Clay-organic Complexes Research Articles

Different effects of resins and asphaltenes concentration of crude oil on sandstone wettability

The influence of asphaltenes in crude oil on sandstone wettability is widely acknowledged. Although asphaltenes are recognized for their stronger polarity compared to resins, resins also contain the similar acidic and nitrogen-containing compounds to those found in asphaltenes. Nevertheless, the impact of resin adsorption on altering sandstone wettability, the different effects of vary concentrations of resins and asphaltenes, and their microscopic mechanisms influencing sandstone surfaces remain ambiguous. Thus, in this study, resins and asphaltenes were isolated from crude oil individually to investigate the different effects of their concentrations on sandstone wettability and the specific reasons. The contact angle measurements, atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and Cryo-environmental scanning electron microscopy (ESEM) were used to examine and explain the wettability changes of Berea sandstone slices before and after exposure to varying concentrations kerosene solutions of resins and asphaltenes. The results reveal that sandstone wettability could not be changed from strongly water-wet to oil-wet, even at resin concentrations as high as 50.0 mg/mL kerosene. In contrast, lower concentrations of asphaltenes, equivalent to a 5.0 mg/mL kerosene threshold, can facilitate the wettability transition process. After the adsorption of resins and asphaltenes, the roughness of the clay surface changes much more significantly than that of the quartz surface. Combined with the observation of ESEM and the results of EDS, it is believed that the resins and asphaltenes preferentially adsorb to clay surfaces, especially chlorite, rather than quartz surfaces. Clay could provide favorable sites for the accumulation of oxygen-containing compounds, leading to enduring clay-organic complexes that serve as anchor molecules for the adsorption of other compounds, ultimately causing the sandstone surface to an oil-wet state. These results may provide theoretical support for better core aging process in the laboratory, surfactant development and enhanced oil recovery procedure optimization in the oilfield.

Long-Term Effects of Organic Amendments on Carbon Stability in Clay–Organic Complex and Its Role in Soil Aggregation

Clay–organic complexes (COC) impart chemical and physical protection to soil carbon (C). In the present study, the aim was to assess the long-term effects of different organic amendments on C stability in COC, distribution of the aggregates, C concentration in the aggregates and labile organic C fractions in the inceptisols located at the research farm situated in the semi-arid sub-tropical climate of India. The results showed that the COC, the percentage of large macroaggregates (LMA) (>2 mm) and the C associated with the aggregates decreased through the soil depths, whereas the other size fractions of soil aggregates (<2 mm) showed an increasing trend. The COC was significantly higher (4.4 times) in soil treatments where farmyard manures (FYM), green manure (GM) and biofertilizers (BF) were applied together (FYM + GM + BF). The organic amendments increased the proportion of LMA over control (no application of organic amendments) to a magnitude of 83 to 101% and the C associated with LMA to a magnitude of 0.48 to 9.8% over control in surface soil. On average, the combined application of FYM, GM and BF exhibited higher C accumulation in almost all soil aggregate fractions, except microaggregates (mA), i.e., (0.25–0.053 mm) size fractions, where application of FYM alone recorded the highest value. Averaged over soil depths, the particulate organic C (POC), dissolved organic C (DOC) and potassium permanganate oxidizable C (POXC) were significantly higher under integrated organic treatments than individual amendments. The significantly higher correlation between COC and the percentage of LMA and aggregate-associated C implied their direct role in soil aggregate formation and their stability. The carbon stability, i.e., retention time of humus in soil, was significantly correlated with soil organic carbon, dissolved organic carbon, particulate organic carbon, potassium permanganate oxidizable C, C mineralization (Cmin), glomalin-related soil protein (GRSP), macroaggregate (MA)-associated C and rice equivalent yield (REY). Overall, the data suggest that the combined application of FYM + GM + BF promotes soil quality under rice–wheat rotation in inceptisols in semi-arid sub-tropical India.

