Kinetics of adsorption and desorption of Pb(II) in aqueous solution on activated carbon by two-site adsorption model

The adsorption and desorption equilibrium and kinetics of lead ions from aqueous solutions on a granular activated carbon (GAC) were examined. Rapid increase followed by slow increase in Pb(II) amount on the GAC was observed as a function of time for the adsorption, while rapid decrease and consecutive very slow decrease was observed in desorption. Based on the experimental results, a two-site adsorption model was proposed for the adsorption and the desorption of Pb(II) under the study conditions. The Pb(II) adsorption on the GAC was estimated to have simultaneously occurred on the strong and the weak adsorption sites. Conventional Langmuir-type kinetic equations were introduced to quantitatively predict the adsorption and desorption with the two-site model by optimizing the parameters to fit the equilibrium and the kinetic experimental results. The equilibrium and kinetic experimental results could be represented by the equations by using one set of the common Langmuir parameters. Resultant kinetic parameters revealed that the adsorption equilibrium constant was two orders of magnitude greater for strong adsorption site than for weak adsorption site, though the maximum number of weak adsorption site was 1.5 times as great as that of strong adsorption site. The strong adsorption equilibrium constant resulted from a small desorption rate constant for the site. The equations were demonstrated to be applicable for predicting other desorption performances as well.     

ADSORPTION OF 2,4-DICHLOROPHENOL IN AQUEOUS SOLUTION ONTO ADSORPTION RESIN MODIFIED BY N-ACETYLANILINE

A hypercrosslinked adsorption resin （ZH-05） modified by N-acetylaniline in the post crosslinking process was prepared. The adsorption properties of ZH-05 toward 2,4-dichlorophenol in comparison with granular activated carbon （GAC） and Amberlite XAD-4 were observed. The present study mainly focuses on the static equilibrium adsorption behaviors, desorption profiles and the proof of chemisorption. The results show that the Langmuir equation can give a perfect fitting to experimental data, and high temperature was favorable for adsorption of 2,4-dichlorophenol on ZH-05. A related equation was used to correlate the amount of chemisorption and the suppositionai chemisorption equilibrium concentration of adsorbate in aqueous solution. The adsorption capacities from different ranges of temperature and the static desorption experiment both reveal the same conclusion, i.e., the adsorption of 2,4-dichlorophenol from water on ZH-05 is a coexistent process of physical adsorption and chemical transition as on GAC.     

Role of titania incorporated on activated carbon cloth for capacitive deionization of NaCl solution

Adsorption isotherms of NaCl on activated carbon cloth (ACC) and titania-incorporated activated carbon cloth (Ti-ACC) under an electric field were investigated to deduce the role of titania in capacitive deionization (CDI) of NaCl. Electrosorption of NaCl on the ACC was significantly increased by titania incorporation, whereas its physical adsorption was considerably decreased, resulting in an improved performance of the Ti-ACC as a CDI electrode. Langmuir isotherms based on a localized and fixed amount of adsorption were suitable for the simulation of electrosorption and physical adsorption of ions on the ACC electrodes. The variances of q(m) and b of Langmuir isotherms with electric potential indicate increases in the number of ions per adsorption site and in electrosorption strength of ions by titania incorporation. A cyclic voltammetric study for ion adsorption on ACC electrodes confirms the reversibility between electrosorption and desorption of ions, regardless of titania incorporation.     

Phenol adsorption onto powdered and granular activated carbon, prepared from Eucalyptus wood

Eucalyptus grandis sawdust, a major waste from the growing Uruguayan wood industry, was used in previous work to prepare powdered activated carbon (PAC). In the present work, granular activated carbon (GAC) was prepared by mixing PAC, carboxymethyl cellulose as a binder, and kaolin as reinforcer. Ultimate analysis and surface characterization of GAC and PAC were performed. Phenol adsorption was used as a way to compare the characteristics of different PAC and GAC preparations. Kinetics and isotherms of the different GAC and PAC were performed in a shaking bath at 100 rpm and 298 K. Phenol concentrations were determined by UV spectroscopy. Some kinetics parameters were calculated; from kinetics results, external resistance to mass transfer from the bulk liquid can be neglected as the controlling step. Isotherms were fitted to Langmuir and Freundlich models, and corresponding parameters were determined. Maximum phenol uptakes for all carbons were determined and correlated with carbon characteristics. Thermogravimertic analysis (TGA) determinations were performed in order to study adsorption characteristics and conditions for GAC regeneration after its use. The results showed that phenol is preferentially physisorbed on the carbon of the granules, though some chemisorption was detected. No adsorption was detected in the kaolin-carboxymethyl cellulose mixture.     

