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The main objective of this study was to optimize the adsorption process of methylene blue on a natural, low-cost adsorbent, Leonurus cardiaca L. biomass powder, in order to maximize dye removal efficiency from aqueous solutions. For this purpose, the Taguchi method was used based on an L27 orthogonal array design considering six controllable factors at three levels. The percentage contribution of each factor was computed using analysis of variance (ANOVA). The optimal adsorption conditions were established. The experimental data from equilibrium and kinetic studies were modelled using specific equilibrium isotherms and kinetic models. Thermodynamic parameters were calculated in order to determine the main adsorption mechanism. The obtained results showed that the ionic strength is the factor that most influences dye adsorption (percentage contribution 72.33%), whereas the adsorbent dose had the least impact. The Sips isotherm and the general kinetic model most accurately characterized the process. The maximum adsorption capacity 103.21 (mg g−1) indicated by the Sips isotherm and the equilibrium time (40 min) were better compared to the values obtained for other bio-adsorbents used for methylene blue adsorption. The main mechanism involved in the adsorption is physisorption, while chemisorption only contributes marginally to the process. [ABSTRACT FROM AUTHOR]

This study aims to investigate the kinetics, isotherms, and thermodynamics of methylene blue (MB) dye adsorption from aqueous solution onto activated carbon prepared from orange peel waste (PO). This material was chemically treated with sulfuric acid, pyrolyzed, and activated in microwave apparatus under nitrogen flow. The resulting activated carbon was supported using cobalt transition metal by a wet impregnation process at different cobalt (Co) contents; the optimum condition was achieved at cobalt impregnations of 20 wt.%. The supported carbon Co20 wt.%-POAC catalyst was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, and Brunauer-Emmett-Teller surface area analysis. The results show that the equilibrium was reached at 270 min with an adsorption capacity of 27 mg·g-1; the Langmuir isotherm was the best model that describes the experimental data. Besides, the pseudo-first-order adsorption model best depicts the adsorption kinetics of the MB by Co20 wt.%-POAC. Thermodynamic analysis shows that the standard Gibb's free energy change (G) has negative values, confirming, therefore, the feasibility and spontaneity of the process. The changes in enthalpy (H°) and entropy (S°) were found to be -2,011 J·mol-1 and18.9 J·K-1·mol-1, respectively. Finally, our results revealed that grafting cobalt onto the surface of the orange peel-activated carbon improves its adsorption capacity, and hence its efficiency in removing MB from wastewater. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr VI) has mutagenic and carcinogenic properties and causes severe health and environmental effects. The chromium's adsorption equilibrium in aqueous media, its mechanisms, and different lignocellulosic wastes have been studied by many researchers. In this way, this paper provides a systematic, updated, and critical overview of Cr (IVI) adsorption by lignocellulosic waste adsorbent. Besides, analyzing the Cr (VI) problems in the aquatic environment addressed to lignocellulosic waste and its properties as adsorbent. Also, it was made a deep revision about important topics such as chemical regeneration and Cr (VI) recovery, characterization techniques, and interfering factors effects (e.g., pH, dosage). In addition, it was studied carefully the adsorption phenomena through several mathematical models of kinetics and isotherms and analyzed the thermodynamics results reported by an important number of research papers. Through this review, it was observed that the lignocellulosic wastes adsorption capacities usually range from 0.32 to 403.23 mg g−1, the adsorbent percentage removal after regenerating cycle ranged between 26.5 and 98.69%, and a greater performance of removing Cr (VI) occurs at pH range 1–6. The pseudo-second-order and Langmuir models were the models that presented the best adjustment of the experimental data for Cr (VI) adsorption, and the thermodynamic nature was spontaneous and endothermic for most cases. Further studies about lignocellulosic waste adsorbents lifecycle, stability, large-scale production, and production cost analysis are still necessary to determine the stability and efficacy of lignocellulosic wastes adsorbents in real effluent treatment. [ABSTRACT FROM AUTHOR]

Pollution of water resources with various organic and inorganic pollutants is one of the biggest challenges of the present age. These infections seriously threaten human health and the lives of plants and animals. To minimize the mischievous effects of polluted water, technology-based smart treatment methods are necessary for sustainable equipping of drinking water. Application of (AAC-co-AM)-g-MCC hydrogels for the percentage removal of dye Methyl volute MV, from aqueous solutions have been studied. The synthesized (AAC-co-AM)-g-MCC hydrogels was described via FTIR, Thermogravimetric analysis (TGA), and UV-visible spectroscopy. The experiments held out in batch method effect of the factor like the solution of pH, initial concentration dye, and solution of temperature on the removal percentage of dye was studied. Contact time was done in 120 min. The data appear that an amount of 0.08 g (AAC-co-AM)-g-MCC hydrogels showed maximum removal percentage capacity of dye (100 mg L-1). Maximum adsorption of MV dye was attained at pH 6.2. It was further proven the adsorption dye onto (AAC-co-AM)-g-MCC hydrogels followed the isotherm Langmuir while the kinetics studies detect that each adsorption method was pseudo-second-order. The thermodynamic factors like enthalpy (ΔHo), change in free energy (ΔGo), and entropy (ΔSo) were determined, and the values negative of ΔGo indicated that the method of removal was spontaneous at wholly values of temperatures. Further, the values of ΔHo indicated the endothermic nature of the method of removal. [ABSTRACT FROM AUTHOR]

