Clay Minerals Kaolinite Research Articles

The influence of flocculant adsorption kinetics on the dewaterability of kaolinite and smectite clay mineral dispersions

Polymer mediated flocculation is central to efficient water recovery from and impoundment volume reduction of mineral waste tailings, particularly where clay minerals comprise a significant proportion. In this study, the adsorption kinetics of four high molecular weight polymeric flocculants onto colloidal, negatively charged kaolinite and smectite clay substrates under orthokinetic conditions has been investigated. For both kaolinite and smectite surfaces, the adsorption rate decreased in the sequence: non-ionic polyacrylamide homopolymer (PAM N) > anionic polyacrylamide-acrylate copolymer (PAM A) > non-ionic polyethylene oxide (PEO) > anionic polyacrylamide 2-acrylamido 2-methylpropane sulphonate copolymer (PAM S). Upon flocculation under laminar flow conditions, optimum subsidence rates for both clay types decreased according to flocculant type in the order PAM S > PEO > PAM A > PAM N, implying slower polymer adsorption rate facilitated higher floc settling behaviour. Calculation of first order rate constants for the adsorption of PAM N, PAM A and PAM S onto kaolinite at 25 °C and 50 °C and subsequent estimation of an activation energy in the range 14–22 kJ mol−1 polymer suggest that the overall energy is distributed among the transition state hydrogen bonds which are PAM polymer structure independent. Rationalisation of the results suggests that under industrially relevant conditions, flocculants with relatively slower tails’ particle attachment kinetics facilitate improved bridging performance and markedly enhanced settling behaviour.

Identification of Microfabric of Kaolinite Clay Mineral Using X-ray Diffraction Technique

A new method is introduced in this study to identify the microfabric (geometric arrangement of platelets) of cohesive soil using standard X-ray diffractometer. Various sampling techniques are used to prepare the Kaolinite clay samples with different microfabrics to assess the consistency and versatility of the proposed method. This method is based on identifying the presence of basal and prism peaks from the X-ray diffraction pattern and corresponding relative intensity values. The present study also demonstrates the conditions for which Scanning Electron Micrographs (SEM) are not capable of accurately identifying the microfabric of cohesive soils. The method proposed in this study uses relative amplitudes of basal and prism peaks avoiding difficult sample and surface preparation procedures, as used by previous researchers in their microfabric identification methods. The proposed method is found to be a rapid and accurate method for identifying the microfabric of Kaolinite clay and should prove to be valuable for routine implementation for studying structured natural clays.

Heterogeneous Reactions of Gaseous HNO3 and NO2 on the Clay Minerals Kaolinite and Pyrophyllite

Airborne clay mineral particles have long atmospheric lifetimes due to their relatively small size. To assess their impact on trace atmospheric gases, we investigated heterogeneous reactions on prototype clay minerals. Diffuse reflectance infrared spectroscopy identified surface-adsorbed products formed from the uptake of gaseous nitric acid and nitrogen dioxide on kaolinite and pyrophyllite. For kaolinite, a 1:1 phyllosilicate, HNO3 molecularly adsorbed onto the octahedral aluminum hydroxide and tetrahedral silicon oxide surfaces. Also detected on the aluminum hydroxide surface were irreversibly adsorbed monodentate, bidentate, bridged, and water-coordinated nitrate species as well as surface-adsorbed water. Similar adsorbed products formed during the uptake of NO2 on kaolinite at relative humidity (RH) of 0%, and the reaction was second order with respect to reactive surface sites and 1.5 +/- 0.1 for NO2. Reactive uptake coefficients, calculated using Brunauer, Emmett, and Teller surface areas, increased from (8.0 +/- 0.2) x 10(-8) to (2.3 +/- 0.4) x 10(-7) for NO2 concentrations ranging from 0.56 x 10(13) to 8.8 x 10(13) molecules cm(-3). UV-visible spectroscopy detected gaseous HONO as a product for the reaction of NO2 on wet kaolinite. The uptake of HNO3 on pyrophyllite, a 2:1 phyllosilicate, resulted in stronger signal for nitric acid molecularly adsorbed on the silicon oxide surface compared to kaolinite. Monodentate, bridged, and water-coordinated nitrate species bound to aluminum sites also formed during this reaction indicating that reactive sites on edge facets are important for this system. The uptake of NO2 on pyrophyllite, gammaBET = (7 +/- 1) x 10(-9), was significantly lower than kaolinite because NO2 did not react with the dominant tetrahedral silicon oxide surface. These results highlight general trends regarding the reactivity of tetrahedral silicon oxide and octahedral aluminum hydroxide clay surfaces and indicate that the heterogeneous chemistry of clay aerosols varies with mineralogy and cannot be predicted by elemental analysis.

