Showing papers in "Clay science in 1999"

Adsorption of some low molecular weight organic acids on nano-ball allophane

Abstract: Aluminol groups such as Al-OH or Al-OH2 are shown to have an important role in adsorbing low molecular organic ompounds, acetic, oxalic and citric acid, on nano-ball allophane samples. The amount of the three organic compounds adsorbed was higher for KyP sample with Si/Al=0.67 than KnP sample with Si/A1=0.99 due to much more aluminol content of the KyP sample. Langmuir and Freundlich adsorption equations were used to describe the adsorption of the organic compounds. At lower pH, the amount of organic compounds adsorbed by nano-ball was as follow: oxalate> citrate> acetate, and at higher pH, citrate> oxalate> acetate. For all cases, the Langmuir and Freundlich parameters tended to decrease with increasing solution pH. Adsorption of acetate by allophane at pH 4-6 fitted with Langmuir model and at pH 8-10 fitted with Freundlich model. For adsorption of oxalate, only at pH 4 suited with the Langmuir model. All the adsorption data of citrate fitted with the Freundlich model. From the observed changes in solution pH with adsorption, reaction mechanism between the three organic compounds and allophane was proposed as follow: a) Deprotonation (release of H+), this was reaction between acetate or citrate and allophane at low pH; b) Dehydroxylation (release of OH-), this was reaction between acetate or citrate and allophane at high pH and reaction of oxalate. At lower pH, Al was easier to be released than Si from KyP, but at highe pH, Si was easier to be released than Al. For KnP, release of Si was much more than Al at all pHs, because the KnP sample contains a lot of condensed Si tetrahedra which is bonded weakly on the fundamental allophane structure.

Organotin compounds and their adsorption behavior on sediments

Abstract: This paper present a brief overview of the occurrence and degradation of organotin compounds in water and sediments, and their sorption behavior on natural sediment particles and pure clay minerals. Oraganotins change in their form from cation to hydroxides in accordance with an increase of pH values, and they would exist as simple neutral hydroxides in aqueous solution under natural environment pH. The concentrations of organotins in water and sediments vary in a wide range according to the degree of contamination of aquatic environment. The concentration of triorganotins in aquatic sediments are generally orders of magnitude higher than the aqueous concentrations. Hence, sorption is a key process determining the transport and fate of triorganotins in aquatic environment. Published sorption coefficients (K) for aqueous tributyltin (TBT) in sediment or particulate matter range from 3.4 × 10 2 to 1.9 × 10 6 (L kg -1 ), but the majority of reported K values have been in the order of 10 3 . It was suggested that the K value increases with increasing the amount of fine particles and expandable minerals in sediment. The effects of salinity on the K value were different depending on the sorbent-to-solution mass ratios used in an experiment. The K values for homo-ionic clay minerals were affected by the type of exchangeable cations and pH. An example of the biological degradation of Bu 3 Sn + in water and sediment was also presented.

Xps and dft study on the migration of lithium in montmorillonite

Abstract: The distribution of lithium in montmorillonite was studied by using X-ray photoelectron spectroscopy (XPS) and compared with calculations based on the density functional theory (DFT). Interlayer Li ion in montmorillonite migrated to octahedral sites by heat treatments at a temperature range from 250 to 350°C for up to 72 hours. Li (Is) binding energy of hectorite used for reference and Li exchanged montmorillonite were 55.0 and 57.0 eV, which were attributed to the octahedral and the exchangeable lithium, respectively. After the heat treatment at 250°C for 18 hours, a new component peak was appeared at 55.4 eV which was attributed to the octahedral lithium ion; and the ratio of the peak area to the total Li (1s) peak area was increased with prolonging the heat treatment. However, even after the heat treatment at 350°C for 72 hours, the lithium ions were distributed to the both sites. Two distinct Li locations in smectites were studied using DFT calculations. One was in the ditrigonal cavity, and the other was in the octahedral sheet of smectite. The optimized structure of the cluster models suggested that the Li ion favorably interacts with a hydroxyl oxygen atom and/or basal oxygen atoms at the bottom of the ditrigonal cavity in the both cases. Calculated 1s binding energy of the Li ion in the octahedral site was smaller than that of the Li ion in the ditrigonal cavity site, which shows good coincidence with the XPS chemical shift of the Li (1s) peak.

New concepts for change in charge characteristics of allophane with phosphate adsorption

Abstract: Observed changes in the amounts of negative and positive charges of allophane with phosphate adsorption (NaH 2 PO 4 in NaCl with total [Na] = 10 mM) were each divided into two components. One is due to increase in solution pH, variable charge characteristics, and the other is net effect caused by the adsorbed phosphate. The net effect increased negative charge and decreased positive charge of allophane. To explain the net effect, we assumed that OH - was initially released from allophane-phosphate adsorption complex just the same amount as the adsorbed H 2 PO 4 - . This situation is comparable with that when the same amount of NaOH was added to original allophane. Then, we compared the reaction of the OH - with functional groups, Si-OH, Al-OH 2 + and P-OH, between the two situations. The comparison indicated that the functional groups of the adsorption complex had more abilities to react with the OH- than those of the original allophane. Inductive effect of the adsorbed phosphate which accelerated deprotonation reaction of inherent functional groups of allophane, Si-OH and Al-OH 2 + , was suggested.

