Attenuation performance of geosynthetic sorption sheets against arsenic subjected to compressive stresses

The attenuation layer method has been considered an effective countermeasure to deal with excavated soils and rocks containing geogenic toxic elements like arsenic (As). The geosynthetic sorption sheet is a geosynthetic product that can be employed in the attenuation layer method applications as a sorption material. The sorption sheets used in the attenuation layer will be inevitably subjected to overburdened loads in the field. In this study, laboratory column experiments are conducted to evaluate the attenuation performance of the geosynthetic sorption sheets coated with hydrotalcite as sorbent against As under different overburden pressure conditions (10, 100, and 200 kPa). Experimental results showed that the cumulative sorption masses of As for 200 kPa cases are approximately 10.5–13.3 times greater than that for 10 kPa cases. Microstructure characterizations of the geosynthetic sorption sheet before and after loading were also detected. More compacted and involved fiber configuration as a result of higher loading produces a more effective contact between As solution and hydrotalcite. The presence of partial dissolution of hydrotalcite is confirmed through the chemical analysis of effluent. However, hydrotalcite would gradually become stable during continuous use

Evaluating temperature effects on leaching behavior of geogenic arsenic and boron from crushed excavated rocks using shaking and nonshaking batch tests

The leaching behavior of arsenic and boron is evaluated in this work through two types of excavated rocks with geogenic contaminants under different temperatures. Excavated rocks with geogenic contaminants are expected to be used in embankments with appropriate countermeasures being taken against the risks brought about by geogenic contamination. The leaching behavior might change because of changes in the ground temperature. However, the effects of temperature on the leaching behavior of such rocks have not been well examined. Herein, batch leaching tests at temperatures between 5 and 60 °C were performed under shaking and nonshaking conditions. Mudstone and shale rock were crushed into particles smaller than 2 mm, which were required for the tests. The tests were carried out for durations ranging from 6 h to 15 days because changes in leaching kinetics also require careful evaluation. After conducting the nonshaking tests for 15 days at 40 °C, the mudstone sample leached arsenic and boron at concentrations of approximately 0.7 and 1.0 mg/L, respectively. The arsenic and boron concentrations were about 20 and 40% higher than those of the sample leached at a temperature of 20 °C. Elevated temperatures were seen to increase the leaching kinetics of the toxic elements. For the shale rock sample, the leaching rate for arsenic was 7.7 × 10⁻²/h at 40 °C, which was about 2.5 times greater than the value at 30 °C. The nonshaking tests showed higher leaching amounts of arsenic and boron than the shaking tests, especially at elevated temperatures. As unrealistic estimations should be avoided, nonshaking tests are suggested. Moreover, nonshaking tests lasting longer than 6 h are necessary due to the relatively slow dissolution of minerals

Effect of acidity on attenuation performance of sandy soil amended with granular calcium-magnesium composite

Utilising naturally contaminated soils and rocks is essential for significantly reducing geo-waste. However, there are no well-established concepts regarding the methods or countermeasures for utilising these soils and rocks, which would realise cost-effectiveness and environmental safety. Therefore, several researches focusing on the attenuation layer method have recently been undertaken. This method involves installing an attenuation layer between the contaminated materials and the ground to prevent ground contamination due to the attenuation capacity. A critical issue in the attenuation layer's design is to evaluate the attenuation performance of the layer material against target chemicals. Several important concerns and questions need to be solved when evaluating the attenuation performance. One is how the acidic leachate might diminish the layer material's attenuation performance. This paper presents the attenuation performance of a soil amended with a granular calcium-magnesium composite against acidic leachate. Batch and column tests, employing arsenic solutions of pH 2, 4 and 6, were applied to evaluate its attenuation performance. Using Freundlich parameter K as an index, the soil's attenuation performance was determined to have improved by at least 40% after the addition of the agent, even when the agent content was 5%. The amended soil's attenuation performance should be similar if the leachate pH is pH 6–4, although it might reduce by up to ~30% for pH 6. If the attenuation layer buffers the acid and provides the leachate with pH > 6, it will assure that the original ground's attenuation capacity is utilised. Considering this work's findings, amended soil can be employed as material for the attenuation layer

Evaluating the arsenic attenuation of soil amended with calcium–magnesium composites of different particle sizes

An attenuation layer composed of ground mixed with stabilising agents can prevent the contamination of the surrounding area when using soils and rocks with geogenic contaminants in embankments. The optimum particle size of the stabilising agent must be selected based on the requirements of the construction site because the mechanical and chemical properties of the attenuation layer are site-specific. However, the relationship between the particle size of the stabilising agent and the attenuation performance of soil–agent mixtures has yet to be fully clarified. This study employs batch sorption tests to evaluate the attenuation of arsenic by a soil mixed with a calcium–magnesium composite with different particle sizes, ranging from powder particles (<0.075 mm in size) to granular particles with diameters between 2.0 and 9.5 mm. Amended soil more effectively attenuates the contaminant than the original soil. In one experiment, a stabilising agent of granular particles (between 2.0 and 9.5 mm) for the amendment increased the soil’s partition coefficient Kd from 14.5 to 22.2 cm³/g, which is more than a 50% improvement in the attenuation. Using a stabilising agent with a smaller particle size for the amendment has a greater impact. Kd increases linearly as the particle size of the stabilising agent decreases down to 0.075 mm. Using the Kd from laboratory tests, simulations with a one-dimensional advection–dispersion equation demonstrate the durability of the attenuation layer. Both the powder and the granular particles show promise as attenuation layer materials

