Sorption of acid red 57 from aqueous solution onto sepiolite

Sepiolite, a highly porous mineral, is becoming widely used as an alternative material in areas where sorptive, catalytic and rheological applications are required. High ion exchange capacity and high surface area and more importantly its relatively cheap price make it an attractive adsorbent. In this study, the adsorption of acid red 57 by natural mesoporous sepiolite has been examined in order to measure the ability of this mineral to remove coloured textile dyes from wastewater. For this purpose, a series of batch adsorption tests of acid red 57 from aqueous sepiolite solutions have been systematically investigated as a function of parameters such as pH, ionic strength and temperature. Adsorption equilibrium was reached within 1h. The removal of acid red 57 decreases with pH from 3 to 9 and temperature from 25 to 55 degrees C, whereas it increases with ionic strength from 0 to 0.5 mol L(-1). Adsorption isotherms of acid red on sepiolite were determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to fit the isotherm data better than the Freundlich model. The physical properties of this adsorbent were consistent with the parameters obtained from the isotherm equations. Approximately, 21.49% weight loss was observed. The surface area value of sepiolite was 342 m2 g(-1) at 105 degrees C, and it increased to 357 m2 g(-1) at 200 degrees C. Further increase in temperature caused channel plugging and crystal structure deformation, as a result the surface area values showed a decrease with temperature. The data obtained from adsorption isotherms at different temperatures have been used to calculate some thermodynamic quantities such as the Gibbs energy, heat and entropy of adsorption. The thermodynamic data indicate that acid red 57 adsorption onto sepiolite is characterized by physical adsorption. The dimensionless separation factor (RL) have shown that sepiolite can be used for removal of acid red 57 from aqueous solutions. The sorption capacity of the sepiolite is comparable to the other available adsorbents, and it is quite cheaper.     

Electrokinetic and adsorption properties of sepiolite modified by 3-aminopropyltriethoxysilane

Surface modification of clay minerals has become increasingly important for improving the practical applications of clays such as fillers and adsorbents. An investigation was carried out on the surface modification of sepiolite with aminopropylsilyl groups in 3-aminopropyltriethoxysilane (3-APT). The zeta potential of the modified sepiolite suspensions was measured as a function of initial electrolyte concentration and equilibrium pH using a Zeta Meter 3.0 for modified sepiolite. The utility of the 3-APT-modified sepiolite was investigated as an adsorbent for removal of various heavy metal ions such as Fe, Mn, Co, Zn, Cu, Cd and Ni from aqueous solutions. The effects of various factors on the adsorption, such as pH, ionic strength and temperature of the solution were studied. The results showed that the amount adsorbed increases with solution pH in the pH range of 1.5 and 7.0; indicated that the modified sepiolite adsorbed Fe and Mn ions more than other metal ions such as Co, Zn, Cu, Cd and Ni. It was found that the temperature had an important effect on metal ion adsorption by the modified sepiolite. The adsorption isotherm has been determined and data have been analyzed according to the Langmuir and Freundlich models.     

Uptake of trivalent chromium ions from aqueous solutions using kaolinite

The sorption of Cr(III) from aqueous solutions on kaolinite has been studied by a batch technique. We have investigated how solution pH, ionic strength and temperature affect this process. The adsorbed amount of chromium ions on kaolinite has increased with increasing pH and temperature when it has decreased with increasing ionic strength. The sorption of Cr(III) on kaolinite is endothermic process in nature. Sorption data have been interpreted in terms of Freundlich and Langmuir equations. The adsorption isotherm was measured experimentally at different conditions, and the experimental data were correlated reasonably well by the adsorption isotherm of the Langmuir, and the isotherm parameters (q(m) and K) have been calculated as well. The enthalpy change for chromium adsorption has been estimated as 7.0 kJ mol(-1). The order of enthalpy of adsorption corresponds to a physical reaction.     

Removal of copper ions from aqueous solutions by kaolinite and batch design

The removal of copper ions from aqueous solutions by kaolinite was investigated by using a batch-type method. Effects of factors such as pH, ionic strength, temperature, acid-activation and calcination on copper adsorption were investigated. The uptake of copper was determined from changes in concentration as measured by atomic absorption spectrometry. The extent of copper adsorption increased with increasing pH and temperature and with decreasing ionic strength, acid-activation and calcination temperature. The Langmuir and Freundlich adsorption models were used to determine the isotherm parameters associated with the adsorption process. The results provide support for the adsorption of copper ions onto kaolinite. Thermodynamic parameters indicated the endothermic nature of copper adsorption on kaolinite. The experimental results were applied a batch design. As a result, the kaolinite may be used for removal of copper ions from aqueous solutions.     

