Humic acid adsorption on fly ash and its derived unburned carbon

Fly ash is solid waste from combustion process, containing oxide minerals and unburned carbon. In this investigation, fly ash has been separated into metal oxide mineral section and unburned carbon. The fly ash with different contents of unburned carbon was employed for humic acid adsorption to investigate the influence of unburned carbon on adsorption. It is found that metal oxides and unburned carbon in fly ash exhibit significant difference in humic acid adsorption. The unburned carbon plays the major role in adsorption. Higher content of unburned carbon in fly ash results in higher surface area and thus higher humic acid adsorption. Fly ash and unburned carbon exhibit adsorption capacity of humic acid of 11 and 72 mg/g, respectively, at 30 degrees C, pH 7. Humic acid adsorption is also affected by ion strength, pH, and temperature. The thermodynamic calculations indicate that the adsorption is endothermic nature with DeltaH(0) and DeltaS(0) as 5.79 kJ/mol and 16.0 J/K mol, respectively.     

Modeling the mechanism involved during the sorption of methylene blue onto fly ash

Batch sorption experiments were carried out to remove methylene blue from its aqueous solutions using fly ash as an adsorbent. Operating variables studied were initial dye concentration, fly ash mass, pH, and contact time. Maximum color removal was observed at a basic pH of 8. Equilibrium data were represented well by a Langmuir isotherm equation with a monolayer sorption capacity of 5.718 mg/g. Sorption data were fitted to both Lagergren first-order and pseudo-second-order kinetic models and the data were found to follow pseudo-second-order kinetics. Rate constants at different initial concentrations were estimated. The process mechanism was found to be complex, consisting of both surface adsorption and pore diffusion. The effective diffusion parameter D(i) values were estimated at different initial concentrations and the average value was determined to be 2.063 x 10(-9)cm2/s. Analysis of sorption data using a Boyd plot confirms the particle diffusion as the rate-limiting step for the dye concentration ranges studied in the present investigation (20 to 60 mg/L).     

Geopolymeric adsorbents from fly ash for dye removal from aqueous solution

Adsorbents from coal fly ash treated by a solid-state fusion method using NaOH were prepared. It was found that amorphous aluminosilicate geopolymers would be formed. These fly ash-derived inorganic polymers were assessed as potential adsorbents for removal of some basic dyes, methylene blue and crystal violet, from aqueous solution. It was found that the adsorption capacity of the synthesised adsorbents depends on the preparation conditions such as NaOH:fly-ash ratio and fusion temperature with the optimal conditions being at 1.2:1 weight ratio of Na:fly-ash at 250-350 degrees C. The synthesised materials exhibit much higher adsorption capacity than fly ash itself and natural zeolite. The adsorption isotherm can be fitted by Langmuir and Freundlich models while the two-site Langmuir model producing the best results. It was also found that the fly ash derived geopolymeric adsorbents show higher adsorption capacity for crystal violet than methylene blue and the adsorption temperature influences the adsorption capacity. Kinetic studies show that the adsorption process follows the pseudo second-order kinetics.     

The physical and surface chemical characteristics of activated carbons and the adsorption of methylene blue from wastewater

Adsorption of a basic dye, methylene blue, from aqueous solutions onto as-received activated carbons and acid-treated carbons was investigated. The physical and surface chemical properties of the activated carbons were characterized using BET-N(2) adsorption, X-ray photoelectron spectroscopy (XPS), and mass titration. It was found that acid treatment had little effect on carbon textural characteristics but significantly changed the surface chemical properties, resulting in an adverse effect on dye adsorption. The physical properties of activated carbon, such as surface area and pore volume, have little effect on dye adsorption, while the pore size distribution and the surface chemical characteristics play important roles in dye adsorption. The pH value of the solution also influences the adsorption capacity significantly. For methylene blue, a higher pH of solution favors the adsorption capacity. The kinetic adsorption of methylene blue on all carbons follows a pseudo-second-order equation.     

