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1.
This study reports the potential ability of non-living biomass of Cabomba caroliniana for biosorption of Cr(III) and Cr(VI) from aqueous solutions. Effects of contact time, biosorbent dosage, pH of the medium, initial concentration of metal ion and protonation of the biosorbent on heavy metal–biosorbent interactions were studied through batch sorption experiments. Cr(III) was sorbed more rapidly than Cr(VI) and the pH of the medium significantly affected the extent of biosorption of the two metal species differently. Surface titrations showed that the surface of the biosorbent is positively charged at low pH while it is negatively charged at pH higher than 4.0. Protonation of the biosorbent increased its capacity for removal of Cr(III), while decreasing that of Cr(VI). FT-IR spectra of the biosorbent confirmed the involvement of –OH groups on the biosorbent surface in the chromium removal process. Kinetic and equilibrium data showed that the sorption process of each chromium species followed pseudo second-order kinetic model and both Langmuir and Freundlich isothermal models. A possible mechanism for the biosorption of chromium species by non-living C. caroliniana is suggested.  相似文献   

2.
The biosorption of chromium (VI) ions from aqueous solutions by two adsorbents viz. mango and neem sawdust was studied under a batch mode. An initial pH of 2.0 was most favorable for chromium (VI) removal by both the adsorbents. The results obtained for the final concentration of chromium (VI) and chromium (DI) at a pH range of 2–8 indicated that a combined effect of biosorption and reduction was involved in the chromium (VI) removal specially when the pH value is lower than 3. The maximum loading capacity was calculated from adsorption isotherms by applying the Langmuir model and found to be higher for neem sawdust (58.82 mg/g). Evaluation of experimental data in terms of biosorption kinetics showed that the biosorption of chromium (VI) by neem sawdust followed pseudo second-order kinetics. Therefore, the rate limiting step may be chemical sorption or chemisorption. The efficiency of this process was examined in using tannery wastewater contaminated with chromium (VI) ions in column mode.  相似文献   

3.
The carbon–alumina composite pellet was developed for the adsorption of acid fuchsin from its aqueous solution. The composite pellet was characterized using Brunauer–Emmett–Teller method, scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy. The adsorption capacity of commercial alumina, commercial activated carbon and the prepared composite pellet was investigated against acid fuchsin, and the adsorption capacity was found to be increased in the order of alumina < carbon–alumina composite pellet < activated carbon. Although the adsorption capacity of carbon–alumina composite pellets was less than that of activated carbon, the use of the pelletized form of the present adsorbent was proven to be advantageous for the use in the packed-bed column. The experimental data were fitted to Langmuir, Freundlich and Temkin adsorption isotherms, and the equilibrium behavior was well explained by Langmuir isotherm. Besides, the kinetic behavior was well predicted by pseudo-second-order kinetics. The effects of inlet dye concentration (10–20 mg/L), feed flowrate (5–15 mL/min) and bed height (2.54–7.62 cm) on the breakthrough characteristics were investigated using a fixed-bed column. The maximum removal capacity in the column study was found to be 343.87 mg/L with an initial dye concentration and flowrate of 20 and 10 mL/min according to Bohart–Adams model. The breakthrough behavior was also effectively described by the Yoon–Nelson and Clark models.  相似文献   

4.
The goal of this study is examination of the mixture between adsorption and permeation process for removing chromium (VI) from the water. Two types of supported membranes are developed: The first one which was made by sol–gel method is called nanoporous and the second one which was made by electrospinning is called nanofiber. The sorption capacity of nanoporous and nanofiber is examined in single batch experiments at various pH values, and it is found that maximum chromium removal is observed for both nanoporous and nanofiber at pH 3.5. Adsorption studies illustrated that the Cr(VI) adsorption onto alumina nanoporous and nanofiber is affected by changes in pH, contact time, dosage of adsorbent, concentration of chromium and solution volume. Langmuir and Freundlich isotherms can be used to explain the adsorption equilibria of Cr(VI) onto alumina nanoporous and nanofiber. It was found that balance adsorption data adequate Langmuir isotherm more than Freundlich model. Adsorption kinetics was found to be fitted to pseudo-second order and Weber and Morris model. The output of multiple linear regressions was run for the second-order response surface model implied that the linear agents of pH, sorbent dosage and Cr(VI) concentration are more significant factors. Manufacturing electrospun alumina nanofiber and sol–gel nanoporous with these cheap materials, renewable and fast methods are so important although the removal percentage is significant.  相似文献   

