Raw Bentonite Research Articles

Amine grafting of acid-activated bentonite for carbon dioxide capture

A low-cost bentonite (ZBent) and acid-activated derived samples have been employed as clay adsorbents to assess their performance for pure CO2 adsorption in a thermogravemetric system. The raw bentonite reached a CO2 uptake of only 6.2 mg/g ads due to its low specific surface area and pore volume. After acid modification, an increase in its specific surface area and pore volume was observed, due to the leaching of octahedral cations and the generation of an amorphous silica phase. However, the degradation of the clay structure only improved slightly the adsorption of CO2. In a next step, raw and acid-treated clay minerals were functionalized with two different amine species (aminopropyl-trimethoxysilane; AP, and diethylene-triamine-trimethoxysilane; DT) by grafting. Unlike the case of DT species, the incorporation of AP moieties favored the chemical interaction between the amines species and the CO2 molecules in all cases. Functionalization with AP molecules increased the adsorption capacity of CO2 up to 29.2 mg/g ads at 30 °C for ZBent-24 h-AP, the material obtained after longer acid treatment time and functionalized with AP. AP-functionalized samples also had good stability and reusability during eight cyclic adsorption/desorption tests.

Clay adsorptive membranes for chromium removal from water

Cost effective clay adsorptive microfiltration membranes were synthesized to remove Cr (III) from high polluted water. Raw and calcined bentonite were mixed in order to decrease the shrinkage and also increase the porosity; then, 20 wt% of carbonate was added and the samples, named B (without carbonate) and B-Ca20 (with 20 wt% calcium carbonate) were uniaxially pressed and after sufficient drying, fired at 1100 degree(C) for 3 hours. Then, physical and mechanical properties of the samples, their phase analyses and microstructure and also their ability for Cr(III) removal from high polluted water (including 1000 ppm Cr (III) ions) were studied. Results showed that the addition of calcium carbonate lead the porosity to increase to 33.5% while contrary to organic pore formers like starch, due to the formation of wollastonite, the mechanical strength not only didn\'t collapse but also improved to 36.77 MPa. Besides, sample B-Ca20, due to the presence of wollastonite and anorthite, could remove 99.97% of Cr (III) ions. Hence, a very economic and cost effective combination of membrane filtration and adsorption technology was achieved for water treatment which made microfiltration membranes act even better than nanofiltration ones without using any adsorptive nano particles.

Structural Property Improvements of Bentonite with Sulfuric Acid Activation and a Test in Catalytic Wet Peroxide Oxidation of Phenol

Abstract The acid activation of bentonite from Middle Anatolia, consisting of mostly montmorillonite, with a hot solution of H2SO4 with different concentrations was carried out. SEM images, nitrogen sorption isotherms and FTIR spectra were used to examine structural changes of the bentonite with acid activation. Acid–base titration method was applied to determine surface acidities. SEM images, nitrogen sorption isotherms indicated that the acid activation caused considerable increases both in the surface area and pore volumes by changing the morphology and aluminum content. FTIR spectra showed the enhancement both in Lewis and Brønsted acidities, significant increases in H–bonding to the structure with acid concentration. Acid treatment gave good structural properties with high surface acidity. Stable structured acid activated bentonite with 2 M was tested in catalytic wet peroxide oxidation (CWPO) of phenol together with raw bentonite. Around 96 % phenol removal was achieved in 135 minutes at reaction temperature of 50 °C while the raw bentonite did not show good results. The data were in agreement with the first order dependency with respect to phenol.

