Removal of Pb(II) from aqueous solutions by carbons prepared from Sal wood (Shorea robusta)

In the present work, physically and chemically activated carbons are prepared using Sal wood (Shorea robusta) sawdust by thermal process and using sulfuric acid as the activation agent to remove Pb(II) from aqueous solutions. Adsorption equilibrium studies have been done at a pH of 4 and a room temperature of 30 °C. It was found that the adsorption isotherms are favorable and chemically activated carbons are better than physically activated carbon in terms of adsorption capacity. Various two-parameter adsorption isotherm models, viz. Freundlich, Langmuir, Temkin and Dubinin-Radushkevich, were used to fit the equilibrium data and it was found that the Freundlich adsorption model provided best-fit. The first-order irreversible unimolecular reaction model and the pseudo-second-order kinetic models were used to fit the kinetic data and it was found that both the models provided good fit. Kinetic and film diffusion studies show that the adsorption of lead(II) on the activated carbons tested in this work are both intra-particle and film diffusion controlled.     

Adsorption of two coffee aromas from synthetic aqueous solution onto granular activated carbon derived from coconut husks

Soluble coffee production requires several processes that cause the loss and degradation of aromas, which reduces the quality of the final product. However, such aromas can be recovered into aqueous solution during the production process. Aromas must be separated from water, and pleasant compounds, such as benzaldehyde, must be separated from unpleasant compounds, such as acetic acid. In this study, the kinetic and thermodynamic parameters of benzaldehyde and acetic acid adsorption from synthetic single-solute aqueous systems onto commercial grade granular activated carbon derived from coconut husks were investigated. The contact time required to attain adsorption equilibrium of benzaldehyde was 6 h, while that of acetic acid was 10 h. Adsorption isotherm data revealed that the adsorption of benzaldehyde and acetic acid was exothermic and spontaneous in nature. Moreover, the isosteric heat of adsorption indicated that the adsorbent surface was energetically heterogeneous. The adsorption equilibrium was fitted according to Langmuir, Freundlich and Temkin isotherms.     

Agave sisalana,a biosorbent for the adsorption of Reactive Red 120 from aqueous solution

The textile industry is one of the largest producers of dye effluent. Treatment of these effluents has to be cost effective hence a number of precursors have been studied as a viable alternative adsorbent. Sisal fibre was converted to activated carbon by chemical methods. Sisal fibre was activated with different activating agents such as H₃PO₄, HCl, HNO₃, NaOH and KOH. The adsorption of Reactive Red 120 (RR 120) dye onto sisal fibre activated carbon (SFAC) from aqueous solution was investigated. Adsorption experiments were carried out at different dye concentrations, initial solution pH and carbon dosage. Batch adsorption studies were carried out using activated carbon produced using phosphoric acid yielded better carbon as it good results in terms of Methylene Blue number and Iodine number. These carbons were used to study the batch adsorption studies. Methylene Blue number and Iodine number of SFAC were found to be 240 mg/g and 855 mg/g, respectively. The BET surface area of the carbon was 885 m²/g. The batch experiments adsorption isotherm studies fitted well to Langmuir isotherm and the adsorption capacity was found to be 110 mg/g. Adsorption kinetics data were tested using pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption data followed a pseudo-second-order reaction.     

Adsorption of carotenes and phosphorus from palm oil onto acid activated bleaching earth: Equilibrium,kinetics and thermodynamics

In this work, the adsorption of carotenes and phosphorus from crude palm oil onto acid activated bleaching earth was investigated under bleaching conditions, i.e. high temperature (90, 105 and 115 °C) and low pressure (less than 50 mbar). Bleaching earth was added to palm oil in a range of 0.5–3.0 wt%. Results presented in this work suggest that adsorption of β-carotene increases with temperature, while phosphorus adsorption was less affected. Both the pseudo-first-order and the pseudo-second-order kinetic model describe efficiently the β-carotene experimental data. Intra-particle diffusion is involved in β-carotene adsorption mechanism, although it is not the sole rate limiting step in the adsorption onto acid activated bleaching earth. Phosphorus adsorption was too fast resulting in a lack of kinetic data. The equilibrium data were described better by Langmuir and Freundlich models, for β-carotene and phosphorus, respectively. A multi-component Freundlich type isotherm was tested. Its competition coefficients were too low, and it assumed the same form as the monocomponent Freundlich. A thermodynamic study demonstrated that β-carotene and phosphorus adsorption is spontaneous, endothermic and an entropy-driven process. Isosteric heat values suggest that the interactions between adsorbate and adsorbent are heterogeneous.     

