Mixed Clay Minerals Research Articles

Evaluation of the Influence of pH on the Release of Exchangeable Cations from a Mixed Clay Mineral Deposit for Replenishment of Soil Nutrients

Soil nutrients consist of minerals such as Ca, Mg, K and Na ions among others which are essential to plant growth. Soils can become deficient in these nutrients on account of pollution, flooding and over cultivation. The soil condition can be ameliorated by addition of clay minerals which are rich in aforementioned cations. The mineralogy of the clay mineral was investigated using X-ray Diffractometer (XRD) and the effect of pH variation on the release of exchangeable cations of the clay mineral deposit were investigated by varying the pH of the solution in which the clay mineral was immersed whereas the amount of the cations released were determined using Atomic Absorption Spectrophotometer(AAS) and Flame Emission Spectrophotometer. Three clay minerals clinochlore, kaolinite and illite were detected. The quantity of cations released from the clay mineral varied with pH; and the pH at which the maximum quantity of the cations were released were pH4 for K+ ions(4.63±0.38cmol/kg), pH7 Ca2+ (12.09±0.96 cmol/kg) and Mg2+(3.48±0.08 cmol/kg) ions and pH8 for Na+(7.81±0.58 cmol/kg) ions respectively for site 1. This trend was observed in the three sites that were studied. This study has revealed that different pH conditions are required if this mixed clay mineral is to be employed in the remediation of nutrient deficiency in any soil in respect of a particular mineral.

Assessment of Clay Deposits Quality from East of Erbil, Kurdistan Region, Iraq for some Ceramic Industries

For the assessment of clay deposits for brick manufacturing, seven clay samples from different locations were collected by channel sampling method from Injana, Mukdadiyah, Bai Hassan formations and Quaternary deposits in Bestana village, the study area is located east of Erbil city (NE Iraq). For ceramic manufacturing, the quality of clay should be measured according to some physical properties. The mineralogical and geochemical study revealed by using X-ray diffraction and chemical characteristics, which represented that all clay samples containing; kaolinite, smectite, illite, and chlorite with some mixed clay and non-clay mineral quartz, calcite, dolomite, and feldspar. The physical properties of clay samples including grain size analysis and Atterberg limits showed that the raw materials contain clay in high proportion, silt in medium proportion, and sand in minor proportion. Plasticity index of the studied samples showed that they are moderately plastic to plastic range. The geochemical analysis of the studied samples showed that the clay raw materials are composed mainly of silica and alumina, which act as refractory material in the ceramic industry. In addition to that, there are different proportions of calcium, iron oxides, magnesium, potassium, and sodium, which are flux oxides.

Soil Chemistry and Clay Mineralogy of an Alluvial Chronosequence from the North Carolina Sandhills of the Upper Coastal Plain, USA

Temporal changes in soil development were assessed on fluvial terraces of the Little River in the upper Coastal Plain of North Carolina. We examined five profiles from each of six surfaces spanning about 100,000 years. Soil-age relationships were evaluated with inter-surface clay mineral comparisons and regression of chemical properties versus previously reported optically-stimulated luminescence ages using the most developed subsoil horizon per profile. Bases to alumina (Bases/Al2O3) ratios have negative correlations with age, whereas dithionite-Fe (FeD) concentrations are positively correlated with time and differentiate floodplain (<200 yr BP) from terrace (≥10 ± 2 ka) soils and T4 pedons (75 ± 10 ka) from younger (T1-T3b, 10 ± 2–55 ± 15 ka) and older (T5b, 94 ± 16 ka) profiles. Entisols develop into Ultisols with exponentially decreasing Bases/Al2O3 ratios, reflecting rapid weatherable mineral depletion and alumina enrichment during argillic horizon development in the first 13–21 kyr of pedogenesis. Increasing FeD represents transformation and illuviation of free Fe inherited from parent sediments. Within ~80–110 kyr, a mixed clay mineral assemblage becomes dominated by kaolinite and gibbsite. Argillic horizons form by illuviation, secondary mineral transformations, and potentially, a bioturbation-translocation mechanism, in which clays distributed within generally sandy deposits are transported to surface horizons by ants and termites and later illuviated to subsoils. T5b profiles have FeD concentrations similar to, and gibbsite abundances greater than, those of pedons on 0.6–1.6 Ma terraces along Coastal Plain rivers that also drain the Appalachian Piedmont. This is likely because the greater permeability and lower weatherable mineral contents of sandy, Coastal Plain-sourced Little River alluvium favor more rapid weathering, gibbsite formation, and Fe translocation than the finer-grained, mineralogically mixed sediments of Piedmont-draining rivers. Therefore, recognizing provenance-related textural and mineralogical distinctions is crucial for evaluating regional chronosequences.

