Study of sedimentary clastic strata of the Tertiary Cebu Formation, Cebu Province, Philippines was carried out to probe the mineralogy and characteristics of the clays contained in the sediments and to propose the geological implications and the mechanisms of their formation or evolution. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) techniques were employed in the experimentation process. Analytical results indicate kaolinite as the major clay component in almost all the samples collected at selected horizons and locations. Allogenic quartz dominantly comprises the non-phyllosilicate impurities and feldspar virtually nil.
The ubiquitous occurrence of kaolinite with other clays however, is exemplimed in terms of 3 mineral assemblages, namely:(1) interstratimed illite/smectite (I/S)-kaolinite, (2) kaolinite-dominated, and (3) interstratimed kaolinite/smectite (K/S). These characterized mineral assemblages essentially portray distinct heterogeneity of horizons and clay associations that suggest formation of the Cebu Formation under particular processes and environment conditions. The interstratimed illite/smectite-kaolinite assemblage and the kaolinite-dominated assemblage are interpreted to have formed with clastic sediments under favorable conditions related to diagenesis with accompanying coalimcation. The I/S in the interstratimed illite/smectite-kaolinite assemblage is suggestive of an intermediate or transitory phase in the illitization of smectite during diagenesis. Progressive dissolution of smectite and precipitation of illite apparently did not attain completion. The interstratimed kaolinite/smectite assemblage is perceived to have evolved by pedogenesis and is likely to have been catalyzed by intense chemical weathering under tropical climate.

抄録全体を表示

We carried out Ca-Al exchange equilibrium experiments on a smectitic soil and calculated Gaines-Thomas selectivity coefficient. The natural logarithm of the Gaines-Thomas selectivity coefficient scattered around 4.6 with no noticeable trend. The natural logarithm of the thermodynamic equilibrium constant calculated with the aid of Rothmund-Kornfeld equation was 4.58 at 298 K and 1 atm, indicating that the soil strongly prefers Al³⁺ to Ca²⁺.
On the basis of the measured Al³⁺-selectivity we numerically examined the effect of cation exchange reactions involving A1³⁺ during the acid extraction of Cd from soils. The results of computation showed that more Cd²⁺ is extracted when the extracting acid dissolves soil minerals and releases A1³⁺. This is due to the higher preference of smectite for Al³⁺ than for H⁺.

抄録全体を表示

The synthesis and thermal decomposition behavior of the phenylalanine/M²⁺-Al layered double hydroxides (Phe/Mg-Al, Mn-Al and Zn-Al LDHs) have been investigated. The Phe/LDH was easily synthesized by the conventional coprecipitation method. The basal spacing of the Phe/LDHs was expanded to 0.86 (Mg-Al), 1.80 (Mn-Al) and 1.86 nm (Zn-Al), respectively, which supported that Phe was intercalated into interlayer space of the LDH as an anion or an amphoteric ion form. The thermal decomposition of the intercalated Phe was influenced by the kind of a divalent metal ion in the LDH basal layer. In particular, the Mn-Al LDH was found to have the strong catalytic action for the decomposition of the intercalated Phe. From the FT-IR, HPLC and NMR measurements, it was proved that the intercalated Phe was decomposed via the formation of N-benzoylbenzamide (NBBA) regardless of the kind of LDHs, which compound never formed in the thermal treatment of Phe itself. Therefore, it is expected that the two dimensional LDH interlayer space can be used as a novel nano-scale reactor for the synthesis or the decomposition reaction of organic compounds.

抄録全体を表示

A total of 57 elements in volcanic ash soils from 18 pedons distributed in Japan were analyzed and the relationships between noncrystalline material content and that of individual elements were examined. The content of the noncrystalline materials was estimated by using acid-oxalate extraction. Oxalateextractable Si (Si_o), Fe (Fe_o) and Al (Al_o) corresponds to the Si content in allophane-imogolite, Fe in ferrihydrite and Al in allophane-imogolite plus Al complexed with humus, respectively. Silicon and alkaline or alkaline-earth elements such as Na, K, Ca, and Sr tended to decrease during the process of volcanic ash soil formation, i.e., andosolization. In contrast, the contents of Al, Y, Zr and the first transition metals tended to increase with the increasing content of noncrystalline materials. The first transition metals showed a high correlation with Fe_o suggesting their similarity in chemical behavior during andosolization. The heavy lanthanoid elements tended to increase with the increasing content of allophane-imogolite.

