Adsorption of phenol by bentonite

The potential of bentonite for phenol adsorption from aqueous solutions was studied. Batch kinetics and isotherm studies were carried out to evaluate the effect of contact time, initial concentration, pH, presence of solvent, and the desorption characteristics of bentonite. The adsorption of phenol increases with increasing initial phenol concentration and decreases with increasing the solution pH value. The adsorption process was significantly influenced by the solvent type in which phenol was dissolved. The affinity of phenol to bentonite in the presence of cyclohexane was greater than that in water and was lowest in the presence of methanol. Methanol was used to extract phenol from bentonite. The degree of extraction was dependent on the amount of phenol adsorbed by bentonite. X-ray diffraction analysis showed that the crystalline structure of bentonite was destroyed when cyclohexane was used. The ability of bentonite to adsorb phenol from cyclohexane decreased as the water to cyclohexane ratio was increased. Furthermore, hysteresis was observed in phenol desorption from bentonite in aqueous solutions. The equilibrium data in aqueous solutions was well represented by the Langmuir and Freundlich isotherm models. The removal of phenol from aqueous solutions was observed without surface modification.     

Enhanced removal of pentachlorophenol by a novel composite: nanoscale zero valent iron immobilized on organobentonite

Nanoscale zero valent iron (NZVI) was immobilized on the organobentonite (CTMA-bent), so as to enhance the reactivity of NZVI and prevent its aggregation. This novel composite (NZVI/CTMA-Bent) was characterized by transmission electron microscope and X-ray diffraction. Good dispersion of NZVI particles on the bentonite was observed. Its performance on removing pentachlorophenol (PCP) was investigated by batch experiments. Results showed NZVI/CTMA-Bent could rapidly and completely dechlorinate PCP to phenol with an efficiency of 96.2%. It was higher than the sum (54.5%) of reduction by NZVI (31.5%) and adsorption by CTMA-Bent (23.0%) separately. The kinetic studies indicated the removal rate of PCP was positively related to the adsorption. We proposed that the adsorption of PCP by CTMA-Bent enhanced the mass transfer of PCP from aqueous to iron surface. Besides, NZVI/CTMA-Bent exhibited good stability and reusability, and CTMA-Bent could also reduce the amount of iron ions released into the solution.     

铁基膨润土对水中磷酸根的吸附热力学及动力学研究

采用铁盐改性制得铁基膨润土,研究了其对水中磷酸根的吸附性能及影响因素,结果表明,通过对膨润土的改性提高了磷的去除率,含磷废水初始pH值的大小对磷的去除率影响不大,初始浓度越低越有利于磷的去除。磷的去除率随改性膨润土的投加量增大而提高,随温度升高而增大。进一步研究表明,改性膨润土对磷的吸附是吸热反应,其吸附等温线可采用Langmuir等温吸附方程拟合;改性膨润土对磷的吸附是快速吸附,在20 min内,磷去除率达70%以上,符合准二级吸附动力学模型。     

纳米有机膨润土对苯酚的吸附性能研究

通过对天然膨润土改性,制备纳米有机膨润土并用于吸附苯酚,探讨了吸附时间、溶液pH、纳米有机膨润土投加量等因素对苯酚吸附的影响。结果表明,吸附在5 min内快速达到平衡,溶液pH可以影响苯酚在溶液中的状态,是影响苯酚吸附性能的重要因素。纳米有机膨润土吸附苯酚的过程可用伪二级反应动力学方程来描述,伪二级吸附速率常数为1.3 g/(mg.min)。吸附等温线符合Langmuir等温方程,在25℃时,Langmuir理论最大吸附容量可达到536.32 mg/g,吸附热力学参数表明吸附过程是自发的、放热的物理吸附过程。     

Sorption kinetics and isotherm modelling of imidacloprid on bentonite and organobentonites