Kinetics of selective adsorption of impurities from a crude vegetable oil in hexane to activated earths and carbons

In this study, the selective removal of several impurities (chlorophylls and pheophytins, carotenoids, free fatty acids and oxidation products) from a solution of crude olive residue oil in n-hexane (miscella) by batch adsorption to different materials was investigated. The following adsorbents were tested: activated diatomaceous earths, powdered and granulated activated carbons. For the majority of the adsorbents used, both Freundlich and Langmuir isotherm models showed a good fit to the adsorption of pigments, free fatty acids (FFA), conjugated hydroperoxides (HP), and final oxidation products (FOP). Sigmoid profiles were observed for the adsorption of chlorophylls, carotenoids, and FOP to the 20-60 mesh carbon, suggesting the presence of pores in the intermediate range (2-50 nm). The FFA isotherm adsorption to the 8-20 mesh carbon can be explained by a multilayer adsorption phenomenon. On the basis of the estimated values for affinity and separation factors, the selective adsorption occurred in the following order for every adsorbent tested: chlorophylls and pheophytins>carotenoids>hydroperoxides>final oxidation products>free fatty acids. The highest adsorption efficiency was observed for the powdered activated carbon.     

大孔树脂间歇和连续吸附纯化花生壳黄酮过程的研究

以AB-8型大孔树脂为吸附剂,纯化花生壳黄酮提取物。通过对花生壳黄酮间歇和连续吸附过程的研究,并用吸附模型对间歇吸附过程进行模拟,发现Langmuir方程和Freundlich方程可以模拟吸附过程。通过对间歇吸附和连续吸附的研究,得到合适的工艺条件,将花生壳黄酮粗提物的纯度从38.08%,提高到52.57%,花生壳黄酮提取物得率为61.70%。表明AB-8型大孔树脂吸附纯化花生壳总黄酮是可行的。     

多磺酸基直接染料在甲壳胺纤维上的吸附

探讨不同温度下甲壳胺纤维对含有6个磺酸基的直接橙39的吸附性能,运用3种吸附理论模型即Langmuir、Freundlich和Redlich-Peterson吸附方程对实验数据进行拟合,对获得的3种理论吸附模型的吸附参数及正规偏差(ND)进行比较。结果表明不同温度下,Freundlich吸附模型偏离实验点的程度较大,而Redlich-Peterson吸附模型最符合甲壳胺纤维对直接橙39的吸附行为,同时伴有吸热现象出现。     

Removal of endosulfan and methoxychlor from water on carbon slurry

A carbon slurry, produced in generators of fuel-oil-based industrial generators was converted into an effective and efficient adsorbent for the removal of endosulfan and methoxychlor from aqueous solution. The adsorbent was chemically treated, activated, characterized, and used for the adsorption of endosulfan and methoxychlor pesticides. The maximum adsorption was found at 90 min, 6.5 pH, 0.025 g/L dose, and 25 degrees C temperature. Langmuir and Freundlich adsorption models were applied to analyze adsorption data, and the former was found applicable to this adsorption system in terms of relatively high regression values. The thermodynamic aspect of the process was also investigated by evaluating certain important parameters (enthalpy, free energy, and entropy of system). Kinetics of adsorption was found to follow the pseudo second order rate equation. The diffusion of pesticides into carbon slurry pores was suggested to be the rate controlling step by applying Bangham's equation. Adsorption on a column was also investigated in a continuous flow system. Adsorption efficiencies of endosulfan and methoxychlor were 34.11 and 36.06 mg/g in batch processes and 32.62 and 33.52 mg/g in column operations, respectively.     

