Aqueous Phase Adsorption of Cephalexin onto Bentonite and Activated Carbon

The adsorption of cephalexin in aqueous solution has been investigated using bentonite and activated carbon as the adsorbents. Batch kinetics and isotherm studies were carried out to evaluate the effect of contact time, adsorbent dosage, pH, particle size, and temperature. Adsorption equilibrium data were well represented by the Langmuir and Freundlich isotherm models. The adsorption intensity was found to be increased as the aqueous phase pH increased, and had a maximum at pH = 6.1. The pseudo-first order, pseudo-second order, and intraparticle diffusion kinetic models were used to describe the kinetic data. The experimental data fitted very well with the pseudo-second-order kinetic model and also followed the simple external and intraparticle model.     

The effects of the thermal treatment of activated carbon on the phenols adsorption

The adsorptive properties of thermally treated activated carbon at 1,500 and 1,800 °C were investigated. The adsorption kinetics and adsorption efficiency of phenol, 4-chlorophenol and 2,4-dichlorophenol from aqueous solutions were examined. The adsorption kinetic data were analyzed using the pseudo-first and pseudo-second order models, while the equilibrium adsorption data were described by the Langmuir and Freundlich isotherms. The adsorption rate and efficiency increased in the order: phenol<4-chlorophenol<2,4-dichlorophenol. The activated carbons were also used for the modification of the carbon paste electrodes for the detection of the phenols based on the differential pulse voltammetry. Compared to the non-modified electrode, all the new paste electrodes showed a significantly greater sensitivity for the detection of the phenols. The signal response was closely related to the porosity of the materials used, and increased with an increase in the adsorption ability and the specific surface area of the modifiers.     

Application of Aqai Stalks as Biosorbents for the Removal of the Dye Procion Blue MX-R from Aqueous Solution

The aqai palm stalk (Euterpe oleracea) is a food residue used in its natural form (AS) and also protonated (AAS) as biosorbents for the removal of the textile dye Procion Blue MX-R from aqueous solutions. This biosorbent was characterized by infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption-desorption curves. The effects of pH, biosorbent dosages, and shaking time on the biosorption capacities were studied. In the acidic pH region (pH 2.0) the biosorption of the dye was favorable. The minimum contact time to obtain the equilibrium was 8 hours for AS and AAS biosorbents. The general order kinetic model provided the best fit to the experimental data compared with the pseudo-first order and pseudo-second order kinetic adsorption models. The equilibrium data were fitted to the Langmuir, Freundlich, and Sips isotherm models. For both dyes the equilibrium data were best fitted to the Sips isotherm model. The enthalpy and entropy of adsorption of PB were obtained from adsorption equilibrium experiments ranging from 298 to 323 K. Simulated dyehouse effluent was used to check the applicability of the proposed adsorbents for effluent treatment.     

Adsorption of Cu(II) and Cr(VI) onto Treated Shorea dasyphylla Bark: Isotherm,Kinetics, and Thermodynamic Studies

The efficacy of treated Shorea dasyphylla bark for Cu(II) and Cr(VI) adsorption was assessed in a batch adsorption system as a function of pH, agitation period, and initial metal concentration. The equilibrium nature of Cu(II) and Cr(VI) adsorption was described by the Freundlich, Langmuir, and Dubinin-Radushkevich isotherms. The maximum monolayer capacities of treated Shorea dasyphylla bark, estimated from the Langmuir equation were 184.66 and 42.72 mg/g for Cu(II) and Cr(VI), respectively. The experimental results were fitted using pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models; the pseudo-second order showed the best conformity to the kinetic data. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) were determined by applying the Van't Hoff equation. The adsorption of Cu(II) and Cr(VI) onto treated Shorea dasyphylla bark was found to be spontaneous and exothermic. The adsorption mechanism was confirmed by means of Fourier transform infrared (FTIR) and Energy dispersive X-ray (EDX) spectroscopy. The dimensionless constant separation factor (R _L), indicated that treated Shorea dasyphylla bark was favorable for Cu(II) and Cr(VI) adsorption.     

