Adsorption kinetics,isotherm,and thermodynamic studies of adsorption of pollutant from aqueous solutions onto humic acid

In the present study,humic acid was used as an adsorbent for the investigation of the adsorption kinetics,isotherms,and thermo-dynamic parameters of hexavalent chromium from aqueous solution at varying pH,temperatures,and concentrations.Adsorption isotherms and equilibrium adsorption capacities were determined by the fittings of the experimental data to three well-known iso-therm models:Langmuir,Freundlich,and Redlich-Peterson.The results showed that the Langmuir and Redlich-Peterson models appear to fit the adsorption better than did the Freundlich adsorption model for the adsorption of chromium onto humic acid.The equilibrium constants were used to calculate thermodynamic parameters such as the change of free energy,enthalpy,and entropy.The derived adsorption constants (logaL) and their temperature dependencies from Langmuir isotherm have been used to calculate the corresponding thermodynamic quantities such as the free energy of adsorption,heat,and entropy of adsorption.The thermo-dynamic data indicate that Cr (VI) adsorption onto humic acid is entropically driven and characterized by physical adsorption.

MICRO-DESCRIPTION OF THE SOLUTE-FIELD AND THE PHASE-FIELD MODEL FOR ISOTHERMAL PHASE TRANSITION IN BINARY ALLOYS

A new phase field method for two-dimensional simulations of binary alloy solidification was studied. A model basing on solute conservative in every unit was developed for solving the solute diffusion equation during solidification. Two-dimensional computations were performed for ideal solutions and Ni-Cu dendritic growth into an isothermal and highly supersaturated liquid phase.

Comparative Study on Constitutive Models to Predict Flow Stress of Fe-Cr-Ni Preform Reinforced Al-Si-Cu-Ni-Mg Composite

The isothermal compression tests were carried out on Gleeble-3500 thermal-mechanical simulation machine in a temperature range of 298-473 K and strain rate range of 0.001-10 s^-1. The experimental results show that the flow stress data are negatively correlated with temperature for temperature softening, and the strain rates sensitivity of this composite increases with elevating temperature. Based on the experimental data, Johnson-Cook, modified Johnson-Cook and Arrhenius constitutive models were established. The accuracy of these three constitutive models was analyzed and compared. The results show that the values predicted by Johnson-Cook model could not agree well with the experimental values. The prediction accuracy of Arrhenius model is higher than that of Johnson-Cook model but lower than that of the Modified Johnson-Cook model.

Adsorption of 5.5’-Disulfonicindigotin(5.5’-DI)onto Green Coconut Fiber(Cocos nucifera L.):Kinetic and Isotherms

Green coconut fiber (Cocos nucifera L.) has been largely used in solid-phase extraction. The effect of the initial dye concentration (1.91, 3.02 and 4.02) × 10-5 mol&#183L-1 and solid phase contact (SPE) time were evaluated at different temperatures (283, 298 and 313) K at pH 2. Kinetic experimental data were applied to three simplified kinetic models: pseudo-first order, pseudo-second order, and intraparticle diffusion. The adsorption of 5.5’-DI onto the solid phase showed excellent fit to the pseudo-second order model. At 283, 298 and 313 K the maximum sorption, qmax,exp, for the lowest initial concentration (Co = 1.91 × 10-5 mol&#183L-1) of 5.5’-DI were (5.01, 5.24 and 6.14) × 10-4 g&#183g-1;for Co = 3.02 × 10-5 mol&#183L-1 (0.93, 1.01 and 1.03) × 10-3

Urban Wastewater Treatment by Adsorption of Organic Matters on Modified Bentonite by(Iron-Aluminum)

In this research, the natural bentonite clay (from Maghnia, western Algeria) was purified (Na+- montmorillonite, CEC = 91 meq/100 g), noted (puri.bent) and modified with mixed hydroxy-Fe-Al (FeAl-PILC). The purified bentonite clay and FeAl-PILC were heated at 383 K for 2 hr and characte-rized by the chemical analyses data, XRD, and N2 adsorption to 77 K techniques. Puri.bent and FeAl-PILC were applied to fix the organic matter (OM) present in urban wastewater from the city of Sidi Bel-Abbes (western Algeria). The adsorption of organic matter was followed by spectro-photometry at 470 nm, and the adsorption data were a good fit with Freundlich isotherm for pu-ri.bent but for FeA-lPILC, were well fit by Elovitch isotherm model. The maximum adsorption ca-pacity (qm) was 571.6 mg/g for puri.bent and 1120.69 mg/g for FeAl-PLC. The degree of OM removal was 67% for puri.bent and 97% for FeAl-PILC. FeAl-PILC can be considered as a promising adsorbent for the removal of OM from wastewater.