Experimental Research of Shale Pellet Swelling in Nano-Based Drilling Muds

The drilling of clay-rich formations, such as shale, is an extremely demanding technical and technological process. Shale consists of mixed clay minerals in different ratios and in contact with water from drilling mud. It tends to swell and cause different wellbore instability problems. Usually, the petroleum industry uses various types of salt and/or polymers as shale hydration inhibitors. The aim of this research was to determine whether nanoparticles can be used as shale swelling inhibitors because due to their small size they can enter the shale nanopores, plug them and stop further penetration of mud filtrate into the shale formation. Swelling of bentonite-calcium carbonate pellets after 2 and 24 h in water and drilling mud (water, bentonite, PAC and NaOH) without nanoparticles and with addition of TiO2 (0.5, 1 and 1.5 wt%) and SiO2 (0.5, 1 and 1.5 wt%) nanoparticles was measured using a linear swell meter. Additionally, granulometric analyses of bentonite as well as the zeta potential of tested muds containing nanoparticles were performed. Based on the laboratory research, it can generally be concluded that the addition of SiO2 and TiO2 nanoparticles in water and base drilling mud reduces the swelling of pellets up to 40.06%.

Salt coagulation or flocculation? In situ zeta potential study on ion correlation and slime coating with the presence of clay: A case of coal slurry aggregation

The aggregation state of mineral slurry by coagulant with the presence of clay nanosheets appears similar to a flocculation gel with the absence of flocculant. The interactions between particles in mixed clay and quartz minerals systems are influenced by the interactions of ion correlation and slime coating, which creates zeta potential variation. Particle concentration has a substantial effect on zeta potential, and coal slurry has a relative high particle concentration. To realize an in situ aggregation study, zeta potential measurement of coal slurry was performed using electrokinetic sonic amplitude (ESA) without dilution at different calcium ion concentrations and pH values. The zeta potentials of three minerals commonly occurring in coal slurry (quartz, kaolinite and montmorillonite) with similar particle concentrations were also measured. The result suggests that aggregation of coal slurry by calcium ions in the presence of clay minerals belongs to fluctuation. The ion correlation and slime coating could be detected by ESA with a decrease in zeta potential under high calcium ion concentration conditions. The face-face coagulated clay nanosheets were formed by ion correlation, acting as a “flocculant chain”. The adsorption force between the “flocculant” and particles is described as a slime coating. This flocculation process is referred to as “salt-clay-coagulation-flocculation” (SCCF). During ion correlation, rearrangement of the electric double layer between face-face spaces causes a reduction of the zeta potential. The super-fine negatively charged clay nanosheets might coat onto the quartz particle surfaces under the effect of electrostatic attraction force and Ca2+ ion correlation. Quartz and clay minerals were oppositely charged because the special adsorption of calcium ions on the clay basal face was restricted in hexatomic rings.

