Adsorption of reactive dyes from aqueous solutions by fly ash: kinetic and equilibrium studies

Adsorption kinetic and equilibrium studies of three reactive dyes namely, Remazol Brillant Blue (RB), Remazol Red 133 (RR) and Rifacion Yellow HED (RY) from aqueous solutions at various initial dye concentration (100–500 mg/l), pH (2–8), particle size (45–112.5 μm) and temperature (293–323 K) on fly ash (FA) were studied in a batch mode operation. The adsorbent was characterized with using several methods such as SEM, XRD and FTIR. Adsorption of RB reactive dye was found to be pH dependent but both RR and RY reactive dyes were not. The result showed that the amount adsorbed of the reactive dyes increased with increasing initial dye concentration and contact time. Batch kinetic data from experimental investigations on the removal of reactive dyes from aqueous solutions using FA have been well described by external mass transfer and intraparticle diffusion models. It was found that external mass transfer and intraparticle diffusion had rate limiting affects on the removal process. This was attributed to the relatively simple macropore structure of FA particles. The adsorption data fitted well with Langmuir and Freundlich isotherm models. The optimum conditions for removal of the reactive dyes were 100 mg/l initial dye concentration, 0.6 g/100 ml adsorbent dose, temperature of 293 K, 45 μm particle size, pH 6 and agitation speed of 250 rpm, respectively. The values of Langmuir and Freundlich constants were found to increase with increasing temperature in the range 135–180 and 15–34 mg/g for RB, 47–86 and 1.9–3.7 mg/g for RR and 37–61 and 3.0–3.6 mg/g for RY reactive dyes, respectively. Different thermodynamic parameters viz., changes in standard free energy, enthalpy and entropy were evaluated and it was found that the reaction was spontaneous and endothermic in nature.     

Adsorption of basic dye on high-surface-area activated carbon prepared from coconut husk: equilibrium, kinetic and thermodynamic studies

Adsorption isotherm and kinetics of methylene blue on activated carbon prepared from coconut husk were determined from batch tests. The effects of contact time (1-30 h), initial dye concentration (50-500 mg/l) and solution temperature (30-50 degrees C) were investigated. Equilibrium data were fitted to Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The equilibrium data were best represented by Langmuir isotherm model, showing maximum monolayer adsorption capacity of 434.78 mg/g. The kinetic data were fitted to pseudo-first-order, pseudo-second-order and intraparticle diffusion models, and was found to follow closely the pseudo-second-order kinetic model. Thermodynamic parameters such as standard enthalpy (DeltaH degrees), standard entropy (DeltaS degrees) and standard free energy (DeltaG degrees) were evaluated. The adsorption interaction was found to be exothermic in nature. Coconut husk-based activated carbon was shown to be a promising adsorbent for removal of methylene blue from aqueous solutions.     

Adsorption characteristics of trivalent chromium on palm oil fuel ash

The metal uptake characteristics of ash particles obtained from the combustion of oil palm solid waste (referred to as palm oil fuel ash) are evaluated using trivalent chromium as a model adsorbate. The equilibrium and kinetic properties of Cr(III) are studied in batch stirred-tank experiments. The extent of Cr(III) removal increases with an increase in solution pH. The maximum equilibrium uptake capacity at pH 6 is 0.31 mmol/g of sorbent. A Langmuir isotherm model with pH-dependent parameters accounts very well for the measured equilibrium data. Modeling studies using a second order irreversible reaction model and a pseudo-first order kinetic model indicate that transient profiles obtained experimentally for a range of initial metal concentrations and sorbent dosages are in good agreement with calculated curves of both models. The two kinetic models can be employed for a useful summary of the experimental data so long as their rate coefficients are empirically correlated with the two system variables: initial metal concentration and sorbent dosage. Electronic Publication     

Adsorption of reactive dye onto carbon nanotubes: equilibrium, kinetics and thermodynamics