皮芯复合离子交换纤维的吸附性能

测定自制皮芯复合离子交换纤维对Zn2+、Cu2+的静态吸附量,研究纤维对Zn2+、Cu2+吸附动力学以及影响吸附性能的主要因素,探讨该纤维材料的化学稳定性和使用再生性能,结果表明：该离子交换纤维对Cu2+、Zn2+吸附的主控步骤为液膜扩散,在实验的浓度范围内(0.005～0.2 mol/L),纤维对这2种金属离子的吸附均属单分子层吸附,其等温吸附可以用Langmuir和Freundlich方程来描述,该纤维对Cu2+、Zn2+吸附速率快,最大吸附量均超过2mmol/g,最佳pH值为8.0～9.0左右,有良好的吸附性能和使用稳定性。     

Heat-treated wood as chromium adsorption material

Heavy metals adsorption with lignocellulosic materials has been heavily researched in the last years. Since heat activation has been used with good results to increase the adsorption capacity of some materials, heat-treated wood might be a better adsorbent. This hypothesis is the basis of the present study. The adsorption tests were made with powdered pine wood, heat-treated at 190–210?°C. All the heat-treated samples showed a significantly higher adsorption compared to untreated wood. The maximum adsorption was obtained at pH 3 for heat-treated wood at 210?°C. The kinetics of the adsorption process fitted a pseudo-second-order reaction (R² 0.990–0.996). Adsorption fitted well both the Langmuir and the Freundlich model, but the Freundlich model presented higher R² (0.988–0.998). The q_max values estimated by the Langmuir plotting were in the range 15.6–19.4 mg/g and the n values from Freundlich isotherms between 1.87 and 2.39. Heat-treated wood was a better adsorption material than untreated wood for chromium adsorption. This can be a good application for the sawdust produced by the processing of heat-treated wood at primary and secondary wood processing mills or for the recycling of heat-treated wood at the end of product life.     

Removal of methylene blue from aqueous media using activated carbon web

Activated carbon web is prepared by controlled pyrolysis of acrylic fibrous waste under the layer of charcoal using physical activation in high-temperature furnace. The carbonization was carried out at 1200 °C under different heating rate (i.e. 150 to 450 °C h^?1) with different holding time (i.e. 0 to 60 min) to decide optimum pyrolysis parameters. The heating rate of 300 °C h^?1 with no holding time revealed higher specific surface area of 280 m² g^?1. The prepared activated carbon web was later employed as adsorbent for removal of methylene blue from aqueous media. The effect of initial dye concentration, adsorbent dosage, stirring speed, and pH of solution was studied. The obtained results were later compared with adsorption isotherms (i.e. Langmuir and Freundlich). The Freundlich model was found to fit closely with results due to heterogeneous adsorption of dye molecules. Finally, virgin activated carbon and dye adsorbed activated carbon were tested for desorption behavior using differential scanning calorimetry and thermo gravimetric analysis. The significant reduction in desorption enthalpy from 172.46 to 52.43 J g^?1 is attributed to less adsorption energies of dye molecules on the surface of activated carbon due to nonhomogeneous distribution of active sites.     

Removal of dark colored compounds from date syrup using activated carbon: A kinetic study

Dark colored compounds in date syrup have been removed using powdered activated carbon (PAC) at different operating conditions including different temperatures (30, 40, 50 and 60 °C), as well as different PAC concentrations (0.04, 0.06, 0.08, 0.1 and 0.12 g ml⁻¹). Adsorption isotherms of Langmuir, Freundlich, Tempkin and Harkins–Jura were selected to fit the equilibrium data at different operating temperatures. The isotherms were correlated based on the absorbance intensity and the concentration of a colored compound, which gives the same absorbance intensity as the real date syrup. Among the adsorption models, the Langmuir isotherm best fitted the experimental data with coefficient of 0.99. To study the adsorption kinetics, the pseudo-first order and the pseudo-second order models were evaluated to fit the experimental data. The pseudo-second order equation fitted the experimental data very well.     

Synthesis and Applications of Functional Polymers from Natural Okra Fibers for Removal of Cu(II) Ions from Aqueous Solution

