颗粒活性炭载纳米零价铁去除水中的Cr(Ⅵ)

以Fe2+溶液为原料、NaBH4为还原剂,采用传统液相还原技术合成了颗粒活性炭(GAC)载纳米零价铁(nZVI)复合材料GAC-nZVI,用扫描电镜对GAC-nZVI进行表征,通过间歇实验考察了其对去除Cr(VI)的影响。结果表明,GAC能阻止nZVI颗粒聚集,合成的GAC-nZVI能有效去除水中的Cr(VI)。在Cr(VI)初始浓度50 mg/L、温度40℃和pH=2.0、投加GAC-nZVI 3.0 g/L的条件下反应5 min,Cr(VI)去除率为99.4%。pH=2.0?4.0时,处理后水中总铬浓度均低于1 mg/L,表明残留少量Cr(III)。随pH值和Cr(VI)浓度增加,Cr(VI)去除率降低;随反应温度和GAC-nZVI投加量增加,Cr(VI)去除率增加。准一级动力学模型可用于描述Cr(VI)的去除过程。相同条件下,GAC-nZVI去除Cr(VI)的反应速率常数达0.19797 min?1,为原颗粒活性炭反应速率常数0.0023 min?1的86倍。随pH值降低或反应温度和GAC-nZVI投加量增加,反应速率常数增加。     

铁盐共沉淀泡沫浮选法去除废水中Cr(VI)的应用研究

采用铁盐共沉淀泡沫浮选法去除废水中Cr(VI),用FeSO4将六价铬还原成三价状态,考察了还原剂用量、捕捉剂品种及pH对总铬去除率的影响。结果表明,对浓度为10 mg/L的含Cr(VI)模拟废水,使用FeSO4作还原剂,LAS作捕捉剂,铁铬摩尔比为7∶1,pH=10,鼓泡10 min的条件下,Cr(VI)去除率可达99.1%。     

光催化法处理含Cr(VI)废水的研究

采用P 25 TiO2作为光催化剂,研究了废水的pH值、Cr(VI)的初始浓度、气氛及有机物等因素对含铬废水中Cr(VI)去解率的影响。结果表明,在pH值为3.0时,光催化反应速率最大;反应气氛对该体系中Cr(VI)的光催化还原无明显影响;苯酚、葡萄糖等有机物的存在能有效地促进Cr(VI)的光催化还原,当加入与Cr(VI)等物质的量的苯酚或葡萄糖时,150 mL反应液[Cr(VI)浓度为0.96 mmol/L],0.15 g光催化剂,经12 W紫外灯照射反应120 m in,Cr(VI)完全被去除,相对于在反应体系中不加有机物时,Cr(VI)光催化还原效率提高了近100%;Cr(VI)的光催化还原符合L-H动力学规律。     

Removal of chromium(VI) from aqueous solutions using polypyrrole-based magnetic composites

PPy/Fe₃O₄/AgCl composites were prepared via in situ polymerization for the removal of highly toxic Cr(VI). The structure and morphology of the prepared composites were characterized by the XRD, SEM, TEM, and VSM examinations. Up to 100 % removal was found with 1000 mg/L Cr(VI) aqueous solution at pH 2.0. The process of Cr(VI) ions’ adsorption was easy to reach equilibrium at higher temperatures. Adsorption results showed that Cr(VI) removal efficiency by the composites decreased with an increase in pH. Adsorption kinetics was described by the pseudo-second-order rate model. Isotherm data fitted well to the Langmuir isotherm model. Desorption experiment showed that the regenerated adsorption of PPy/Fe₃O₄/AgCl can be reused successfully for three times successive adsorption–desorption cycles without appreciable loss of its original capacity.     

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.     