The adsorption efficiency of carbon nanotubes for Procion Red MX-5B at various pHs and temperatures was examined. The amount adsorbed increased with the CNTs dosage; however, the adsorption capacity initially increased with the CNTs dosage (<0.25 g/l) and then declined as the CNTs dosage increased further (>0.25 g/l). The linear correlation coefficients and standard deviations of Langmuir and Freundlich isotherms were determined and the results revealed that Langmuir isotherm fitted the experimental results well. Kinetic analyses were conducted using pseudo first- and second-order models and the intraparticle diffusion model. The regression results showed that the adsorption kinetics were more accurately represented by a pseudo second-order model. Changes in the free energy of adsorption (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees), as well as the activation energy (E(a)) were determined. DeltaH degrees and DeltaS degrees were 31.55 kJ/mol and 216.99J/molK, respectively, at pH 6.5 and 41.47 kJ/mol and 244.64 J/molK at pH 10. The activation energy was 33.35 kJ/mol at pH 6.5. DeltaH degrees, DeltaG degrees and E(a) all suggested that the adsorption of Procion Red MX-5B onto CNTs was by physisorption.     

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).     

The adsorption of basic dye (Astrazon Blue FGRL) from aqueous solutions onto sepiolite, fly ash and apricot shell activated carbon: kinetic and equilibrium studies

In this study, sepiolite, fly ash and apricot stone activated carbon (ASAC) were used as adsorbents for the investigation of the adsorption kinetics, isotherms and thermodynamic parameters of the basic dye (Astrazon Blue FGRL) from aqueous solutions at various concentrations (100-300 mg/L), adsorbent doses (3-12 g/L) and temperatures (303-323 K). The result showed that the adsorption capacity of the dye increased with increasing initial dye concentration, adsorbent dose and temperature. Three kinetic models, the pseudo-first-order, second-order, intraparticle diffusion, were used to predict the adsorption rate constants. The kinetics of adsorption of the basic dye followed pseudo-second-order kinetics. Equations were developed using the pseudo-second-order model which predicts the amount of the basic dye adsorbed at any contact time, initial dye concentration and adsorbent dose within the given range accurately. The adsorption equilibrium data obeyed Langmuir isotherm. The adsorption capacities (Q0) calculated from the Langmuir isotherm were 181.5 mg/g for ASAC, 155.5 mg/g for sepiolite and 128.2 mg/g for fly ash at 303 K. Thermodynamical parameters were also evaluated for the dye-adsorbent systems and revealed that the adsorption process was endothermic in nature.     

Batch removal of malachite green from aqueous solutions by adsorption on oil palm trunk fibre: equilibrium isotherms and kinetic studies

Oil palm trunk fibre (OPTF)--an agricultural solid waste--was used as low-cost adsorbent to remove malachite green (MG) from aqueous solutions. The operating variables studied were contact time, initial dye concentration, and solution pH. Equilibrium adsorption data were analyzed by three isotherms, namely the Freundlich isotherm, the Langmuir isotherm, and the multilayer adsorption isotherm. The best fit to the data was obtained with the multilayer adsorption. The monolayer adsorption capacity of OPTF was found to be 149.35 mg/g at 30 degrees C. Adsorption kinetic data were modeled using the Lagergren pseudo-first-order, Ho's pseudo-second-order and Elovich models. It was found that the Lagergren's model could be used for the prediction of the system's kinetics. The overall rate of dye uptake was found to be controlled by external mass transfer at the beginning of adsorption, then for initial MG concentrations of 25, 50, 100, 150, and 300 mg/L the rate-control changed to intraparticle diffusion at a later stage, but for initial MG concentrations 200 and 250 mg/L no evidence was found of intraparticle diffusion at any period of adsorption. It was found that with increasing the initial concentration of MG, the pore-diffusion coefficient increased while the film-diffusion coefficient decreased.     

Adsorption of reactive dye from an aqueous solution by chitosan: isotherm, kinetic and thermodynamic analysis

The adsorption of Remazol black 13 (Reactive) dye onto chitosan in aqueous solutions was investigated. Experiments were carried out as function of contact time, initial dye concentration (100-300mg/L), particle size (0.177, 0.384, 1.651mm), pH (6.7-9.0), and temperature (30-60 degrees C). The equilibrium adsorption data of reactive dye on chitosan were analyzed by Langmuir and Freundlich models. The maximum adsorption capacity (qm) has been found to be 91.47-130.0mg/g. The amino group nature of the chitosan provided reasonable dye removal capability. The kinetics of reactive dye adsorption nicely followed the pseudo-first and second-order rate expression which demonstrates that intraparticle diffusion plays a significant role in the adsorption mechanism. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy and entropy of adsorption. The positive value of the enthalpy change (0.212kJ/mol) indicated that the adsorption is endothermic process. The results indicate that chitosan is suitable as adsorbent material for adsorption of reactive dye form aqueous solutions.     

