STUDIES ON THE ADSORPTION OF FURFURAL FROM AQUEOUS SOLUTION ONTO LOW-COST BAGASSE FLY ASH

The present study deals with the sorptive removal of furfural from aqueous solution by carbon-rich bagasse fly ash (BFA). Batch studies were performed to evaluate the influence of various experimental parameters, namely, initial pH (pH₀), adsorbent dose, contact time, initial concentration, and temperature on the removal of furfural. Optimum conditions for furfural removal were found to be pH₀ ≈ 5.5, adsorbent dose ≈4 g/L of solution, and equilibrium time ≈4 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient of furfural is of the order of 10^-13 m²/s. Equilibrium adsorption data on BFA was analyzed by Freundlich, Langmuir, Dubnin-Radushkevich, Redlich-Peterson, and Temkin isotherm equations using regression and error analysis. The Redlich-Peterson isotherm was found to best represent the data for furfural adsorption onto BFA. Adsorption of furfural on BFA is favorably influenced by a decrease in the temperature of the operation. Values of the change in entropy (ΔS⁰) and heat of adsorption (ΔH⁰) for furfural adsorption on BFA were negative. The high negative value of change in Gibbs free energy (ΔG⁰) indicates the feasible and spontaneous adsorption of furfural on BFA.     

STUDIES ON THE ADSORPTION OF FURFURAL FROM AQUEOUS SOLUTION ONTO LOW-COST BAGASSE FLY ASH

The present study deals with the sorptive removal of furfural from aqueous solution by carbon-rich bagasse fly ash (BFA). Batch studies were performed to evaluate the influence of various experimental parameters, namely, initial pH (p H ₀), adsorbent dose, contact time, initial concentration, and temperature on the removal of furfural. Optimum conditions for furfural removal were found to be p H ₀ ≈ 5.5, adsorbent dose ≈4 g/L of solution, and equilibrium time ≈4 h. The adsorption followed pseudo-second-order kinetics. The effective diffusion coefficient of furfural is of the order of 10^?13 m²/s. Equilibrium adsorption data on BFA was analyzed by Freundlich, Langmuir, Dubnin-Radushkevich, Redlich-Peterson, and Temkin isotherm equations using regression and error analysis. The Redlich-Peterson isotherm was found to best represent the data for furfural adsorption onto BFA. Adsorption of furfural on BFA is favorably influenced by a decrease in the temperature of the operation. Values of the change in entropy (ΔS ⁰) and heat of adsorption (ΔH ⁰) for furfural adsorption on BFA were negative. The high negative value of change in Gibbs free energy (ΔG ⁰) indicates the feasible and spontaneous adsorption of furfural on BFA.     

REMOVAL OF METAL IONS FROM AQUEOUS SOLUTIONS USING PYROLYZED RICE HUSKS: ADSORPTION KINETICS AND EQUILIBRIA

Four carbon/silica-containing materials obtained by pyrolysis of rice husks were characterized and their adsorption properties towards some metal ions were evaluated. GC/MS analysis and FT-IR spectroscopy were applied for identification of functional groups finely dispersed on the surface. Their amounts were gravimetrically determined after extraction with acetone. The specific surface area and porosity of the materials were characterized by the Brunauer-Emmett-Teller (BET) method and by mercury porosimetry, respectively. The adsorption properties of the carbonized rice husks towards Fe(III), Pb(II), Cr(III), and Cu(II) ions in single- and multicomponent aqueous solutions also containing Ni(II), Co(II), Mn(II), and Cd(II) were studied in a batch system. The effects of contact time, acidity of initial solutions, and metal ion concentrations were followed. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to analyze kinetic data. Equilibrium experimental data were fitted to linear Langmuir and Freundlich models. The maximum adsorption capacities for single- and multicomponent adsorption were calculated and compared with literature data. A correlation between the adsorption properties of pyrolyzed rice husks and their textural and surface parameters was established. Possibilities for desorption of the investigated ions were estimated.     

PRODUCTION OF LOW-COST CARBON ADSORBENTS FROM AGRICULTURAL WASTES AND THEIR IMPACT ON DYE ADSORPTION

This study concerns utilizing commonly available agricultural wastes like mustard stalk, jute stalk, sesame stalk, wheat straw, bagasse, and rice husk in a proper and efficient way. As a part of this research, activated carbon has been prepared from these wastes by a two-stage activation process with a carbonization stage up to 325°C as a first stage followed by chemical activation using zinc chloride as an activation agent. The effects of temperature, time, and impregnation ratio on activation have been studied. The batch adsorption technique has been utilized to obtain information for treating effluents from the dye industry. Methylene blue dye has been chosen as the standard. Adsorption data have been modeled using the Freundlich and Langmuir adsorption isotherms and first- and second-order kinetic equations and intraparticle diffusion model. Specific surface area was determined by the methylene blue spot test. The results indicate that such carbons can be employed as low-cost alternatives to expensive commercial activated carbon in wastewater treatment to remove water-soluble dyes.     