Integrated reservoir characterization of the Paleozoic and Mesozoic sandstones of the El Ouar field, Algeria

This study presents the interpretation of depositional environment and petrophysical properties of Mesozoic and Paleozoic reservoirs from the south-eastern Berkine Basin, Algeria by integrating core analyses and geophysical logs. Sedimentary structures and ichnofossils identified from 100 m of recovered cores have been interpreted to characterize the depositional settings of the studied reservoirs. During the mid-late Triassic, fluvial to marginal marine processes deposited the TAGS and TAGI reservoirs, while the Palaeozoic megasequences are characterized by shallow marine reservoirs (tidal bars and foreshore deposits) interbedded with thin marine shales. Porosity and water saturation have been estimated from geophysical logs and calibrated with core-based laboratory measurements. An empirical relationship between core porosity and permeability has been established for the El Ouar area and the same has been employed to generate a continuous and confident permeability profile against the target reservoir formations. Petrophysical characterization indicates a higher porosity and permeability in Triassic and Carboniferous sandstones than the Devonian F6 members. Triassic TAGS and TAGI sandstones possess the highest reservoir qualities in the El Ouar field. The Thorium and Potassium content available from spectral gamma-ray data have been utilized to identify the clay types associated with various sandstone reservoirs (Illite in Triassic sandstone, Kaolinite in Carboniferous units, mixed clay and Th bearing heavy mineral dominance in Devonian units). The study will be helpful for understanding of hydrocarbon resource potential and subsequent production planning in the study area.

Thermal analysis and FT-IR spectroscopy of synthetic clay mineral mixtures

Common clays and especially mixed-layered or interstratified clay minerals are generally mixtures of predominantly clay mineral along with minor quantity of another clay mineral, wherein the ratio of the components will determine the resulting properties of these clay materials. This study focuses on IR spectroscopy and TG/DTA analysis and their contribution to the identification of clay minerals in two-component mixtures. Identifying clay minerals in such mixtures by means of thermal analysis is often complicated by the similarity of the thermal effects of the individual clay components. Similarity in thermal behavior is mainly connected with the origin, chemical variability and crystal structure of phyllosilicates. The main problem is overlapping thermal effects of clay minerals or thermal effects related to accessory minerals (calcite, quartz, etc.) on DTA curve. A similar problem also appears in the identification of mixed clay mineral structures by infrared spectroscopy. There are also more or less overlapping absorption bands in the infrared spectra for the mixtures of clay minerals. In this paper, the prepared clay mixtures were supposed to partially simulate the natural mixed clay structures and a minimum content of detectable minerals in clay mixtures were determined according to characteristic peaks on the DTA curves and absorption bands in FT-IR spectra. The results of both methods showed that kaolinite is the most reliable detectable mineral. The detection limit for thermal analysis corresponds to 3% mass kaolinite in admixture with chlorite or montmorillonite, and 1% mass kaolinite for both of these mixtures is based on IR spectroscopy. In case of montmorillonite and chlorite, the identification by FT-IR spectroscopy shows detection limit only 30% mass in contrast to TG/DTA with the detection limit of 5% mass for montmorillonite and 5% mass or 10% mass for chlorite. The obtained results can be effectively used to solve problems in identification of clay minerals in sedimentary rocks, which is very important for subsequent applications in geotechnical, geothermal, and mining activities.

Influence of Clay Content and Montmorillonite Content on Swelling Behavior of Expansive Soils

Swelling behavior of an expansive soil is principally governed by the contents of montmorillonite mineral and clay present in it. Studies attributing the swelling behavior to the presence of montmorillonite mineral are numerous, but defining an intricate relationship between clay and montmorillonite contents is almost nil. Thus, a comprehensive study is undertaken in this technical note that can aid in quantifying the exact influence of clay content (CC) and/or montmorillonite content in clay content (MCCC) on the swelling behavior. Interrelating CC and MCCC parameters is also another objective of the paper. Several numbers of different expansive soils were collected from different regions of India and experiments were conducted to quantify free swell index (FSI), CC, and MCCC. The results demonstrate that it is not only CC, but also MCCC has a remarkable influence on the swelling behavior. It has, particularly, been noticed from the interpretation of results that the role of mixed clay minerals, which is contrasting to a common belief that it is only MCCC primarily contributes to the swelling phenomenon and is least attempted by research fraternity, cannot be subdued. The study finds that between MCCC and CC, the former parameter seems to be more reliable for accurate prediction of swelling potential. The relationship between CC and MCCC seems to be linear up to MCCC of 40%. Beyond MCCC of 40%, CC apparently clustered between 30 and 60% only. MCCC, even though, found in minor quantity, exhibited significant influence on the FSI. The results presented in the study bear a practical significance for the safe design of foundation systems, buried pipelines, etc., in/on the expansive soils.