燃烧福建无烟煤的循环流化床锅炉飞灰及其未燃炭分析

以三个燃烧福建无烟煤的商业CFB锅炉电厂飞灰为研究对象，分析飞灰的粒径和含碳量分布；观察并区分了飞灰中煤炭、烟怠、半焦和灰渣等颗粒的表面形貌；测定了飞灰炭的反应活性并与入炉煤作比较；并研究了飞灰炭的来源。结果表明，采用单级分离装置的CFB锅炉，粒径在0.0385mm～0.0500mm的飞灰质量最多，未燃炭份额也最高；而采用双级分离装置的CFB锅炉，飞灰质量分布和飞灰炭份额的峰值则出现在粒径为0.0500mm~0.0750mm处。飞灰主要由三种形貌的颗粒组成，颗粒状的未燃炭、絮团状的灰渣、和介于两者之间的半焦。与入炉煤相比，飞灰炭的反应活性较高，主要来源于入炉煤中的细粉和燃烧早期因破碎和磨蚀而产生的、来不及在炉膛中燃尽的细小含炭颗粒。入炉煤中易破碎、反应性较高的亮煤是构成电厂CFB锅炉飞灰炭的主要成分。     

Competitive Adsorption of Methylene Blue and Rhodamine B on Natural Zeolite: Thermodynamic and Kinetic Studies

A batch system was applied to study the adsorption behavior of methylene blue (MB) and rhodamine B (RB) in single and binary component systems on natural zeolite. In the single component systems, the zeolite presents higher adsorption capacity for MB than RB with the maximal adsorption capacity of 7.95×10^?5 and 1.26×10^?5 mol/g at 55°C for MB and RB, respectively. Kinetic studies indicated that the adsorption followed pseudo‐second‐ order kinetics and could be described by a two‐step diffusion process. For the single component systems, the adsorption isotherm could be fitted by the Langmuir model. In the binary component system, MB and RB exhibit competitive adsorption on the zeolite. The adsorption is approximately reduced to 50% and 60% of single component adsorption systems of MB and RB, respectively at an initial concentration of 6×10^?6 mol·L^?1 at 25°C. In the binary component system, kinetic and adsorption isotherm studies demonstrate that the experimental data are following pseudo‐second‐order kinetics and Langmuir isotherm and kinetic data are fairly described by a two‐step diffusion model. Effect of solution pH on adsorption of MB and RB in both single and binary component systems was studied and the results were described by electrostatic interactions.     

Synthesis of NiO coated chitosan-cenosphere buoyant composite for enhanced adsorptive removal of methylene blue

The objective of the present study is to utilize fly ash cenosphere to remove methylene blue (MB) from the water streams. Nickel oxide is a typical semiconductor used as proficient adsorbent material for degradation of dye with environment friendly applications due to its excellent chemical stability and high catalytic activity. The chitosan cenosphere buoyant composite coated with NiO was synthesized with hydrothermal grafting reaction using silane coupling agent and epichlorohydrin as a cross-linking reagent. The batch adsorption experiments were carried out with a cationic dye, methylene blue as a representative organic pollutant to investigate the adsorptive capabilities of the composite as adsorbent. The influence of pH (2-12), initial concentration of dye (50–200 mg/L), temperature (37–47 °C) and contact time (0–24 h) were taken as parameters in the study. On the relative elimination of MB, the effect of time and temperature were investigated. The adsorption kinetics for MB was correlated and found to observe the pseudo-second order kinetic model, whereas the equilibrium adsorption isotherm follows the Langmuir model (R² > 0.99). The results indicate that the floating fly ash cenosphere coated with NiO proved to be more responsive for enhanced degradation of methylene blue.     

超细粉煤灰吸附亚甲基蓝的机理研究

以西安西郊热电厂粉煤灰(XFA),西安灞桥热电厂粉煤灰(BFA)和陕西渭河电厂粉煤灰(WFA)为原料,球磨后经旋风分级再用布袋收集逸出物分别得到超细粉煤灰XUFA、BUFA和WUFA。研究了超细粉煤灰对亚甲基蓝的吸附动力学、热力学以及pH值对吸附的影响。结果表明,超细粉煤灰对亚甲基蓝的吸附性能明显好于原粉煤灰。超细粉煤灰对亚甲基蓝的吸附性能按顺序为WUFA>XUFA>BUFA。粉煤灰颗粒粒度、比表面积和活性组分(SiO2 Al2O3)含量是影响粉煤灰吸附性能的主要因素。WUFA对亚甲基蓝的吸附符合Langmuir吸附等温式,而XUFA和BUFA对亚甲基蓝的吸附符合Freundlich吸附等温式。超细粉煤灰对亚甲基蓝的吸附均符合二级吸附动力学模型,吸附过程由颗粒内扩散过程控制。当溶液pH由2增加到8时,超细粉煤灰吸附量增加,后随pH值增加,吸附量略有下降。     

