Increase In Surface Loading Research Articles

Diffusion-controlled adsorption–desorption of C6 hydrocarbons by multiwall carbon nanotubes

The adsorption–desorption of n-hexane, cyclohexane, and benzene on multiwall carbon nanotubes is investigated using the quartz crystal microbalance technique. Desorption kinetics is found to be diffusion-controlled. The standard Fickian diffusion models for short and long times have been applied to quantify the desorption kinetics. Considering surface diffusion as a rate-limiting step of desorption, the estimated surface diffusion coefficients for all hydrocarbons are of order 10-14 m2/s. This is an order of magnitude lower compared to surface diffusion coefficient on various carbon materials. The surface diffusion coefficient increases with an increase in surface loading.

Adsorption thermodynamics and isosteric heat of adsorption of Thymol onto sodic, pillared and organic bentonite

We studied the temperature effects on thymol adsorption on sodium and modified clays from Nador, Morocco. The clay samples used for these analyses were purified and modified by sodium, Al13 and Cetyl Pyridinium chloride before they were used as an adsorbent for the adsorption of thymol from aqueous solution in batch adsorption procedure. The adsorption experiments were carried out as a function of temperature. The adsorption was found to be strongly dependent on the temperature. The Freundlich isotherm model showed an excellent fit to the equilibrium adsorption data. This equation indicates that the logarithm of KF is a linear function of temperature, and it decreases with temperature. The mean free energy (E) estimated from the Rankine (Calendar) modified model indicated that there is a significant relationship between adsorbed quantity and temperature and the primary mechanism governing the sorption process was a physisorption mechanism. The Arrhenius and Eyring equations were used to obtain the activation parameters such as activation energy (Ea), and enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) of activation for the adsorption system. Thermodynamic studies suggested the spontaneous and endothermic nature of adsorption of thymol green by sodium and purified bentonite. The isosteric heat of adsorption (ΔHX) was also determined from the equilibrium information using the Clausius–Clapeyron equation. ΔHX increased with increase in surface loading, indicating some lateral interactions between the adsorbed molecules.

Biosorption of Direct Fast Scarlet 4BS from aqueous solution using the green-tide-causing marine algae Enteromorpha prolifera.

Enteromorpha prolifera, the marine algae frequently causing green tide in the littoral areas in recent years, was investigated as a feasible biosorbent to remove azo dye Direct Fast Scarlet 4BS (DFS-4BS) from aqueous solution. The FTIR spectra of the acid-treated Enteromorpha prolifera (ATEP) biomass before and after dye sorption were used to identify the main functionalities involved in the biosorption process. Results of batch experiments showed that the adsorption capacity of ATEP was dependent on solution pH, ATEP dosage and temperature. The adsorption kinetics followed the pseudo-second order rate equation, while the adsorption isotherm could be well described by the Langmuir model with maximum sorption capacity of 318.87mg·g-1, demonstrating the excellent performance of ATEP as a biosorbent to remove DFS-4BS from aqueous solution. The negative values of free energy change (ΔG°) and positive value of enthalpy change (ΔH°) confirmed that the sorption of DFS-4BS onto ATEP was spontaneous and endothermic in the temperature range of 303-333K. The isosteric heat of adsorption increased with the increase of surface loading, suggesting that the ATEP biomass had heterogeneous surface and lateral interactions might exist among adsorbed molecules. According to the sorption results and the FTIR spectra, it was deduced that the adsorption mechanism involved hydrogen bonding, electrostatic attraction and bonding, and hydrophobic and van der Waals interaction.