Functional groups (?COOCH₃ and ?NH₂) in natural okra fiber had been introduced by free radical graft polymerization of methyl methacrylate (MMA) and acrylamide (AAm) from their binary solution using ascorbic acid/H₂O₂ as a redox initiator at a temperature of 45°C for 90 min. Factors affecting the grafting of lignocellulosic fiber such as feed molarity and comonomer composition were investigated. The grafted copolymers were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM-EDX), and thermogravimetric analysis (TGA). Functional groups were tested for their potential application in the removal of copper ions from aqueous solutions. Batch experiments were performed to evaluate the adsorption capacity of the maximum grafted cellulosic fibers toward the Cu (II) ions. Pseudo-first-order and pseudo-second-order kinetic models were studied to analyze the Cu²⁺ adsorption process and results showed that the pseudo-second-order model was more suitable than the pseudo-first-order model. Further, Langmuir, Freundlich, and Tempkin models were also applied to describe the adsorption isotherm of Cu²⁺ by different fiber adsorbents. The results indicate that the Langmuir model fitted the adsorption equilibrium data better than other two models. The maximum monolayer capacity q_m calculated using the Langmuir isotherm for raw and MMA+AAm grafted fiber were 4.89 and 33.05 mg/g, respectively.     

Adsorptive Removal of Patulin from Apple Juice Using Ca‐Alginate‐Activated Carbon Beads

This study aimed to investigate the adsorption of patulin from apple juice by Ca‐alginate‐activated carbon (Ca‐alginate‐AC) beads. The capacity of patulin was determined by high‐performance liquid chromatography. The results showed that Ca‐alginate‐AC beads have significant ability to reduce patulin from contaminated apple juice. Furthermore, the adsorption process did not affect the quality of apple juice. The effects of contact time, initial patulin concentration, adsorbent dose, and temperature were assessed. The removal percentage of patulin increased with contact time, adsorbent dose, and temperature. A reduction was also noted to bind patulin at increased levels of contamination. The equilibrium data were fitted to Langmuir, Freundlich, and Temkin isotherm models and the isotherm constants were calculated at different temperatures. The adsorption equilibrium was best described by the Freundlich isotherm (R² > 0.990). The pseudo 1st‐order model was found to describe the kinetic data satisfactorily. Thermodynamic parameters such as standard Gibbs free energy (ΔG??), standard enthalpy (ΔH?), and standard entropy (ΔS?) were evaluated. The results showed that the adsorption was spontaneous and endothermic nature.     

珍珠纤维直接染料染色热力学

选用直接湖蓝5B(C.I.直接蓝15)对珍珠纤维和普通粘胶散纤维进行染色,比较了Freundlich、Langmuir和Redlich-Peterson 3种吸附模型对实验数据的模拟结果,探讨了染色温度对3种吸附模型吸附常数的影响。结果表明:Langmuir吸附模型比Freundlich更适合于描述C.I.直接蓝15在珍珠纤维和普通粘胶纤维上的吸附,但C.I.直接蓝15在珍珠纤维和普通粘胶纤维上的吸附最适合用Redlich-Peterson热力学吸附模型来描述;随着染色温度的升高,C.I.直接蓝15在珍珠纤维和普通粘胶纤维的Redlich-Peterson吸附常数KR降低,吸附常数aR和异质因子β变化不明显。     

Removal of Cr(VI) from aqueous solutions by modified walnut shells

Walnut shell (WNS) (Juglans regia) has been utilised as an adsorbent for the removal of Cr(VI) ions from aqueous solutions after treatment with citric acid. The modification reaction variables, such as citric acid level (5-10 g), reaction time (0-24 h), and temperature (110-130 °C) were studied in batch experiments. The rate of adsorption was studied under a variety of conditions, including initial Cr(VI) concentration (0.1-1.0 mM), amount of adsorbent (0.02-0.20 g), pH (2-9), temperature and contact time (10-240 min). Adsorption of Cr(VI) is in all cases pH-dependent showing a maximum at equilibrium pH values between 2.0 and 3.0 for citric acid modified walnut shell (CA-WNS). The applicability of the Langmuir, Freundlich and D-R adsorption isotherms has been tested for the equilibrium. Maximum adsorption capacities of CA-WNS and untreated WNS under experimental conditions were 0.596 and 0.154 mmol/g for Cr(VI) ions, respectively.     

