ADSORPTION OF METHYLENE BLUE FROM AQUEOUS SOLUTION ON ATTAPULGITE

Batch adsorption experiments were carried out for the removal of methylene blue （MB） from aqueous solution using attapulgite as adsorbent. The effects of various parameters such as temperature, contact time, the pH value, and attapulgite dosage on the adsorption performance were investigated. The standard curve and regression equation were established by spectrophotometry. The adsorption experimental results showed that the adsorption equilibrium data were well in accord with Langmuir adsorptive model. The optimal result was acquired under the experimental condition of attapulgite dosage 0.18g, MB concentration 50.0mg/L, pH 10, and adsorption time 20min at room temperature.     

Removal of malachite green from dye wastewater using mesoporous carbon adsorbent

Mesoporous carbon was synthesized for the removal of a cationic dye malachite green (MG) from aqueous solution. The studies were carried out under various experimental conditions such as contact time, dye concentration, adsorption dose and pH to assess the potentiality of mesoporous carbon for the removal of malachite green dye from wastewater. The sorption equilibrium was reached within 30 min. In order to determine the adsorption capacity, the sorption data were analyzed using linear form of Langmuir and Freundlich equation. Langmuir equation showed higher conformity than Freundlich equation. More than 99% removal of MG was reached at the optimum pH value of 8.5. From kinetic experiments, it was concluded that the sorption process followed the pseudo-first-order kinetic model. This study showed that mesoporous carbon can be recommended as an excellent adsorbent at high pH values.     

Deposition efficiency of fractal-like aggregates in fibrous filters calculated using Brownian dynamics method

Nonspherical particles, such as fractal-like aggregates emitted by diesel engines, are commonly met in the ambient air. Some of them are believed to be carcinogenic to humans, thus their efficient removal is of crucial practical importance. A fibrous filter is the device commonly used for aerosol purification but the literature lacks experimental data concerning aggregates filtration. Effect of aggregates' parameters (fractal dimension, primary particle radius) as well as fiber diameter and air velocity on the filtration efficiency is investigated theoretically using the modified Brownian dynamics method. Three different expressions for the friction coefficient evaluation for the aggregates were examined. The results obtained indicate that structure of an aggregate, filter structure and process conditions strongly influence the aggregates deposition efficiency, which significantly differs from the values determined for mass-equivalent spherical particles. The results determined using the Brownian dynamics approach were compared with the values calculated using classical single fiber theory and noticeable discrepancy was observed for the most penetrating particles, while both approaches agree for the limiting cases of small or large particles. Peclet number based on the mobility radius and the interception parameter based on the outer radius are the proper criteria to describe diffusional and deterministic deposition of aggregates.     

Biosorption of Cr(VI) ions from aqueous solutions: kinetics, equilibrium, thermodynamics and desorption studies

Cr(VI) is a major water pollutant from industrial effluent whose concentration is to be reduced within the permissible limit. Present study reports a systematic evaluation of six different natural adsorbents for the removal of Cr(VI) from aqueous solutions in batch process. The adsorption kinetic data were best described by pseudo-second order model. The values of mass transfer coefficient for Cr(VI) adsorption indicated that the velocity of the adsorbate transport from the bulk to the solid phase was quite fast. The effective diffusivity of Cr(VI) removal for all the adsorbents were of the order of 10(-10) m(2)/s which suggested chemisorption of the process. The adsorption process was jointly controlled by film diffusion and intraparticle diffusion. Maximum monolayer adsorption capacities onto the natural adsorbents used were comparable to the other natural adsorbents used by other researchers. The thermodynamic studies and sorption energy calculation using Dubinin-Radushkevich isotherm model indicated that the adsorption processes were endothermic and chemical in nature. FT-IR studies were carried out to understand the type of functional groups responsible for Cr(VI) binding process. Desorption study was carried out with different concentration of NaOH solutions. Application study was carried out using electroplating industrial wastewater.     