In this study date pits of two types of date-palm trees (Phoenix Dactylifera L.), in Saudi Arabia were used as bio-sorbents for heavy metals (e.g. lead and copper) from aqueous solutions. Investigation of equilibrium time and the effect of different concentrations of metals were performed. Adsorption capacity of bio-sorbents increases with increasing concentration of metal ions. Maximum adsorption capacity at room temperature of Sukkari date pits was 17.53 mg g-1 and 9.86 mg g-1 for lead and copper ions, respectively. Whereas, Khalas date pits showed maximum adsorption capacity at 14.1 mg g-1 and 7.91 mg g-1 for lead and copper ions, respectively at room temperature. Equilibrium isotherm models, (Langmuir and Freundlich models), were used for analysis of equilibrium experimental results. these models describe the experimental data well. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) has recently gained plenty of attention as an effective adsorbent for gold recovery from leaching solutions, primarily due to its larger surface area compared to activated carbon (AC). In this study, the adsorption behavior of gold glycinate complex (Au gly 2 −) on GO surface was investigated using equilibrium isotherm and kinetic studies for the first time. The optimal conditions for adsorption were determined using an experimental design software (DX-13) based on the response surface method (RSM). These conditions were found to be a pH of 10.5, GO dosage of 0.6 g L−1, gold concentration of 6 mg L−1, and contact time of 10 h, resulting in the adsorption percentage of 74.2% and adsorption capacity of 7.4 mg g−1. The equilibrium isotherm studies indicated that the adsorption process adhered to the Freundlich isotherm model. Additionally, the results of the kinetic study revealed that the pseudo-second-order model exhibited a stronger correlation with the experimental data compared to other kinetic models. Surface analysis studies using Fourier transform infrared (FTIR) spectrometer, X-ray diffraction (XRD), and scanning electron microscope with energy dispersive X-ray (SEM-EDX) spectroscopy demonstrated that the remarkable recovery of Au gly 2 − was mainly attributed to the presence of oxygen containing functional groups on the GO surface. • The optimum conditions of Au gly 2 − adsorption on graphene oxide (GO) were found. • Adsorption capacity and adsorption percent were 7.4 mg g−1 and 74.2%, respectively. • The adsorption process followed the Freundlich isotherm and pseudo-second order kinetic model. • Chemical interaction of Au gly 2 − on GO followed a multilayer heterogeneous and reversible adsorption. • Adsorption of Au gly 2 − was related to the porous structure, and the oxygenous functional groups on GO surface. [ABSTRACT FROM AUTHOR]

Phosphate, which can cause eutrophication of the aquatic environment, can be effectively removed by an adsorption process using calcium-containing adsorbents. In this study, Ca-carbon foam was prepared by a simple method that entailed addition of Ca during the manufacturing process of carbon foam, and the phosphate removal characteristics of the prepared foam were analyzed using kinetic, equilibrium isotherm, and artificial neural network (ANN) models. The phosphate adsorption capacity decreased with an increase in the solution pH from 3.05 to 6.99. Furthermore, phosphate adsorption increased with increasing time, and the kinetic data were found to be well described by a pseudo-second- order model. The Freundlich isotherm provided the best fit of the equilibrium data, which indicates multilayer adsorption of phosphate on the Ca-carbon foam. The phosphate adsorption capacity as a function of three operational parameters—solution pH, initial phosphate concentration, and time—was well predicted by an ANN model (R² > 0.993), and the optimal ANN for the process of phosphate adsorption on Ca-carbon foam had a 3–20–1 structure with 20 hidden layers. The solution pH was the most influential operational parameter out of all the examined parameters. The results of these analyses are expected to be useful in designing the process of phosphate adsorption from aqueous solutions. [ABSTRACT FROM AUTHOR]

The potential of raw date pits as a natural, widely available and low-cost agricultural waste has been studied in order to adsorb cationic dyes from an aqueous solution. Date pits were characterized by FTIR, SEM, BET, and XRD analysis. To optimize removal of two industrial dyes, basic red 2 (BR2) and methyl violet (MV), from aqueous solution using date pits, response surface methodology (RSM) is employed. Tests were carried out as per central composite design (CCD) with four input parameters namely contact time, temperature, initial concentration of adsorbate, and pH. Second-order polynomial model better fits experimental data for BR2 and MV and optimum values were then determined. In the optimum conditions, kinetic study was conducted and the pseudo-second-order model was found the best fitted model compared to pseudo-first-order model. Moreover, it was shown that intraparticle diffusion was not the sole controlling step and could be associated with other transfer resistance. On other hand, equilibrium isotherms were obtained for BR2 and MV and their maximum adsorption capacities were 92 and 136 mg g−1 respectively. Two-parameter isotherm models like Langmuir, Temkin, Freundlich, Dubinin–Radushkevich, and Halsay were investigated to fit equilibrium data. Three error functions of residual root mean square error, chi-square statistic, and average relative error were used to comfort us in the selected models, which were actually Dubinin–Radushkevich and Langmuir for BR2 and Frendlich, Temkin, and Halsay for MV. [ABSTRACT FROM AUTHOR]

For the first time the feasibility of using an alkaline wastewater coming from the pulp and paper industry as an activator, partially (50 vol%) replacing commercial sodium hydroxide, in the production of cork-based activated carbons was evaluated. The activated carbons showed the highest value of specific surface area ever reported for cork-based activated carbons (1670 m 2 /g), surpassing several other commercial and waste-based ones. These eco-friendly cork and paper waste-based activated carbons were then evaluated as methylene blue adsorbent materials. The influence of contact time, methylene blue initial concentration and adsorbent amount on the methylene blue removal efficiency by the activated carbons was studied. Extremely fast (>99.9% removal in 5 min) and efficient methylene blue adsorption (uptake of 350 mg/g) by the cork and paper waste-based adsorbents was achieved, which demonstrates the huge potential of these innovative adsorbents. These activated carbons were produced using two unexplored industrial by-products (alkaline wastewater and cork) and, therefore, may be an inexpensive source of activated carbons, which can be used for the effective removal of dyes from wastewaters. Furthermore, despite the very large surface area and high removal efficiency this is not a nano material (being around 30–50 μm in size), its capabilities being due to its unique cork-derived microstructure, and hence it can be handled and removed/filtered much more easily than nanocarbons, and without any associated health or environmental risks. [ABSTRACT FROM AUTHOR]

