt% Na₂SiO₃ which had been predetermined to be an optimum reagent for an agglomeration. The agglomerated soils were mixed with the other soils with particle size bigger than 0.075 mm for leaching tests. Several leaching solutions were evaluated for their leaching performances for Co-60 and Cs-137 from simulated soil wastes, and the 0.1 M HCl solution was shown to be the most effective one. Leaching tests for radioactive soils in a column showed that the radioactive soils contaminated with Co-60 and Cs-137 radionuclides could be decontaminated down to the potential release criteria (∼100 Bq/kg) by using the appropriate conditions of an agglomeration-leaching process.     

Micromixing using induced-charge electrokinetic flow

The mixing effect of induced-charge electrokinetic flow (ICEKF) in a rectangular microchannel with embedded conducting hurdles is investigated in this paper. A correction method is suggested to estimate numerically the induced zeta potential on the conducting surface. Two-dimensional pressure-linked Navier-Stokes equation is used to model the flow field in the channel. The numerical results show flow circulations generated from the induced non-uniform zeta potential distribution along the conducting hurdle surfaces. It is demonstrated that the local flow circulations provide effective means to enhance the flow mixing between different solutions. The mixing enhancement effect is experimentally validated using PDMS based microchannels with embedded platinum hurdles. The dependence of the degree of mixing enhancement on the hurdle geometries and hurdle numbers is also predicted. The mixing using ICEKF described in this paper can be used in various microfluidics and lab-on-a-chip applications.     

锂离子电池硅碳复合负极材料结构设计与研究进展

综述了锂离子电池(LIBs)中使用的硅/碳(Si/C)复合负极材料的最新研究进展,从结构设计原理、材料合成方法、形态特征和电化学性能方面进行了总结,并分析了各种结构设计对改善性能的作用机理。讨论并提出了合理的Si/C负极材料结构设计以实现商业化的其余挑战和前景。     

放射性废水处理技术研究进展

在核电站发电的各个环节都会产生不同程度的放射性废水,如何安全有效地处理放射性废水对于核能的安全利用显得尤为重要。简单介绍了放射性废水的不同来源,综述了国内外目前关于放射性废水处理的研究报道,总结分析了化学沉淀法、离子交换法、膜分离法、吸附法等不同处理方法对放射性废水中放射性污染物的处理效果,并对放射性废水的处理技术以及实际应用方面进行了展望。     

现代混凝土技术对混凝土抗裂性影响之综述

鉴于各界对混凝土开裂的关注，本文专门就现代混凝土技术对混凝土抗裂性的影响进行了分析、综述。结果表明，减水剂、矿物掺和料的使用以及现代混凝土的低水胶比、低骨胶比增加了混凝土开裂的风险，恶化了混凝土的抗裂性，且随混凝土强度等级的提高混凝土开裂的风险增大。     

己二酸生产中的废气净化技术及其影响因素

以辽阳石化公司硝酸氧化醇酮制备己二酸装置为研究对象,研究了己二酸生产中废气的净化技术及废气消减过程中的影响因素。NO,NO2的净化采用水吸收法,以尾气中NOx含量和回收硝酸浓度为主要考察指标,设计了四因素三水平的正交试验,通过试验得出的优化工艺条件为:喷淋水流量7m3/h、补充空气量900m3/h、吸收温度14℃、吸收压力0.155 MPa,尾气中NOx体积分数为420×10-6,回收硝酸质量分数35%。N2O的净化采用催化分解法,并对影响其分解效果的3个因素进行了研究。结果表明,入口温度应随催化剂活性减弱逐渐升高,进气浓度最好维持在11.0%～11.2%,原料气中含水不利于催化分解。     

Treatment of liquid radioactive waste using microorganisms

The article deals with the problem of managing liquid nitrate-containing radioactive waste. A fundamentally new method for preliminary treatment that allows one to decrease the volume of these waste based on denitrification or anaerobic nitrate respiration (reducing nitrates to molecular nitrogen) has been developed. Microorganisms isolated from repository radioactive waste that is resistant to high salinity and ionizing radiation were used in the work. Based on laboratory studies on denitrification in model solutions of liquid radioactive waste, a design for a denitrifying reactor was developed and its basic parameters were calculated.     

