硅藻土原位生长Nb2O5纳米棒及表面Cr(VI)吸附转化行为研究

以活化铌酸为铌源, 草酸铵为沉积剂, 十二烷基苯磺酸钠为模板剂, 采用水热法在硅藻土表面原位生长Nb₂O₅纳米棒。采用SEM、TEM、XRD、BET、FT-IR和XPS等分析方法对样品进行表征, 反应14 h后, Nb₂O₅纳米棒长度为500~700 nm, 直径为25~35 nm; 硅藻土原位生长Nb₂O₅纳米棒样品比表面积为157 m²/g。研究了样品对Cr(VI)的吸附与光还原行为, 可见光条件下对Cr(VI)吸附量可达220 mg/g; 紫外光条件下, 可将表面吸附的Cr(VI)转变为Cr(III), 样品经过5次循环使用后, 对Cr(VI)(100 mg/L)降解率仍能保持在93%左右。样品可对重金属污染废水中Cr(VI)进行吸附与毒性降解一体化去除。     

改性凹凸棒土吸附剂去除水中的Cr(VI)

以凹凸棒土为载体,合成了乙二胺(EDA)改性凹凸棒土(ATP)吸附剂EDA/ATP复合材料。采用FTIR、TGA对吸附剂进行表征,同时将其应用于对水中Cr(VI)的吸附,研究了溶液初始浓度、吸附时间、溶液pH、Cl?与PO₄3?阴离子浓度对吸附的影响。FTIR和TGA结果表明乙二胺已成功接枝到凹凸棒土表面。吸附实验表明,25℃时EDA/ATP复合材料对Cr(VI)的最大吸附容量为153.78 mg·g?1,吸附在800~900 min内达到平衡,吸附符合Freundlich吸附等温模型和拟二级动力学模型;在初始溶液pH为2~10条件下,随着pH的增加,吸附量先增加再降低,pH为3时,吸附量最大;Cl?对吸附影响较小,PO₄3?对吸附的影响较大,当PO₄3?浓度达到20 mmol·L?1时,Cr(VI)最大吸附量下降了83 mg·g?1;实验表明EDA/ATP可作为一种潜在处理水中Cr(VI)的吸附剂。      

纺锤形ZrO2纳米粒子的制备与生长机理研究

以ZrOCl2·8H2O和NaOH为原料,用水热法在200℃,12h下合成了单斜相纺锤形ZrO2纳米粒子,并通过改变相关实验条件,对ZrO2纳米粒子的形成机理进行了研究。利用X射线粉末衍射（XRD）、扫描电子显微镜（SEM）和电子能谱（EDS）等分析手段进行表征,结果表明,此方法合成的纺锤形ZrO2纳米粒子结晶形较好,纯度高,且能大量合成。     

C@K2Ti6O13分级纳米材料对Cr(VI)的吸附去除

Cr(VI)具有非常大的生物毒性, 去除溶液中的Cr(VI)是当前的一个研究热点。本研究制备了C@K₂Ti₆O₁₃分级纳米材料, 并用不同表征手段对材料的物相和结构等进行表征, 进一步探究了初始pH、吸附时间、离子强度等对C@K₂Ti₆O₁₃复合纳米结构吸附Cr(VI)的影响。实验结果表明C@K₂Ti₆O₁₃复合纳米结构对Cr(VI)有较强的吸附能力, 1 h内去除率能够达到50%以上, 其吸附动力学符合准二级动力学模型, 吸附热力学符合Langmuir等温吸附模型, 表明这种分级纳米材料在环境治理方面应用潜力巨大。     

TiO_2-煤系高岭土纳米复合物的制备及其吸附性能

为改性煤系高岭土,以原矿煤系高岭土和硫酸钛为原料,采用水热法合成TiO_2-煤系高岭土纳米复合物,并研究其对有机染料的吸附性能。结果表明,当染料质量浓度为100 mg/L、吸附液体积为20mL、吸附剂用量为50mg、吸附时间为60min、溶液pH=12时,TiO_2-煤系高岭土纳米复合物对阳离子型染料次甲基蓝的吸附率达到95. 5%,对阴离子型染料刚果红在中性条件下的吸附率达到98. 0%,分别比原矿提高30%和24%;复合物对2种染料的吸附均符合准二级吸附动力学模型,同时也符合Langmuir吸附等温式,属于单分子层吸附。     

