Expandable Clay Minerals Research Articles

Oxytetracycline interactions at the soil–water interface: Effects of environmental surfaces on natural transformation and growth inhibition of Azotobacter vinelandii

The mechanism of oxytetracycline (OTC) adsorption to a silty clay loam soil was investigated using sorption isotherm experiments, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction spectroscopy (XRD). Sorption data fit well to a cation-exchange capacity sorption model. Spectroscopic data indicate that the interactions between oxytetracycline and silty clay loam soil were primarily through electrostatic interactions between the protonated dimethylamino group of OTC and the negatively charged moieties on the surface of the soil. Based on XRD results, OTC adsorption appeared to inhibit the ethylene glycol solvation of the expandable clay minerals, suggesting that OTC had diffused into the clay interlayer space. The presence of adsorbed OTC did not significantly affect the transformation frequency of the soil bacterium Azotobacter vinelandii with plasmid DNA (soil alone 3 × 10(6) ± 4 × 10(6) and soil with adsorbed OTC 4 × 10(6) ± 0.5 × 10(6) ). Growth was inhibited by adsorbed OTC, although a greater mass of adsorbed OTC was required to achieve the same degree of inhibition as the system of dissolved OTC alone. These results suggest that the interactions of tetracyclines at the soil-water interface will affect the growth of sensitive microorganisms in soil microbial communities.

Moisture expansion associated to secondary porosity: an example of the Loseros Tuff of Guanajuato, Mexico

The old mining city of Guanajuato in middle Mexico preserves one of the most important historical legacies in colonial buildings, the UNESCO declared the city World Heritage Site in 1988. Practically all the colonial constructions were built with natural stones from the neighbourhood, of which stands a greenish to reddish vulcanite, called Loseros Tuff. Although the Loseros Tuff is widely used in historical buildings in the city. It shows significant deterioration and weathering effects, principally in the parts where the tuff shows a coarse grain size. The petrographic, petrophysical, mineralogical and geochemical properties of the Loseros Tuff were analysed in order to determine the causes, effects, behaviour and response to deterioration of this volcanic rock. The results of the investigations suggest that in addition to the parameters like the grain size and the porosity properties, the pore radii distribution is decisive for the effectiveness of porosity and the water transport into the rock. It is recognized that once the liquid water invades the rock the dissolution of the matrix occurs, which is accompanied by a sudden moisture expansion favoured by the newly formed secondary porosity and the high content of expandable clay minerals.

Adsorption of heavy metal ions on mesoporous silica-modified montmorillonite containing a grafted chelate ligand

The objective of this work is development of a new adsorbent on the base of an organoclay with a chelating ligand covalently attached to the clay mineral surface. The presence of a chelating ligand in the clay structure significantly improves its ability to immobilize heavy metal ions from contaminated sludge of wastewater. Montmorillonite and kaolinite were chosen as typical examples of expandable and non-expandable clay minerals. A two-step modification procedure comprised of sequential modification with oxides and grafting of a chelating agent to the modified clay minerals was used. Modifications with silica and ferric oxide were conducted by reacting the dispersed raw clay minerals with tetraethoxysilane and ferric nitrate solution. A chelating ligand, N-[3-(trimethoxysilyl)propyl]ethylenediamine triacetic acid trisodium salt, was introduced into interlayer space of raw and modified clay minerals in aqueous solutions. Laboratory tests of the organoclay efficiency for purification of wastewater were conducted with the most promising sample, i.e., organoclay with the highest specific loading of chelating agent. Experiments were conducted with model wastewater containing either individual or mixed heavy metal ions. The modified organoclay displayed high adsorption capacity for heavy metal cations even in acidic media. The method of modification presented in this work can be used for synthesis of efficient adsorbents for applications in contaminated areas.