A novel method to calculate the gas adsorption of mixed minerals

Five groups of methane isotherm adsorption tests were carried out at 61 °C under a pressure range of 0–25 MPa, including four groups of pure clay minerals (illite, montmorillonite, chlorite, kaolinite, for brief they are expressed as Ill, Mont, Chl, and Kaol respectively) and a group of mixed minerals by four pure clay minerals in equal mass ratio. The experimental results showed the order of methane adsorption of pure clay minerals: Kaol > Ill > Mont > Chl. And the composition of clay minerals was obtained by XRD experiments. The result showed that the four samples were of high purity, both of which were greater than 90%. In addition, the results of low-pressure nitrogen adsorption experiments showed the order of specific surface area: Kaol > Ill > Mont > Chl, which is consistent with the order of methane adsorption. The methane adsorption is positively correlated to the specific surface area. The adsorption data was fitted to the Langmuir–Freundlich model to establish the method to calculate the adsorption of mixed minerals. The result showed that the parameters of the adsorption model of mixed clay minerals can be obtained by summing the parameters of the adsorption model of the pure minerals contained in the mixture according to their constituent mass ratio and the feasibility of this result was also verified by literature data. Overall, once the mass ratio in mixed clay minerals gets known, its theoretical adsorption can be calculated.

Quantification of clay mineral microporosity and its application to water saturation and effective porosity estimation: A case study from Upper Ordovician reservoir, Libya

The relative volume of clay minerals contributing to the microporosity is the main feature that influences the estimation of water saturation in hydrocarbon reservoirs. For developing a genuine understanding of reservoir quality, the present study elucidated the petrography, quantification of clay minerals, and microporosity, besides their effect on the petrophysical parameters. The ratified method is an integration of core data, SEM (Scanning Electron Microscopy), XRD, and thin section. The most identified clay minerals in order of decreasing abundance are kaolinite (45%), Illite (35%), a mixed layer (10%), smectite (5%) and others are 5%. The estimation of clay mineral microporosity was based on the SEM photomicrographs. Mixed clay minerals have a variety of textures with microporosity values that range from 10 to 55%. In this regard, the clay microporosity data was used to calculate the effective clay volume; the clay bound water, the effective water saturation and porosity. As a result, the estimated values are decreased when the microporosity is considered, except for the effective volume of clay minerals which is approximately twice (52.5%) as the original dry mineral volume. Moreover, the microporosity based water saturation decreased dramatically when compared to log values up to 22. 37%. The above-estimated values correlated with both core and log readings using linear regression. The derived relationships with a high correlation coefficient (R2) were used to extrapolate microporosity, clay bound water, effective saturation and effective porosity in the uncored well interval. The correlation coefficient R2 is higher than 90%.

A Thermal Event in the Ordos Basin: Insights from Illite 40Ar-39Ar Dating with Regression Analysis