Adsorption of naphthalene onto the carbon adsorbent from waste ion exchange resin: equilibrium and kinetic characteristics

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants that can result in serious health problems and genetic defects in humans. In this research, a spherical microporous carbon adsorbent (CR-1) had been obtained by carbonization and activation of the waste polysulfonated cation exchange resin. Naphthalene was adopted as a model compound to examine the adsorption effectiveness for removing PAHs from the aqueous solution by CR-1. Nonlinear isotherms models, i.e., Freundlich, Langmuir, Brunauer–Emmett–Teller and Polanyi–Dubinin–Manes models were tested to fit experimental data. The adsorption equilibrium data of naphthalene on CR-1 was fitted well by the Polanyi–Dubinin–Manes model. Through both isotherm modeling and constructing “characteristic curve”, Polanyi theory was useful to describe the adsorption process of naphthalene by CR-1, providing evidence that a micropore filling phenomenon is involved. In addition, among the tested kinetic models in this study (e.g., pseudo-first-order and pseudo-second-order equations), the pseudo-first-order equation successfully predicted the kinetic adsorption process.     

Microwave drying optimization and kinetic modeling of fly ash from municipal solid waste incineration

As a kind of hazardous waste, municipal solid waste incineration fly ash (MSWI FA) needs to be stored in a dry state in the process of landfill, transportation, and comprehensive utilization. Therefore, from the perspective of safety and sustainable development, it is necessary to dry as the pretreatment of MSWI FA. In this paper, MSWI FA drying experiments were carried out under different microwave power, different initial moisture content, and different particle size distribution conditions. The drying characteristics of MSWI FA were explored and the thin-layer drying kinetic model was used to explore the basic theory of the dynamics of MSWI FA drying process for the first time. The fitting analysis of the experimental data showed that the drying efficiency of MSWI FA increases gradually with the increase of microwave power and fly ash particle size, and the drying process of MSWI FA could be well represented by the Diffusion approach model (R² greater than 0.99). Through Fick's second law calculation, it was found that when the microwave power was increased from 400w to 800w, the surface diffusion coefficient increased from 1.11 × 10^-12 m²/s to 2.92 × 10^-12 m²/s, which further showed that the microwave power has a significant effect on the drying efficiency of MSWI FA.     

Adsorption isotherm and kinetic modeling of 2,4-D pesticide on activated carbon derived from date stones

In this work, the adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) on activated carbon derived from date stones (DSAC) was studied with respect to pH and initial 2,4-D concentration. The experimental data were analyzed by the Freundlich isotherm, the Langmuir isotherm, and the Temkin isotherm. Equilibrium data fitted well with the Langmuir model with maximum adsorption capacity of 238.10 mg/g. Pseudo-first and pseudo-second-order kinetics models were tested with the experimental data, and pseudo-first-order kinetics was the best for the adsorption of 2,4-D by DSAC with coefficients of correlation R(2)>or=0.986 for all initial 2,4-D concentrations studied. The results indicated that the DSAC is very effective for the adsorption of 2,4-D from aqueous solutions.     

Photooxidation processes for an azo dye in aqueous media: modeling of degradation kinetic and ecological parameters evaluation