An Investigation of the Swelling Kinetics of Bentonite Systems Using Particle Size Analysis

Particles size distribution (PSD) is introduced as a tool for analysis of bentonite aggregation and swelling kinetics. Raw Ca-bentonite was purified using a combined wet sieving and sedimentation processes, followed by thermochemical treatment with Na2CO3 to increase its swelling capacity. The detailed analysis of the PSD shows a strong correlation between the PSD and the swelling process. For the chemically treated raw bentonite, PSD revealed two different peaks representing unswelled and swelled particles along with some aggregates. The swelling is shown to be a kinetically controlled process that depends on time, temperature, and bentonite chemical composition. At the beginning of the chemical treatment, the effect of aggregates was more dominant; therefore, the viscosity did not increase much with particle size. However, the combined chemical and thermal treatment has enhanced the Na-activation process and boosted bentonite swelling. The rheological measurements have shown enhancement in the viscosity and confirmed the PSD findings. The same optimal treatment conditions are obtained from both rheological measurements and PSD analysis. A model is developed based on classical reaction rate kinetics and used to describe the conversion from unswelled to swelled particles. The PSD has a strong correlation with the physical properties of the suspension such as the viscosity. The swelling rate fits a second order model with a rate constant, k, in the range 0.002 to 0.124 h−1 and an activation energy, E, of 87 kJ/mol. PSD analysis together with the developed kinetic model are powerful tools for studying the swelling kinetics of bentonites.

Optimizing a low added value bentonite as adsorbent material to remove pesticides from water

A local low value bentonite from Southern Spain (Raw Bentonite), previously decarbonated (Bent), was modified to improve its pesticide adsorption capacity with Fe3+, hexadecyltrimethylammonium (HDTMA) and the biopolymer chitosan (CH). Adsorption of pesticides on powdered samples showed that Fe3+ and HDTMA were appropriate modifiers for this purpose. The modification was optimized by saturation with Fe3+ (Bent-Fe) and hexadecyltrimethylammonium (Bent-HDTMA) and the obtained adsorbents were characterized by several physicochemical techniques (X-ray diffraction, thermogravimetric analysis, X-ray fluorescence, physisorption of N2). Their adsorption capacity to remove three widely used pesticides in Andalusian crops (terbuthylazine, tebuconazole and MCPA) from water was assessed and compared with the commercial organoclay Cloisite® 10A (Clo10). The modified bentonites adsorbed the selected pesticides in a percentage ranging from 30 to 100%, whereas sorption on Clo10 ranged from 30 to 90%. For their possible use as filtering beds, Bent-HDTMA, Bent-Fe and Clo10 were granulated by using three different binders (colophony resin and carnauba and bee waxes) at three different mixing ratios and the water resistance and pesticide adsorption of the granules were measured. Results showed that the granulation process did not alter the pesticide adsorption capacity of the powdered modified bentonites, and both waxes granules (carnauba and bee wax) showed better behavior than resin granules. In this work, we succeeded in the preparation of granulated adsorbents derived from a low cost material with similar behavior against a high purity smectite (precursor of Cloisite® 10A). This raises an alternative for this waste material to be used in filter systems for removing pesticides from contaminated water.

Adsorptive removal of diclofenac and ibuprofen from aqueous solution by organobentonites: Study in single and binary systems

Organobentonite adsorbents were prepared by treating raw bentonite (RB) with three different cetyltrimethylammonium bromide concentrations (0.5, 1 and 2CEC). The prepared adsorbents were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), Thermogravimetric analysis (TGA) and Specific surface area (BET). The adsorbents were then tested for their ability to remove diclofenac (DIC) and ibuprofen (IBU) from aqueous solution at different conditions (pH, adsorbent dosage, initial drug concentration, and contact time) in order to determine the optimum conditions for adsorption. The kinetics in single drug solution follows pseudo-second order kinetic model. The adsorption isotherms of the two drugs obeyed both the Langmuir and Freundlich isotherm models with the saturation adsorption amount onto 2CECRB of 600.6 and 194.9 mg/g for DIC and IBU, respectively. In adsorption from mixed drug solutions, DIC and IBU show competitive adsorption. Hydrophobic interactions play an important role during the sorption process. In addition, 2CECRB could be regenerated and reused after four cycles.