• VPSA cycle can reduce the feed pressure from ∼18 bar to 6 bar. • H 2 with high purity (>99.99%) and recovery (>92%) can be separated from COG by VPSA. • The effect of vacuum and compression on specific power consumption is comparable. • The partial pressure form LDF mass transfer model is used in mass conservation. • The flow direction of the pressure equalization step affects the mass transfer zone. Hydrogen is a major component of coke oven gas (COG) and can be used in gas-based direct reduction iron processes to help the steel industry achieve the carbon peaking and carbon neutrality goals. However, the high compression power consumption is the main drawback of the current PSA cycle since the COG needs to be compressed from atmospheric pressure to ∼18 bar to achieve a hydrogen production with purity >99.9% and recovery < 85%. Here in this study, we experimentally demonstrate by using a 4-bed 12-step lab-scale VPSA rig filled with activated carbon RB3 and can obtain a hydrogen product with a purity of 99.67% and a recovery of 91.97% at a feed pressure of only 5.17 bar. We then constructed a non-isothermal non-adiabatic VPSA model using our in-house code and validated the model against experimental breakthrough and VPSA cycles. Parametric optimization produced a H 2 product of 99.995% purity and 92.29% recovery at a slightly increased adsorption pressure of 6 bar and a vacuum pressure of 0.02 bar with 10.21 mol.H 2 /kg.ads/hr productivity and 7.09 kJ/mole.H 2 specific power. We also confirmed that light product purge at vacuum pressure can effectively improve the H 2 purity and the gas flow direction of the pressure equalization step has a significant effect on the mass transfer front. Our research presents the success of low-pressure hydrogen production from COG, which will greatly accelerate the transformation of COG utilization and promote the decarbonization of the iron and steel industry. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, the adsorption capacity of anthill was investigated as a low‐cost adsorbent to remove the heavy metal ions, lead (II) ion (Pb2+), and zinc (II) ion (Zn2+) from an aqueous solution. The equilibrium adsorption isotherms of the heavy metal ions were investigated under batch process. For the study we examined the effect of the solution's pH and the initial cations concentrations on the adsorption process under a fixed contact time and temperature. The anthill sample was characterized using a scanning electron microscope (SEM), X‐ray fluorescence (XRF), and Fourier transform infrared (FTIR) techniques. From the SEM analysis, structural change in the adsorbent was a result of heavy metals adsorption. Based on the XRF analysis, the main composition of the anthill sample was silica (SiO2), alumina (Al2O3), and zirconia (ZrO2). The change in the peaks of the spectra before and after adsorption indicated that there was active participation of surface functional groups during the adsorption process. The experimental data obtained were analyzed using 2‐ and 3‐parameter isotherm models. The isotherm data fitted very well to the 3‐parameter Radke–Prausnitz model. It was noted that Pb2+ and Zn2+ can be effectively removed from aqueous solution using anthill as an adsorbent. [ABSTRACT FROM AUTHOR]

In this paper, a sludge-based adsorbent (SBA) was prepared from biochemical sludge from a wastewater treatment plant by chemical activation using 3.0 M ZnCl2 followed by pyrolysis at 700˚C for 1 h in an anoxic atmosphere. The physical and chemical properties of the SBA were characterized by N2 adsorption, scanning electron microscopy (SEM), Fourier Transform infrared red (FT-IR) spectroscopy, X-ray diffraction (XRD), and Boehm titrations. The adsorption behavior of dimethyl phthalate (DMP) on the SBA was studied in batch reactors by investigating a range of variables including pH, DMP concentration, and adsorption time. The optimal pH for DMP adsorption was found out to be around 6, as this gave the best surface charge interactions. Adsorption equilibrium isotherms and the kinetics models of DMP adsorption on the SBA were also investigated. Experimental data indicated that the Freundlich model was most applicable to the adsorption process to show the SBA’s heterogeneous surface supporting sites of varied affinities with DMP. In addition, the adsorption kinetics of DMP on SBA was described by the pseudo-second-order kinetic model suggesting that the chemical adsorption was the predominant rate-limiting stage of the adsorption process. It was demonstrated that the SBA is a low-cost promising and highly effective product for removal of DMP from aqueous solutions. The effectiveness of the SBA can be explained in terms of the π-electron interactions, electrostatic interactions, and H-bonding interactions contributing its high adsorption capacity. [ABSTRACT FROM AUTHOR]

In the present study, we have used a simple and cost-effective removal technique by a commercially available Fe-Al-SiO2 containing complex material (hardened paste of Portland cement (HPPC)). The adsorbing performance of HPPC and modified HPPC with perlite for removal of cefixime from aqueous solutions was investigated comparatively by using batch adsorption studies. HPPC has been selected because of the main advantages such as high efficiency, simple separation of sludge, low-cost and abundant availability. A Taguchi orthogonal array experimental design with an OA16(45) matrix was employed to optimize the affecting factors of adsorbate concentration, adsorbent dosage, type of adsorbent, contact time and pH. On the basis of equilibrium adsorption data, Langmuir, Freundlich and Temkin adsorption isotherm models were also confirmed. The results showed that HPPC and modified HPPC were both efficient adsorbents for cefixime removal. [ABSTRACT FROM AUTHOR]