Error analysis of equilibrium studies for the almond shell activated carbon adsorption of Cr(VI) from aqueous solutions

In this study, the preparation of activated carbon from almond shell with H2SO4 activation and its ability to remove toxic hexavalent chromium from aqueous solutions are reported. The influences of several operating parameters such as pH, particle size and temperature on the adsorption capacity were investigated. Adsorption of Cr(VI) is found to be highly pH, particle size and temperature dependent. Four adsorption isotherm models namely, Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich were used to analyze the equilibrium data. The Langmuir isotherm provided the best correlation for Cr(VI) onto the almond shell activated carbon (ASC). Adsorption capacity was calculated from the Langmuir isotherm as 190.3 mg/g at 323 K. Thermodynamic parameters were evaluated and the adsorption was endothermic showing monolayer adsorption of Cr(VI). Five error functions were used to treat the equilibrium data using non-linear optimization techniques for evaluating the fit of the isotherm equations. The highest correlation for the isotherm equations in this system was obtained for the Freundlich isotherm. ASC is found to be inexpensive and effective adsorbent for removal of Cr(VI) from aqueous solutions.     

Adsorption of Acid Red 57 from aqueous solutions onto surfactant-modified sepiolite

The adsorption of Acid Red 57 (AR57) onto surfactant-modified sepiolite was investigated in aqueous solution in a batch system with respect to contact time, pH and temperature. The surface modification of surfactant-modified sepiolite was controlled using the FTIR technique. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 90 min, whereas diffusion is not only the rate controlling step. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Freundlich model agrees with experimental data well. The activation energy, change of free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of AR57 onto surfactant-modified sepiolite. The results indicate that surfactant-modified sepiolite could be employed as low-cost material for the removal of textile dyes from effluents.     

Adsorption of Acid Blue 193 from aqueous solutions onto DEDMA-sepiolite

The adsorption of Acid Blue 193 (AB193) onto dodecylethyldimethylammonium (DEDMA)-sepiolite was investigated in aqueous solution in a batch system with respect to contact time, pH and temperature. The surface modification of DEDMA-sepiolite was examined by the FT-IR technique. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well with the pseudo-second-order kinetic model and also followed the simple external diffusion model up to initial 10 min and then by intraparticle diffusion model up to 75 min, whereas diffusion is not only the rate-controlling step. The adsorption capacities of natural sepiolite and DEDMA-sepiolite at pH 1.5 and 20 degrees C were (1.19 and 2.57) x 10(-4) mol g(-1), respectively. The above results indicate that DEDMA-sepiolite has around two times higher adsorption capacity than natural sepiolite. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Freundlich model agrees with experimental data well. The activation energy, change of Gibbs free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of AB193 onto DEDMA-sepiolite.     

Jute stick powder as a potential biomass for the removal of congo red and rhodamine B from their aqueous solution

Jute stick powder (JSP) has been found to be a promising material for adsorptive removal of congo red (C.I. 22120) and rhodamine B (C.I. 45170) from aqueous solutions. Physico-chemical parameters like dye concentration, solution pH, temperature and contact time have been varied to study the adsorption phenomenon. Favorable adsorption occurs at around pH 7.0 whereas temperature has no significant effect on adsorption of both the dyes. The maximum adsorption capacity has been calculated to be 35.7 and 87.7mg/g of the biomass for congo red and rhodamine B, respectively. The adsorption process is in conformity with Freundlich and Langmuir isotherms for rhodamine B whereas congo red adsorption fits well to Langmuir isotherm only. In both the cases, adsorption occurs very fast initially and attains equilibrium within 60min. Kinetic results suggest the intra-particle diffusion of dyes as rate limiting step.     

Silkworm exuviae--a new non-conventional and low-cost adsorbent for removal of methylene blue from aqueous solutions

In this paper, silkworm exuviae (SE) waste, an agricultural waste available in large quantity in China, was utilized as low-cost adsorbent to remove basic dye (methylene blue, MB) from aqueous solution by adsorption. Kinetic data and sorption equilibrium isotherms were carried out in batch process. The adsorption kinetic experiments revealed that MB adsorption onto SE for different initial dye concentrations all followed pseudo-second order kinetics and were mainly controlled by the film diffusion mechanism. Batch equilibrium results at different temperatures suggest that MB adsorption onto SE can be described perfectly with Freundlich isotherm model compared with Langmuir and D-R isotherm models, and the characteristic parameters for each adsorption isotherm were also determined. Thermodynamic parameters calculated show the adsorption process has been found to be endothermic in nature. The analysis for the values of the mean free energies of adsorption (E(a)), the Gibbs free energy (ΔG(0)) and the effect of ionic strength all demonstrate that the whole adsorption process is mainly dominated by ion-exchange mechanism, which has also been verified by variations in FT-IR spectra and pH value before and after adsorption and desorption studies. The results reveal that SE can be employed as a low-cost alternative to other adsorbents for MB adsorption.     