Bentonite was modified by quaternary ammonium cations viz. cetytrimethylammonium (CTA), cetylpyridinium (CP), rioctylmethylammonium (TOM) and pcholine (PTC) at 100% cation exchange capacity of bentonite and was characterized by X-ray diffraction, CHNS elemental analyser and Fourier transform infrared spectroscopy. The sorption of imidacloprid on organobentonites/bentonite was studied by batch method. Normal bentonite could adsorb imidacloprid only upto 19.31–22.18% while all organobentonites except PTC bentonite (PTCB), enhanced its adsorption by three to four times. Highest adsorption was observed in case of TOM bentonite (TOMB) (76.94–83.16%). Adsorption kinetic data were fitted to pseudo-first-order, pseudo-second-order and intraparticle diffusion models. For normal bentonite data were best fitted to pseudo-first-order kinetic, while for organobentonites fitted to pseudo-second-order kinetics. Sorption data were analysed using Freundlich, Langmuir, Temkin and Dubinin–Radushkevich isotherm models. Data were well fitted to Freundlich adsorption isotherm. Product of Freundlich adsorption constant and heterogeneity parameter (K_f.1/n) was in following order: TOMB (301.87) > CTA bentonite (CTAB) (152.12) > CP bentonite (CPB) (92.58) > bentonite (27.25). Desorption study confirmed hysteresis and concentration dependence. The present study showed that the organobentonite could be a good sorbent for removal of imidacloprid from natural water sample also. Percentage adsorption and Distribution coefficient (mL g^?1) value of different adsorbent was in following order: TOMB (74.85% and 297.54) > CTAB (55.78% and 126.15) > CPB (45.81% and 84.55) > bentonite (10.65% and 11.92).     

Removal of congo red from aqueous solution by bagasse fly ash and activated carbon: kinetic study and equilibrium isotherm analyses

Present investigation deals with the utilisation of bagasse fly ash (BFA) (generated as a waste material from bagasse fired boilers) and the use of activated carbons-commercial grade (ACC) and laboratory grade (ACL), as adsorbents for the removal of congo red (CR) from aqueous solutions. Batch studies were conducted to evaluate the adsorption capacity of BFA, ACC and ACL and the effects of initial pH (pH(0)), contact time and initial dye concentration on adsorption. The pH(0) of the dye solution strongly affected the chemistry of both the dye molecules and BFA in an aqueous solution. The effective pH(0) was 7.0 for adsorption on BFA. Kinetic studies showed that the adsorption of CR on all the adsorbents was a gradual process. Equilibrium reached in about 4h contact time. Optimum BFA, ACC and ACL dosages were found to be 1, 20 and 2 g l(-1), respectively. CR uptake by the adsorbents followed pseudo-second-order kinetics. Equilibrium isotherms for the adsorption of CR on BFA, ACC and ACL were analysed by the Freundlich, Langmuir, Redlich-Peterson, and Temkin isotherm equations. Error analysis showed that the R-P isotherm best-fits the CR adsorption isotherm data on all adsorbents. The Freundlich isotherm also shows comparable fit. Thermodynamics showed that the adsorption of CR on BFA was most favourable in comparison to activated carbons.     

Characterization of an adsorbed humin-like substance on an allophanic soil formed via catalytic polycondensation between catechol and glycine, and its adsorption capability to pentachlorophenol

An allophanic soil (AS) catalyzed the formation of dark-colored polymers via polycondensation reactions between catechol and glycine. The organic carbon content of the AS was increased from 0.16% to 1.3%, indicating that some of the dark-colored polymers had been adsorbed to the AS. The characteristics of the dark-colored polymers adsorbed on the AS were similar to those of a humin that is not extractable with an aqueous alkaline solution. Such a humin-like substance (HuLS) was separated from the AS by treatment with a mixture of HF and HCl. The HuLS and humic acid-like substance (HaLS), comprising the acid-insoluble fraction in the reaction mixture, were characterized by elemental analysis, size exclusion chromatography, pyrolysis-GC/MS and ¹³C NMR. However, the structural features of HaLS and HuLS had many points in common. These results suggest that HuLS-AS can be regarded as an organo-clay complex formed by the strong adsorption of HaLS to the AS. The adsorption of pentachlorophenol (PCP) to AS and HuLS-AS was examined at pH 5.5. At this pH, the zeta potential of the HuLS-AS showed a negative value. It would, therefore, be expected that pentachlorophenolate anions would adsorb with difficulty to HuLS-AS because of electrostatic repulsion. Nevertheless, the adsorption coefficient for PCP to HuLS-AS, as estimated by the Freundlich isotherm, was seven times larger than that for AS. These results show that HuLS, when adsorbed on the AS surface, has the capability to enhance the adsorption of PCP.     

