Removal of Cr (VI) from Aqueous Solution Using Ultrafine Coal Fly Ash

Coal fly ashes WSRA and BQRA were ball milled for 5 h to produce their ultrafine coal fly ashes WSUA and BQUA, respectively. Batch kinetic, isotherm and pH effect on adsorption were studied to evaluate removal of Cr (VI) from aqueous solutions by ultrafine coal fly ashes comparing with raw coal fly ashes. The kinetics of adsorption indicates the process to be intraparticle diffusion controlled and follows the Lagergren first-order kinetics for all coal fly ashes. The first-order rate constants (k1) of Cr (V...     

Biosorption mechanism of Cr （Ⅳ） onto cells of Synechococcus sp.

The biosorption mechanism of Cr （Ⅳ） ions on Synechococcus sp. biosorbent was studied by analyzing the biosorption kinetics as well as speciation change and bond formation during the biosorption process. The kinetics study shows that the adsorption process of Cr （Ⅳ） consists of a very fast stage in the first several minutes, in which more than half of the saturation adsorption is attained, and a slower stage that approximately follows the first order kinetic model, basically Freundlich isotherm models were observed. Comparative studies of FT-LR spectra of K2Cr2O7, free cells of Synechococcus sp., and Cr-bound cells of Synechococcus sp show that the speciation of chromium that binds to the cells ofSynechococcus sp. is Cr （Ⅲ）, instead of Cr （Ⅳ）, and the carboxylic, alcoholic, amido and amino groups may be involved in the binding of Cr （Ⅲ）. Integrative analyses of the surface electric potential, the effect of pH value on adsorption behavior of Cr （Ⅵ）, and the results of FT-IR show that the biosorption of Cr （Ⅵ） follows two subsequent steps, biosorption of Cr2O7 ^2- by electrostatical force at the protonated active sites and reduction of Cr2O7^2- to Cr^3＋ by the reductive groups on the surface of the biosorbents.     

Adsorption and desorption properties of D318 resin for Cr（Ⅵ）

The adsorption capability of D318 resin for Cr(VI) was investigated by chemistry analysis. Experimental results show that D318 resin has the best adsorption ability for Cr(VI) at pH=3.16 in HAc-NaAc medium. The statically saturated adsorption capacity of the resin is 265.4 mg/g. The thermodynamic adsorption parameters, enthalpy change ΔH and free energy change ΔG ₂₉₈ of the adsorption reaction are 4.81 and −5.16 kJ/mol, respectively. The apparent activation energy E _a is 22.4 kJ/mol. The adsorption behavior obeys the Freundlich isotherm. The molar coordination ratio of the functional group of resin to Cr(VI) is 3:2. Cr(VI) adsorbed on D318 resin can be eluted by 5%NaOH-5%NaCl quantitatively. Foundation item: Project (Y304121) supported by the Natural Science Foundation of Zhejiang Province, China     

Influence of coal fly ash particle size on structure and adsorption properties of forming adsorbents for Cr<Superscript>6+</Superscript>

Forming adsorbents FFA-R, FFA-A and FFA-B were prepared from different particle size coal fly ashes FA-R, FA-A and FA-B, their average particle sizes (d ₅₀) were 15.75, 3.61 and 1.73 μm respectively. The structure and adsorption properties for Cr⁶⁺ of forming adsorbents from aqueous solution were studied. The results show that forming adsorbent prepared from the coal fly ash with smaller particle size exhibits higher specific surface area, higher pore volume and better adsorption properties for Cr⁶⁺.The adsorption kinetics of Cr⁶⁺ on FFA-R, FFA-A and FFA-B fitts the second order kinetic model and the second adsorption rate constants are 7.523, 3.197 and 2.187 mg·g^-1· min^-1/2, respectively. The adsorption of Cr⁶⁺ on FFA-R, FFA-A and FFA-B can be described in terms of Langmuir isotherms better, and the adsorption processes are spontaneous and exothermic.     