Effect of clay mineralogy on the feasibility of electrokinetic soil decontamination technology

To evaluate the effect of clay mineralogy on the feasibility of electrokinetic soil remediation technology, we contaminated six soils with Cu(II), Zn(II) and Pb(II) and performed electroremediation for 570 h. Cation exchange resin saturated with H⁺ was placed between soil and cathode to prevent soil alkalinization and trap the migrated heavy metal cations. After the treatment, the heavy metal cations were sequentially extracted with water, 1 M MgCl₂ and hot 6 M HCl. In soils dominated by crystalline clay minerals, Cu(II) and Zn(II) significantly migrated from anode end and accumulated at the cathode end forming sparingly soluble hydroxides. Removal rates of Cu(II) and Zn(II) were highest in a soil dominated with kaolinite and crystalline hematite. In humic–allophanic and allophanic soils, the high pH-buffering capacity of allophane kept the soil pH above 5, even at the anode end, and Cu(II) and Zn(II) did not migrate significantly. In all soils, the migration of Pb(II) was infinitesimal due to the formation of insoluble PbSO₄ and very strong surface complexation at the mineral surfaces. These results show that the reactivity of component clay minerals to H⁺ and heavy metal cations has a crucial effect on the efficiency of the electrokinetic remediation technology and it is not effective for remediation of allophanic soils. The results also indicate that allophanic soils may be useful as a barrier material in landfill sites.     

The efficacy of using electrokinetic transport in highly-contaminated offshore sediments

Contaminated offshore mud samples from two regions of Abu Dhabi were tested for selected element removal using electrokinetics. The efficacy of the test results were compared for low and high salinity pore fluids applied to the mud samples. All samples showed some degree of removal efficiency at the anode end of each specimen by 24-h duration tests. The significance of the work was that similar removal efficiencies of about 20 ± 10% were achieved in both the low and high salinity specimens of these heavily contaminated offshore muds, revealing the potential of electrokinetic treatment in marine environments. The electroosmotic efficiency, as measured by the cumulative volume of flow per Coulombs of charge, was 0.002 cm³/C for the low salinity and 0.006 cm³/C for the high salinity samples. These values compared well with the electroosmotic efficiency of 0.008 cm³/C reported for a synthetic soil reference matrix of high electrolyte content. The low electroosmotic efficiency showed that although flow was achieved in all specimens, the mass transport was mainly dominated by electromigration as expected, and not by electrosmosis.     

Formulating a low-alkalinity, high-resistance and low-heat concrete for radioactive waste repositories

Investigations were carried out in order to formulate and characterize low-alkalinity and low-heat cements which would be compatible with an underground waste repository environment. Several systems comprising Ordinary Portland Cement (OPC), a fast-reacting pozzolan (silica fume (SF) or metakaolin (MK)) and, in some cases, a slow-reacting product (fly ash (FA) or blastfurnace slag (BFS)) were compared. Promising results were obtained with some binary mixtures of OPC and SF, and with some ternary blends of OPC, SF and FA or BFS: pH of water in equilibrium with the fully hydrated cements dropped below 11. Dependence of the properties of standard mortars on the high contents of FA and SF in the low-pH blends was examined. Combining SF and FA seemed attractive since SF compensated for the low reactivity of FA, while FA allowed to reduce the water demand, and dimensional variations of the mortars. Finally, low-heat (ΔT < 20 °C under semi-adiabatic conditions) and high strength (≈ 70–80 MPa) concretes were prepared from two low-pH cements: a binary blend made from 60% of OPC and 40% of SF, and a ternary blend including 37.5% OPC, 32.5% SF and 30% FA.     

Removal of lindane using electrokinetic soil flushing coupled with air stripping

Journal of Applied Electrochemistry - This paper evaluates the remediation of soil spiked with lindane using a combined treatment consisting of electrokinetic soil flushing (EKSF) with air...     