Oxidized multiwalled carbon nanotubes as adsorbent for the removal of manganese from aqueous solution

A batch adsorption process was applied to investigate the removal of manganese from aqueous solution by oxidized multiwalled carbon nanotubes (MWCNTs). In doing so, the thermodynamic, adsorption isotherm, and kinetic studies were also carried out. MWCNT with 5–10-nm outer diameter, surface area of 40–600 m²/g, and purity above 95 % was used as an adsorbent. A systematic study of the adsorption process was performed by varying pH, ionic strength, and temperature. Manganese-adsorbed MWCNT was characterized by Raman, FTIR, X-ray diffraction, XPS, SEM, and TEM. The adsorption efficiency could reach 96.82 %, suggesting that MWCNT is an excellent adsorbent for manganese removal from water. The results indicate that second-order kinetics model was well suitable to model the kinetic adsorption of manganese. Equilibrium data were well described by the typical Langmuir adsorption isotherm. Thermodynamic studies revealed that the adsorption reaction was spontaneous and endothermic process. The experimental results showed that MWCNT is an excellent manganese adsorbent. The MWCNTs removed the manganese present in the water and reduced it to a permissible level making it drinkable.     

Kinetic, equilibrium isotherm and thermodynamic studies of Cr(VI) adsorption onto low-cost adsorbent developed from peanut shell activated with phosphoric acid

A particular agricultural waste, peanut shell, has been used as precursor for activated carbon production by chemical activation with H₃PO₄. Unoxidized activated carbon was prepared in nitrogen atmosphere which was then heated in air at a desired temperature to get oxidized activated carbon. The prepared carbons were characterized for surface area, surface morphology, and pore volume and utilized for the removal of Cr(VI) from aqueous solution. Batch mode experiments were conducted to study the effects of pH, contact time, particle size, adsorbent dose, initial concentration of adsorbate, and temperature on the adsorption of Cr(VI). Cr(VI) adsorption was significantly dependent on solution pH, and the optimum adsorption was observed at pH 2. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to analyze the kinetic data obtained at different initial Cr(VI) concentrations. The adsorption kinetic data were described very well by the pseudo-second-order model. Equilibrium isotherm data were analyzed by the Langmuir, Freundlich, and Temkin models. The results showed that the Langmuir adsorption isotherm model fitted the data better in the temperature range studied. The adsorption capacity which was found to increase with temperature showed the endothermic nature of Cr(VI) adsorption. The thermodynamic parameters, such as Gibb’s Free energy change (ΔG°), standard enthalpy change (ΔH°), and standard entropy change (ΔS°) were evaluated.     

皂土对CuCl2的吸附性能

研究了CuCl2在荷结构负电荷皂土上的吸附性能,考察了pH、无机以及有机添加剂等因素的影响,并结合IR和XRD实验结果探讨了吸附机理。研究表明,皂土对CuCl2有很强的吸附能力,其吸附动力学和吸附等温线分别符合准二级速率方程和Langmuir方程。初始pH增大,吸附量增加。无机以及有机添加剂均能能明显抑制吸附。Cu2+在皂土上的吸附层在微观上可分为因化学键合作用而形成的内络合层和因静电作用而形成的外络合层。     

皂土对CuCl_2的吸附性能

研究了CuCl2在荷结构负电荷皂土上的吸附性能,考察了pH、无机以及有机添加剂等因素的影响,并结合IR和XRD实验结果探讨了吸附机理。研究表明,皂土对CuCl2有很强的吸附能力,其吸附动力学和吸附等温线分别符合准二级速率方程和Langmuir方程。初始pH增大,吸附量增加。无机以及有机添加剂均能能明显抑制吸附。Cu2＋在皂土上的吸附层在微观上可分为因化学键合作用而形成的内络合层和因静电作用而形成的外络合层。     

Catalytic oxidation of pentachlorophenol in contaminated soil suspensions by Fe+3-resin/H2O2