Removal of Cr（Ⅲ） and Cr（Ⅵ） from aqueous solution by adsorption on sugarcane pulp residue

Sugarcane pulp residue (SPR), a waste from sugar-refinery, which possesses a large surface area, can be used for removing chromium (Cr(III) and Cr(VI)) from wastewater. In this work, the kinetics, isotherms of Cr(III) and Cr(VI) adsorption and their removal by SPR were investigated. The results show that the removal percentages of Cr(VI) and Cr(III) increase with increasing SPR dosage and temperature and decrease with increasing SPR particle size and the initial concentration of chromium ions. However, the influence of pH value on the Cr(VI) removal differs from that of the Cr(III) removal. The Cr(VI) removal percentage decreases with increasing pH values, while the Cr(III) removal percentage increases with increasing pH value. The adsorption kinetics of Cr(VI) and Cr(III) well fits with pseudo-second-order model. Langmuir adsorption isotherm can well describe the adsorption phenomena of chromium ions with the maximum adsorption capacity of 0.567 mg/g for Cr(VI) and 3.446 mg/g for Cr(III). Moreover, SPR reveals higher adsorption capacity for Cr(III) than that for Cr(VI), which implies that SPR has more potential application for Cr(III)-containing wastewater treatment than that for Cr(VI)-containing wastewater treatment. Foundation item: Projects(2006AA06Z374, 2007AA021304) supported by the National High-Tech Research and Development Program of China; Project(2008SK2007) supported by the Key Program of Science and Technology of Hunan Province, China     

Selective leaching of chromium-containing slag by HCl

A batch of column experiments was carried out to investigate the change of Cr（Ⅵ） concentration leached out from chromium-containing slag with HCI as leaching agent, and to study influences of pH, ratio of solid mass to solution volume, flow velocity and temperature on Cr（Ⅵ） leaching. The optimal parameters were obtained for Cr（Ⅵ） leaching and a fitting model was established to describe the procedure of Cr（Ⅵ） leaching. The results show that Cr（Ⅵ） concentration in leachate increases with decreasing pH and increasing flow velocity and temperature. Moreover, Cr（Ⅵ） leaching percentage increases with increasing ratio of solid mass to solution volume. The optimal parameters for Cr（Ⅵ） selective leaching are as follows： pH=3.0, 1：5 of ratio of solid mass to solution volume, 180 mL/min of flow velocity and 40 ℃ of temperature. The procedure of Cr（Ⅵ） leaching fits well with the model： v= 1.87t^-0.54, indicating that the leaching rate of Cr（Ⅵ） declines in an exponential order of-0.54.     

CNTs 改性及水体中 Cr（VI）离子的吸附性能研究

为了脱除水体Cr（VI）,600℃下于Fe2Ni/γ-Al2O3上苯催化化学气相分解（catalytic chemical vapor decomposition ）制备碳纳米管（ carbon nanotubes , CNTs ）,粗 CNTs 经混酸（H2SO4/HNO3,3∶1, volume ratio,体积比）,超声氧化纯化,纯化的同时赋予其表面功能基团,进一步地,表面包覆功能分子聚乙烯醇（ polyvinyl alcohol ,PVA）。系统探讨了改性CNTs对高浓度水体Cr（ VI）离子的吸附脱除,结果表明,CNTs的氧化纯化使其表面植入-COOH、-OH等功能基团,进一步地,富含羟基功能基团的PVA分子在CNTs表面包覆,赋予CNTs表面活性的同时,显著提高CNTs的亲水性能。观察到了随氧化纯化和PVA修饰的CNTs上高浓度Cr（ VI）离子吸附的逐步和明显提升,吸附热力学和动力学研究表明,CNTs表面Cr（ VI）的吸附符合Freundlich热力学和准二级动力学特征。随氧化纯化和PVA修饰, CNTs对水体Cr （ VI ）吸附性能的提高可能与CNTs亲水性能的提升以及表面功能化基团对Cr（ VI）的化学吸附的促进相关联。     

Adsorption of D113 resin for dysprosium(III)

