Palygorskite Samples Research Articles

Brazilian palygorskite as an alternative to commercial adsorbents for methylene blue: A discussion about composition, morphology and pore profile

Palygorskite has attracted particular attention as a specialized adsorbent due to its high specific surface area, porous texture and abundant surface groups, but its processing for commercial products makes the resulting material more expensive. In this scope, the aim of this work is to evaluate the potential of Brazilian naturally occurring palygorskite samples with low processing degree as an alternative to commercial palygorskites adsorbents for methylene blue, evaluating samples with different compositions, morphologies and microporous profiles. Materials were characterized using FTIR, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and surface area analysis (BET method). The Brazilian ones were processed in bar and disk mills and passed through a # 325 mesh sieve system. All samples showed common palygorskite X-ray diffraction patterns and specific surface area ranging from 100 to 147 m2/g. The application of clay samples was investigated for the adsorption of methylene blue (MB) dye, and the influence time of adsorption, initial dye concentration and adsorbent dosage were evaluated. The methylene blue adsorption was best described by the pseudo-second order model. The adsorption kinetics of methylene blue by palygorskite conforms to the pseudo-second-order model (R2 = 0,9997). The maximum removal capacity for methylene blue was determined to be 694 (±36.53) mg/g. Additionally, the Freundlich model demonstrated the most favorable mathematical fit. Adsorption capacities varied between 49 and 150 mg/g for 300 mg/L MB solutions, with noteworthy performance exhibited by Brazilian samples, achieving up to twice the adsorption compared to their commercial counterparts, despite possessing lower specific surface areas. The presence of two distinct pore modes, centered at 25 and 45 Å, proved pivotal in the sample with the highest adsorption capacity, reaching adsorption equilibrium at 40 min.

Adsorption of Glyphosate by Palygorskite

Glyphosate affects ecosystems due to exposure of non-target crops and is a persistent contaminant at low concentrations. The application of palygorskite to reduce glyphosate contamination in Brazil is an environmentally friendly way to remediate impacted areas. This research evaluated palygorskite application for glyphosate adsorption present in a synthetic effluent. Palygorskite samples were ore dressed by wet granulometric classification and wet magnetic separation and submitted to organophilization with cetyltrimethyl ammonium bromide solutions at concentrations of 0.01, 0.1, 1.0 and 1.5% (w/w), and the organo-palygorskite was applied in glyphosate adsorption tests. After ore dressing there was an increase in its cation exchange capacity from 19 to 41 meq 100 g-1 and the surface area was 149 g m-2. The 1.0% organo-palygorskite adsorbed about 86% of glyphosate from synthetic aqueous effluent. Based on this high adsorption yield, the organo-palygorskite is a potential adsorbent for remediation of effluents containing the toxic herbicide glyphosate.

Thermally Modified Palygorskite Usage as Adsorbent in Fixed-Bed Reactor for High Concentration NH4+-N Removal and Further Application as N-Fertilizer in Hydroponic Cultivation.

Palygorskite sample (Pal) underwent thermal treatment at 400 °C (T-Pal) to be used as adsorbent for the removal of 200 mg NH4+-N/L from artificial solution. After thermal treatment, the sample was characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). For NH4+-N removal, T-Pal was added as a bed matrix in fixed-bed reactor experiments and the effect of flow rate was determined. It was indicated that with the flow rate increase from 10 mL/min to 50 mL/min, fewer liters of the solution were purified, rendering a longer residual time of interactions, which is optimal for NH4+-N removal from T-Pal. The maximum removed amount was calculated at 978 mg NH4+-N (qtotal), suggesting T-Pal is a promising ammonium adsorbent. The data of kinetic experiments were applied to Clark, Yoon–Nelson, and Thomas kinetic models, with Clark having the best fit, highlighting a heterogenous adsorption. At the end of kinetic experiments, T-Pal applied in hydroponic cultivations and presented a sufficient release rate, which was found utilizable for saturated T-Pal usage as N fertilizer that satisfactory results were deemed concerning lettuces characteristics and growth.

