Showing papers in "Clay science in 2000"

Adsorption of molybdate on nano-ball allophane.

Abstract: Adsorption behavior of Mo (Na 2 MoO 4 ) on three nano-ball shaped allophane samples was different between lower (up to 0.1 mM) and higher (0.2 to 1.6 mM) Mo concentrations. The difference may be due to chemical species of Mo in solution: at lower concentration, Mo exists as monomeric H 2 MoO 4 , HMoO 4 - and MoO 4 2- , and at higher concentrations as polymeric forms. The monomeric molybdate species, especially the anionic species, had very strong affinity for the allophane at lower pH where the allophane had much surface positive charge and essentially no negative charge. All of the molybdate added at equilibrium pH 3.7 to 3.9 and initial concentration up to 0.1 mM, 200 mmol kg -1 , was adsorbed on allophane samples with lower Si/Al ratio. With increasing pH, the affinity or amount of adsorption decreased markedly. At equilibrium pH near 5, adsorption isotherm was Langmuir type, whereas at higher pH such as 6 or 8 the isotherm was linear or Freundlich type. The strong interaction between molybdate anion and positively charged allophane was concluded as electrostatic one followed by ligand exchange reaction between Mo-O - and aluminol groups. At higher Mo concentrations, more than 0.2 mM, shape of the isotherms were linear indicating further polymerization reaction on the allophane surfaces, and partial destruction of allophane structure was observed as Si and Al release with the adsorption.

Flocculation behavior and properties of Na-montmorillonite treated with four organic polymers.

Abstract: Four organic polymers were mixed with Na-montmorillonite. Two cationic polymers include a high molecular weight polyacrylamide (494C) and a low molecular weight polymer (587C). Two anionic polymers include a high molecular weight polyacrylamide (836A) and a low molecular weight polymer (Aerotil). Each clay suspension series were allowed to stand for 24 hours and were centrifuged, and the clay plugs were washed and dried. The dried samples were investigated by XRD, IR and CEC measurement. The suspended clay containing anionic polymers was not flocculated at any concentrations of polymer. But the suspensions containing two cationic polymers were rapidly flocculated at almost all concentrations. The d(001) montmorillonite spacings after treated with cationic polymer 587C showed 1.55 nm suggesting the polymers may have entered the interlayer spaces. The polymer 494C-treated sample produced double peaks of 1.26 and 1.48 nm in XRD. It indicates that the low molecular weight polymer was more apt to penetrate into interlayers of montmorillonite than the high molecular weight polymer. And cationic polymer 494 may be adsorbed mainly on the outside surface of clay, and some polymers may penetrate into only interlayers in the margin of montmorillonite particles because of its high molecular weight. Cationic polymer 587 is most strongly bonded to Na-montmorillonite because of high positive charge. CEC of polymer 587-treated sample was reduced markedly suggesting polymer blocks CEC sites. But anionic polymers are not effective in flocculating Na-montmorillonite, and may not be adsorbed on clay.

Clay mineralogical approach to the slip-surface formation in the o'dokoro landslide, niigata, central japan

Abstract: Samples were collected form the O'dokoro landslide in Niigata prefecture for the mineralogical analysis. The O'dokoro landslide occurs in the sheared belts, located 5 km west from the Itoigawa-Shizuoka Tectonic Line and is positioned in the serpentinite melange. Lamellar serpentinite sample from the bedrock serpentinite bodies contained less than 20% of clay in the particle-size distribution, and the clay fraction consisted of antigorite with a small amount of talc. No other minerals were detected and no mineralogical difference with the particle-size fraction was noticed. In contrast, the clayey material (the fault clay) sampled from the fault-fractured seams which is expected to have a mineralogical similarity to the slip surface, showed the clay content of 50%. The clay fraction was dominated by vermiculite and chlorite accompanied by smectite, talc and amphiboles. Antigorite was not identified, and progress of vermiculization of chlorite was indicated. Chlorite in the fault clay was regarded as Mg- or MgFe-chlorite and was possibly formed by serpentinization of mafic minerals. Vermiculite was probably transformed from chlorite by faulting. Argillation and the increase in the swellability of minerals were proposed to make favorable the slip-surface formation in the O'dokoro landslide in the sheared belts.