5.
Phanerochaete chrysosporium, a white rot basidiomycete, was immobilized over Luffa cylindrica sponge discs, treated with 0.1 N HCl and its potentiality for the removal of hexavalent chromium [Cr(VI)] from water was investigated in both batch and in up-flow fixed-bed bioreactor. The acid treatment of biomass increased the uptake capacity and percentage removal of Cr(VI) from 33.5 to 46.5 mg g?1 and 67 to 92 %, respectively. Maximum uptake of Cr(VI) was achieved at pH 2, temperature 40 °C after 100 min of contact time. The Cr(VI) sorption on the biomass was better explained by Langmuir isotherm. Thermodynamic studies indicated that the process was spontaneous and endothermic. Sorption kinetic study showed that pseudo-second-order model best correlates the Cr(VI) sorption on the biomass as compare to pseudo-first-order kinetic model. The performance of fixed-bed bioreactor was evaluated at different bed heights (5, 15 and 25 cm) and flow rates (1.66, 4.98 and 8.33 mL min?1) by using bed depth service time model. Response surface methodology statistical method was applied for optimizing the process parameters. FTIR analysis showed that amino groups were mainly involved in adsorption of Cr(VI).  相似文献   

6.
The batch removal of Cr(VI) from aqueous solution using lignocellulosic solid wastes such as sawdust and pine leaves under different experimental conditions was investigated in this study. The influence of pH, temperature, contact time, initial concentration of Cr(VI) and particle size on the chromium removal was investigated. Adsorption of Cr(VI) is highly pH-dependent and the results indicate that the optimum pH for the removal is 2. The capacity of chromium adsorption at equilibrium by these natural wastes increased with absorbent concentration. Temperature in the range of 20–60 °C showed a restricted effect on the adsorption capacity of pine leaves, but had a considerable effect on the adsorption capacity of sawdust. The capacity of chromium adsorption at the equilibrium increased with the decrease in particle sizes. The suitability of adsorbents was tested with Langmuir and Freundlich isotherms and their constants were evaluated. Results indicated that the Freundlich model gave a better fit to the experimental data in comparison with the Langmuir equation. The study showed that lignocellulosic solid wastes such as sawdust and pine leaves can be used as effective adsorbents for removal of Cr(VI) from wastewater.  相似文献   

7.
The removal of hexavalent chromium from wastewater streams has received an considerable attention in recent years, since it can cause harmful effects on the environment. Several approaches, including adsorption, are recognized to tackle this problem, but unfortunately most of these processes are impressed with practical conditions of the experiments. The main objective of this study was to recognize applicable conditions for Cr(VI) removal from an industrial drainage using nature-derived adsorbents (brown coal and modified zeolite) and to make the process more adaptive by using adsorbents conjointly. Batch experiments were carried out by agitating Cr(VI) stock solution with adsorbents at room temperature. The influence of main operating parameters was explored, and the best proportion of the adsorbents was determined. Maximum sorption of Cr(VI) onto brown coal was observed at pH = 4 by adding 60 g L?1 adsorbent to contaminated solution. In case of using zeolite, the modification process was required, and the pH indicated a weak influence in a wide range (2–8). Optimum dosage of modified zeolite for Cr(VI) removal was 10 g L?1. The hybrid application of adsorbents with the mass ratio of brown coal/modified zeolite at (3:1) was capable of removing more than 99% of Cr(VI) from contaminated wastewater in the natural pH range of the wastewater. The adsorption of Cr(VI) by brown coal and modified zeolite followed Langmuir and Freundlich isotherm models, respectively. Sorption of Cr(VI) onto both brown coal and modified zeolite fitted well to pseudo-second-order rate reaction.  相似文献   

