| 1. |
Akiko Nakano, Effect of soil surface characteristics on denitrification activity and induced calcium carbonate precipitation on the surface., Proceedings of the 9ICEG (9th International Congress on Environmental Geotechnics) Chania, Greece., 10.53243/ICEG2023-32, 2023.06. |
| 2. |
Applying MICP by denitrification in soils: A process analysis
The process of microbially induced carbonate precipitation (MICP) by denitrification was investigated in relation to its potential use as a ground improvement method. Liquid batch experiments indicated that the substrate solution had an optimum carbon-nitrogen ratio of 1·6 and confirmed that combining nitrate reduction and calcium carbonate precipitation leads to an efficient conversion, at which the pH is buffered slightly below 7 and the accumulation of toxic intermediate nitrogen compounds is limited. Sand column experiments confirmed that the volume and distribution of the gas phase strongly depend on the stress conditions. The produced gas volume is inversely related to the pore pressure and can be predicted based on a mass balance analysis, assuming conservation of mass and using theoretical laws of physics. At low pore pressure, the gas formed and accumulated at the top of the column, whereas calcium carbonate precipitation occurred mostly at the bottom near the substrate inlet; an excess amount of gas was produced, which vented from the sand columns and induced cracks in the sand at low confining pressures, which negatively affected the sand-stabilising effect of the calcium carbonate minerals.. |
| 3. |
Effect of Salinity on Lead Sorption and Migration of Clay Liner Materials
Batch sorption test and selective sequential extraction were conducted for two types of bentonite mixture using basalt soil and Andosol to examine the effect of salinity for their lead sorption abilities. Increase in salt concentration of solution decreased the lead sorption of the soil mixtures. Particularly exchangeable phase of lead sorbed in basalt soil mixture decreased with the increase in the salt concentration. Due to the high buffer capacity of allophane contained in Andosol, Andosol mixture exhibited the higher lead sorption ability than basalt soil mixture. Buffer Prediction of lead leaching by convection-diffusion equation showed that the high salt concentration increased the mobility of lead in the clay liner. The leaching speed of basalt soil mixture was the three times higher than that of Andosol mixture. These results suggest that Andosol is effective material for reduction of lead mobility in clay liner.. |
| 4. |
Geochemical assessment of arsenic contamination in well water and sediments from several communities in the Nawalparasi District of Nepal
Arsenic contamination of well water is a serious issue in the Nawalparasi District of the Terai region in Nepal. A local investigation was carried out on 137 tube wells in 24 communities of the district in December 2011. The investigation revealed that the average arsenic concentration in the tube wells was 350 μg/L, and that nearly 98 % of the wells exceeded the WHO guideline arsenic level limit of 10 μg/L. Highly contaminated well water, with more than 400 μg/L of arsenic, was found within the limited depth ranges of 18–22 and 50–80 m. High arsenic levels exceeding 500 μg/L were detected in shallower wells at Patkhauli, Mahuawa, Thulokunwar, and Goini located between 27.517° and 27.543°N and between 83.648° and 83.748°E. Boring sampling at five communities of Kashiya, Goini, Sanokunwar, Thulokunwar, and Mahuawa revealed two aquifers located at the two depths around 14–22 and 41–50 m in each community. Dark gray or black-colored peaty clay layers rich in organic matter were distributed at depths of 18–21 m beside the upper aquifers with high arsenic concentration in each community. Positive correlations were shown between iron and arsenic in the sediments from the five communities. It can be inferred that these results were caused by dissolution of iron-oxyhydroxide molecules with arsenic from solid phases. Microbial metabolisms have a great potential to induce the dissolution and release arsenic attached on the solid phases into aqueous phases depending on the level of redox potential and pH.. |
| 5. |
Akiko Nakano, Li Loretta, Masami Ohtsubo, Takahiro Higashi, Motohei Kanayama, Lead Sorption Characteristics of Bentonites from Japan and U.S.A in View of Their Mineralogy and Chemistry, Clay Science, 2013.12. |
| 6. |
Variation of Microstructure with Consolidation Proceeding for Sand-Clay Mixed Soils
The macroscopic behaviors of soil ground such as compression and deformation consist of the integrated microscopic behaviors of soil particles and pores such as movement and entrapment. Resultant compression and deformation of soil ground are mlutiple behaviors, because of the wide variation for soil particle shape, size and type, a charge and chemical action of clay particles and the heterogeneity for structure of pore size distribution. The conventional consolidation tests were carried out to investigate the consolidation characteristics for sand-clay mixed soils, and their pore size distributions and microstructures were examined by using mercury-intrusion porosimetry (MIP) and scanning electron microscope (SEM). As a result, it was found that small intra-aggregate pores were not compressed until all macro pores have been collapsed due to the consolidation proceeding, and the largest interaggregate pores were the first affected.. |