Nanohybrid materials from the intercalation of imidazolium ionic liquids in kaolinite

A series of novel organic–inorganic nanohybrid materials were obtained by the intercalation in the interlamellar spaces of the clay mineral kaolinite, of ionic liquids based on imidazolium derivatives. The intercalation procedure was successfully accomplished via a melt reaction strategy using the dimethylsulfoxide–kaolinite intercalate (DMSO-K) as a precursor. 13C MAS NMR as well as XRD, TGA/DTA and FTIR studies confirmed the complete displacement of DMSO molecules by the imidazolium salts during the intercalation process. Increase of the basal spacing from 1.1 nm in DMSO-K to 1.3–1.7 nm in the nanohybrid materials was observed, indicating that imidazolium derivatives are oriented in a way such that the imidazole ring is parallel, or slightly tilted by an angle of 10–25°, with respect to the kaolinite internal surfaces. The number of moles of organic material loaded in the nanohybrids was obtained from several independent measurements. The intercalation of the imidazolium salts increases the thermal stability of the resulting material by more than 150 °C with respect to DMSO-K. After heating under air at 300 °C for two hours, XRD showed that the structure of the intercalates was kept with only a slight decrease of the intercalation ratio. The original kaolinite structure was recovered after heating the intercalate at 350 °C for an additional two hours. This observed high thermal stability is promising for the use of these nanohybrid materials as precursor for the synthesis of new nanocomposites by incorporation of polymer in kaolinite at high temperature.

Significance of kinetic theories on the recrystallization of kaolinite

Mathematical methods have been extensively used for the analysis of data obtained from non-isothermal thermal analysis of kaolinite or other clay minerals and Kissinger description is frequently considered. It is based on an Avrami-type transformation and an Arrhenian dependence of the reaction rate. In general, the calculation of the activation energy uses an incorrect neglect of the temperature dependence of the transformation rate. For kaolinite, Kissinger method applied to dehydroxylation gives an activation energy close to the measured enthalpy change for the reaction, but for recrystallization the activation energy exceeds the enthalpy change by a factor as high as 30. It is related to the complex character of recrystallization, since nucleation and crystal growth simultaneously occur, with the existence of both spinel and mullite phases. Consequently, the temperature dependence of recrystallization cannot be assumed to be Arrhenian. An interpretation is also found with Polanyi–Wigner equation applied to kaolinite transformations. Using thermodynamic data of entropy variation, the recrystallization rate should attain very high values, ranging from 5 to 10 order of magnitude over standard values for solid transformations. These observations cast some doubts on calculated activation energy of kaolinite recrystallization obtained from Kissinger kinetic method.

Modification of clay barriers with a cationic surfactant to improve the retention of pesticides in soils

In this work, the efficiency of reactive clay barriers in the immobilisation of organic pesticides in a sandy soil was studied. Reactive barriers were prepared by modification of montmorillonite, kaolinite and palygorskite clay minerals, and of a clayey soil with the cationic surfactant octadecyltrimethylammonium bromide (ODTMA). Percolation curves of the pesticides linuron, atrazine and metalaxyl of different hydrophobic character, were obtained in columns packed with a natural sandy soil with these barriers intercalated under saturated flow conditions. The cumulative curves in the unmodified soil indicated a leaching of pesticides greater than 85% of the total amount of compound added. After barrier intercalation, the breakthrough curves (BTC) indicated a dramatic decrease in the amounts of linuron leached in all columns and a significant modification of the leaching kinetics of atrazine and metalaxyl. Retardation factors, R, of the pesticides in the columns were significantly correlated with the organic matter content (OM) derived from the ODTMA of the organo clay/soil barriers ( r 2 ≥ 0.78). Significant correlations were also found between these R factors and the pore volume values corresponding to the maximum peaks of the BTCs ( r 2 = 0.83; p < 0.01) or the total volumes leached ( r 2 = 0.44; p < 0.05) for the pesticides atrazine and metalaxyl. The results obtained point to the interest in the use of reactive clay barriers for almost complete immobilisation of hydrophobic pesticides or for decreasing the leaching of moderately hydrophobic pesticides coming from point-like sources of pollution. These barriers would avoid the generation of elevated concentrations of these compounds in the soils due to their rapid washing.