Influence of Calcium Ion Pre-treatment on Phosphate Adsorption onto Magnetic Zirconium/Iron-modified Bentonite

Two kinds of magnetic zirconium/iron-modified bentonites (ZrFeBTs), including magnetic zirconium/iron modified raw bentonite (ZrFeRBT) and magnetic zirconium/iron-modified Ca2+-pretreated bentonite, (ZrFeCaBT) were prepared and characterized. Their phosphate adsorption characteristics were compared to determine the effect of the Ca2+ pre-treatment on the adsorption of phosphate onto ZrFeBTs. The results showed that the as-prepared ZrFeBTs contained Fe3O4 and Zr, and the content of exchangeable Ca2+ in ZrFeCaBT was much higher than that in ZrFeRBT. The adsorption isotherm data exhibited good agreement with the Langmuir isotherm model, with maximum monolayer phosphate adsorption capacities of 8.70 mg·g-1 and 11.5 mg·g-1 for ZrFeRBT and ZrFeCaBT, respectively. The isotherm and kinetics studies showed that the adsorption of phosphate on ZrFeBTs was a chemisorption process. The phosphate adsorption capacities for ZrFeBTs decreased with increasing solution pH. The ZrFeBTs exhibited a high selective adsorption for phosphate in the presence of anions and cations, including Cl-, HCO3-, SO42-, NO3-, Na+, K+, Mg2+, and Ca2+. Furthermore, coexisting Ca2+ greatly enhanced the adsorption of phosphate onto ZrFeBTs. The pre-treatment of raw bentonite with Ca2+ significantly improved the adsorption of phosphate onto ZrFeBTs.

Kinetics and thermodymics studies for the removal of bromocresol purple using raw bentonite clay and activated carbon from <i>Vachellia nilotica</i> pod as adsorbents

The adsorption of Bromocresol purple (BCP) onto Raw Bentonite Clay (RBC) and activated carbon from Vachellia nilotica (AVNP) was investigated using batch adsorption process. The adsorbents were characterized using Fourier transform spectrometer (FTIR) and Scanning Electron Microscope (SEM). The study of adsorption Kinetics and Thermodynamics were carried out. The pseudo –second order kinetic exhibits the best fit with the experimental data with R2 values close to 1 and experimental values qe (mg/g) 7.197 and 5.169 for RBC and AVNP are more closer to the calculated qe 7.246 and 5.263.The negative values of Gibbs free energ change, ΔG of -5.98 to -7.75 and -2.77 to -4.36kJ/mol for RBC and AVNP respectively shows the process to be spontaneous. Positive values of enthalpy, ΔH, confirm the endothermic character of the adsorption process. Lower ΔH values of 11.01 and 11.98kJ/mol for adsorption of dye onto raw bentonite clay and activated carbon respectively, suggests that the adsorption is physical in nature..Keywords: Bromocresol purple, Raw Bentonite clay, activated Vachellia nilotica pods kinetics, thermodynamic

Citric Acid Modified Bentonite for Congo Red Adsorption

Raw bentonite (RB) was chemically modified by citric acid (CA) to obtain a low-cost and environment-friendly citric acid incorporated bentonite (CAB) adsorbent, which was applied for the adsorptive removal of Congo Red (CR). The effect of adsorbent dosage, contact time, ionic strength, surfactant and pH on adsorption was investigated. Adsorption equilibrium data fitted well with Langmuir model while the Langmuir adsorption capacity of CR on CAB reached up to 384 mg·g‒1. Furthermore, CR adsorption on CAB followed pseudo-second kinetic model while intra-particle diffusion was not the only rate-limiting step as determined from intra-particle diffusion model investigation. RB and CAB were characterized by XRD, FT-IR and BET techniques. A proposed mechanism for the adsorption of CR over CAB suggested chemical adsorption phenomenon mainly controlled by chelation, hydrogen bonding and fixing.