Terrestrial influences on carbon burial at sea

Over geologic time, a primary driver for change in atmospheric concentrations of gases such as methane, CO2, and O2 is burial of organic matter in marine sediments. After photosynthetic organisms produce organic matter and O2, these compounds are typically respired to CO2 in short order. However, burial of organic matter in sediments sequesters carbon for eons, allowing O2 to build up and playing a small role in reducing CO2 in the atmosphere. The exact mechanisms and rates of organic matter burial are therefore significant terms that need to be understood to fully comprehend earth processes. Organic matter preservation is linked to the burial of minerals, many of which are terrestrially derived. The favored hypothesis explaining organic–mineral associations is that the abundance of mineral surface area somehow protects organic matter from degradation. In this way, ocean sediments containing fine-grained minerals bury more organic matter than coarse-grained sediments. The mechanistic details of this remain poorly elucidated, but the relationship in the modern ocean is reasonably well described: ≈1 mg of C is buried along with each square meter of external mineral surface. This approach excludes the internal surfaces of expandable clay minerals, which have previously been thought to be relatively unimportant (1). The one notable exception to this generality occurs in suboxic and anoxic portions of the ocean, where organic matter is preserved in excess of 1 mg C per external square meter. It has generally been assumed that external mineral surface area controls “baseline” amounts of organic matter burial and that anoxia enhances burial. In PNAS, Kennedy and Wagner. (2) bring a unique perspective to this paradigm. They show that mineralogy, not just surface area, can play a large role in controlling organic matter burial. By measuring the internal surface area of expandable clays and relating that to changes in organic matter burial in Cretaceous black shales, they illustrate a process whereby both mineralogy and anoxia amplify carbon storage. The amplification effect seems to occur rapidly, on a temporal scale of decades rather than millenia.

Kinetics of non-exchangeable potassium release as a function of clay mineralogy and soil taxonomy in calcareous soils of southern Iran

The release of non-exchangeable potassium from 16 calcareous soils collected from southern Iran was examined. For this study, a method was used involving a total of 14 successive 15-min extractions with 0.01 M CaCl2 as an extractant. Cumulative potassium released from soils was in the range of 144–509 mg kg−1 for surface and 115–445 mg kg−1 for subsurface soils. The studied soils were categorized into two groups based on the cumulative K released, clay mineralogy and soil taxonomy. (I): Smectitic soils including Vertisols, Vertic subgroups and some Alfisols and Inceptisols; (II) other soils including Mollisols, Entisols, and other subgroups of Inceptisols and Alfisols. Cumulative K release was significantly (p < 0.01) higher in Group I than in group II. The release kinetics of non-exchangeable K showed the best fit to Elovich, parabolic and power function kinetic models. The Elovich and parabolic release rate constants were significantly (p < 0.05) higher in Group I than in Group II. Greater K release rate constants in Group I soils could be due to the heavy soil texture and domination of expansible clay minerals.

Substituting non-natural agents in UV-protection cream by a mixture of clay with Ganoderma pfeifferi extract

To investigate the potential of substituting non-natural agents in sunscreen, mixtures of some clays with Ganoderma pfeifferi extract were examined in regard to their protection abilities against ultraviolet (UV) radiation in the wavelength range 250–400 nm. Some mixtures showed remarkably high UV-protection potential in comparison with corresponding clay cream devoid of the fungal extract. Depending on interlayer charge of the dominant clay mineral contained in the clays, the interaction between the fungal extract and the clay mineral played a key role in the UV-protection ability of the mixtures. The optimal clay in the mixture with the G. pfeifferi extract for sunscreens was dominated by expandable clay minerals with low interlayer charge.