3,5-Dinitrosalicylic Acid Adsorption Using Granulated and Powdered Activated Carbons

Some nitroaromatic compounds are found in wastewater from industries such as the weapons industry or the wine industry. One of these compounds is 3,5-dinitrosalicylic acid (DNS), widely used in various tests and frequently found as an emerging pollutant in wastewater and to which the required attention has not been given, even though it may cause serious diseases due to its high toxicity. This study investigated the adsorption of DNS using granulated activated carbon (GAC) and powdered activated carbon (PAC) at different temperatures. The results show that in equilibrium, the adsorption takes place in more than one layer and is favorable for the removal of DNS in both GAC and PAC; The maximum adsorption capacity was obtained at 45 °C, with values of 6.97 mg/g and 11.57 mg/g, respectively. The process is spontaneous and exothermic. In addition, there was a greater disorder in the solid-liquid interface during the desorption process. The predominant kinetics using GAC (7.14 mg/g) as an adsorbent is Elovich, indicating that there are heterogeneous active sites, and when PAC (10.72 mg/g) is used, Pseudo-second order kinetics predominate, requiring two active sites for DNS removal. External mass transfer limitations are only significant in GAC, and ATR-FTIR studies in PAC demonstrated the participation of functional groups present on the adsorbent surface for DNS adsorption.     

Novel three-stage kinetic model for aqueous benzene adsorption on activated carbon

We propose a novel kinetic model for adsorption of aqueous benzene onto both granular activated carbon (GAC) and powdered activated carbon (PAC). The model is based on mass conservation of benzene coupled with three-stage adsorption: (1) the first portion for an instantaneous stage or external surface adsorption, (2) the second portion for a gradual stage with rate-limiting intraparticle diffusion, and (3) the third portion for a constant stage in which the aqueous phase no longer interacts with activated carbon. An analytical solution of the kinetic model was validated with the kinetic data obtained from aqueous benzene adsorption onto GAC and PAC in batch experiments with two different solution concentrations (C(0)=300 mg L(-1), 600 mg L(-1)). Experimental results revealed that benzene adsorption for the two concentrations followed three distinct stages for PAC but two stages for GAC. The analytical solution could successfully describe the kinetic adsorption of aqueous benzene in the batch reaction system, showing a fast instantaneous adsorption followed by a slow rate-limiting adsorption and a final long constant adsorption. Use of the two-stage model gave incorrect values of adsorption coefficients in the analytical solution due to inability to describe the third stage.     

Adsorption and biotransformation of 17β-estradiol in biological activated carbon adsorbers

As the first systematic study dealing with the adsorption of estrogens by granular activated carbon (GAC), the removal behavior of 17β-estradiol (E2) and its biotransformation product of estrone (E1) in fixed GAC columns was examined using four biological activated carbon (BAC) columns (BAC-1～BAC-4) generated by coating four GAC columns with detached microorganisms from the riverbed sediment of a representative drinking river water source containing lower content of natural organic matter (NOM). For comparison, parallel adsorption experiments were also performed using another four GAC columns (GAC-1～ GAC-4) packed by strictly following the configurations of four BAC columns. Adsorption experimental results obtained by intermittently spiking E2 over a total running period about 350 days into the river water mixed with or without a peaty water containing higher content of NOM showed that E2 was readily removed by adsorption and the combined adsorption/biodegradation. The vertical profiles of E2 and E1, which have great significance for better understanding and optimization of the adsorption process for removal of human estrogens, were also obtained.     

Theoretical and Experimental Study on the Adsorption and Desorption of Methane by Granular Activated Carbon at 25 ℃

A theoretical and experimental study was conducted to accurately determine the amount of adsorption and desorption of methane by various Granular Activated Carbon(GAC)under different physical conditions.To carry out the experiments,the volumetric method was used up to 500 psia at constant temperature of 25℃.In these experiments,adsorption as well as desorption capacities of four different GAC in the adsorption of methane,the major constituent of natural gas,at various equilibrium pressures and a constant temperature were studied.Also,various adsorption isotherm models were used to model the experimental data collected from the experiments.The accuracy of the results obtained from the adsorption isotherm models was compared and the values for the regressed parameters were reported.The results shows that the physical characteristics of activated carbons such as BET surface area,micropore volume,packing density,and pore size distribution play an important role in the amount of methane to be adsorbed and desorbed.     