MODIFIED PLANTAIN PEEL AS CELLULOSE-BASED LOW-COST ADSORBENT FOR THE REMOVAL OF 2,6-DICHLOROPHENOL FROM AQUEOUS SOLUTION: ADSORPTION ISOTHERMS,KINETIC MODELING,AND THERMODYNAMIC STUDIES

In this study, the feasibility of using modified plantain peel to remove 2,6-dichlorophenol from iaqueous solutions was investigated under batch mode. The effects of physical factors such as initial 2,6-dichlorophenol concentration, contact time, biosorbent particle size, biosorbent dosage and temperature on the removal process were evaluated. The results showed that biosorption of 2,6-dichlorophenol was dependent on these factors. The equilibrium biosorption data were analyzed by the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) adsorption isotherm models. The four tested isotherm models provided good fits to the experimental data obtained at 30°C; however, the Freundlich isotherm model provided the best correlation (R² = 0.9874) of the experimental data. The maximum monolayer biosorption capacity (Q _max ) was found to be 14.25 mg/g. The biosorption kinetics data of 2,6-dichlorophenol were analyzed by pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, and liquid film diffusion models. The five kinetic models fitted well to the biosorption kinetic data; however, the pseudo-second-order kinetic model gave the best fit when the biosorption mechanism was controlled by film diffusion. Thermodynamic quantities such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), standard entropy change of biosorption (ΔS°), and activation energy (E_a) were evaluated, and it was found that the biosorption process was spontaneous, feasible, endothermic in nature and of dual nature, physisorption and chemisorption; however, the physisorption process was dominant. Therefore, modified plantain peel has potential for application as an effective bioadsorbent for removal of 2,6-dichlorophenol from aqueous solution.     

The biosorption of Cr(VI) ions by dried biomass obtained from a chromium-resistant bacterium

The biosorption potential of many different kinds of biomaterials has been widely studied. However, there is little data on the biosorption mechanism of Cr(VI) by dried biomass. So the bio-removal of Cr(VI) ions from aqueous solutions was investigated using dried biomass from a chromium-resistant bacterium. The bacterium was isolated from dewatered sludge samples that were obtained from a sewage treatment plant. Equilibrium and kinetic experiments were performed at different metal concentrations, pH values, and biosorbents dosages. The biomass was characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The functional groups in the Bacillus cereus biomass which may play a role in the biosorption process were identified by Fourier transform infrared spectroscopy. The biosorption process was found to be highly pH dependent and the optimum pH for the adsorption of Cr(VI) was 2.0±0.3 at 30±2 °C. The experimental data fit well with Langmuir and Freundlich models as well as a pseudo-second order kinetic model. The mechanism for the biosorption was also studied by fitting the kinetic data with an intra-particle diffusion model and a Boyd plot. External mass transfer was found to be the rate-determining step for the adsorption process. Biosorption could be an alternative mechanism besides bio-oxidation and bio-reduction for the bioremediation of heavy metals.     

Removal of copper ions from aqueous solution by adsorption using LABORATORIES-modified bentonite (organo-bentonite)

Equilibrium, kinetic and thermodynamic aspects of the adsorption of copper ions from an aqueous solution using linear alkylbenzene sulfonate (LABORATORIES) modified bentonite (organo-bentonite) are reported. Modification of bentonite was performed via microwave heating with a concentration of LABORATORIES surfactant equivalent to 1.5 times that of the cation exchange capacity (CEC) of the raw bentonite. Experimental parameters affecting the adsorption process such as pH, contact time and temperature were studied. Several adsorption equations (e.g., Langmuir, Freundlich, Sips and Toth) with temperature dependency were used to correlate the equilibrium data. These models were evaluated based on the theoretical justifications of each isotherm parameter. The Sips model had the best fit for the adsorption of copper ions onto organo-bentonite. For the kinetic data, the pseudo-second order model was superior to the pseudo-first order model. Thermodynamically, the adsorption of copper ions occurs via chemisorption and the process is endothermic (ΔH⁰>0), irreversible (ΔS⁰>0) and nonspontaneous (ΔG⁰>0).     