8.
典型铬渣污染场地铬污染特征研究   总被引：1，自引：0，他引：1  
选取西南岩溶区某傍河铬渣堆场为研究对象,对场地不同位置与深度的土壤及地下水样品进行采集,通过数理统计对Cr在场地中的空间分布特征以及场地对地下水的影响进行了分析。结果表明:土壤中总Cr浓度的水平分布具有差异性,表层土壤Cr浓度由上游到下游呈明显降低趋势,变化率为3.59;深层饱水带土壤中总Cr浓度分布受到地下水流场的影响,场地下游土壤铬浓度明显高于上游;杂填土垂向剖面的铬浓度分布不同于坡残积红黏土,杂填土中铬浓度随着深度的增加而增加,浓度与土壤深度的关系可用y=63.88ln（x）-75.221来表示;而在红黏土中剖面中,铬大量聚集在土壤表层,后随着深度的增加铬浓度逐渐降低,接近基岩面有升高趋势;场地地下水中Cr（Ⅵ）的浓度受深层土壤中总Cr浓度的影响,两者呈正相关。   相似文献   

9.
The development of a fast, effective, simple and low-cost procedure for chromium speciation is an analytical challenge. In this work, a new and simple method for speciation and determination of chromium species in different matrices was developed. Sepia pharaonis endoskeleton nano-powder was used as an adsorbent for the dispersive micro-solid-phase extraction. Finally, the desorbed chromium was determined using a graphite furnace atomic absorption spectrometer. The experimental results showed that Cr(III) could be quantitatively extracted by the adsorbent, while Cr(VI) adsorption was negligible. Concentrated H2SO4 and ethanol reduced Cr(VI)–Cr(III), and total chromium content was assessed as Cr(III). Then, the Cr(VI) concentration in the sample was calculated as the difference. The optimum conditions were obtained in terms of pH, adsorbent amount, contact time, and type, concentration and volume of eluent. Under the optimum conditions that involved the speciation of chromium ions from 25 mL of the water samples at pH 7.0 using 0.025 g of the adsorbent with contact time of 5 min, the method was validated in terms of linearity, precision and accuracy. The calibration curve was linear over the concentration range of 0.01–25.00 μg L?1 for Cr(III). The obtained limit of detection for the proposed method was 0.003 µg L?1. The maximum adsorption capacity of the adsorbent was found to be 995.57 mg g?1. The proposed method was validated by the speciation of Cr(III) and Cr(VI) in different real water and wastewater samples with satisfactory results.  相似文献   

10.
Nanoscale zero-valent iron particles (NZVI) produced by using green tea (GT) extract as a reductant can remove Cr(VI) from water effectively, which can be utilized in groundwater remediation. In order to define the reaction mechanism and removal effect in the aquifer, in this study, GT-NZVI particles were prepared and measured by some characterization methods to define their surface performance, and then batch and one-dimensional experiments were carried out to reveal the reaction properties of GT-NZVI and Cr(VI) in groundwater. The results showed that the prepared GT-NZVI particles were regular spherical with a diameter of 10–20 nm, which could disperse in water stably. The main component of GT-NZVI was α-Fe with superficial polyphenols as a stabilizer. GT-NZVI suspension had good ability to reduce the Cr(VI) to Cr(III) in water. When the concentration of GT-NZVI was 1 g/L, the removal efficiency of Cr(VI) with an initial concentration of 100 mg/L reached 92.8% in 1 h reaction. In column tests, GT-NZVI passed through the natural sand column successfully with an average outflow percentage of 71.2%. The simulated in-situ reaction zone (IRZ) with GT-NZVI was used to remediate Cr(VI) contaminated groundwater. The outflow concentration of Cr(VI) kept in 0.14–0.32 mg/L corresponding to the outflow rate below 0.32% within 15 days, and the removal efficiency of Cr(VI) by IRZ with GT-NZVI decreased with the increase of aquifer medium particle size, groundwater flow rate and ionic strength. Most of Cr(III) as reduzate was adsorbed or immobilized on the surface or in the lattice of GT-NZVI, which indicated effective immobilization for chromium.  相似文献   