Optimum isotherm equation and thermodynamic interpretation for aqueous 1,1,2-trichloroethene adsorption isotherms on three adsorbents

Aqueous 1,1,2-trichloroethene (TCE) adsorption isotherms were obtained on Ambersorb^1® 563 and 572 adsorbents and Filtrasorb^2® 400 granular activated carbon (GAC). The data for Ambersorb 563 adsorbent covers TCE concentrations from 0.0009 to 600 mg/L. The data for each adsorbent was fit to 15 isotherm equations to determine an optimum equation.The best equation for the TCE adsorption isotherms is the Dubinin-Astakov (DA) isotherm. The DA isotherm coefficients were used to estimate the TCE micropore volume and the adsorption potential distribution. For each adsorbent, the TCE micropore volume is equivalent to the N₂ porosimetry micropore volume. The mean adsorption potential is 18.8, 13.0, and 8.9 kJ/mol, with coefficients of variation of 0.37, 0.53, and 0.67, for Ambersorb 563 and 572 adsorbents and Filtrasorb 400 GAC, respectively. Thus, Ambersorb 563 adsorbent has the most energetic and most homogeneous adsorption volume, while Filtrasorb 400 GAC has the least energetic and most heterogeneous adsorption volume. For these reasons, Ambersorb 563 adsorbent has the highest TCE capacity at low concentrations, whereas Filtrasorb 400 GAC has the highest TCE capacity at high concentrations. The performance of Ambersorb 572 adsorbent is generally intermediate to the other two adsorbents.     

Comparative Study of the Adsorption from Aqueous Solutions and the Desorption of Phenol and Nonylphenol Substrates on Activated Carbons

Adsorption of phenol and nonylphenol from aqueous solutions on microporous activated carbons has been studied. The phenol isotherm changes from L-shaped for surface oxygen group free carbon (I sample) to a two-stepped isotherm for oxidized carbon (IN sample, HNO(3) treated) Furthermore, the adsorbed amounts diminish in about 25% on IN carbon. It is proposed that a change in the adsorption mechanism take place; i.e., weak interaction forces between the pi electrons in phenol and the pi electron in carbon are present on the original I carbon, while a donor-acceptor complex on the oxidized IN carbon is operating between basic surface oxygen groups and phenol aromatic rings. The shape of nonylphenol isotherms is two-stepped for both carbons. The introduction of acidic oxygen surface groups on the carbon enhances the specific nonylphenol adsorption by about 40%. This may be interpreted as being due to the fact that nonylphenol is hydrogen-bonded to the oxidized carbon surface by means of acidic groups. Thermal desorption experiments indicate that phenol is mainly physisorbed. Thermal desorption further confirms that nonylphenol is possibly bonded to oxygen surface groups by hydrogen bonds. Copyright 2001 Academic Press.     

Removal of nickel (II) ions from aqueous solutions using modified activated carbon: A kinetic and equilibrium study

Removal nickel from the aquatic environment is a serious environmental problem in view of public health. The present article studies the applicability of activated carbon, obtained from graphite, as a source of adsorbents to remove nickel from the aqueous polluted water. Activated carbon was obtained by steam activation of graphite and then was oxidized by nitric acid followed by modification with Tetraethylenepentamine (TEPA). The applicability of graphite activated carbon (GAC), and modified activated carbon by Tetraethylenepentamine (GACA) to remove nickel ions Ni(II) from aqueous media was studied. The effect of pH, initial concentration, contact time, and the temperature was evaluated during Ni(II) removal operating in a batch process. Experimental results show that the studied activated carbon have a good adsorption capacity for Ni(II) ions and could reduce the concentrations of it in the groundwater. A maximum removal efficient of Ni(II) was observed at 55°C. The experimental data showed an endothermic and spontaneous process, which was fitted to Langmuir isotherm. Based on our results, we can conclude that it is possible to use GAC and GACA for removing Ni(II) effectively from groundwater.     

