生物质吸附材料对Cr(VI)的吸附还原研究进展

重金属污染是当今工业发展所面临的一个重要环境问题,传统处理含铬废水的方法具有工艺简单、操作方便等优点,但存在二次污染、处理成本高等问题。寻找成本低、去除效率高的重金属废水处理方法是当下研究的一个重要方向。本工作介绍了生物质吸附法对含铬废水的处理研究,简述了生物质材料在金属吸附回收领域的优势,分析了当前生物质吸附材料的研究内容和发展现状,归纳了目前常用的物理、化学改性方法,并详细介绍了改性生物质材料对Cr(VI)的吸附效果,然后根据吸附剂表面活性基团与吸附质之间相互作用的类型,分析总结了生物质吸附材料对Cr(VI)的四种吸附机理以及在吸附过程中氨基、羟基、硫醇等活性基团作为电子供体对Cr(VI)的还原机理。最后,从研究与应用的角度,对生物质吸附材料吸附还原Cr(VI)的未来研究方向做出展望。     

Cr (VI) adsorption from aqueous solutions on grafted chitosan

Chitosan was grafted on the surface of a cotton gauze (20, 50, and 100 mg chitosan g⁻¹ cotton) to improve its stability in aqueous solutions. The adsorption of hexavalent chromium ions from water on the grafted chitosan was evaluated to determine, by means of linear and nonlinear models, the kinetic and isotherm adsorption of the process. The kinetics of pseudo second-order, pseudo first-order, and adsorption isotherms type II were obtained, that is, a monolayer adsorption on nonporous adsorbents with physical adsorption was present. The most probable energy of adsorption corresponded to a physisorption with hydrogen bond interactions between chromium ions and ammonium groups. Moreover, three different cross-sectional areas of hexavalent chromium ions were calculated and used to estimate the specific surface area employed by active sites to adsorb metal ions in terms of chitosan or cotton mass. Finally, the percentage of the area occupied by chromium ions on the surface was estimated by dividing the resulting specific surface area in terms of cotton mass by the specific surface area of cotton reported in literature. As a result, it was determined that the occupied area is between 6% (for 20 mg chitosan g⁻¹ cotton)-24% (for 100 mg chitosan g⁻¹ cotton) from the total area of cotton.     

Reduction of Cr(VI) to Cr(III) and removal of total chromium from wastewater using scrap iron in the form of zerovalent iron(ZVI): Batch and column studies

This work experimentally investigates Cr(VI) reduction to Cr(III) using waste scrap iron in the form of zerovalent iron (ZVI) collected from the mechanical workshop of the Institute, both in batch and continuous operation. The reduction of Cr(VI) to Cr(III) was found to be complete (～100%) depending on the experimental conditions. Lower pH values favour Cr(VI) reduction. Two concurrent reactions take place, that is reduction of Cr(VI) by Fe⁰ (ZVI) and by Fe²⁺ generated due to H⁺ corrosion of iron. Maximum around 22%, 11% and 2% Cr(III) remained dissolved in solution while the experiments were carried out at initial pH of 2, 4.67 and 7. Higher ZVI loading increases Cr(VI) reduction rate, however, consumption of iron is noted to be higher. The results indicate that the bed is exhausted rapidly at higher pH, initial Cr(VI) concentration and flow rate. This is attributable to predominance passivation of ZVI surface forming Cr(III)–Fe(III)‐oxide layer. SEM analysis of ZVI before and after the experiments confirms formation of passive oxide on iron surface is responsible for deterioration of Cr(VI) reduction efficiency due to its blanketing effect.     

ZSM-5沸石分子筛吸附模拟含铬废水的研究

本论文以正硅酸乙酯为硅源、偏铝酸钠为铝源、四丙基氢氧化铵为模板剂,利用水热合成法制备ZSM-5沸石分子筛并将其应用到吸附水中六价铬的研究,考察了吸附时间、铬酸钾溶液pH值、吸附剂用量、吸附温度对吸附效果的影响。结果表明,最佳吸附条件是:吸附剂的使用量为0.5g,铬酸钾溶液pH值为5,吸附时间为60 min,吸附温度为30℃,此时,六价铬的去除率最高,达到了93.46%。     

