Adsorption characteristics of toxic chromium(VI) from aqueous media onto nanosized silver nanoparticles-treated activated carbon

The present study reports the use of nanomaterial, e.g. Ag nanoparticles (AgNPs), immobilized activated carbon as an effective solid adsorbent for removal of toxic chromium(VI) from water. Chromium(VI) uptake was found favorable in acidic media at pH ≤ 3. Based on Langmuir model, monolayer adsorption capacities of chromium(VI) found equal 93.5 mg/g. The results fitted well with pseudo second-order and Langmuir models. The mechanism of adsorption was explored using the intra-particle diffusion model and the liquid-film model. Chromatographic separation of chromium(VI) was achieved. The AC-AgNPs was successfully recycled for five successive adsorption–desorption cycles indicating its high reusability.     

Adsorption of lead(II) from aqueous solution by activated carbon prepared from Eichhornia

Activated carbon prepared from Eichhornia was used for the adsorptive removal of Pb(II) from aqueous solution. As the raw material for the preparation of the activated carbon is an aquatic weed, the production of this carbon is expected to be economically feasible. Parameters such as agitation time, metal ion concentration, adsorbent dose and pH were studied. Adsorption equilibrium was reached in 100 min for a solution containing 15 mgdm^?3 and 125 min for solutions containing 20 and 25 mgdm^?3 Pb(II), respectively. Adsorption parameters were determined using both Langmuir and Freundlich isotherm models. The adsorption capacity was 16.61 mgg^?1 at pH 3.0 for particle sizes of 125–180 µm. Pb(II) removal increased as the pH increased from 2 to 4 and remained constant up to pH 10.0. Desorption studies were also carried out with dilute hydrochloric acid to recover both carbon and Pb(II). Quantitative desorption of Pb(II) from carbon indicates that adsorption of metal ion is by ion exchange. © 2002 Society of Chemical Industry     

Adsorption of flavour esters on granular activated carbon

This article reports on the liquid phase adsorption of flavour esters onto granular activated carbon. Ethyl propionate, ethyl butyrate, and ethyl isovalerate were used as adsorbates, and Filtrasorb 400 activated carbon was chosen as the adsorbent. Sips, Toth, Unilan, and Dubinin‐Radushkevich isotherm equations which are generally used for heterogeneous adsorbents were used to fit the data. Although satisfactory in fitting the data, inconsistency in parameter values indicated these models to be inadequate. On the other hand the Dubinin‐Radushkevich model gave more consistent and meaningful parameter values and adsorption capacities. By employing the Dubinin‐Radushkevich equation, the limiting volume of the adsorbed space, which equals the accessible micropore volume, was determined, and found to correlate with the value from carbon dioxide adsorption.     

活性炭对苯酚的吸附研究

进行了活性炭处理含苯酚废水的应用研究,考察了影响苯酚吸附效果的因素。确定了处理水中苯酚的最佳条件:吸附平衡时间为30 min;最佳pH值为6左右;苯酚初始浓度为10 mg/L;投炭量为20～25 mg/L;苯酚的吸附率高达97.4%;温度对苯酚吸附率的影响不明显。研究了活性炭对苯酚的吸附动力学特性,分别用伪一级动力学方程、伪二级动力学方程、修正伪一级动力学方程和颗粒内扩散模型进行拟合,对于不同浓度的苯酚废水都只有伪二级动力学方程拟合程度比较高,伪二级动力学方程更为真实地反映苯酚在活性炭上的吸附机理。     

活性炭处理含铬废水的方法

活性炭具有优良的吸队性和还原性，已广泛用于废水处理工业，阐述了活性炭处理含铬废水的基本原理，采用吸附－还原联用处理含铬废水，介绍了其工艺流程、特点及处理过程中的注意事项。实践证明，经处理的废水中六价铬含量达国家排放标准。     