Microporous activated carbons prepared from palm shell by thermal activation and their application to sulfur dioxide adsorption

Textural characterization of activated carbons prepared from palm shell by thermal activation with carbon dioxide (CO(2)) gas is reported in this paper. Palm shell (endocarp) is an abundant agricultural solid waste from palm-oil processing mills in many tropical countries such as Malaysia, Indonesia, and Thailand. The effects of activation temperature on the textural properties of the palm-shell activated carbons, namely specific surface area (BET method), porosity, and microporosity, were investigated. The activated carbons prepared from palm shell possessed well-developed porosity, predominantly microporosity, leading to potential applications in gas-phase adsorption for air pollution control. Static and dynamic adsorption tests for sulfur dioxide (SO(2)), a common gaseous pollutant, were carried out in a thermogravimetric analyzer and a packed column configuration respectively. The effects of adsorption temperature, adsorbate inlet concentration, and adsorbate superficial velocity on the adsorptive performance of the prepared activated carbons were studied. The palm-shell activated carbon was found to have substantial capability for the adsorption of SO(2), comparable to those of some commercial products and an adsorbent derived from another biomass.     

Water adsorption with hysteresis effect onto microporous activated carbon fabrics

Understanding the adsorption of water vapor onto activated carbons is important for designing processes to remove dilute contaminants from humid gas streams, such as providing protection against chemical warfare agents (CWAs), or against toxic industrial compounds (TICs) used in a terrorist chemical attack. Water vapor isotherms for Calgon BPL granular activated carbon (GAC), military ASZM-TEDA GAC, electrospun activated carbon nanofibers (ACnF), Calgon Zorflex^™ activated carbon cloth, and Novoloid-based activated carbon fiber cloth (ACFC) are presented. Of particular interest are the ACFC isotherms, which exhibit an unusually high degree of hydrophobicity. The ACFC isotherms also show a correlation between water vapor adsorption hysteresis and the level of activation. Water vapor isotherm models from the literature are compared.     

Competitive adsorption isotherm modelling of heterocyclic nitrogenous compounds,pyridine and quinoline,onto granular activated carbon and bagasse fly ash

In the present study, simultaneous adsorption of quinoline and pyridine onto adsorbents such as granular activated carbon (GAC) and bagasse fly ash (BFA) from pyridine–quinoline binary aqueous solution was studied at various temperatures (288–318 K). Gathered equilibrium adsorption data were further analysed using various multicomponent competitive isotherm models such as non-modified and modified competitive Langmuir isotherms, extended-Langmuir isotherm, extended-Freundlich model, Sheindorf–Rebuhn–Sheintuch (SRS) model, and non-modified and modified competitive Redlich–Peterson isotherm model. It was observed that increase in pyridine concentration decreased the total adsorption yield and the individual adsorption yield for both the quinoline and pyridine for both the adsorbents GAC and BFA at all the temperatures studied. Identical trend was observed during the equilibrium uptake of pyridine on to GAC and BFA with an increase in quinoline concentration. The extended-Freundlich model satisfactorily represented the binary adsorption equilibrium data of quinoline and pyridine onto GAC and BFA.     

Application of Double-Dielectric Barrier Discharge Plasma for Removal of Pentachlorophenol from Wastewater Coupling with Activated Carbon Adsorption and Simultaneous Regeneration

Wastewater containing pentachlorophenol (PCP) was treated by granular activated carbon (GAC) adsorption and double-dielectric barrier discharge (D-DBD) plasma. A packed bed D-DBD reactor was applied for removal of PCP on GAC and GAC regeneration, where the discharge gap was filled with GAC. PCP degradation efficiency of 65% and GAC regeneration efficiency (RE) of 87% were achieved. Effects of discharge power, treatment time and O₂ flow rate on PCP degradation and GAC regeneration were investigated. Increasing discharge power, treatment time and O₂ flow rate were favorable for PCP degradation, and also contributed to GAC RE. C–Cl bonds in PCP were cleaved by D-DBD plasma. Effect of D-DBD plasma on physical and chemical properties of GAC during GAC regeneration process was characterized by N₂ adsorption and Boehm titration. This study is expected to demonstrate the feasibility of applying D-DBD plasma for efficient organic wastewater treatment by coupling with GAC adsorption.     

Synthesis and Characterization of Microporous Silica Prepared with Sodium Silicate and Organosilane Compounds

Microporous silica gels were prepared in the pH range of 3–4 using sodium silicate as a silica source. Surface polarity of these gels was modified by grafting hydrophobic groups into the silica gel matrix with the help of hydrophilic solvents (acetone, acetonitrile, ethanol and methanol) and alkoxysilane compounds containing nonhydrolyzable alkyl groups. The porous framework and hydrophobicity of the silica gels were evaluated using nitrogen adsorption/desorption and water adsorption measurement techniques. All the measured isotherms were found to be type I which is indicative of microporosity. The surface area and microporosity of these samples were estimated by analyzing the measured nitrogen adsorption/desorption data using BET, Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. The micropore size distribution was determined from their nitrogen adsorption isotherms using the slit-pore model of the Horvath-Kawazoe equation. Silica gels with high surface area (over 500 m²/g) as well as high microporosity (over 0.2 cc/g) were obtained at gelation pH of 3.50 from the water-solvent system.     

