Removal of airborne hexavalent chromium using alginate as a biosorbent

Airborne hexavalent chromium has been classified as a human respiratory carcinogen and long term exposure has been known to cause ulceration and perforation of the nasal septum, bronchitis, asthma, and liver and kidney damage. Chromium electroplating plants are the major sources of atmospheric chromium and packed-bed scrubbers are the common control devices used to reduce emission of chromic acid mist from electroplating bathes. The feasibility of a new method to remove this pollutant using alginate beads as a biomass derivative was investigated by one factor at a time approach and Taguchi experimental design. Polluted air with different chromium mist concentrations (10–5000 μg/m3) was contacted to alginate beads (3.3–20 g/L), floating in distilled water with adjusted pH (3–7), using an impinger at different temperatures (20 and 35oC), and various velocities (1.2 and 2.4 m/s). Although there were no statistical significant differences between factor levels, the higher ions removal efficiencies were achieved at lower levels of air velocities, pollution concentrations, higher levels of pHs, temperatures, and sorbent concentrations.     

Ionic solid-impregnated sulphate-crosslinked chitosan for effective adsorption of hexavalent chromium from effluents

Microwave-assisted tetrabutyl ammonium-impregnated sulphate-crosslinked chitosan was synthesized for enhanced adsorption of hexavalent chromium. The adsorbent obtained was extensively characterized using Fourier transform infrared, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray studies. Various isotherm models such as Langmuir, Freundlich and Dubinin–Radushkevich were studied to comprehend the adsorption mechanism of hexavalent chromium by the adsorbent. Maximum adsorption capacity of 225.9 mg g^?1 was observed at pH 3.0 in accordance with Langmuir isotherm model. The sorption kinetics and thermodynamic studies revealed that adsorption of hexavalent chromium followed pseudo-second-order kinetics with exothermic and spontaneous behaviour. A column packed with 1 g of adsorbent was found to give complete adsorption of Cr(VI) up to 900 mL of 200 mg L^?1 solution which discerns the applicability of the adsorbent material for higher sample volumes in column studies. The effective adsorption results were obtained due to both ion exchange and ion pair interaction of adsorbent with hexavalent chromium. Greener aspect of overall adsorption was regeneration of the adsorbent which was carried out using sodium hydroxide solution. In the present study, the regenerated adsorbent was effectively reused up to ten adsorption–desorption cycles with no loss in adsorption efficiency.     

Removal of hexavalent chromium from aqueous solution by barium ion cross-linked alginate beads

Barium ion cross-linked alginate beads have shown great affinity to toxic hexavalent chromium ions in aqueous solution, in contrast to the traditionally used calcium alginate beads. Our adsorption experiments were carried out by the batch contact method. The optimal pH for removal was found to be pH 4. The equilibrium was established in 4 h, and the removal efficiency of chromium(VI) was found to be 95 %. The adsorption data were applied to Langmuir, Freundlich, Dubinin–Redushkevich (D–R), and Temkin isotherm equations. Both Langmuir and Freundlich isotherm constants indicated a favorable adsorption. The value of mean sorption energy calculated from D–R isoterm indicates that the adsorption is essentially physical. The high maximum chromium(VI) adsorption capacity was determined from the Langmuir isotherm as 36.5 mg/g dry alginate beads. The chromium(VI) adsorption data were analyzed using several kinetic models such as the pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models, and the rate constants were quantified. Our study suggests that barium alginate beads can be used as cost-effective and efficient adsorbents for the removal of chromium(VI) from contaminated waters.     

Optimization of a PRB structure with modified chitosan restoring Cr(VI)-contaminated groundwater

Hexavalent chromium is a soluble, mobile, and highly toxic metal ion in groundwater. Adsorption by permeable reactive barriers (PRBs) with special sorbent is a common method to remove hexavalent chromium. A series of experiments have been performed to remove hexavalent chromium in groundwater under PRB with modified chitosan. Therefore, in this paper, the authors first estimated adsorption characteristics of the modified chitosan in a column test, and then calibrated the PRB adsorption parameters in a sandbox test, and finally designed an optimal width, length, and depth of the PRB with the same reactive media in a three-dimensional aquifer. The results showed that the modified chitosan might be a potential adsorption medium. The design schemes can meet the water quality standard of 0.1 mg/L Cr(VI). Heterogeneity of dispersion is a crucial factor when designing the PRB. Therefore, the design of the PRB structures can be appropriate and serve as reference for groundwater remediation.     