N-Octyl Quaternized P4VP Interaction With Orange Telon

The removal of orange Telon from aqueous solutions by poly(N-octyl-4-vinylpyridiniumbromide) copolymer was investigated. Batch adsorption experiments were carried out to study the effect of experimental parameters on the orange Telon adsorption equilibrium. The adsorption characteristics of copolymer to ward orange Telon in dilute aqueous solution were followed using UV-Vis spectrophotometry. Adsorption equilibrium was reached within 60 min for 0.03 g of poly(4-vinylpyridine quaternized at 58%. The kinetic of adsorption is best described by a pseudo-second-order model. Results also showed that the equilibrium modeling of orange Telon removal process was described by Langmuir isotherms. The maximum adsorption capacity determined from the Langmuir isotherm was 76.4 mg g^{? 1}. The study of the thermodynamic parameters showed that the adsorption of orange Telon on copolymer is an exothermic process and the randomness decreases at the solid-solution interface during the adsorption of dye on the copolymer.     

Use of oxide minerals to abate fluoride from water

The removal of fluoride from aqueous solutions has been investigated using various oxide ores such as refractory grade bauxite, feed bauxite, manganese ore, and hydrated oxides of manganese ores (WAD). The refractory grade bauxite showed promising results. The studies were carried out as functions of contact time, pH, concentration of adsorbents, concentration of adsorbate, and temperature. The adsorption was rapid during the initial 5 min but equilibrium was attained within 120 min. The adsorption followed first-order kinetics. The present system followed the Langmuir adsorption isotherm model. Various thermodynamic parameters such as free energy, enthalpy, entropy, and equilibrium constants were calculated. The isosteric heat calculations showed that the adsorption process followed a heterogeneous model.     

Kinetic,Equilibrium and Isotherm Studies of Cadmium Removal from Aqueous Solutions by Oxidized Multi‐Walled Carbon Nanotubes and the Functionalized Ones with Thiosemicarbazide and Their Toxicity Investigations: A Comparison

The multi‐walled carbon nanotubes (MWCNTs) were first oxidized by nitric acid to form a MWCNT‐COOH. Then, it was modified with thiosemicarbazide to produce MWCNT‐semi. Thus, these carbon materials, MWCNTs, MWCNT‐COOH and MWCNT‐semi, have been used as efficient adsorbents for the removal of cadmium from aqueous solutions. The influence of variables including pH, concentration of the cadmium, amount of adsorbents and contact time was investigated by the batch method. The kinetic studies carried out using different kinetic models such as pseudo‐first‐order, pseudo‐second‐order, and intraparticle diffusion models. The sorption process with each adsorbent was well described by pseudo‐second‐order kinetics which it was agreed well with the experimental data. The values of regression coefficient of various adsorption isotherms like Langmuir, Freundlich and Tempkin to obtain the characteristic parameters of each model have been carried out. The results showed which the Langmuir isotherm for all adsorbents and Tempkin model for MWCNT‐COOH and MWCNT‐semi was found to best represent the measured sorption data. Toxicity of these samples was evaluated in human embryonic kidney HEK293 and human breast cancer SKBR3 cell lines after culturing cells for 24 h. Cellular investigations showed that the modified MWCNTs in particular MWCNT‐semi have considerably significant toxic impact on SKBR3 as compared to HEK293 at concentration 3 µg/mL.     

Enzymatic Treatment and Detoxification of Acid Orange 7 from Textile Wastewater

A crude preparation of horseradish roots was used as a low-purity source of horseradish peroxidase (HRP) in dye decolorization experiments. The technical feasibility of the process was studied in bench scale for enzymatic removal of acid orange 7 (AO7), a synthetic dye. Further studies were carried out to understand the effects of process parameters such as pH value, H(2)O(2) level, concentrations of the synthetic dye, and HRP during enzyme-mediated dye degradation. Experimental data revealed that the concentration of AO7, pH of the aqueous phase, amount of the enzyme, and H(2)O(2) level played significant roles on the overall enzymatic reaction. Polyethylene glycol, as an anti-inactivation of HRP, in various concentrations showed no significant effect on the decolorization. The experimental data of initial reaction rates were fitted using an analytical equation proposed by Michaelis-Menten. The acute toxicity tests using Daphnia magna exhibited that the enzymatic treatment significantly decreased the toxicity of the dye solution.     