The preparation of polyurethane foam combined with pH-sensitive alginate/bentonite hydrogel for wound dressings

Polyurethane (PU) foam was combined with protein drug-loaded pH-sensitive alginate-bentonite hydrogel for wound dressings. Alginate is a linear copolymer composed of 1–4-linked β-D-mannuronic acid (M) and its c-5-epimer α-Lguluronic acid (G). The amount of (M) and (G) and their sequential distribution are varied depending on the alginate source. Soluble sodium alginate can become a hydrogel when cross-linked with divalent cations and has widespread applications in the food, drink, pharmaceutical and bioengineering industries. Recently, it has been also proposed as a biomaterial for drug delivery systems. Bentonites are the natural inorganic polymers consisting of a large proportion of expandable clay minerals with a three-layer structure such as montmorillonite, beidellite, nontronite, etc. They are important adjutants and supports for medical products, and they have many useful physicochemical, mechanical, and biological properties such as absence of toxicity, indifference to other raw materials, sorption, swelling, and complex formation properties. Alginate-bentonite hydrogels were prepared at concentration ratios of 10/0, 7/3, 5/5, 3/7. PU foams were prepared using hydrophilic polyols. We investigated the controlled release of a protein drug from PU foam combined with alginate-bentonite hydrogel at different pH values of 4.2, 5.2, 7.2, 8.2. The mechanical properties and cytotoxicity tests of this foam were also studied.

Erosion Study of New Orleans Levee Materials Subjected to Plunging Water

During Hurricane Katrina, overtopping water caused erosion and subsequent failure of several sections of I-type flood walls in New Orleans. Erosion stemmed from the kinetic energy of water falling from the top of the flood wall, unlike the typical surface erosion caused by shear flow. This study evaluated the effects of important parameters of levee soils—fines content, degree of compaction (DOC), clay mineralogy, and water content in relation to the erosion behavior of New Orleans levees subjected to the plunging water. In general, test results showed that a higher fines content contributed to greater erosion resistance. The trend became unclear when fines content exceeded 20–25%. A higher degree of compaction did not necessarily contribute to greater erosion resistance. Underwater soaked soils showed much less erosion resistance than nonsoaked soils. Soils containing expansive clay minerals showed less erosion resistance than soils containing nonexpansive clay minerals.

Obliquity forcing of Quaternary glaciation and environmental changes in NE Siberia

Reconstructing Quaternary glacial and environmental changes in the vast, high-northern latitudes of Siberia is essential for a better understanding of global past climate variability and its potential solar forcings. Two sediment outcrops in the Dyanushka Valley in the southwestern foreland of the Verkhoyansk Mountains, northeast Siberia, were investigated using a multi-proxy approach (lithostratigraphy, geochemistry, palynology, and radiocarbon and IRSL dating). Three piedmont glaciations reached the outcrop sites. The glacial advances are dated to >140, ∼119–92 and ∼78–53 ka and thus, within dating uncertainties, correspond to obliquity minima during marine isotope stages (MIS) 6, 5d, and 4. This chronology corroborates and refines previous studies that have documented the successively more restricted glacial extents in Siberia during the course of the last glacial cycle. The observed glaciation pattern is out of phase with global ice volume estimates and probably indicates a strong aridisation trend. Additionally, the results show that the geochemical and mineralogical composition of the sediments contains information about provenance. Sediments originating from the Verkhoyansk Mountains are generally enriched in TiO 2, MgO, P 2O 5, Fe 2O 3, Cr, illite, and chlorite, whereas sediments derived from the Lena River contain more expandable clay minerals, Ba, Sr. Alkane patterns as biomarker proxies turn out to be particularly valuable where poor preservation of pollen is an issue, and, generally speaking, vegetation reconstruction helps distinguishing between ‘warm versus cold mode’ sediments.

Peat or no peat: Why do the Rajang and Mahakam Deltas differ?