Pentachlorophenol (PCP) is a wood preserving agent that is commonly found in contaminated soils at wood treatment sites. The catalytic properties of Fe+3-resin for the oxidation of PCP in aqueous solution and soil suspension with H2O2 were tested. Batch tests in aqueous solution were performed at various dosages of catalyst and H2O2, and reaction temperatures. The results showed that the oxidation of PCP in aqueous solution depends on the dose of H2O2 and the temperature. Essentially complete oxidation of 100 mgl(-1) PCP was obtained with 0.5% Fe+3-resin catalyst, 0.1 M H2O2 and at a reaction temperature of 80 degrees C. The oxidation of PCP achieved in three different soil suspensions was more than 94% within 30-50 min. Moreover, it was demonstrated that the same Fe+3-resin could be reused for at least six cycles of PCP oxidation in soil solutions without loss in efficiency unless the pH of the reaction falls below 5. It was proposed that the loss in used Fe+3-resin catalyst activity could be related to the leaching of Fe+3 at low pH.     

松树锯末对亚甲基蓝（MB）的吸附研究

采用松树锯末以及改性松树锯末对模拟废水中的亚甲基蓝进行吸附实验研究。研究结果表明，当亚甲基蓝的初始浓度为50 mg/L、pH为6、锯末投加量为1 g/L时，改性前后的锯末对亚甲基蓝的吸附量最大，分别为29.9 mg/g和60.6 mg/g。同时，对改性前后的锯末做了吸附等温线拟合及动力学研究。结果表明，吸附等温线均能很好地符合Langmuir吸附模式，吸附过程符合拟二级动力学方程。     

合成碳羟基磷灰石对水中双酚A的吸附性能研究

利用废弃蛋壳为原料、尿素为添加剂，合成纳米碳羟基磷灰石(CHAP)用于吸附水中双酚A（BPA）。利用红外光谱、扫描电镜和X射线能谱测试技术对CHAP样品表面化学进行了表征，同时考察了环境因子pH值、吸附时间和BPA初始浓度对吸附的影响。实验结果表明，CHAP对BPA去除率在酸性（pH=3～6）溶液中较好，而在中性和碱性环境中减弱。通过静态吸附实验数据计算分析得知，CHAP对BPA吸附符合Langmuir和Freundlich等温式，准二级动力学模型比准一级动力学模型能更好地描述CHAP对BPA吸附动力学行为。     

Sorption-desorption behaviour of 2,4-dichlorophenol by marine sediments

Batch kinetic and isotherm experiments were conducted to determine the sorption-desorption behavior of 2,4-dichlorophenol from seawater solutions by marine sediments containing various amounts of organic carbon (from 1.02% to 12.72% dry weight). The results indicated linear type isotherms for sorption and desorption in all marine sediments studied. The observed difference in linear sorption coefficients between sorption and desorption was indicative of sorption hysteresis. The kinetic experiments showed that equilibrium was established in less than 20 h. The study is significant with respect to sediment remediation in contaminated harbors and coastal areas.     

Adsorption of 2,4-dichlorophenoxyacetic acid and 4-chloro-2-metylphenoxyacetic acid onto activated carbons derived from various lignocellulosic materials

Adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-metylphenoxyacetic acid (MCPA) from aqueous solution onto activated carbons derived from various lignocellulosic materials including willow, miscanthus, flax, and hemp shives was investigated. The adsorption kinetic data were analyzed using two kinetic models: the pseudo-first order and pseudo-second order equations. The adsorption kinetics of both herbicides was better represented by the pseudo-second order model. The adsorption isotherms of 2,4-D and MCPA on the activated carbons were analyzed using the Freundlich and Langmuir isotherm models. The equilibrium data followed the Langmuir isotherm. The effect of pH on the adsorption was also studied. The results showed that the activated carbons prepared from the lignocellulosic materials are efficient adsorbents for the removal of 2,4-D and MCPA from aqueous solutions.     