Activated carbon blended with grape stalks powder: Properties modification and its application in a dye adsorption

In this study, activated carbon was blended with grape stalks powder to adsorb methylene blue (MB) dye with various concentrations from a wastewater. For this purpose, five independent variables involving pH (2–13), contact time (5–270 min), grape stalks powder dosage (0.1–10 g/l), methylene blue initial concentration (20–300 mg/l), and activated carbon dosage (0.1–10 g/l) for methylene blue adsorption were studied. The Central Composite Design (CCD) under Response Surface Methodology (RSM) was applied to estimate the independent variables effects on the methylene blue adsorption. The pseudo- first order, pseudo-second order, Elovich and intraparticle diffusion models were employed to study the adsorption kinetics and isotherm. The Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models were applied to investigate the adsorption isotherm. It was concluded that the intraparticle diffusion isotherm and pseudo-second order kinetic models could show the best results. Furthermore, some data such as physical adsorption (by analyzing FTR and applying some standard equations) and mean free energy (E) were discovered in this research. Finally, activated carbon blended with grape stalks powder as an effective bio-adsorbent for the methylene blue reduction from a wastewater was introduced.     

Equilibrium, kinetics, mechanism, and process design for the sorption of methylene blue onto rice husk

Batch experiments were carried out for the sorption of methylene blue onto rice husk particles. The operating variables studied were initial solution pH, initial dye concentration, adsorbent concentration, and contact time. Equilibrium data were fitted to the Freundlich and Langmuir isotherm equations and the equilibrium data were found to be well represented by the Langmuir isotherm equation. The monolayer sorption capacity of rice husks for methylene blue sorption was found to be 40.5833 mg/g at room temperature (32 degrees C). The sorption was analyzed using pseudo-first-order and pseudo-second-order kinetic models and the sorption kinetics was found to follow a pseudo-second-order kinetic model. Also the applicability of pseudo second order in modeling the kinetic data was also discussed. The sorption process was found to be controlled by both surface and pore diffusion with surface diffusion at the earlier stages followed by pore diffusion at the later stages. The average external mass transfer coefficient and intraparticle diffusion coefficient was found to be 0.01133 min(-1) and 0.695358 mg/g min0.5. Analysis of sorption data using a Boyd plot confirms that external mass transfer is the rate limiting step in the sorption process. The effective diffusion coefficient, Di was calculated using the Boyd constant and was found to be 5.05 x 10(-04) cm2/s for an initial dye concentration of 50 mg/L. A single-stage batch-adsorber design of the adsorption of methylene blue onto rice husk has been studied based on the Langmuir isotherm equation.     

An evaluation of coal fly ash as an adsorbent for the removal of methylene blue from aqueous solutions: kinetic and thermodynamic studies

Abstract

In this study the effect of the dose and particle size of the adsorbent, initial dye concentration, initial pH, contact time and temperature were investigated for the removal of by means of fly ash (FA) methylene blue (MB) from an aqueous solution. The FA dose was found to be 2.0?g and the under 270 mesh sized particles were found to be effective particles for adsorption. The adsorption process reached its maximum value at 0.5?mg/L dye concentration and attained equilibrium within 10?minutes. The adsorption isotherm was found to follow the Langmuir model. The estimated adsorption free energy (ΔG^o), enthalpy change (ΔH^o), and entropy change (ΔS^o) for the adsorption process were ?37.77?kJ mol^?1, ?13.44?kJ mol^?1 and 122 J mol^?1 K^?1 respectively at 298 K. The maximum adsorption capacity is 0,12?mg g^?1 at 298 K and 0,07?mg g^?1 at 398 K. The adsorption process was exothermic, feasible and spontaneous. The positive value of ΔS^o shows the affinity of FA for MB while the low value of ΔG^o suggests a physical adsorption process.     