Effect of nanotechnology on heavy metal removal from aqueous solution

The effect of nanotechnology on cadmium and zinc removal from aqueous solution was investigated. In order to characterize micro and nano phragmites australis adsorbent, we analyzed the data via FTIR, SEM, PSA, and EDX. The effect of various parameters such as p H, contact time, amount of adsorbent and initial concentration, was investigated. The optimum p H for the removal of cadmium for micro and nano phragmites australis adsorbent was 7, and for the removal of zinc by the micro adsorbent was 7 and by nano adsorbent was 6. The equilibrium time of zinc was 90 min and for the adsorption of cadmium by micro and nano adsorbent were 90 and 30 min, respectively. The optimum dose of micro adsorbent for the removal of cadmium was 0.7 g, and the other dose for the removal of zinc and cadmium was 0.5 g. The evaluation of adsorbent's distribution coefficient showed that the highest rates of distribution coefficient with initial concentration of 5, 10, 30, and 50 mg/L were 394.83, 587.62, 759.39 and 1101.52 L/kg, respectively, which were observed in nano adsorbent. Desorption experiments for the nano adsorbent in three cycles were done. Among kinetics models, our experimental data were more consistent with Hoo kinetic model and for isotherm models, Freundlich isotherm was more consistent. The results show that nanotechnology could increase the performance of adsorbents and enhance the efficiency of the adsorption of cadmium and zinc ions.

A numerical simulation of latent heating within Typhoon Molave

The weather research and forecasting（WRF） model is a new generation mesoscale numerical model with a fine grid resolution（2 km）, making it ideal to simulate the macro-and micro-physical processes and latent heating within Typhoon Molave（2009）. Simulations based on a single-moment, six-class microphysical scheme are shown to be reasonable, following verification of results for the typhoon track, wind intensity, precipitation pattern, as well as inner-core thermodynamic and dynamic structures. After calculating latent heating rate, it is concluded that the total latent heat is mainly derived from condensation below the zero degree isotherm, and from deposition above this isotherm. It is revealed that cloud microphysical processes related to graupel are the most important contributors to the total latent heat. Other important latent heat contributors in the simulated Typhoon Molave are condensation of cloud water, deposition of cloud ice, deposition of snow, initiation of cloud ice crystals, deposition of graupel, accretion of cloud water by graupel, evaporation of cloud water and rainwater,sublimation of snow, sublimation of graupel, melting of graupel, and sublimation of cloud ice. In essence, the simulated latent heat profile is similar to ones recorded by the Tropical Rainfall Measuring Mission, although specific values differ slightly.

Soils Developed from Dolomitic Shale in the Yichang Area, China and Adsorption Characteristics for Phenol

Recently, the problem of phenolic organics pollution has become increasingly serious. More and more strategies have been developed to remove phenolic organics from water, including oxidation, adsorption, chemical precipitation, etc. Among them, adsorption technology has attracted great attention due to its advantages of high efficiency, simplicity and easy operation. In this study, the natural shale soil without any modification was directly used as adsorbent to remove phenol from aqueous solutions. The shale soil samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption-desorption isotherms. Detailed kinetics and isotherm studies of phenol adsorption onto shale were investigated. According to the results of the orthogonal test, the influence degree of the four factors on the removal of phenol by soil samples was operating temperature > adsorbent dosage > contact time > pH. The adsorption kinetics of phenols by the soil corresponded with the pseudo-second-order kinetic model. Thermodynamic studies indicated that Freundlich adsorption isotherm model could better describe phenol removal characteristics than Langmuir adsorption isotherm model. And the maximum adsorption capacity was found to be 9.68 mg/g for phenol. It is concluded that shale soil without any modification or activated methods could be employed as a low-cost alternative adsorbent for wastewater treatment.