花生壳制活性炭及其脱六价铬研究

本文研究了用花生壳制备活性炭和用此活性炭去除水溶液中的Cr（Ⅵ）。采用化学活化法,即用H2SO4、H3PO4、ZnCl2、KOH活化花生壳中的炭。同时研究了这些活化剂的浓度和用量、热解时间和温度对活性炭性能的影响。采用亚甲基蓝吸附实验评价活性炭的性能。结果表明H3PO4和ZnCl2是良好的活化剂,KOH和H2SO4效果较差。溶液的pH值对活性炭吸附Cr（Ⅵ）的能力有很大影响。活性炭的吸附能力随着pH值的降低而升高,同时在不同的pH值下,炭的吸附速率也不同。pH值越低,Cr（Ⅵ）被吸附的越快。等温实验结果表明,在pH值等于2时,用H3PO4和ZnCl2活化的活性炭对Cr（Ⅵ）的吸附能力分别达到125．0和83．3mg·g^-1。花生壳活性炭吸附Cr（Ⅵ）的机理比较复杂,与溶液的pH值有关。在pH值等于2时,等温吸附可以用Langmuir模型模拟;在pH值等于2～7时,可以用Freundlich模型模拟。     

Use of activated carbon for the recovery of chromium from industrial wastewaters

A technique for the removal and recycling of hexavalent chromium from electroplating industries was developed. It involves a two-phase process which consists of (1) the use of an activated carbon bed for the accumulation of chromium onto the surface of activated carbon followed by (2) the regeneration of the carbon leading to a concentrated chromium solution with potential for reclamation or reuse within the plating operation. Results from continuous flow experiments showed that in excess of 99% chromium removal efficiency can be achieved. It was also revealed that regeneration of the exhausted carbon under acidic conditions recovered chromium in the trivalent state with concentrations as high as 3 g dm⁻³, more than 12 times the influent concentration. The adsorption capacity of the activated carbon was found to increase with successive cycles of adsorption/regeneration. However, when regeneration was achieved under alkaline conditions, the chromium was recovered in the hexavalent state with concentrations as high as 8·4 g dm⁻³, in excess of 33 times the chromium influent concentration. In addition, under caustic regeneration conditions, the data showed that the adsorption capacity in this case decreases with the increased number of exhaustion cycles. Mass balance calculation for both acid and caustic regeneration indicated that in both cases the regeneration process was incomplete with a recovery efficiency averaging around 50%. In an attempt to maximise the recovery efficiency, a combination of caustic followed by acid regeneration was applied to the exhausted activated carbon and the results led to a drastic improvement in the total recovery process (85–98%). These results clearly show that activated carbon is a viable candidate for the removal and recovery of chromium from electroplating industries. The critical advantage in the use of activated carbon is (1) the ability to regenerate and thus prepare a concentrated chromium solution for potential reclamation or recycle to the plating operation, and (2) the potential of avoiding the generation of hazardous sludge for land disposal. ©1997 SCI     

Cadmium and zinc adsorption onto activated carbon: Influence of temperature,pH and metal/carbon ratio

The adsorption characteristics of cadmium and zinc onto a granular activated carbon were studied. Cadmium and zinc removals increased on raising pH and temperature, and decreased on raising the molar metal/carbon ratio. The adsorption processes were modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with an overall bidentate species. A dependence of the SCF constant on pH, the molar metal/carbon ratio and temperature was observed, and a correlation for log K_ads was determined. The SCF model successfully predicted cadmium and zinc removals.     

Adsorption of chromium by activated carbon from aqueous solution

Adsorption isotherms of Cr(III) and Cr(VI) ions on two samples of activated carbon fibres and two samples of granulated activated carbons from aqueous solutions in the concentration range 20–1000 mg/l have been studied. The adsorption isotherms have been determined after modifying the activated carbon surfaces by oxidation with nitric acid, ammonium persulphate, hydrogen peroxide and oxygen gas at 350°C and after degassing at different temperatures. The adsorption of Cr(III) ions increases on oxidation and decreases on degassing. On the other hand, the adsorption of Cr(VI) ions decreases on oxidation and increases on degassing. The increase of Cr(III) and the decrease of Cr(VI) on oxidation and the decrease of Cr(III) and the increase of Cr(VI) on degassing have been attributed to the fact that the oxidation of the carbon surface enhances the amount of acidic carbon–oxygen surface groups while degassing eliminates these surface groups. Thus while the presence of acidic surface groups enhances the adsorption of Cr(III) cations, it suppresses the adsorption of Cr(VI) anions.     