SPECIATION OF ALUMINUM IN HYDROXYALUMINUM AND HYDROXYALUMINOSILICATE IONS FIXED BY MONTMORILLONITE, USING 27Al-NMR AND ICP-AES

Abstract: We tried to elucidate the chemical species of hydroxyaluminum (HyA) and hydroxyaluminosilicate (HAS) ions intercalated into the Mt focusing on the Al by means of 27 Al-NMR, inductively coupled plasma atomic emission spectroscopy (ICP-AES), differential thermal analysis (DTA), x-ray diffraction (XRD), and fourier-transform infrared (FTIR). Using 27 Al-NMR and ICP-AES, the Al in a Al-OH-Si(OH) 4 mixture was separated into three fractions; Al 13 , Al SYM , and Al NON . The Al 13 and Al SYM were quantitatively determined by 27 Al-NMR at 62.5 and 0 ppm, respectively. The Al NON was defined as the Al which can be determined by ICP-AES but not by 27 Al-NMR. The Al SYM was attributed to electrically-symmetric octahedral Al including monomer (and dimer) HyA ions, and the Al NON was attributed to electrically-asymmetric Al including HAS and/or polymer HyA ions. Among the HAS and HyA solutions prepared, the proportion of Al 13 ion was higher in the smaller Si/Al ratio. The HAS solutions with the Si/Al ratio greater than 0.24 contained no Al 13 ion. As result of adsorption kinetics of Al 13 , Al SYM , Al NON , and orthosilicic acid in three solutions on the montmorillonite (Mt), most of the adsorption reaction occurred within I min., and Al 13 and HAS ions were selectively adsorbed by Mt compared with the Al SYM . The HyA-Mt complex showed a great expansion in the d-spacing compared with Mt, and the d-spacing of the HyA-Mt was 1.64 nm and its peak was broad. On the other hand, the strongest peak of the HAS-Mt was mostly at around 1.80 nm, irrespective of the Si/Al ratios of the HAS ions used. Intercalation of HAS ions may occur completely since the enlargement of the d-spacing was clearly seen by XRD and no specific absorption bands were not seen by FTIR. Most of the thermal characteristics of the Mt would be modified by the intercalated HAS ions with a higher Si/Al ratio greater than 0.05. These results indicate that, upon the intercalation of Mt, the outer surface properties detectable by the FTIR were not modified greatly, while the internal surface structure of the complex detected by XRD and DTA analyses was modified greatly. Al 1 3 ions could not be fixed in the interlayer space of the Mt, and most of the changes was brought by the fixation of HAS ions in the internal space of Mt.

EFFECT OF HyA-INTERLAYERING ON NH4/Ca SELECTIVITY OF EXPANDABLE LAYER SILICATES

Abstract: Hydroxy-interlayering in vermiculites (Vt) and montmorillonites (Mt) is very common in acid soils and sediments which causes significant changes in many physical, chemical, electrochemical and mineralogical properties of the host clays. Cation exchange capacity and selectivity are essential parameters that influence cation distribution between adsorbed and solution phases, and their mobility in the soil profile. Adsorption and exchange isotherms for NH 4 -Ca system were derived using Vt and Mt clays interlayered with hydroxyaluminum (HyA) ions of initial basicities of 1.0 and 2.5. The principal objective of this study was to clarify the effect of hydroxy-interlayering on the NH 4 /Ca selectivity of the host clays. Vermiculite in contrast to Mt, showed more preferential adsorption and exchange of NH 4 over Ca. The HyA-interlayering greatly increased NH 4 /Ca selectivity of Vt, whereas that of Mt was little affected. The greater NH 4 /Ca selectivity of Vt in comparison to Mt might be a result of higher layer charge density in the former predominantly of tetrahedral origin. The HyA-interlayering might have increased the NH 4 /Ca selectivity through making the clay interlayers propped open, occupying the Ca adsorbing sites and/or exerting steric hindrance to the entry of more hydrated, larger Ca ions. Larger amount of HyA adsorption at higher initial basicity of the HyA ionic solution appeared to increase NH 4 /Ca selectivity, especially of Vt. The greater NH 4 /Ca selectivity of Vt, Mt, and HyA-Vt/Mt as well as the effect of HyA-interlayering on this parameter were limited to low NH 4 -saturation.