Application of artificial neural networks for formulation and modeling of dye adsorption onto multiwalled carbon nanotubes

In this study, an artificial neural network (ANN) has been developed to predict the adsorption amount of dye (methylene blue) onto multiwalled carbon nanotubes. Batch experiments have been carried out to obtain experimental data. Important parameters in the adsorption system such as initial dye concentration, adsorbent dosage, temperature, pH and contact time have been used as the inputs of the network, while the output is the final concentration of dye in aqueous solution after adsorption. The neural network structure has been optimized by testing various training algorithms and different number of neurons in a hidden layer. An empirical equation for determination of final dye concentration in aqueous solutions after adsorption has been developed by using the weights of the optimized network. The results of the optimized ANN have been compared with conventional models in equilibrium and kinetic fields. According to error analysis and determination coefficient, the ANN was found to be the most appropriate model to describe this adsorption process. Sensitivity analysis showed that initial dye concentration, pH and contact time are the most effective parameters in this process. The influence percentages of these parameters on the output were 28, 24 and 24 %, respectively.     

Thermodynamic and kinetic parameters of ofloxacin adsorption from aqueous solution onto modified coal fly ash

Batch adsorption experiments were carried out for the removal of ofloxacin from aqueous solution using modified coal fly ash as adsorbent. The effects of various parameters such as contact time, initial solution concentration and temperature on the adsorption system were investigated. The optimum contact time was found to be 150 min. The adsorption isotherm data fit well with the Langmuir model, and the kinetic data fit well with the pseudo-second order and the intra-particle diffusion model. Intra-particle diffusion analysis demonstrates that ofloxacin diffuses quickly among the particles at the beginning of the adsorption process, and then the diffusion slows down and stabilizes. Thermodynamic parameters such as ΔG, ΔH, and ΔS were also calculated. The negative Gibbs free energy change and the positive enthalpy change indicated the spontaneous and endothermic nature of the adsorption, and the positive entropy change indicated that the adsorption process was aided by increased randomness.     

Preparation of thorium oxalate–silica sorbent and its application for the sorption of americium from aqueous solutions

A new sorbent, thorium oxalate incorporated in silica gel matrix was prepared. This material was characterized by X-ray, Thermo-gravimetric Analysis, surface area and porosity analysis. The material was obtained in the form of granular particles in the mesh size range of 80–150 American Standard of Testing Materials, yielding good liquid flow, when packed in ion exchange column. This sorbent was investigated for the sorption of americium from various aqueous media such as nitric acid, oxalic acid and sulphuric acid by distribution coefficient studies. Column experiments were carried out to study the practical application of this sorbent for removal of americium from oxalic acid-nitric acid solutions. Elution studies were also carried out for the recovery of americium.     

Theoretical consideration of osmotic pressure in aqueous protein/salt systems based on extended hard core Lennard-Jones potential

A simple and analytical pair potential function was developed to represent the osmotic pressures in aqueous protein/salt systems under various conditions. Based on a hard core Lennard-Jones (HCLJ) potential model, the new potential function considers various interactions by extending the attractive Lennard-Jones potential. A temperature-dependent coefficient term was introduced to take into account the specific properties of given materials. Comparison of the new potential function with the HCLJ model in hydrocarbon and water systems showed that consideration of the temperature dependence in the potential function was effective, especially for strong polar systems such as water. To predict the osmotic pressures of aqueous lysozyme/(NH(4))(2)SO(4) solutions of various ionic strength and pH, the energy parameters of lysozyme were correlated with the experimental cloud point temperature. The proposed model agreed fairly well with the experimental osmotic pressure data with only previously obtained parameters.     

