Natural Bentonite Clay Research Articles

Removal process of an industrial dye using a biosorbent: characterization, kinetic, equilibrium, and thermodynamic studies

Adsorption-based removal is a highly efficient environmental phenomenon employed to eliminate various dyes, such as crystal violet (CV), which is prevalently used in the textile industry and subsequently discharged into natural ecosystems. This study aims to utilize natural bentonite clay sourced from Algeria for the extraction of cationic dye (CV) from wastewater. The characterization of the bentonite was conducted using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD). Evaluations assessed the impact of various parameters including pH, stirring time, temperature, and initial dye concentration on the adsorption efficiency. Optimal conditions for the maximal adsorption of CV were determined to be 430.18 mg g-1 at an adsorbent-to-dye solution ratio of 1 g L-1, pH 11.06, an equilibrium time of 40 minutes, and a temperature of 40°C. The adsorption kinetics were best described by the pseudo-second-order model, while the Freundlich isotherm model aptly described the adsorption isotherms. Thermodynamic parameters underscored the spontaneous and exothermic nature of the crystal violet removal process using raw bentonite. This research provides novel insights into the effective removal of a cationic dye from water and wastewater using Algerian bentonite clay.

Removal of Pb(II) ions from aqueous solutions using natural and HDTMA-modified bentonite and kaolin clays

This work focused on the removal of Pb(II) from aqueous solution using kaolin and bentonite clays modified with hexadecyl trimethyl ammonium bromide (HDTMA). The clays were characterized using a zetasizer, scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Brunauer-Emmet-Teller (BET), Fourier-transform infrared (FTIR) spectroscopy and thermal gravimetric analysis (TGA). Factors that influence the adsorption of Pb(II) from aqueous solution, namely pH, contact time, adsorbent mass, ionic strength, temperature and initial Pb(II) concentration were investigated. The results show that HDTMA was successfully incorporated into the kaolin and bentonite clay structures. The most favorable parameters for the adsorption of Pb(II) ions onto all adsorbents was pH of 6.0, temperature of 25 °C and adsorbent mass of 200 mg. Adsorption isotherms and kinetic studies showed that the adsorption of Pb(II) onto kaolin, bentonite and organobentonite clays followed the Langmuir isotherm and pseudo-first order kinetic model, while the adsorption onto organobentonite was better explained by the Freundlich isotherm and pseudo-second order kinetic model. Maximum monolayer adsorption capacity of organobentonite, calculated from the Langmuir model was 18.75 mg/g, which is higher than that obtained for the unmodified bentonite (14.71 mg/g); while for organokaolin it was 2.26 mg/g, which is less than that of the unmodified kaolin (4.19 mg/g). Thermodynamic studies showed that the reactions were exothermic and unfavoured at high temperatures. The adsorbents also showed good removal efficiency for up to four regeneration cycles.

High surface area inorganic minerals show promise in protecting carbon from soil organic amendments

Protecting soil organic compounds could assist with global efforts to mitigate climate change, as well as improve soil health. Recent research has indicated that high surface area inorganic minerals (HSAIMs) can protect soil organic matter (OM). We evaluated if adding HSAIMs to soils can protect carbon from common organic inputs added to fallow soils prior to planting. Four added HSAIMs were investigated – two manufactured zeolites, one natural zeolite and bentonite clay – along with a carbon-rich (peat moss) and carbon-poor (composted cow manure) OM source. The added HSAIMs and organic sources were incorporated into a microbially active (clayey Vertisol) and inactive (sandy Arenosol) soil at application rates of 20 tonnes.ha–1 for the minerals and 60 tonnes.ha–1 for the organics. The treatments were incubated for three months under laboratory conditions and were subjected to continuous wetting-drying cycles. Peat moss resulted in higher organic carbon (Corg) and OM losses than cow manure. Moreover, the addition of HSAIMs to the Peat Moss+Arenosol treatments appeared to slightly enhance these losses, albeit not significantly (p>0.05). Carbon/nitrogen (C/N) ratios revealed that the Arenosol treatments were depleting soil N to access the carbon provided by the peat moss. For all other treatment combinations, the addition of HSAIMs promoted greater retention of Corg (p<0.05 in one treatment combination) and OM (p<0.05 in four treatment combinations), relative to the controls. Modelling carbon balances using OM data was more effective than using direct Corg values, due to strong Corg measurement variance. Modelled Corg data revealed the added HSAIMs achieved up to 25 % carbon protection, with the manufactured zeolites particularly effective. The study shows promise for added HSAIMs to protect carbon released from decomposing organic amendments added to fallow soils. However, addition of these minerals to N-limited soils receiving carbon-rich amendments might accelerate carbon losses.