Ca2+ removal from water by the use of Na-palygorskite for potential water softening

Abstract Sodium-treated palygorskite (Na-Pal) sample was investigated for the sorption of Ca2+ ions with the aim of treating water hardness. The effective modification of the mineral with Na+ was verified by XRD and FT-IR techniques. Batch kinetic experiments in standard solutions were performed proving that 30 g/L of Na-Pal were highly satisfactory as the Ca2+ removal reached the 85% for 100 mg/L Ca2+ initial concentration, which is very promising for the softening of moderate or hard waters. The Ca2+ removal found to be pH and temperature independent, with high removal rates at room temperature and common pH values of water samples (pH 4–12), rendering these circumstances ideal for the low-cost maintenance of the procedure that took place within the first 5 min. The linear form of the Langmuir isotherm model expressed better (R2 = 1) the Ca2+ sorption, which means that takes place at specific homogeneous sites of Na-Pal. Thermodynamic analysis proved the non-spontaneous (positive ΔG0), physical, and exothermic nature (ΔH0 = −10.8197 kJ/mol) of the reaction, while the kinetic models proved the chemisorption of Ca2+ by Na-Pal.

Comparison of Surface Properties of Sepiolite and Palygorskite: Surface Energy and Nanoroughness.

The surface properties of two sepiolite samples and one palygorskite sample were compared using inverse gas chromatography (IGC). Samples were previously conditioned at appropriate temperatures for the removal of all zeolitic water. Dispersive (or Lifshitz–van der Waals) component of the surface energy (γsd), specific interactions (−ΔGas) with π electron donor bases (1-alkenes), and nanomorphology indices based on the injections of cycloalkanes and a branched alkane were measured. From IGC data, at 240 °C, it was found that the palygorskite was clearly distinguished from the sepiolites. The palygorskite possessed a lower γsd, larger −ΔGas with 1-alkenes, and remarkably higher . Slight differences could also be observed between the two sepiolite samples with the same origin. The results were rationalized in terms of the structural features of the two studied minerals. The larger channels of the sepiolite allow for a better insertion of the n-alkanes (longer retention times) while excluding the bulkier probes, such as cyclooctane or 2,2,4-trimethylpentane. Accordingly, the corresponding γsd values were larger and the values were lower (higher surface nanoroughness) for the sepiolites. Regarding Lewis acid–base properties, all the sample’s surfaces evidenced a very strong amphoteric character. The present results highlight the potential of the evaluated samples for, e.g., adsorption processes with volatile organic compounds or matrix–filler interactions regarding the production of composite structures with Lewis acid–base matrices.

Raw and modified palygorskite in water treatment applications for low-concentration ammonium removal.

Raw palygorskite (Pal) samples went under acid (H-Pal), NaCl (Na-Pal), and CaCl2 treatment (Ca-Pal) in order to be examined as ammonium (NH4 + ) sorbents from aqueous solutions. The samples were characterized by XRD and FT-IR techniques to examine potential structural differences after modifications, and batch kinetic experiment series were applied to determine the optimal conditions for NH4 + removal. According to thermodynamic analysis, the removal reaction for sodium- and calcium-treated samples was endothermic (ΔΗ0 >0, 1.65kJ/mol and 24.66kJ/mol, respectively), in contrast with the exothermic reactions of raw and acidic-treated palygorskite samples (ΔΗ0 <0, -37.18kJ/mol and -27.56kJ/mol respectively). Moreover, each sample presented a different order of sorbed ions preference, whereas the strong affinity for Ca2+ sorption was common in all cases since the NH4 + removal inhibited. Nevertheless, a similar pattern was followed for raw and modified samples at isotherm study, rendering the linear form of Freundlich isotherm to express better the NH4 + sorption on palygorskite sample, indicating that it is a heterogeneous procedure. In all cases, the NH4 + maximum uptake was within 15min using 8g/L of each sorbent, especially for the Na-Pal sample, which could reach almost 100% removal of low concentration NH4 + . PRACTITIONER POINTS: Modified palygorskite samples were tested for NH4 + removal from aqueous solutions. NaCl-treated palygorskite had the higher removal efficiency, which could reach almost 100% removal of low concentration NH4 + . NH4 + maximum uptake was within 15 minutes using 8 g/L of each sorbent. NH4 + adsorption was an endothermic reaction for NaCl- and CaCl2 -treated palygorskite sorbents. NH4 + adsorption was an exothermic reaction for raw and acid-treated palygorskite sorbents.