| 7. |
HUONG NGUYEN THI LAN, OHTSUBO MASAMI, LI LORETTA, HIGASHI TAKAHIRO, KANAYAMA MOTOHEI, NAKANO AKIKO, HEAVY METAL CONTAMINATION OF SOIL AND RICE IN WASTEWATER-IRRIGATED PADDY FIELD IN A SUBURBAN AREA OF HANOI, VIETNAM, Clay science, 13, 6, 205-215, 2008.06, The present paper deals with the heavy metal contamination of soil and rice grain in the paddy field subjected to the irrigation water polluted with wastes from various industrial plants in Hanoi. Soil and rice grain samples were taken at different distances (0-50 m) from the edge of the paddy field. The retention and potential mobility of heavy metals were assessed based on the contents of total and fractionated heavy metals in the soil and their leachability. The concentration of the fractionated heavy metals was determined by selective sequential extraction method. Heavy metal contents in the rice grain were also assessed. The average concentration of the metals in the soil was in the order: Cu (202 mg kg^) > Zn (192 mg kg^) > Cr (185 mg kg^) > Pb (159 mg kg^) > Ni (45 mg kg^) > Cd (4 mg kg^). The heavy metal concentrations in the soil exceeded the permissible level of the Vietnamese standard for Cd, Cu, Pb and Zn. The results of selective sequential extraction procedure indicated that dominant fractions were oxide, organic and residual materials for Cd, Ni, Pb and Zn, and organic and residual materials for Cr, and an organic material for Cu. Leaching tests with deionized water and acid solutions indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order: Cd > Ni > Cr > Pb > Cu > Zn. By leaching with deionized water and acid solutions, all heavy metals were released fully from exchangeable fraction, and Cd and Ni were fully from carbonate and oxide fractions. The average concentration of heavy metals in the rice grain was in the order: Zn (14.4mg kg^) > Cu (6.9 mg kg^) > Cr(3.1 mg kg^) > Pb (2.1 mg kg^) >Ni (1.4 mg kg^) > Cd (0.1 mg kg^). The concentrations of Cu, Ni, and Zn in the rice grain met the WHO standard while the concentrations of Cr and Pb exceeded the permissible level of the standard. The concentrations of Cd met the Vietnamese standard while those of Pb exceeded the permissible level of the standard. Transfer coefficient for the metals was in the order: Zn>Ni>Cu>Cd≈Cr>Pb.. |
| 8. |
Effects of Salt Leaching on the Consolidation Characteristics of Ariake Clay
This paper describes the effects of salt leaching on the change in pore water salinity, physical properties and consolidation characteristics for undisturbed and remolded Ariake marine clay. The undisturbed clay specimens placed in consolidation rings were subjected to salt leaching with distilled water. The pore water salinity, pH and hydraulic conductivity during leaching were recorded, and Atterberg limits, shear strength and consolidation parameters for undisturbed and remolded specimens were determined before and after leaching. Due to reduction in pore water salinity from 10.8 to 0.01mg/L through the permeation of distilled water equivalent to 12 pore-volumes, the strength of remolded specimen exhibited marked decrease while the strength of undisturbed specimen slightly increased. This led to a dramatic increase in the sensitivity of the specimen from 10 to 594. The main clay mineral of Ariake clay is smectite, and the behaviors of the specimens mentioned above were explained in terms of the low swelling nature of the smectite. Salt leaching reduced both the consolidation yield stress and compression index of the undisturbed specimen. The hydraulic conductivity of undisturbed specimen was decreased by 60% by salt leaching, which led to a reduction in the consolidation coefficient of the specimen by about 50%. Decreases in the consolidation yield stress, compression index and hydraulic conductivity due to salt leaching was attributed to the change in particle orientation from flocculated to orientated structure under a given consolidation pressure.. |
| 9. |
Role of Carbonate for Pb Sorption in Some Bentonites
Bentonite is widely used for clay liner materials because of high swelling, low hydraulic conductivity, and the high sorption capacity of contaminants such as heavy metals. In this paper, batch sorption tests and selective sequential extraction tests were conducted to evaluate sorption capacity and forms for lead, using three types of bentonites from Japan and US with different physical, chemical, and mineralogical properties. Cation exchange and carbonate phase were predominant for the sorption of lead by bentonites; the carbonate phase was dominant at high equilibrium pH, while the cation exchange phase became dominant as equilibrium pH decreases. The ratio of carbonate phase was greater for the bentonite with higher amount of carbonate, so was the maximum Pb retained. The Japanese bentonites sorbed greater amount of Pb than the US bentonite as they contained more carbonate. The formation of cerussite (PbCO3) primarily contributes to Pb sorption by carbonate, so does partially the formation of Pb hydroxycarbonatecomplexes.. |