The granular activated carbon/MnFe2O4composite with a mass ratio of 2:1 was synthesized using a simple chemical coprecipitation procedure and used for the removal of As(III) and As(V) from synthetically prepared wastewater. Physicochemical analysis of the composite was carried out through Brunauer, Emmett and Teller surface area and total pore volume, Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Micrograph and Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). The impact of various adsorption parameters such as the initial pH, adsorbent dose, contact time, temperature and initial arsenic concentration were systematically investigated to evaluate the optimum operating conditions. Nonlinear regression analysis was employed to identify the best-fit isotherm on the basis of three correlation coefficients and three error functions and also to predict the parameters involved in one one-parameter, six two-parameter, nineteen three-parameter, three four-parameter and one five-parameter isotherms. The maximum adsorption capacities estimated using the Langmuir model were 1253 mg/g for As(III) and 1314 mg/g for As(V) at 30 °C temperature and 70 min contact time. The results showed that As(III) and As(V) removal was strongly pH-dependent with an optimum pH value of 7.0 and 4.0, respectively. The mean adsorption energy (E) calculated from the D–R model indicated the nature of adsorption being ion exchange type. [ABSTRACT FROM AUTHOR]

The potential of Lantana camara L. in raw (LR) and modified form (LM) for adsorptive removal of two basic dyes, namely Rhodamine B (RB) and methylene blue (MB), from aqueous solution has been investigated. The adsorbent was characterized by various analytical techniques. The results obtained indicate that adsorption of the dyes strongly depends on pH, initial dye concentration, contact time, and presence of surfactant in batch mode and on flow rate and bed depth in column mode. Kinetic studies revealed that removal of the dyes was governed by pseudo-second-order kinetics and a film diffusion mechanism controls the overall rate of the sorption process. The equilibrium adsorption data were interpreted using various isotherm models, and the data were best fit by the Freundlich isotherm model. Modified adsorbent displayed improved adsorption capacity for RB and MB of 34.24-147.05 mg/g and 23.25-111.12 mg/g, respectively, at 30 °C. Thermodynamic parameters indicated that the dye removal process was spontaneous, endothermic, and chemical in nature. The highest desorption efficiency of spent adsorbent was achieved using sulfuric acid (1 M). The results show that LM has considerable potential for removal of RB and MB from aqueous solution. [ABSTRACT FROM AUTHOR]

Abstract: The present study investigates the possibility of using low cost agriculture waste as doum-palm seed coat for the removal of nickel ions from aqueous solutions. Two activated carbons had been prepared from raw doum-palm seed coat (DACI and DACII); as well, the raw material was used as an adsorbent (RD). Batch adsorption experiments were performed as a function of pH of solution, initial nickel ions concentration, dose of adsorbent and contact time. Adsorption data were modeled using Langmuir, Freundlich, Temkin and D–R Models. Different error analysis conforms that the isotherm data followed Freundlich models for all adsorbents. Adsorption kinetic data were tested using pseudo-first order, pseudo-second order and Elovich model. Adsorption mechanism was investigated using the intra-particle diffusion model. Diffusion coefficients were calculated using the film and intraparticle diffusion models. Kinetic studies showed that the adsorption of Ni2+ ions onto RD, DACI and DACII followed pseudo-second order kinetic model, and indicates that the intra-particle diffusion controls the rate of adsorption but it is not the rate limiting step. [Copyright &y& Elsevier]

Highlights: [•] Polyphosphazene nanotube as an adsorbent could be facilely synthesized. [•] The adsorbent owns numerous electron-rich N and P atoms and hydroxyl groups. [•] The adsorbent was an efficient and specific adsorbent for the removal of MB. [•] The pseudo-second-order model could be better to describe the adsorption of MB. [•] The MB adsorption onto PZS nanotubes was endothermic and spontaneous. [Copyright &y& Elsevier]

Highlights: [•] Adsorption isotherm of racemic guaifenesin on Chiralcel OD was measured. [•] Adsorption kinetic of racemic guaifenesin on Chiralcel OD was studied. [•] Separation process of racemic guaifenesin was predicted by chromatographic model. [•] Chromatographic model included the column model and extra column dead volume. [ABSTRACT FROM AUTHOR]

The stalk of Lamiding demonstrates a strong potential as a low-cost, readily available biosorbent for the removal of Cd(II) from aqueous medium. Its capacity under optimized conditions of 2.0 h shaking time, 1.0 h settling time and ambient pH is 46.9 mg g-1 at the monolayer coverage according to the Langmuir adsorption model, and 58.5 mg g-1 according to the Sips model when the multilayer adsorption effects are incorporated. The kinetics of adsorption of the system can be explained by the Lagergren pseudo second order model, while the adsorption of Cd(II) by Lamiding is confirmed by X-ray fluorescence spectroscopy. [ABSTRACT FROM AUTHOR]

In the present study adsorption behavior of methylene blue and rhodamine B from aqueous solution using adsorbent prepared from ' Hyptis suaveolens' (Vilayti Tulsi) was investigated as a function of parameters such as initial concentration, adsorbent dose, pH, contact time and temperature. The adsorption process was pH dependent. The thermodynamic parameters such as $$ {{\Updelta}}G,{{\Updelta}}H \,{\text{and}} \,{{\Updelta}}S $$ were calculated to investigate the nature of adsorption, their values indicate that the adsorption process is favorable. The first-order, second-order and intra-particle diffusion models were used to describe the kinetic parameter. The Freundlich and Langmuir adsorption models were applied to describe the adsorption equilibrium. Column study was conducted for both dyes. [ABSTRACT FROM AUTHOR]

