Equilibrium and kinetic data and process design for adsorption of Congo Red onto bentonite

The adsorption of Congo Red onto bentonite in a batch adsorber has been studied. Four kinetic models, the pseudo first- and second-order equations, the Elovich equation and the intraparticle diffusion equation, were selected to follow the adsorption process. Kinetic parameters; rate constants, equilibrium adsorption capacities and correlation coefficients, for each kinetic equation were calculated and discussed. It was shown that the adsorption of Congo Red onto bentonite could be described by the pseudo second-order equation. The experimental isotherm data were analyzed using the Langmuir, Freundlich and Temkin equations. Adsorption of Congo Red onto bentonite followed the Langmuir isotherm. A single stage batch adsorber was designed for different adsorbent mass/treated effluent volume ratios using the Langmuir isotherm.     

Adsorption of phenol by MMT-CTAB and WPT-CTAB: Equilibrium,kinetic, and thermodynamic study

In this study, the phenol adsorption capacity of cetyltrimethylammonium bromide modified clays (MMT-CTAB) and cetyltrimethylammonium bromide modified pulp tea (WPT-CTAB) were studied. In batch adsorption experiments performed with MMT-CTAB, the effects of parameters such contact time, phenol concentration, pH of solution and adsorbent dosage were investigated. The effect of temperature on phenol adsorption onto MMT-CTAB and WPT-CTAB was examined; equilibrium and thermodynamic studies were completed. The highest phenol removal was found at pH 4.0 for MMT-CTAB and WPT-CTAB. To analyze the kinetics of phenol adsorption onto MMT-CTAB, the pseudo first-order and pseudo second-order kinetic models were applied. The kinetic data fitted better to the pseudo second-order model than the pseudo first-order kinetic model for MMT-CTAB. The characterization of adsorbents in phenol adsorption was clarified with the FTIR technique. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated for each adsorption process. The adsorption process was found to be exothermic and spontaneous for phenol adsorption by MMT-CTAB and WPT-CTAB. The results were analyzed with the Langmuir, Freundlich, Temkin and Harkins–Jura equations using linearized correlation coefficients at different temperatures. The Langmuir equation was found to best represent the equilibrium data for phenol adsorption onto MMT-CTAB and WPT-CTAB.     

An adsorption study of Al(III) ions onto chitosan

The adsorption of Al(III) from aqueous solutions onto chitosan was studied in a batch system. The isotherms and the kinetics of adsorption with respect to the initial Al(III) concentration and temperature were investigated. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms. Equilibrium data fitted very well to the Langmuir model in the entire concentration range (5-40 mg/L). The negative values of free energy (DeltaG degrees ) and enthalpy (DeltaH degrees ) for the adsorption of Al(III) onto chitosan indicated that the adsorption process is a spontaneous and exothermic one. Two simplified kinetic models, based on pseudo first-order and pseudo second-order equations, were tested to describe the adsorption mechanism. The pseudo second-order kinetic model resulted in an activation energy of 56.4 kJ/mol. It is suggested that the overall rate of Al(III) ion adsorption is likely to be controlled by the chemical process. The values of the enthalpy (DeltaH(#)) and entropy (DeltaS(#)) of activation were 53.7 kJ/mol and -164.4 J/molK, respectively. The free energy of activation (DeltaG(#)) at 30 degrees C was 103.5 kJ/mol.     

Dye adsorption on unburned carbon: kinetics and equilibrium

Unburned carbon in fly ash is an important by-product from coal combustion. In this investigation, unburned carbon has been separated from fly ash and been employed as a low cost adsorbent for a basic dye adsorption (Rhodamine B) in aqueous solution. Adsorption isotherm and kinetics of adsorption have been investigated using batch experiments. It is found that dye adsorption capacity depends on initial concentration, pH of solution, and temperature. The adsorption isotherm can be described by Langmuir model and the adsorption capacity of Rhodamine B at 30, 40, and 50 degrees C can reach 9.7 x 10(-5), 1.14 x 10(-4), and 1.5 x 10(-4)mol g(-1), respectively. The pseudo first- and second-order kinetic models have been employed to fit the dynamic adsorption. It is found that the dynamic adsorption follows the pseudo second-order model. Thermodynamic calculations indicate that the adsorption is endothermic reaction with DeltaH degrees at 25 kJ mol(-1).     