Kinetics for the Removal of Paraquat Dichloride from Aqueous Solution by Activated Date (Phoenix dactylifera) Stone Carbon

For the adsorption of Paraquat dichloride (1,1′-dimethyl-4,4′-bipyridyl dichloride) from synthetic aqueous solutions, batch experiments were carried out to study the kinetics of Paraquat dichloride onto calcium oxide activated date (Phoenix dactylifera) stone carbon powder (particle size dia. about 0.85 mm). Studies were conducted at various initial concentrations of 75 mg/L, 100 mg/L, and 125 mg/L of Paraquat dichloride with 8.0 g/L of adsorbent dose. The equilibrium time was found to be 140 minutes. Maximum removal was observed at pH 9.0. The regression analysis for the experimental data showed that the removal kinetic profiles followed a pseudo-second order kinetic models for all initial concentrations, pH, temperature, and salinity of sorbate. The experimental data were analyzed using Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. Thermodynamic parameters, such as standard change in Gibbs free energy, standard change in enthalpy, and standard change in entropy, were evaluated, indicating that the overall adsorption process was exothermic and spontaneous in nature.     

Preparation of calix[4]arene-based sporopollenin and examination of its dichromate sorption ability

The present study describes the preparation of a new calix[4]arene-based sporopollenin material and its application for the removal of Na₂Cr₂O₇ from aqueous solution. The novel calix[4]arene-based sporopollenin material was prepared via the immobilization of dihydrazine amide derivative of p-tert-butylcalix[4]arene (3) onto the modified sporopollenin. The newly prepared calix[4]arene-based sporopollenin is characterized by using different analytical techniques such as FT-IR spectroscopy, scanning electron microscope and Elemental analysis. The batch wise sorption study was carried out to optimize various experimental parameters such as the effect of sorbent dosage, pH, temperature and Cr(VI) anion concentration. It has been found that the sorption of Cr(VI) anion on calix[4]arene-based sporopollenin was highly pH dependent and maximum sorption was achieved at pH 1.5. The sorption behavior was also evaluated by Langmuir, Freundlich and Dubinin Radushkevich isotherms. The value of correlation coefficient (R ²) showed a good agreement with Freundlich isotherm model. Result of study demonstrated that calix[4]arene-based sporopollenin proved to be highly effective for the removal of Cr(VI).     

Adsorption of Pb(II) on a composite material prepared from polystyrene-alumina and activated carbon: Kinetic and thermodynamic studies

The ability of polystyrene-alumina-activated carbon composite as a synthetic adsorbent was investigated for the removal of Pb(II) ions from aqueous solutions. Various physico-chemical parameters such as pH, initial metal ion concentration, adsorbent dosage and contact time were studied. The optimum solution pH for the maximum adsorption of Pb(II) was found to be 4. Kinetic data were best described by pseudo-second-order model. The adsorption process followed both Langmuir and Freundlich adsorption isotherms at 30 °C. Thermodynamic studies indicated that the adsorption was spontaneous and endothermic in nature. Desorption studies were carried out by batch and column operations and it was found that 97% Pb(II) could be recovered by the column process using 0.1 M HCl as eluent.     

Optimization of ammonium removal from waste water by natural zeolite using central composite design approach

The aims of the present study are to investigate removal of ammonium ion from wastewater using natural Western Azarbaijan zeolite and to optimize effective parameters by experimental design. In order to remove ammonium ions from aqueous solutions, experiments were carried out using column method as functions of the initial ammonium concentration, flow rate and pH of the solution. The results clearly confirmed that all mentioned parameters have vital affects on removing ammonium ions from wastewater and effluents, so got optimized. Central composite design with response surface methodology was applied for the optimization of main experiment parameters. The significance of the independent variables and their interactions were tested by the analysis of variance ANOVA and f-test statistics. Optimization of the variables for maximum removal efficiency by natural zeolite was performed using the quadratic model. The model predicted maximum removal efficiency under the optimum conditions including initial ammonium concentration of 30?mg?l^?1; flow rate of 1?ml?min^?1 and pH 6, which was very close to the experimental value determined in column experiment. The cation exchange capacity of natural Western Azarbaijan zeolite was found to be 1.79?meq?g^?1. Based on the experimental results, it can be concluded that the natural Western Azarbaijan zeolite has an excellent potential for removing ammonium ions from aqueous solutions and it is suggested as a suitable material for wastewater treatment.     