Comparison analysis of linear least-square method and non-linear method of three widely used isotherms (Langmuir, Freundlich, and Redlich-Peterson) were examined to experiment with Remazol Red (C.I. 18221) onto pistachio nut shells at a solution temperature of 293 K. All three isotherm equations showed a better fit to the experimental equilibrium data. The results show that the Langmuir model shows the best fit compared to Freundlich and Redlich-Peterson models using the linear method. However, when using the non-linear method the Freundlich and Langmuir models show the best fit compared to others. Redlich-Peterson isotherm is a special case of Langmuir isotherm when the Redlich-Peterson isotherm constant g was unity. [ABSTRACT FROM AUTHOR]

Abstract: Equilibrium studies were carried out for adsorption of an insecticide (Methomyl) form aqueous solutions onto a prepared cotton stack activated carbon (CTAC) in a batch adsorption system. Parameters affecting adsorption capacity including contact time, adsorbent size (dp =355:800μm) and temperature (T=25:60°C) were investigated. Three mathematical models, Langmuir, Freundlich and Redlich-Peterson were employed for fitting the equilibrium data. Linear regression was used to determine the best fit and was found that the equilibrium data are best represented by Langmuir model thus suggesting the monolayer sorption of methomyl. The Langmuir constants (qmax = KL/aL) decreases with the increasing of temperature as well as decreasing the particle size of adsorbent. The adsorption capacity was found 72.85 mg/g at 25°C and decreased to 47.36 mg/g when temperature increased to 60°C . The value of enthalpy change was calculated (H = -2.35 kJ/mol) indicating that the removal process was exothermic and physical in nature. A single stage batch adsorber was designed for the adsorption of methomyl onto CSAC based on the optimum isotherm. [Copyright &y& Elsevier]

The removal of some of pollutants including catechol, 3-methylcatechol, 3-methoxycatechol, and 2,3-dihydroxybenzoic acid by adsorption onto activated carbon cloth (ACC) at 35.0 ± 0.1°C was investigated. The equilibrium experimental data were fitted to Langmuir, Freundlich, Temkin, Langmuir-Freundlich, and Redlich-Peterson isotherms. Also the kinetic experimental data were fitted to the pseudo-first-order and pseudo-second-order kinetic models. It was found that the pseudo-second-order model describes the kinetic of adsorption better than the other one. By comparing the obtained results with the previously reported data, it can be concluded that ACC is a high efficient adsorbent for removal of phenolic compounds from aqueous solutions. [ABSTRACT FROM AUTHOR]

The aim of this paper was to assess the biosorption properties of extracellular polymeric substances (G-EPS, P-EPS and W-EPS) extracted from three different activated sludges called AS-G, AS-P and AS-W. The compositions of the EPSs were determined. Sludge grown in lab had more EPS than those from a Sewage Treatment Plant, and that sludge fed on glucose had more EPS than if fed on peptone. The biosorption capacities of the EPSs with two metals Cu and Zn were examined successively. The maximal biosorption capacity of EPS is increased in the following order: G-EPS > W-EPS > P-EPS. All EPSs showed stronger binding properties for Zn than Cu, and this adsorption process was described well by Langmuir and Freundlich models, respectively. The excellent fit between pseudo second-order equations and adsorption process indicates that the chemisorption may be the rate limiting step. FTIR analyses revealed that the main chemical groups involved in the interactions between metals were apparently alcohol, carboxyl and amino. These groups were part of the EPS structural polymers, polysaccharides, proteins and hydrocarbon-like products. [ABSTRACT FROM AUTHOR]

In the present study, adsorption of Congo red dye on carbon mesoporous surface has been investigated. Mesoporous carbon CMK-3 adsorbent with high surface area and large pore volume was prepared and its textual and structural properties were characterized by X-ray powder diffraction patterns (XRD) and nitrogen physisorption isotherms. Adsorption experiments were carried out as batch studies at different contact time, pH, initial dye concentration and salt concentration. The dye adsorption was rapidly attained after 60 min of contact time. Removal of dye in acidic solutions was better than in basic solutions. The adsorption of dye increased with increasing initial dye concentration and salt concentration. The equilibrium data were analyzed by the Langmuir, Freundlich and Temkin models, which revealed that Langmuir model was more suitable to describe the Congo red adsorption than other models. Experimental data were analyzed using pseudo-first-order, pseudo-second-order, elovich and intra-particle kinetic models. It was found that kinetics followed a pseudo-second-order equation. Thermodynamic study showed that the adsorption was a exothermic process. [ABSTRACT FROM AUTHOR]

A batch system was applied to study the adsorption equilibrium and kinetics of chlorobenzene (CB) from aqueous solution by powdered activated carbon (PAC). Adsorption isotherm was determined at 25°C and the experimental data obtained were mathematically modeled with the Langmuir, Freundlich, Langmuir-Freundlich and Toth equations. Non-linear regression and Chi-square (χ2) analysis have been undertaken to determine the best isotherm and isotherm parameters. The Langmuir-Freundlich model yielded the best fit to the experimental data. The influence of two experimental parameters, initial CB concentration and PAC dose, on the adsorption kinetics was evaluated. The kinetics data obtained were modeled by pseudo-first-order, pseudo-second-order, and Langmuir-Freundlich kinetic models, respectively. The rate constants of Langmuir-Freundlich kinetic model obtained by extended geometric method are independent of initial CB concentration and PAC dose. The results show that the adsorption amount and relative removal of CB at any time for any initial CB concentration and any PAC dose can be estimated directly with the rate constants by using the Langmuir-Freundlich kinetic model. [ABSTRACT FROM AUTHOR]