The effect of some operating variables on the adsorption of lead and cadmium ions on kaolinite clay

Modification of kaolinite clay mineral with orthophosphate (p-modified sample) enhanced adsorption of Pb and Cd ions from aqueous solutions of the metal ions. Increasing pH of solutions of metal ions, increasing adsorbent dose and increasing concentration of metal ion, increased the adsorption of metal ions. Adsorption of both metal ions simultaneously on both unmodified and p-modified samples indicates that adsorption of one metal ion is suppressed to some degree by the other. The presence of electrolyte and their increasing concentration reduced the adsorption capacities of both unmodified and p-modified samples for the metal ions. Ca-electrolytes had more negative effect on the adsorption capacities of the adsorbents than Na-electrolytes. Ca-electrolytes reduced adsorption capacities of the adsorbents for Pb and Cd ions. From Langmuir plots it was observed that these electrolytes increased the binding energy constant of the metal ions unto the adsorbents especially on the p-modified samples. The rate of adsorption of Pb and Cd ions on p-modified adsorbent were increased and equilibrium of metal ion solution were more quickly reached (8 min for Pb ions and 12 min for Cd ions) with p-modified adsorbent as against 20 min for adsorption of both metal ions on unmodified adsorbent when 200 mg/L of metal ion solutions were used during the kinetic studies. When adsorption data were fitted against Langmuir, Freundlich, Toth and Langmuir–Freundlich isotherms, satisfactory fits were found with the Freundlich isotherm. However, at low concentration of metal ions, data also showed satisfactory fits to Langmuir isotherm.

KAOLINIZATION OF SAPROLITE DEVELOPED ON PAN AFRICAN GRANITE OF BATIE DISTRICT, WEST PROVINCE OF CAMEROON

The weathering process of the Pan African granitic rock of Batie was mineralogically investigated by means of Microprobe analysis (EPMA), X-ray diffraction (XRD), X-ray fluorescent (XRF), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The porphyritic granite is composed of biotite, feldspar and quartz as main minerals, whereas epidote, chlorite, kaolinite and mica clay mineral are secondary products. Mica clay mineral and kaolinite are main constituent clay minerals in the granite saprolite (weathered granite). Mica clay mineral predominantly occurs at the lower part of the investigated profile associating with a small amount of kaolinite. The granite saprolite at the top part of the profile consists mainly of platy kaolinite with a small amount of lath shape mica clay mineral. Mica clay mineral was formed in the hydrothermal clay veins occurring in the weathering profile. It is inferred that mica clay mineral occurred in the altered granite was formed by hydrothermal activity. Detailed observations of morphological variation by TEM with X-ray analysis revealed that crystal size and shape reasonably explain the transformation sequence of kaolinite as weathering proceeds. Close relationship between crystal size and morphology is obtained. Etch pits developed on quartz and K-feldspar grains are commonly observed. However, shape and size of the etch pits are quite complicated suggesting none monotonous micro-weathering condition. Etch pits found in the upper part are much rougher than those of the lower part. Based on the results obtained, weathering condition of the Batie granite was discussed mainly from the standpoint of clay mineralogy.

Enhanced terrestrial weathering/runoff and surface ocean carbonate production during the recovery stages of the Paleocene‐Eocene thermal maximum

The carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the Paleocene‐Eocene thermal maximum (PETM) (circa 55 Ma). The rapid release of large quantities of carbon into the ocean‐atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion (CIE). The brevity (120–220 kyr) of the PETM reflects the rapid enhancement of negative feedback mechanisms within Earth's exogenic carbon cycle that served the dual function of buffering ocean pH and reducing atmospheric greenhouse gas levels. Detailed study of the PETM stratigraphy from Ocean Drilling Program Site 690 (Weddell Sea) reveals that the CIE recovery period, which postdates the CIE onset by ∼80 kyr, is represented by an expanded (∼2.5 m thick) interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate. Collectively, the micropaleontological and sedimentological changes preserved within the CIE recovery interval reflect a transient state when ocean‐atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths. A prominent peak in the abundance of the clay mineral kaolinite is associated with the CIE recovery interval, indicating that continental weathering/runoff intensified at this time as well (Robert and Kennett, 1994). Such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering/runoff and carbonate precipitation helped sequester carbon during the PETM recovery period (e.g., Dickens et al., 1997; Zachos et al., 2005).

Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 °C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100–500 rpm) and time ( 15 / 60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of “honeycomb” particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20–22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5–7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.

Interactions of uranium with bacteria and kaolinite clay

We assessed the accumulation of uranium (VI) by a bacterium, Bacillus subtilis, suspended in a slurry of kaolinite clay, to elucidate the role of microbes on the mobility of U(VI). Various mixtures of bacteria and the koalinite were exposed to solutions of 8 × 10 − 6 M- and 4 × 10 − 4 M-U(VI) in 0.01 M NaCl at pH 4.7. After 48 h, the mixtures were separated from the solutions by centrifugation, and treated with a 1 M CH 3COOK for 24 h to determine the associations of U within the mixture. The mixture exposed to 4 × 10 − 4 M U was analyzed by transmission electron microscope (TEM) equipped with EDS. The accumulation of U by the mixture increased with an increase in the amount of B. subtilis cells present at both U concentrations. Treatment of kaolinite with CH 3COOK, removed approximately 80% of the associated uranium. However, in the presence of B. subtilis the amount of U removed was much less. TEM–EDS analysis confirmed that most of the U removed from solution was associated with B. subtilis. XANES analysis of the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both revealed that it was present as U(VI). These results suggest that the bacteria have a higher affinity for U than the kaolinite clay mineral under the experimental conditions tested, and that they can immobilize significant amount of uranium.

Densification behaviour of a red firing Brazilian kaolinitic clay

This study focuses on the complexity of the densification of a Brazilian kaolinitic clay sintered in air at various temperatures. The used kaolinitic clay comes from a large structural ceramics production region in South-Eastern Brazil (Campos-RJ). The samples were dry pressed in a cylindrical die and sintered at temperatures ranging from 750 °C to 1150 °C. XRD and SEM were used to identify the present phases and the densification level. The densification was measured by five parameters: specific surface, linear shrinkage, water absorption, apparent density, and compressive strength. The results revealed that sintering is governed by different mechanisms according to the temperature. A series of phase transformations takes place during sintering, which play an important role on the densification. Below 950 °C, sintering is governed by solid state diffusion mechanisms. Above 950 °C, sintering is governed by viscous flow mechanism with high influence on the densification of the green body. In addition, the red clay presented a refractory behaviour during firing due the high amount of kaolinite clay mineral, high loss on ignition, and the presence of gibbsite, which impairs sintering, resulting in greater porosity of the specimens.

Mineralogical, geochemical and palynological studies of late holocene mangrove sediments from northeastern Pará state, Brazil

Mangroves constitute an expressive ecosystem in the northeastern Amazon region and one of the best examples of them is located in the marine coastal plain of Para State close do Braganca City in northern Brazil. They were the subjects of our multidisciplinary researches carried out in past years. The gotten data included palynology, mineralogy, multi-element geochemistry and radiocarbon dating in order to get information about their formation conditions and transformation. This can help identify how this environment changed during the late Quaternary, mostly the paleoclimatic and continental-marine interaction in the region. The geological descriptions, the physicochemical data, the mineralogical and chemical composition and the multi-element geochemistry allow the identification of two zones in the 640-cm long drill core collected from the mangrove deposits. One acid, reduced and high salinity, rich in organic matter, clay minerals (smectite and kaolinite), halite, pyrite and feldspars from the surface up to 300 cm; and the other from 300 to 640 cm in depth, alkaline, oxidizing, with low salinity, and rich in diatoms and quartz. The chemical composition displays a signature of terrigenous material like latosol derived from the Barreiras Formation, and of marine influence (Sr, Ba, Na, K, Mg, Cl and F), as sources of material for the mangrove sediments. The pollen analyses and radiocarbon dates allow to identify three zones: the first two zones correspond to the near surface zone, deposited of low rates, in the last 1770 yr. The third zone can be correlated to alkaline and oxidizing zone. It was deposited from 2170 to 1770 yr. BP under high rates. The pollen diagram shows the domain of humid climate and the mineralogy and chemistry indicate a contribution of marine incursion and strong evaporation and oxidation close to the land surface