羟基铁铝柱撑膨润土在含铬废水处理中的应用

以FeCl3、AlCl3和Na2CO3配制柱化剂,以钠基膨润土为原料,制备了羟基铁铝柱撑膨润土,并研究了其作为絮凝剂对含Cr(Ⅵ)废水的处理效果.结果表明:羟基铁铝柱撑膨润土对Cr(Ⅵ)有很好的去除效果,羟基铁铝柱撑膨润土投加量、pH及搅拌时间对Cr(Ⅵ)的吸附有较明显的影响,其中羟基铁铝柱撑膨润土投加量的影响最为显著...     

Biosorption of hexavalent chromium from aqueous solutions using raw coconut fiber as a natural adsorbent

Abstract

This work aims to evaluate the Cr(VI) removal efficiency and adsorption capacity of the raw coconut fiber from synthetic aqueous solutions through the operational parameters as well as to represent the mechanisms of removal by kinetic and isotherm models. The experimental study was conducted in batch system and the optimum conditions for the adsorption of this metal by the biomass were according to: pH 2, contact time of 270?min, and 10?g/L of adsorbent dosage concentration. The removal efficiency obtained for Cr(VI) solutions was 99.2% at concentrations of 25–50?mg/L. For the highest concentrations, the removal decreased from 96.3% to 74.4%, when Cr(VI) solutions ranged from 100?mg/L to 250?mg/L, respectively. The adsorption kinetics was applied and showed a good agreement for pseudo-second-order and Elovich models, which point out a chemisorption. For the adsorption capacity at equilibrium conditions, the best fit was for the Redlich–Peterson isotherm indicating favorable adsorption and monolayer coverage.     

Effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution by modified polyethyleneimine

A novel flocculant with the capacities of reduction and chelation was prepared in this paper. The flocculant, called polyethyleneimine–sodium xanthogenate (PEX), was synthesized by modifying polyethyleneimine with carbon disulfide and sodium hydroxide. The effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution with PEX was investigated by using flocculation experiments. The results showed that in the single-ion system (only including Cr(III) or Cr(VI) in the solution), the final Cr(III) decreased with the increase in pH from 2.0 to 10.0, while the final Cr(VI) increased at first and then decreased with the increase in this pH range studied. The removal of Cr(III) was not desirable at pH lower than 7.0, whereas the final Cr(VI) concentration reached the minimum value of 0.145 mg/L at pH 2.0. In the mixture system of Cr(III) and Cr(VI), the variation tendency for the removal of Cr(III) or Cr(VI) was very similar to that obtained in the single-ion system. The oxidation–reduction potential, zeta potential, and final pH in the supernatant were also measured to analyze the above results. Furthermore, FTIR spectra revealed that dithiocarboxylic acid groups on the macromolecular chains of PEX played a major role in the Cr(VI) reduction and Cr(III) chelation.     

Bacterial cellulose/PANi mat for Cr(VI) removal at acidic pH

Remediation of hexavalent chromium - Cr(VI) at acidic pH using polyaniline coated bacterial cellulose porous mat (BC/PANi) is presented and the possible mechanism is discussed. The efficacy of BC/PANi mats in remediation of Cr(VI) was studied by varying pH (pH 1, 2, 3, and 5) and initial Cr(VI) concentrations (250–1000 ppm) of the solution. The BC/PANi (50 mg) mat was able to completely reduce 2000 ppm Cr(VI) into Cr(III) in a 20 ml solution at pH ~ 1 in 24 h. An increasing chromium removal efficiency was observed with decreasing solution pH; reaching a maximum removal capacity of ~920 mg/g at pH 1. The proposed mechanism of negatively charged Cr(VI) ions removal by BC/PANi mat is adsorption and simultaneous reduction into Cr(III), followed by desorption of Cr(III) from the mat. The role of temperature and co-existing anions like sulphate, nitrate and chloride found in industrial sludge were also investigated for removal efficiency of Cr(VI) at acidic pH ~ 1. The adsorption kinetics of Cr(VI) on polyaniline surface followed a pseudo-second-order model with reduction of Cr(VI) into Cr(III) as rate-limiting step. The reduced Cr(III) from the media was further recovered by neutralizing the pH of the solution.     