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     

A simple sulfuric acid pretreatment method to improve the adsorption of Cr(VI) by chitosan

An optimum pH of 5.0 for the adsorption of Cr⁶⁺ by chitosan was determined by using a stirred‐batch reactor method at constant pH. When a column containing chitosan was used to bind Cr⁶⁺ in a situation where pH could not be held constant because of pH changes caused by the chitosan itself, significant binding occurred only at solution pH 1 and 2. When chitosan was pretreated with sulfuric acid in a range of 7–70 mol % sulfuric acid : moles glucosamine residue, maximum binding occurred at pH 6.0. Under these conditions, a column containing 0.500 g acid‐treated chitosan (35% mole ratio) reduced the concentration of Cr⁶⁺ in 713 bed volumes of 25 ppm Cr⁶⁺ solution to ≤5 ppm in the effluent. A similar column of pretreated chitosan reduced Cr⁶⁺ concentration in 1042 bed volumes of industrial chromium plating rinse water initially containing 18 ppm Cr⁶⁺ to ≤5 ppm. Capacity experiment results indicated 60 mg chromium bound per gram of treated chitosan at pH 6.0. Commercial resin IRA‐67 was also investigated as a Cr⁶⁺ binding agent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2808–2814, 2004     

Electrospinning of polyacrylonitrile nanofibers embedded with zerovalent iron and cerium oxide nanoparticles,as Cr(VI) adsorbents for water treatment

Zerovalent iron (ZVI) and cerium oxide (CeO₂) nanoparticles (NPs) embedded in polyacrylonitrile nanofibers (NFs) were obtained via electrospinning. Each NF was characterized using Fourier transform infrared spectroscopy and X-ray diffraction. The scaffold morphology and average diameter of the NFs were determined using scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) mapping and Raman spectroscopy were used to characterize the NPs dispersion in the NFs. The Cr(VI) removal efficiency (%E) of ZVI and CeO₂ NPs was compared with the efficiency of their corresponding NFs. CeO₂ NPs showed 79% Cr(VI) removal; the efficiency was better for their NFs (96%). Regeneration of ZVI NFs was 98 %E. ZVI NPs were the best adsorbent with 99.9% efficiency. An adsorption mechanism was proposed using Langmuir, Freundlich, and Temkin isotherm models. SEM–EDS analyses revealed that Cr adsorbed on the NP and NF surfaces. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48663.     

电镀废水中铬(VI)分析的研究进展

综述了近5年来电镀废水中铬(VI)的分析测定方法,主要包括分光光度法、催化光度法、荧光光度法、原子吸收法、电化学法、化学传感器法、化学发光法及共振光散射法等。     

粉煤灰微波改性及其对含铬废水的吸附性能

将取自于西安市西郊热电厂的原粉煤灰(FA)球磨5h得到超细粉煤灰(UFA),再经过微波辐照处理得到微波辐照改性超细粉煤灰(MFA),并研究其对含铬废水的吸附性能.动力学研究结果表明,改性粉煤灰对Cr(VI)的吸附符合二级吸附动力学模型,通过模型计算出的FA,UFA和MFA的二级吸附速率常数(k2)分别为2.45×10-2 ,3.88×10-2 和5.14×10-2g·mg-1·min-1; 热力学研究结果表明,吸附过程可以用Langmuir方程描述.     

生物除铬的机理研究

本论文主要是研究厌氧微生物作为生物絮凝剂吸附六价铬的吸附特性及机理。污泥中的微生物以杆菌为主。污泥吸附沉降性良好。污泥在吸附时间40 min内,不会解析,吸附效果最好。在污泥吸附能力达到饱和时,加入营养经过一段时间后,其吸附能力会部分恢复。     