Influence of Nano-bentonite in Hydraulic Conductivity Performance

Nano-clay is one of the innovation recently been studies as one of the enhancing materials to the soils. By adding a slight amount of nano-clay can improve some of behaviour such as hydraulic conductivity. Therefore, this research will investigate the performance of the hydraulic behaviour of different percentage of nano-clay in developing new soil liner design to be used in landfill. To complete the objectives, bentonite was pulverized by the process of high energy milling to obtain nano-bentonite. The milling sample is being analysed using Zeta Potential Analyzer and Field Emission Scanning Electron Microscope (FESEM). The laboratory studies were conducted by the determination geotechnical properties of the liquid limit, plastic limit, plasticity index shrinkage limit, particle density, compaction characteristic and also hydraulic conductivity value of raw bentonite mixed with 0%1%,2% and 3% of nano-bentonite. The laboratories result shows that the value of liquid limit, plastic limit, particle density and maximum dry density is increase in every addition of nano percentages meanwhile the value of plasticity index, optimum moisture content and hydraulic conductivity is decrease after adding nano-bentonite in the sample. The result shows the improvement of the soil by the geotechnical properties with addition of small amount of nano-bentonite.

Sodium polyacrylate modification method to improve the permeant performance of bentonite in chemical resistance

Bentonite, an important geotechnical material in the fields of environmental geotechnical engineering, can effectively adsorb harmful substances from the environment and fuel oil. This study investigated the formulation of sodium polyacrylate-modified bentonite that improves the permeant performance in the context of chemical resistance. The optimum material mix ratio and synthesis process were determined through multiple experiments. To better understand the sodium polyacrylate/bentonite interaction, the swelling index, filtrate loss, cation exchange capacity (CEC) and hydraulic conductivity performance in solutions of Pb(NO3)2 and acid were compared. The microstructures of raw bentonite and sodium polyacrylate bentonite were analyzed using scanning electron microscopy and infrared spectroscopy. The results showed that the microstructure of modified bentonite was characterized by isolated cavities, whereas the original configuration comprised a stacked layer, and the free swell index (FSI) increased from 25 to 50 mL/2 g. The modified bentonite showed a significant improvement in terms of chemical resistance through FSI testing and filtrate loss experiments, particularly in hydraulic conductivity tested in acidic and saline solutions. The permeability decreased by an order of magnitude through the modification process under the deionized water condition, and the chemical resistance increased to more than 40 mM in the Pb(NO3)2 solution. In addition, the CEC increased from 62.06 to 96.1 meq./100 g as a result of sodium polyacrylate modification.

ADSORPTION OF AMMONIA BY BASE ACTIVATED BENTONITE CLAY KINETIC AND EQUILIBRIUM STUDIES

Nitrogen compounds are essential elements for living organisms. The increased concentration of ammonia in ionized (NH4+) and non-ionized form (NH3) in surface waters causes negative effects on aquatic organisms, since it enters into the nitrogen cycle, and thus contributes to the eutrophication of water. The presence of higher concentrations of ammonia in surface waters than natural ones is the result of faecal contamination through the sewage system or runoff from arable areas which were treated with fertilizer. Water contaminated with ammonia can be purified by various methods: biological (nitrification-denitrification method), oxidation with chlorine, chemical precipitation, membrane filtration, etc. One of the alternative methods is removal by adsorption with natural materials such as clay and zeolite. Bentonite clay was marked off as a suitable adsorbent of cationic pollutants due to the permanent negatively charged surface. Тhe textural properties (specific surface, porosity) and structural properties of bentonite clay (the distance between the layers, the type of ions in the space between the layers) and consequently its adsorption capacity for pollutants is changed with the activation by acid or base and intercalation. There is very little literature data on the application of bentonite clay for removal of ammonium ions. Therefore, the aim of this work is activating the raw bentonite clay with a base and its application as an adsorbent for removal of ammonium ions from aqueous solutions. The influence of the adsorption conditions (adsorbent dose, temperature, pH, adsorbate concentration and contact time) on the amount of removed ammonia from the aqueous solution was investigated. Equilibrium data were analyzed by Langmuir, Freundlich and Dubinin-Radushkevich isotherms. The best agreement with experimental data was obtained by Langmuir isotherm (R2 = 0.987). The following kinetic models were applied: the pseudo-first order, pseudo-second order, and the intra-particle diffusion model. The pseudo-second order model is most suitable for describing the adsorption of ammonium ions onto the base activated bentonite from aqueous solutions (R2 = 0.997). Removal of ammonium ions by activated clay is a pH-dependent and endothermic process, the adsorption degree of pollutants is increased with rising temperature. The highest adsorption capacity of the base activated bentonite clay of 26.82 mg/g was obtained in a solution of pH 6 and a temperature of 40 °C, at an adsorbent dose of 2 g/dm3 and аt an adsorbate concentration of 100 mg/dm3. By activating the adsorbent in a 1 M NaOH solution, the adsorption ability of the bentonite clay towards ammonium ions is improved. The results of this study show that the base activated bentonite clay is a potential adsorbent material for ammonia, i.e. ammonium ions.