ADSORPTION of BILE ACIDS ON CEREAL TYPE FOOD FIBERS

A study involving measurement and analysis of adsorption of common bile acids, namely cholic, deoxycholic, and lithocholic acids, on cereal type dietary fibers was conducted. the selected food fibers were oat fiber, rice fiber, barley fiber, corn bran, and wheat bran, which are all extensively used in processed foods. the adsorption data were measured at 37C and 25C, which correspond to approximate human body and room temperatures. Influence of particle size reduction, due to grinding, on a fiber's bile acid binding capacity was examined by using macro size (35–60 mesh) and micro size (100–300 mesh) fibers as adsorbents. the investigation also included the effects of medium pH and the chemical composition. the experimental data were correlated with the Langmuir and the Freundlich isotherms in order to utilize the data in future predictions and simulations.
It was found that the particle size reduction, accompanied by surface area increase, has a significant influence on the adsorption capacity of the fiber. Macro size fibers adsorbed the same bile acid with the following trend: oat > barley > rice > wheat > corn; while micro size fibers followed a somewhat different trend: rice > barley > oat > wheat > corn. This was due to the surface area change after grinding, and a positive correlation between the surface area and the adsorption capacity was observed in each case. the adsorption was favored by acid pH surroundings, and it was positively correlated with the hydrophobicity of the bile acid. were adsorbed on the same fiber with the following trend: lithocholic acid > deoxycholic acid > cholic acid. Fibers adsorbed more bile acid at 25C than they did at 37C. However, the increase in the uptake capacities were not very signipcant.     

Removal of hexavalent chromium from wastewater using a new composite chitosan biosorbent

A new composite chitosan biosorbent was prepared by coating chitosan, a glucosamine biopolymer, onto ceramic alumina. The composite bioadsorbent was characterized by high-temperature pyrolysis, porosimetry, scanning electron microscopy, and X-ray photoelectron spectroscopy. Batch isothermal equilibrium and continuous column adsorption experiments were conducted at 25 degrees C to evaluate the biosorbent for the removal of hexavalent chromium from synthetic as well as field samples obtained from chrome plating facilities. The effect of pH, sulfate, and chloride ion on adsorption was also investigated. The biosorbent loaded with Cr(VI) was regenerated using 0.1 M sodium hydroxide solution. A comparison of the results of the present investigation with those reported in the literature showed that chitosan coated on alumina exhibits greater adsorption capacity for chromium(VI). Further, experimental equilibrium data were fitted to Langmuir and Freundlich adsorption isotherms, and values of the parameters of the isotherms are reported. The ultimate capacity obtained from the Langmuir model is 153.85 mg/g chitosan.     

Removal of chlorophenols from wastewater using red mud: an aluminum industry waste

Removal of toxic substances from wastewaters using low-cost alternatives to activated carbon is an important area in environmental sciences. Efforts have been made to convert red mud, an aluminum industry waste, into a low-cost potential adsorbent, and the final material has been used for the removal of phenol, 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol from wastewater. It is pertinent to mention that phenol and chlorophenols are highly carcinogenic and an priority class of pollutants which needs to be removed from effluents before discharge into water bodies. 2,4-Dichlorophenol and 4-chlorophenol are sorbed by the developed adsorbent up to 94-97%, while the removal of 2-chlorophenol and phenol was up to 50-81%. The removal of phenols and its derivatives was achieved up to 98% by column experiments at a flow rate of 0.5 mL/min. The order of removal was 2,4-dichlorophenol > 4-chlorophenol > 2-chlorophenol > phenol, and the removal takes place through a particle diffusion mechanism. The adsorption was found to be endothermic in nature and follows both Langmuir and Freundlich models. Estimation of the phenols was carried out by capillary electrophoresis, and the adsorbent has been successfully tried for the removal of chlorophenols from a wastewater. The developed process is very useful, economic, rapid, and reproducible for the removal of phenols.     

Decolorization of melanoidin by activated carbon obtained from bagasse bottom ash

A synthetic melanoidin is used as a model for the colorant in sugar syrup to study the mechanism of adsorption on activated carbon (AC) obtained from bagasse bottom ash (BBA). The equilibrium adsorption capacities, fitted with Langmuir and Freundlich models increased with increasing temperatures. Thermodynamic parameters for BBA–AC indicate that the adsorption process is endothermic and spontaneous. No new peaks or no peak shifts were observed in IR spectra as a result of adsorption of the melanoidin on BBA–AC. This indicates a physical adsorption mechanism, which was confirmed by the fact that the melanoidin could be completely desorbed by distilled water. Overall, 8.3 kg BBA–AC was able to reduce melanoidin concentration from 100 mg l⁻¹ to ?10 mg l⁻¹ in 1 m³ effluent.