Three photooxidation processes, UV/H(2)O(2), UV/S(2)O(8)(2-) and UV/O(3) were applied to the treatment of model wastewater containing non-biodegradable organic pollutant, azo dye Acid Orange 7 (AO7). Dye degradation was monitored using UV/VIS and total organic carbon (TOC) analysis, determining decolorization, the degradation/formation of naphthalene and benzene structured AO7 by-products, and the mineralization of model wastewater. The water quality during the treatment was evaluated on the bases of ecological parameters: chemical (COD) and biochemical (BOD(5)) oxygen demand and toxicity on Vibrio fischeri determining the EC(50) value. The main goals of the study were to develop an appropriate mathematic model (MM) predicting the behavior of the systems under investigation, and to evaluate the toxicity and biodegradability of the model wastewater during treatments. MM developed showed a high accuracy in predicting the degradation of AO7 when considering the following observed parameters: decolorization, formation/degradation of by-products and mineralization. Good agreement of the data predicted and the empirically obtained was confirmed by calculated standard deviations. The biodegradability of model wastewater was significantly improved by three processes after mineralizing a half of the initially present organic content. The toxicity AO7 model wastewater was decreased as well. The differences in monitored ecological parameters during the treatment indicated the formation of different by-products of dye degradation regarding the oxidant type applied.     

Adsorptive removal of direct azo dye from aqueous phase onto coal based sorbents: a kinetic and mechanistic study

This communication presents the results pertaining to the investigation conducted on color removal of trisazo direct dye, C.I.Direct Brown 1:1 by adsorption onto coal based sorbents viz. charfines, lignite coal, bituminous coal and comparing results with activated carbon (Filtrasorb-400). The kinetic sorption data indicated the sorption capacity of the different coal based sorbents. The sorption interaction of direct dye on to coal based sorbents obeys first-order irreversible rate equation and activated carbon fits with the first-order reversible rate equation. Intraparticle diffusion studies revealed the dye sorption interaction was complex and intraparticle diffusion was not only the rate limiting step. Isothermal data fit well with the rearranged Langmuir adsorption model. R(L) factor revealed the favorable nature of the isotherm of the dye-coal system. Neutral solution pH yielded maximum dye color removal. Desorption and interruption studies further indicated that the coal based sorbents facilitated chemisorption in the process of dye sorption while, activated carbon resulted in physisorption interaction.     

Adsorptive removal of Auramine-O: kinetic and equilibrium study

Present study deals with the adsorption of Auramine-O (AO) dye by bagasse fly ash (BFA) and activated carbon-commercial grade (ACC) and laboratory grade (ACL). BFA is a solid waste obtained from the particulate collection equipment attached to the flue gas line of the bagasse fired boilers of cane sugar mills. Batch studies were performed to evaluate the influences of various experimental parameters like initial pH (pH(0)), contact time, adsorbent dose and initial concentration (C(0)) for the removal of AO. Optimum conditions for AO removal were found to be pH(0) approximately 7.0 and equilibrium time approximately 30 min for BFA and approximately 120 min for activated carbons. Optimum BFA, ACC and ACL dosages were found to be 1, 20 and 2g/l, respectively. Adsorption of AO followed pseudo-second order kinetics with the initial sorption rate for adsorption on BFA being the highest followed by those on ACL and ACC. The sorption process was found to be controlled by both film and pore diffusion with film diffusion at the earlier stages followed by pore diffusion at the later stages. Equilibrium isotherms for the adsorption of AO on BFA, ACC and ACL were analyzed by Freundlich, Langmuir, Dubinin-Radushkevich, and Temkin isotherm equations using linear correlation coefficient. Langmuir isotherm gave the best correlation of adsorption for all the adsorbents studied. Thermodynamic study showed that adsorption of AO on ACC (with a more negative Gibbs free energy value) is more favoured. BFA which was used without any pretreatment showed high surface area, pore volume and pore size exhibiting its potential to be used as an adsorbent for the removal of AO.     

Development and characterization of epoxy nanocomposites based on nano-structured oil palm ash

The aim of this study is to utilize the bio-agricultural waste as filler material for composite production which are abundantly available and low cost compared to the silica, alumina etc. The lacks of sufficient scientific information about the utilization of the oil palm ash (OPA) on composites production were the driving force for the choice of this work. Furthermore, the effect of filler loading percentage on physical, mechanical, thermal and morphology properties of the epoxy nanocomposites were studied. It was concluded that the size of the OPA had been successfully reduced from macromolecular to the nano-size range by high energy ball milling and was confirmed by TEM analysis. The density of the nano-structured OPA filled epoxy composites revealed that increasing filler loading will eventually increase the density. The tensile and flexural strength attained maximum value when the filler loading was 3%. Also, increase in the thermal stability was observed in case of 3% filler loading and was attributed to the increase in cross-linking of the epoxy resin in the presence of nano-stuctured OPA and having minimum particle to particle interaction and well dispersed nanoparticles.     