Adsorptive desulfurization of model gasoline by using modified bentonite

ABSTRACTThis work involved the investigation on the removal of organic sulfur compounds from the model liquid fuels by using adsorption desulfurization (ADS) method. For this purpose, removal of 4-methyl dibenzothiophene (4-MDBT) in model gasoline streams with raw bentonite, nanobentonite and nanobentonite modified by nanomagnetite, active carbon and Ni(NO3)2.9H2O was considered. Various factors influencing the desulfurization capability, including loading and baking temperature were investigated. Thermo-gravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) showed that the ability of modified bentonite to adsorb 4-MDBT depends strongly on surface chemistry, particularly on the presence of basic oxygen-containing groups and acid content. The adsorbents tested for desulfurization capacity at breakthrough followed the order: 30wt% Fe3O4/30wt% Active carbon/40% Na -Nanobentonite > 30wt% Fe3O4/30wt% Active carbon/40% Ca – Nanobentonite > 30wt % Fe3O4/70% Ca-Nanobentonite > 15wt % Fe3O4/15wt% Ni/70% Ca– Nanobentonite. The results of preliminary tests for raw bentonite and nanobentonite were not significant in comparison with the modified nanobentonites: a, b, c, d samples, (about 40% lower than the four sample models). The optimum calcination temperature was 800°C. The multivariate methods were used for optimization of acceptance parameters. A Plackett–Burman design (PBD) was chosen as a screening method to estimate the relative influence of the factors that can be affected on the analytical response. Results show that surface area, pore size and pore volume of the bentonite can be increased several times using the impregnation method by 30wt% Fe3O4/30% active carbon. Also, the surface morphology of the bentonite is changed with this modification.

Effect of a calcined Westerwald bentonite as supplementary cementitious material on the long-term performance of concrete

The objective of using supplementary cementitious materials (SCMs) in cement is to reduce costs and the overall CO2 output of the cement production. Against the background of an increasing demand for cement and a decreasing availability of common SCMs, calcined clays serve as alternative material for the industrial-scale manufacture of composite cements. In the presented study, a raw bentonite clay of high volume capacity and small exploitation options was selected to check its pozzolanic activity after suitable thermal treatment and the consequent effects on the concrete performance. The results show that, at high cement substitution rates of 30%, the properties of the concrete were not changed to a significant extent. In certain durability issues namely sulphate resistance, inhibition of alkali silica reaction (ASR) and chloride migration, the mixture with calcined clay even performed better than the reference. Other properties like final strength and frost and de-icing salt resistance were changed in an uncritical way. Negative effects were observed on the early strengths and on the carbonation velocity. However, giving careful consideration to these aspects during concrete projecting, the calcined clay would be a suitable material for the majority of concrete applications.