Isotherm, Kinetic, and Thermodynamic Characteristics for Adsorption of 2,5-Xylenol onto Activated Carbon

The adsorption of the major tar compound, 2,5-xylenol, derived from the plant cell cultures of Taxus chinensis, onto activated carbon was examined at different initial 2,5-xylenol concentrations, durations, and temperatures. From the analysis of adsorption isotherms, the Langmuir isotherm model showed good fit to the equilibrium adsorption data. It was found that adsorption capacity decreased with increasing temperature, and the adsorption of 2,5-xylenol onto activated carbon was favorable. The obtained kinetic data for 2,5-xylenol adsorption with activated carbon agreed well with the pseudo-second-order kinetic model. By using intraparticle diffusion model, intraparticle diffusion and boundary layer diffusion did not play a dominant role in 2,5-xylenol adsorption. Thermodynamic parameters were calculated, which indicated that the adsorption was non-spontaneous, irreversible and exothermic nature. The isosteric heat of adsorption decreased with increase in surface loading, indicating a heterogeneous surface.

Application of ethylenediamine hydroxypropyl tamarind fruit shell as adsorbent to remove Eriochrome black T from aqueous solutions – Kinetic and equilibrium studies

ABSTRACTEthylenediamine Hydroxypropyl Tamarind Fruit Shell (EDAHP-TFS) was synthesized to remove Eriochrome Black T (EBT) from aqueous solutions. Maximum adsorption occurred at pH 2.0 and equilibrium time 2 h. Adsorption increased with increase in initial concentration and temperature. Adsorption kinetics obeyed the pseudo-second-order model and indicates a partial ion exchange, followed by the complexation mechanism. Lower E# (4.48 kJ/mol) represents film diffusion as the rate-limiting step. EBT removal followed the Sips isotherm model with a maximum adsorption capacity of 0.237 mmol/g at 30ºC. Isosteric heat of adsorption (ΔHi) decreased with increase in surface loading, indicating heterogeneous adsorption sites. Desorption studies were carried out and 96.4% recovery was achieved at pH 11.0.

Thorium(IV) Recovery from Water and Sea Water Using Surface Modified Nanocellulose/Nanobentonite Composite: Process Design

Thorium(Th) contamination in the ground water an emerging environmental issue and Th recovery from sea water and nuclear wastewater is of high significance, as it is a major player in the energy sector. For the adsorption and recovery of Th, polymer grafted bio materials are reported as most efficient materials. P(IA/MAA)-g-NC/NB was prepared and all the steps in the synthetic routes were monitored using FTIR, SEM–EDS, and XRD, TG. Efficiency in removal of Th(IV) by P(IA/MAA)-g-NC/NB was tested by batch adsorption technique. The pH dependent Th(IV) adsorption process, was optimized at 4.5 and adsorption equilibrium was achieved within 120 min. Experimental kinetic data correlates well with pseudo-second-order equation, indicates adsorption was chemical process via ion exchange followed by complexation reaction, also could explain the film diffusion process of adsorption. Sips isotherm proved to best fit for the adsorption of Th(IV) onto P(IA/MAA)-g-NC/NB with maximum adsorption capacity of 95.19 mg/g. Thermodynamic studies revealed the endothermic nature, feasibility and spontaneity of the adsorption process. ΔHx and ΔSx were decreased to a small extent from −5.567 to −3.439 kJ/mol and increased from 11.18 to 18.39 J/mol, respectively, with increase in surface loading from 50 to 70 mg/g, indicating that the surface of the onto P(IA/MAA)-g-NC/NB is having energetically heterogeneous surface and there may be some lateral interactions between the adsorbed Th(IV) ions Repeated adsorption–desorption study over six cycles, adsorption percentage decreases from 99.0 to 94.6 %, proved the efficiency of P(IA/MAA)-g-NC/NB as an effective adsorbent for the removal and recovery of Th(IV) from aqueous solutions. Complete removal of Th(IV) ions from seawater containing 10 mg/L with a dose of 0.25 g/L P(IA/MAA)-g-NC/NB achieved. Batch adsorption system as double stage reactor designed from the adsorption isotherm data of Th(IV) by constructing operational lines. From these could be concluded that P(IA/MAA)-g-NC/NB is a promising candidate for the effective removal and removal of Th(IV) from industrial effluents phase and sea water. The maximum adsorption capacity Qs for Ceralite IRC-50 calculated which was found to be 179.67 mg/g which are considerably lower than those for P(IA/MAA)-g-NC/NB.