Adsorption characteristics of brilliant green dye on kaolin

Experimental investigations were carried out to adsorb toxic brilliant green dye from aqueous medium using kaolin as an adsorbent. Characterization of kaolin is done by measuring: (i) particle size distribution using particle size analyzer, (ii) BET surface area using BET surface analyzer, and (iii) structural analysis using X-ray diffractometer. The effects of initial dye concentration, contact time, kaolin dose, stirring speed, pH and temperature were studied for the adsorption of brilliant green in batch mode. Adsorption experiments indicate that the extent of adsorption is strongly dependent on pH of solution. Free energy of adsorption (DeltaG0), enthalpy (DeltaH0) and entropy (DeltaS0) changes are calculated to know the nature of adsorption. The calculated values of DeltaG0 at 299K and 323K indicate that the adsorption process is spontaneous. The estimated values of DeltaH0 and DeltaS0 both show the negative sign, which indicate that the adsorption process is exothermic and the dye molecules are organized on the kaolin surface in less randomly fashion than in solution. The adsorption kinetic has been described by first-order, pseudo-second-order and intra-particle-diffusion models. It was observed that the rate of dye adsorption follows pseudo-second-order model for the dye concentration range studied in the present case. Standard adsorption isotherms were used to fit the experimental equilibrium data. It was found that the adsorption of brilliant green on kaolin follows the Langmuir adsorption isotherm.     

Crystal violet adsorption on industrial waste (hog fuel ash): equilibrium kinetics with process optimization by response surface modeling

Clean Technologies and Environmental Policy - The adsorptive removal of crystal violet from aqueous solution utilizing hog fuel ash, an industrial solid waste, available abundantly is reported in...     

苯酚在竹炭上的吸附平衡和动力学研究

研究了20℃下苯酚在3种竹炭上的吸附平衡和动力学。采用低温下氮气吸附法测定了3种竹炭的BET比表面积和孔径分布,并用SEM观察了其微观形貌。根据Langmuir吸附等温线模型和Freundli ch模型分别对吸附数据进行拟合,结果表明Freundli ch吸附等温线模型能较好的用来描述苯酚在竹炭上的吸附平衡,并确立了20℃下苯酚在竹炭上吸附的Freundlich模型表达式;竹炭的BET比表面积和中孔容积越大,饱和吸附量也越大;对同一种竹炭,随竹炭用量的增加,溶液中苯酚残余浓度就越低,而竹炭用量与达到饱和吸附的时间无关。     

Equilibrium modeling and kinetic studies on the adsorption of basic dye by a low-cost adsorbent: coconut (Cocos nucifera) bunch waste

In this paper, the ability of coconut bunch waste (CBW), an agricultural waste available in large quantity in Malaysia, to remove basic dye (methylene blue) from aqueous solution by adsorption was studied. Batch mode experiments were conducted at 30 degrees C to study the effects of pH and initial concentration of methylene blue (MB). Equilibrium adsorption isotherms and kinetics were investigated. The experimental data were analyzed by the Langmuir, Freundlich and Temkin models of adsorption. The adsorption isotherm data were fitted well to Langmuir isotherm and the monolayer adsorption capacity was found to be 70.92 mg/g at 30 degrees C. The kinetic data obtained at different concentrations have been analyzed using a pseudo-first-order, pseudo-second-order equation and intraparticle diffusion equation. The experimental data fitted very well the pseudo-second-order kinetic model.     

Adsorption of acid dye onto organobentonite

Removal of Acid Red 151 from aqueous solution at different dye concentrations, adsorbent doses and pH has been studied. The bentonite clay has been modified using cationic surfactants, which has been confirmed using XRD and FT-IR analyses. Experimental result has shown that the acidic pH favours the adsorption. The adsorption isotherms are described by means of Langmuir and Freundlich isotherms. The adsorption capacity has been found to be 357.14 and 416.66 mg g(-1) for the cetyldimethylbenzylammonium chloride-bentonite (CDBA-bent) and cetylpyridinium chloride-bentonite (CP-bent), respectively. Kinetic studies show that the adsorption followed second-order kinetics.