Removal of Cobalt Ions from Aqueous Solution by Adsorption onto Cross-Linked Calcium Alginate Beads

The removal of cobalt ions from dilute aqueous solutions using cross linked calcium alginate beads as the adsorbent is reported in this article. The influence of various experimental parameters such as pH, initial metal ion concentration, contact time and solid to liquid ratio were studied. The adsorption data were applied to Langmuir and Freundlich isotherm equations and various static parameters were calculated. It was observed that the uptake of cobalt ions was found to increase with time and that maximum adsorption was obtained within the first 60 minutes of the process. These results indicate that the cross linked calcium alginate beads have potential for removing cobalt ions from industrial waste water.     

Synthesis and characterization of <Emphasis Type="Italic">β</Emphasis>-cyclodextrin–carboxymethyl cellulose–graphene oxide composite materials and its application for removal of basic fuchsin

A novel β-cyclodextrin–carboxymethyl cellulose–graphene oxide composite material (β-CD–CMC–GO) was synthesized, and its application as excellent adsorbents was carried out for removal basic fuchsin (BF) in aqueous solution. The structure and morphology of β-CD–CMC–GO composite material were characterized by using FTIR, SEM, TEM, XRD, TG and DSC methods. The composites could remove basic fuchsin from aqueous solution efficiently. The adsorption experiment was carried out and the optimum experimental conditions were ascertained. The highest adsorption efficiency was obtained 97.3% at 0.015 g/mL dosage of β-CD–CMC–GO, the temperature of 25 °C and time of 2.5 h. Adsorption kinetics, adsorption isotherm and adsorption thermodynamic were used to analyze the adsorption system. The experimental data of adsorption kinetics of system were well followed by pseudo-second-order equation. The adsorption isotherm data were fitted using Langmuir isotherm model and Freundlich isotherm model. The maximum adsorption capacity of basic fuchsin reached 58.65 mg/g. The thermodynamic parameters indicated that the adsorption process was spontaneous and exothermic. The adsorbent has excellent regeneration ability and reproducibility. The proposed method shows that the β-CD–CMC–GO could be applied to removal of basic fuchsin in wastewater with satisfactory result.     

A simplified method to estimate kinetic and thermodynamic parameters on the solid-liquid separation of pollutants

The aim of the present study was to propose a simplified experimental-theoretical method for estimating the kinetic and thermodynamic parameters for the solid-liquid separation of pollutants by using kinetic studies with batch reactors, i.e., the removed quantity of dissolved ion as a function of time at different initial concentration. This method was applied to the removal of uranyl ion (UO(2+)(2)) from aqueous solutions onto synthetic manganese oxide (birnessite). The pseudo-second-order kinetics and one-site saturation models were proposed to fit the experimental and calculated data, the fitting parameters being estimated by nonlinear regression, using the least-squares method. For initial concentration range 0.2-11.8 microM, the results showed that the uranyl removal process in dispersed batch reactors can be efficiently modeled by the proposed models. Then, several kinetic and thermodynamic parameters were calculated, such as maximal removed quantity of uranyl, q(r,max), half-removal time, t(1/2), initial rate of uranyl-ion removal, v(0), initial uranyl-removal coefficient, K, maximal rate of uranyl removal, v(0,max), mass transfer coefficient, D(transfer), equilibrium Langmuir constant, K(L), and constant separation factor, K(s). These parameters make it possible to demonstrate that the removal of U onto birnessite is favorable, and that the maximum surface coverage of the uranyl ions represents about 3% of vacant sites in the Mn layer.