Adsorption of Zn2+ ions onto NaA and NaX zeolites: Kinetic,equilibrium and thermodynamic studies

The adsorption of Zn²⁺ onto NaA and NaX zeolites was investigated. The samples were synthesized according to a hydrothermal crystallization using aluminium isopropoxide (Al[OCH(CH₃)₂]₃) as a new alumina source. The effects of pH, initial concentration, solid/liquid ratio and temperature were studied in batch experiments. The Freundlich and the Langmuir models were applied and the adsorption equilibrium followed Langmuir adsorption isotherm. The uptake distribution coefficient (K_d) indicated that the Zn²⁺ removal was the highest at minimum concentration. Thermodynamic parameters were calculated. The negative values of standard enthalpy of adsorption revealed the exothermic nature of the adsorption process whereas the negative activation entropies reflected that no significant change occurs in the internal structure of the zeolites solid matrix during the sorption of Zn²⁺. The negative values of Gibbs free energy were indicative of the spontaneity of the adsorption process. Analysis of the kinetic and rate data revealed that the pseudo second-order sorption mechanism is predominant and the intra particle diffusion was the determining step for the sorption of zinc ions. The obtained optimal parameters have been applied to wastewater from the industrial zone (Algeria) in order to remove the contained zinc effluents.     

Studies on biosorption equilibrium and kinetics of Cd2+ by Streptomyces sp. K33 and HL-12

The sorption of Cd(2+) by Streptomyces sp. K33 and HL-12 was investigated. The removal efficiency increased with pH, but no obvious differences with different temperatures. Fourier transform infrared (FT-IR) was used to characterize the interaction between Cd(2+) and K33 and HL-12. Results revealed that the presence of amino, carboxyl, hydroxyl and carbonyl groups were responsible for the biosorption of Cd(2+). Strain HL-12 had more changes in the functional groups than K33. Biosorption equilibrium was established earlier by strain K33 than that by HL-12, and K33 had higher adsorption ratio. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms were used to describe the adsorption experiment, Langmuir model fitted the experiment data best. Strain K33 showed greater sorption capacities with 38.49 mg Cd(2+)/g dry cells. Pseudo-first-order and second-order kinetic models were used to describe the kinetic data, and second-order kinetic model fitted better. About 70% recovery of Cd(2+) could be obtained at pH 相似文献   

Contact time optimization of two-stage batch adsorber design using second-order kinetic model for the adsorption of phosphate onto alunite

The adsorption of phosphate onto alunite in a batch adsorber has been studied. Four kinetic models including pseudo first- and second-order equation, intraparticle diffusion equation and the Elovich equation were selected to follow the adsorption process. Kinetic parameters, rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the adsorption of phosphate onto alunite could be described by the pseudo second-order equation. Adsorption of phosphate onto alunite followed the Langmuir isotherm. A model has been used for the design of a two-stage batch adsorber based on pseudo second-order adsorption kinetics. The model has been optimized with respect to operating time in order to minimize total operating time to achieve a specified amount of phosphate removal using a fixed mass of adsorbent. The results of two-stage batch adsorber design studies showed that the required times for specified amounts of phosphate removal significantly decreased. It is particularly suitable for low-cost adsorbents/adsorption systems when minimising operating time is a major operational and design criterion, such as, for highly congested industrial sites in which significant volume of effluent need to be treated in the minimum amount of time.     

Removal of trivalent chromium from water using low-cost natural diatomite

Trivalent chromium was removed from the artificial wastewater using low-cost diatomite in batch and continuous systems. In batch system, four different sizes and five different amount of sorbent were used. The effect of the temperature on sorption was evaluated with using three different temperatures. As a result of the experiments, 85% of the trivalent chromium was removed from the wastewater in conditions of using 1.29 mm grain material at 30 °C temperature for 60 min in batch system but chromium removal was 82% at 30 °C temperature for 22 min and 97% from the wastewater at 30 °C temperature for 80 min in continuous system. Also, the equilibrium adsorption isotherms have been analyzed by Langmuir and Freundlich models. The Langmuir isotherms have the highest correlation coefficients. Langmuir adsorption isotherm constants corresponding to adsorption capacity, q₀, were found to be 28.1, 26.5 and 21.8 mg Cr³⁺/g diatomite at 15, 30 and 45 °C, respectively. Adsorption process was an exothermic process as a result of thermodynamic parameters calculations. The kinetic data of the sorption showed that the pseudo second-order equation was the more appropriate, which indicate that the intraparticle diffusion is the rate-limiting factor.     

Comparison of the efficiency of palladium and silver nanoparticles loaded on activated carbon and zinc oxide nanorods loaded on activated carbon as new adsorbents for removal of Congo red from aqueous solution: Kinetic and isotherm study

The adsorption of Congo red (CR) into three new adsorbents including Palladium and silver nanoparticles loaded on activated carbon (Pd NPs-AC, Ag NPs-AC) and zinc oxide nanorods loaded on activated carbon (ZnO-NRs-AC) in a batch method has been studied following the optimization of effective variables including pH, amount of adsorbents and time. The experimental data was fitted to conventional kinetic models including the pseudo first-order and second-order Elovich and intraparticle diffusion model and based on calculated respective parameters such as rate constants, equilibrium adsorption capacities and correlation coefficients. It was found that for all adsorbents the removal process follows the pseudo second other kinetic model with involvement of interparticle diffusion model. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Tempkin and Dubinin and Radushkevich equations and it was found for all adsorbents that the removal process followed the Langmuir isotherm.     