Four samples from a Permian reservoir in the Ordos Basin of North China were separated into twelve fractions in grain sizes of < 0.5, 0.5–1 and 1–2 μm. Using the 40Ar-39Ar step-heating method, all of the fractions essentially yielded plateau ages ranging from 172.5 to 217.1 Ma. These scattered plateau ages might not have been obtained from pure diagenetic illites but from mixed clay minerals, although the samples were disaggregated using a gentle freeze-thaw cycle to free them of non-clay minerals. A regional thermal event, as suggested by several proxies, led to intensive illitization as a distinct diagenetic process when the Yanshanian Movement triggered magmatism around the entire North China Block during the Jurassic to Cretaceous. Thermal illites formed during a short time period, whereas detrital illites came from various sources. The scattered plateau ages could have resulted from mixed degassing of thermal and detrital illites. Within one sample, the plateau ages decrease with the diminution of grain sizes, but it is difficult to extrapolate to the detrital-illite-free ages. Because the plateau age is a mixture of ages for thermal and detrital illites, this regression analysis studies the dependence of the plateau ages on the synthetic values of contents and ages of detrital illites instead of on the grain sizes. Comparing the samples to one another, the plateau ages show the same trend among the different grain sizes. Weighted by the contents and ages of detrital illites, linear regression analysis revealed the relationship between the plateau ages and the relative weight proportions. Based on iterated calculations, a thermal event age and a set of weight proportions were derived. The regressed thermal event age is 163.3±1.6 Ma, which coincides with regional thermal activities and links to gas accumulation.

Hydraulic conductivity and leachate removal rate of genetically different compacted clays

Genetically different clays were compacted, contaminated and cured for 21 days with natural leachate from an old active waste disposal site and subsequently remolded at both West Africa (WA) and Modified AASHTO (MA) energies of compaction. The clays were thereafter investigated with a view to understanding the effect of contamination on hydraulic conductivity and mineralogy of the clays, soil–leachate interaction, influence of the energy of compaction and rate of leachate removal with time. Clay mineralogy revealed the presence of mixed clays including Anatase, Calcite, Hematite, Kaolinite, Quartz and Illite. The presence of these mixed clay minerals confers both attenuation and containment properties on the clays and, hence, makes the soils suitable for use as barriers in landfills. Hydraulic conductivity of the undisturbed and uncontaminated clays reduced with increase in energy of compaction from WA to MA. Leachate addition resulted in varied responses from the clays attributable to the different genealogy of the soils. Furthermore, the rate of leachate removal for the soils was observed to be 3.0 × 10-3 cm/s for SMP 1, 4.0 × 10-3cm/s for SMP 2 and 8.0 × 10-2 cm/s for SMP 5. These observations from the different soils are in agreement with results recorded in terms of consistency, hydraulic conductivity, mineralogy and compaction properties. However, influence of leachate on the structure of the genetically different soils played a contributory role in alteration of their mineralogy and, hence, their hydraulic conductivity.

Adsorption Behavior of Cd2+ and Zn2+ onto Natural Egyptian Bentonitic Clay

In the present work, an Egyptian bentonitic clay sample has been structurally characterized using different techniques such as XRD, IR, SEM, and EDX analyses then evaluated as a sorbent for heavy metal ions removal. The characterization results showed that the clay sample is in the bentonite form with montmorillonite and kaolinite as mixed-clay minerals. The specific surface area (SSA) and cation exchange capacity (CEC) were determined using methylene blue test and they were found to be 367 m2/g and of 85 meq/100 g, respectively. The applicability of this clay sample for Cd (II) and Zn (II) removal from aqueous media was tested using batch procedures. Experimental parameters affecting the removal process were analyzed to get optimum conditions for the process. The experimental kinetic data were fitted very well to pseudo-second order with very high correlation coefficients. The Freundlich model appeared to correlate the adsorption data much better than Langmuir model with maximum adsorption capacities of 8.2 and 9.45 mg/g for Cd2+ and Zn2+, respectively. Successful application of the studied adsorbent for the removal of Cd2+ and Zn2+ ions from natural water samples greatly supports its potential for practical application.