Modification of the textural properties of palygorskite through microwave assisted acid treatment. Influence of the octahedral sheet composition

Five palygorskite samples from different geological environments including lacustrine and perimarine deposits and hydrothermal fillings were treated by a microwaveassisted acid leaching process inaqueous HNO3 solution (0.2 M). In all cases, the samples have been characterized by X-ray fluorescence (XRF), X-ray diffraction (FTIR), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption at −196 °C and Scanning electron microscope (SEM). The mineralogical study indicates that palygorskite is the predominant mineral although the presence of other associated minerals has been observed including: quartz, calcite, dolomite, feldspars, smectite, illite-mica and traces of chlorite and sepiolite. After the acid treatment the main mineralogical change is the disappearance of the carbonates, not being observed in any case the occurrence of amorphous silica. Palygorskite remains virtually unchanged from acid attack in four of the samples studied. Only in the sample with the highest Mg(II) content (Mace), mineralogical and chemical data evidence the partial solution of the octahedral layer in the fibrous clay mineral due to the release of magnesium. The textural study indicates significant differences in the specific surface area of the samples ranging from 75 to 225 m2 g−1, this variation being related mostly to the purity of the samples. Under similar experimental conditions, palygorskite is more resistant to acid attack than magnesian clay minerals (saponite or sepiolite). In addition, a relationship has been observed between the magnesium content of palygorskite and the susceptibility to microwave-assisted acid attack. In all cases, an increase in the specific surface area value has been observed, reaching a highest SBET value of 354 m2 g−1 for Mace sample after 16 min of microwave-assisted acid treatment as a consequence of the partial leaching of its octahedral sheet, although its fibrous structure is maintained yet.

Effects of pH on the gel properties of montmorillonite, palygorskite and montmorillonite-palygorskite composite clay

The effects of pH on the structures, compositions, morphologies, Zeta potential, and gel properties of montmorillonite, palygorskite and their composite clays were investigated in the study. With the increase in pH, the above properties of montmorillonite, palygorskite and their composite clays showed different changing trends. The compositions of montmorillonite and palygorskite basically remained unchanged in the pH range of 1–13. The dissociation and dispersion degrees of montmorillonite sheets, the separation and dispersion degrees of palygorskite fiber cluster and the absolute value of Zeta potential increased. The viscosity of palygorskite sample firstly increased and then decreased. The viscosity of montmorillonite and composite clay samples increased and the increase was rapid especially at pH above 12. The viscosity of montmorillonite and composite clay samples reached 9151 mPa·s at pH 13, but the viscosity of composite clay sample was lower than that of montmorillonite at the same pH value. The influencing factors of viscosity mainly included the dissociation degree of montmorillonite sheets, the separation degree of palygorskite fibers and the Zeta potential. The higher degrees of dissociation and dispersion corresponded to the higher viscosity. With the increase in the absolute value of Zeta potential, the viscosity of montmorillonite and composite samples increased, but the viscosity of palygorskite increased firstly and then decreased. The potential mismatch between palygorskite and montmorillonite was responsible for the lower actual viscosity of the composite sample compared to the calculated viscosity.

Adsorption of Salmonella in Clay Minerals and Clay-Based Materials

A series of clay minerals and clay-based materials have been tested to eliminate one of the most dangerous bacteria we can find in the water: Salmonella. It has been proven that the use of clays and their PCH materials can be a suitable method for removing Salmonella from water. The results of this initial study show that all the materials analyzed have great salmonella adsorption capacities ranging from the lowest value observed in the mont-PCH sample (0.29 × 1010 CFU g−1) to the highest value observed in the natural palygorskite sample (1.52 × 1010 CFU g−1). Macroporosity, accessible external surface area, and the presence of silanol groups in the external surface of the particles appears to be the controlling factors for Salmonella adsorption capacity while it seems that the structural characteristics of the clay minerals and their respective PCH does not affect the adsorption capacity.

Comparative Analysis of Palygorskite Samples From Different Occurrences in Guadalupe (Piauí, Brazil)

Palygorskite is a clay mineral that has several industrial and environmental applications. Palygorskite main deposits in Brazil are located in the municipality of Guadalupe, Piauí. A comparative study was performed with five samples of palygorskite from different locations through ore dressing and chemical and mineralogical characterization, using the XRD, XRF and methylene blue titration techniques. According to the results, there are significant differences in the samples composition. Among them, the most significant difference was the cation exchange capacity (CEC) value, which ranged from 24.0 to 41.0 meq.100 g-1, followed by the content of some oxides and the crystalline phases present. Despite coming from the same region, the samples contained distinct impurities.