活性炭纤维吸附废水中酚的研究

通过静态和动态试验对活性炭纤维吸附废水中的酚进行了研究,测定了吸附等温线,考察了活性炭纤维的用量、苯酚浓度,以及过柱流速对吸附的影响.结果表明,活性炭纤维对苯酚的动态吸附容量为256 mg/g随着活性炭纤维用量的增加,处理水稳定时间延长;苯酚浓度越高,穿透时间越短;过柱流速越大,穿透时间越短;吸附饱和后的活性炭纤维再生后,吸附容量几乎不变.     

热改性活性炭吸附有机气体的性能

根据热重分析结果,确定了活性炭热改性的温度条件;采用Boehm滴定、傅式转换红外光谱仪（FTIR）、比表面积分析仪对活性炭表面物化性质进行了测试;以甲苯、丙酮、二氯乙烷、甲醇为吸附质,在283K下进行了固定床吸附实验,探讨了改性前后活性炭表面结构变化与吸附量之间的关系,同时计算了相应的动力学参数和吸附能。实验结果表明,热改性可以改善活性炭的孔径分布和改变表面官能团的分布,吸附量与有效孔容呈明显的线性关系;一阶动力学方程和二阶动力学方程均可描述四种吸附质在活性炭上的吸附过程;孔内扩散模型表明改性活性炭对有机气体的吸附速率均大于未改性活性炭;四种吸附质在活性炭上的吸附能均小于20kJ?mol-1,表明活性炭对四种有机气体以物理吸附为主。     

Mechanisms of Cr(VI) removal from water by various types of activated carbons

The removal mechanisms of Cr(VI) from water using different types of activated carbons, produced from coconut shell, wood and dust coal, were investigated in this project. Different types of activated carbons have different surface characteristics. The coconut shell and dust coal activated carbons have protonated hydroxyl groups on the surface (H‐type carbons), while the surface of the wood‐based activated carbon has ionised hydroxyl groups (L‐type carbons). The adsorption kinetics of chromium onto the activated carbons at pH values ranging from 2 to 6 were investigated. It was found that the optimum pH to remove total chromium was 2 for wood‐based activated carbon, while for coconut shell and dust coal activated carbons, the optimum pH was around 3–4. The difference in the optimum pH for different activated carbons to remove Cr(VI) from water can be explained by the different surface characteristics and capacity of the activated carbons to reduce Cr(VI) to Cr(III). © 1999 Society of Chemical Industry     

Anthracene removal from water onto activated carbon derived from vehicular tyre

The present study focuses on adsorptive removal of anthracene by application of activated carbon developed from waste vehicular tyres (VTAC). Different experimental parameters were varied to examine their influence on anthracene adsorption. The results reveal that concentration of anthracene in aqueous phase reduces continuously with enhancement in shaking time. After a period of 75 min, the adsorption of anthracene on VTAC was observed to be in equilibrium. The adsorption of anthracene was >99% in presence of 14–20 mg and an adsorbent dose of 8 mg was used to analyse the effect of other parameters in the present study. As pH of solution is lowered, rise in adsorption capacity of VTAC was observed. The obtained data were applied to Langmuir and Freundlich isotherms for studied PAH adsorption. The second order kinetics was suggested to be better fitted with R² values >0.95. Intra-particle diffusion and Boyd-Reichenberg model were applied for investigating the mechanism of adsorption.     