How argillaceous reservoirs exhibit better quality than silty mudstones? Anomalous behavior of shale gas-bearing properties of continental fine-grained sediments in Southwest China and its possible forcing mechanisms

Achieving a thorough understanding of how primary sedimentary granularity drives considerable heterogeneity in internal reservoir attributes of terrigenous fine-grained deposits is of great significance. We investigated the quantitative differentiation and its corresponding driving forces of physical reservoir properties and pore-structure characteristics of silty-mud sediments in the Upper Triassic Xujiahe Formation (SW China) using a multi-method approach. The results show that the micro-mesopore volume and surface area of mudstones/shales are apparently higher than those of silty mudstones and a remarkable threefold rise in average permeability also presents. Extensively distributed bitumen pores occurring mostly along brittle mineral grains or forming clay-organic complexes make considerable contributions to shrinking microcracks. Furthermore, an evidently higher concentration of clay minerals in mudstone/shale reservoirs is primarily responsible for development of the two types of clay inter-crystalline pores distributed along grain aggregates and between well-oriented platelets. These two major causes facilitate the formation of micro-bedding fractures/non-bedding microfractures and connected fracture and pore-fracture networks, and also high-quality argillaceous reservoirs by strongly enhancing storage spaces and seepage capacities. Finally, a conceptual model is established for interpreting a differential reservoir-forming mechanism and corresponding two-sided effects on petrophysical and reservoir quality properties for continental silty-mud sediments.

Study of organic-matter intercalated vermiculitic phases in the hydromorphic red earth sediments

Al-hydroxy intercalated vermiculitic phases have been widely observed in pedogenic environment, but soil organic intercalations have rarely been reported. In the present study, mixed-layer illite–vermiculite (I/V) with organic matter (OM) intercalation under hydromorphic conditions in the Xuancheng red earth sediments was investigated in order to better understand the interlayer components occurring in mixed-layered clay minerals and the formation of this unusual OM interlayered mixed-layer clay species. Selective extraction of organic fillings by ammonium ethylene diamine tetraacetic acid (EDTA) and acid ammonium oxalate (NH4OX) showed that the components associated with organic complexes in the interlayer space of the 2:1 clays are mainly Fe- and A1-(oxy)hydroxides, which block substantial swelling after ethylene glycol solvation and complete collapse after heating. The OM interlayer filling contains CH3(CH2), CO, COO-, and NH functional groups and are resistant to H2O2 extraction although the binding intensity to the interlayer surface may change. Upon heating to ~300 °C the OM filling escapes from the interlayer space which causes the collapse of the 2:1 clay species. Alteration of primary illite during pedogenesis causes release of K and intercalation of hydrated cations in the interlayer space, and also leaching of Al and Fe. There is accumulation of exchangeable cations and Al and Fe oligomers in the interlayer region, which affects the behavior of I/V clays on glycolation and heating. Hydromorphic conditions favor the transformation of organic polymers into small size organic acids, and thus, favor the intercalation of interlayer OM filling into the 2:1 clays. Pedogenesis processes involves both the weathering of clay minerals and the decomposition of OM, leading to formation of interlayer clay-organic complexes in a hydromorphic soil.

Adsorption characteristics of clay‐organic complexes and their role in shale gas resource evaluation

AbstractAdsorbed gas can share a significant portion of total gas content in shale reservoirs. At the same time, the adsorption characteristics of clay‐organic complexes which commonly exist in reservoir formations differ from other lithologies. To better understand the effect of adsorption characteristics of clay‐organic complexes on shale gas storage mechanism and estimation of resources, clay‐organic complexes were extracted from original core samples obtained from shales of Niutitang (NTT) and Longmaxi (LMX) formations in the northern Guizhou region, China. Petrophysical and adsorption experiments were performed and results show that the adsorbability of the clay‐organic complexes is obviously higher than regular shales in the reservoir. Therefore, the gas contents calculated based on the adsorbability of clay‐organic complexes are higher by 30%‐70% than that based on regular shales. Combined with other measured petrophysical properties, the NTT and LMX shales display a promising potential for further exploration and development. The clay‐organic complexes may accumulate in certain areas in the reservoir, and these accumulated areas could form the “sweet spots” for shale gas development. Methodologies and results presented in this study are beneficial in more accurately understanding gas storage mechanism, estimating gas resources and identifying sweet spots in shale reservoirs.