交联薯渣黄原酸酯对废水中Cr(Ⅵ)的吸附研究

交联薯渣黄原酸酯(CCX)废水中Cr(Ⅵ)离子的吸附,探讨了pH值、温度、吸附时间、CCX含硫量、Cr(Ⅵ)初始浓度等因素对其吸附效果的影响。结果表明,当CCX加入量为理论加入量的3.0倍时,pH为2.5,在45℃下搅拌反应50 min,对Cr(Ⅵ)的吸附容量为37.76 mg/g,去除率达到99.69%,处理后的废水中Cr(Ⅵ)浓度为0.15 mg/L,低于国标排放标准(0.5 mg/L)。并通过红外光谱和热重分析,对CCX吸附Cr(Ⅵ)的机理进行了探讨。     

Removal of Chromium(VI) and Chromium(III) from Aqueous Solution by Grainless Stalk of Corn

Abstract

Grainless stalk of corn (GLSC) was tested for removal of Cr(VI) and Cr(III) from aqueous solution at different pH, contact time, temperature, and chromium/adsorbent ratio. The results show that the optimum pH for removal of Cr(VI) is 0.84, while the optimum pH for removal of Cr(III) is 4.6. The adsorption processes of both Cr(VI) and Cr(III) onto GLSC were found to follow first-order kinetics. Values of k _ads of 0.037 and 0.018 min^?1 were obtained for Cr(VI) and Cr(III), respectively. The adsorption capacity of GLSC was calculated from the Langmuir isotherm as 7.1 mg g^?1 at pH 0.84 for Cr(VI), and as 7.3 mg g^?1 at pH 4.6 for Cr(III), at 20°C. At the optimum pH for Cr(VI) removal, Cr(VI) reduces to Cr(III). EPR spectroscopy shows the presence of Cr(V) + Cr(III)-bound-GLSC at short contact times and adsorbed Cr(III) as the final oxidation state of Cr(VI)-treated GLSC. The results indicate that, at pH ≈ 1, GLSC can completely remove Cr(VI) from aqueous solution through an adsorption-coupled reduction mechanism to yield adsorbed Cr(III) and the less toxic aqueous Cr(III), which can be further removed at pH 4.6.     

Removal of Ag(I) and Cr(VI) by Complexation-Ultrafiltration and Characterization of the Membrane by CFSK Model

Removal of Ag(I) and Cr(VI) by complexation-ultrafiltration, anionic polyacrylamide being the complexation agent, has been reported. Effects of operating variables such as initial metal ions concentration in feed, feed pH, polymer-to-metal ions ratio, and applied pressure on the removal of metal ions were studied at a constant feed flow rate of 15 L/min. Maximum rejection obtained were close to 100% for Ag(I) and 94% for Cr(VI) ions in single ion system; and for binary ions system it is 87% for Ag(I) and 76% for Cr(VI) ions. The membrane was characterized using the combined-film theory-Spiegler-Kedem (CFSK) model.     

Removal process and mechanism of hexavalent chromium by adsorption-coupled reduction with marine-derived Aspergillus niger mycelial pellets

In order to remove hexavalent chromium(Cr(Ⅵ)) from solutions efficiently, the mycelial pellets with a marine-derived fungus Aspergillus niger as a biosorbent were prepared. The effects of removal process parameters such as solution pH, initial Cr(Ⅵ) concentration and biomass concentration on Cr(Ⅵ) removal process were investigated. The results showed that Cr(Ⅵ) removal rate up to 100% could be achieved under optimized conditions, which indicated the excellent Cr(Ⅵ) removal performance of the Asp...     