PRODUCTION OF LOW-COST CARBON ADSORBENTS FROM AGRICULTURAL WASTES AND THEIR IMPACT ON DYE ADSORPTION

This study concerns utilizing commonly available agricultural wastes like mustard stalk, jute stalk, sesame stalk, wheat straw, bagasse, and rice husk in a proper and efficient way. As a part of this research, activated carbon has been prepared from these wastes by a two-stage activation process with a carbonization stage up to 325°C as a first stage followed by chemical activation using zinc chloride as an activation agent. The effects of temperature, time, and impregnation ratio on activation have been studied. The batch adsorption technique has been utilized to obtain information for treating effluents from the dye industry. Methylene blue dye has been chosen as the standard. Adsorption data have been modeled using the Freundlich and Langmuir adsorption isotherms and first- and second-order kinetic equations and intraparticle diffusion model. Specific surface area was determined by the methylene blue spot test. The results indicate that such carbons can be employed as low-cost alternatives to expensive commercial activated carbon in wastewater treatment to remove water-soluble dyes.     

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.     

坡缕石对水中亚甲基蓝的吸附动力学

研究了坡缕石对水中亚甲基蓝的吸附动力学,在初始浓度为120～210mg/L,转速为100～200r/min,温度为298～328K时,坡缕石对亚甲基蓝的吸附动力学数据均符合准二级速率方程.结果表明:坡缕石对亚甲基蓝的吸附仅在外表面吸附,吸附表观活化能为13.92 kJ/mol,说明此吸附并不是由单一的化学吸附为速率控制步骤,是由化学吸附和液膜扩散共同控制的吸附过程.     

INTRAPARTICLE DIFFUSION-CONTROLLED KINETICS OF ADSORPTION OF PHENOL ON ION EXCHANGE RESINS

A multi-section method was proposed to describe the batch adsorption system under intraparticle diffusion-controlled kinetics with a nonlinear adsorption isotherm. The intraparticle diffusivity of phenol on the anion exchange resins determined by using the proposed method was compared with the values determined from D-K and modified D-K methods. It was found that the intraparticle diffusivity determined in this study was reasonable.     

EQUILIBRIUM,KINETICS, AND BREAKTHROUGH STUDIES FOR ADSORPTION OF Cr(VI) ON CHITOSAN

Wastewater containing low levels of pollutants can be effectively treated by the adsorption technique. In the present work, an adsorption study was carried out using chitosan as adsorbent in a fixed-bed column for the removal of Cr(VI) from wastewater solutions. The column performance of Cr(VI) adsorption onto chitosan was studied at different bed heights (3–9 cm), flow rates (50–200 mL/min), initial metal concentrations (2–10 mg/L), pH values (2–7), and temperatures (30°–60°C). The equilibrium data for the batch adsorption of Cr(VI) on chitosan were tested using the Langmuir, Freundlich, and BET isotherm models. The Langmuir model was found to be the most suitable, with a maximum adsorption capacity of 35.7 mg/g and a correlation coefficient (R ²) = 0.952. The experimental data were found to fit well with the pseudo-second-order kinetic model, with R ² = 0.999. The dynamics of the adsorption process was modeled using the Adams-Bohart, Thomas, and mass transfer models. The models were used to predict the breakthrough curves of adsorption systems and to determine the characteristic design parameters of the column. The adsorption data were observed to fit well with all three models. The model parameters were derived using MATLAB software. In order to compare quantitatively the applicability of adsorption dynamic models in fitting to experimental data, the percentage relative deviation (P) was calculated and found to be less than 5, confirming that the fit is good for all three models.     

MODELING OF COPPER ION REMOVAL FROM AQUEOUS SOLUTIONS USING MODIFIED SILICA BEADS

Silica beads, containing 2-hydroxy-5-nonylacetophenoneoximc (LIX84) were prepared in order to examine the removal of copper ions from aqueous waste solutions. The process for copper ion removal using the modified silica beads was mathematically modeled using both a non-equilibrium model and an equilibrium model. The external mass transfer coefficient and effective diffusivity inside the bead pore were estimated by matching the experimental data and predicted values from the model, and the results were compared. The results of the two models were similar and in good agreement because of the relatively faster reaction rate than mass transfer rate. Sensitivity analyses showed that the external mass transfer has more influence on the copper ion removal system because of hydrophobic effects.     