11.
The photoreduction efficiency of toxic hexavalent chromium into non-toxic trivalent chromium was studied using local low-cost material and modern technology. The materials involved different iron–titanium oxide nanopowders synthesized via simple hydrothermal–hydrolysis process. X-ray diffraction and high-resolution transmission electron microscope were employed to study the structural properties of the as-prepared samples. The effects of molar ratio (Fe/Ti) and hydrothermal temperature on spectroscopic properties have been investigated using Fourier transform infrared FT-IR spectroscopy. The photocatalytic performance of hexavalent chromium was systematically studied at various conditions including initial concentration of Cr(VI), hydrothermal temperature and Fe/Ti ratios of mixed iron–titanium oxide powders. It has been found that the highest photoreduction efficiencies of Cr(VI) were 95.7 and 86.2% at initial concentrations 10 and 60 ppm of Cr(VI), respectively. The synthesized mixed Fe2O3–TiO2 photocatalyst exhibited higher efficiency of about 88% under visible light irradiation. The as-prepared mixed oxide catalyst exhibited high photocatalytic conversion efficiency and recycling stability in comparison with different commercial catalysts.  相似文献   

12.
Adsorption and desorption of uranium(VI) from dilute aqueous solutions by Eucalyptus citriodora distillation sludge was studied in a batch mode. The potential of Eucalyptus citriodora distillation sludge to remove uranium(VI) from aqueous solutions has been investigated at different conditions of solution pH, metal ion concentrations, biosorbent dosage, biosorbent particle size, contact time and temperature. The results indicated that biosorption capacity of Eucalyptus citriodora distillation sludge was strongly affected by the medium pH, the biosorbent dose, metal ion concentrations and medium temperature. Reduction in particle size increased the biosorption capacity. Langmuir and Freundlich isotherm models were applied to biosorption data to determine the biosorption characteristics. An optimum biosorption capacity (57.75 mg/g) was achieved with pH 4.0, particle size 0.255 mm, biosorbent dose 0.5 g/100 mL and initial uranium(VI) concentration of 100 mg/L. Uranium(VI) removal by Eucalyptus citriodora distillation sludge was rapid, the equilibrium was established within 60 min and pseudo-second-order model was found to fit with the experimental data. The biosorption process decreased with an increase in the temperature indicating its exothermic nature. Pretreatments of biomass with different reagents affected its biosorption capacity. A significant increase (34 %) in biosorption capacity (83.25 mg/g) was observed with benzene treatment. Fourier-transform infra-red studies showed the involvement of carbonyl, carboxyl and amide groups in the biosorption process. The results indicated that sulfuric acid had the best effects as an eluent showing 93.24 % desorption capacity.  相似文献   

13.
In this work, synthesis of chitosan beads impregnated with nano-γ-Al2O3 (AlCB) was carried out. The characteristics of the synthesized adsorbent were obtained by using Brunauer Emmett and Teller technique and Scanning Electron Microscopy method. The use of AlCB in continuous removal of chromium, lead, nickel and cadmium ions from liquid solution was studied using fixed-bed column system. Bed depths and flow rate effects on breakthrough and uptake capacity of the adsorbent in column were also examined. Dynamic parameters of the adsorption were calculated by using bed depth service time (BDST) and Thomas models. In both models, the data were analyzed by error analyzing and combining the values of determined coefficient (R 2) from regression analysis. The adsorption capacities of AlCB in breakthrough were 158.33, 183.33, 63.33 and 31.67 mg/g for chromium, lead, nickel and cadmium, respectively. In addition, BDST model was found to be an acceptable kinetic model to describe the experimental data.  相似文献   

14.
The removal of the chromium (VI) ion from aqueous solutions with the Lewatit FO36 ion-exchange resin is described at different conditions. The effects of adsorbent dose, initial metal concentration, contact time and pH on the removal of chromium (VI) were investigated. The batch ion exchange process was relatively fast and it reached equilibrium after about 90 min of contact. The ion exchange process, which is pH dependent showed maximum removal of chromium (VI) in the pH range 5.0–8.0 for an initial chromium (VI) concentration of 0.5 mg/dm3. The equilibrium related to Lewatit FO36 ion- exchange capacity and the amounts of the ion exchange were obtained using the plots of the Langmuir adsorption isotherm. It was observed that the maximum ion exchange capacity of 0.29 mmol of chromium (VLVg for Lewatit FO36 was achieved at optimum pH value of 6.0. The ion exchange of chromium (VI) on this cation-exchange resin followed first-order reversible kinetics.  相似文献   