Sorption behavior of nano-TiO2 for the removal of selenium ions from aqueous solution

Titanium dioxide nanoparticles were employed for the sorption of selenium ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, and temperature. The sorption was found to be fast, and to reach equilibrium basically within 5.0 min. The sorption has been optimized with respect to the pH, maximum sorption has been achieved from solution of pH 2–6. Sorbed Se(IV) and Se(VI) were desorbed with 2.0 mL 0.1 mol L⁻¹ NaOH. The kinetics and thermodynamics of the sorption of Se(IV) onto Nano-TiO₂ have been studied. The kinetic experimental data properly correlate with the second-order kinetic model (k₂ = 0.69 g mg⁻¹ min⁻¹, 293 K). The overall rate process appears to be influenced by both boundary layer diffusion and intraparticle diffusion. The sorption data could be well interpreted by the Langmuir sorption isotherm. The mean energy of adsorption (14.46 kJ mol⁻¹) was calculated from the Dubinin–Radushkevich (D–R) adsorption isotherm at room temperature. The thermodynamic parameters for the sorption were also determined, and the ΔH⁰ and ΔG⁰ values indicate exothermic behavior.     

Linear and non-linear regression analysis for the sorption kinetics of methylene blue onto activated carbon

Batch kinetic experiments were carried out for the sorption of methylene blue onto activated carbon. The experimental kinetics were fitted to the pseudo first-order and pseudo second-order kinetics by linear and a non-linear method. The five different types of Ho pseudo second-order expression have been discussed. A comparison of linear least-squares method and a trial and error non-linear method of estimating the pseudo second-order rate kinetic parameters were examined. The sorption process was found to follow a both pseudo first-order kinetic and pseudo second-order kinetic model. Present investigation showed that it is inappropriate to use a type 1 and type pseudo second-order expressions as proposed by Ho and Blanachard et al. respectively for predicting the kinetic rate constants and the initial sorption rate for the studied system. Three correct possible alternate linear expressions (type 2 to type 4) to better predict the initial sorption rate and kinetic rate constants for the studied system (methylene blue/activated carbon) was proposed. Linear method was found to check only the hypothesis instead of verifying the kinetic model. Non-linear regression method was found to be the more appropriate method to determine the rate kinetic parameters.     

Adsorption of Cd(II), Cu(II) and Ni(II) ions by Lemna minor L.: effect of physicochemical environment

The free floating macrophyte Lemna minor L. was harvested locally. Untreated, acid pretreated (H2SO4), alkali pretreated (NaOH) biomass were used for adsorption of copper, cadmium and nickel ions from aqueous solutions. The effect of initial pH, initial metal concentration and multi metal interaction were carried out in a batch system. The equilibrium adsorption was reached within 40-60 min. The Langmuir and Freundlich models were used for describing of adsorption isotherm data. The maximum adsorption capacities of alkali pretreated biomass were determined as 83, 69 and 59 mg g(-1) for the Cd(II), Cu(II) and Ni(II) ions, respectively. The pseudo first- and second-order intraparticle diffusion models were used to describe the adsorption kinetics. The experimental data fitted to pseudo second-order kinetic. Adsorption capacity decreased with acid pretreatment; however alkali pretreatment was not affected significantly adsorption capacity and adsorption capacity a little increased according to native biomass. The FT-IR results of Lemna biomass showed that biomass has different functional groups and these functional groups are able to react with metal ions in aqueous solution.     

Removal of cationic dyes from aqueous solution using an anionic poly-gamma-glutamic acid-based adsorbent

Natural polymeric materials are gaining interest for application as adsorbents in wastewater treatment due to their biodegradable and non-toxic nature. In this study, a biopolymer, poly-gamma-glutamic acid (gamma-PGA) derived from bacterial sources (Bacillus species) was evaluated for its efficiency in removing basic dyes from aqueous solution. Sorption studies under batch mode were conducted using C.I. Basic blue 9 (BB9) and C.I. Basic green 4 (BG4) as test dyes. Equilibrium process conformed well with the Redlich-Peterson isotherm equation and the monolayer sorption capacity obtained from the Langmuir model was 352.76 and 293.32mg/g for BB9 and BG4 dyes, respectively. The kinetic studies of dye sorption on gamma-PGA gave high coefficients of determination (>0.98) for a pseudo second-order equation. An ion-exchange model, which assumes adsorption as a chemical phenomenon, was also found to fit the kinetic data precisely. The dye sorption largely depended on the initial pH of the solution with maximum uptake occurring at pH above 5. About 98% of the dye adsorbed on gamma-PGA could be recovered at pH 1, which facilitates the reuse of spent gamma-PGA.     