Pore characteristics of lacustrine mudstones from the Cretaceous Qingshankou Formation, Songliao Basin

Cretaceous Qingshankou ([Formula: see text]) mudstone of lacustrine origin is the major source rock for conventional hydrocarbon currently being produced in the Daqing and Jilin oilfields of the Songliao Basin, which is one of the largest continental basins in the world. Therefore, elucidating the geochemical and petrological characteristics of the [Formula: see text] mudstone is important to help determine its quality as an economically viable source for shale oil production. In our study, eight dark mudstone core samples from the [Formula: see text] formation were subjected to total organic carbon (TOC), Rock-Eval pyrolysis, X-ray diffraction, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and low-pressure [Formula: see text] gas adsorption (LPGA-[Formula: see text]) experiments. Geochemical and petrological analysis results indicated the presence of a high TOC content, which originated mainly from alginate and some plant-derived organic matter, whereas bitumen was frequently present in mudstones with thermal maturity in the oil-generation stage. The [Formula: see text] mudstones were comprised mainly of clay minerals, followed by quartz, feldspar, and carbonates. The LPGA-[Formula: see text] experiments revealed the presence of nanoscale slit-shaped pores, and the contribution from mesopores to the total pore volume was the highest in most of the samples. The average pore diameters (APDs) of the mudstone samples were all smaller than 20 nm (4.36–17.79 nm). We determined that there was a clear positive correlation between the APD and the free oil content; however, there were no clear correlations between the APDs and the quartz, carbonate, and TOC contents. FEM studies revealed the presence of intergranular pores with widths of approximately 10 μm, micron-level autogenetic organic matter pores within spores, organic matter pores caused by the hydrocarbon generation effect within organic matter or clay-organic complexes, and intraparticle pores within clays or pyrite framboids. The microlevel intergranular pores might play an important role in shale oil accumulation from source rock of lacustrine origin.

Investigation of adsorption of 5-Chlorouracil onto montmorillonite: An IR and Raman spectroscopic study

Abstract In this study, the adsorption of 5-Chlorouracil (5-ClU) on natural montmorillonite from Anatolia was investigated using FT-IR and Raman spectroscopy. The 5-ClU is a thymine antagonist and has some antitumor properties. The comparison of the vibrational spectra of the adsorbed 5-ClU with those of the free molecule provided data on the nature and characteristics of the clay organic complexes. The intercalation of 5-ClU within montmorillonite has been shown by X-ray diffraction to increase the interlayer spacing. Vibrational spectroscopy indicates that adsorbed 5-ClU molecules on montmorillonite are coordinated to exchangeable cations, directly or indirectly through water bridges.

Clay-organic complexes in a Polish loess soil

AbstractComplexes formed between clay and soil organic matter are important for carbon sequestration and for soil physical quality. Here, we use samples of loessial soil from South-East Poland to explore the phenomenon of complexing in loess. Soil samples were collected from a single catchment 8 years after the introduction of strip tillage and their compositions were characterized by traditional methods. Complexing was characterized in terms of the content of non-complexed clay which was estimated in two ways: firstly, by measurement of the content of readily-dispersible clay (which was assumed to be the non-complexed clay); and secondly, by calculation using algorithms that had been developed and evaluated previously. The calculations were based on the concept that, at carbon saturation, the clay/organic carbon mass ratio is equal ton. The calculations were done with a range of values ofn. It was assumed that the correct value ofnwas that which gave the greatest coefficient of correlation between the measured values of clay dispersion and the predicted values of non-complexed clay. For the loess used, the optimum value wasn= 14.

Soil organic matter fractions as affected by tillage and soil texture under semiarid Mediterranean conditions