水中Ni~(2+)在粒状沸石/活性炭复合材料上的吸附研究

采用廉价的煤矸石为主要原料,添加一定量的沥青粉制备了沸石NaA/活性炭粒状复合材料,并以此作为吸附剂,研究了水溶液中Ni~(2+)在该复合材料中的吸附行为,考察溶液的初始浓度、吸附时间和pH对吸附的影响.结果表明溶液较高的pH值有利于Ni~(2+)在吸附剂上的吸附;随Ni~(2+)初始浓度的增大复合材料的吸附量增大,而Ni~(2+)的去除率随之减小;Ni~(2+)在复合材料上的吸附接近Langmuir-Freundlich等温吸附模型,反映了吸附表面的多相性及两类吸附中心在复合材料上的共存性;吸附速率遵循准二级吸附动力学模型.     

含碱性表面基团活性炭去除Cr(Ⅵ)的研究

介绍了用氧化剂和高温处理制取含碱性表面基团活性炭的方法，测定了它们的离子交换空量。研究了溶液pH和Cr(Ⅵ）的初始浓度对Cr（Ⅵ）去除率的影响。讨论了含碱性表面基团活性炭对溶液中Cr(Ⅵ）的去除机理。     

Adsorption of cationic dye from aqueous solutions by activated carbon

Batch sorption experiments were carried out to remove a cationic dye, methylene blue (MB), from its aqueous solutions using a commercial activated carbon as an adsorbent. Operating variables studied were pH, stirring speed, initial methylene blue concentration and temperature. Adsorption process was attained to the equilibrium within 5 min. The adsorbed amount MB dye on activated carbon slightly changed with increasing pH, and temperature, indicating an endothermic process. The adsorption capacity of methylene blue did not significantly change with increasing stirring speed. The experimental data were analyzed by various isotherm models, and found that the isotherm data were reasonably well correlated by Langmuir isotherm. Adsorption measurements showed that the process was very fast and physical in nature. Thermodynamic parameters such as the adsorption entropy (ΔS^o) and adsorption enthalpy (ΔH^o) were also calculated as 0.165 kJ mol⁻¹ K⁻¹ and 49.195 kJ mol⁻¹, respectively. The ΔG^o values varied in range with the mean values showing a gradual increase from −0.256 to −0.780 to −2.764 and −7.914 kJ mol⁻¹ for 293, 313, 323 and 333 K, respectively, in accordance with the positive adsorption entropy value of the adsorption process.     

Adsorption of fulvic acids from aqueous solutions by carbon nanotubes

Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g^?1 at 5 °C and equilibrium concentration of 18 mg dm^?3. The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (ΔG⁰), standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰), have been obtained. Acidic conditions (pH = 2–5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm^?3). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions. Copyright © 2007 Society of Chemical Industry     

Adsorption of thiram from aqueous solution on activated carbon and sepiolite

Adsorption of thiram on activated carbon and acid-heat treated sepiolite from aqueous solution at 10° C, 20° C, 30° C and 40° C has been studied. The adsorption isotherms may be classified as L type of the Giles classification which suggests that there is no strong competition from the solvent for adsorption sites. The experimental data points have been fitted to the Langmuir equation in order to calculate the adsorption capacities of the solids as well as their surface areas available to the thiram molecules. The removal efficiency (P) has been calculated for both adsorbents resulting that activated carbon is more effective (P = 98–100%) in removing thiram from aqueous solution than acid-heat treated sepiolite (P = 14–52%).     

Adsorption of phenol,cresol isomers and benzyl alcohol from aqueous solution on activated carbon at 278, 298 and 323 K

Adsorption of phenol, o-, m-, p-cresol and benzyl alcohol has been measured from their aqueous solutions on activated carbon at 278, 298 and 323 K in their complete solubility range. An anomalous temperature dependence of adsorption of these compounds has been observed. Desorption measurements at 278 K show that the adsorption is not reversible in the lower concentration range. This behaviour, as well as the anomalous temperature dependence, has been attributed to chemical transformations which the adsorbed species undergo on the activated carbon surface. © 1998 SCI.