The adsorption of methyl orange dye from aqueous solution onto penta-bismuth hepta-oxide nitrate, Bi5O7NO3, synthesized by precipitation method, was studied in a batch adsorption system. The effects of operation parameters such as adsorbent dose, initial dye concentration, pH and temperature were investigated. The adsorption equilibrium and mechanism of adsorption was evaluated by Langmuir and Freundlich isotherm and different kinetic models, respectively. The results indicate that adsorption is highly dependent on all operation parameters. At optimum conditions, the adsorption capacity was found to be 18.9 mg/g. The adsorption data fits well with the Langmuir isotherm model indicating monolayer coverage of adsorbate molecules on the surface of Bi5O7NO3. The kinetic studies show that the adsorption process is a second-order kinetic reaction. Although intra-particle diffusion limits the rate of adsorption, the multi-linearity plot of intra-particle model shows the importance of both film and intra-particle diffusion as the rate-limiting steps of the dye removal. Thermodynamic parameters show that the adsorption process is endothermic, spontaneous and favourable at high temperature. [ABSTRACT FROM AUTHOR]

Abstract: Adsorption of an insecticide (methomyl) onto natural clay have been investigated as a possible alternative method for its removal from aqueous solutions. The study was aimed to use low cost material as a step towards cleaner environment. The influence of system variables, such as particle size (dp ) and temperature on the adsorption capacity have been studied. It was found that natural clay reached equilibrium with methomyl solution in time less than 3h. The experimental data were fitted to equilibrium isotherm models, Langmuir, Freundlich and Redlich–Peterson. A dimensionless separation factor, , was used to judge the favorable adsorption. The results indicated that percentage of insecticide removal ranged from 27.6 to 32.9 for initial concentration varied from 43.71 to 19.99mg/l. The effect of temperature showed the exothermic nature of the process. The enthalpy change (ΔH) of adsorption has been evaluated and it has a value of, −17.54kJ/mol. The Langmuir model fit the experimental data significantly better than Freundlich and Redlich–Peterson models. A chart based on material balance using single batch adsorber was constructed for different percentage of methomyl removal using the Langmuir isotherm where the mass of natural clay required to treat a specified volume of solution is calculated. [Copyright &y& Elsevier]

Abstract: The utilization of modified wheat residue (MWR) as sorbent to remove the anionic dye (Reactive Red-24, RR-24) from aqueous solution was studied. MWR was prepared and characterized by specific surface area, SEM, zeta potential, FTIR and elemental analysis. Sorption experiments were carried out as a function of sorbent dosage, pH, contact time and concentration of dye. Results indicated that a mass of amine groups were grafted into the framework of MWR. It was shown that pseudo-second-order kinetic equation could best describe the sorption kinetics. The equilibrium sorption data were well represented by the Langmuir isotherm equation. The maximum sorption capacity of MWR for RR-24 was 200.0mg/g, which showed higher capacity than those of previous work and a similar capacity compared to those of commercial activated carbon. The results indicated that MWR could be employed as an excellent and low-cost sorbent for removal of anionic dye from aqueous solution. [Copyright &y& Elsevier]

Abstract: An activated carbon was prepared from the stalk of the scrap aquatic plant loosestrife, by H3PO4 activation and then was evaluated for its ability to adsorb 2,4,6-trichlorophenol (TCP). The effects of solution pH, agitation time, TCP initial concentration, and temperature on TCP adsorption were investigated. The equilibrium adsorption data of TCP on activated carbon were analyzed by Langmuir, Freundlich and Temkin isotherm models. The Temkin model gave the best correlation with the experimental data. The adsorption was found to follow the pseudo-second-order kinetics. The intraparticle diffusion model was used to determine the mechanism of the adsorption process. Thermodynamic parameters such as standard enthalpy (ΔH o), standard entropy (ΔS o), and standard free energy (ΔG o) were obtained. Adsorption of TCP is exothermic with ΔH o at −12.87kJ/mol. [Copyright &y& Elsevier]

Abstract: This paper presents a study of the removal of ammonium ion from aqueous solutions using natural Chinese (Chende) zeolite. A series of experiments was conducted to examine the effects of solution pH, particle size, contact time, adsorbent dosage, and the presence of other cation- and anion species on ammonium removal. The findings indicated that these parameters named had a significant effect on the removal of ammonium by the zeolite. The effect of other cations on the removal of ammonium followed the order of preference Na+ >K+ >Ca2+ >Mg2+ at identical mass concentrations, and the effect of the presence of individual anions followed the order of preference carbonate>chloride>sulfate>phosphate at identical mass concentrations of ammonium ions. Kinetic analysis showed that the adsorption of ammonium on zeolite at different ranges of particle size well followed the pseudo-second-order model and followed the intra-particle diffusion model only during the initial 60min of the adsorption process. Equilibrium isotherm data was fitted to the linear Langmuir- and Freundlich models with the latter model providing the better description of the process (R 2 =0.991–0.997) compared to the former (R 2 =0.902–0.989). [Copyright &y& Elsevier]

Abstract: The adsorption of methyl orange and methyl violet from aqueous solutions by Phragmites australis activated carbon (PAAC) was studied in a batch adsorption system. The adsorption studies include both equilibrium adsorption isotherms and kinetics. Several isotherm models were investigated and the adsorption isotherm data were best represented by the Temkin isotherms. The kinetic data were well described by the pseudo-second-order kinetic model. The mechanism of the adsorption process was determined from the intraparticle diffusion model. The results indicate that PAAC could be employed as a low-cost alternative for the removal of the textile dyes from effluents. [Copyright &y& Elsevier]