Removal of Cr(VI) from aqueous solutions by low-cost biosorbents: marine macroalgae and agricultural by-products

In this study, adsorption of Cr(VI) onto the four low-cost biosorbents (Laminaria japonica, P. yezoensis Ueda, rice bran and wheat bran) was investigated depending on solution pH, contact time, adsorbent concentration and adsorption isotherms by employing batch adsorption technique. The adsorption capacities were significantly influenced by solution pH, with lower pH favoring higher Cr(VI) removal for various biosorbents. The ionic strength of NaCl was also observed to have a significant impact on the Cr(VI) adsorption due to the competition of Cl(-) in the aqueous solutions. The batch equilibrium data were correlated to Langmuir and Freundlich isotherms and the data fitted better to the Freundlich isotherm equation. The apparent thermodynamic parameters were calculated for each of the four biosorbents and the obtained numerical values showed that the Cr(VI) adsorption onto the various low-cost biosorbents is spontaneous, entropy-driven and endothermic processes. The batch kinetic data were correlated to the pseudo-first order and pseudo-second order models and the data fitted better to the pseudo-second order equation. An intraparticle diffusion model was applied to investigate the adsorption mechanisms. The adsorption capacities for various biosorbents studied in this work were inversely proportional to the adsorbent concentrations.     

Adsorption behaviors of some phenolic compounds onto high specific area activated carbon cloth

Adsorption of phenol, hydroquinone, m-cresol, p-cresol and p-nitrophenol from aqueous solutions onto high specific area activated carbon cloth has been studied. The effect of ionization on adsorption of these ionizable phenolic compounds was examined by studying the adsorption from acidic, basic and natural pH solutions. Kinetics of adsorption was followed by in situ UV spectroscopy over a period of 90 min. First-order rate law was found to be valid for the kinetics of adsorption processes and the rate constants were determined. The highest rate constants were obtained for the adsorption from solutions at the natural pH. The lowest rate constants were observed in basic solutions. The rate constants decreased in the order p-nitrophenol approximately m-cresol>p-cresol>hydroquinone approximately phenol. Adsorption isotherms were derived at 30 degrees C and the isotherm data were treated according to Langmuir, Freundlich and Tempkin isotherm equations. The goodness of fit of experimental data to these isotherm equations was tested and the parameters of equations were determined. The possible interactions of compounds with the carbon surface were discussed considering the charge of the surface and the possible ionization of compounds at acidic, basic and natural pH conditions.     

Biosorption of methylene blue from aqueous solution by fallen phoenix tree's leaves

A new adsorbent, the fallen phoenix tree's leaf, has been investigated in order to remove methylene blue (MB) from aqueous solutions. Variables of the system, including contact time, leaf dose, solution pH, salt concentration and initial MB concentration, were adopted to study their effects on MB biosorption. The results showed that as the dose of leaf increased, the percentage of MB sorption increased accordingly. There was no significant difference about the quantity of MB adsorbed onto leaf as the pH was within the range 4.5-10.0. The salt concentration has negative effect on MB removal. The equilibrium data were analyzed using the Langmuir and the Freundlich isotherms. The results of non-linear regressive analysis are that the Langmuir isotherm is better fit than the Freundlich isotherm at different temperature according to the values of determined coefficients (R(2)) and chi(2)-statistic (SS). The Langmuir monolayer saturation capacities of MB adsorbed onto leaf are 80.9, 83.8, 89.7mgg(-1) at 295, 309 and 323K, respectively. Using the equilibrium concentration contents obtained at different temperatures, various thermodynamic parameters, such as DeltaG degrees , DeltaH degrees and DeltaS degrees , have been calculated. The thermodynamics parameters of MB/leaf system indicate spontaneous and endothermic process. It was concluded that an increase in temperature be advantage to adsorb MB onto leaf.     