Natural Moroccan bentonite clay as an adsorbent for nutrient removal from synthetic leachate: Performance and evaluation

To ensure the protection of public health and environmental integrity, while also meeting effluent regulation standards, it is critical to treat leachate due to its composition of hazardous substances before it is introduced into the environment. Pollution from leachate is characterized by several indicators, including COD, BOD5, conductivity, pH, and the presence of various ions such as ammonium, nitrite, nitrate, chloride, and orthophosphate. This research examines the adsorption properties of natural bentonite clay from Nador, located in eastern Morocco, for its efficacy in removing ammonium, nitrate, and nitrite ions from synthetic leachates. We present the outcomes of adsorption experiments utilizing bentonite clay to eradicate these nitrogen-based ions from artificial leachate, using UV adsorption spectroscopy for the measurement of ion concentrations before and after adsorption. Additionally, the study evaluates the efficiency of bentonite clay in adsorption, identifying the optimal amount of clay required for effective pollutant reduction. Our results demonstrate that, following a 24-hour mixing period, the adsorption rates for ammonium, nitrate, and nitrite ions were roughly 48%, 40%, and 85% at 35 °C, and 40%, 15%, and 25% at 25 °C, respectively. These findings suggest that modulation of agitation duration and temperature can significantly improve adsorption efficiency, with elevated temperatures facilitating shorter reaction times and higher adsorption rates for nitrogen ions. Ultimately, the research confirms the potential of bentonite clay as an effective medium for the removal of these contaminants from landfill leachate, offering a promising approach for enhancing environmental sustainability.

Expanded bentonite clay by bio-adhesive resins and its impact on the mechanical, adhesion, and ultrasonic properties of NR/SBR/polyester cords systems

The improvement of the compatibility between two nonpolar rubber blends has a pivotal role to obtain superior blend properties. In this work, we utilized a facile and biofriendly modification approach of natural bentonite (BT) clay by two renewable resins, namely antibacterial gum rosin (GR) and soybean long oil alkyd resin (LAR). Which are considered to be toxicity-free reinforcing substance, thus preserving the bio-character of the substance. They used to increase the interlayer spacing distance between the BT galleries. This was proven by XRD and FT-IR. Natural rubber (NR)/styrene-butadiene rubber (SBR) blend was loaded with variable proportions of EBT-based GR and LAR bio-resins ranging from 3 to 15 wt.%. The ultrasonic and tensile properties were used to assess the compatibility between the rubber blends. The outcomes revealed that NR/SBR-3EBT-GR and NR/SBR-15EBT-LAR nanocomposites possessed higher tensile strength and rapture at break. Furthermore, the proposed mechanism of EBT by GR and LAR bio-resins with NR/SBR blend was studied. The both nanocomposites were then subjected to different measurements such as morphology by SEM and TEM, H-pull-out adhesion between rubber blends and polyester (PET) cords, and antibacterial activity. These new filled blend systems can be effective supporting a wide range of potential applications such as green tubeless tires technologies.