Influence of firing temperature on the ceramic properties of clays from Campos dos Goytacazes, Brazil

The characteristics of two clays used for red ceramic production in Campos dos Goytacazes, southeast of Brazil, were investigated. Characterization was performed by X-ray diffraction, chemical analysis, as well as granulometric and plasticity measurements. Technological properties related to water absorption, linear shrinkage and flexural strength were obtained from specific tests. Samples were prepared by pressing clay bodies at 20 MPa, which were then fired at temperatures from 850 to 1200 °C. The results showed that both clays from three deposits are highly plastic due to the elevated percentage of kaolinitic clay minerals. The samples richer in clay minerals present higher linear shrinkage as well as a decrease in water absorption in comparison to the others. The effectiveness of these clays for red ceramic production has been discussed in terms of the Winkler diagram.

Influence of firing temperature on the ceramic properties of clays from Campos dos Goytacazes, Brazil

The characteristics of two clays used for red ceramic production in Campos dos Goytacazes, southeast of Brazil, were investigated. Characterization was performed by X-ray diffraction, chemical analysis, as well as granulometric and plasticity measurements. Technological properties related to water absorption, linear shrinkage and flexural strength were obtained from specific tests. Samples were prepared by pressing clay bodies at 20 MPa, which were then fired at temperatures from 850 to 1200 °C. The results showed that both clays from three deposits are highly plastic due to the elevated percentage of kaolinitic clay minerals. The samples richer in clay minerals present higher linear shrinkage as well as a decrease in water absorption in comparison to the others. The effectiveness of these clays for red ceramic production has been discussed in terms of the Winkler diagram.

SORPTION OF PHENOXYACETIC ACID HERBICIDES ON THE KAOLINITE MINERAL SURFACE – AN AB INITIO MOLECULAR DYNAMICS SIMULATION

Full atomic position optimizations and ab initio molecular dynamics simulations at room temperature were performed in a study of the adsorption of phenoxyacetic acid herbicides on the octahedral surface of a kaolinite layer formed from hydroxyl groups. The studied molecules are bound strongly to the surface hydroxyl groups via hydrogen bonds formed through the carboxyl group. Particularly strong bonding with the hydrogen atom approximately midway between the two adjacent oxygen atoms was observed between the OH group of the carboxyl group and one of the surface OH groups. Molecular dynamics simulations showed proton jumps within this strong hydrogen bond. Kaolinite surface hydroxyl groups are chemically active and able to act as proton donors or acceptors. Additional interactions were observed between atoms of the aromatic parts of the adsorbed molecules and the surface hydroxyl groups. The phenoxyacetic acids are significantly more strongly bound than acetic acid to the octahedral kaolinite surface. This strong bonding of the phenoxyacetic acids to the kaolinite layer surface indicates a strong retention capability in the soil matrix and a significant contribution of kaolinite clay minerals to the “bound residue” phenomenon.

Sorption of 17 β-estradiol onto selected soil minerals

Sorption of the endocrine-disrupting chemical 17 β-estradiol (E 2) from aqueous solutions to goethite, an iron oxide, and the clay minerals kaolinite, illite, and montmorillonite (K and Ca forms) was measured at 25 °C. The clay minerals sorbed more E 2 than the oxide, with sorption capacity increasing in the order goethite ⩽ illite < kaolinite ⪡ montmorillonite. Uptake by goethite was rapid, with the maximum sorption (ca. 10% E 2 sorbed from a 1 ppm solution) reached within seconds. Initial sorption to the clay minerals was similar, but then it continued more slowly until about 10–15% of the total estradiol had been taken up after a period of 3 days by kaolinite and illite, and about 65% by montmorillonite. There was little pH dependence on the sorption, except for the goethite case where a sorption maximum occurred at pH 7–7.5. Most of the sorbed E 2 was desorbed from goethite, kaolinite, and illite into water or methanol easily and quickly (within seconds), but none was desorbed into either solvent from montmorillonite. These results suggest that E 2 is adsorbed at the surfaces of goethite, kaolinite and illite, but taken up into the interlayer spaces of montmorillonite. The c-axis spacing of montmorillonite decreased after sorbing E 2, indicating expulsion of water upon uptake of E 2 into the interlayer regions.