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation

Abstract

Hydrolyzed products of Al(III) have affinity below pH_zpc for oppositely charged mono and bi‐nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA/cm² current density. Cathodic adsorption of chromium boosted up Cr(VI) removal during EC. Simultaneous electro‐ and chemical‐dissolution lead to high current efficiency of about 178%. Both the pH and the coagulant dosage have a significant impact on Cr(VI) removal in the pH ranges from 4.9 to 7.0. CC with alum and aluminum sulfate (AS) removed about 11% and 12% of Cr(VI). Co‐adsorption of divalent SO₄ ^2? ions with Cr(VI) is responsible for the lower removal observed with chemical coagulants. About 0.061 and 0.099 mole of SO₄ ^2? was adsorbed per mole Al in the precipitate in the pH range 4.9 to 7.0 with AS and alum. A higher coagulant dosage increases the removal of Cr(VI) but adversely affects the removal efficiency (Cr(VI) removed per unit of Al dosing). Cell current density (CD) has shown little effect on Cr(VI) removal and the pH elevation at the same charge density. Higher initial Cr(VI) concentration improves the removal efficiency as the species of Cr(VI) is acidic in solution and decreases the pH elevation rate.     

Preparation of magnetic zeolite/chitosan composite using silane as modifier for adsorption of Cr(VI) from aqueous solutions

This study aimed to prepare an efficient, cost-effective, and separable magnetic zeolite/chitosan composite (MZFA/CS) adsorbent from solid waste to deal with the water pollution of Cr(VI). The MZFA/CS was characterized by X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) techniques. Then, the effect of pH, temperature, initial concentration of Cr(VI) ions, and contact time was considered in the study. For a sorbent dose of 0.1 g in 50 mL of a Cr(VI) solution, at a contact time of 30 min, temperature of 30°C, and a pH of 3, an adsorption capacity (q_e) of 16.96 mg g⁻¹ was achieved. Adsorption kinetics and isotherm data obtained for all adsorption systems were well-fitted by pseudo-second-order and Langmuir models, respectively. The thermodynamic study suggested that the adsorption process is spontaneous and endothermic in nature. In summary, the adsorbent with better separability (Ms = 16.83 emu g⁻¹) and adsorbability was successfully fabricated.     

Removal of Cr(VI) from aqueous solution by London plane leaves

The effect of initial metal concentration, contact time and solution temperature on the removal of Cr(VI) from solution by waste London plane leaves, generated by the pruning of street trees, was investigated in batch mode conditions. The removal of Cr(VI) was highly concentration‐dependent and mainly governed by physico‐chemical adsorption under the weak acidic conditions studied. The equilibrium data fit well in the Langmuir isotherm model. The Langmuir constants were calculated at different temperatures and both the adsorption capacity and adsorption intensity increased with rising temperature. The endothermic nature of the Cr(VI) adsorption was confirmed by the thermodynamic parameters. The study has shown that the waste leaves can be used as an effective adsorbent for removal of Cr(VI) from wastewater. Copyright © 2003 Society of Chemical Industry     

Comparison Between the Cr(VI) Adsorption by Hydrotalcite and Hydrotalcite-Gibbsite Compounds

Cr(VI) adsorption from aqueous solutions on Mg-Al hydrotalcite and Mg-Al hydrotalcite-gibbsite with Al/(Al+Mg) ratios (R) of 0.3 and 0.6 (MgAlHT_{R = 0.3} and MgAlHTG_{R = 0.6}) was investigated as a function of the pH and chromium concentration. The results showed that the maximum Cr(VI) adsorption by Mg-Al compounds do not depend on the value of R at pH 7. In addition, the chromate equilibrium sorption capacity for MgAlHTG_{R = 0.6} is at least 4.8 times higher than that for MgAlHT_{R = 0.3} at pH 5. The Cr(VI) maximum capacities of MgAlHT_{R = 0.3} and MgAlHTG_{R = 0.6} at pH 7 were similar, 6.5 and 6.8 mgCr(VI)/g, respectively.     

Multiwalled CNTs for Cr(VI) removal from industrial wastewater: An advanced study on adsorption,kinetics, thermodynamics for the comparison between the embedded and non‐embedded carboxyl group

The adsorption capabilities of multiwalled carbon nanotubes (MWCNTs) with and without the embedded carboxyl group for the removal of parts per million levels of hexavalent chromium were examined as a function of several parameters, namely contact time, pH of initial solution, initial concentration of Cr(VI), adsorbent dosage as well as temperature of solution. Adsorption isotherms have been utilized to explain the adsorption mechanism. Ion exchange, intra‐particle diffusion, and electrostatic interactions are found to be the fundamental mechanisms describing the adsorption of Cr(VI). The maximum adsorption capacities of Cr(VI) ion by raw MWCNTs and functionalized MWCNTs were found to be 84.75 and 78.13 mg · g^?1, respectively, as calculated by the Langmuir adsorption isotherm model. This is with regard to the electron‐rich atoms inside the functional group which repels the negatively charged dichromate ions. Kinetic studies were performed, and the data was found in good agreement with the pseudo‐second‐order.     