Mineralogical and Geochemical Discrimination of the Occurrence and Genesis of Palygorskite in Eocene Sediments on the Northeastern Tibetan Plateau

AbstractPalygorskite is a widely used indicator of semiarid to arid environments in paleoclimate studies. In this study, we present detailed mineralogical and geochemical investigations exploring the genesis of palygorskite found in Eocene fluvial sediment in the northern Qaidam Basin on the northeastern Tibetan Plateau. The presence of two types of palygorskite is revealed, based on their crystallinity characteristics and distinctive rare earth element (REE) patterns in the coexisting clay fraction. Well‐crystallized palygorskite samples are characterized by remarkably negative Ce anomalies and obvious middle rare earth element enrichment. Poorly crystallized palygorskite samples generally exhibit positive Ce anomalies and less pronounced middle rare earth element enrichment, which resemble those of nonpalygorskite‐bearing clay samples. Given the presence of an overall oxidized fluvial sedimentary environment, we attribute the well‐crystallized palygorskite (which has textures comprising long, interwoven fibers) to direct precipitation (i.e., neoformation) occurring within a reducing environment during early/postdepositional processes while the poorly crystallized palygorskite (which is characterized by short, club‐shaped single crystals) originates as catchment‐delivered detritus. These poorly crystallized palygorskites occur mostly in 49.5–47.0 Ma and are accompanied by decreasing kaolinite content, increasing chlorite content, and abundant xerophytic spore‐pollen from the Qaidam Basin, and its neighboring Xining Basin. Collectively, these evidences suggest that a less humid climate followed after the Early Eocene Climate Optimum.

Effect of acid activation of palygorskite on their toluene adsorption behaviors

Abstract In this paper, acid-activated palygorskite (APal x ) samples were prepared by a facile acid treatment method with different concentrations of HCl (0.5, 1, 3, 5 and 7 mol/L). The dynamic toluene adsorption performances of APal x were evaluated and the relevant adsorption mechanism was discussed. The prepared adsorbents were characterized using X-ray diffraction (XRD), elemental analysis, transmission electron microcopy (TEM), nitrogen adsorption-desorption isotherms and Fourier-transform infrared spectroscopy (FTIR). The results show that the palygorskite has a good resistant ability to acid attack, the structure still remains when the acid concentration is as high as 7 mol/L. Acid activation could significantly enhance the surface area (228, 250, 271, 273, 329 and 308 for Pal, APal0.5, APal1, APal3, APal5 and APal7, respectively) and porosity of palygorskite. APal5 has the best toluene adsorption capacity (90.4 mg/g) due to its highest S BET (329 m 2 /g) and V micro (0.055 cm 3 /g). The adsorption performance in terms of dynamic toluene adsorption capacities follows the order of Pal (44.6 mg/g) x to become a promising candidate for the adsorption of volatile organic compounds in practical applications.

Thermally activated palygorskites as agents to clarify soybean oil

Palygorskite, a fibrous clay mineral, exhibits excellent adsorbent properties. This study was conducted to assess the potential activation of palygorskite and to obtain thermally activated samples to use as clarifying agents for soybean oil. Previously, the palygorskite samples were thermally activated at various temperatures in the range of 100–900°C for 24h. The natural and activated samples were characterized using the following techniques, XRD, XRF, FTIR, SEM, SSA, CEC and thermal analysis, to observe the structural and morphologic alterations after thermal treatment. These characterizations indicated that the primary changes to the palygorskite surface referred to losses of structural water: physically adsorbed, zeolitic and coordination water molecules. The sample was activated above 700°C, which potentiated the clarification of the soybean oil by the removal of the carotenoid dye and other pigments, and exhibited higher performance compared with the natural palygorskite.