The inherent complexity of soil organic matter (SOM) and its stabilization processes make suitable the identification of SOM fractions that reflect the management-induced changes in soil organic carbon (SOC) dynamics. This is of special interest in semiarid regions where the capacity of soil for agricultural production is limited. This study aims to evaluate the effect of different tillage and soil management practices on the distribution of C among SOM fractions and determine the influence of soil texture on the protection of SOC in a semiarid Mediterranean region (Aragon, NE Spain). Under on-farm conditions, pairs of adjacent fields under long-term no tillage (NT) and conventional tillage (CT) were compared in five different cereal production areas. In all cases, a nearby undisturbed soil under native vegetation (NAT) was included. Results indicate that the two isolated mineral-associated OM (Min) fractions, d-Min and μagg-Min (outside and within stable microaggregates, respectively), constituted the main part of total SOC (mean contributions of 54 and 26%, respectively) and were not consistently affected by soil management. Soil clay was a determinant factor for d-Min-C and total SOC (r2=0.60–0.70; P<0.001), indicating that chemical stabilization, through clay–organic complexes, seems to be a main preservation mechanism in the studied soils. Physical protection seems to be another SOC stabilization process in these soils due to strong correlation found between μagg-Min-C and the mass of water-stable microaggregates (r=0.900; P<0.0001). With smaller contributions to total SOC, the two labile fractions, coarse and fine particulate OM (cPOM and fPOM) were sensitive to soil management and their concentrations decreased as soil disturbance increased (NAT>NT>CT). The highest differences between NT and CT corresponded to fPOM at the soil surface where this fraction was 1.2–3 times higher under NT. Higher soil stratification ratios in NT, always >2 for the POM fractions, indicate an improvement in soil quality with long-term NT adoption in this semiarid Mediterranean region.

Micro- and nano-environments of carbon sequestration: Multi-element STXM–NEXAFS spectromicroscopy assessment of microbial carbon and mineral associations

Soil represents the largest reservoir of terrestrial organic C, and plays a critical role in global C cycling. In light of predicted climate change and a more unified approach to mitigate greenhouse gas emissions, the soil's ability to sequester C, and thus to act as a sink or a source for atmospheric CO2 has received growing interest. Organomineral assemblages are a unique niche in C cycling, with large capacity for storing anthropogenic C. However, the underlying biogeochemical mechanisms for C sequestration through organomineral associations are not yet well understood. One of the major challenges to study C sequestration in organomineral assemblages is lack of non-invasive analytical tools with a potential to obtain molecular-level information about the interactions between C and mineral components in submicron geochemical environments. In the present study, we have effectively employed synchrotron-based STXM–NEXAFS spectroscopy to access the K- and L-edges of biogeochemically relevant elements (C, N, Ca, Fe, Al, Si) to identify and image micro- and nano-C sequestration environments, and conduct submicron-level investigation of the compositional chemistry and other interactive features of C and minerals present in these hotspots using ultrathin section of intact organomineral assemblage. The C K-edge NEXAFS spectromicroscopy micrographs clearly demonstrated the existence of spatially distinct seemingly terminal micro- and nano-C repository zones, where organic C was sequestered in apparent agglomeration in the investigated organomineral assemblage. These submicron-C repository environments were only a few micrometers apart from each other; yet they were considerably different compositionally from each other. The organic C in the first repository environment was pyrogenic in origin, largely composed of quinone, phenols, ketones and aromatic ring structures. However, the second hotspot was dominated by filament-like structure, with striking similarity to the C 1s NEXAFS spectral signatures of organic C isolated from soil fungal and bacteria, and dominated by resonances from aliphatic-C and CN bonds of imidazol structures, carboxyl/carbonyl-C, amide- and O-alkyl-C functionalities. The composition of organic C in the organomineral interface around the strand-like structure was highly complex and composed of polysaccharides, amino sugars, amino acids, nucleic acids, and phospholipid fatty acid structures with polar and non-polar termini. The chemistry of mineral matter in the organomineral interface was also equally complex, ranging from Ca, Fe and Al ions, Fe and Al oxides, hydroxides and oxyhydroxides to phyllosilicates, which could provide a variety of polyvalent cations, hydroxyl surface functional groups and edge sites that can attract and bind microbial biomolecules. Based on the enormous complexity of the organic C functionalities and the coexistence of various inorganic components in the organomineral interface, it is possible to suggest that no single binding mechanism could be accountable for the organic C stored in the investigated submicron-C repository environment. Our results seem to suggest that the apparent C sequestration in the micro- and nano-C repository environment appear to be the cumulative result of physical protection and heterogeneous binding mechanisms ranging from ion exchange, hydrogen bonding, and hydrophobic bonding on silicate clay–organic complexes to adsorption on external and internal surfaces of clay minerals.