Adsorption Isotherm and Kinetic Study of Methane on Palm Kernel Shell-Derived Activated Carbon

Activated carbon(AC)was synthesized from palm kernel shell(PKS)using different activating agents,i.e.,steam,carbon dioxide(CO 2),and CO 2-steam,in order to analyze the impact of acti-vating agents on the pore opening of AC.In this study,AC produced from PKS was found to have great potential as an adsorbent for methane storage.The different molecular diffusivity and reac-tivity of the combination of CO 2 and steam succeeded in producing AC with the highest burn-offof 78.57%,a surface area of 869.82 m 2/g,a total pore volume of 0.47 cm 3/g,and leading to maximum methane gas adsorption capacity of 4.500 mol/kg.All types of ACs exhibited the best fit with the Freundlich isotherm model,with the correlation coefficient(R 2)ranging from 0.997 to 0.999,indicating the formation of multilayer adsorption.In addition,the adsorption kinetic data for all ACs followed the pseudo-first-order model showing that the rate of adsorption was dependent on both the adsorbent and the adsorbate and was governed primarily by physical ad-sorption between the pore surface and methane gas.The results of intraparticle diffusion model indicated that the adsorption of methane was affected by both pore diffusion and exterior layer diffusion due to the different adsorption rates.

Applicable models for multi-component adsorption of dyes:A review

Adsorption is one of the several techniques that has been successfully used for dyes removal.Since most industrial colored effluents contain several components including dyes,having a strong knowledge about the scope of competitive adsorption process is a powerful key to design an appropriate system.This is mainly because of the complexity brought about by the increasing number of parameters needed for process description which complicates not only the process modeling but also the experimental data collection.A multicomponent adsorption model should be based on fundamental soundness,speed,and simplicity of calculation.For such systems,competition will change the adsorbent-adsorbate attractions.Thus,there is major concern to develop an accurate and reliable method to predict dye adsorption behavior in multi-component systems.This article covers topics such as the theory of dyes adsorption in multi-component systems along with applicable models according to the consistent theories presented by researchers.

Synthesis and application of biocompatible nontoxic nanoparticles for reclamation of Ce^3＋ from synthetic wastewater： Toxicity assessment, kinetic, isotherm and thermodynamic study

The aim of present study is to synthesize forsterite nanoparticles（FRST） for the reclamation of cerium ions（Ce3＋） from synthetic wastewater.The aim to synthesize FRST nanoparticles is due to its biocompatible and nontoxic nature.The formation of nanoparticles with average diameter of 58 nm was confirmed by TEM analysis.SEM images of bare FRST nanoparticles show a heterogeneous surface with porous nature.BET surface area of FRST nanoparticles is calculated to be 33.69 m2/g.The significant uptake of Ce3＋ ions can be obtained for all the selected concentrations（25-150 mg/L） within 2 h of adsorbent—adsorbate interaction.The pH study shows that by increasing pH from acidic to alkaline range,higher removal can be achieved.Temperature study demonstrates the endothermic nature of Ce3＋adsorption.The value of sticking probability suggests very high sticking probability of Ce3＋ ion for FRST nanoparticles.Ce3＋ uptake is favored by higher temperature and with the increase in temperature from298 to 328 K,Langmuir adsorption capacity increases from 36.45 to 42.99 m2/g.Applicability of FRST nanoparticles was also investigated for other light and heavy rare earth elements in single solute and multisolute systems,FRST nanoparticles show the significant removal of divalent metallic pollutants as well.The assessment of chemical toxicity of treated wastewater was carried out with the bioluminescent photobacterium（Vibrio fischeri） and decreased toxicity was observed in treated water samples.The outcome of present study suggests that the FRST nanoparticles can be efficiently utilized for the removal of Ce3＋ ions and a wide range of other pollutant species as well.

Selective removal of phenol by spherical particles of α-,β- and γ-cyclodextrin polymers： kinetics and isothermal equilibrium

Spherical particles of α-,β- and γ-cyclodextrin （CD） polymers to efficiently remove phenol from waste water were prepared by reverse suspension polymerization with epichlorohydrin as crosslinker in liquid paraffin. By controlling the amounts of crosslinker and water, well- defined spherical polymer particles with controllable size were obtained. Due to the selective inclusion associations between CD groups and phenol, these CD spherical polymer particles were demonstrated to be ideal candidates for removal of phenol. Among them β-CD polymer particles showed the best performance. The kinetics and isothermal equilibrium models were used to fit the experimental data of phenol removal from aqueous solution using these CD polymer particles. It was found that the kinetics followed the Ho and Mckay equation, suggesting that the adsorption process of phenol was controlled by diffusion and the host-guest interaction between CD and phenol. Equilibrium isothermal data can be well fitted by the Freundlich equation. The negative free energy change indicated the spontaneous nature of adsorption of phenol by α-,β- and γ-CD spherical polymer particles, while the lowest free energy for β-CD polymer reflected its best adsorption ability, compared to α- and γ- CD polymer particles.