The adsorption behavior and mechanism of D113 resin for Dy(III) was investigated by using the method of resin adsorption. Experimental results show that the optimum medium pH of adsorption of D113 resin for Dy³⁺ is pH=6.00 in the HAc-NaAc medium. The static adsorption capacity of D113 resin for Dy³⁺ is 292.7 mg·g⁻¹. The optimum eluant is 0.5 mol·L⁻¹ HCl. The adsorption rate constant is k ₂₉₈=6.8×10⁻⁶s⁻¹. The apparent activation energy of D113 resin for Dy(III) is 14.79 kJ·mol⁻¹. The adsorption behavior of D113 resin for Dy(III) obeys the Freundlich isotherm. The adsorption parameters of thermodynamic are ΔH=14.48 kJ·mol⁻¹, ΔS=54.69 J·mol⁻¹·K⁻¹, ΔG=−1.82 kJ·mol⁻¹.The adsorption mechanism of D113 resin for Dy³⁺ was confirmed by chemical analysis and IR spectra. Funded by the Natural Science Foundation of Zhejiang Province (No.201027), Foundation of Zhejiang Provincial Education Bureau (No.20040551) and Zhoushan Science Technology Bureau (No.04114)     

Synthesis of 1,4-benzenedicarbonyl thiourea resins and their adsorption properties for Ag（I）

Several 1,4-benzenedicarbonyl thiourea resins (BTR) were synthesized through interfacial polymerization between 1,4-benzenedicarbonyl diisothiocyanate and polyamine. Their structures were confirmed by FT-IR. The adsorption properties (including the effect of adsorption time, pH, initial concentrations and temperature) of BTR-1, BTR-2 and BTR-3 for Ag(I) were investigated by batch tests. The results show that the adsorption equilibria of BTR-1, BTR-2, BTR-3 for Ag(I) are achieved after about 10 h. Their equilibrium adsorption capacities are 7.11, 6.75 and 6.23, respectively, and the adsorption process accords with G. E. Boyd equation and Langmuir adsorption isotherm as well. The adsorption capacities increase with the increase of pH (the highest uptake values are observed at pH being about 6–7). The thermodynamic parameters of BTR-1 were calculated. The results show that ΔH ^Θ; and ΔS ^Θ are 6 958.8 J/mol and 64.28 J/(mol·K), respectively, and ΔG ^Θ at 20, 30, 40 and 50 °C are −11.79, −12.52, −13.16 and −13.8 kJ/mol, respectively. The silver-loaded resins can be quantitatively eluted by a solution containing 6% thiourea in 1 mol/L HNO₃.     

Removal of anionic ions from single material solution by bauxite tailings modified with FeCl3·6H2O

The adsorbabilities of the unmodified and modified bauxite tailings for Cr（Ⅵ）, As（Ⅴ） and F（Ⅰ） ions were investigated. Batch experiments were carried out to determine the removal rate as a function of adsorbent dosage, solution pH value and shaking time. The results show that the maximum removal rates of Cr（Ⅵ）, As（Ⅴ） and F（Ⅰ ） are respectively 99%, 99% and 90% by using the modified bauxite tailings. The isoelectric point of the unmodified bauxite tailings is 3.6, and that of the modified bauxite tailings is 5.0, which shifts to lower pH values in Cr（Ⅵ） solution. This indicates a specific adsorption of the anionic species on the modified bauxite railings. A new band of Cr2O72 appears in the FTIR, showing that Cr（Ⅵ） is adsorbed on the modified bauxite railings in the form of chemistry adsorption. The adsorption data of Cr（Ⅵ） on the modified bauxite tailings are well described by Freundlich model. The investigations of kinetic models show that pseudo-second-order kinetic model provides the best correlation for the experimental data.     