Utilization of the natural Jordanian bentonite clay in hydraulic cement mortars

Utilization of the natural Jordanian bentonite clay in hydraulic cement mortars

Adsorption performance of bentonite and clay for Zn(II) in landfill leachate

BackgroundThe increasing prevalence of the Galvanized and dry battery industries has led to a rise in zinc proportions in landfills, posing environmental risks. This study explores the potential of bentonite, renowned for its metal adsorption capability, as a landfill barrier material.MethodsAdsorption characteristics of Zn(II) in natural bentonite and Shanghai clay were investigated. Various factors affecting Zn(II) adsorption, including pH, Na ion strength, contact time, initial Zn(II) concentration, and adsorption temperature, were analyzed through batch-type adsorption tests.ResultsThe change in pH and Na strength demonstrates no significant impact on the adsorption of Zn(II) onto bentonite, highlighting the strong selectivity of bentonite for Zn(II). Conversely, the equilibrium adsorption capacity of Zn(II) onto clay increases with rising pH or decreasing ion strength. The Zn(II) adsorption onto bentonite is well-described by the pseudo-second-order, intra-particle diffusion, and Elovih models, each achieving an R2 value exceeding 0.9. While both physical and chemical adsorption coexist in Zn(II) adsorption onto bentonite or clay, the primary determinant of the adsorption rate is chemical adsorption. The adsorption onto bentonite is spontaneous, whereas onto clay it is not. The mechanism involves van der Waals forces, ion exchange, and chemical actions such as inner-sphere complexation for Zn(II) adsorption onto both bentonite and clay.

Comparative Study of the Physico-Chemical Properties of Sorbents Based on Natural Bentonites Modified with Iron (III) and Aluminium (III) Polyhydroxocations

A comparative study of the physicochemical properties of natural bentonite clays of Pogodayevo (Republic of Kazakhstan, mod. 1) and Dash-Salakhli (Republic of Azerbaijan, mod. 2) deposits and modification of the bentonite clay with polyhydroxocations of iron (III) and aluminium (III). The amount of bentonite in the concentration of iron (aluminum) was 5 mmol Me3+/g. It was established that the modification of natural bentonites using polyhydroxocations of iron (III) (mod. 1_Fe_5-c, mod. 2_Fe_5-c) and aluminum (III) (mod. 1_Al_5-c, mod. 2_Al_5-c) by the method of “co-precipitation” leads to a change in their chemical composition, structural and sorption properties. The results showed that hydroxy-aluminum cations ([Al3O4(OH)24(H2O)12]7+) and poly-hydroxyl-Fe or polyoxo-Fe were intercalated into clay layers, which led to an increase in the values of d001 and specific surface areas compared to those of the original bentonite, from 37 to 120 m2/g for the Pogodaevo bentonite and from 51 to 172 m2/g respectively, for bentonite from the Dash-Salakhli deposit. It is shown that modified sorbents based on natural bentonite are finely porous objects with a predominance of pores of 1.5–8.0 nm in size. As a result, there is a significant increase in the specific surface area of sorbents. Modification of bentonite with polyhydroxocations of iron (III) and aluminum (III) by the “co-precipitation” method also leads to an increase in the sorption capacity of the sorbents obtained with respect to nickel (II) cations. Modified bentonites were used for the adsorption of Ni (II) ions from the model solution. Ni (II) was absorbed in a neutral pH solution. The study of equilibrium adsorption showed that the data are in good agreement with the Langmuir isotherm model. The maximum adsorption capacity of the Ni (II) obtained from the Langmuir equation was 25.0 mg/g (mod. 1_Al_5-c), 18.2 mg/g (mod. 2_Al_5-c) for Al-bentonite and 16.7 mg/g (mod. 1_Fe_5-c), 10.1 (mod. 2_Fe_5-c) for Fe-bentonite. The kinetics of adsorption is considered. The high content of Al-OH anion exchange centers in them determines the higher sorption activity of Al-modified bentonites.

An Effective Melon Fly Control Strategy Based on Disinfection and Soil Productivity Management

The research employs both the literature and experimental data in order to develop reasonable strategies for melon fly control. The objects of research were sierozem soils of the Zhanakorgan region (Kyzylorda region), bentonite clays of the Sauran region (Turkestan region), and vermicompost obtained at the production site of the Research Institute “Ecology” at the International Kazakh-Turkish University, named after Khoja Ahmed Yasawi. The competitive agent ‘Vermiserbent’ was developed by combining sulphur-perlite-containing waste (SPCW), vermicompost, and natural bentonite clay. When incorporated into the soil, it serves as both an insecticide and a fertiliser recovery agent. The disinfection and enrichment of barren Sierozem soils in southern Kazakhstan could provide an eco-friendly approach to protect cucurbits (melon, watermelon, and pumpkin) against the melon fly. The average yield of watermelon treated with Vermiserbent increased by 2.3 t/ha compared to the control, melon by 4.6 t/ha, and pumpkin by 5.6 t/ha. The marketability of gourds as watermelons and melons after treatment with fertiliser increased by 1.2 times, and pumpkin by 1.1 times. The findings of studies conducted in agricultural fields in the Turkestan and Kyzylorda regions have shown that it is possible to produce environmentally sound gourds using a mixture of vermicompost, bentonite, and SPCW.