Removal of Cr(VI)from aqueous solution by Rice-husk-based activated carbon prepared by Dual-mode heating method

Rice husk-based activated carbon was prepared with the help of zinc chloride using microwave and electrical dual-mode heating.The pore characteristics and chemical properties of rice husk-based activated carbon(RH-AC)were characterized by BET,XRD,Raman spectra,FTIR and pHIEP(pH of isoelectric point).The specific surface area of RH-AC is 1719.32 m^(2)/g with a total pore volume of 1.05 cm^(3)/g.The performance of RH-AC for removing Cr(VI)from aqueous solution was examined considering the variation of the contact time(0-120 min),pH value(2.0-9.0),adsorbent dose(0.5-3.0 g/L),initial concentration(28-145 mg/L)and solvent temperature(15-45℃).The ideal pH for Cr(VI)removal is between 2.0 and 3.0 with the equilibrium time of 90 min,achieving the maximum adsorption capacity of 56.82 mg/g with the pH of 3.0.Comparable study on the established kinetic models and isotherms to simulate the removal of Cr(VI)by RH-AC was carried out to sort out the inherent mechanism of the absorption.Reasonable agreements could be obtained by the pseudo-second-order kinetic model and Langmuir,Freundlich and Tempkin isothermal models.Results from Body model simulation suggest that external mass transfer was the essential cause for rate-controlling in the adsorption process of Cr(VI).

Activated carbon adsorption of quinolone antibiotics in water:Performance,mechanism,and modeling

The extensive use of antibiotics has led to their presence in the aquatic environment, and introduces potential impacts on human and ecological health. The capability of powdered activated carbon （PAC） to remove six frequently used quinolone （QN） antibiotics during water treatment was evaluated to improve drinking water safety. The kinetics of QN adsorption by PAC was best described by a pseudo second-order equation, and the adsorption capacity was well described by the Freundlich isotherm equation. Isotherms measured at different pH showed that hydrophobic interaction, electrostatic interaction, and dispersion force were the main mechanisms for adsorption of QNs by PAC. A pH-dependent isotherm model based on the Freundlich equation was developed to predict the adsorption capacity of QNs by PAC at different pH values. This model had excellent prediction capabilities under different laboratory scenarios. Small relative standard derivations （RSDs）, i.e., 0.59%-0.92% for ciprofloxacin and 0.09%-3.89% for enrofloxacin, were observed for equilibrium concentrations above the 0.3 mg/L level. The RSDs increased to 11.9% for ciprofloxacin and 32.1% for enrofloxacin at μg/L equilibrium levels, which is still acceptable. This model could be applied to predict the adsorption of other chemicals having different ionized forms.

Removal of copper by modified chitosan adsorptive membrane

In this study,a novel adsorptive membrane was prepared from chitosan as the functional polymer and some additive blend solutions by solution casting method.The modified chitosan membrane was characterized by FTIR and its Water Swelling Ratio(WSR).The adsorption of copper ions on the adsorptive membrane was investi-gated in batch experiments.The results obtained from the experiments indicated that the membrane had a good adsorption capacity for copper ions,the optimal ionic strength and pH were 0.1 and 5–6,respectively.Compared with the Langmuir isotherm model,the experimental data were found to be following the Freundlich model.