Adsorption studies of a microporous phthalocyanine network polymer

The adsorption/desorption of N2 at 77 K and the adsorption from aqueous solution at 298 K of four organic probe molecules of different sizes (phenol, 4-nitrophenol, orange II, naphthol green B) were studied for a phthalocyanine network polymer of intrinsic microporosity (PIM) and for an activated carbon (Darco 20-40 mesh). N2 sorption analysis gave similar surface areas for the PIM and the carbon (610 and 545 m2 g(-1), respectively) but showed differences in pore size distribution, the PIM being essentially microporous (pore size < 2 nm), with a high proportion of ultramicropores (<0.7 nm), while the carbon had a broader pore size distribution, extending into the mesopore region. The carbon acted as an adsorbent for all the organic probe molecules studied, while the PIM was more selective, adsorbing the smaller molecules but rejecting the large dye naphthol green B. The PIM offers selectivity combined with a well-defined chemical structure incorporating catalytic sites.     

Desorption of chloroorganic compounds from a bed of activated carbon

The desorption of 1,2-dichloroethane from a bed of DTO activated carbon after adsorption from aqueous solution has been investigated. The desorption process was carried out using steam. The basic characteristics of the process were determined. The studies were performed in the temperature range 100-160 degrees C. A steam consumption indicator reduces with an increase of temperature from 100 to 140 degrees C. An elevation of temperature above 140 degrees C does not cause an improvement in the desorption efficiency. The number of performed cycles does not reduce the adsorption capacity of used activated carbon. Studies on the regeneration of the bed saturated with a seven-component mixture of chloroorganic compounds at temperature of 140 degrees C were carried out. The degree of removal of the sum of chloro-derivatives exceeded 0.96 at a volume ratio of steam (recalculated on the condensate) to bed of about 10. It was found that the dechlorination proceeds during desorption at elevated temperature. The quantitative ratio of chloro-derivatives in the desorbate was changed in comparison to the composition of wastewater directed to the adsorption.     

Surface area and microporosity of carbon aerogels from gas adsorption and small- and wide-angle X-ray scattering measurements

A carbon aerogel was obtained by carbonization of an organic aerogel prepared by sol-gel polymerization of resorcinol and formaldehyde in water. The carbon aerogel was then CO(2) activated at 800 degrees C to increase its surface area and widen its microporosity. Evolution of these parameters was followed by gas adsorption and small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) with contrast variation by using dry and wet (immersion in benzene and m-xylene) samples. For the original carbon aerogel, the surface area, S(SAXS), obtained by SAXS, is larger than that obtained by gas adsorption (S(ads)). The values become nearly the same as the degree of activation of the carbon aerogel increases. This feature is due to the widening of the narrow microporosity in the carbon aerogel as the degree of activation is increased. In addition, WAXS results show that the short-range spatial correlations into the assemblies of hydrocarbon molecules confined inside the micropores are different from those existing in the liquid phase.     

Microwave assisted preparation of efficient activated carbon from grapevine rhytidome for the removal of methyl violet from aqueous solution

Grapevine rhytidome (the outer layer of bark on trunk), as an abundant and low-cost precursor, was used to prepare granular activated carbon with high surface area for the removal of methyl violet from aqueous solution. Microwave heating source was used to reduce the treatment time and energy consumption. To optimize the preparation, the effects of the different parameters, such as phosphoric acid concentration, acid/precursor weight ratio, impregnation time, microwave power, radiation time, and oven heating time on the ability of the samples for removal of methyl violet were studied. The obtained activated carbon was characterized by N₂ adsorption/desorption, SAXS, TEM and SEM methods. The adsorption of methyl violet onto the activated carbon was studied from both equilibrium and kinetic point of view and the results were compared with the commercial granular activated carbon. The rate of adsorption onto the prepared activated carbon was faster than commercial activated carbon. Different kinetic models were used to analyze the experimental kinetic data. The obtained activated carbon showed higher adsorption capacity (more than twice) for the adsorption of methyl violet in comparison with the commercial one. The equilibrium data were analyzed using different isotherm models. Adsorption was found to be maximum in the pH range 7-9.