Degradation of pesticides by heterogeneous Fenton using iron-exchanged clays

The aim of this research is to study the feasibility of using low-cost and natural bentonite and kaolinite clays, compared with commercial bentonite, as raw materials to prepare catalysts for the removal of two emerging pollutants, the neonicotinoid pesticides nitenpyram and acetamiprid, by heterogeneous Fenton process. The raw materials were subjected to a simple ion exchange method to improve their textural properties using a solution containing ferric cations followed by calcination at 500 °C. Results show high activity for all the catalysts in the removal of these pesticides, Stability tests were carried out confirming the high stability of these materials.

Synthesis and Characterization of Methoxy-Exfoliated Montmorillonite Nanosheets as Potential Carriers of 5-Fluorouracil Drug with Enhanced Loading, Release, and Cytotoxicity Properties.

Natural bentonite clay (BE) underwent modification steps that involved the exfoliation of its layers into separated nanosheets (EXBE) and further functionalization of these sheets with methanol, forming methoxy-exfoliated bentonite (Mth/EXBE). The synthetically modified products were investigated as enhanced carriers of 5-fluorouracil as compared to raw bentonite. The modification process strongly induced loading properties that increased to 214.4 mg/g (EXBE) and 282.6 mg/g (Mth/EXBE) instead of 124.9 mg/g for bentonite. The loading behaviors were illustrated based on the kinetic (pseudo-first-order model), classic isotherm (Langmuir model), and advanced isotherm modeling (monolayer model of one energy). The Mth/EBE carrier displays significantly higher loading site density (95.9 mg/g) as compared to EXBE (66.2 mg/g) and BE (44.9 mg/g). The loading numbers of 5-Fu in each site of BE, EXBE, and Mth/EXBE (>1) reflect the vertical orientation of these loaded ions involving multi-molecular processes. The loading processes that occurred appeared to be controlled by complex physical and weak chemical mechanisms, considering both Gaussian energy (<8 KJ/mol) as well as loading energy (<40 KJ/mol). The releasing patterns of EXBE and Mth/EXBE exhibit prolonged and continuous properties up to 100 h, with Mth/EXBE displaying much faster behaviors. Based on the release kinetic modeling, the release reactions exhibit non-Fickian transport release properties, validating cooperative diffusion and erosion release mechanisms. The cytotoxicity of 5-Fu is also significantly enhanced by these carriers: 5-Fu/BE (8.6% cell viability), 5-Fu/EXBE (2.21% cell viability), and 5-Fu/Mth/EXBE (0.73% cell viability).

Selective adsorption of gadolinium from real leachate using a natural bentonite clay

This article investigated the recovery of Gd3+ from real leachate of phosphogypsum (PG) using natural bentonite clay. Firstly, a detailed adsorption study was performed using synthetic Gd3+ solutions. Then, it was investigated the clay performance in the real PG leachate. The characterization results indicate classical bentonite characteristics, such as rugosity and an SBET 91.3 m² g−1, with meso (Dp =3.82 nm) and macroporous (Dp =52.6 nm). In addition, it was identified that the major functional groups are hydroxyl and silicate, with the presence of organic matter. The initial pH solution effect indicates that the optimum removal of Gd3+ is at pH (6), attributing to the pHpzc being at 5.75 and the negatively charged surface above the pHpzc. The Avrami fractional order model was the most suitable for describing the experimental kinetic data. The Langmuir was the proper model for describing the adsorption isotherms, indicating that the Gd3+ forms a monolayer at the surface of the bentonite. The maximum adsorption capacity at pH 6.0 was 121.5 mg g−1. The thermodynamic parameters indicate that the adsorption is spontaneous, with a standard enthalpy change of − 92.30 kJ mol−1, indicating an ionic exchange, where the Gd3+ tends to be organized at the surface, according to the standard entropy change of − 206.0 J K−1 mol−1. The fixed bed adsorption test showed that Gd3+ could be adsorbed for up to 200 min without regeneration. Regeneration results show that the citric acid is more efficient in desorbing the Gd3+ from the bentonite, reaching up to 8 cycles without efficiency loss. Finally, the bentonite clay could selectively recover Gd3+ from the real PG leachate.