Recovery of NH4^＋ by corn cob produced biochars and its potential application as soil conditioner

NH4^＋ ion, a main pollutant in aquatic systems, not only causes eutrophication in rivers and lakes but also contributes to fish toxicity. In this study, an eco-friendly biosorbent was prepared from the pyrolysis of corn cob, a low-cost agricultural residue. The biochars produced by pyrolysis of corn cob at 400℃ and 600℃ were characterized and investigated as adsorbents for NH4＋ -N from an aqueous solution. The biochars were characterized through elemental analysis, Brunauer-Emmett-Teller-N2 surface area analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Batch experiments were conducted to investigate the NH4＋ adsorption process of the corn cob biochars. The Freundlich isotherm model fitted the adsorption process better than the Langmuir and Dubinin-Radushkevich isotherm models. Moreover, the adsorption process was well described by a pseudo-second-order kinetic model. Results of thermodynamic analysis suggested that adsorption was a nonspontaneous exothermic process. Biochars produced at 400℃ had higher adsorption capacity than those produced at 600℃ because of the presence of polar functional groups with higher acidity. The exhausted biochar can be potentially used as soil conditioner, which can provide 6.37 kg NH4＋-N-t^-1 （N fertilizer per ton of biochar）.

Removal of perfluorinated surfactants from wastewater by adsorption and ion exchange--Influence of material properties,sorption mechanism and modeling

Perfluorooctane sulfonate（PFOS） has attracted increasing concern in recent years due to its world-wide distribution, persistence, bioaccumulation and potential toxicity. The influence of sorbent properties on the adsorptive elimination of PFOS from wastewater by activated carbons, polymer adsorbents and anion exchange resins was investigated with regard to their isotherms and kinetics. The batch and column tests were combined with physicochemical characterization methods, e.g., N2 physisorption, mercury porosimetry, infrared spectroscopy, differential scanning calorimetry, titrations, as well as modeling. Sorption kinetics was successfully modelled applying the linear driving force（LDF） approach for surface diffusion after introducing a load dependency of the mass transfer coefficient βs.The big difference in the initial mass transfer coefficient βs,0, when non-functionalized adsorbents and ion-exchange resins are compared, suggests that the presence of functional groups impedes the intraparticle mass transport. The more functional groups a resin possesses and the longer the alkyl moieties are the bigger is the decrease in sorption rate.But the selectivity for PFOS sorption is increasing when the character of the functional groups becomes more hydrophobic. Accordingly, ion exchange and hydrophobic interaction were found to be involved in the sorption processes on resins, while PFOS is only physisorptively bound to activated carbons and polymer adsorbents. In agreement with the different adsorption mechanisms, resins possess higher total sorption capacities than adsorbents. Hence, the latter ones are rendered more effective in PFOS elimination at concentrations in the low μg/L range, due to a less pronounced convex curvature of the sorption isotherm in this concentration range.

Preparation of solar-enhanced AlZnO@carbon nano-substrates for remediation of textile wastewaters

Photoactive aluminum doped ZnO(AlZnO)was synthesized by sol-gel method.After that,AlZnO photocatalyst was deposited on five carbon-based materials(CBMs)using ultrasonic route followed by solid-state mixing using ball mill.The CBMs used were poly aniline(PANI),carbon nitride(CN),carbon nanotubes(CNT),graphene(G),and carbon nanofibers(CNF).The crystal phases,elemental compositions,morphological,and optical properties of the AlZnO@CBMs composites were investigated.Experimental results revealed that two of AlZnO@CBMs composites exhibited superior bleaching efficiency(100%removal)and photocatalytic stability(three cycles)for 50μmol/L Methylene Blue(MB)contaminated water after 60 min irradiation in visible light at pH 6.5,0.7%H2O2,and 5 g/L inorganic salts.Under optimum conditions,AlZnO@CBMs nanocomposites were employed for the treatment of mixed dyestuffs composed of MB,Methyl Orange(MO),Astrazone Blue FRR(BB 69),and Rhodamine B(RhB)dyes under dark,ultraviolet,visible,and direct sunlight.For mixed dyestuffs,the AlZnO@G achieved the highest dye sorption capacity(60.91μmol dye stuffs/g)with kinetic rate 8.22×10^-3 min^-1 in 90 min via multi-layer physisorption(Freundlich isotherm)on graphene sheet.In additions,AlZnO@CN offered the highest photo-kinetic rate(Kphoto)of^54.1×10^-3 min^-1(93.8%after 60 min)under direct sunlight.Furthermore,the selective radical trapping experiment confirmed that the holes and oxidative superoxide radicals are crucial on dyes photodegradation pathway.Owing to their superior performance,AlZnO@G and AlZnO@CN nanocomposites can offer an effective in-situ solar-assisted adsorption/photocatalytic remediation of textile wastewater effluents.