Adsorption of atrazine from aqueous solution using unmodified and modified bentonite clays

Properties of raw bentonite clay of Afuze in Edo state which are abundant and cheap bentonite mineral in Nigeria as adsorbents for the removal of atrazine in aqueous solution were investigated. The bentonite clay-types were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry and X-ray diffraction (XRD). Batch adsorption experiments were carried out to determine the equilibrium characteristics, thermodynamics and kinetics of the sorption processes. The data obtained were subjected to Langmuir, Freundlich and Temkin isotherm equations, while pseudo-first-order, pseudo-second-order rate equations, intra-particle diffusion and Elovich models were considered for kinetics and mechanism. The results showed that the adsorption processes were described by different isotherm models; they were all spontaneous (∆G ranges from − 938.34 to − 6263.58 kJ/mol) and exothermic (range of ∆H is − 252.73 to − 1057.08 kJ/mol), and with decreased randomness, ∆S (− 3.110 to − 0.581 J.mol/K). Pseudo-second-order kinetics model gave the better fit for all the sorption processes which implies physisorption process as the rate limiting step. Thus, bentonite clay-types can be used to adsorb atrazine.

Experimental and Modeling Study on the Curing Properties of Natural Rubber Composites Filled with Varying Proportions of Carbon Black, Modified Bentonite and Raw Bentonite

The aim of this study was to investigate the effect of replacing carbon black (CB) with inexpensive and environmentally friendly fillers – bentonite (BNT) and modified bentonite (M-BNT), on the curing properties of natural rubber (NR) composites. A control sample (unfilled NR) and thirteen NR composites filled with varied proportions of CB (x1), M-BNT (x2), and BNT (x3) based on a third degree – simplex lattice mixture design of experiment (DOE) were prepared in this study. Rheometric results showed that 33% substitution of CB with M-BNT provides the highest elastic torque values. Mixture of 10phr CB and 5phr M-BNT (CB/M-BNT/BNT 10/5/0) produces synergistic effect on curing. The presence of CB increases vulcanization rate due to its high basicity and low oxygen content while M-BNT serves as vulcanizing accelerator due to the present amine groups. Coefficients of reduced hierarchical models showed that the main factors contributed mainly on the curing parameters: β1 for the torque values, β2 for the scorch and curing time, and β3 for CRI. High values of coefficient of determination (r2) were computed particularly for MH (98.20%), ΔS (99.13%), ts2(95.68%), tc90(95.70%) and CRI (95.97%) establishing best fit between the model and experimental values.

Synthesis of highly active and stable Al/Zr pillared clay as catalyst for catalytic wet oxidation of phenol

Natural bentonite clay was used in the synthesis of single and mixed oxide Al/Zr pillared clay catalysts by means of ultrasonic treatment during the aging and intercalation steps. The raw bentonite and pillared clay catalysts were characterized using high resolution scanning electron microscopy with energy dispersive system (HRSEM-EDS), powder X-ray diffraction (PXRD), N2 adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, cation exchange capacity, zeta potential and all the catalysts evaluated in the catalytic wet air oxidation (CWAO) of phenol. Calcination of the synthesized Al/Zr-PILCs at 500 °C for 120 min yielded optimum physical properties with BET surface area of 230 m2/g, pore volume of 0.115 cm3/g and basal spacing of 1.92 nm and with good thermal stability. Complete removal of phenol was obtained after 120 min and 88% TOC was removed after 180 min in aqueous solution under mild reaction conditions of 100 °C and 10 bar after. Catalyst reusability studies showed that the Al/Zr-PILCs catalyst demonstrated excellent chemical and structural stability with insignificant leaching of Zr4+ after six consecutive catalytic runs. The Al/Zr-PILCs catalyst therefore demonstrated excellent catalytic properties in the CWAO of phenol in aqueous solution.