Carbonization of Clay-Organic Complexes and Its Possible Applications

Carbonization of Clay-Organic Complexes and Its Possible Applications

Sorption of organic compounds by hydroxy-interlayered clays through chelation and humification processes

This experiment was carried out to study the interaction of citric acid, hydroquinone and catechol on Montmorillonite and hydroxy-interlayered Montmorillonite clays. Montmorillonite (Mt) and its interlayered, viz., hydroxy-Fe (FeMt), mixed hydroxy-Fe,Al (Fe,AlMt), and hydroxy-Al (AlMt) counterparts were used for the study. Clay–organic complexes were prepared by aging clay suspensions at adjusted pH of 6, for 30 days after adding organics at the rate of 300 cmol/kg of clay. Controls without organics, namely, Mt, FeMt, Fe,AlMt, and AlMt, were aged and separated similarly. The CEC, specific surface area and total C were determined, and X-ray diffraction patterns were obtained for the separated solid phase. Final pH of each suspension was recorded and the absorbance spectra between 400 and 600 nm were obtained in the supernatants of clay–catechol and clay–hydroquinone suspensions. Final average pH of the clay suspensions in citrate (Ct), hydroquinone (HQ) and catechol (CC) systems were 6.8, 5.9 and 4.7, respectively. Specific surface area and CEC in FeMt, Fe,AlMt and AlMt clays increased significantly after aging with citric acid. Amounts of Fe and Al determined in the supernatant solutions of clay–catechol and clay–hydroquinone systems were in the range of 0 to 18 cmol(+)/kg of clay while in clay–citrate systems were 170 to 347 cmol(+)/kg of clay. The d-spacings of AlMtCt and Fe,AlMtCt were 1.26 nm and 1.24 nm, respectively, which were lower than the original values of 1.40 nm and 1.43 nm for AlMt and Fe,AlMt. Similarly, FeMtCt reported lower d-spacing of 1.26 nm in comparison to its original d-spacing of 1.33 nm in FeMt, after aging with citrate. Hydroxy-interlayered clays aged with HQ and CC did not show large changes in d-spacings. The absorbance values measured at 400 nm in catechol and hydroquinone systems were in the range of 0.16–0.95 and 0.05–0.21, respectively. The amounts of organic C retained by the solid phases in catechol systems were significantly greater than that for hydroquinone or citrate systems. Results of the study showed that the citric acid had caused the dissolution of the hydroxy-interlayer polymers in hydroxy-interlayered clay minerals, while hydroxy-interlayered clays catalyzed the formation of catechol- and hydroquinone-derived humic substances.

Adsorption of phenol and chlorophenols on pure and modified sepiolite

In this work, pure sepiolite and sepiolite modified by nitric acid (HNO3), ethylenediaminetetraacetic acid (EDTA) and hexadecyltrimethylammonium (HDTMA) were used ad adsorbents. The changes on the surface were studied by IR spectroscopy. The adsorption of solutions of phenol and phenol derivatives in pure ethanol on these adsorbents were examined by means of gas chromatography. It was found that the adsorption capacities of the clay-organic complexes (sepiolite-EDTA and sepiolite- HDTMA) were higher than those of pure sepiolite and sepiolite-HNO3.

Adsorption of aniline, phenol, and chlorophenols on pure and modified bentonite

In the present study, pure bentonite and bentonite modified by HNO3, EDTA, and HDTMA are adsorbents. The changes on the surfaces of bentonite samples are studied by IR spectroscopy. The adsorption of aniline, phenol, and phenol derivatives on these adsorbents is examined by means of gas chromatography. As the result of these examinations, it is seen that the adsorption capacities of clay-organic complexes (bentonite-EDTA and bentonite-HDTMA) are higher than those of bentonite-HNO3 and pure bentonite.

Ascomycete diversity in soil-feeding termite nests and soils from a tropical rainforest.

Molecular microbial ecology has revealed remarkable biodiversity - prokaryotic and eukaryotic - in numerous soil environments. However, no culture-independent surveys of the termitosphere exists, although termites dominate tropical rainforests. Here, we focused on soil feeders, building nests with their soil-born faeces, enriched with clay-organic complexes, thus contributing to the improvement of soil fertility. In order to assess the fungal community composition of these termitaries compared with soils not foraged by termites, samples of the two types were collected in the Lopé rainforest, Gabon, and processed for generation of fungal internal transcribed spacer (ITS) clone libraries. Although primers were universal, most of the recovered sequences represented Ascomycete that were previously uncharacterized and the proportions of which reached 72.5% in soils and 80% in termitaries. Their affiliation with identified fungi was analysed in performing a phylogenetic tree based on 5.8S rDNA. Furthermore, the ascomycete communities of soil-feeding termitaries and soils shared only 6.3% of sequences. This discrepancy of composition between soil and nest may result from the building behaviour of termites, as the organic matter in the nest is chemically modified, and some vacant ecological microniches are available for more specialized fungi.