Rice husk ash as an adsorbent for methylene blue—effect of ashing temperature

Utilization of one waste material to control pollution caused by another is of high significance in the remediation of environmental problems. Rice husk, an abundantly available agricultural waste, can be used as a low cost adsorbent for dyes and heavy metals in effluent streams. The possible utilization of rice husk ash as an adsorbent for methylene blue dye from aqueous solutions has been investigated. Ash samples from husks of two origins were prepared at different temperatures and their physical, chemical spectroscopic and morphological properties were determined. XRD, FTIR and SEM were some of the techniques adopted for the characterization. The samples were also analyzed for bulk density, pH, nitrogen adsorption properties and lime reactivity. Experiments of methylene blue adsorption on the ash samples were conducted using batch technique and a comparative study was made. Results were analyzed using linear, Langmuir and Freundlich isotherms. The values of separation factor indicate that most of the ash samples do adsorb the dye molecules, but in varying quantities. Calcination at 900^∘C reduces the adsorption capacity of the ash to a great extent. Regression analysis shows that the experimental data fits both Langmuir and Freundlich isotherms for certain concentration limits. The adsorbate species are most probably transported from the bulk of the solution into the solid phase through intra-particle diffusion process. Kinetics of adsorption was found to follow pseudo second order rate equation with R ²∼ 0.99. The highest adsorption capacity (Q ₀) achieved is found to be ∼690 mg/g, which is even higher than the values reported for activated carbon from rice husk. The adsorption capacity of the ash samples are in good agreement with their surface area and pore volume.     

Removal of Phenolic and Lignin Compounds from Bleached Kraft Mill Effluent by Fly Ash and Sepiolite

This study aimed to remove phenolic and lignin compounds from paper mill industry (4500 m³/h) wastewaters, which is discharged to sea from a plant located in the western Turkey. As adsorbent, fly ash, raw sepiolite and heat-activated sepiolite were used. The effect of factors such as, particle size, temperature and pH on adsorption process was investigated. From kinetic studies, equilibrium time was found as 1 h for both. The kinetic data supports pseudo-second order model but shows very poor fit for pseudo-first order model. Intraparticle model also shows that there are two separate stages in sorption process, namely, external diffusion and pore diffusion. Adsorption isotherms for fly ash and activated sepiolite were obtained at two different temperatures. From experiments carried out at different pHs, it was observed that pH plays an important role in the adsorption process in removing of both lignin and phenolic compounds, providing both ionizating the compounds and modifying sorbent surfaces. It was also observed that heat-activated sepiolite is more effective than raw sepiolite and fly ash to remove these compounds. Adsorption of lignin and phenolic compounds increases with decreasing particle size. In addition, the efficiency of adsorption decreases with increasing adsorption temperature for both fly ash and untreated sepiolite.     

表面活性剂改性有机沸石对废水中亚甲基蓝的吸附行为

用表面活性剂十六烷基三甲基溴化铵(CTMAB)和十二烷基硫酸钠(SDS)复合改性沸石,制备了阴阳离子表面活性剂改性沸石,利用X射线衍射和红外吸收光谱表征了改性前后沸石的结构,并研究了改性沸石对亚甲基蓝的吸附行为.结果表明,改性后沸石的吸附性能明显增强;在溶液pH 8、常温,吸附时间100 min、改性沸石用量20 g/...     

Adsorption of Congo red from aqueous solution onto calcium-rich fly ash

The adsorption of Congo red from solution was carried out using calcium-rich fly ash with different contact times, concentrations, temperatures, and pHs. While the amount of dye adsorbed per unit weight of fly ash increases with increasing concentration and temperature, it decreases slightly with increasing pH. The adsorption was between 93 and 98% under the conditions studied. Kinetic studies showed that the adsorption process obeyed the pseudo-second-order kinetic model. It was also determined that the adsorption isotherm followed Freundlich and Dubinin-Radushkevich models. From thermodynamic studies, it was seen that the adsorption was spontaneous and endothermic. Desorption studies suggested that desorption was 29.18% in the presence of 0.1 N HCl and was 47.21% in the presence of CH(3)COOH (50% v/v). This indicated that most of the dye was held by fly ash via chemisorption as well as ion exchange. Furthermore, FTIR study also shows that a chemisorption process occurs between CR and fly ash, probably indicating dye/fly ash complexing.     