以正丁醇为热液介质合成ZrO_2粉体的形貌特点

以氧氯化锆和氨水为反应原料、正丁醇为介质在热液条件下进行了合成纳米ZrO2的实验.对合成的ZrO2进行了XRD和SEM表征.结果表明,在150℃和180℃、填充度为75%的醇热实验条件下均能合成晶粒度为纳米级的氧化锆粉体;粉体是由四方相ZrO2和单斜相ZrO2组成的混合物;粉体的形貌为不规则多面体,随着反应时间的延长,晶粒沿棱柱长轴生长;在180℃条件下反应3h,长径比达到6:1.     

介孔分子筛MCM-41的制备及其对Cr6+的吸附

以鞍山铁尾矿为硅源,CTAB为模板剂,采用水热法合成出介孔分子筛MCM-41。采用XRD、BET、HRTEM对样品进行了表征。将该介孔分子筛MCM-41应用于水中Cr6+离子的吸附,研究了吸附时间、吸附剂用量、初始浓度对分子筛吸附性能的影响,并探讨了吸附过程的表观吸附动力学模型及吸附等温模型。结果表明,增加吸附时间、吸附剂用量、初始浓度有利于分子筛对Cr6+离子的吸附。Cr6+的吸附过程遵循二级表观吸附动力学模型;在吸附剂表面的吸附遵循Langmuir吸附等温线模型。     

胶原纤维对水中Cr(Ⅵ)的吸附性能研究

胶原纤维(CF)作为吸附剂去除水中Cr(Ⅵ),研究了CF去除Cr(Ⅵ)时溶液pH值、温度、吸附剂用量和Cr(Ⅵ)初始浓度对去除效率的影响。结果显示,CF对Cr(Ⅵ)的去除率随溶液pH值降低而升高,在pH值为2.0时达到最大,随吸附剂用量增大而增大,随Cr(Ⅵ)初始浓度增加而减小,CF对Cr(Ⅵ)的吸附量随吸附剂用量增加而减小;随Cr(Ⅵ)初始浓度增加而增加,最后趋于稳定。吸附平衡时间为6h,最佳吸附温度为40℃。测定了吸附等温线和吸附动力学曲线,结果表明,Freundlich等温方程能更好地描述CF对Cr(Ⅵ)的吸附,吸附动力学符合伪二级吸附速率方程。FT-IR和SEM-EDS分析表明,CF表面含有大量氨基羧基及羟基等活性官能团,CF对Cr(Ⅵ)的吸附过程存在铬酸根阴离子与质子化活性官能团的静电吸附作用和离子交换作用。     

硅藻土原位生长Nb_2O_5纳米棒及表面Cr(Ⅵ)吸附转化行为研究

以活化铌酸为铌源,草酸铵为沉积剂,十二烷基苯磺酸钠为模板剂,采用水热法在硅藻土表面原位生长Nb_2O_5纳米棒。采用SEM、TEM、XRD、BET、FT-IR和XPS等分析方法对样品进行表征,反应14 h后,Nb_2O_5纳米棒长度为500~700 nm,直径为25~35 nm;硅藻土原位生长Nb_2O_5纳米棒样品比表面积为157 m~2/g。研究了样品对Cr(Ⅵ)的吸附与光还原行为,可见光条件下对Cr(Ⅵ)吸附量可达220 mg/g;紫外光条件下,可将表面吸附的Cr(Ⅵ)转变为Cr(Ⅲ),样品经过5次循环使用后,对Cr(Ⅵ)(100 mg/L)降解率仍能保持在93%左右。样品可对重金属污染废水中Cr(Ⅵ)进行吸附与毒性降解一体化去除。     