Design and Synthesis of New Functional Materials Using the Interstices of Inorganic Host Structure

Effective use of the interstices of inorganic host structures is the key to develop new functional materials. The interstices in layer structured crystals are most versatile; the reaction concerning the interlayer space is called intercalation. Some examples of new functional materials developed using interstices are briefly reviewed, such as clay-organic complexes, porous pillared materials, interlayer grafting, anion exchangeable compounds, and layer structured nitride superconductors. A new silicon clathrate superconductor with a Si-sp3 cage structure is also introduced.

Whither Bio-Science?

Click to increase image sizeClick to decrease image size Additional informationNotes on contributorsSushil MukhopadhyaySushil Mukhopadhyay as a post-graduate student in the University of Calcutta, came under the influence of Acharya P C Roy, The 'Father of Indian Chemistry. He specialized in Physical Chemistry although his first love was for Physics. He obtained a First Class and stood 1st in Physical Chemistry and also completed the Associateship course of IARI, New Delhi, in soil Science and Agricultural Chemistry, in 1938. In 1945, he was awarded the DSc degree of the University of Calcutta for his work on the electrochemical properties of hydrogen clays. During the period 1943–1947, Prof Mukherjee worked on a project for making an inventory of agricultural resources which involved extensive survey work in eastern India, including the inaccessible coastal regions of east Bengal, the hills of Assam, and the jungles of the Orissa and Central India. It laid the foundations of soil survey work in India.In 1947, Prof. Mukherjee joined the Chemistry Department of the University of Calcutta as a Lecturer, later as a Reader, till 1957. Prof. Mukherjee research carrier spans from late thirties till today.Prof Mukherjee's list of publications (around 200 numbers) gives only the barest picture of the true extent of his work, for he refused to take any credit even in publications by his own doctoral student. His major areas of research are clay minerals, membrane electrodes, humic substance, clay-organic complexes, soil nutrients and also various aspects of physical chemistry, agricultural, environmental and social science research. During the heydays of his research, Prof Mukherjee came under the influence of Acharya S N Bose, FRS, from whom he imbibed the idea of science education through mother tongue. This he put into action during his stay in Indonesia.In Indonesia, Prof Mukherjee worked as an UNESCO Professor and Consultant from 1957 to I960. A Linguist by nature, he had an excellent command over German, French, Russian, Dutch and Indonesian. Later he wrote monographs in Indonesian on Chemistry, Physics and Mathematics.On his return to, India, he joined as Professor of Macromolecules at the Indian Association for Cultivation of science, Calcutta and within a year moved to the newly formed Kalyani University as the professor of Chemistry and Dean, Faculty of Science. In 1968, he became the Vice-Chancellor of the University of Kalyani. In the same year, he became a member of the committee on Science and Technology, Government of India and came in close contact with Mrs Indira Gandhi. In 1976, Prof Mukherjee returned to Calcutta as Director, Bose Institute and within a year became the Vice-Chancellor of the University of Calcutta. He retired from the University of December 31, 1978. Prof. Mukherjee is a Fellow of the Indian National Science Academy, Foundation Fellow of the National Academy of Agricultural Science, the first President of the West Bengal Academy of Science and Technology and former President of Indian Society of Soil Science, Platinum Jubilee Distinguished Service Award of Indian Science Congress Association, Dr B C Roy Birth Centenary Oration and the DSc Degrees (Honoris Causa) of the Universities of Kalyani and Burdwan. Prof. Mukherjee served as Secretary and Editor of the Indian Chemical Society and Indian Society of Soil Science and as Editor, Indian Journal of History of Science; he is currently Editor of Everyman's Science. He is currently President, IASC, Seniormost Member of the Council, Bose Institute, Vice-President, Asiatic Society and Vice-Chairman, Commission of Compilation of History of science in India. Prof, Mukherjee has co-authored a book of Soil Science and another of Genetics. He is also involved in literary activities.