Abstract: A batch system was applied to study the adsorption of methyl violet from aqueous solution by granular activated carbon. The adsorption studies include both equilibrium and kinetics. Equilibrium data were mathematically modeled using the Langmuir–Freundlich isotherm. The equilibrium data were fitted to the isotherm with n =1 very well. Maximum adsorption capacity of 0.095g/g at equilibrium was achieved. The kinetics of adsorption were evaluated by pseudo-first-order and pseudo-second-order models. Also extended geometric method has been applied to estimate the adsorption and desorption rate constants of Langmuir kinetics. By the obtained concentration-independent rate constants, the kinetics of adsorption were modeled by Langmuir kinetics. The stochastic numerical simulation has been applied to simulate the adsorption kinetic data of methyl violet at different concentrations. [Copyright &y& Elsevier]

Abstract: The biosorption process for removal of cobalt(II) and zinc(II) by aerobic granules was characterized. Single component and binary equimolar systems were studied at different pH values. The equilibrium was well described by Redlich–Peterson adsorption isotherm. The maximal adsorption capacity of the granules, in single systems (55.25 mg g−1 Co; 62.50 mg g−1 Zn) compared with binary systems (54.05 mg g−1 Co; 56.50 mg g−1 Zn) showed reduction in the accumulation of these metals onto aerobic granules. The kinetic modelling of metal sorption by granules has been carried out using Lagergren equations. The regression analysis of pseudo second-order equation gave a higher value, indicating that chemisorption involving valent forces through the sharing or exchange of electrons between sorbent and sorbate may be the rate limiting step. The initial biosorption rate indicated that aerobic granules can adsorb Co(II) more rapidly than Zn(II) from aqueous solutions. Meanwhile, FTIR and XPS analyses revealed that chemical functional groups (e.g., alcoholic and carboxylate) on aerobic granules would be the active binding sites for biosorption of Co(II) and Zn(II). [Copyright &y& Elsevier]

Abstract: The adsorption isotherm was determined for phenol in methanol/water on a C-8 stationary phase using frontal analysis in staircase mode, assuming different total column porosities, from 1 to 87%. Each set of adsorption isotherm data, with a certain column porosity, was fitted to various adsorption models and the generated parameters were used to calculate overloaded elution band profiles that were compared with experiments. It was found that the bi-Langmuir model had an optimum fit for a porosity that corresponds well with the value found experimentally. The adsorption energy distribution (AED) calculations and error analysis confirmed a bimodal energy distribution. It was also found that band profiles can be accurately predicted with a quite arbitrary chosen porosity, under prerequisite that a wrong but flexible adsorption model is chosen instead of the correct one. The latter result is very useful for quick optimizations of preparative separations where the exact value of the column porosity is not available. [Copyright &y& Elsevier]

Abstract: The potential use of calcium alginate beads for removal of dyes from colored effluents in dynamic batch mode has been studied. Basic black dye, which is one of the most commonly used dyes in leather industry, has been chosen for the study. The parameters that affect the dye adsorption such as contact time, initial concentration of dye, solution pH and temperature have been investigated and optimized conditions have been determined. Maximum adsorption capacity of 57.70mgg−1 has been achieved at an initial concentration of 300mgL−1, with 4gL−1 of alginate dosage, at pH 4.0 and at room temperature (30±1°C). Adsorption isotherm studies clearly indicate that the Langmuir isotherm shows a better fit for adsorption of the dye by alginate beads, implying a homogeneous and monolayer binding surface. Kinetic data of adsorption of dye on to calcium alginate beads fits well to pseudo-second order kinetic model. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° have been determined, which indicates a spontaneous endothermic adsorption process. [Copyright &y& Elsevier]

Dynamic batch experiments were carried out for the biosorption of basic blue dye on to the green macro algae Caulerpa scalpelliformis. The factors affecting the sorption process such as the initial concentration of the dye, pH of the solution, the adsorbent dosage and the time of contact were studied. It has been observed that the sorption process was significantly affected by the pH of the initial dye solution. The sorption kinetics was found to follow the second-order kinetic model. The Boyd's plot confirmed the external mass transfer as the rate-limiting step. The average effective diffusion coefficient was found to be 1.652 × 10- 5 cm2/s. Sorption equilibrium studies demonstrated that the biosorption followed Freundlich isotherm model, which implies a heterogeneous sorption phenomenon. Optimized parameters were used to treat the commercial effluent containing the dye. Complete color removal was observed in two stages of treatment with the seaweed. [ABSTRACT FROM AUTHOR]

The adsorptive removal of boron from aqueous solution by using the neutralized red mud was studied in batch equilibration technique. The effects of pH, adsorbent dosage, initial boron concentration and contact time on the adsorption were investigated. The experiments demonstrated that boron removal was of a little fluctuation in pH range of 2–7 and it takes 20min to attain equilibrium. The adsorption data was analyzed using the Langmuir and the Freundlich isotherm models and it was found that the Freundlich isotherm model represented the measured sorption data well. [Copyright &y& Elsevier]

Abstract: The adsorption properties of local clinoptilolite (Serbia) towards Cs+, Co2+, and Sr2+ were investigated by batch equilibration technique. The influence of equilibration time, initial metal cation concentration, solution pH and presence of EDTA on these properties was studied and discussed. Kinetic data were found to be well fitted with pseudo-second order kinetic model. Cs+ is preferably adsorbed by the natural clinoptilolite, followed by Sr2+ and Co2+. The Langmuir adsorption isotherm was used to determine the adsorption capacities from both single and mixed metal solutions. At pH range of 3–12 the adsorption of Cs+ remains almost constant, while at low pH (2–3) the adsorption is lesser. At initial pH range of 2–10 adsorption of Sr2+ remains approximately stable, whereas at initial pH>10 adsorption increases significantly. The adsorption of Co2+ is low at low pH but increased remarkably with increasing pH and precipitated at pH>8. Cs+ adsorption on the clinoptilolite was not affected by the presence of EDTA, while the presence of EDTA hinders the adsorption of Co2+ and Sr2+ on clinoptilolite. [Copyright &y& Elsevier]