Adsorption of nickel and copper onto natural iron oxide-coated sand from aqueous solutions: study in single and binary systems

Natural iron oxide-coated sand (NCS), extracted from the iron ore located in North-West of Tunisia, was employed to investigate its capacity to remove copper and nickel from aqueous solutions. The aim of this work was to characterize the considered sorbent (NCS) and to assess the possibility of removing nickel and copper from aqueous solutions by this sorbent. The effects of agitation time, pH, initial metal ion concentration and temperature on the removal of these metals were studied. In order to study the sorption isotherm, two equilibrium models, the Freundlich and Langmuir isotherms, were analyzed. The effect of solution pH on the adsorption onto NCS was studied in the pH range from 2 to 7 and 2 to 9 for copper and nickel respectively. The adsorption was endothermic and the computation of the parameters, DeltaH degrees, DeltaS degrees and DeltaG degrees, indicated that the interactions were thermodynamically favourable. Experiments with Cu and Ni adsorption measured together showed that Cu severely interfered with Ni adsorption to the NCS and vice versa under the conditions of the two coexisted ions adsorption.     

Factors influencing the removal of fluoride from aqueous solution by calcined Mg-Al-CO3 layered double hydroxides

Layered double hydroxides (LDH) calcined at different temperatures (denoted as CLDH) have been demonstrated to recover their original layered structure in the presence of appropriate anions. In the light of this so-called "memory effect", a study of removal of fluoride from aqueous solution by calcined Mg-Al-CO(3)-LDH has been carried out. The LDH calcined at 500 degrees C had the highest capacity of removal of fluoride ion, because of retention of its intrinsic structure. The CLDH with an Mg/Al ratio of 2 has a remarkable ability to adsorb anions. The adsorption loading is higher for the calcined Mg-Al-LDH than for calcined Zn-Al and Ni-Al-LDH. The influence of varying the conditions for removal of fluoride, such as the pH of aqueous solution, the initial fluoride concentration, the dosage of adsorbent, and temperature on removal of fluoride have been investigated. The influence of co-existing anions in fluoride aqueous solution indicates that the percentage of removal of fluoride increased in order PO(4)(3-) < Cl(-) approximately SO(4)(2-) < Br(-) < NO(3)(-). It was found that maximum removal of fluoride from aqueous solutions was obtained in 6h at pH 6.0 with an initial concentration of 50 mg/L, and that the retention of fluoride ions by the CLDH material was 98% or higher. The residual fluoride concentration was found to be 0.4 mg/L with an initial concentration of 20 mg/L, which meets the national standard for drinking water quality. The Freundlich isotherm and Langmuir isotherm were used to fit the data of equilibrium experiments. The results of X-ray diffraction, FT-IR and TG-MS demonstrate that the adsorption phenomenon is accompanied by rehydration with concomitant uptake of fluoride ions to rebuild the initial layered structure.     

Adsorption of EDTA on activated carbon from aqueous solutions

In this study, the adsorption of EDTA on activated carbon from aqueous solutions has been investigated in a batch stirred cell. Experiments have been carried out to investigate the effects of temperature, EDTA concentration, pH, activated carbon mass and particle size on EDTA adsorption. The experimental results manifest that the EDTA adsorption rate increases with its concentration in the aqueous solutions. EDTA adsorption also increases with temperature. The EDTA removal from the solution increases as activated carbon mass increases. The Langmuir and Freundlich equilibrium isotherm models are found to provide a good fitting of the adsorption data, with R(2) = 0.9920 and 0.9982, respectively. The kinetic study shows that EDTA adsorption on the activated carbon is in good compliance with the pseudo-second-order kinetic model. The thermodynamic parameters (E(a), ΔG(0), ΔH(0), ΔS(0)) obtained indicate the endothermic nature of EDTA adsorption on activated carbon.     

Isotherm, thermodynamic, kinetics and adsorption mechanism studies of methyl orange by surfactant modified silkworm exuviae

This paper reports on the development of organo-modified silkworm exuviae (MSE) adsorbent prepared by using hexadecyltrimethylammonium bromide (HDTMAB) for removing methyl orange (MO), a model anionic dye, from aqueous solution. The natural and modified samples were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FT-IR). Batch adsorption experiments were carried out to remove MO from its aqueous solutions using SE and MSE. It was observed that the adsorption capacity of MSE is 5-6 times of SE. The different parameters effecting on the adsorption capacity such as pH of the solution, initial dye concentration, temperature and contact time have been investigated. Analysis of adsorption results obtained at different temperatures showed that the adsorption pattern on the MSE can be described perfectly with Langmuir isotherm model compared with Freundlich and Dubinin-Radushkevich (D-R) isotherm models, and the characteristic parameters for each adsorption isotherm were also determined. The adsorption process has been found exothermic in nature and thermodynamic parameters have been calculated. The adsorption kinetic followed the pseudo-second order kinetic model. The results of FT-IR, EDS and desorption studies all suggest that methyl orange adsorption onto the MSE should be mainly controlled by the hydrophobic interaction mechanism, along with a considerable contribution of the anionic exchange mechanism. The results indicate that HDTMAB-modified silkworm exuviae could be employed as low-cost material for the removal of methyl orange anionic dye from wastewater.     

