Kazuhiko Egashira

Swelling and mineralogy of smectites in paddy soils derived from marine alluvium, Japan

Abstract A low-swelling smectite exhibiting little intra-crystalline swelling even after saturation with Na was found in paddy soils derived from marine alluvium of Ariake Bay in Kyushu, Japan. The low-swelling smectite was considered to be beidellite-nontronite mineral containing as much as 10% Fe2O3. The low-swelling characteristics of this smectite are ascribed to the considerable substitution of Fe2+ for Al3+ in the ochtahedral layer which depresses the dissociation of unit layers of smectite. Transformation of low-swelling to high-swelling smectite is believed to be due to the oxidation of Fe2+ to Fe3+ in the octahedral layer.

Modification of different grades of Korean natural zeolites for increasing cation exchange capacity

Abstract Three different grades of Korean natural zeolites which contained clinoptilolite or both clinoptilolite and mordenite were treated with 2 M NaOH solution at 103°C during different times ranging from 1 to 16 h. The reacted products were all identified as zeolite NaP by X-ray diffraction and scanning electron microscopy. Zeolite NaP was formed from both clinoptilolite and mordenite but not from coexisting primary minerals such as feldspars and quartz. During the reaction, a large amount of Si was dissolved into solution. The cation exchange capacities of the products after 8 or 16 h reaction were higher by more than 2 times than those of the corresponding raw materials. The purity in zeolite NaP of the products depended on the purity of the raw materials.

Transformation of a low-grade Korean natural zeolite to high cation exchanger by hydrothermal reaction with or without fusion with sodium hydroxide

Abstract A low-grade Korean natural zeolite in which clinoptilolite coexists with quartz and feldspars was treated hydrothermally with 3, 4 and 5 M NaOH solutions during different times ranging from 4 to 40 h, either with or without fusion with NaOH powder at 550°C during 2 h as a pretreatment. Zeolite Na-P, zeolite Na-X and hydroxysodalite were identified as the reacted products, depending on the reaction conditions such as NaOH concentration and reaction time. The fusion with NaOH powder prior to the hydrothermal reaction brought about zeolitization of feldspars in the starting material, whereas it hardly occurred in the hydrothermal reaction without the fusion treatment. Cation exchange capacity (CEC) of the products with the fusion treatment was 410 cmol(+)/kg for zeolite Na-P at room temperature and 400 cmol(+)/kg for zeolite Na-X and hydroxysodalite at 80°C. These values were strikingly high in comparison with the CEC of 69 cmol(+)/kg of the starting low-grade natural zeolite.