Evaluation of cation exchange capacity of montmorillonite using caesium chloride

Abstract: The use of caesium chloride wa.s investigated for the purpose of measuring cation exchange capacity of montmorillonite. In the preliminary experiment, the montmorillonite was saturated with various monovalent Cations by washing with LiCl, NaCl, KCI, RbCl, CsCl, and NH 4 Cl in order to examine the effect of exchangeable cation species on the dispersibility of montmorillonite. As the electrolyte concentration of the equilibrium solution was stepwise decreased, the Li-, Na-, K- and NH 4 -saturated clays began to disperse. Critical concentration for dispersion was 0.1 to 0.25 mol L for Li and Na saturation and 2.5 to 5 mmol L -1 for K and NH 4 saturation. Dispersion of clays was thought to cause errors in quantification of the negative charge because of loss of the dispersed clay during the experimental procedure. The use of K + , Rb + or NH 4 + was considered to have the risk of interlayer fixation by the clay from the viewpoint of the ionic radius. Therefore, Cs + was judged to be appropriate as an index cation for CEC determination. The use of CsCl for evaluation of CEC of montmorillonite was compared with the use of NaCl and showed the following advantages: (1) since the montmorillonite saturated with Cs exhibited little dispersion or swelling, the manipulation of the experiment was improved, leading to reduction in the experimental efforts; (2) saturation with Cs made the negative adsorption of Cl - negligible, so that Cs adsorption on the clay could directly estimate the negative charge of the clay without correction for the negative adsorption; (3) there was little risk of contamination in determining Cs. As the result of the combined effect of these merits, the higher reproducibility was obtained to estimate the amount of the negative charge using Cs + as an index cation compared with the conventional method. In addition, flocculation effect of Cs saturation enabled the measurement of the higher pH system, which had been previously difficult.

Preparation and characterization of thick and stable sol of β-FeOOH nano-particles

Abstract: Partial neutralization of FeCl 3 solution gives sol of akaganeite (β-FeOOH). We examined the effects of neutralization rare and salt concentration during aging on the size and stability of formed particles. We found that instantaneous neutralization and immediate desaltation is the necessary condition to obtain stable sol of nano-particles of akaganeite. The approximate size of particles obtained by neutralizing 1 mol L -1 FeCl 3 solution by instantaneous mixing with solid NaHCO 3 at a NaHCO 3 /Fe mol ratio of 2.0 and immediately desaltation by dialysis was 30 A in width and 120 A in length. The size of the particles in the sol did not change even after 6 months. The sol particles had a specific surface area of 380 m 2 g -1 .

Benzophenone-sensitized cyclodimerization of cinnamic acid in hydrotalcite interlayers : A study of the sensitization behavior

Abstract: Aromatic ketone-sensitized cyclodimerization was studied in the presence of an anion exchange, clay, hydrotalcite. Uv irradiation of the clay suspension coadsorbing trans-cinnamate and 4-benzoylbenzoate ions resulted in the efficient formation of a syn-head-to-head dimer. The ratio of the cis/dimer was significantly affected by the introduction of heavy atom substituents of the sensitizers in high concentrations but not in lower concentrations. Dimerization was revealed to be 10 times more efficient than E - Z isomerization by extrapolating to infinitely smaller concentrations of the sensitizers. The sensitization mechanism through the formation of an exciplex between the excited singlet 4-benzoylbenzoate and trans-cinnamate is presented on the basis of the efficient formation and stereoselectivity of the cyclodimer. A fluorescent probe, the 2-naphthoate ion, intercalated in the clay interlayers was shown to increase its fluorescence intensity in the presence of a sensitizer, implying the validity of a singlet sensitization mechanism via an exciplex formation. The turnover number for the energy transfer exceeded 40 per sensitizer molecule, thus the cyclodimerization was found to proceed catalytically with the sensitizers.

Clay mineralogy and chemistry of alteration halos associated with gypsum vein deposits from mainit area, mabini geothermal field, calumpan peninsula, philippines

Abstract: In Mabini geothermal field, low-sulphidation style of mineralization is encountered at approximately epithermal level to surficial environment as manifested by the presence of alteration halos, open space-filling gypsum deposits and warm grounds. The most impressive thermal manifestations are the altered grounds found in the pre Plio-Pleistocene andesite-basaltic sequence located in Mainit area, South of Mabini. Such altered grounds occur in patches and are partially covered by recent tuff layers. Their mode of formation can be ascribed to the NW and NE trending fault structures that provide permeability for circulating hydrothermal fluid. The observed assemblages of clay minerals in major halos are induced by two fronts of alteration, i.e., argillization and sericitization. They are found to associate intimately with gypsum vein mineralization. Their distribution exhibits a characteristic zonality whose succession in the direction away from the gypsum lode is: kaolinite-illite zone, flanked by an illite-mixed layer illite/smectite (I/S)-smectite zone and a chlorite-mixed layer chlorite/smectite(C/S)-smectite assemblage further away.