炭化柚子皮对废水中双酚A的吸附

采用磷酸二氢钾活化原材料柚子皮，分别在300℃和600℃对活化后柚子皮进行炭化，制得吸附剂（CC300和CC600），通过静态吸附实验研究了炭化柚子皮对双酚A的吸附性能。采用比表面积分析仪对炭化柚子皮进行表征，实验考察了pH值、吸附时间和温度对双酚A吸附的影响，并详细研究了炭化柚子皮对双酚A的吸附行为和机理。结果表明，高温炭化柚子皮（CC600）吸附双酚A能力比低温炭化（CC300）的强，其吸附较好地满足Langmuir和Freundlich等温方程；动力学研究表明，其吸附速率快，在150min内能达到吸附平衡，准二级动力学模型较好地描述该吸附行为，相关系数高达0．99：计算了热力学参数△G、△H和△S的值,△G为负值,说明该吸附过程为自发过程。     

Removal of a cationic dye from aqueous solutions by adsorption onto bentonite clay

The ability of bentonite to remove malachite green from aqueous solutions has been studied for different adsorbate concentrations by varying the amount of adsorbent, temperature, pH and shaking time. Maximum adsorption of the dye, i.e. >90% has been achieved in aqueous solutions using 0.05 g of bentonite at a pH of 9. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated from the slope and intercept of the linear plots of ln K_D against 1/T. Analysis of adsorption results obtained at 298, 308, 318 and 328 K showed that the adsorption pattern on bentonite seems to follow the Langmuir, Freundlih and D–R isotherms. The temperature increase reduces adsorption capacity by bentonite, due to the enhancement of the desorption step in the mechanism. The numerical values of sorption free energy (E_a) of 1.00–1.12 kJ mol⁻¹ indicated physical adsorption. The kinetic data indicated an intraparticle diffusion process with sorption being first order. The rate constant k was 0.526 min⁻¹. The concentration of malachite green oxalate was measured before and after adsorption by using UV–Vis spectrophotometer.     

Zn / Al 双金属氧化物对水中硫酸根离子的吸附性能简

研究了用Zn/Al水滑石制得的Zn/Al双金属氧化物（Zn/Al-300）吸附剂对水中硫酸根离子的吸附，考查了吸附剂投加量、初始pH等因素对硫酸根离子吸附的影响。结果表明，Zn/Al-300对水中硫酸根离子的吸附符合Langmuir吸附等温方程，理论最大吸附量为62.5 mg/g。运用动力学方程进行拟合，吸附过程符合准二级动力学方程；溶液的pH影响吸附剂对硫酸根的吸附，在pH=5.5时硫酸根的去除率最大；X射线衍射结果显示，水滑石经过焙烧后丧失了原有的构形，并在吸附硫酸根离子后重新恢复水滑石的部分层状结构。吸附机制主要为Zn/Al-300从溶液中获取阴离子以重建水滑石的晶体结构，即“记忆效应”。对吸附后的双金属氧化循环应用4此后，吸附容量几乎不变，说明双金属氧化物具有可循环型。通过将Zn/Al-300与其他几种吸附剂的经济性分析，表明此吸附剂在使用过程中具有一定优势。     

Application of zeolite-activated carbon macrocomposite for the adsorption of Acid Orange 7: isotherm, kinetic and thermodynamic studies

In this study, the adsorption behavior of azo dye Acid Orange 7 (AO7) from aqueous solution onto macrocomposite (MC) was investigated under various experimental conditions. The adsorbent, MC, which consists of a mixture of zeolite and activated carbon, was found to be effective in removing AO7. The MC were characterized by scanning electron microscopy (SEM), energy dispersive X-ray, point of zero charge, and Brunauer–Emmett–Teller surface area analysis. A series of experiments were performed via batch adsorption technique to examine the effect of the process variables, namely, contact time, initial dye concentration, and solution pH. The dye equilibrium adsorption was investigated, and the equilibrium data were fitted to Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm model fits the equilibrium data better than the Freundlich isotherm model. For the kinetic study, pseudo-first-order, pseudo-second-order, and intraparticle diffusion model were used to fit the experimental data. The adsorption kinetic was found to be well described by the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process is a spontaneous and endothermic process. The SEM, Fourier transform infrared spectroscopy, ultraviolet–visible spectral and high performance liquid chromatography analysis were carried out before and after the adsorption process. For the phytotoxicity test, treated AO7 was found to be less toxic. Thus, the study indicated that MC has good potential use as an adsorbent for the removal of azo dye from aqueous solution.