Abstract: Equilibrium adsorption isotherm for the removal of basic dye (Methylene Blue) from aqueous solution using bituminous coal-based activated carbon has been investigated. Liquid phase adsorption experiments were conducted and the maximum adsorptive capacity was determined. The effect of experimental parameters, namely, pH and adsorbent particle size were studied. Equilibrium data were mathematically modelled using the Langmuir, Freundlich and Redlich–Peterson adsorption models to describe the equilibrium isotherms at different solution pH values and particle sizes, and isotherm constants were determined. The results indicate the potential use of the adsorbent for the removal of Methylene Blue (MB) from aqueous solution. Maximum adsorption capacity of 580mg/g at equilibrium was achieved. It was found that pH plays a major role in the adsorption process. The optimum pH for the removal of MB from aqueous solution under the experimental conditions used in this work was 11. The Redlich–Peterson isotherm was found to best fit the experimental data over the whole concentration range as indicating from the high values of the correlation coefficients (r 2 >0.99). [Copyright &y& Elsevier]

Abstract: Comparison analysis of linear least square method and non-linear method for estimating the isotherm parameters was made using the experimental equilibrium data of safranin onto activated carbon at two different solution temperatures 305 and 313K. Equilibrium data were fitted to Freundlich, Langmuir and Redlich–Peterson isotherm equations. All the three isotherm equations showed a better fit to the experimental equilibrium data. The results showed that non-linear method could be a better way to obtain the isotherm parameters. Redlich–Peterson isotherm is a special case of Langmuir isotherm when the Redlich–Peterson isotherm constant g was unity. [Copyright &y& Elsevier]

To explore the mechanism of adsorbates onto selected resin and provide a theoretical basis for the reduction of acidity in hawthorn fruit juice. In this study, the adsorption processes of titratable acidity (TA) and total flavonoids (TF) from hawthorn fruit juice onto macro-porous adsorption resins were studied. The experimental data were fitted by two widely used isotherm models namely, Langmuir and Freundlich. Kinetics of the adsorption processes were fitted by Pseudo-first-order, Pseudo-second-order kinetics, Elovich kinetics and Web and Morris intra-particle diffusion model. The experiment data showed D315 resin exhibited the highest adsorption capacity, Q e = 176.28 mg/mL, and selectivity coefficient, α = 3.588. The results also showed that the adsorption of adsorbates on D315 resin correlated better with the Langmuir isotherm model. The adsorption processes of adsorbates were better fitted by pseudo-second-order kinetics. In addition, the adsorption process of TA and TF on D315 resin is chemical adsorption, spontaneous and endothermic. The results indicated that D315 resin had a good adsorption effect on TA in hawthorn fruit juice and provided the theoretical basis for further exploration. • Hawthorn fruit juice; Resins; Equilibrium isotherm; Kinetics; Thermodynamics. • To explore the mechanism of adsorbates onto resins for the reduction of acidity in hawthorn fruit juice. • The adsorption of adsorbates on D315 resin correlated better with the Langmuir isotherm model. • The adsorption processes of adsorbates were better fitted by pseudo-second-order kinetics. • The adsorption process of TA and TF on D315 resin is chemical adsorption, spontaneous and endothermic. [ABSTRACT FROM AUTHOR]

Adsorption of copper ions out of aqueous solution by preparing activated carbon from unripe Musa paradisiaca peel (UmpP) with KOH was investigated. Estimation of the adsorption constants was achieved by adopting the Langmuir and Freundlich models. Results revealed that the adsorption process was fast and equilibrium was reached at 55 mins. The adsorption efficiency was highly influenced by the pH of the solution, and the maximum adsorption was attained at pH 7.5. In addition, an increase in adsorption capacity was observed with increase in contact time and initial copper concentration. The adsorption process was explained by both Langmuir and Freundlich models having R2 value of 0.9977 and 0.9959 at 303 K respectively and R2 value of 0.9922 and 0.9904 at 308 K respectively. The maximum adsorption capacity of KOH-modified UmpP at the specified conditions was found to be 9.980 and 9.766 mg/g at 303 and 308 K respectively. Sequel to modelling the kinetic data, the Pseudo-second-order model gave the best fit with R2 = 0.9990 and 0.9977 at 303 and 308 K respectively, indicating that the adsorption process is restricted to chemisorption. KOH-modified UmpP can serve as an economically and environmentally viable sorbent for the removal of copper from contaminated waters. [ABSTRACT FROM AUTHOR]

Excess phosphorus in waterways can cause serious eutrophication, a phenomenon which could eventually result in water quality crisis. Thus, there is a need to seek appropriate ways to remove phosphorus from wastewater. This investigation evaluates the potential of two types of sorbents, granular zeolite (A) and globular zeolite (B), for phosphorus removal. The comparative adsorption of phosphorus from aqueous solutions by A and B is tested using batch experiments. For A and B, the assessed optimum pH is 1.8 and 2.0, sorbent dosage 2.5 and 30 g (per 100 ml aqueous solution, and the contact time intervals 20 and 40 min, respectively. The initial phosphorus concentration for both sorbents was 20mg/L. The analysis of the results demonstrates that sorbent A has better adsorption characteristics than B. To describe the equilibrium adsorption isotherms, Langmuir and Freundlich models are applied to the data. The Langmuir isotherm adequately describes adsorption for both of these sorbents, with an R² goodness of fit of 0.9792 for A and 0.9835 for B, respectively. [ABSTRACT FROM AUTHOR]