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Adsorption of o-, m- and p-nitrophenols onto organically modified bentonites

Experiments were conducted on the adsorption characteristics of o-, m- and p-nitrophenols by organically modified bentonites at different temperatures. Two organobentonites (HDTMA-B and PEG-B) were synthesized using hexadecyltrimethylammonium bromide (HDTMABr) and poly(ethylene glycol) butyl ether (PEG). Synthesized HDTMA-B and PEG-B were characterized by XRD, FTIR and DTA-TG analyses and their specific surface area, particle size and pore size distributions were determined. BET surface areas and basal spacings (d(001)) of the HDTMA-B and PEG-B were found to be 38.71 m(2)g(-1), 69.04 m(2)g(-1) and 21.96 Å, 15.17 Å, respectively. Increased adsorption with temperature indicates that the process is endothermic for o-nitrophenol. On the other hand m- and p-nitrophenols exhibited lower rates of adsorption at higher temperatures suggesting a regular exothermic process taking place. Results were analyzed according to the Langmuir, Freundlich and Dubinin-Redushkevich (D-R) isotherm equations using linearized correlation coefficient at different temperatures. R(L) separation factors for Langmuir and the n values for Freundlich isotherms showed that m- and p-nitrophenols are favorably adsorbed by HDTMA-B and, p-nitrophenol is favored by PEG-B. Adsorption of o-, m- and p-nitrophenols as single components or from their binary mixtures on HDTMA-B and, p-nitrophenol on PEG-B are all defined to be physical in nature.

The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kütahya bentonite

The effect of the Na2CO3 activation on the rheological properties of a bentonite from Kutahya (Turkey) was investigated. The bentonite was activated with Na2CO3 at different dosages (1–15 g Na2CO3/100 g bentonite). The activated samples were examined by chemical and X-ray diffraction analysis. The calcium bentonite was completely converted to sodium bentonite when the Na2CO3/bentonite ratio was 2.5%. The rheological values showed a maximum after addition of 2.5% Na2CO3 (bentonite concentrations 2–6% w/w). At 2.5 g Na2CO3/100 g bentonite, the shear stress was also measured at several NaCl and Na-hexametaphosphate concentrations. NaCl addition decreased the rheological properties up to NaCl concentrations of 0.005 mol l−1. Further addition of NaCl increased the rheological properties again. The addition of Na-hexametaphosphate caused a decrease in the rheological properties to a constant value higher phosphate concentrations. The lowest yield stress was obtained around pH 7.

Modification of rheology and permeability of Turkish ceramic clays using sodium silicate

Abstract Rheological properties of two ceramic clays (Sindirgi and Kure) having different chemical and mineral compositions were determined. The variation in viscosity for suspensions having 50%, 55% and 60% (w/w) clay was measured as a function of initial loading of sodium silicate. The relationship between shear rate (0–120 s −1 ) and shear stress (0–350 Pa) was determined for these suspensions in the presence of various amounts of sodium silicate. The effect of the amount of clay on the suspension thixotropy properties was investigated for original and treated suspensions. Slip viscosities of 1500, 500 and 100 cP were evaluated and the suspensions were filtered to obtain cakes. From rheological measurements, thixotropy properties changes were correlated with increased solid and electrolyte in the suspension and the clay mineral type. In addition, results showed that the permeability, the porosity and the casting rate increase with the viscosity in the clay suspensions and the permeability decreases with decreasing porosity. When the clay ratio in the suspensions is 50% (w/w) and the viscosity 1500 cP, the porosity and the permeability values obtained in each sample are higher than the others.

Desorption of Salicylic Acid from Modified Bentonite by Using Supercritical Fluids in Packed Bed Column

ABSTRACT Desorption of salicylic acid from organically modified bentonite by using supercritical fluids (SCFs) was studied. The parameters, such as pressure, temperature, SCF flow rate, and cosolvent (entraîner) concentration, were investigated. A desorption yield of 40 wt% salicylic acid was obtained by using supercritical CO2 by operating at low pressure (300 bar), low temperature (40°C), and 2 mL CO2/min, it reached up to 77 wt% in the presence of ethanol as cosolvent 10 vol%. Similarly, a maximum desorption yield of 76wt% salicylic acid was obtained by using supercritical C02 by operating at high pressure (500 bar), high temperature (80°C), and 2 mL SC CO2/min, it reached up to 98 wt% in the presence of ethanol as cosolvent 10vol%. Hence, it was concluded that the mean contents in the desorbed solute are approximately 1.5-2-fold higher by addition of 10vol% ethanol than only supercritical CO2 desorption process.

Sulphuric Acid Activation of a Calcium Bentonite

The objective of this work was to determine the changes of thermal and surface properties of a bentonite from Çankιrι after activation using different concentrations of H2SO4 solutions (0.5–4 M). XRD, FTIR, DTA, and TG analyses of the samples were performed to examine the structural changes of the bentonite before and after acid activation. DTA peaks showed an exothermic change in the temperature region 900–1000°C. Changes at low acid concentrations resulted from cation exchange (exchangeable cations with H ions) and removal of impurities from the bentonite. Differences of surface properties and thermal properties at higher acid concentrations (2–4 M H2SO4) were caused by structural changes and partial decomposition of the samples. Surface area measurements showed that with the increase of concentration of H2SO4 solution the total BET surface area increased, while the maximum value of specific surface area (240.9 m2/g) was attained by the sample activated with 2 M H2SO4. Activation with higher concentrations (3–4 M) caused a decrease in the surface area. The particle size distributions of the original and acid-activated samples showed that the acid activation strongly affected the particle sizes of the particles. While 97.8% of the original bentonite sample is less than 10 µm in size, 97.8% of the activated samples with 0.5 M acid and 92% of the activated sample with 4 M acid are less than 28.25 µm in size.