柚子皮对水中六价铬的吸附性能研究

采用柚子皮制备生物吸附剂用于去除水中的Cr（VI）,考察了pH值、柚子皮投加量、柚子皮粒径、溶液离子强度、反应温度等因素对吸附效果的影响。结果表明,当溶液中Cr（VI）离子初始浓度15mg／L、pH 1．5、反应温度25℃、柚子皮投加量1．Og／100mL、吸附时间7h时,Cr（VI）离子去除率可达90％以上。柚于皮对Or（VI）离子的吸附过程可以用Langmuir和Freundlich吸附等温模型来描述,吸附等温线线性相关性均较显著,吸附过程符合准二级动力学方程。柚子皮对水中Cr（VI）离子吸附性能较好,且运行成本低,可推广应用于水中重金属离子的治理。     

响应面法优化空气氛围下制备S-nZVI对水中Cr(VI)的去除

在空气氛围下制备硫化纳米零价铁（SnZVI）,通过SEM、XRD等进行表征,并对其去除水中Cr（VI）进行研究。以Cr（VI）去除率为响应值建立了4因素5水平的响应面模型。SEM和XRD结果显示S-nZVI具有片状结构,主要成分为Fe⁰并含有少量的FeS和铁氧化物。响应面法分析结果表明模型可信度高,适用于模拟4种因素对S-nZVI去除Cr（VI）的影响。以伪一级、伪二级动力学模型拟合S-nZVI去除Cr（VI）,结果显示伪二级动力学模型R²为0.999拟合度更好,说明S-nZVI对Cr（VI）的去除主要以化学吸附为主,平衡吸附量达到156.3mg/g.     

Synthesis and characterization of montmorillonite inorgano-intercalation compound assisted by microwave irradiation

A montmorillonite inorgano-intercalation compound(MIIC) was synthesized by using a purified Na-exchanged bentonite (PNaB) as a matrix and Al-pillaring ion as an intercalating reagent under microwave irradiation. The synthesized products were characterized by X-ray diffraction (XRD), ²⁷Al magic angle sample-spinning nuclear magnetic resonance (²⁷Al MAS NMR), specific surface area (BET) measurement, and adsorption density determination. The results show that, at 5% solid (PNaB) concentration and 7 minutes irradiation in a 130 W microwave oven, the basal spacing d ₍₀₀₁₎ of the synthesized MIIC increases to 1.740 nm from the original 1.218 nm of PNaB. The MIIC has much higher adsorptive densities to F⁻ and Cr⁶⁺ from aqueous solution than the PNaB. The adsorption isotherm of F⁻ on the MIIC follows the Freundlich equation, and the increased adsorption is mainly due to the porous structure of the MIIC which created larger adsorption surfaces. The adsorption isotherm of Cr⁶⁺ on MIIC follows the Langmuir equation and the adsorption is mainly monolayer as a result of chemisorptions.     

零价铁/阳离子表面活性剂/生物炭对水体Cr(VI)的吸附研究

以常见柳条为生物炭原料,通过十六烷基三甲基氯化铵（CTMAC）进行阳离子表面活化,与零价铁、海藻酸钠混合制备了零价铁/阳离子表面活性剂/生物炭（Fe⁰?MBC）凝胶微球,探讨了其对水体Cr（VI）的吸附能力。借助XRF、FTIR、XRD以及Zeta电位等分析手段,对Fe⁰?MBC凝胶微球的结构与性能进行研究。通过分析反应时间、环境温度及pH对吸附的影响,在吸附动力学、等温线模型的基础上,初步探讨了吸附机制。通过吸附?解析循环实验,研究了Fe⁰?MBC凝胶微球的再生性能。结果表明,Fe⁰?MBC凝胶微球对Cr(VI)的吸附与准一级动力学和Langmuir等温吸附模型拟合度较高;Cr初始质量浓度100 mg/L、负载质量分数分别为5%和10%的零价铁的CTMAC活化生物炭对Cr（VI）的去除率在2 h时分别为89%、97%,最大饱和吸附量分别为33.777 9、42.562 0 mg/g;Fe⁰?MBC凝胶微球作为一种成本低、效率高的环境功能材料,对去除废水中的Cr(VI)具有良好的应用前景。     