Chemical Analysis of Rock and Water from dug Wells in a Residential Area in Lagos State, Nigeria

Samples of rock deposit dug out from wells at Alimosho local government in Lagos state, Nigeria were characterized for chemical composition and ultimate utilization. Fourier Transform Infrared Spectroscopy (FTIR), X-Ray diffraction (XRD) and Atomic Absorption Spectroscopy (AAS) were used to identify the rock as a mixed clay rock containing 35.04% Illite, 25.64% Illite plus Quartz, 22.20% Kaolinite and 17.09% Feldspar. This was corroborated by cation determination that showed the rock to be predominantly clayey rock. The mean concentrations of lead and copper in water of the wells in the rock location are 0.004mg/L and 0.05mg/L respectively while cadmium is less than detectable limit. The well water in the area studied is therefore not contaminated by these heavy metals. Heavy metals removal by the mixed clay from polluted underground water was studied using AAS. A general increase of sorption was observed with increase in the adsorbent dosage. 20g of the rock adsorbed a higher percentage of copper (80.23%) than lead and cadmium that were 70.25% and 65.83% respectively. The percentage of heavy metals adsorbed confirms the use of mixed clay minerals as a contaminants removal from the underground polluted water. The rock adsorbed copper readily than cadmium and lead. The maximum amount of lead removed from the contaminated underground water of the defunct battery site across the adsorbent dosage (5g, 10g, 15g and 20g) were 1.20mg/L, 3.19mg/L, 3.69mg/L and 4.09mg/L respectively indicating the effect of increase in adsorbent dosage in remediating the lead contaminated water. This data showed that the rock can be used to remove these heavy metals from contaminated water.

Rare earth and major element geochemistry of Eocene fine-grained sediments in oil shale- and coal-bearing layers of the Meihe Basin, Northeast China

The Meihe Basin is a Paleogene pull-apart basin. Long-flame coal, lignite and oil shale are coexisting energy resources deposited in this basin. Ninety-seven samples, including oil shales, coals, brown to gray silt and mudstone, have been collected from the oil shale- and coal-bearing layers to discover the rare earth element geochemistry. The total REE contents of oil shales and coals are 137–256μg/g and 64–152μg/g respectively. The chondrite-normalized patterns of oil shales and coals show LREE enrichments, HREE deficits, negative Eu anomalies and negligible Ce anomalies.The chemical index of alteration (CIA) as well as some trace elements is often used to reflect the paleoenvironment at the time of deposition. The results show that fine-grained sediments in both layers were deposited in dysoxic to oxic conditions and in a warm and humid climate, and coals were deposited in a warmer and more humid climate than oil shales. Oil shales and coals are both in the early stage of diagenesis and of terrigenous origin. Besides, diagrams of some major, trace and rare earth elements show that the fine-grained sediments of both layers in the Meihe Basin are mainly from the felsic volcanic rocks and granite, and that their source rocks are mostly deposited in the continental inland arc setting.The analysis of major elements shows that Si, Al, K and Ti, in both layers, are found mainly in a mixed clay mineral assemblage and that Si is also found in quartz. Sodium occurs primarily in clay minerals, whereas Ca is found mainly in the organic matter. In the coal-bearing layer, iron is mainly controlled by organic matter rather than detrital minerals. In contrast, in the oil shale-bearing layer, neither detrital minerals nor organic matter exert a control on the iron content. Analyzing the relationship between rare earth elements and major elements shows that REEs in the oil shales and the coals are both of terrigenous origin and are mainly controlled by detrital minerals rather than by organic matter. In both layers, REEs have no relationship with fine-grained phosphates, and during the weathering process, the REEs were not very mobile and were resistant to fractionation.

Vanadium and Nickel Speciation in Pulverized Coal and Petroleum Coke Co-combustion

Vanadium and nickel in emissions from fossil-fuel combustion and in the fly ash can be an environmental concern. The fly ash from the combustion of a 70% coal/30% petroleum coke blend in a 500 MW pulverized-fuel utility boiler was studied by a variety of X-ray, optical microscopy, and electron beam methods. The fly ash V and Ni are present in heterogeneous silicates, glass, sulfates, oxides and oxyhydroxides, and crystalline and/or amorphous mixed clay minerals, and also in Ni, detrital ferromagnesian silicates. Vanadium- and Ni-bearing spinels are incorporated into magnetite structures. Multiwalled nanotubes encapsulate V and Ni, and C60, C70, and C80 fullerenes and their derivatives are present.