抄録全体を表示

Change in surface charge of nano-ball allophane after sulfate adsorption was studied. Cation exchange capacity (CEC) was found to increase with increasing pH as well as after sulfate adsorption, with KnP (allophane sample with high Si/Al ratio) having higher CEC value as compared to KyP (low Si/Al ratio). The increase in CEC after adsorption for both samples was attributed to the charge carried by the anion. However, plotting the increase in CEC vs. the amount of sulfate adsorbed showed a slope of much less than 1, which showed that most of the sulfate adsorption occurred as bidentate reaction. This can be attributed to the adsorption mechanism with sulfate being adsorbed through ligand exchange aside from anion exchange reaction. Further, the adsorption of sulfate on allophane enhanced the deprotonation of the near silanol group, thus providing a new negative charge, thus an increase in the CEC. Molecular orbital calculation using MOPAC program affirmed these experimental results. The amount of positive charge or AEC on the other hand was found to decrease after sulfate adsorption for both KyP and KnP samples. The decrease in AEC was much lower than the sulfate adsorption, although more sulfate than AEC was adsorbed. This implies that some AEC site remains after much sulfate adsorption, providing nutrients such as Cl^- and NO₃^- for plants.

抄録全体を表示

Removal and fixation of As (III) and As (V) from aqueous solution by soil/bentonite mixtures were studied to develop reliable clay liners for waste landfill sites. One of two soils such as, Masatsuchi. soil (weathered granite) and Murram soil (pumice) was used as a main body of the liner, and Wyoming bentonites were mixed with the soils because of its superior impermeability. As the result of batch experiments, it was shown that large part of As was removed by Masatsuchi soil without pH buffer, andth e result was better than those of Murram soil. Both soils appeared to have best adsorption of As (V) and As (III) within pH ranges of 3-6.5 and 7-9.5 at where the dominant species in the aqueous solution were H₂AsO₄^- and H₂AsO₃^-, respectively. A long-term leak test showed that Masatsuchi soil-Wyoming bentonite combination had the ability to remove all the As (III) from 4 ppm aqueous solution for more than 100 days.

抄録全体を表示

The study was conducted to characterize Fe/Mn, layer silicate minerals in the concretions of Okinawan and Brazilian soils and investigated their micromorphological features. Concretions and soil samples of Okinawa (Luvisol) and Miyako (Cambisol) Islands were developed from Ryukyus limestone, while Brazilian samples of Cambisol and Ferralsol were originated from sandstone rock. Fe/Mn minerals in both experimental sites were characterized using the successive selective dissolution procedure followed by the treatments of sodium hydroxide, hydroxylamine hydrochloride (HAHC) at 25°C and 60°C and dithionite-citrate-bicarbonate (DCB) in combination with X-ray diffraction technique (XRD). Elemental composition and micromorphological information on Fe/Mn minerals and their associated layer silicates were investigated using inductive coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopic (SEM) techniques respectively. XRD and SEM techniques were successfully able to investigate and distinguish the major minerals in Okinawan and Brazilian samples were kaolinite (Ka), gibbsite (Gb), illite, quartz, and goethite (Ge), while the rear natural minerals of birnessite and smectite were investigated from the samples of Cambisol in Miyako and Luvisol in Okinawa respectively. Elemental analysis also confirmed that Brazilian samples did not contain any Mn oxide minerals. Detailed micromorphology of minerals exhibited that poorly crystalline birnessite has a blade or plate-like habit, which forms globular aggregates inside veins and cavities and widely spread smectite mineral in Okinawan samples showed a honeycombed polygonal pattern. Well-developed hexagonal kaolinite and gibbsite crystallites were also observed in Okinawan samples, while the book-like structure of kaolinite crystals with beveled edges in Brazilian samples imbedded inside concretions. Goethite crystals in Brazil samples are acicular and consist of several domains within the crystals along the needle axis and these acicular crystals arranged into stars, while cloudy shape of hematite crystals aggregated with kaolinite and imbedded inside silicate minerals to produce hard iron concretions.

抄録全体を表示