Mineralogy and Trace Element Contents of the Upper Carboniferous Coals from the Asma-Dilaver and Gelik Mines in Zonguldak, Turkey

This study is mainly focused on mineralogy and trace element contents of the 5 bituminous coal seams, upwards Cay, Acilik, Sulu, Hacimemis, and Kurul, from the Asma-Dilaver and Gelik underground mines in the Zonguldak Basin, Turkey. In addition, some properties of the Akalin seam from Karayigit (2001) were also used in the present study. The coal seams are located in the lower-middle part of the coal-bearing Kozlu Formation of the Westphalian A (Upper Carboniferous) age and are extensively exploited in the underground mines for mainly metallurgical cokes. A total of 43 channel coal samples that represent the whole coal thickness have been evaluated in the present study. The coal samples on an air-dried basis were characterized by variable ash yields and low total S contents. The identifiable minerals by X-ray diffraction in whole-coal samples include clay minerals (kaolinite, illite, and chlorite), quartz, calcite, dolomite, pyrite, and siderite. All calcite and dolomite, and some siderite and pyrite, were formed in cleat-fracture infillings. Calcite contents are much higher in the samples from the Asma-Dilaver mines than the Gelik mines, while their dolomite and pyrite contents are relatively lower. Accessory mineralogy in selected samples was determined with scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX). Elemental concentrations of the coal samples analyzed using inductively coupled plasma-mass spectrometry (ICP-MS) are relatively low, and the majority have variations in their contents among coal seams. The seam means of elemental concentrations, except for trace elements Cs, Mn, Rb, and Th in some seams, fall within the ranges of values for most world coals. Some trace elements (Sc, Cr, Cu, Ga, Rb, REEs, Y, Cs, Hf, Ba, Ta, Nb, Th, W, Zr, U, Zn, Pb, Bi, Tl, Be, Mo, and Co) in all the samples correlate positively with the ash yields, indicating that they are primarily associated with mineral matter. The remaining trace elements As, Cd, Ge, Mn, Sb, and Sr have no correlation with the ash yield.

Multi-component of heavy metal contaminants adsorptivity and compatibility onto variable charge clay mineral.

This work examines the adsorptivity of different combinations of lead, copper and cadmium ions onto the clay mineral kaolinite covering a wide range of concentrations of single, binary and ternary solutions. Batch adsorption equilibrium tests were used. The results of single Pb 2+ , Cu 2+ and Cd 2+ solutions were compared with those of binary Pb 2+ Cu 2+ , Pb 2+ Cd 2+ , Cu 2+ Cd 2+ and ternary Pb 2+ Cu 2+ Cd 2+ solutions. Results indicate that the adsorptivity of heavy metal ions is slightly lower in binary and ternary solutions than for single ion species in the solution. Lead shows a higher selectivity on kaolinite of the three heavy metal ions, while Cu 2+ and Cd 2+ give very similar selectivities.

Proposal for a new plasticity chart

This study investigates the consistency limits of the pure clay minerals kaolinite and montmorillonite, and their respective mixtures with fine silica sand in various proportions. Plotting the plasticity index data as a function of the liquid limit allows the zones where mixtures with the same clay contents fall to be defined. In particular, the line corresponding to 50% clay (designated as the 0·5C-line) makes it possible to distinguish the points that lie below the line, namely clay, from the points lying above the line in the silt zone. The clay zone includes inorganic soils with clay contents ≥50%, whereas the silt zone includes inorganic soils composed of silt and/or sand (2–425 μm) in percentages &gt;50%. A new plasticity chart, which aims to classify soils (&lt;425 μm) using the Atterberg limits, is defined herein. It differs from Casagrande's plasticity chart, especially in terms of its silt and clay zones, whose positions are reversed compared with Casagrande's chart. This can be explained by the fact that, contrary to what is commonly believed, in inorganic soils—liquid limits being equal—the plasticity index increases as the clay content decreases. Save only a few exceptions, the examples of inorganic soils plotted on the new plasticity chart lie above the 0·5C-line in the silt zone or below the line in the clay zone when their clay contents are less or greater than 50% respectively. On Casagrande's plasticity chart, the same soils lie above the A-line in the clay zone, regardless of their clay contents (9·7–100%). Only the kaolinite samples (relatively pure) lie below the A-line in the silt zone.