岡山大学における核燃料物質の安全管理のための劣化ウランと天然ウランの鑑別について

In Japan, the Law for the Regulation of Nuclear Source Materials, Nuclear Fuel Materials and Reactors (Regulation Law) controls the nuclear fuel materials such as thorium (Th), uranium (U) and plutonium (Pu). Under the Regulation Law, all related materials and reactors are needed to register to the Government. In Okayama University, many nuclear fuel materials, mainly uranium compounds, are registered and stored in 11 departments, separately. Discrimination between depleted uranium and natural uranium is important for the observance of the Regulation Law and the safety management of the nuclear fuel materials in the Okayama University. However, the discrimination of the two kind of uranium has poorly analyzed. In this study, we analyzed several uranium compounds by using γ-ray spectrometry to determine whether the depleted uranium or not

Basic study on the effects of the archeological investigation and the construction work on the environmental radiation

In this paper, we investigated how the excavation of ruins and the construction work affected the environmental radiation in the Shikata campus of Okayama University (S-campus). The environmental radiation was steady in the S-campus until 1997, but began to change since 1998, while the ruin's survey and the construction work started frequently after 1998 in the S-campus. In general, the soil and the concrete include the natural radioisotope (uranium series and thorium series, etc). When ruins are surveyed, it is necessary to move a large amount of the soil. In addition, a large amount of the concrete is used for the construction work. To measure the environmental radiation, the monitor posts were set up on the east and west sides of the building of the Radioisotope Center (RIC). We sampled the soil in the container in each place. We used the high-purity germanium detector to analyze them. The monitor posts showed the difference in the in-air dose rate in each place in the S-campus. The in-air dose rate at the east side of the RIC was higher than that at the west side. The result of analysis showed that the soil includes the (40)K at the east side. While the specific activity of the 40K was 0.849Bq/g at the east side, the (40)K was hardly detected in the soil at the west side. The each soil included the 214-lead and 214-bismus ((214)Pb, (214)Bi), however, there was no significant difference in the specific activity of the each soil. The concrete included (40)K, whose specific activity was 0.492Bq/g. It was suggested that the change of the environmental radiation was attributed to radon and its daughter nuclides in the soil rather than the radiation from the concrete in the buildings

Effects of some physical conditions on leaching rate of radon from radioactive minerals originating from some hot springs

In order to determine the best physical conditions for leaching more radon from minerals into water, we measured the leaching rate of radon from radioactive minerals under the conditions of some different grain sizes and water temperatures. Water temperature affected the leaching rate of radon although the grain size did not significantly affect it. Furthermore, we proposed ultrasonic irradiation to the mixture of a mineral and water as the method of leaching more radon. Ultrasonic irradiation was efficient to leach more radon from the mineral soaked in water because of ultrasonic cavitation.</p

Sorption-desorption column tests to evaluate the attenuation layer using soil amended with a stabilising agent

Sorption-desorption column tests using acrylic columns (ϕ 5 cm × h 10 cm) were employed to evaluate the sorption performance of an attenuation layer against geogenic contamination. The attenuation layer material was silica sand amended with 1, 5, or 10% of a stabilising agent. The main component of the agent was magnesium oxide. The sorption behaviour of the materials was determined by a fluoride solution (C₀ = 80 mg/L F-), while the desorption behaviour was determined by distilled water. Breakthroughs (C/C₀ > 0.05) occurred after approximately 1, 20, and 50 PVF for stabilising agent contents of 1, 5, and 10%, respectively. The one-dimensional advection-dispersion equation modelled the breakthrough curves obtained from the tests. The predictions gave unrealistic estimates, especially for the breakthrough point where C/C₀ = 0.05. For the 1% agent content, approximately 20% of the sorbed mass, Ss, was desorbed, but the percentage of desorbed mass, Sd, was much smaller for the higher agent contents. The difference between the sorbed and desorbed masses was defined as the immobilised fraction, Ss - Sd. For the 5% agent content, Ss - Sd = 4.0 mg/g. The results suggest that when silica sand is amended with magnesium oxide as an agent, the mixture can immobilise the fluoride in the attenuation layer

Radioactivity and radon emanation fraction of the granites sampled at Misasa and Badgastein

The chemical composition was analyzed and the radioactivity, radon exhalation rate and emanation fraction were measured to investigate the characteristics of the granites sampled at Misasa and Badgastein, world famous for radon therapy. The Misasa granite was probably composed of quartz, albite and microcline. The Badgastein granite was probably composed of quartz and muscovite. The radon exhalation rates and emanation fractions of the Misasa granite were much higher than those of the Badgastein granite, regardless of the Ra-226 activity concentrations

Serum amyloid A-induced IL-6 production by rheumatoid synoviocytes

AbstractIn this study, we investigated the role of serum amyloid A protein (SAA) in the production of interleukin-6 (IL-6) using rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS). Recombinant SAA stimulation induced the production of pro-inflammatory cytokine, IL-6, from RA-FLS. The signaling events induced by SAA included the activation of the mitogen-activated protein kineases, p38 and JNK1/2 and the activation of nuclear factor-kappa B (NF-κB). Inhibitor studies have shown SAA-induced IL-6 production to be down-regulated by NF-κB inhibition and partially inhibited by p38 or JNK inhibitors. Our findings demonstrate that SAA is a significant inducer of IL-6, which is critically involved in RA pathogenesis