季铵化壳聚糖及其絮凝六价铬性能的研究

以3-氯-2-羟丙基三甲基氯化铵(CTA)为改性剂接枝改性了壳聚糖,制备得到了2-羟丙基三甲基壳聚糖季铵盐(CTA-CTS),用红外光谱和核磁共振表征了产物的结构;用得到的产品处理含Cr2O72-的模拟电镀废水,研究了接枝时间、废水的pH值、CTA-CTS的质量浓度对Cr(Ⅵ)去除能力的影响。结果表明:接枝反应主要发生在—NH2上,并以反应时间为10.0h的产品对Cr(Ⅵ)的去除能力较强,在pH值为5.0,CTA-CTS的质量浓度为100mg/L左右时,对Cr(Ⅵ)的去除率可达95%。     

Polyaniline/akaganéite nanocomposite for detoxification of noxious Cr(VI) from aquatic environment

In this work, a removal of toxic hexavalent chromium Cr(VI) ion from aqueous solution was investigated and studied using nanocomposite of polyaniline (PANI) and akaganéite nanoparticles (NP). HCl doped PANI, and akaganéite NPs were prepared by chemical oxidative polymerization and co-precipitation techniques, respectively. The synthesized materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), and high-resolution transmission electron microscope (HRTEM). It was indicated that the formed oxide NPs were consisted of akaganéite as dominant phase plus minor phases of hematite, magnetite, and/or maghemite. HRTEM images of the prepared nanocomposite demonstrated that the phases of oxide NPs embedded in the nanocomposite had the same crystallinity and morphology of pristine oxide NPs. It was found that size of nanocomposite particles has diameter ranged from 8.95 to 16.21 nm. Cr(VI) removals in a wide pH range from 2 to 9 were appropriated for prepared nanocomposite. The nanocomposite has demonstrated high removal percentage of 99.2 % and removal capacity of 17.36 mg/g for 7.0 mg/L Cr(VI) polluted aqueous solution at pH 2.0 for 5-min contact time. The synthesized nanocomposite was applied to remove Cr(VI) from a leather tanning wastewater sample with efficiency of 93.4 %.     

Fe2+-modified Vermiculite for the Removal of Chromium (VI) from Aqueous Solution

A novel adsorbent: Fe²⁺-modified vermiculite was prepared in a two-step reaction. Adsorption experiments were carried out as a function of pH, contact time, and concentration of Cr(VI). It was found that Fe²⁺-modified vermiculite was particularly effective for the removal of Cr(VI) at pH 1.0. The adsorption of Cr(VI) reached equilibrium within 60 min, and the pseudo-second-order kinetic model best described the adsorption kinetics. The adsorption data follow the Langmuir model more than the Freundlich model. At pH 1.0, the maximum Cr(VI) sorption capacity (Q _max ) was 87.72 mg · g^?1. Desorption of Cr(VI) from Fe²⁺-modified vermiculite using NaOH treatment exhibited a higher desorption efficiency by more than 80%. The sorption mechanisms including electrostatic interaction and reduction were involved in the Cr (VI) removal. The results showed that Fe²⁺-modified vermiculite can be used as a new adsorbent for Cr(VI) removal which has a higher adsorption capacity and a faster adsorption rate.     

Ion-crosslinked carboxymethyl cellulose/polyaniline bio-conducting interpenetrated polymer network: preparation,characterization and application for an efficient removal of Cr(VI) from aqueous solution

A simple, cheap, and environmentally friendly bio-conducting interpenetrated polymer blend network was prepared and introduced as a highly efficient system with suitable physical and mechanical properties for industrial removal of toxic Cr(VI) ions from aqueous solution. Carboxymethyl cellulose/polyaniline (CMC/PANI) interpenetrated network (IPN) blend was prepared by simple simultaneous ion-cross-linking of CMC and PANI chains using Al³⁺ cations. The CMC/PANI bio-conducting nanocomposite was characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy equipped with an "energy dispersive X-ray spectroscopy" (SEM–EDX) technique. The CMC/PANI blend, ion-cross-linked by Al³⁺ cations, showed good stability and high surface area, proper for the removal of toxic Cr(VI) ions of the aqueous solution. Batch removal experiments were accomplished and the impression of effective variables including solution pH, initial concentration of Cr(VI) ions, contact time, and adsorbent dosage were checked and optimized. The outcome of our findings revealed that the removal of Cr(VI) ions by CMC/PANI nanocomposite IPN strongly depends on solution pH. The removal information was matched with the Langmuir adsorption isotherm model and the utmost monolayer adsorption capacity at pH 2 was 136.98 mg/g at 25 °C. The pseudo-second-order kinetics were operated and the thermodynamic parameters suggested spontaneous and exothermic nature of the adsorption process. Consequences indicated that CMC/PANI nanocomposite IPN could be an affective eco/environmentally friendly adsorbent for the removal of Cr(VI) ions from aqueous solutions.