Abstract Coastal and deltaic Holocene peat accumulations around the equatorial island of Borneo, Southeast Asia, have served as models for economic coal-bearing sequences in the stratigraphic record. Although climatic conditions, vegetational communities, and sedimentary regimes are comparable, peat accumulations are not found on both the western and eastern sides of the island. The Rajang River delta and coastal plain, Sarawak, East Malaysia, are covered in areally extensive, thick peat deposits that have attained at least a thickness of > 13 m in ombrogenous peat domes (Marudi, Baram River). Peat-swamp biomass began to accumulate over Pleistocene podzols when sea level stabilized ∼ 7.5 ka and delta progradation was initiated. The Mahakam River delta and coastal plain, East Kalimantan, Indonesia, also began progradation at this time, but there is no evidence in any part of the coastal region for peat accumulation. Rather, poorly developed organic-rich gleysols occur throughout the delta plain. Both the Rajang River and Mahakam River deltas are tidally influenced, fine-grained systems, with a sediment provenance in the Central Massif. Sediment transported through the Rajang River delta differs in that as much as 60% of the clay minerals deposited in the system are mixed layer (I/S) and expandable (K/E) clays that act to restrict pore water flow in the tidal and overbank deposits that comprise the delta plain. These result in the development of an aquiclude above which paludal conditions develop, promoting accumulation of organic matter. In contrast, there is a low proportion of mixed layer and expandable clays transported in the Mahakam River system. This precludes the development of a stilted water table within the delta, allowing for organic matter recycling without peat accumulation. The presence of a high proportion of expandable clay minerals on the western side of Borneo is a reflection of the weathering and eroding source rocks on this side of the Central Borneo Massif.

High-temperature X-ray powder diffraction as a tool for characterization of smectites, layered double hydroxides, and their intercalates with porphyrins

We have analyzed expandable clay minerals and layered double hydroxides with different interlayer ions by high-temperature X-ray powder diffraction (HT-XRD) with comparison to thermal analysis (DTG/DTA) coupled with evolved gas analysis (EGA). We described in detail their thermal behaviour with emphasis to the differences among samples related to their crystallochemical characteristics. Porphyrin-intercalated smectites have a quite unique thermal behaviour as monitored by HT-XRD; the intercalates with tetrakis(1-methyl-4-pyridinio)porphyrin have a basal spacing of about 1.4 nm and are thermally stable up to ca. 600 °C. The resolution of the individual dehydration steps of smectites (from 2-layer hydrate via 1-layer hydrate to the anhydrous form) is much better in HT-XRD then in DTG/EGA curves. Layered double hydroxides (LDHs) have a varying thermal stability depending on their chemical composition and crystallinity. LDHs intercalated with porphyrin anions are thermally stable up to 350–400 °C.

Lipid Peroxidation Induced by Expandable Clay Minerals

Small-sized environmental particles such as 2:1 phyllosilicates induce oxidative stress, a primary indicator of cell damage and toxicity. Herein, potential hazards of clay particle uptake are addressed. This paper reports that the content and distribution of structural Fe influence the ability of expandable clay minerals to induce lipid peroxidation (LP), a major indicator of oxidative stress, in biological matrices. Three smectite clays, hectorite (SHCa-1) and two nontronites (NAu-1) and (NAu-2) containing varying total content and coordination environment of structural Fe, were selected. Screening and monitoring of LP was conducted using a thiobarbituric acid reactive substances (TBARS) assay. The higher content of TBARS in nontronites than that in SHCa-1 suspensions was explained because structural Fe contributes to LP. The observed lack of correlation between TBARS content and the extent of Fe dissolution indicated that the formation of TBARS is surface controlled. Results showing a high TBARS content in SHCa-1 but not in nontronite supematant solutions was explained because the former contains distinct, soluble chemical component(s) that could (i) induce LP by its (their) own right and (ii) whose chemical affinity for organic ligands used as inhibitors is weak. Clays serve as stronger inductors than 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) but are much weaker than FeSO4. The outcome of this work shows that LP is clay surface-controlled and dependent on clay structural composition.