15.
张亭亭  李江山  薛强  王平  熊欢  梁仕华 《岩土力学》2019,40(12):4652-4658
采用硫酸亚铁（FeSO4）对Cr(VI)污染土进行稳定化处理。研究了Fe(II)/Cr(VI)摩尔比和养护龄期对污染土稳定过程中的铬赋存形态及浸出特性的影响规律。结果表明：随着Fe(II)/Cr(VI)摩尔比和养护龄期的增加,Cr(VI)和总Cr的浸出浓度降低,稳定土中Cr(VI)的含量降低,当摩尔比为3时,Cr(VI)和总Cr的浸出浓度均低于我国《危险废弃物鉴别标准 浸出毒性鉴别》（GB/T50853―2007）的限值;当摩尔比为10时,稳定土中Cr(VI)的含量低于我国《土壤环境质量标准》（GB15618―2008）中工业和商业用地的限值（30 mg/kg）;当摩尔比为20时,低于居住用地限值（5 mg/kg）。形态提取试验结果表明：FeSO4改变稳定土中铬的赋存形态,可促使铬从弱酸态向可还原态和可氧化态转化,而对残渣态的铬影响不大。Cr(VI)的浸出浓度与稳定土中的Cr(VI)含量均存在指数函数关系,且浸出试验不能全面、客观地评价铬污染土稳定效果。  相似文献   

16.
In this study, nickel ions adsorption from zinc ingot factory wastewater by brown algae (Sargassum glaucescens) and chitosan/polyvinyl alcohol nano-fiber membrane at continuous system was studied. The continuous process included a biosorption reactor and fixed-bed reactor that were optimized by predicting two batch steps with response surface modeling, based on the Box–Behnken in the novel approach. Nano-biosorbent characterized by scanning electron microscopy, Brunauer–Emmett–Teller and Fourier transform infrared spectrometer analysis. Maximum biosorption in this continuous system was at pH 6, biosorbent doses 8 g L?1 S. glaucescens and 0.48 g L?1 nano-fiber. The study of the reaction rate showed kinetic data best fitted by pseudo-first-order model with R 2 > 0.95 than pseudo-second-order and intraparticle diffusion models. Biosorption equilibrium data were performed using Langmuir isotherm and Freundlich isotherm, Langmuir isotherm fit better with equilibrium data.  相似文献   

17.
Chromium is a redox-dynamic element that has many industrial uses. As a consequence, it is often introduced at elevated levels into the surface environment through human activity. Additionally, ultramafic rocks such as serpentinite are commonly enriched in chromium, and thus can also lead to appreciable levels of this element within soils and waters. In the trivalent state, it poses little hazard to biological activity, but, unfortunately, in the hexavalent state it is very toxic to living matter. One must therefore assess the oxidation state of Cr in a given system and determine the potential for transformation between valence states. The objective of this paper to is review and provide new insight on reduction reactions of Cr(VI) within natural environments. A number of aerobic and anaerobic bacteria demonstrate the enzymatic ability to reduce Cr(VI) to Cr(III); two species can even grow using Cr(VI) as the terminal electron acceptor in respiration. The ability to reduce chromium in itself is not evidence that the process will take place at appreciable levels in natural environments, however. Reduced materials such as ferrous iron or hydrogen sulfide may compete with biological pathways in the reduction of Cr(VI). On the basis of measured reaction rates and derived rate expressions, we demonstrate that biological pathways are not likely to contribute to the reduction of chromate in anaerobic systems. Ferrous iron will dominate the reduction of chromate at pH values greater than ～ 5.5, whereas hydrogen sulfide will dominate at pH values below this value. In contrast, bacteria may be the principal means by which Cr(VI) is converted to Cr(III) in aerobic environments. Thus, the process by which Cr(VI) is reduced will depend primarily on the aeration status of the system, and secondarily on pH and the concentrations of specific reduced phases.  相似文献   