The water effect on instrumental hardness and adhesiveness of clay mixtures for pelotherapy

This study was designed to assess several clay-water mixtures in terms of their instrumental texture to identify candidates for use as peloids in pelotherapy. Eight commercially available clays (including three from Spanish quarries) were characterized in terms of their mineralogical composition (X-ray diffraction). Using each clay, series of mixtures containing different proportions of distilled water were prepared and hardness and adhesiveness measurements made using a Brookfield® texture analyzer. The data obtained were then used to derive exponential equations describing the hardness and adhesiveness of the mixtures depending on their water content. Four new parameters were also defined: reference water content for adequate hardness and adhesiveness and water content required to reduce hardness or adhesiveness by half. The bentonites composed of Mg-smectite with interlayer Na, need the higher water contents to obtain hardness/adhesiveness values in the range of Spanish peloids, follow the bentonites composed of Mg-smectite with divalent interlayer cations and dioctahedral smectites (Al-smectite). Sepiolite and palygorskite samples also need high water contents. Kerolite-stevensite and kaolins showed the lower water contents. According to the equations and parameters defined, peloids similar to those currently used in spas could be tailored for pelotherapy.

Sorption of Cd2+ on mercapto and amino functionalized palygorskite

Mercapto and amino functionalized palygorskite samples were prepared by nanotexturization method, respectively, and applied for the sorption of Cd2+ from aqueous solution to investigate the sorption mechanism and assess the application potential for the remediation of Cd polluted water and soils. The samples before and after sorption were characterized through XRD, FTIR, 29Si CP/MAS NMR and XPS. The sorption thermodynamics, kinetics and mechanisms of Cd2+ sorption on mercapto and amino functionalized palygorskite were studied. Langmuir isotherm was proved to describe the sorption data better and pseudo second order kinetic model could fit the sorption kinetic processes well. Functionalization increased the sorption amounts significantly compared to pristine palygorskite. The positive enthalpy change confirmed that the sorption process was endothermic. The positive entropy changes revealed that sorption of Cd2+ was driven by entropy changes. Combined the results of analyses of the diffraction peaks by XRD, vibration modes of functional groups by FTIR, chemical shifts by 29Si CP/MAS NMR and binding energies of key elements by XPS, the sorption mechanisms were complexation with mercapto or amino groups, and surface precipitation of CdCO3.

A comparative study about adsorption of natural palygorskite for methylene blue

Various methods including acid treatment, heat treatment and surface modification have been used to improve the adsorption properties of natural palygorskite. However, the comparative study about the effect of source of palygorskite on the adsorption properties remains a gap to be filled. Here we first studied the structure and chemical composition of three palygorskite samples from Jiangsu, Anhui and Gansu Provinces of China using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and X-ray Fluorescence Spectrometry (XRF). Subsequently, the adsorption properties of the palygorskites for methylene blue (MB) were evaluated and compared. The palygorskite from Jiangsu (JSHS) is Mg-poor and has an analogous dioctahedral structure. The palygorskite from Anhui (AHGS) is Mg-rich, and has an intermediate structure of dioctahedron and trioctahedron. The palygorskite from Gansu (GSHN) also has an intermediate structure of dioctahedron and trioctahedron, but is associated with muscovite, clinochlore, dolomite and feldspar. The maximum adsorption capacity of the palygorskites from JSHS, GSHN, AHGS for MB at 303K is 158.03, 98.34, 77.92mg/g, respectively. It was found that a lower Mg content and the dioctahedral structure of palygorskite are favorable to its adsorption for MB. More negative value of Gibbs free energy (△G0) for JSHS further illustrates that JSHS has higher efficiency in removing the MB molecules than the others. The adsorption mechanism studies suggest that the zeolitic H2O plays a fundamental role in the interaction between MB and palygorskite.

Effects of Sodium Salts Organic Acids Modification on the Microstructure and Dispersion Behavior of Palygorskite Nano-Powder via High-Pressure Homogenization Process

High-pressure homogenization could disaggregate the crystal bundles of palygorskite and favor the adsorption of electrolyte ions onto its surface through the produced cavitation, shear, and turbulence forces, and has evident influences on the micromorphologies and properties of clay. In this work, a series of palygorskite samples modified with sodium citrate, sodium benzoate, sodium lactate, sodium acetate, and sodium propionate were obtained under the condition of high-pressure homogenization. The effects of type and concentration of sodium salts organic acids on the microstructure, morphology, surface charge, and physicochemical property of palygorskite were studied through x-ray diffraction (XRD), N2 adsorption–desorption isotherm, field emission scanning electron microscopy, zeta potential, rotational viscosity, and rheological measurements. XRD results confirmed that the crystal structure of homogenized palygorskite was not changed after introduction of sodium salts organic acids, but the aggregates were effectively disaggregated. Modification of palygorskite with sodium citrate made the surface more negatively charged, and the samples exhibited higher specific surface area and rheological properties. This work provided a method to improve the rheological properties of palygorskite suspension through dispersion of clay in sodium citrate solution followed by homogenization at 30 MPa.