Influence of an aerobic selector on copper and hexavalent chromium biosorption by activated sludge

The influence of an aerobic selector on biosorption of Cu and Cr(VI) by activated sludge was studied. In‐vitro batch adsorption tests were performed using sludge harvested from bench‐scale activated sludge systems. Metal biosorption by activated sludge was rapid with equilibrium usually reached within an hour. Adsorption behaviour closely followed a Freundlich isotherm model. Experimental data suggested that an aerobic selector increased the biosorption of the metal ions by activated sludge, confirming observations by others in a similar study but with different heavy metals. Freundlich isotherms indicated that the biosorption capacity of activated sludge was increased by 15% for Cu and 30% for Cr(VI). Activated sludge from both systems had a greater biosorption capacity for Cu than for Cr(VI). The effects of pH and sludge concentration were also investigated. The results indicate that these parameters may influence the biosorption characteristics of activated sludge. © 2002 Society of Chemical Industry     

Separation of Uranyl Ions on Starch-Based Functional Hydrogels: Mechanism and Kinetics

In this article, we report the mechanism and kinetics of adsorption of uranyl ions on starch-based functional hydrogels. The hydrogels were prepared from starch in native or hydrolyzed/oxidized form by crosslinking with N,N-methylenebisacrylamide. The hydrogels synthesized from the oxidized starch have carboxylic groups at C-6 position. The effect of the structure and external environmental factors, i.e., contact time, temperature, ion strength, and simulated seawater (0.55 M NaCl and 3 mM NaHCO₃), was investigated on the uranyl adsorption behavior of hydrogels. The adsorption of uranyl ions was rapid as the highest adsorption was observed after 6 h and at 40°C. The sorbents also exhibited appreciable ion uptake even from the simulated seawater. The equilibrium data was analyzed using Langmuir and Freundlich adsorption isotherms and pseudo-first order and pseudo-second order kinetic models. Evidence of adsorption was obtained by characterization of the uranyl ions-loaded hydrogels by FTIR spectroscopy and also by elution with 0.1 N HCl.     

椰壳炭对肌酐吸附性能及动力学研究

采用水蒸气活化法制备得到微孔发达的椰壳活性炭,并研究其对肌酐的吸附性能。以850℃活化所得微孔率最高的活性炭为吸附剂,考察了活性炭投加量、吸附时间、溶液pH值及肌酐初始质量浓度对肌酐吸附性能的影响,并采用准一级、准二级动力学方程对实验数据进行拟合处理。结果表明,制备所得4种椰壳活性炭对肌酐均有较强的吸附能力;微孔率越高,吸附量越大;37℃下,椰壳活性炭对肌酐的吸附平衡时间为6 h,平衡吸附量达到97.88 mg/g;酸性环境更有利于肌酐吸附;平衡吸附量随肌酐初始质量浓度增加而升高;吸附过程符合准二级动力学模型,以化学吸附为主。     

Removal of Methylene Blue from Aqueous Solutions by using Cold Plasma,Microwave Radiation and Formaldehyde Treated Acorn Shell

In this paper, cold plasma (CPTAS), formaldehyde (FTAS), and microwave radiation treated (MTAS) acorn shell obtained from Quercus petraea tree as biosorbent was characterized and its dye removal ability at different dye concentrations was studied. The isoelectric point, functional groups and morphology of acorn shell was investigated as adsorbent surface characteristics. Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and UV–Vis spectrophotometry were used. Methylene blue (MB) was used as model cationic dye. The Langmuir and Freundlich adsorption isotherm models were applied to describe the equilibrium isotherms. The results indicated that the data for adsorption of MB onto treated acorn shell fitted well with the Langmuir isotherm model. Comparison of adsorption capacities of CPTAS with FTAS has shown a significant increase by as much as about 30 mg/g (33.32%) in MB adsorption.The pseudo-first order, pseudo-second order kinetic models were examined to evaluate the kinetic data, and the rate constants were calculated. Adsorption kinetic of dyes followed pseudo-first order kinetics. Thermodynamic parameters such as free energy, enthalpy, and entropy of dye adsorption were obtained. The results indicated that acorn shell could be used as a natural biosorbent for the removal of cationic dyes.     