Kinetics and equilibrium studies for the adsorption of Acid Red 57 from aqueous solutions onto calcined-alunite

The adsorption of Acid Red 57 (AR57) onto calcined-alunite was examined in aqueous solution in a batch system with respect to contact time, pH and temperature. The first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 90 min. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The equilibrium data are successfully fitted to the Langmuir adsorption isotherm. The Langmuir isotherm constant, K(L), was used to evaluate the changes of free energy, enthalpy and entropy of adsorption for the adsorption of AR57 onto calcined-alunite. The results indicate that calcined-alunite could be employed as low-cost material for the removal of acid dyes from textile effluents.     

Immobilisation of TiO2-nanoparticles on sewage sludge and their adsorption for cadmium removal from aqueous solutions

In this study, pure TiO₂-nanoparticles and TiO₂/sewage sludge (TS) as biomass material were synthesised via a sol–gel method. The adsorption potential of nanosized TiO₂ and TS for removal of Cd(II) was investigated in a batch system. The prepared adsorbents were characterised using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The XRD analysis showed that pure TiO₂ is in amorphous phase before calcination and in anatase phase at annealing temperature of 400 °C. TiO₂/sewage sludge that calcined at 400 °C (TS⁴⁰⁰) was found to be the best adsorbent for cadmium removal from aqueous solution. Kinetic and isotherm studies were carried out by considering the parameters, pH, initial concentration and contact time. The optimum pH value for Cd(II) adsorption onto TS⁴⁰⁰ was found to be 6. Langmuir isotherm showed better fit than Freundlich isotherm and the maximum adsorption capacity was found to be 29.28 mg/g which is higher than that of many other adsorbents reported in literature. The sorption kinetic data were well fitted with a pseudo-second-order model. These results demonstrated that TS⁴⁰⁰ was readily prepared and is the promising and effective solid material for the removal of Cd(II) from aqueous solutions.     

Equilibrium studies for trimethoprim adsorption on montmorillonite KSF

In this study, the adsorption of trimethoprim (TMP) on montmorillonite KSF was studied under different conditions (pH, ionic strength, temperature). The results indicate that a pH value of 5.04 is optimum value for the adsorption of TMP on KSF. The adsorption kinetics was interpreted using pseudo-first-order kinetic model, pseudo-second-order kinetic model and intraparticle diffusion model. The pseudo-second-order model provides the best correlation with the experimental data of KSF adsorption. The adsorption data could be fitted with Freundlich, Langmuir and Dubinin-Radushkevich equation to find the characteristic parameters of each model. It was found that linear form of Langmuir isotherm seems to produce a better model than linear form of Freundlich equation. From the Langmuir and Freundlich equation, the adsorption capacity values raised as the solution temperature decreased. From DR isotherm, it was also determined that the type of adsorption can be considered as ion-exchange mechanism. Determination of the thermodynamic parameters DeltaH(0), DeltaS(0) and DeltaG(0) showed that adsorption was spontaneous and exothermic in nature. It was also added that adsorption of TMP by KSF may involve physical adsorption.     

Removal of Cu(II) ions by activated poplar sawdust (Samsun clone) from aqueous solutions

In this work, adsorption of Cu(II) ions on sawdust (SD) and activated sawdust (ASD) has been studied by using batch adsorption techniques. The equilibrium adsorption level was determined to be a function of the pH, initial Cu(II) concentration, and adsorbent dosage. The equilibrium nature of Cu(II) adsorption has been described by the Freundlich and Langmuir isotherms. The experimental adsorption data were fitted to the Langmuir adsorption model both sawdust and activated sawdust. The equilibrium capacity of sawdust and activated sawdust were 5.432 and 13.495 mg copper per g adsorbent, respectively at room temperature and natural pH. The maximum adsorption capacity was obtained at the maximum zeta potential value that -74.5 mV (pH 5) for activated sawdust and at -48.4 mV (pH 4) for sawdust. It was observed that activated sawdust was a suitable adsorbent than sawdust for removal of Cu(II) from aqueous solutions.