Influence of Anions on the Electrokinetic and Colloidal Properties of Palygorskite Clay via High-Pressure Homogenization

A series of palygorskite samples modified with electrolytes including KCl, KBr, KI, KH 2 PO 4 , KHSO 4 , K 2 HPO 4 , K 2 SO 4 , and K 3 PO 4 were prepared with the aid of high pressure homogenization. The changes of electrokinetic and rheological properties, as well as suspension stability of obtained palygorskite, were investigated through measurement of the zeta potential, flow curve, and sedimentation volume. The influences of charge, concentration, and type of anions on surface charge density of palygorskite were compared. The correlation among the surface charge, the rheological behavior, and suspension stability of palygorskite was discussed. The homogenization process could favor the migration of anions onto palygorskite. It was found that the structure maker anions (H 2 PO 4 − , HSO 4 − , HPO 4 2 − , SO 4 2 − , and PO 4 3 − ) made the surface of palygorskite more negatively charged. The flow curve measurements demonstrated that the association capacity of rods depended on the surface potential of palygorskite. A stable suspension was obtained when palygorskite was dispersed in K 2 SO 4 solutions and homogenized at 30 MPa.

An infrared spectroscopic comparison of four Chinese palygorskites

Infrared spectroscopy has been used to characterize and compare four palygorskite mineral samples from China. The position of the main bands identified by infrared spectra is similar, but there are some differences in intensity, which are significant. In addition, several additional bands are observed in the spectra of palygorskite and their impurities. This variability is attributed to differences in the geological environment, such as the degree of weathering and the extent of transportation of the minerals during formation or deposition, and the impurity content in these palygorskites. The bands of water and hydroxyl groups in these spectra of palygorskite samples have been studied. The characteristic band of palygorskite is observed at 1195cm−1. Another four bands observed at 3480, 3380, 3266 and 3190cm−1 are attributed to the water molecules in the palygorskite structure. These results suggest that the infrared spectra of palygorskites mineral from different regions are decided not only by the main physicochemical properties of palygorskite, but also by the amount and kind of impurities.

Relationship between the geochemistry of organic matter and the generation of palygorskite in Jiangsu-Anhui border and Gansu Province, China

Soluble organic matter had been separated from several palygorskite and bentonite samples in the Jiangsu-Anhui border area (across Jiangsu Province and Anhui Province) and Linze County in Gansu Province of China and was analyzed with the techniques and methods of organic geochemistry. The composition and distribution of hydrocarbons were analyzed by gas chromatography (GC). Organic stable carbon isotopic ratios (δ13C) in typical samples were determined. The abundance of soluble organic matter in all clay samples analyzed was low. In Jiangsu-Anhui samples, the preservation states of organic matter are different; hydrocarbons in organic matter have some features of aquatic plankton but are short of the input of terrigenous higher plants; organic δ13C in a palygorskite of Yongxiaoshan in Xuyi County, Jiangsu Province, is −6.72‰. These features may be typical of a sedimentary environment of closed or semi-closed and relatively isolated different waters near coast or seashore. On the contrary, in samples from Gansu, the preservation states of organic matter are good; the GC graphs of hydrocarbons show that the precursors of the organic matter are from a mixed source of aquatic organisms and land-sourced higher plants; organic δ13C of a palygorskite from Yangtai of Gansu is −15.62‰. It indicated that the sedimentary environment may be an inland salty lake. Preliminary results suggest that palygorskite minerals in the Jiangsu-Anhui area may be evolved from rapidly accumulated fine material or volcanic ash, but clays in Gansu Province may be transformed from terrigenous inorganic clastic components carried to the lake through river and then deposited. The generation process of the samples studied in the paper seems to be related to salty water.