Removal of Cr(VI) From Aqueous Solution by Turkish Vermiculite: Equilibrium,Thermodynamic and Kinetic Studies

Abstract

The adsorption of Cr(VI) from aqueous solution by Turkish vermiculite were investigated in terms of equilibrium, kinetics, and thermodynamics. Experimental parameters affecting the removal process such as pH of solution, adsorbent dosage, contact time, and temperature were studied. Equilibrium adsorption data were evaluated by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Langmuir model fitted the equilibrium data better than the Freundlich model. The monolayer adsorption capacity of Turkish vermiculite for Cr(VI) was found to be 87.7 mg/g at pH 1.5, 10 g/L adsorbent dosage and 20°C. The mean free energy of adsorption (5.9 kJ/mol) obtained from the D–R isotherm indicated that the type of sorption was essentially physical. The calculated thermodynamic parameters (ΔG ^o , ΔH ^o and ΔS ^o ) showed that the removal of Cr(VI) ions from aqueous solution by the vermiculite was feasible, spontaneous and exothermic at 20–50°C. Equilibrium data were also tested using the adsorption kinetic models and the results showed that the adsorption processes of Cr(VI) onto Turkish vermiculite followed well pseudo-second order kinetics.     

Utilization of Raw and Activated Date Pits for the Removal of Phenol from Aqueous Solutions

Activated carbons prepared from date pits, an agricultural waste byproduct, have been examined for the adsorption of phenol from aqueous solutions. The activated carbons were prepared using a fluidized bed reactor in two steps; carbonization at 700 °C for 2 hours in N₂ atmosphere and activation at 900 °C in CO₂ atmosphere. The kinetic data were fitted to the models of intraparticle diffusion, pseudo‐second order, and Lagergren, and followed more closely the pseudo‐second‐order chemisorption model. The isotherm equilibrium data were well fitted by the Freundlich and Langmuir models. The maximum adsorption capacity of activated date pits per Langmuir model was 16 times higher than that of nonactivated date pits. The thermodynamic properties calculated revealed the endothermic nature of the adsorption process. The uptake of phenol increased with increasing initial phenol concentration from10 to 200 ppm and temperature from 25 to 55 °C, and decreased with increasing the solution pH from 4 to 12. The uptake of phenol was not affected by the presence of NaCl salt.     

改性膨润土对苯胺与苯酚混合液的吸附性能

研究酸活化膨润土和有机改性膨润土对苯胺和苯酚混合溶液的吸附性能,结果表明,酸活化膨润土对苯胺的吸附效果明显优于苯酚,具有较强的吸附选择性;有机膨润土对苯胺和苯酚的吸附无明显差别。吸附动力学研究表明,酸活化膨润土与有机改性膨润土对苯胺的吸附均符合准二级吸附动力学模型,相关系数分别为R²=0.999 8和R²=0.997 9。酸活化膨润土对苯胺的吸附符合Freundlich等温线模型,有机膨润土对苯胺的吸附数据对Freundlich等温线模型与Langmuir等温线模型均有较好的拟合。     

A comparative study of removal of Cu(II) from aqueous solutions by locally low-cost materials: marine macroalgae and agricultural by-products