Characterization and applicability of the natural Iraqi bentonite clay for toxic cationic dye removal: Adsorption kinetic and isotherm study

This research targets to adsorb the organic dye (methylene blue, MB) from aqueous media using natural Iraqi bentonite clay (NIBC). Several analytical methods (e.g., XRD, FTIR, SEM-EDX, XRF, pHpzc, and BET) analysis were conducted to inspect the physicochemical characteristics of the NIBC. Adsorption key variables, including dosage of adsorbent (0.02–0.1 g), pH (2–10), and initial concentrations (10–150 mg/L) were inspected for determining their impacts on MB dye removal. The Redlich-Peterson isotherm demonstrated the best account for the equilibrium adsorption of MB. The NIBC's highest adsorption capacity (qmax) for MB was 256 mg/g. The kinetics of the adsorption of MB by NIBC matched the pseudo-second-order model. This study demonstrates that the NIBC could be utilized to successfully remove MB from aqueous environments.

Composites of bentonite mixed with natural fibers as acoustic absorption material

Noise pollution is a very common problem that causes a negative impact on society. Long exposure to high levels of noise might lead to dire health consequences such as irritability, headaches, stress, anxiety, and hearing loss. The use of acoustic sound-absorbing materials may decrease noise propagation when they are used as insulation and consequently reduces the negative impact. Different composite materials made with natural waste have been studied showing a wide range of thermal, physical, ecological, and economic properties that impact mainly the application of sound absorption. In this work we focused on a composite of natural bentonite clay mixed with coconut or nopal fibers, varying the fiber weight ratio. An impedance tube was used to quantify the reflection, transmission, and absorption acoustic coefficients in a frequency range of 50 Hz to 10,000 Hz. The type and percentage of crystalline compounds and the functional groups of the natural clay were analyzed by X-ray diffraction and FTIR spectroscopy, respectively. Morphological analysis of the fibers was carried out using a scanning electron microscope (SEM), and thermogravimetric analysis (TGA) technique was used to determine thermal stability. A hardness test was performed on the samples with 3 months of aging, this test was repeated 10 times for each of the samples and 2 different samples were used for each composition. The results show a difference in the three acoustic coefficients related to fiber weight ratio. The lower weight of clay the higher magnitude of the absorption coefficient. The clay-coconut composites present better absorbing properties than clay-nopal composites, although the magnitude of this coefficient increases as a function of frequency for both composites. The highest reflection coefficient is presented in the clay samples, and the lowest transmission coefficient is shown in the coconut sample. In addition, TGA suggested bentonite improves the thermal stability of the composite. The experimental acoustic characterization shows that both types of composites could be used as a green material for sound absorption application and thermally insulating.

Characterization of Natural Ca-Bentonite Clays from Ebenebe in Anambra State, Nigeria, Impregnated with Ca(NO3)2, Zn(NO3)2 and KOH for use as Catalysts for Viscosity Reduction in Transesterification Reaction of Castor Oil

Natural Ca-Bentonite from Ebenebe in Anambra State, Nigeria, was successfully impregnated with Ca (NO3)2, Zn (NO3)2 and KOH and further calcined under different conditions of temperature and time using standard methods. Both the natural and impregnated bentonite clays were characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Fluorescence Spectroscopy (XRF) and Scanning Electron Microscopy (SEM) and then applied as catalysts in transesterification reaction of refined castor oil. Viscosity reduction test was used to ascertain the best catalyst for the transesterification. FTIR spectra of the activated clay catalysts show the formation of new functional groups, as the intensity of the Al-O-H stretching group (3633cm-1) of the natural clay increased with slightly higher wavelengths of 3640cm-1, 3644cm-1, 3644cm-1, 3644cm-1, 3640cm-1and 3644cm-1 for CaB2, CaB3, ZnB2, ZnB3 KB400, and KB700 catalysts respectively. XRF result identified the natural bentonite clay as Ca-bentonite clay with Ca-oxide having the most dominant component of 76.71%. XRF chemical compositions of the six activated Ca-bentonite clay catalysts when compared to the natural Ca-bentonite clay confirmed successful impregnation. The SEM images of all the prepared catalysts showed that impregnation and calcination changed the surface morphology of the natural clay. Finally, transesterification reactions of refined castor oil samples were done with 3%w/w natural and impregnated Ca-bentonite catalysts, methanol to oil ratio of 6:1, 2 hours reaction time and 65oC reaction temperature. Results obtained showed a descending order of catalyst viscosity reduction ability to be KB700 &gt; CaB3 &gt; CaB2 &gt; ZnB3 &gt;NCB &gt; ZnB2 &gt; KB400.

