Cation exchange capacity (CEC) of nano-ball allophane measured at same equilibrium pH increased with molybdate adsorption at initial molybdate concentrations of 0.1 and 1.6mM. The increase in CEC was attributed either to deprotonation of silanol group near the adsorption site and/or negative charge carried by the molybdate. Great differences in the amounts of molybdate adsorption between the two initial molybdate concentrations (0.1mM and 1.6mM) was not reflected in the change in CEC. This may be due to polymerization of molybdate at higher concentrations (more than 0.2mM), therefore, increase in CEC was ascribed to adsorption of monomeric molybdate species. Increase in CEC was greater for allophane samples with lower Si/Al ratios than for allophane sample with higher Si/Al ratio, in agreement with the trend of adsorption. Ab inito molecular orbital calculations indicated that Bonsted acidity of silanol group of allophane near adsorption site increased with the molybdate adsorption. The increase in acidity together with free Mo-OH or Mo-O^- groups of molybdate adsorbed in monodentate form contributes the increase in CEC with the molybdate adsorption.

View full abstract

Sediment traps were deployed at two sites at depths of 1, 592 m (Site 1) or 1, 761 m (Site 2) in the West Caroline Basin from June 4, 1991 to April 15, 1992. A sediment core was collected from the same location as the sediment trap Site 1. In this paper, we describe the clay-sized mineral composition of samples from the sediment trap sites and the clay-mineral composition of the sediment core. The chemical composition and morphological features of the clay minerals are also described. Finally we discuss factors influencing sedimentary processes based on the clay-sized mineral composition and the chemical and morphological characteristics of the clay minerals.

View full abstract

Two hundred forty-one surface sediment samples collected from the Sea of Okhotsk, the Sea of Japan, and the East China, South China, and Philippine seas, including the Gulf of Thailand, were used in this study.
Clay mineral compositions of the clay fractions (<2üm) of the samples were determined by X-ray diffraction, and the distributions of clay minerals such as smectite, illite, chlorite, and kaolinite in the seas were investigated. The clay mineral distributions reflected the influences of various factors such as the geology and soils of the surrounding land areas, river runoff, and transportation by wind and sea currents. The high concentration of smectite in sediments of the Sea of Okhotskand off the east coast of Luzon Island in the Philippines reflected volcanic influences. The high concentration of illite in the East China Sea and farther east was attributed to sediment discharge from the Yellow and Yangtze rivers of China and to aeolian transport from China. Chlorite tended to be more abundant at higher latitudes. Kaolinite was the least abundant of the four clay minerals, but kaolinite content was relatively higher in the sediments of the South China Sea, that is, at low latitudes. In addition, the chemical compositions and morphologies of 18 clay mineral particles contained in 11 sediment samples were analyzed by means of analytical transmission electron microscopy (ATEM). Smectite occurred most frequently as Al-Fe (Al³⁺>Fe³⁺in the octahedral sheet) beidellite, but in the Philippine Sea, Fe-Al beidellite was found. Saponite was not abundant, but was found in every sea. Sediments of the Sea of Okhotsk contained Fe-Mg chlorite, whereas the sediments of the other seas contained Mg-Fe chlorite. Illite was dioctahedral, and the potassium content of the interlayer sheet tended to decrease toward the lower latitudes. Although clay mineral morphology did not clearly differ from area to area, the morphologies of the clay mineral particles examined in the present study all reflect a clastic origin.

View full abstract

Conversion of waste coal fly ash, released mainly from thermal power plants, to artificial zeolite is important in view of environmental conservation and recycle of resources. To reduce cost for the artificial zeolite synthesis, we applied seawater instead of tap or distilled water for preparation of NaOH solution. The reaction products with NaOH concentrations of 1.0 and 2.0M at 121 and 144°C had cation exchange capacity (CEC) values from 230 to 286 cmol (+) kg^-1, and the CEC values increased with increasing NaOH concentration and temperature. The X-ray diffraction (XRD) analyses showed that zeolite component in the products was Na-Pl having similar structure to phyllipsite. The XRD patterns and CEC values of the products were almost the same with corresponding products with distilled water. When the temperature was raised to 178°C, CEC decreased and analcime was formed especially at higher NaOH concentrations. These results indicate that the seawater containing waste heat of turbine generator in thermal power plants can be used in synthesis of artificial zeolite, and that the use of the waste hot seawater will save heat energy and water cost in the artificial zeolite production.

View full abstract

Mechanism of change in charge development after orthosilicic acid adsorption on two low Si/Al and one high Si/Al nano-ball allophane samples were studied. The change in charge characteristics was found to be governed by equilibrium pH, and amounts and form of the acid adsorbed. Increase in cation exchange capacity CEC after adsorption correlated highly with adsorption below the pK₁ of the acid. Increases in CEC and decreases in anion exchange capacity were marginal below equilibrium pH 8 due to the adsorption of the neutral species, H₄SiO₄, of the acid. Molecular orbital calculations indicated polymerization of the silanol group by the neutral species of the acid at pH < 8 as being more feasible than adsorption at the aluminol site confirming the high Si/Al sample to be a SiO₄ tetrahedral product of the low Si/Al samples. At pH >8, change in CEC was greater in the low Si/A1 samples than their higher Si/Al counterpart as a result of their higher preference for the anion species, H₃SiO₄^- of the acid. Increase in CEC, which was astronomical at pH > pK₁ of the acid, was attributed to a permanent charge imparted onto the mineral by adsorption of the anion species of the acid at the Al-OH₂ site.