Cation Exchange Reactions of Vermiculite With Cu-Triethylenetetramine as Affected by Mechanical and Chemical Pretreatment

AbstractThe cation exchange capacity (CEC) is a characteristic property of expandable clay minerals, such as smectites and vermiculites. The aim of this work was to examine the cation exchange behavior of vermiculite using the Cu-triethylenetetramine (Cu-trien) CEC method and the influence of mechanical and chemical pretreatment, with the ammonium acetate method serving as a reference. The Cu-trien method makes rapid and direct CEC measurements possible. Three different kinds of mill were used to grind a vermiculite sample from Russia, in order to reduce the particle size to &lt;10 µm. The Netzsch CGS 10 dry mill reduced the particle size more effectively than the other grinding methods. Chemical pretreatments were used to remove carbonates, organic matter, Fe oxides, and divalent exchangeable cations from vermiculite samples prior to CEC measurements. Subsamples of ground and chemically pretreated vermiculite samples were saturated with Na, Li, Mg, Ca, and Cu cations to determine the effect of exchangeable cations on measured CEC values. Chemical pretreatment, monovalent cation pretreatment, and 48 h of shaking time were needed to measure vermiculite CEC values effectively using the Cu-trien method.

Engineering characteristics of a glacio-lacustrine clay deposit in a semi-arid climate

Parent material composition, particle disintegration by glaciers and lacustrine environment govern the geological development and engineering characteristics of clay deposits in southern Saskatchewan. The pre-existing expansive clay minerals were preserved due to the restrained leaching in the Regina Lake and the prevalent aridity in the area. The main objective of this paper was to develop a fundamental understanding of the clay deposit for the use in the design and construction of civil infrastructure. The results indicated the presence of expansive clay minerals in the deposit, with smectite accounting for 35% of the material. The major exchangeable cation was found to be Ca2+ which accounted for more than half of the total measured cation exchange capacity of 40 (cmol(+)/kg). The most likely exchange complex governing water adsorption of the clay was determined to be Ca2+-smectite. Alongside a high initial saturation (86%), this complex resulted in moderate volume changes in the clay. The swelling pressure was fully developed within the first hour of the constant volume test. The corrected swelling pressure was determined to be 120 kPa leading to an estimated heave of 36 mm in the surface layer of the deposit. The compression index and the swelling index were found to be 0.25 and 0.08, respectively.

Interaction of montmorillonite with phenothiazine dyes and pyronin in aqueous dispersions: A visible spectroscopy study

Abstract Layer charge is one of the key parameters used for the characterisation of expandable clay minerals, smectites. It determines most significant properties of the material which are important from the industrial application point of view. This work is related to a novel method introduced to characterize the layer charge of smectites, based on using cationic organic dyes as molecular sensors. One xanthene and four phenothiazine cationic dyes were tested using reduced charge montmorillonites (RCMs) and compared with methylene blue, which has been used most frequently. The characterization of the charge was based on the formation of molecular assemblies (H- and J-aggregates) composed by dye cations, which were easily detectable using absorption spectroscopy in the UV/VIS spectrum. More detailed characterization of the spectra required calculations of second-derivative curves. For all of the reaction systems tested in this work, the molecular aggregation increased with the layer charge of RCMs. Slight to moderate differences in the formation of dye assemblies related to the differences in the molecular structures of the individual dye cations. For example, the molecular asymmetry of azure A brought about the formation of coexistent species of similar structures. The structure of the heteroaromatic skeleton affected the extent of the aggregation and spectral changes with time. The presence of reactive, non-substituted amino groups in thionine cations probably partially decomposed in the clay mineral colloids based on high-charge RCMs. Any of the tested dyes could be used as molecular sensors for empirical characterization of the layer charge of clays taking into account the differences mentioned above.

Morava River floodplain development during the last millennium, Strážnické Pomoraví, Czech Republic

Floodplain sediments deposited along the lower course of the Morava River (eastern Czech Republic), were studied in the Strážnické Pomoraví region to describe the alluvial history of the river over the last millennium. The sediments exposed in up to 5 m high erosional river banks were analysed using mineral magnetic, geochemical and chemical approaches. The age model of the sedimentary sequences was constructed from radiocarbon dates in association with 206Pb/207Pb and POP (DDT, PCB) analysis and 137Cs activity data. The Cu-trien method was used for stratigraphically correlating these deposits based on the variation of expandable clay minerals in the sediments. The resulting stratigraphic pattern reveals the alluvial history of the currently active river channel system since the end of the first millennium AD. Fine overbank clayey sediments deposited during the `Mediaeval Warm Period' were eroded from cultivated fields newly formed during Mediaeval colonization between 1250 and 1450. These fine deposits are overlain by coarser floodplain sediments of the `Little Ice Age', indicating a change in the sediment source since the sixteenth century AD, and a substantial increase in the sediment load in the second half of twentieth century. The Strážnické Pomoraví floodplain deposits represent a valuable palaeoenvironmental archive of the last millennium, containing records of fluvial processes considerably altered by human activities.