木质素-聚吡咯复合纳米粒子的制备及其Ag+吸附性能

以酶解木质素和吡咯单体为原料,通过原位聚合法制备了木质素-聚吡咯(EHL-PPY)复合纳米粒子。而后以银离子为吸附质,系统地研究了EHL-PPY复合纳米粒子的银离子吸附性能,考察了吸附剂浓度,吸附时间和银离子初始浓度对吸附容量和吸附率的影响。在35℃时,该复合纳米粒子对银离子的饱和吸附容量为882.0 mg/g,吸附完成后,银离子被还原为直径为22~56 nm的单质银颗粒。研究表明,EHL-PPY复合纳米粒子可作为低成本银离子吸附剂使用。     

Chromium(VI) biosorption by dried Rhizopus arrhizus: effect of salt (NaCl) concentration on equilibrium and kinetic parameters

Some industrial wastewaters contain high quantities of salts besides heavy metal ions. The presence of salt ions leads to high ionic strength, which may significantly affect the performance of the biosorption process so the effect of salts on the biosorption of heavy metal ions should be investigated. In this study the biosorption of chromium(VI) from saline solutions on dried Rhizopus arrhizus was studied as a function of pH, initial chromium(VI) and salt (NaCl) concentrations in a batch system. The biosorption capacity of R. arrhizus strongly depended on solution pH and maximum chromium(VI) sorption capacity of sorbent was obtained at pH 2.0 both in the absence and in the presence of increasing concentrations of salt. Chromium(VI)-salt biosorption studies were performed at this pH value. Equilibrium uptakes of chromium(VI) increased with increasing chromium(VI) concentration up to 250mgl(-1) and decreased considerably by the presence of increasing concentrations of salt. At 100mgl(-1), initial chromium(VI) concentration, dried R. arrhizus biosorbed 78.0mgg(-1) of chromium(VI) in 72h without salt medium. When salt concentration was raised to 50gl(-1), this value dropped to 64.0mgg(-1) of chromium(VI) at the same conditions resulting in 17.9% decrease of biosorption capacity. The equilibrium sorption data were analysed by using Freundlich, Langmuir, Redlich-Peterson and Langmuir-Freundlich (Sips), the two and three parameters adsorption models, using non-linear regression technique and isotherm constants were evaluated depending on salt concentration. The Langmuir-Freundlich (Sips) was the best suitable adsorption model for describing the biosorption of chromium(VI) individually and in salt-containing medium. Pseudo-first-order, pseudo-second-order and saturation type kinetic models described the biosorption kinetics accurately at all chromium(VI) concentrations in the absence and in the presence of changing concentrations of salt. Isotherm and saturation type kinetic constants varied due to the level of salt were expressed as a function of initial salt concentration.     

Adsorption of chromium from aqueous solutions by maple sawdust

This paper presents the data for the effect of adsorbent dose, initial sorbate concentration, contact time, and pH on the adsorption of chromium(VI) on maple sawdust. Batch adsorption studies have been carried out. An empirical relationship has been obtained to predict the percentage chromium(VI) removal at any time for known values of sorbent and initial sorbate concentration. Under observed test conditions, the equilibrium adsorption data fits the linear Langmuir and Freundlich isotherms. The experimental result inferred that chelation ion exchange is one of the major adsorption mechanisms for binding metal ions to the maple sawdust.     

Use of adsorption using granular activated carbon (GAC) for the enhancement of removal of chromium from synthetic wastewater by electrocoagulation

The present work deals with removal of hexavalent chromium from synthetic effluents in a batch stirred electrocoagulation cell with iron-aluminium electrode pair coupled with adsorption using granular activated carbon (GAC). Several working parameters such as pH, current density, adsorbent concentration and operating time were studied in an attempt to achieve higher removal capacity. Results obtained with synthetic wastewater revealed that most effective removal capacities of chromium (VI) could be achieved when the initial pH was near 8. The removal of chromium (VI) during electrocoagulation, is due to the combined effect of chemical precipitation, coprecipitation, sweep coagulation and adsorption. In addition, increasing current density in a range of 6.7-26.7mA/cm2 and operating time from 20 to 100min enhanced the treatment rate to reduce metal ion concentration below admissible legal levels. The addition of GAC as adsorbent resulted in remarkable increase in the removal rate of chromium at lower current densities and operating time, than the conventional electrocoagulation process. The method was found to be highly efficient and relatively fast compared to existing conventional techniques.     