Effect of calcium, sodium and chloride ions on the growth of imogolite tubes as measued by gel forming property

Abstract: To examine the effect of coexisting salts on the yield and gel forming property of synthetic imogolite, neutralized solutions of Si(OH) 4 and AlCl 3 with added NaCI and CaCl 2 were heated at 96°C. X-ray diffraction (XRD) on the freeze-dried products showed that the yield of imogolite decreased as the salt concentration increased. The gel volume determined by alkalinization and centrifugation of the heated sols approximately paralleled the intensity of imogolite peaks in XRD. The examination of the relationship between the ion concentrations and the gel volume showed that the gel forming property was solely determined by the chloride ion concentration and the accompanying cations had little effect under the present experimental conditions.

Adsorptive mechanisms of orthosilicic acid on nano-ball allophane.

Abstract: Adsorption of orthosilicic acid on two low Si/Al (KyP and KiP) and one high Si/Al (KnP) nano-ball allophane samples was found to be controlled by the species type of the acid. There seemed to be a higher preference for the anion species to the neutral species. Adsorption increased with increasing solution pH with the highest adsorption occurring at initial pH 10. Further increase in pH, however, led to reduced levels in adsorption, particularly in the KnP sample due to repulsion between the negatively charged silanol groups and the anion species of the acid. Adsorption was higher in the low Si/Al samples due to their relatively higher number of aluminol groups per unit mass. The estimated Zero Point of Silicon Adsorption, which was pH dependent, was found to be higher in the KnP sample due to its higher inherent Si content. Adsorption data conformed only to the Freundlich model with the Freundlich parameters increasing with increasing solution pH to a maximum at initial pH 10. Release of Al occurred only at pH 10 and was highly correlated with Si adsorption in the low Si/Al samples suggesting a partial replacement of Al with Si at the pore region.

Mineralogy of ohyunuma explosion crater lake, Hokkaido, Japan. Part 1 : Geochemistry, hydrology, and bulk mineralogy

Abstract: Lake Ohyunuma, which is an active explosion crater lake located at Noboribetsu Spa of southwest Hokkaido, Japan, has been investigated to elucidate the dynamics of clay formation processes under the acid hydrothermal conditions. The Ohyunuma lake water is characterized by distinct stratification of temperature and chemicals forming two layers. The upper layer water is relatively low-temperature (about 40°C), low-salinity, oxidized, sulfate-rich, chloride-poor acid (pH 2.4) solution, whereas the lower layer water is relatively high-temperature (max. 121°C), high-salinity, sulfide and chloride-rich acid (pH 2.7) solution. The distribution of minerals constituting the lake sediments is controlled by many factors such as location of discharge points, transportation by river waters, lake bottom topography, and flow rate and direction of lake water, in addition to in situ dissolution and precipitation processes of the minerals. Based on the lines of evidence such as calculations of saturation indexes and examinations by XRD, TEM, and AFM, the origin of the minerals was inferred as follows: elemental sulfur and pyrite are precipitated through the entire water column of Lake Ohyunuma involving both the upper and lower layer waters; the portions of them are also derived from the molten sulfur pool filled in the high temperature vent sites, associating with turbulent discharges. Alunite is precipitated in the lower layer waters and also formed locally in the upper layer waters by mixing of more acid stream and discharge waters which contain much more Al and sulfate ions. Smectite is of allogenic origin as it is mostly derived from the surrounding altered rocks, and the exchangeable cation composition deduced from the bulk sediment data is a function of temperature and solution composition. Kaolinite and halloysite may be initially translocated from the surrounding altered rocks and then they are undergoing dissolution during settling of the particles in the upper layer waters, but the dissolved materials are recrystallized as kaolinite in the lower layer waters. Most of silica minerals such as quartz, α-cristobalite, and tridymite are of allogenic origin. Diagenetic modification of the minerals with burial is not significant through the sediment column (0-67 cm depth) recovered in the present study.