Routine investigation of structural parameters of dioctahedral smectites by the Rietveld method

Abstract X-ray powder diffraction (XRD) in combination with the Rietveld method is a common technique for crystal structure analysis. However, almost all minerals of the smectite group show turbostratic disorder preventing the direct application of Rietveld refinement. Ufer et al. (2004) proposed to overcome this limitation by using a single layer model with the BGMN program. This model is now routinely used for quantitative phase analysis of smectite-containing samples. However, the refinement of some important structural features, such as the layer charge density (LCD) and the octahedral iron content has not been achieved successfully yet. Typically, these structural features can be obtained only by analytical methods which require purified smectite samples. The project was firstly aimed to prove the validity of the refinement of selected structural parameters by using a set of purified and well-characterized samples and then applied this method to raw bentonites with natural impurities. The Rietveld refinements were carried out on the X-ray powder diffraction patterns of the Cu-triethylenetetramine (Cutrien) exchanged dioctahedral smectites to avoid the problems of unknown cation species and complex hydration behavior in the interlayer. The refinements of the occupancy of octahedral iron and the LCD led to reasonable results for iron-poor purified samples. The application of the structure model to Cutrien -exchanged smectite-rich samples with natural impurities, e.g. bentonites without previous purification, showed that some important structural details of turbostratically disordered dioctahedral smectites can be determined by the Rietveld method from XRD patterns of the Cutrien -exchanged samples. The technique may be applied in routine structural characterization of raw smectites in bulk rock samples without a prior chemical analysis of purified smectite fractions.

Effective fluoride adsorption by aluminum oxide modified clays: Ethiopian bentonite vs commercial montmorillonite

This study focuses on the chemical modification of Ethiopian bentonite and commercial montmorillonite with aluminum oxi-hydroxide (AO) for the purpose of defluoridation from aqueous solution. The chemical modification was achieved by preparing AO-modified adsorbents at different pH values. The adsorbent materials were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) and point of zero charge (PZC). From the modified adsorbents, AO-Mont at pH 5 (AO-Mont 5) showed a slight shift of d 001 at 2θ = 7.5o reflection toward the lower angle 2θ = 7.0o as a result of the Al 2 O 3 insertion into interlayer space. The elemental composition from XRF further showed the increment of Al content accompanied with a decrease in the exchangeable cations in the modified samples and higher content of Al was observed in AO-Mont 5. In addition, the PZC initially 8.5 and 2.5 for raw bentonite and montmorillonite clays were increased to 10 and 8.5 in AO-Bent 5 and AO-Mont 5, respectively. Adsorption of fluoride on these modified adsorbents was studied as a function of preparation pH, contact time, solution pH and co-existing anions. AO-Mont prepared at pH 5, which contained higher content of Al resulted better fluoride removal performance. AO-Bent 5 and AO-Mont 5 have shown five and nine fold increase in fluoride removal capacity, respectively as compared to their respective unmodified clays. The experimental data fitted well with Freundlich adsorption isotherm model which indicated that the surface of the adsorbent is heterogeneous and adsorption of fluoride followed a multilayer sorption. Hence AO-modified Bent and Mont adsorbents prepared at pH 5 can be considered as potential adsorbents for defluoridation from drinking water. KEY WORDS : Defluoridation, Aluminum oxide, Bentonite, Montmorillonite Bull. Chem. Soc. Ethiop. 2018 , 32(2), 199-211. DOI: https://dx.doi.org/10.4314/bcse.v32i2.2

Characterisation of the Egyptian Pliocene bentonite from the Sohag region for pharmaceutical use

This paper aims to prepare purified Na-bentonite with improved properties for its use in the pharmaceutical industry. Calcium bentonite from the Sohag region of Egypt was activated with various proportions of sodium carbonate (2, 3, 5 and 8 wt.%). Additionally, bentonite was purified by sedimentation to eliminate impurities, especially quartz. The results of X-ray diffraction (XRD) and swelling volume data confirmed that raw bentonite was converted to sodium bentonite using 5% Na2CO3. The sodium bentonite (M5) obtained by activation met the chemical and microbiological requirements set by the pharmacopoeias regarding toxic trace elemental contents (As, Pb and Cd), the absence of E. coli, the total contents of aerobic microbes and physicochemical properties such as swelling volume, pH and sedimentation volume. Therefore, (M5) bentonite can be designated as being potentially appropriate for pharmaceutical applications. The cation exchange capacity (CEC), surface area, porosity, pH, gel formation and swelling volume data indicated that M5 bentonite could be used to formulate oral suspensions and in topical application.