Chemostratigraphic correlation of sediments containing expandable clay minerals based on ion exchange with Cu(II) triethylenetetramine

AbstractCopper(II) triethylenetetramine [Cu(trien)]2+ is an agent suitable for the 1-step determination of the cation exchange capacity (CEC) of many geomaterials using a procedure much less laborious than other, commonly used methods. It is also suitable for the determination of the composition of original exchangeable cations. In contrast to other common ions used for CEC analysis, the Cu(II) complex with triethylenetetramine, [Cu(trien)]2+, is specific for expandable clay minerals. The robustness of [Cu(trien)]2+ analysis was verified using reference clays, ion-exchanged reference clays, sediments, and soils. The [Cu(trien)]2+-based CEC of expandable clay minerals is not influenced significantly by ferrihydrite, goethite, manganite, birnessite, calcite, and gypsum. Birnessite, calcite, and gypsum admixtures affect the composition of the evolved cations. [Cu(trien)]2+ does not recover the entire CEC of soils (but rather that of the clay minerals only) which contain components other than clays which contribute to the CEC, e.g. soil organic matter. In a series of loess with buried paleosols and recent soils the [Cu(trien)]2+-based CEC ranged from 30 to 110% of total CEC obtained by traditional BaCl2 methods. The relative ratio of Ca to Mg, the prevailing exchangeable cations in soils and sediments in exogenic environments, are similar after [Cu(trien)]2+ and conventional BaCl2 treatments. The Ca/Mg ratio in the exchangeable fraction was used successfully for chemostratigraphic correlation of paleolacustrine sediments from a large lake in the Upper Carboniferous basins of eastern equatorial Pangaea and a series of recent flood plain sediments of the meandering Morava River in the Czech Republic. The Ca/Mg ratio obtained by [Cu(trien)]2+ analysis is proposed as a novel tool for the chemostratigraphic correlation of sediment series containing expandable clay minerals.

An unusual occurrence of probable Pleistocene corestone within a Cretaceous dioritic enclave, Peninsular Ranges, California