CATION EXCHANGE CAPACITIES OF SAFRANIN, TOLUIDINE AND ALIZARIN COMPLEXES WITH MONTMORILLONITE

To obtain information about the cation exchange capacity (CEC) of montmorillonite as affected by the sorption of charged organic molecules, montmorillonite samples were loaded with different amounts of positively charged molecules of safranin, toluidine blue, and negatively charged alizarin red S. Dye sorption by the clay was carried out by equilibrating samples with different concentrations of the dye. The adsorbed amounts were determined from initial and final dye concentrations using spectrophotometric methods. The CEC of the clay-organic complexes were determined by the BaCl{sub 2} base exchange capacity method. The CEC was found to decrease linearly with the increase in the amount of safranin and toluidine in the complex, giving rise to a 1:1 charge neutralization ratio. For alizarin the CEC increased linearly but was not in proportion to the amounts of alizarin in the complex. This noncumulative phenomenon was attributed to the hindering of free diffusion of exchanging cations by the adsorbed molecules.

Adsorption Mechanisms of Phenol and Methylphenols on Organoclays

Eight clay–organic complexes were synthesized by placing quaternary ammonium cations (QUATs) on to bentonite (B) and kaolinite (K) by cation exchange. The organic cations used were hexadecyltrimethylammonium (HDTMA), dodecyltrimethylammonium (DDTMA), trimethylphenylammonium (TMPA) and tetramethylammonium (TMA). These organoclays were characterized via their organic carbon contents with the aid of XRD and FT-IR spectroscopic analyses. The organoclays were examined for their ability to adsorb phenol (P) and several of its methyl congeners [2,4-dimethylphenol (2,4-DMP) and 2,4,6-trimethylphenol (2,4,6-TMP)]. It was shown that inorganoclays (Na–clays) and organokaolinites were incapable of adsorbing any of these organic pollutants. It was also determined that the adsorption of phenol compounds from water decreased in the order: 2,4,6-TMP &gt; 2,4-DMP &gt; P for HDTMA–B and DDTMA–B, 2,4-DMP &gt; P &gt; 2,4,6-TMP for TMPA–B and P &gt; 2,4-DMP &gt; 2,4,6-TMP for TMA–B. With n-hexane as a solvent a different adsorption trend was found, which depended on the type and degree of solvent interaction with the organic compounds and the organoclays. It was observed that the degree of adsorption of phenols on to organoclays was dependent on the relative adsorbent-adsorbate energies and adsorbate–solvent interactions. The adsorption isotherms of phenols on to organophilic clays were evaluated according to the Giles classification.

Sorption of Selected Cationic and Neutral Organic Molecules on Palygorskite and Sepiolite

AbstractPalygorskite and sepiolite show a high sorption capacity for organic molecules. Adsorption of 2 organic cations, methylene blue (MB) and crystal violet (CV), by palygorskite and sepiolite were examined. The maximum sorption of MB and CV far exceeded the cation exchange capacity (CEC) of these minerals. This shows that, besides the contribution of free negative sorption sites (P-), the sites satisfied with sorption of single cations (PXi0) and neutral sorption sites (N) on clay surfaces may contribute to the sorption of organic cations. The number of neutral sites was determined by examining the sorption of 2 neutral organic molecules, triton-X 100 (TX100) and 15 crown ether 5 (15C5), and by application of the Langmuir isotherm.To determine the contribution of different sites, an adsorption model that applies the Gouy-Chapman equation and takes into account the formation of different clay-organic complexes in a closed system was employed. Application of this model to sorption data provided the calculation of binding coefficients for neutral sites, as well as the surface potential of the minerals at different sorbate concentrations.At sorption maxima, for both palygorskite and sepiolite, the contribution of neutral sites for sorption of organic cations was the highest, followed by the PXi0 sites in case of CV sorption, while in sorption of MB the contribution of P- sites was the second highest. The Fourier transform infrared (FTIR) patterns of clay-organic cation complexes compared with pure clays confirm that the sorption of organic cations is by silanol groups located at the edge of fibrous crystals, which account for neutral sorption sites.