SMECTITE IN MARINE QUICK-CLAYS OF JAPAN

Clayey sediments of marine origin having sensitivities (ratio of undisturbed to remolded shear strength) as high as 1000 at a reduced salt concentration are found around Ariake Bay, Kyushu, Japan. The clay fraction of the sediments contains smectite as a principal mineral (33–42%) in contrast to the illitic composition of most previously described quick-clays. However, this smectite is a low-swelling type, and the Na-form expands only to about the same extent as the Ca-form and gives a sediment volume almost equal to that of the Ca-clay. This low-swelling smectite appears to consist of packets of unit layers even after saturation with Na, and thus reacts like the kaolinite or illite of conventional quick-clays.РезюмеГлиняные осадки морского происхождения, имеющие чувствительности (отношение несмущенной и смущенной прочностей при срезе) такие большие как 1000 при уменьшенной концентрации соли, находятся в районе бухты Ариаке, Кыусху, Япония. Глинистая фракция осадков содержит смектит как основной минерал 33-42%) в противоположность к иллитовому составу большинства ранее описанных зыбучих глин. Однако, этот смектит является мало-набухающего типа, и Nа-форма расширяется только до примерно такого же самого уровня как Са-форма и приводит к почти равному объему осадков как и Са-глина. Кажется, что этот мало-набухающий смектит состоит из пакетов элементарных слоев даже после насыщения натрием, и тогда он реагирует как каолинит либо иллит обычных зыбучих глин. [Е.С.]RésuméDes sédiments argileux d’origine marine ayant des sensitivités (proportion de la force non dérangée à la force remoulée) atteignant 1000 à une concentration de sel réduite sont trouvés autour de la Baie Ariake, Kyushu, Japon. La fraction argile des sédiments contient de la smectite comme minéral principal (33–42%) contrairement à la composition illitique de la plupart des argiles rapides décrits précédemment. Cette smectite est cependant du type à bas gonflement, et la forme-Na s’épand seulement approximativement autant que la forme-Ca et donne un volume de sédiment presqu’égal à celui de l’argile-Ca. Cette smectite à bas gonflement semble consister de paquets de couches unitaires même après avoir été saturée de Na, et par conséquent elle réagit comme la kaolinite ou l’illite d’argiles rapides conventionnels. [D.J.]ResümeeTonige Sedimente mariner Entstehung, die bei reduzierter Salzkonzentration Sensitivitäten (Verhältnis der ungestöten zur Scherfestigkeit der durchkneteten Probe) von etwa 1000 haben, wurden um die Ariake Bay, Kyushu, Japan, gefunden. Die Tonfraktion der Sedimente enthält Smektit als häufigstes Mineral (33–42%) im Gegensatz zur illitischen Zusammensetzung der meisten früher beschriebenen Quick-tone. Dieser Smektit quillt jedoch nur wenig, und die Na-Form quillt etwa nur so viel wie die Ca-Form und ergibt ein Sedimentvolumen, das dem von Ca-Tonen entspricht. Dieser schlechtquellende Smektit scheint aus Paketen von Einzellagen zu bestehen, sogar nach der Sättigung mit Na, und verhält sich daher wie der Kaolinit oder Illit von herkömmlichen Quicktonen. [U.W.]

Heavy metal characterization of river sediment in Hanoi, Vietnam.

Abstract Industrial and municipal waste water is directly discharged to rivers in Hanoi, Vietnam. Sediments were collected from different sites of three rivers in the industrialized and densely‐populated area of Hanoi City and examined for total heavy metals and metal fractions using sequential extraction. Concentration of the total heavy metals ranged from the background levels to over the maximum permissible levels to crop growth. Concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) ranged from 0.27 to 4.50,78 to 517, 37 to 309, 37 to 174, 43 to 361, and 93 to 4,950 mg kg‐1, respectively. Total concentration of heavy metals varied from site to site and tended to be higher in the site where manufacturing companies are located. Heavy metals were accumulated in the site and were not moved away to be redistributed in the whole area. Distribution of heavy metals in different chemical forms in the air‐dry state depended on their total concentration. In the low concentration range, Cr, Cu, Ni, and Zn were for the most part concentrated in the residual fraction. When concentration is equal to or above the maximum permissible level to crop growth, Cr, Ni, and Zn were mostly concentrated in the iron‐manganese (Fe‐Mn) oxides fraction and Cu was in the organic fraction. Irrespective of the total concentration, Cd was highly associated with the exchangeable and carbonate fractions, while the sum of the Fe‐Mn oxides and residual fractions accounted for 80 to 96% of total Pb.

Aggregate stability as an index of erodibility of ando soils

Erosion experiments were carried out under laboratory conditions to determine the index of credibility of Ando soils. Eighteen soil samples were collected in Kyushu. A simple regression analysis was used to relate the amount of soil loss to the physical and chemical properties, including mechanical composition, clay ratio, aggregate stability, dispersion ratio, erosion ratio, air-dry ratio, organic matter content and pH. Among them, the aggregate stability (>53 μm) showed the highest and negative correlation coefficient (r = —0.956**) to the amount of soil loss, followed by the dispersion ratio (r=0.874**) and the erosion ratio (r=0.701**). Correlation coefficients of the other properties were not significant at level. The aggregate stability was proposed as an index of credibility of Ando soils. The breakdown of sand-size aggregates is the first manifestation of water erosion in Ando soils.