Experimental Study on the Influence of Clay Minerals on the Yield Stress of Debris Flows

AbstractIt is common knowledge that a relationship exists between the volumetric sediment concentration, the percentage of clay mineral content, and the activity of clay minerals (which is related to the clay type) and the yield stress of a debris flow mass. In this paper, the effect of four types of common clay minerals (montmorillonite, illite, chlorite, and kaolin) on the yield stress of mixtures were investigated in a quantitative way. Laboratory experiments were carried out with single and mixed clay mineral types, various volumetric concentrations, and percentages of clay mineral content. For the same clay content and same volumetric concentration, a decreasing effect was found, respectively, of montmorillonite>illite>kaolin on the yield stress of the flow mixture, whereas the effect of chlorite was equal to that of kaolin. A concept of equivalent clay mineral percentage (P0) is introduced in this paper, in which the value of 1 is taken as the characteristic coefficient of kaolin in the experiments....

Plant Availability Index by Potassium Exchange Isotherms in Selected Rice Soils of Lesser Himalayas

Potassium (K) exchange isotherms (quantity–intensity technique, Q/I) and K values derived from the Q/I relationship provide information about soil K availability. This investigation was conducted to study Q/I parameters of K, available K extracted by 1 N ammonium acetate (NH4AOc) (exchangeable K plus solution K), K saturation percentage (K index, %), and the properties of 10 different agricultural soils. In addition, the relationship of mustard plant yield response to the K requirement test based on K exchange isotherms was investigated. The Q/I parameters included readily exchangeable K (ΔK0), specific K sites (KX), linear potential buffering capacity (PBCK), and energy of exchange of K (EK). The results of x-ray diffraction analysis of the oriented clay fractions indicated that some mixed clay minerals, illite clay minerals, along with chlorite/hydroxy interlayered vermiculite and kaolinite were present in the soils. The soil solution K activity ratio at equilibrium (AR0) ranged from 8.0 × 10−4 to 3.1 × 10−3 (mol L−1)0.5. The readily exchangeable K (ΔK0) was between 0.105 to 0.325 cmolckg−1 soil, which represented an average of 88% of the exchangeable K (Kex). The soils showed high capacities to maintain the potential of K against depletion, as they represented high linear potential buffering capacities (PBCK) [13.8 to 50.1 cmolc kg−1/(mol L−1)0.5. The EK values for the soils ranged from −3420 to −4220 calories M−1. The percentage of K saturation (K index) ranged from 0.7% to 2.2%. Analysis of variance of the dry matter (DM), K concentrations, and K uptake of mustard plants indicated that there were no significant differences among the adjusted levels of K as determined by the exchange-isotherm curve.

Mechanisms of heavy metal sorption on alkaline clays from Tundulu in Malawi as determined by EXAFS