Freeze and Thaw Effect on Asphalt Concrete Mixtures Modified with Natural Bentonite Clay

This study aimed to investigate the effect of freeze and thaw (FT) cycles on the performance of asphalt concrete (AC) mixtures modified by partial replacement of mineral filler of the aggregate with natural bentonite clay (NBC) in order to reduce damage that occurs due to rapid FT cycles within the pavement structure. After exposure to FT cycles, AC mixture stability is reduced and becomes lower than minimum requirements, which leads to earlier damage of pavement. In order to enhance the AC mixture’s abilities to sustain severe FT cycles, this study used NBC amounts as a substitute for mineral filler by weight of its portion of the total aggregate: 5%, 10%, 15%, and 20%. Marshall stability, flow, and FT cycles were tested, and interior damage degree was assessed by a nondestructive test called ultrasonic pulse velocity (UPV). The results revealed the viability of combining NBC with asphalt mixtures for the purpose of improving the mixtures’ properties, particularly in environments where asphalt pavement is exposed to alternating FT cycles. The results also revealed that replacement of filler with NBC by 5% in AC mixtures reduced the damage caused over 8 continuous weeks of rapid FT cycles by 13%, which, in future applications, would reduce maintenance cost and prolong the pavement’s service life.

The removal of manganese ions from industrial wastewater using local Saudi and commercial bentonite clays

Manganese compounds exist naturally in the environment as solids in soils and small particles in water. Human industrial activities and the burning of fossil fuels increase the manganese concentration in the air. Studies have shown that exposure to manganese has extremely dangerous, toxic effects on humans, resulting in ailments such as the “metal fume fever” which produces symptoms such as metallic taste in the mouth, headache, fever and chills, anxieties, chest tightness, and cough. This has led many researchers to try different techniques to eliminate this harmful metal from the environment. Among methods, adsorption is one of the most effective and efficient for the removal of contaminants, such as heavy metals, from wastewater. We focused on local (from Saudi Arabia) and commercial (from India) bentonite clay to verify the importance of natural bentonite clay as an adsorbent for water treatment. While other purification techniques are expensive, bentonite clay is cheap, natural, and accessible. Therefore, we investigated how the concentration of the solution pH, temperature, adsorbent amount, contact time and bentonite procedure (washing and heat treatment) affect the removal process. Our results demonstrated success in the local bentonite clay's adsorptive capacities, and we encourage the generalization of its use in the Saudi kingdom's industries.

Comparative Study of the Physical and Chemical Properties of Natural Bentonite Clay of the Dash-Salakhli Deposit and Synthetic Montmorillonite

Comparative Study of the Physical and Chemical Properties of Natural Bentonite Clay of the Dash-Salakhli Deposit and Synthetic Montmorillonite

Катализатор на основе бентонитовой глины, модифицированной метасиликатом натрия для гетерогенного процесса типа Фентона – Раффа

Natural bentonite clay with a montmorillonite content of 98 %, modified with a solution of sodium metasilicate, has high catalytic activity in the reaction of oxidative degradation of organic azo dyes with hydrogen peroxide by the Fenton-Ruff mechanism in a neutral medium. The activity is due to the presence of iron cations contained in the structure of montmorillonite, as well as protonated silanol and aluminol groups on the surface of the edges of aluminosilicate layers, which are the acid centers of Brensted. The degree of conversion of azo dye from cinema blue with an initial concentration in a solution of 20 mg/l was 99 % in 4 – 6 minutes of contact, at room temperature. The resulting material is well filtered and can be recommended for wastewater treatment from organic substances.

Investigation of the adsorption characteristics of Pb(II) onto natural kaolinite and bentonite clays

Investigation of the adsorption characteristics of Pb(II) onto natural kaolinite and bentonite clays