Performance of rice husk ash produced using a new technology as a mineral admixture in concrete

This article investigates the use of a new technique for the controlled combustion of Egyptian rice husk to mitigate the environmental concerns associated with its uncontrolled burning and provide a supplementary cementing material for the local construction industry. The reactor used provides efficient combustion of rice husk in a short residency time via the suspension of processed particles by jets of a process air stream that is forced though stationary angled blades at high velocity. Investigations on the rice husk ash (RHA) thus produced included oxide analysis, X-ray diffraction, carbon content, grindability, water demand, pozzolanic activity index, surface area, and particle size distribution measurements. In addition, concrete mixtures incorporating various proportions of silica fume (SF) and Egyptian RHA (EG-RHA) produced at different combustion temperatures were made and compared. The workability, superplasticizer and air-entraining admixture requirements, and compressive strength at various ages of these concrete mixtures were evaluated, and their resistance to rapid chloride penetrability and deicing salt surface scaling were examined. Test results indicate that contrary to RHA produced using existing technology, the superplasticizer and air-entraining agent requirements did not increase drastically when the RHA developed in this study was used. Compressive strengths achieved by concrete mixtures incorporating the new RHA exceeded those of concretes containing similar proportions of SF. The resistance to surface scaling of RHA concrete was better than that of concrete containing similar proportions of SF. While the chloride penetrability was substantially decreased by RHA, it remained slightly higher than that achieved by SF concrete.     

In-situ immobilization of Sr radioactive isotope using nanocrystalline hydroxyapatite

Hydroxyapatite was used as the inert matrix for in-situ immobilization of strontium (Sr) radioactive isotopes at room temperature. A nano-emulsification method was applied to synthesize Sr-substituted calcium hydroxyapatite (Ca_1?xSr_x)₁₀(PO₄)₆(OH)₂. The concentration of incorporated Sr was in the range of 0 ≤ x ≤ 1. Immobilization of Sr was evaluated using a stable isotope instead of radioactive isotope. The effect of strontium concentration on the crystal structure was studied and the results have showed that in the whole concentration range, Sr forms solid solutions with the host hydroxyapatite crystal structure. Powders comprised of nanometre sized particles were obtained and their properties, such as crystallite and particle size, changes in lattice parameters as function of dopant content and thermal stability, were further examined. It was found that the crystal structure of obtained powders is thermally stable at high temperatures. No secondary phases were formed in as-prepared powders or during calcination. The results in this study showed that nano-emulsion strategy provides a simple pathway for synthesis of a single-phase Sr-substituted hydroxyapatite, which can be used for immobilization of Sr radioactive isotopes.     

砼研究中的现代纳米技术

在简要介绍砼研究中的现代纳米技术的基础上,分析了水泥基材料中的纳米级孔隙结构,探讨了纳米级孔隙对水泥基材料耐久性的影响。在水泥基材料中加入纳米材料能提高其性能并为其增加某些特殊功能。纳米水泥基材料是未来水泥砼发展的方向,纳米水泥技术是对传统水泥砼材料进行改进的重要途径。     

Nanoscale sensor analysis using the immersed molecular electrokinetic finite element method

The concentration and detection of molecular biomarkers remain as a challenge to develop point-of-care diagnostic devices. An electric field induced concentration has been studied for such purposes but with limited success due to limited efficacy. This paper presents a computational study for investigating the molecular concentration and retention efficacy of single nanowire (SNW) and dendritic nanotip (DNT) sensors. Our computational results indicate that compared to a DNT, the SNW sensor produces higher dielectrophoretic (DEP) forces in the vicinity of the terminal end of the tip. Furthermore, the magnitude of the DEP force increases exponentially as the diameter of the SNW is decreased, resulting in a further improved retention efficacy of NPs. However, the SNW sensor's concentration efficacy was not much improved for NPs smaller than 10 nm diameter when the nanowire diameter was reduced from 500 to 50 nm. Compared to the SNW, the DNT sensor showed improved concentration efficacy due to multiple points of electric field concentrations, which retard the exponential decay of the DEP force resulting in a greater widespread region where the DEP force dominates the Brownian motion forces. When oligonucleotides are used as a target particle, the DEP force can be used to elongate oligonucleotides to further enhance the concentration and retention efficacy.     

Application of sorption-reagent materials in the technology of liquid radioactive waste treatment

Some examples of sorption-reagent materials and variants of their application in the practice of treating liquid radioactive waste have been considered. The data on the strontium sorption on samples of a sorption-reagent material under dynamic conditions at different degrees of dilution and different concentrations of seawater have been presented. These data demonstrate that the most efficient practical applications of sorption-reagent materials consist of decontaminating of seawater concentrates of strontium radionuclides. This task is stated during treatment of liquid radioactive waste (LRW) streams at the Fukushima-1 NPP (Japan), where reverse osmosis concentrates constitute the main problem of localization of the aftermath of the disaster that occurred in 2011.     

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.