In this study, adsorption of Cu(II) onto the five locally abundantly low-cost biosorbents (Laminaria japonica, P. yezoensis Ueda, rice bran, wheat bran and walnut hull) was investigated depending on initial solution pH, contact time, adsorbent concentration and reaction temperature. Cu(II) removal was pH-dependent for various biosorbents investigated. For P. yezoensis Ueda, rice bran, wheat bran and walnut hull, the batch equilibrium data were correlated to Langmuir and Freundlich isotherms and the data fitted better to the Langmuir isotherm equation and yielded Langmuir monolayer capacity of 5.04, 10.41, 6.85 and 3.52 mg/g at the temperature of 20°C, respectively. In the case of Laminaria japonica, the equilibrium data obeyed the Hill-der Boer equation for the whole initial concentration ranges of 0–200 mg/L examined, but only to Langmuir and Freundlich equations for the initial concentration less than 120 mg/L at various temperatures. The apparent thermodynamic parameters were calculated for each of the five biosorbents (ΔH = 9.25–40.04 kJ/mol; ΔG = –17.60 to –24.16 kJ/mol and ΔS = 85.81–228 J/mol K). The numerical values obtained showed that Cu(II) adsorption is a spontaneous, entropy-driven and endothermic process. 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 (the pseudo-second order rate constants, k_2,e = 0.1059–0.9453 g/(mg min); the correlation coefficients, r = 0.9816–0.9993).     

Kinetics,equilibrium and thermodynamic studies on biosorption of hexavalent chromium by dead fungal biomass of marine Aspergillus niger

Quite a number of reports are available on metal binding capacity of different groups of microorganisms. However, reports on the equilibrium studies on biosorption by marine fungi are quite inadequate. The present study was carried out in a batch system using dead biomass of marine Aspergillus niger for the sorption of Cr(VI). The removal rate of Cr(VI) was increased with a decrease in pH and an increase in Cr(VI) and biomass concentration. A. niger exhibited the highest Cr(VI) uptake of 117.33 mg g^?1 of biomass at pH 1.0 in the presence of 400 mg l^?1 Cr at 50 °C. Kinetics studies based on fractional power, zero order, first order, pseudo-first order, Elovich, second order and pseudo-second order rate expressions have also been carried out. The experimental data were analyzed using five, two-parameter isotherms (Langmuir, Freundlich, Dubinin–Radushkevich, Temkin and Halsey). It was observed that Langmuir model exhibited the best fit to experimental data. Thermodynamic parameters of the biosorption (ΔG°, ΔH° and ΔS°) were also determined.     

Isotherms,kinetics, and thermodynamic studies for adsorption of pigments and oxidation products in oil bleaching from catfish waste

Abstract

The aim of this work was to study the bleaching of oil extracted from the heads of the catfish by thermomechanical process through equilibrium, kinetics, and thermodynamics adsorption studies. The condition for the bleaching step was with 1% (w/w) adsorbent composed of 95% activated earth and 5% activated carbon (w/w). The pseudo-first order and pseudo-second order models were the most appropriate to represent the adsorption kinetics. The temperature of 80?°C increased the adsorption capacity of the two adsorbates, and the activation energies values were of 47.47 and 44.82?kJ mol^?1, respectively, for the adsorption of carotenoids and peroxides. The Langmuir model was the most appropriate to describe the bleaching equilibrium curves. The thermodynamic parameters revealed that the processes were endothermic, favorable, and spontaneous and the interaction between adsorbent and adsorbate was physical.     

H1020树脂吸附糖精的动力学和热力学研究

研究了大孔树脂H1020对糖精（邻苯甲酰磺酰亚胺）的吸附性能。在温度为303.15、308.15、313.15和318.15 K条件下分别测定了吸附平衡数据。分别采用了拟一级动力学模型和拟二级动力学模型对实验数据进行模拟,结果表明拟二级动力学方程更适合描述H1020型大孔树脂对糖精的吸附过程。用Langmuir和Freundlich吸附等温方程对实验数据进行拟合,结果表明糖精在大孔树脂H1020上的吸附平衡符合Freundlich吸附等温方程。计算糖精吸附过程的吸附焓变、吸附自由能和吸附熵变,根据吸附热力学值可判断出H1020型大孔树脂对糖精的吸附过程是自发的、放热的物理吸附。