     

Removal of Cr(VI) from Aqueous Solutions by a Bacterial Biofilm Supported on Zeolite: Optimisation of the Operational Conditions and Scale‐Up of the Bioreactor

The aim of this study was to investigate the feasibility of a bioreactor system and its scale‐up to remove Cr(VI) from solution. The bioreactor is based on an innovative process that combines bioreduction of Cr(VI) to Cr(III) by the bacterium Arthrobacter viscosus and Cr(III) sorption by a specific zeolite. Batch studies were conducted in a laboratory‐scale bioreactor, taking into account different operating conditions. Several variables, such as biomass concentration, pH and zeolite pre‐treatment, were evaluated to increase removal efficiency. The obtained results suggest that the Cr removal efficiency is improved when the initial biomass concentration is approximately 5 g L^–1 and the pH in the system is maintained at an acidic level. Under the optimised conditions, approximately 100 % of the Cr(VI) was removed. The scale‐up of the developed biofilm process operating under the optimised conditions was satisfactorily tested in a 150‐L bioreactor.     

A high Cr (VI) absorption efficiency and easy recovery adsorbent: Electrospun polyethersulfone/polydopamine nanofibers

Cr (VI) is a highly toxic pollutant to humans, to achieve high adsorption capacity, easy recovery, and good reusability, polyethersulfone/polydopamine (PES/PDA) ultrafine fibers were prepared successfully. A series of preparing effect factors were investigated systematically and the optimum one is 8.5 pH value at room temperature and 2 g/L dopamine concentration. And then they were used as an adsorbent for the removal of Cr (VI) ions from wastewater. The effect factors pH, the adsorbent dosage, and time were discussed on Cr (VI) adsorption process and the Cr (VI) adsorption behavior was investigated. It is found that the maximum Cr (VI) adsorption capacity is 115.2 ± 4.8 mg/g at pH = 3 using 0.06 g PES/PDA with 80 mins. The Cr (VI) adsorption process followed the pseudo-second-order model (r² ≥ 0.99) and adsorption isotherms were fitted to the Langmuir model (R² ≥ 0.999). Furthermore, the Cr (VI) adsorption mechanism was supposed according to the X-ray photoelectron spectroscopic results. Finally, PES/PDA ultrafine fibers were considered to be a promising adsorbent with good stability (decomposing temperature, 356°C), high adsorption efficiency (112.1 ± 2.5 mg/g), and good reusability (three times) on the coexistence of anions and the actual industry wastewater environment.     

Adsorption of chromium(VI) from aqueous solution by Artist’s Bracket fungi

The objective of this study was to investigate Artist’s Bracket (AB) fungi for the removal of Cr(VI) from aqueous solutions. The effects of pH, adsorbent dosage, temperature, contact time and initial concentration of Cr(VI) were evaluated. The optimal pH value for the removal of Cr(VI) was at pH 2. Moreover, the results showed that the adsorption of Cr(VI) decreased by increasing the initial Cr(VI) concentration and pH. The absorption of Cr(VI) on AB can be described by both Freundlich and Langmuir isotherm models. In addition, both pseudo-first-order and pseudo-second-order kinetic model well described the adsorption of Cr(VI) onto AB.