18.
Adsorption of chromium and copper in aqueous solutions using tea residue   总被引：5，自引：3，他引：2  
In this study, adsorption of copper and chromium was investigated by residue of brewed tea (Tea Waste) from aqueous solutions at various values of pH. It was shown that adsorbent dose, copper and chromium ion concentrations in such solutions influence the degree of these heavy metal ions’ obviation. The adsorption level of the prepared solutions was measured by visible spectrophotometer. The tea residue adsorbed copper (II) and chromium (VI) ions at initial solution pH by 25 % and 3 %, respectively. During the experiments the peak adsorption occured in hydrated copper nitrate aqueous solution at pH range of 5–6. Likewise the maximum adsorption appeared in potassium chromate aqueous solution at pH range of 2–3. In addition, tea residue adsorbed about 60 mg/g of copper (II) ion at pH=5, while chromium adsorption was registered at about 19 mg/g at pH=2. The data obtained at the equilibrium state, was compared with Langmuir and Freundlich models. Results showed that regarding the kinetics of adsorption, the uptake of copper (II) and chromium (VI) ions by tea residue was comparatively faster, with the adsorption process exhaustion completed within the first 20 min of the experiments. Furthermore, results revealed that adsorption data concerning the kinetic phase is closely correlated with a pseudo-second order model with R2> 0.99 for copper (II) and chromium (VI) ions  相似文献   

19.
The discharge of industrial effluents containing hexavalent chromium can be very harmful for the environment. Therefore, Cr(VI) should be removed from contaminated water, and especially from wastewater, to prevent its discharge into the environment. This study is aimed at analyzing the factors that affect the removal of Cr(VI) with the use of almond green hull and ash adsorbent. The effects of pH (2–10), adsorbent dose (2–24 g/L), Cr(VI) concentration (10–100 mg/L), exposure time (1–60 min), and temperature (5–50 °C) were examined. The surface morphology, pore size of adsorbent surfaces were characterized with SEM, EDX, FTIR. Maximum removal occurred at pH = 2. Results showed that the removal yield increased with the rise of exposure time and temperature. The data indicate that due to limited site on adsorbent surface, the removal efficiency decreased as initial Cr(VI) concentration increased. When the adsorbent dose was increased, the removal yield increased in the case of the bioadsorbent as well; however, in the ash adsorbent, there was an increase followed by a decreasing trend. The study highlights that almond green hull can be more efficient than its ash in the removal of Cr(VI) from aqueous solution. As a general result of study, it can be argued that almond green hull bioadsorbent and the obtained carbon are able to remove Cr(VI) from aqueous solutions; thus, they can be used as efficient and economical substitutes for existing adsorbents like activated carbon, for the removal of chromium from polluted aqueous solutions.  相似文献   

20.
The oxidation states of chromium in GSJ JSO-2 (artificially contaminated soil) and three other geochemical reference materials (GSJ JSO-1, JLS-1 and JMS-1) were observed using X-ray near edge structure (XANES). For comparison, other artificially contaminated soil materials (mimic-JSO-2) were prepared by adding Cr(VI) into JSO-1. Their oxidation states of chromium were determined using XANES. The chromium contents were 1118 μg g-1 for JSO-2, 1352 μg g-1 for mimic-JSO-2 and 69-113 μg g-1 for the other reference materials. Most chromium was present as hexavalent in mimic-JSO-2. No hexavalent species were detected in other samples. These results for chromium oxidation state in JSO-2 and mimic-JSO-2 obtained with XANES resembled those obtained from a chemical extraction method. The present JSO-2 has no trace of Cr(VI), although Cr(VI) was added as a major species during preparation. On the other hand, the content of Cr(VI) obtained in mimic-JSO-2 agreed with the original Cr(VI) content. A time-elapse study showed that Cr(VI) contents in mimic-JSO-2 decreased gradually to 70% of the original abundance during 240-day preservation in dry conditions. Moreover, the abundance of Cr(VI) decreased markedly to 15% after 240 days in the wet mimic-JSO-2 containing 20% m/m of water. These experiments suggested that soil humidity enhanced the reduction of Cr(VI) and that Cr(VI) was reduced even in dry conditions. Consequently, it is reasonable to infer that Cr(VI) doped into JSO-2 was completely reduced to Cr(III) during the preservation period of 5 years. The certification of the long-term stability of the chemical form in reference materials will be much more important in future.  相似文献   

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