View full abstract

Chlorites from Byrapur, Bhaktarhalli and Tagadur mine areas in Nuggihalli schist belt, belonging to the greenstone belt of South India, were investigated for determining the crystallochemical characteristics of these product phases arising from low-grade metamorphism of ultramafic rocks of komatiitic lineage. The analytical equipments used for such investigation were EPMA, ⁵⁷Fe Mössbauer spectroscopy, XRD and IR. The physicochemical properties of these chlorites are found to lie between aluminian clinochlore and clinochlore varieties. The cell parameters calculated from major XRD peaks reveal the crystallographic parameters, the range of which are: for aluminian-clinochlore, a=5.3027 to 5.3172 Å, b=9.2721 to 9.2796 Å, c=14.3496 to 14.4078 Å, β=97.984° to 98.085°, V=700.9790 to 701.5324 ų; for clinochlore, a=5.2815 to 5.3495 Å, b=9.1897 to 9.2502, c=14.1634 to 14.2814 Å, β=95.200 to 96.554°, V=692.8576 to 695.8528 ų; and for Cr-clinochlore, a=5.3310 to 5.3190 Å, b=9.1303 to 9.2790Å, c=14.3395 to 14.3370 Å, β=94.589° to 97.670°, V=695.7210 to 701.2580 ų.
In all the samples octahedral sites are mostly occupied by Al^VI, Fe and Mg. The chemical variation is largely controlled by the isomorphous replacement of Mg²⁺by Al^VI which has effected the Fe²⁺-Mg²⁺ substitution. The shrinkage resulting from octahedral Al³⁺ substitution is balanced by the expansion effected by Fe-Mg substitution. The octahedral site (M4) occupied by Al³⁺ is smaller than when occupied by Mg²⁺ or Fe²⁺. The initial Al3+ occupancies of the two M4 sites change with progressive oxidation and metamorphism.
The Mössbauer spectrum of a chlorite sample depicts five symmetric doublets for iron, three of which are assigned to Fe²⁺ at cis and trans positions of talc layer, and in brucite layer; the other two are assigned to Fe ³⁺ at trans position and tetrahedral site. The iron distribution over the octahedral site signifies oxidation of Fe²⁺ only at trans position, while at the cis and brucite positions Fe²⁺ remains unaffected. The Mössbauer results of this chlorite suggest the Fe³⁺ occupancy in octahedral sites was the result of oxidation (following chloritisation) and the distribution of other cations in the other two sites remained unaffected.
The oxidation of chromite grains would release Cr³⁺ and Al³⁺ from theoctahedral sites and these released cations would react with contiguous serpentine (antigorite) to form Cr-clinochlore. The Al³⁺ content of Cr-clinochlore is seen to be distinctly related to the degree of oxidation of the associated chromite-a greater degree of oxidation of chromite is related to a higher Al³⁺ content with a concomitant lowering Mg²⁺ and Si⁴⁺ contents in the associated Cr-clinochlore. Using the geothermometry of Xie et al.(1997) the temperature of formation of these chlorites (Al^IVranging from 1.398 to 2.540) are found to lie between 263 and 463°C; this wide range of temperature may arise from polymetamorphism experienced by the area.

View full abstract

Natural cultivation experiments using coal ash, reservoir sediments and Yellow River sediments were carried out to determine the applicability of using these wastes to remediate desertificated soil in Inner Mongolia, China. In the experiments, the microorganisms multiplied more when coal ash was applied to the desertificated soil. Under optical microscope, abundant bacteria were observed in porous surfaces and inside of coal ash particles thereby indicating that the addition of coal ash to desertificated soil hastens the breeding of bacteria, improves soil quality and could be used in afforestation practices. The effects of ash on soil can be explained in two ways: first, in terms of its chemical characteristics (the coal ash contains C, N, P and K); and second, in terms of its micromorphology (it is porous).
In natural cultivation experiments, the mixing of reservoir sediments and/orYellow River sediments with the coal ash helped multiply bacteria. These experiments suggest that coal ash and reservoir sediments can be utilized to help solve some of the most serious environmental issues facing China today.

View full abstract

A method to determine negative and positive charge of clays applying Cs⁺ and Cl^- as an index cation and anion respectively was proposed. Special attention was paid for pH and electrolyte concentration in equilibrium solution so as to relatethe charge characteristics with dispersion behavior of clays. In order to establish the proposed method as suitable charge determination, interlayer fixation of Cs⁺ was compared with that of K⁺ and Na⁺ by using some reference and soil clays including vermiculite and mica. As a result, Cs⁺ was not virtually fixed by any type of clays unless drying process was included. The flocculating effect of Cs⁺ enabled negative charge determination in the systems with high pH and low electrolyte concentration which was difficult to quantify with Na⁺ due to the dispersion of fine particles.The charge characteristics evaluated by the proposed method indicated that the montmorillonite was the typical clay mineral with permanent charge. In contrast, pH and electrolyte concentration dependence of the sericite suggested the characteristicproperty of variable charge rather than permanent. This observation was discussed from the aspect of the assumed heterogeneity of surface charge sites in the sericite.

View full abstract

Pottery stone occurs at Takehara Mine located in the eastern end of Okayama City. The mineral assemblages of ore consist mainly of quartz-sericite and quartzsericite-albite together with scarce quartz-kaolinite. The deposit is divided into three mineral assemblage zones: namely, a kaolinite zone (quartz-kaolinite ±albite), a sericite zone (quartz-sericite-albite) and an albite zone (quartz-albite-sericite). The albite and sericite zones comprise most of the deposit. The pottery stone in this mine is formed by hydrothermal alteration of Cretaceous rhyolite. K-Ar dating indicates 72-76 Ma for this deposit, which is the same age as the roseki (pyrophyllite) deposit in the Mitsuishi area of Okayama Prefecture.

View full abstract