MODELING OF COPPER ION REMOVAL FROM AQUEOUS SOLUTIONS USING MODIFIED SILICA BEADS

Silica beads, containing 2-hydroxy-5-nonylacetophenoneoximc (LIX84) were prepared in order to examine the removal of copper ions from aqueous waste solutions. The process for copper ion removal using the modified silica beads was mathematically modeled using both a non-equilibrium model and an equilibrium model. The external mass transfer coefficient and effective diffusivity inside the bead pore were estimated by matching the experimental data and predicted values from the model, and the results were compared. The results of the two models were similar and in good agreement because of the relatively faster reaction rate than mass transfer rate. Sensitivity analyses showed that the external mass transfer has more influence on the copper ion removal system because of hydrophobic effects.     

KINETICS AND MECHANISM OF THE REACTION BETWEEN OZONE AND O-CRESOL IN AQUEOUS SOLUTIONS

The stopped-flow spectrophotomctric method was applied to study the kinetics of the ozonation of o-cresol in aqueous solutions of pH values varying from 2 to 9 at 10 to 40°C. The fast reaction between o-cresol and ozone is second order overall with first order in each reactant. The ozonation rale increases with the temperature and pH value of the solution. In neutral solutions, the overall rate constant increases from 422,000 M^-1S^-1 at 10°C to 1,549,000 M^-1 S^-1 at 40°C. The activation energy is about 30 KJ/mol in the neutral solutions; it increases slightly with the acidity of the solution.

A mechanism based on the initial attack of ozone moleculesat the ortho and para positions of o-cresol is proposed for the ozonation reaction. According to this mechanism, three moles of ozone are required to react with each mole of o-cresol resulting in the rupture of the aromatic ring and production of various acids. The oxidation products were identified by these and other investigators. The proposed mechanism yields a second order kinetics for the overall reaction, as confirmed by the kinetic experiments.     

MULTICOMPONENT LIQUID PHASE ADSORPTION IN BATCH PART II EXPERIMENT ON CARBON ADSORPTION FROM SOLUTIONS OF PHENOL,O-CRESOL,AND 2,4-DICHLOROPHENOL

Experiments were conducted on carbon adsorption from solutions of phenol, o-cresol, and 2,4-dichlorophenol in various combinations. The equilibrium data were found in general agreement with predictions based on the ideal adsorbed solution (IAS) theory. The kinetic measurements suggest that the adsorption process can be described by the film-surface diffusion (FSD) model. By using the algorithms developed in Part I and based on the rate and equilibrium data obtained from single adsorbate adsorption measurements, concentration histories of the individual adsorbate of carbon adsorption from solutions containing phenol, o-cresol and 2,4-dichlorophenol can be predicted with sufficient accuracy.     

MULTICOMPONENT LIQUID PHASE ADSORPTION IN BATCH PART II EXPERIMENT ON CARBON ADSORPTION FROM SOLUTIONS OF PHENOL, O-CRESOL, AND 2,4-DICHLOROPHENOL

Experiments were conducted on carbon adsorption from solutions of phenol, o-cresol, and 2,4-dichlorophenol in various combinations. The equilibrium data were found in general agreement with predictions based on the ideal adsorbed solution (IAS) theory. The kinetic measurements suggest that the adsorption process can be described by the film-surface diffusion (FSD) model. By using the algorithms developed in Part I and based on the rate and equilibrium data obtained from single adsorbate adsorption measurements, concentration histories of the individual adsorbate of carbon adsorption from solutions containing phenol, o-cresol and 2,4-dichlorophenol can be predicted with sufficient accuracy.     

甲基丙烯酰胺制甲基丙烯酸甲酯反应动力学研究

本文通过实验测定了工业生产条件范围内，甲基丙烯酰胺（MAM）与甲醇（MeOH)水溶液在硫酸存在的条件下酯化反应生成甲基丙烯酸甲酯（MMA）的反应动力学数据。反应条件为：70－90℃，MAM：MeOH:H2O:H2SO4=1:2:3:1.7mol/molγ-丁内酯（γ－B.L)为均相剂。     

HEAVY METALS REMOVAL FROM AQUEOUS SOLUTIONS USING TiO2, MgO,AND Al2O3 NANOPARTICLES

This study investigated the removal of Cd²⁺, Cu²⁺, Ni²⁺, and Pb²⁺ from aqueous solutions using nanoparticle sorbents (TiO₂, MgO, and Al₂O₃) with a range of experimental approaches. The maximum uptake values (sum of four metals) with multiple component solutions were 594.9, 114.6, and 49.4 mg g^?1, for MgO, Al₂O₃, and TiO₂, respectively. The sorption equilibrium isotherms were described using the Freundlich and Langmuir models. The best interpretation for experiment data was given by the Freundlich model for Cd²⁺, Cu²⁺, and Ni²⁺ in single- and multiple-component solutions. A first-order kinetic model adequately described the experimental data using MgO, Al₂O₃, and TiO₂. SEM-EDX both before and after metal sorption and soil solution saturation indices (SI) in MgO nanoparticles indicated that the main sorption mechanism for heavy metals was attributable to adsorption and precipitation, whereas heavy metal sorption by TiO₂ and Al₂O₃ adsorbents was due to adsorption. These nanoparticles may potentially be used as efficient sorbents for heavy metal removal from aqueous solutions. MgO nanoparticles were the most promising sorbents because of their high metal uptake.     