MINERALOGY OF OHYUNUMA EXPLOSION CRATER LAKE, HOKKAIDO, JAPAN Part 2 : DYNAMICS OF KAOLINITE FORMATION

Abstract: Numerical simulations, based on both batch and continuously stirred tank reactor (CSTR) models, have been made to assess the effects of flow on the dissolution and growth processes of kaolin minerals under acid hydrothermal conditions of the Lake Ohyunuma, using the kinetic data of the minerals determined experimentally. Our previous geochemical and mineralogical studies showed that the Ohyunuma lake water forms two layers with distinct stratification of temperature and chemicals. The bottom sediments contain both halloysite and kaolinite. The upper layer water has been kept undersaturated with respect to the two minerals for longer years than the duration at which all particles of the minerals have been completely dissolved if it were a batch system. This contradiction is caused not only by continuous supply of the solid materials, but also by continuous inflows of undersaturated solutions from the outside of the lake. The existence of flows assists kinetically the stabilization of kaolin minerals even within undersaturated solutions such as the upper layer water of the Ohyunuma. The lower layer water is supersaturated with respect to kaolinite and undersaturated with respect to halloysite. Relatively coarse-grained particles of halloysite which have deposited on the lake floor are undergoing further dissolution under the lower layer water conditions, so supplying material for nucleation and subsequent growth of kaolinite. The entire transformation process of halloysite to kaolinite taking place in the Lake Ohyunuma is basically controlled by the growth kinetics of kaolinite. The transformation time, defined as the time when all halloysite particles disappear, was estimated to be a couple of years when the lower layer was assumed to be a batch system. In the CSTR system, however, the transformation time increases with increasing the supersaturation of inflowing solutions because the dissolution rate of halloysite decreases. The terminal supersaturation of solution at the point which the transformation is completed has been situated at intermediate values between the equilibrium solubility products of halloysite and kaolinite, similar to the observed supersaturation values of the lower layer waters, though it is strongly dependent on the supersaturation of inflowing solution and the residence time of the waters. Consequently, the Al concentration of Lake Ohyunuma can be said to be controlled by the dynamic dissolution and growth processes of minerals involving halloysite, kaolinite. and possibly alunite in the flow system, while the Si concentrations obey the solubility curve of amorphous silica.

Rheological behavior of aqueous suspension of terra-cotta compositions in terms of newtonian factor, consistency factor and viscosity

Abstract: Utilization of common clay in admixtures with various other substances for fabrication of utility goods and art objects are widely in practice. However, slip casting of slurries of such crude materials poses several problems in shaping of green bodies because of poor reproducibility due to lack of sufficient knowledge on the rheological properties of those suspensions. In the present investigation, suspensions containing common clay, quartz and fly ash have been selected for evaluating rheological properties of those suspensions with an ultimate objective of preparing slips with reproducible castability. Newtonianity of those suspensions were evaluated by rotational type viscometer and an attempt was made to explain the behavior of suspensions in terms of Newtonian factor `n' consistency factor `k' and viscosity V. Different factors responsible for affecting `n', `k' and `ri' were analyzed and their inter relationship established. It was found that the suspensions were of pseudo plastic in nature with a marked tendency towards becoming Newtonian. Rheological parameters like `n', `k' and `ri' were found to be extremely electrolyte sensitive. The entire phenomenon was explained by assuming floc structure and deflocculations were interpreted in terms of electrolytic as well as mechanical forces. Castability of suspension was found to be related to `n', `k' and V.