Biosorption kinetics, thermodynamics and isosteric heat of sorption of Cu(II) onto Tamarindus indica seed powder

Biosorption of Cu(II) by Tamarindus indica seed powder (TSP) was investigated as a function of temperature in a batch system. The Cu(II) biosorption potential of TSP increased with increasing temperature. The rate of the biosorption process followed pseudo second-order kinetics while the sorption equilibrium data well fitted to the Langmuir and Freundlich isotherm models. The maximum monolayer Cu(II) biosorption capacity increased from 82.97 mg g −1 at 303 K to 133.24 mg g −1 at 333 K. Thermodynamic study showed spontaneous and endothermic nature of the sorption process. Isosteric heat of sorption, determined using the Clausius–Clapeyron equation increased with increase in surface loading showing its strong dependence on surface coverage. The biosorbent was characterized by scanning electron microscopy (SEM), surface area and porosity analyzer, X-ray diffraction (XRD) spectrum and Fourier transform infrared (FTIR) spectroscopy. The results of FTIR analysis of unloaded and Cu(II)-loaded TSP revealed that NH 2, OH, C O and C O functional groups on the biosorbent surface were involved in the biosorption process. The present study suggests that TSP can be used as a potential, alternative, low-cost biosorbent for removal of Cu(II) ions from aqueous media.

Adsorption thermodynamics, kinetics and isosteric heat of adsorption of malachite green onto chemically modified rice husk

Rice husk treated with NaOH was tested as a low cost adsorbent for the removal of malachite green from aqueous solution in batch adsorption procedure. The adsorption experiments were carried out as a function of solution pH, initial dye concentration, contact time and temperature. The adsorption was found to be strongly dependent on pH of the medium. The Freundlich isotherm model showed good fit to the equilibrium adsorption data. The mean free energy ( E) estimated from the Dubinin–Radushkevich model indicated that the main mechanism governing the sorption process was chemical ion-exchange. The kinetics of adsorption followed the pseudo-second-order model and the rate constant increased with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the activation parameters such as activation energy ( E a), and enthalpy ( ΔH #), entropy ( ΔS #) and free energy ( ΔG #) of activation for the adsorption system. Thermodynamic studies suggested the spontaneous and endothermic nature of adsorption of malachite green by treated rice husk. The isosteric heat of adsorption ( ΔH X ) was also determined from the equilibrium information using the Clausius–Clapeyron equation. ΔH X increased with increase in surface loading indicating some lateral interactions between the adsorbed dye molecules.

Study of equilibrium and thermodynamic adsorption of α-picoline, β-picoline, and γ-picoline by Jordanian zeolites: Phillipsite and faujasite

In the present study the ability of phillipsite and faujasite to remove α-picoline, β-picoline, and γ-picoline from aqueous solution in the broad range of concentrations (1–500 mg L −1) was investigated. Adsorption equilibrium was carried out at different initial concentrations, sorbent concentrations, and temperatures. Brunauer–Emmett–Teller (BET), the Harkins–Jura, the Smith, and the Halsey equations were applied to the experimental data. The data fitted the BET model best. The overall adsorption of α-, β-, and γ-picoline on phillipsite and faujasite followed the order: faujasite α-picoline < phillipsite α-picoline < faujasite β-picoline < phillipsite β-picoline < faujasite γ-picoline < phillipsite γ-picoline. The values of change in Gibbs free energy (Δ G°), enthalpy (Δ H°), and entropy (Δ S°) were calculated. Thermodynamic study revealed that the adsorption of picolines onto phillipsite and faujasite was an exothermic process. Isosteric heat of adsorption was found to decrease with the increase in surface loading.