Abstract We here document an unusual occurrence of probable Pleistocene corestone within an ∼ 5 m by ∼ 5 m dioritic enclave contained within a Cretaceous tonalitic pluton, Santa Margarita Ecological Reserve, SW California. The enclave lies within ∼ 3.5 km of the seismically active ∼ 1.5–2 Ma Elsinore fault zone, and may have been subjected to ∼ 70–90 ground shaking events since ∼ 22,000–18,000 years ago. The studied corestone is elliptical with major axis measuring ∼ 55 cm and minor axis ∼ 26 cm in length. It is surrounded by a discontinuous ∼ 7 cm thick rind that breaks apart under slightly greater finger pressure than does the surrounding saprolite. In order to assess changes in the physical and chemical properties of the corestone, rind, and saprolite we collected along an ∼ 66.5 cm long traverse 4 samples from the corestone, 1 from the rind, and 5 from the saprolite for bulk and grain density, porosity, and major and trace element analyses. Textural and clay mineral data, along with the redistribution of elemental mass, indicate that the weathering of biotite, and to much lesser degrees apatite and the An-rich cores of plagioclase, played critical roles in the production of saprolite especially in a narrow ∼ 20 cm wide zone adjacent to the rind of the corestone. Within this zone bulk densities reach their minimum values, while porosities and positive volume strains reach their maximums. In addition, the maximum loss of K, Fe, Mn, and Ca mass occurred just inside this region, and is paralleled by the highest CIA values and highest additions of Si and Rb mass. In contrast, the masses of Na and Sr are progressively increased and decreased, respectively along the entire sampling traverse while the loss of Mg, Ti, and P mass is episodic with the greatest losses occurring within the narrow zone adjacent to the rind and at the end of the traverse. The above observations indicate that the conversion of biotite to expandable mixed-layered clay minerals, aided by the alteration of the An-rich cores of plagioclase, produced sufficient stress on grain boundaries that a weakening or loss of intercrystalline cohesion occurred. However, unlike the well documented isovolumetric development of saprolite in other areas, at the study site saprolitization was accompanied by a volume expansion. We speculate that repeated ground shaking in response to earthquakes generated in the nearby Elsinore fault zone may be responsible for this difference. Important byproducts of ground shaking would include additional weakening or loss of intercrystalline cohesion, and the production and enhancement of new and older fluid pathways respectively. The fact that the most intensely altered material at the study site lies adjacent to the boundary between the rind and saprolite, suggests that this interface acted to guide fluid flow around the corestone and rind and into the adjacent saprolite where elemental mass was redistributed down various paths leading to the underlying water table. Most of the leached elemental mass was removed from the area of the sampling traverse, but small increases in Si, Rb, and Na mass suggest redistribution of these elements from elevated areas outside the area sampled during this study. The result of the above complex set of processes is a variably porous and chemically altered saprolitic enclave that is still undergoing modification as it adjusts to the vicissitudes of the paralithic environment and continuing ground shaking during earthquakes generated along the Elsinore fault.

Damage to buildings on expansice soils in Kibaha, Tanzania

Many buildings have been constructed with little knowledge of the presence and effect of swell-shrink soils in Kibaha, Tanzania. This study points out the presence of potentially expansive soils in the area. It provides a brief summary of field observations of damaged buildings on expansive soils in the case area. It brings together the details of site topography, geology, geotechnical parameters, climatic conditions, ground investigations and laboratory test results. Soils with significantly expansive properties have been identified in the case study. Principally, the geologic setting of the area indicates the presence of expansive clay minerals. The cyclic wetting and drying weathering of the area is significantly linked to the structural damage plaguing buildings on these expansive soils. Subsequently, the laboratory tests show that the soils have liquid limits greater than 50%, plastic limits between 15% and 30% and shrinkage limits less than 17%. The free swells are greater than 100% while the swell pressures of 50kPa are made known in the oedometer tests. X-ray diffraction tests show that the smectite-group minerals of about 50% are present in the soils. Furthermore, the extents and causes of damages on existing buildings are diagnosed in correlation with the swelling potential. Finally, a number of recommendations to address the problems are put forward.Journal of Building and Land Development Vol. 13 (2) 2006: pp. 32-40

Synthesis of hectorite–TiO 2 and kaolinite–TiO 2 nanocomposites with photocatalytic activity for the degradation of model air pollutants

We studied the synthesis and photocatalytic activity of small-sized TiO 2 supported on hectorite and kaolinite. Deposition of TiO 2 on the clay mineral surface was conducted by using a sol–gel method with titanium isopropoxide as precursor. Anatase TiO 2 particles formation was achieved by hydrothermal treatment at 180 °C. Material characterization was conducted using XRD, SEM, XPS, ICP-OES, BET and porosimetry analysis. fficiency in synthesizing clay–TiO 2 composites depended strongly on the clay mineral structure. Incorporation of anatase in hectorite, an expandable clay mineral, was found to be very significant (> 36 wt.% Ti) and to be followed by important structural changes at the clay mineral surface. Instead, no major structural modifications of the clay were observed for kaolinite–TiO 2, as compared with the untreated material. Photocatalytic performance of clay–TiO 2 composites was evaluated with ATR-FTIR following the oxidation of adsorbed toluene and d-limonene, two model air pollutants. In either case, the photocatalytic removal efficiency of these hydrophobic substrates by the synthesized clay–TiO 2 composites was comparable to that observed using pure commercial TiO 2 (Degussa P25).