基于密度泛函理论的燃煤飞灰未燃尽碳与烟气砷作用机理

基于密度泛函理论研究了燃煤飞灰中未燃尽碳（unburned carbon， UBC）组分对气态单质砷As及其氧化物AsO、AsO₂和As₂O₃的作用机理。结果表明，单质砷优先吸附于碳桥位，吸附能在（-5.95）-（-5.88） eV。AsO分子中的砷、氧原子分别与碳原子成键时，吸附构型最稳定，吸附能最低为-7.87 eV。当AsO₂在未燃尽碳表面解离形成一个AsO和表面活性氧时，体系最稳定，吸附能为-10.65 eV。当三角双锥As₂O₃分子以两个氧原子首先碰撞未燃尽碳表面时，将解离形成AsO和AsO₂小分子，并分别与表面碳成键，此时体系吸附能相较于未解离情形而言显著降低，达到-10.64 eV。飞灰未燃尽碳与AsO或AsO₂小分子的结合较紧密，局部倾向于形成特殊的五元环结构。毒性最强的三价态砷As₂O₃，相较于As、AsO和AsO₂而言，化学性质稳定，不易发生吸附。将其催化裂解为AsO、AsO₂小分子，有望成为可行的燃煤电厂烟气砷污染控制措施。     

Adsorption of methylene blue and orange II onto unmodified and surfactant-modified zeolite

Adsorption of cationic methylene blue and anionic orange II onto unmodified and surfactant-modified zeolites was studied using a batch equilibration method. The effects of equilibrium time, solution pH, and sorption temperature were examined. The results suggested that 2% sodium dodecyl benzenesulfonate (SDBS)- and 3% sodium dodecyl sulfate (SDS)-modified zeolites had higher adsorption capacities for methylene blue than the unmodified zeolite, while 2% cetylpyridinium bromide hexadecyl (CPB)- and 2% hexadecylammonium bromide (HDTMA)-modified zeolites were the best adsorbents for orange II. The adsorption conditions were optimized, and the mechanisms of adsorption are briefly discussed.     

Adsorption of indigo carmine from aqueous solution using coal fly ash and zeolite from fly ash

Coal fly ash, a waste generated at the Figueira coal-fired electric power plant located in Brazil, was used to synthesize zeolite by hydrothermal treatment with NaOH solution at 100 °C for 24 h. The fly ash (FA) and this synthesized zeolite (ZM) that was characterized predominantly as hydroxy-sodalite were used as adsorbents for anionic dye indigo carmine from aqueous solutions. The samples were analyzed by instrumental neutron activation analysis (INAA) for the determination of As, Co, Fe, La, Mo, Na, Sb, Sc, Sm, Th, U and Zn. Effects of contact time and initial dye concentration were evaluated in the adsorption processes. The kinetics studies indicated that the adsorption followed the pseudo-second order kinetics and that surface adsorption and intraparticle diffusion were involved in the adsorption mechanism for both the adsorbents. The Langmuir isotherm model provided the best correlation of the experimental data. The maximum adsorption capacity was found to be 1.48 mg L⁻¹ for FA and 1.23 mg L⁻¹ for ZM. Laboratory leaching and solubilization tests conducted to classify this ZM as if was a waste residue according to the Brazilian regulation classified it as a residue non-hazardous and non-inert.     

Film-pore-concentration-dependent surface diffusion model for the adsorption of dye onto palm kernel shell activated carbon

The rate of dye adsorption from aqueous effluents onto palm kernel shell (PKS) activated carbon has been studied experimentally using the batch adsorption method. The adsorption rates of methylene blue on PKS for systems of different initial dye concentrations are modeled using a film-pore-concentration dependent surface diffusion (FPCDSD) model. The FPCDSD model is sufficiently general and can be reduced easily to describe other simplified models. Using the FPCDSD model, only a single set of mass transfer parameters is required to describe the methylene blue/PKS system for different initial concentrations. A different set of mass transfer parameters are needed to obtain the best fitting if the pore diffusion is not included in the model.     

Investigation of the factors affecting organic cation adsorption on some silicate minerals

In this study, the effects of some factors on the adsorption of a basic dye (methylene blue) on bentonite and sepiolite samples were studied. These factors are cation (Na(+) and Ca(2+)) saturation of the samples and pH and ionic strength of the dye solution. The adsorption data were found to conform to the Langmuir equation within the concentration range studied and Langmuir constants were determined for each of the samples. The adsorption capacities of the samples were found to increase with cation saturation. Changes in the pH of the dye solution had no significant influence on the adsorption capacity and adsorption capacities were found to decrease with increasing ionic strength. The maximum sorption capacity of methylene blue exceeded the cation exchange capacity of bentonite and sepiolite.