Humic acid-immobilized polymer/bentonite composite as an adsorbent for the removal of copper(II) ions from aqueous solutions and electroplating industry wastewater

In this study, humic acid (HA) was immobilized onto amine-modified polyacrylamide/bentonite composite (Am-PAA-B) which was prepared by direct intercalation polymerization technique and the product (HA-Am-PAA-B) was used as an adsorbent for the removal of copper(II) ions from aqueous solutions. The surface characteristics of bentonite, Am-PAA-B and HA-Am-PAA-B were investigated. The adsorbent behaved like a cation exchanger and more than 99.0% Cu(II) ions’ removal was observed at the pH range 5.0–6.0. Kinetic and isotherm experiments showed that amount of Cu(II) ions adsorbed increases with increase of the initial concentration and temperature. The adsorption kinetic data were interpreted by pseudo-first-order and pseudo-second-order rate equations. The suitability of Langmuir, Freundlich and Dubinin–Radushkevich (D-R) adsorption models to the equilibrium data was investigated. The Langmuir isotherm was found to provide the best theoretical correlation of the experimental equilibrium data. The thermodynamic and kinetic activation parameters were derived to predict the nature of adsorption process and discussed in detail. The isosteric heat of adsorption was constant even after increase in surface loading. The removal efficiency of HA-Am-PAA-B was tested using electroplating industry wastewater. The desorption of adsorbed Cu(II) ions was achieved by 0.1 M HCl and four adsorption/desorption cycles were performed without significant decrease in the adsorption capacity.

Adsorption of α-picoline onto rice husk ash and granular activated carbon from aqueous solution: Equilibrium and thermodynamic study

Abstract In the present study, the batch adsorption experiments were carried out to calculate the adsorption capacities of rice husk ash (RHA) and commercial grade granular activated carbon (GAC) for the adsorption of α-picoline (Pi) from aqueous solutions. The effect of various parameters like initial pH (pH0), adsorbent dose (m), contact time (t), initial concentration (C0) and temperature (T) on the adsorption of Pi from the aqueous solutions was studied. The maximum uptake of Pi was observed to be 2.34 mg g−1 at lower concentration (50 mg dm−3) and 15.46 mg g−1 at higher concentration (600 mg dm−3) using 20 kg m−3 of RHA and the maximum uptake of Pi by GAC was observed to be 4.55 mg g−1 at lower concentration (50 mg dm−3) and 36 mg g−1 at higher concentration (600 mg dm−3) using 10 kg m−3 of GAC at normal temperature. The equilibrium data can be best represented by Radke–Prausnitz isotherm equation. However, Toth and Redlich–Peterson isotherm equations also represent the equilibrium data adequately. The values of change in Gibb's free energy ( Δ G ° ), enthalpy (ΔH°) and entropy (ΔS°) were calculated. Thermodynamic study revealed that the adsorption of Pi onto RHA and GAC is an endothermic process. Isosteric heat of adsorption was found to be decreasing with an increase in surface loading. The acidic water and dilute acids showed higher desorption efficiency for Pi from RHA and GAC. Thus GAC can be regenerated by using acidic water and acids. However, RHA can be disposed off by using it as a fuel in furnaces to recover its energy value.

Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K2S2O8/Na2S2O3 initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (Ea) and enthalpy (ΔH#), entropy (ΔS#) and free energy (ΔG#) of activation for the adsorption process. The value of Ea for adsorption was found to be 10.84kJ·mol−1 and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64·10mg·g−1 at T=303K. The thermodynamic parameters such as changes in free energy (ΔG∘), enthalpy (ΔH∘), and entropy (ΔS∘) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.