零价铁(ZVI)去除水中的As(Ⅲ)

采用市售还原铁粉(零价铁,ZVI)及其与石英砂的复合物为吸附剂,对水中As(Ⅲ)的吸附分别做了分批试验和连续性试验。分批试验结果表明,ZVI吸附水中As(Ⅲ)的去除效果受pH主导,其最佳pH范围4～9,ZVI主要通过其表面吸附及其腐蚀产物对As(Ⅲ)的吸附共沉淀作用达到对As(Ⅲ)的去除,同时,在ZVI腐蚀的过程中还伴有在ZVI表面As(Ⅲ)的氧化、还原作用,As(Ⅲ)的氧化受ZVI腐蚀过程的影响,其氧化过程主要发生在Fe²⁺氧化为Fe³⁺的阶段;连续性试验利用ZVI与石英砂复合物对模拟含砷废水进行吸附研究,从吸附柱进水至吸附饱和共20 d时间,经计算,ZVI对As(Ⅲ)的吸附容量为89.90 mg·g^-1,ZVI腐蚀产物在石英砂表面的晶态类型对As(Ⅲ)的吸附容量有影响,无定形态的ZVI腐蚀产物对As(Ⅲ)的吸附容量最大,质量分数和原子分数分别可达到6.73%和2.15%。     

分子筛对重金属废水吸附性能的实验研究

为验证分子筛对重金属废水的处理效果,以实际含锰废水为研究对象,采用13X分子筛,通过实验研究了吸附材料用量、吸附时间、搅拌转速和溶液pH对Ca²⁺、Mn²⁺、Mg²⁺吸附效果的影响。结果表明：吸附材料用量增加对Mn²⁺、Mg²⁺的吸附影响较大;随着吸附时间增长,各金属离子去除率增加;适当的转速有利于金属离子的吸附,但各金属离子对应的最佳转速各不相同;pH提高,能够促进分子筛对金属离子的吸附。13X分子筛对金属离子的吸附机理为离子交换吸附和表面吸附。研究表明,13X分子筛在处理低浓度含锰重金属废水方面表现出良好的应用前景。     

Simultaneous Removal of Nickel(II) and Chromium(VI) from Aqueous Solutions and Simulated Wastewaters by Foam Separation

The present investigation was carried out to study the feasibility of foam separation for simultaneous removal of two types of inorganic hazardous contaminants, nickel(II) cations and chromium(VI) anions, from aqueous solutions and simulated wastewaters. The effects of pH of the solution, Ni/Cr ratio, collector and frother concentrations, induction and flotation time, and solution ionic strength on the co-removal efficiency of nickel(II) and chromium(VI) were studied. At the optimum conditions, removals more than 99.5% were obtained for nickel(II) and chromium(VI). The concerned contaminants were effectively removed when they coexisted at low as well as at high concentrations. Coflotation of nickel(II) and chromium(VI) from tap water and simulated electroplating wastewater resulted in removal percentages higher than 99.5% with residual concentrations below their permissible limits in potable water. High removal percentages, DFs, ERs, and VRs were achieved for their radionuclides, ⁶³Ni(II) and ⁵¹Cr(VI), from simulated radioactive process wastewater. The results obtained in this study suggest the feasibility of the developed foam separation process for treatment, in a single-step, of wastewaters contaminated with cationic and anionic inorganic pollutants.     

泥炭吸附法去除废水中重金属

介绍了天然廉价矿物泥炭的物理化学性质,综述了泥炭的改性方法及其对多种重金属离子的吸附容量．分析了pH、改性方法、竞争离子浓度等因素的影响。并对泥炭吸附重金属离子的机理和规律进行了总结．其吸附机理有离子交换、络合、表面吸附、化学吸附等四种,吸附一般符合Langmuir吸附等温式或Freundlich吸附等温式。最后展望了泥炭在重金属废水处理中的应用前景,提出了一些建议。