Biosorption of cadmium(II), zinc(II) and lead(II) by Penicillium simplicissimum: Isotherms, kinetics and thermodynamics

The isotherms, kinetics and thermodynamics of Cd(II), Zn(II) and Pb(II) biosorption by Penicillium simplicissimum were investigated in a batch system. The effects of pH, initial metal ions concentration, biomass dose, contact time, temperature and co-ions on the biosorption were studied. Adsorption data were well described by both the Redlich–Peterson and Langmuir model. Chemical ion-exchange was found to be an important process based on free energy value from Dubini–Radushkevich isotherm for all metal ions. The results of the kinetic studies of all metal ions at different temperature showed that the rate of adsorption followed the pseudo second-order kinetics well. The thermodynamics constants ΔG°, ΔH° and ΔS° of the adsorption process showed that biosorption of Cd(II), Zn(II) and Pb(II) ions on Penicillium simplicissimum were endothermic and spontaneous.     

Equilibrium and kinetic modeling of adsorption of reactive dye on cross-linked chitosan beads

The adsorption of reactive dye (Reactive Red 189) from aqueous solutions on cross-linked chitosan beads was studied in a batch system. The equilibrium isotherms at different particle sizes (2.3-2.5, 2.5-2.7 and 3.5-3.8mm) and the kinetics of adsorption with respect to the initial dye concentration (4320, 5760 and 7286 g/m(3)), temperature (30, 40 and 50 degrees C), pH (1.0, 3.0, 6.0 and 9.0), and cross-linking ratio (cross-linking agent/chitosan weight ratio: 0.2, 0.5, 0.7 and 1.0) were investigated. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms and isotherm constants. Equilibrium data fitted very well to the Langmuir model in the entire saturation concentration range (0-1800 g/m(3)). The maximum monolayer adsorption capacities obtained from the Langmuir model are very large, which are 1936, 1686 and 1642 g/kg for small, mediumand large particle sizes, respectively, at pH 3.0, 30 degrees C, and the cross-linking ratio of 0.2. The pseudo first- and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step, instead of mass transfer. The initial dye concentration and the solution pH both significantly affect the adsorption capacity, but the temperature and the cross-linking ratio are relatively minor factors. An increase in initial dye concentration results in the increase of adsorption capacity, which also increases with decreasing pH. The activation energy is 43.0 kJ/mol for the adsorption of the dye on the cross-linked chitosan beads at pH 3.0 and initial dye concentration 3768 g/m(3).     

Adsorption characteristics of noble metals on the strongly basic anion exchanger Purolite A-400TL

Ion exchange is an alternative process for uptake of noble metals from aqueous solutions. In the present study, the sorption of Pd(II), Pt(IV), and Au(III) ions from aqueous solution was investigated by using Purolite A-400TL (strongly basic anion exchanger, gel, type I) in a batch adsorption system as a function of time (1 min–4 h). Initial Pd(II) concentration (100–1000 mg/L), beads size (0.425–0.85 mm), rate of phases mixing (0–180 rpm), and temperatures (ambient, 313 K) were taken into account during the Pd(II) sorption process. Moreover, the column flow adsorption study was carried out, and the breakthrough curves were obtained for Pd(II) ions. The equilibrium, kinetic, desorption, and ion-exchange resin reuse studies were carried out. The experimental results showed that Purolite A-400TL—the strongly basic anion-exchange resin could be used effectively for the removal of noble metal ions from the aqueous medium. The kinetics of sorption process is fast and the resin could be reused without reduction of capacity (three cycles of sorption–desorption, the reduction of capacity is smaller than 1 %). The column studies indicated that in the dilute acidic solution (0.1 M HCl) the working anion exchange capacity is high (0.0685 mg/cm³) in comparison with the other SBA resins examined under the same experimental conditions, e.g., Amberlite IRA-458 (0.0510 mg/cm³), Amberlyst A-29 (0.0490 mg/cm³), Dowex MSA-1 (0.0616 mg/cm³), Dowex MSA-2 (0.0563 mg/cm³), Varion ADM (0.0480 mg/cm³), and Varion ATM (0.0490 mg/cm³) etc. The highest % of Pd(II) desorption was obtained using thiourea, acidic thiourea, sodium hydroxide, and ammonium hydroxide as eluting agents (%D1 was in the range of 23.9–46.9 mg/g).