A comparative study of two chelating ion-exchange resins for the removal of chromium(III) from aqueous solution

Macroporous resins containing iminodiacetic acid (IDA) groups (Lewatit TP 207 and Chelex-100) were investigated as a function of concentration, temperature and pH for their sorption properties towards chromium(III). The chromium(III) ions sorbed onto the resin and in the equilibrium concentration were determined by inductively coupled plasma spectrophotometer. The maximum sorption for chromium ions was observed at pH 4.5. Solution pH had a strong effect on the equilibrium constant of Cr(III). The equilibrium constants were 320 and 7 at pH value 4.5 for Lewatit TP 207 and Chelex-100 resin, respectively. The Langmuir isotherm was used to describe observed sorption phenomena. Both the sorbents had high bonding constants with Lewatit TP 207 showing stronger binding. The equilibrium related to adsorption capacity and energy of adsorption was obtained by using plots of Langmuir adsorption isotherm. It was observed that the maximum adsorption capacity of 0.288 mmol of Cr(III)/g for Chelex-100 and 0.341 mmol of Cr(III)/g for Lewatit TP 207 was achieved at pH of 4.5. The rise in temperature caused a slight increase in the value of the equilibrium constant (K_c) for the sorption of chromium(III) ion.     

Solid phase extraction of chromium(VI) from aqueous solutions by adsorption of its ion-association complex with cetyltrimethylammoniumbromide on an alumina column

A simple approach has been developed for the solid phase extraction of chromium(VI) based on the adsorption of its ion-association complex with cetyltrimethylammoniumbromide (CTABr) on an alumina column. The effect of various parameters such as acidity, stability of the column, sample volume, effect of diverse ions, etc. have been studied in detail. The adsorbed complex could be eluted using sodium hydroxide and the concentration of chromium has been established using visible spectrophotometry after complexation with diphenyl carbazide. The calibration graph was linear in the range 0-0.5 microg mL(-1) chromium(VI) with a detection limit of 5 microg L(-1). A highest preconcentration factor of 25 could be obtained for 250 mL sample volume. The data from the column studies were also studied using the Thomas model of adsorption. The experimental results obtained were correlated with the proposed model of adsorption. The Thomas rate constant k was found to be 0.0025 L/min mg and the maximum adsorption capacity q(o) was found to be 0.36 mgCr/g alumina at an initial chromium(VI) concentration of 1 mg L(-1). The validity of the method has been checked by applying it to study the recovery of chromium in spiked water samples and electroplating wastewater.     

Hexavalent chromium removal from wastewater using aniline formaldehyde condensate coated silica gel

A resinous polymer, aniline formaldehyde condensate (AFC) coated on silica gel was used as an adsorbent in batch system for removal of hexavalent chromium from aqueous solution by considering the effects of various parameters like reaction pH, dose of AFC coated silica gel, initial Cr(VI) concentration and aniline to formaldehyde ratio in AFC synthesis. The optimum pH for total chromium [Cr(VI) and Cr(III)] adsorption was observed as 3. Total chromium adsorption was second order and equilibrium was achieved within 90-120 min. Aniline to formaldehyde ratio of 1.6:1 during AFC synthesis was ideal for chromium removal. Total chromium adsorption followed Freundlich's isotherm with adsorption capacity of 65 mg/g at initial Cr(VI) 200mg/L. Total chromium removal was explained as combinations of electrostatic attraction of acid chromate ion by protonated AFC, reduction of Cr(VI) to Cr(III) and bond formation of Cr(III) with nitrogen atom of AFC. Almost 40-84% of adsorbed chromium was recovered during desorption by NaOH, EDTA and mineral acids. AFC coated silica gel can be effectively used for treatment of chromium containing wastewaters as an alternative.     