Monitoring Surface and Subsurface Water Storage Using Confined Aquifer Water Levels at the Savannah River Site, USA

Surface and subsurface water storage is an important component of hydrologic models, needed to account for groundwater recharge, lateral water movement, and evapotranspiration. Yet methods for estimating above‐ and belowground water storage include substantial uncertainties. This paper demonstrates that water levels in the Gordon aquifer (a confined aquifer at the USDOE Savannah River Site, near Aiken, SC) fluctuate in response to changes in total water storage. An increase in surface loading is known to cause a measurable increase in aquifer fluid pressure whenever the aquifer skeletal compressibility is sufficiently large. Water levels in the Gordon aquifer respond rapidly during precipitation events, which is consistent with increased loading that compresses the aquifer at depth. Instantaneous barometric and loading efficiencies of approximately 6 and 91%, respectively, are consistent with a poorly consolidated aquifer. Because the aquifer has a high loading efficiency, it behaves like a geological weighing lysimeter that appears to estimate water storage. Following precipitation events, aquifer water levels decline over time, presumably due to unloading by evapotranspiration plus net lateral water export. The water‐storage signal is improved by incorporating (i) the lagged response between aquifer load and borehole water‐level changes and (ii) the removal of periodic Earth tides.

Study of the behavior of adsorbing CS 2 by activated carbon

The adsorption of carbon disulfide on one raw and three modified activated carbon samples at different temperatures from 303 K to 333 K and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus. The amounts of carbon disulfide adsorbed by three modified carbon samples are all larger than that of the raw one. It is found that organic amine is more effective than KOH as active ingredient for modification of activated carbon. The Freundlich equation is found to be the best model to fit the isotherm data for the four carbon samples at different temperatures studied. The isosteric heats of adsorption on the four carbon samples, derived from the adsorption isotherms using the Clapeyron equation, decrease with increase of surface loading. The heat of adsorption lies between 17.7 and 51.4 kJ/mol, where the carbon sample modified with KOH and ethylenediamine has the highest value with the exception of the case of high surface coverage (> 3.5 mmol/g). It is also found that the choice of adsorption isotherm has a significant influence on the values of isosteric heat of adsorption calculated. The isosteric heats of adsorption at zero surface loadings for the four carbon samples are 53.93, 53.87, 45.17 and 65.54 kJ/mol respectively and the carbon sample modified with KOH and ethylenediamine has the highest value. Analysis of the thermodynamic data shows the mobility of adsorbed carbon disulfide increases with increase of surface loading in all cases. The observed entropy change associated with the adsorption is higher than the theoretical value for the mobile adsorption but lower than the theoretical value for the localized adsorption in all cases except the carbon sample modified with KOH and ethylenediamine at higher surface coverage (> 4 mmol/g). The observed entropy change also decreases with increase of surface loading in all cases.

Performance of duckweed-covered sewage lagoons—II. Nitrogen and phosphorus balance and plant productivity

Laboratory scale experiments were performed in a non-continuous batch reactor system with 0.8 to 41.2 l with domestic sewage exposed to constant light intensity, temperature and humidity. The contribution of duckweed ( L. gibba) to N and P removal in duckweed-covered sewage lagoons (DSL) was studied at NH + 4 concentration of 25–96 mg/l with 10, 30, 70 and 95 cm deep reactors, and liquid mixing intensity of 0, 0.3, 1.0, 2.3 and 34.1 W/m 3. Duration of each experiment was 20 d with biomass harvesting every 5 d. N and P removal at extreme depths and extreme mixing intensities was compared with that in covered control reactors without duckweed. For a given N input, depth as an independent variable would not affect overall N removal except through increase of surface loading, whereas mixing had a significant positive effect at high Kj–N concentration. TP removal was stronger correlated with depth than with surface loading λ P. At low nitrogen surface loading λ N of 183 kg N/ha, TN removal could be completely attributed to duckweed uptake, whereas at high λ N (>300 kg N/ha), which correlated with high NH + 4 concentration, N uptake was inhibited to less than 50% of total removal. TP removal increased from 8.25 kg P/ha 20 d at higher Kj–N concentration (102 mg N/l) to 18.66 kg P/ha 20 d at lower concentrations (26 mg N/l). P uptake increased from 2.54–6.90 kg P/ha 20 d by introducing mixing (2.3 W/m 3). Relative growth rate decreased from 0.19 to 0.05 d −1 for initial concentrations of 25–96 mg NH + 4-N/l, respectively. N and P removal followed first-order kinetics.