Development of a first-order kinetics-based model for the adsorption of nickel onto peat

The use of peat for the removal of nickel from aqueous solutions has been investigated at various pH values by means of static conditions. The present research shows that the ability of Ni to hind to peat increases as the pH value increases. The solutions reach adsorption equilibrium rapidly. A reasonable kinetic model, first-order in nickel concentration, has been developed and fitted to the adsorption of nickel (Ⅱ) onto peat. The first-order model provides a good correlation to the experimental data. The characteristic parameters of the Langmuir isotherm were determined at various temperatures. The relationship between kinetics and equilibrium isotherms was established through the forward- and backward-rate-constants, k and k2, and the equilibrium constant, K.     

Methane adsorption behavior on coal having different pore structures

The adsorption of methane onto five dry coal samples was measured at 298 K over the pressure range from 0 to 3.5 MPa using a volumetric method. The isotherm data were fitted to the Langmuir and the Freundlich equations. The kinetic data were fitted to a pseudo second order equation, the linear driving force equation (LDF), and an intra-particle diffusion model. These results showed that higher methane adsorption is correlated with larger micro-pore volumes and specific surface areas. The adsorption was related to the narrow micro-pore size distribution when the previous two parameters are large. The kinetics study showed that the kinetics of methane adsorption onto these five dry coal samples followed a pseudo second order model very well. Methane adsorption rates are controlled by intra-particle diffusion. The faster the intra-particle diffusion, the faster the methane adsorption rate will be.     

Competitive adsorption of heavy metal ions on peat

The uptake capacities, and the adsorption kinetics, of copper, Cu(Ⅱ), nickel, Ni(Ⅱ), and cadmium, Cd(Ⅱ), on peat have been studied under static conditions. The results show that the adsorption rates are rapid: equilibrium is reached in twenty minutes. The adsorption of copper, nickel and cadmium is pH dependent over the pH range from 2 to 6. The adsorption kinetics can be excellently described by the Elovich kinetic equation. The adsorption isotherm fits a Langmuir model very well. The adsorption capacifies follow the order Cu2 ＞Ni2 ＞Cd2 in single-component systems and the competitive adsorption capacities fall in the decreasing order Cu2 ＞ Ni2 ＞Cd2 in multi-component systems. The adsorption capacities of these three heavy metal ions on peat are consistent with their observed competitive adsorption capacities.     

Adsorption of copper（ Ⅱ ） and chromium（Ⅵ） on diaspore

The adsorption of Cu（ Ⅱ ） and Cr（Ⅵ） on diaspore was studied with the help of X-ray diffraction analysis, BET measurement, zeta potential measurement and atomic adsorption spectrometry. The adsorption equilibrium almost reaches within 60 min. The adsorption isotherms of Cu（ Ⅱ ） and Cr（Ⅵ） could be well described by the Langmuir equation. The adsorption capacities of Cu（Ⅱ） and Cr（Ⅵ） are 1.944 and 1.292 mg/g, respectively. The adsorption percentage of Cr（Ⅱ ） increases with the increment of solution pH, but the adsorption percentage of Cr（Ⅵ） decreases. This could be explained by zeta potential theoretical and electrostatic attraction between metal ions and diaspore surface.     

粉煤灰合成沸石对亚甲基蓝的吸附热力学和动力学研究

为了扩大粉煤灰的再利用领域,本文采用水热合成法制备了沸石;同时以其作为吸附材料,用于吸附染料亚甲基蓝的研究,考察了溶液初始p H值、吸附时间等因素对吸附效果的影响,并进一步拟合吸附动力学和吸附等温线,初步分析了吸附机理。结果表明：粉煤灰合成的沸石对亚甲基蓝具有较好的吸附能力;p H值是影响吸附效果的一个重要参数;沸石对亚甲基蓝的吸附过程在90 min达到吸附平衡;沸石对亚甲基蓝的吸附过程符合二级反应动力学和Langmuir吸附等温方程,说明该吸附过程是以化学吸附为主且典型的单分子层吸附。