Platy layer silicate minerals for controlling residual strength in landslide soils of different origins and geology

We use a ring-shear apparatus to examine the relationship between the residual strength and mineralogical properties of landslide soils and find a significant relation between the residual strength parameter, φr, and the total content of layer silicate minerals prone to preferred orientation within the bulk soil. In this context, the total content of smectite, vermiculite, chlorite, and mica in the sub-425-μm soil fraction is a suitable mineralogical parameter for estimating the magnitude of φr. Plotting φr as a function of total mineral content forms a chair-shaped curve, based on which we classify landslide soils into three groups. In the first group of soils, sliding appears to be controlled by minerals such as quartz, feldspar, calcite, dolomite, and layer silicate minerals other than smectite, vermiculite, chlorite, and mica and their φr is almost constant at ∼32°. In the second group of soils, the controlling mineralogical factor for sliding quickly shifts from nonpreferred-orientation minerals to preferred-orientation minerals and φr decreases from 30° to 10°. In the third group of soils, sliding is well controlled by preferred-orientation layer silicate minerals and φr gradually decreases from 10° to 5°. The results show that the relationship can be used for predicting φr of a wide range of landslide soils that differ in geology, soil type, mineralogical properties, and shear strength.

Rare earth element and clay minerals of paddy soils from the central region of the Mekong River, Laos

Abstract The rare earth elements (REE) content, particle-size distribution, and clay mineralogical composition were analyzed for the paddy soils collected from the central region of the Mekong River, Laos, to study the origin and inherent potentiality of soils. REE as the chondrite-normalized curve of the plot of Ce/Eu against Eu/Sm were found to be useful for grouping soils according to their origins. The soils in the upper area (Luang Prabang Province, approximate elevation 300–400 m) were estimated to originate from the composite materials of the sediment derived from local granite and limestone and the sediment transported by the Mekong River. The predominant clay mineral was mica and its weathering product or kaolins, and the mineralogical composition varied from site to site. The soils were generally characterized by high clay and silt contents. Inherent potentiality was evaluated to be of intermediate to high level. The soils in the lower area (Vientiane Prefecture and Borikhamxay Province, approximate elevation 90–150 m) were estimated to originate from sediment transported by the Mekong River or from sediment derived from local sandstone. The soils originating from the Mekong River sediment were medium-textured and mica-dominated and were evaluated to be at the intermediate level of inherent potentiality. The soil originating from the sediment of local sandstone was coarse-textured and contained mica and kaolinite as the predominant clay minerals. Its inherent potentiality was evaluated to be poor.

LOW-SWELLING SMECTITE IN A RECENT MARINE MUD OF ARIAKE BAY

Abstract A low-swelling smectite was found in a recent marine mud of Ariake Bay. The Na-clay of this mud swells but to the same extent as the Ca-clay and its dominant interparticle force is not repulsion between individual particles. The sediment volume at low salt concentration and the specific viscosity of the Na-clay were almost equal to those of the Ca-clay. The liquid limit of the Na-mud decreased with decreasing NaCl concentration and was lower than that of the Ca-mud.

Groundwater–soil–crop relationship with respect to arsenic contamination in farming villages of Bangladesh – A preliminary study

To clarify the groundwater-soil-crop relationship with respect to arsenic (As) contamination, As concentration was measured in tubewell (TW) water, surface soil from farmyards and paddy fields, and fresh taro (Colocasia esculenta) leaves from farmyards in the farming villages of Bangladesh. The As concentration in TW water from farmyards was at least four times higher than the Bangladesh drinking water standard, and the concentration in fresh taro leaves was equal to or higher than those reported previously for leafy vegetables in Bangladesh. As concentration of surface soils in both farmyards and paddy fields was positively correlated with that of the TW water. Further, the concentration in surface soil was positively correlated with levels in fresh taro leaves in the farmyard. This study, therefore, clarified the groundwater-soil-crop relationship in farmyards and the relationship between groundwater-soil in paddy fields to assess the extent of As contamination in Bangladeshi villages.