Chromium(III), copper(II), zinc(II), cadmium(II), mercury(II) and lead(II) cations are among the most common heavy metal pollutants in industrial waste waters. In our continued work on cost effective wastewater heavy metal removal agents and methods using local material, this study examines the interactions of chromium(III), copper(II), zinc(II), cadmium(II), mercury(II) and lead(II) cations with natural mixed clay minerals from Tundulu in Malawi using extended X-ray absorption fine structure (EXAFS) spectroscopy. The mixed clays were previously characterised and found to contain illite, low ordered kaolinite, mixed layer minerals and the non-clay mineral carbonate fluoroapatite with a mean pH PZC of 9.63. The EXAFS analyses provided qualitative evidence that oxygen atoms occupy the first coordination shells in all the studied central atoms. The metal species on the clay mineral surfaces seem to be adsorbates and/or precipitates of hydrolysis products. Chromium(III) forms a polynuclear hydrolysis complex on the mineral surface with Cr–O bond and Cr⋯Cr distances of 2.00 and 3.03 Å, respectively, which is indicative of a chain structure with edge sharing CrO 6 octahedra. Copper(II) is bound to phosphate groups on the surface at low pH and has a first shell of coordinated oxygen atoms with Jahn–Teller distortion as revealed by different Cu–O bonds of 1.96 Å for the equatorial ones, at 2.30 and 2.65 Å for the axial oxygens, and a Cu–P distance at 3.29 Å is distinguished as well. Upon treatment at neutral pH copper(I) oxide seems to be the main precipitation product on the clay surface. At neutral pH zinc(II) forms also polynuclear hydrolysis complexes with Zn–O bond and Zn⋯Zn distances of 2.01 and 3.11 Å, respectively, which shows the presence of edge sharing ZnO 4 tetrahedra. Cadmium(II) is adsorbed to the clay surfaces as a six-coordinated CdO 6 complex in octahedral fashion, but it is not possible to distinguish if cadmium is hydrated or partly hydrolysed. Mercury(II) is present as linear O–Hg–O units but without any observable Hg⋯Hg distance at high pH showing that mercury(II) is hydrolysed but not present as mercury(II) oxide. At low pH, linear O–Hg–Hg–O units are present showing that mercury(II) is reduced to mercury(I). No precise chemical environment around the lead(II) could be obtained for the lead(II) treated clays due to formation of different hydrolysis structures with multiple coordination numbers by lead(II) salts on the mixed clays.

Environmental perturbation in the southern Tethys across the Paleocene/Eocene boundary (Dababiya, Egypt): Foraminiferal and clay mineral records

Foraminiferal and clay mineral records were studied in the upper Paleocene to lower Eocene Dababiya section (Egypt). This section hosts the GSSP for the Paleocene/Eocene boundary and as such provides an expanded and relatively continuous record across the Paleocene/Eocene Thermal Maximum (PETM). Deposition of illite–smectite clay minerals is interpreted as a result of warm and arid conditions in the southern Tethys during the latest Paleocene. Benthic foraminiferal assemblages are indicative of seasonal variation of oxygen and food levels at the seafloor. A sea-level fall occurred in the latest Paleocene, followed by a rise in the earliest Eocene. Foraminiferal diversity and densities decreased strongly at the P/E boundary, coinciding with the level of global extinction of benthic foraminifera (BEE) and start of the Carbon Isotope Excursion (CIE) and PETM. In the lower CIE, the seafloor of the stratified basin remained (nearly) permanently anoxic and azoic. A sudden increase in mixed clay minerals (kaolinite and others) suggests that warm and perennial humid conditions prevailed on the continent. High levels of TOC and phosphathic concretions in the middle CIE are evidence for increased organic fluxes to the sea floor, related to upwelling and to augmented continental runoff. Low densities of opportunistic taxa appeared, indicating occasional ephemeral oxygenation and repopulation of the benthic environment. The planktic community diversified, although conditions remained poor for deep-dwelling taxa. An increase in illite–smectite dominated clay association is considered to mark the return of a seasonal signature on climatic conditions. During the late CIE environmental conditions changed to seasonally fluctuating mesotrophic conditions and diverse and rich benthic and planktic foraminiferal communities developed. Post-CIE planktic faunas consisted of both deep and shallow-dwelling taxa and buliminid-dominated benthic assemblages reflect fluctuating mesotrophic conditions. The frequent environmental perturbations during the CIE/PETM at Dababiya provided a rather specialized group of foraminiferal taxa (i.e., Anomalinoides aegyptiacus) the opportunity to repopulate, survive and subsequently dominate by a hypothesized capacity to switch to an alternative life strategy (population dynamics, habitat shift) or different metabolic pathway. The faunal record of Dababiya provides insight into the cause and development of the BEE: various severe global changes during the PETM (e.g., ocean circulation, CaCO 3-dissolution, productivity and temperature changes) disturbed a wide range of environments on a geologically brief timescale, explaining together the geographically and temporally variable character of the BEE. This allowed a number of specific but different foraminiferal assemblages composed of stress-tolerant and opportunistic taxa to be successful during and after the periods of environmental perturbations associated with the PETM.