Removal of toxic chromium from wastewater using green alga Ulva lactuca and its activated carbon

Biosorption of heavy metals can be an effective process for the removal of toxic chromium ions from wastewater. In this study, the batch removal of toxic hexavalent chromium ions from aqueous solution, saline water and wastewater using marine dried green alga Ulva lactuca was investigated. Activated carbon prepared from U. lactuca by acid decomposition was also used for the removal of chromium from aqueous solution, saline water and wastewater. The chromium uptake was dependent on the initial pH and the initial chromium concentration, with pH approximately 1.0, being the optimum pH value. Langmuir, Freundlich, Redlich-Peterson and Koble-Corrigan isotherm models were fitted well the equilibrium data for both sorbents. The maximum efficiencies of chromium removal were 92 and 98% for U. lactuca and its activated carbon, respectively. The maximum adsorption capacity was found to be 10.61 and 112.36 mg g(-1) for dried green alga and activated carbon developed from it, respectively. The adsorption capacities of U. lactuca and its activated carbon were independent on the type of solution containing toxic chromium and the efficiency of removal was not affected by the replacing of aqueous solution by saline water or wastewater containing the same chromium concentration. Two hours were necessary to reach the sorption equilibrium. The chromium uptake by U. lactuca and its activated carbon form were best described by pseudo second-order rate model. This study verifies the possibility of using inactivated marine green alga U. lactuca and its activated carbon as valuable material for the removal of chromium from aqueous solutions, saline water or wastewater.     

Removal of hexavalent chromium from aqueous solutions by D301, D314 and D354 anion-exchange resins

Removal of hexavalent chromium from electroplating industry wastewater is obligatory in order to avoid pollution. Batch shaking experiments were carried out to evaluate the adsorption capacity of resins (D301, D314 and D354) in the removal of chromium from aqueous solutions. Varying experimental conditions were studied, including Cr(6+) concentrations, resin amounts, initial pH, contact time and temperatures. The ion-exchange process, which is pH-dependent, indicated the maximum removal of Cr(6+) in the pH range of 1-5 for an initial concentration 100 ppm of Cr(6+). It was found that more than 99.4% of the removal was achieved under optimal conditions. High adsorption rates of chromium for the three resins were observed at the onset, and then plateau values were gradually reached within 30 min. The experimental results obtained at various concentrations (27+/-1 degrees C) showed that the adsorption pattern on the resins have followed Langmuir isotherms and the calculated maximum sorption capacities of D301, D314 and D354 were 152.52, 120.48 and 156.25mg/g, respectively. The thermodynamic parameters (free energy change DeltaG, enthalpy change DeltaS and entropy change DeltaH) for the sorption have been evaluated. It was also found that the adsorption of chromium on these anion-exchange resins follows first-order reversible kinetics.     

Kinetics of removal of chromium from water and electronic process wastewater by ion exchange resins: 1200H, 1500H and IRN97H

The removal of chromium from aqueous solution by an ion exchange resin is described. Ion exchange resins 1200H, 1500H and IRN97H show a remarkable increase in sorption capacity for chromium, compared to other adsorbents. The adsorption process, which is pH dependent show maximum removal of chromium in the pH range 2-6 for an initial chromium concentration of 10mg/l. The metal ion adsorption obeyed linear, Langmuir and Freundlich isotherms. The adsorption of chromium on these cation exchange resins follows first-order reversible kinetics and pseudo-first-order kinetics. The intraparticle diffusion of chromium on ion exchange resins represents the rate-limiting step. The uptake of chromium by the ion exchange resins was reversible and thus have good potential for the removal/recovery of chromium from aqueous solutions. We conclude that such ion exchange resins can be used for the efficient removal of chromium from water and wastewater.     

Lifetime and regeneration of immobilized titania for photocatalytic removal of aqueous hexavalent chromium

Immobilized titania (TiO2) batch reactors reduced hexavalent chromium (Cr(VI)) in the form of potassium dichromate (K2Cr2O7) to trivalent chromium (Cr(III)) in aqueous solution at pH 3 under 171 W/m2 light intensity. The light source was a 125-W ultraviolet (UV) lamp. The Cr(VI) reduction showed zero-order kinetics (k0), while the Cr(VI) adsorption fitted with first-order kinetics (k(1st)). Adsorption capacity increased with increasing initial Cr(VI) concentration, and the area of immobilized TiO2 limited the reduction efficiency. The lifetime of fresh immobilized TiO2 was approximately 14 h. In addition, the regeneration of TiO2 with 3M sodium hydroxide (NaOH) was necessary to improve adsorption reaction.