减压膜蒸馏及其应用于易挥发性有机物分离的研究现状

本文叙述了减压膜蒸馏分离技术及其机理，并讨论了其应用于水溶液中易挥发性有机物分离的研究现状。     

REACTIVE EXTRACTION OF LEVULINIC ACID FROM AQUEOUS SOLUTIONS WITH TRI-n-OCTYLAMINE (TOA) IN 1-OCTANOL: EQUILIBRIA,KINETICS, AND MODEL DEVELOPMENT

Levulinic acid, a carboxylic acid containing a ketone structure, can be used as an acidulant in foods and beverages. Reactive extraction is a promising alternative for the recovery of carboxylic acids from aqueous streams. The design of an amine extraction process requires kinetic data for the acid-amine + solvent system used. In this study, equilibrium and kinetic data on the extraction of levulinic acid from aqueous solutions using tri-n-octylamine (TOA) in 1-octanol have been determined. The mass transfer coefficients of levulinic acid, TOA, and 2:1 levulinic acid-amine complex in 1-octanol were calculated from the acetic acid mass transfer coefficient, which was determined by measuring its fluxes of simple diffusion from kerosene to water. Based on the Hatta number and the criterion given by Doraiswamy and Sharma, the reaction regime has been found to be instantaneous reaction regime occurring at the interface on the organic phase side. An extraction model comprising equilibrium complexation constant w.r.t 2:1 levulinic acid-TOA complex formation, K_E2i (14.794 (m³ kmol^?1)²), and complex mass transfer coefficient, k_B2A (2.193 × 10^?6 m s^?1), has been developed.     

ADSORPTION KINETICS AND EQUILIBRIA OF BASIC DYES ONTO ZEOLITE IN SINGLE AND BINARY COMPONENT SYSTEMS

Adsorptive removal of Basic Blue 3 (BB 3) and Basic Red 18 (BR 18) by a clinoptilolite-type natural zeolite from their single-component solutions has been studied in the temperature range of 298–328 K. Experimental equilibrium results are well described by the Freundlich and the Langmuir isotherm models. The model parameters obtained for single-solute systems at 298 K have been used for the prediction of adsorption isotherms in binary dye solutions using multicomponent isotherm models. Competitive adsorption results between BB 3 and BR 18 in binary solutions satisfactorily fit the extended Freundlich, extended Langmuir, and modified Langmuir models. A site distribution function that gives information about affinity of adsorption sites for competing species in binary systems has been mathematically calculated using the Freundlich parameters. Time-dependent results for single and binary dye solutions have been analyzed according to a pseudo-second-order kinetic model based on chemisorption and a McKay model assuming two resistance diffusion processes, respectively. The diffuse reflectance FT-IR spectra indicate that the dyes are adsorbed via electrostatic interactions in external rings of clinoptilolite by replacing the zeolitic water in a single system, and they diffuse through the liquid associated with zeolitic water in TO₄ tetrahedra (T: Al, Si) in a mixed solution.     

STUDY OF HG(II) REMOVAL FROM AQUEOUS SOLUTION USING LIGNOCELLULOSIC COCONUT FIBER BIOSORBENTS: EQUILIBRIUM AND KINETIC EVALUATION

Lignocellulosic coconut wastes such as pith and fiber, which are abundantly available and cheap, have the potential of being used as low-cost biosorbents for heavy metal ion removal. In this study, pristine (CF-Pristine) and NaOH-treated (CF-NaOH) coconut fibers were used as a biosorbent for Hg(II) removal from an aqueous solution. The coconut fiber biosorbent (CFB) was characterized by scanning electron microscopy (SEM) and Fourier transform-infrared (FTIR) spectroscopy. The Hg(II) sorption capacities obtained for CF-Pristine and CF-NaOH were 144.4 and 135.0 mg/g, respectively. Both the equilibrium and kinetic data of Hg(II) sorption onto CFB followed the Langmuir isotherm model and a pseudo-second-order kinetic model, respectively. A further analysis of the kinetic data suggested that the Hg(II) sorption process was governed by both intraparticle and external mass transfer processes, in which film diffusion was the rate-limiting step. These results demonstrated that both pristine- and alkali-treated coconut wastes could be potential low-cost biosorbent alternatives for the removal of Hg(II) from aqueous solutions, such as water containing Hg(II) produced in the oil and gas industry.