ADSORPTION OF SOME ORGANIC COMPOUNDS BY HEXADECYLTRIMETHYLAMMONIUM - BENTONITE

In this study, the removal of organic contaminants from wastewater has been studied by using hexadecyltrimethylammonium bentonite (HDTMAbentonite). HDTMA-bentonite was synthesized by placing quaternary ammonium surfactant (hexadecyltrimethylammonium bromide) on the sodium bentonite (Na-B) by cation exchange. The sorption of organic pollutants was examined by batch equilibration method at 25°C. As organic contaminants polar compounds (methylene blue, benzoic acid and salicylic acid) and nonpolar compounds (toluene and xylene) were used. The concentrations of the organic pollutants used ranged from 0 to 700 mg/L. Methylene blue, benzoic acid and salicylic acid sorptions to HDTMA-bentonite were characterized by relatively strong solute uptake. Toluene and xylene sorptions to HDTMA-bentonite were weaker.

Investigation of Graphene/Ag Nanocomposites Synthesis Parameters for Two Different Synthesis Methods

Graphene/Ag nanocomposites were prepared with two different approaches; (i) sequential reduction of graphene oxide and silver nitrate (AgNO3), (ii) simultaneous reduction of graphene oxide and AgNO3 with hydrazine hydrate. The effect of synthesis parameters such as AgNO3 amount, concentration of AgNO3 solution, reducing agent amount, concentration of reducing agent solution, on the mean size and particle size distribution of Ag nanoparticles deposited on graphene nanosheets were examined. The structure and morphology of the prepared nanocomposites were characterized with Fourier transform infrared spectrophotometer (FTIR), UV-visible spectra, scanning electron microscope (SEM), transmission electron microscope (TEM), and Raman spectra. Based on experimental data shown in this work Ag nanoparticles with smaller sizes (3.04 ± 0.64 nm) and narrower size range (2–6 nm, approximately % 90) that homogenously deposited on graphene nanosheets were obtained by simultaneous reduction method, compared to sequential reduction method.

Adsorption of Aromatic Hydrocarbons on BTEA–bentonites

Organobentonites were synthesized using benzyltrimethyl-ammonium bromide (BTEA) with five different exchange degrees. At low concentrations, the amounts of BTEA exchanged did not reach the value of the cation-exchange capacity (CEC) of the bentonite. To obtain full displacement, it was necessary to add an amount of BTEA four-times greater than the CEC. Synthesized organobentonites were characterized by X-ray diffraction, particlesizeanalysis and infrared spectroscopy. The basal spacings of the organobentonites increased slightly with increasing amounts of BTEA cations. Particle-size analyses of the original bentonite and organobentonites showed that the organobentonites contained a greater number of coarse particles than present in the original bentonite. Toluene and xylenes were used as solutes to determine the adsorption properties of the BTEA–bentonites. The 4BTEA–bentonite was evaluated as an adsorbent of water-soluble aromatic hydrocarbons including toluene and xylenes.

Regeneration of Modified Bentonite Loaded with Phenol Using Supercritical Fluids

The desorption of phenol from organically modified bentonite (ODTMA–bentonite) using supercritical fluids was studied. Parameters such as pressure, temperature, supercritical fluid flow rate and co-solvent (entrainer) concentration were investigated. The maximum desorption of phenol (ca. 98 w/w%) using supercritical CO2 (SC CO2) was obtained by operating at 500 bar, 353 K and 3.33 × 10−8 m3 SC CO2/s. In the presence of ethanol as a co-solvent (10 v/v%), the maximum desorption of phenol attained a value of 97 w/w% using supercritical CO2 at low temperature (313 K) and pressure (300 bar) and a high supercritical fluid flow rate (3.33 × 10−8 m3 SC CO2/s). In addition, the results showed that the regenerated ODTMA–bentonite retained its adsorption power towards phenol even after several regeneration cycles. It was therefore concluded that exhausted/used organobentonites might be regenerated via processes involving supercritical fluid extraction.

SORPTION CHARACTERISTICS OF ORGANIC COMPOUNDS ON THREE HEXADECYL-TRIMETHYLAMMONIUM-SMECTITES HAVING DIFFERENT CATION EXCHANGE CAPACITIES

The removal of organic contaminants from wastewater has been studied by using hexadecyltrimethylammonium bentonites (HDTMA-bentonites) having different cation exchange capacity (CEC). HDTMA-bentonites were synthesized by placing quaternary ammonium surfactant (hexadecyltrimethylammonium bromide) on Cankiri sodium bentonite (CNa-B) having 85 meq/100 g clay, Kütahya calcium bentonite (KCa-B) having 65 meq 7100 g clay and Cankiri calcium bentonite (CCa-B) having 47,5 meq/100 g clay by cation exchange. The sorption of organic pollutants was examined by batch equilibration method at 25°C. As organic contaminants, polar compounds (methylene blue, benzoic acid and salicylic acid) and nonpolar compounds (toluene and xylenes) were used. The concentrations of the organic pollutants used ranged from 0 to 700 mg/L. Methylene blue, benzoic acid and salicylic acid sorptions to HDTMA-bentonites were characterized by relatively strong solute uptake. Toluene and xylene sorptions to HDTMA-bentonite were weaker. The effectiveness of HDTMAbentonites increased with CEC. It is concluded that high CEC HDTMA bentonite was a highly effective adsorbent for removing salicylic acid, benzoic acid and methylene blue. Author to whom correspondence should be addressed (e-mail: calimli@science.ankara.edu.tr) 349 Vol. 15. No. 4, 1999 Sorption Characteristics Of Organic Compounds On Three Hexadecyl-Trimelhylammonium-Smectites