Decontamination of hexavalent chromium and tri-ethyl phosphate stimulants through photacatalytic oxidation

In this paper, the photocatalytic decontamination of hexavalent chromium and tri-ethyl phosphate, two important wastewater contaminants, are studied by the ultraviolet / nano-titanium dioxide process. The pH value and synergic effect between the oxidation of tri-ethyl phosphate and the reduction of hexavalent chromium were investigated in different concentrations of tri-ethyl phosphate and hexavalent chromium. Furthermore, the effects of ultraviolet and nano-titanium dioxide were investigated in a solution which contained tri-ethyl phosphate and hexavalent chromium. Results of adsorptions showed that hexavalent chromium was adsorbed better in acidic pH while the better adsorption for tri-ethyl phosphate was occurred in alkalinity pH. The reduction rate of hexavalent chromium was higher in acidic solutions while it was obtained at natural pH for tri-ethyl phosphate. In co-adsorption of hexavalent chromium and triethyl phosphate pollutants, tri-ethyl phosphate slightly increased adsorption of hexavalent chromium, but hexavalent chromium had no influence on the adsorption of tri-ethyl phosphate on nano-titanium dioxide particles. In contrast, triethyl phosphate has an improving effect on the reduction reaction rate of hexavalent chromium which increases with the interaction of the concentration of tri-ethyl phosphate in mixture. The same is true for the oxidation rate of tri-ethyl phosphate.     

Biotransformation potential of hexavalent chromium by Bacillus pumilus-S4, Pseudomonas doudoroffii-S5 and Exiguobacterium-S8 in association with hydrophytes

Three chromium-resistant bacteria Bacillus pumilus-S4, Pseudomonas doudoroffii-S5 and Exiguobacterium-S8 were isolated from chromium-contaminated wastewater/soil and could resist very high concentrations of potassium chromate in Luria agar (up to 25 mg ml^?1) and acetate minimal medium (2 mg ml^?1). The strains showed growth at diverse pH and temperatures and could resist multiple heavy metals. Pseudomonas doudoroffii-S5 reduced (8.27 mg hexavalent chromium 24 h^?1) at a lower initial potassium chromate concentration (100 μg ml^?1), but overall more chromate (28.4 mg hexavalent chromium 24 h^?1) was reduced at a higher initial concentration (1,000 μg ml^?1). The addition of various heavy metals (zinc sulphate, copper sulphate, and manganese sulphate at 50 μg ml^?1) in the chromium reduction media did not significantly affect the hexavalent chromium reduction potential of these isolates. The chromium removal/detoxification potential of these strains increased when used in conjunction with hydrophytes Eichornia crassipes and Pistia stratiotes. Interestingly, the whole process runs automatically with less energy input, that is, the bacterial strains support the growth of plant while in turn the plant releases exudates that help bacterial growth.     

Photocatalytic reduction of hexavalent chromium with commercial Fe/Ti oxide catalyst under UV and visible light irradiation

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.     

Functionalized nanobiomaterials: high-performance sorbents for chromium remediation from water streams

In present work, fabrication of functionally tailored nanobiomaterials paraben-modified nanocellulose (PNC) and (2,3-epoxypropyl) trimethylammonium chloride-modified nanocellulose (EPTMAC-NC) for the remediation of trivalent and hexavalent chromium, respectively, from water streams has been done. The resulting PNC and EPTMAC-NC were characterized before and after sorption of chromium using spectroscopic and microscopic techniques. The sorption performance of PNC (23.92 mg/g; 95.67 %) and EPTMAC-NC (23.99 mg/g; 95.94 %) was evaluated for trivalent and hexavalent chromium, respectively, at 0.5 g biosorbent dose; 500 mL sample volume; 25 mg/L chromium conc.; 40 min kinetic time; pH (6.5 for trivalent and 2.5 for hexavalent chromium) and 298 K temperature. From isothermic, kinetic and thermodynamic modeling, the sorption of trivalent and hexavalent chromium was physisorption, spontaneous, feasible and endothermic in nature. These findings expose new path in the line of high performance, scalable and economic nanobiomaterials for the abatement of toxic metals from water streams.     

Development of functionalized carrageenan,chitosan and alginate as polymeric chelating ligands for water softening

Chitosan, carrageenan and alginate are among the most abundant biopolymers in nature. They were prepared in uniform beads shape with a diameter of 2 mm ± 10%, using the encapsulator for removal of calcium, magnesium and iron cations from hard water. Solutions of 100–500 mg/L were prepared from each cation, and the detection of cations was carried out using atomic absorption spectrometer. Carrageenan and chitosan were able to chelate the three cations without further modification. However, alginate beads succeeded to chelate iron and magnesium and failed to chelate any calcium ions; in contrast, it increased the initial calcium concentration! That could be due to the pre-cross-linking of alginate beads using calcium chloride solution, which may be leaked back to the solution. However, grafting the alginate beads with polyethyleneimine and bromoacetic acid rectified this problem and the new functional group, –COOH, has been proved using the FT-IR. Optimization of the results in terms of beads weight (0.25–3.0 g) and cations concentrations (100–500 mg/L) has shown that most biopolymeric beads can chelate 85–100% of the cations in concentrations up to 500 mg/L. According to our finding, we came up with the recommendation to use chitosan for chelation of calcium and iron as it showed 100% chelation efficiency of both cations, whereas carrageenan is highly recommended for chelation of iron and magnesium, as it showed 100 and 98% chelation efficiency, respectively. Further work can be done on the reusability of the beads and scale up for the industrial use.     

Adsorption of chromium and copper in aqueous solutions using tea residue

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     

中试尺度下可渗透反应墙位置优化模拟——以铬污染地下水场地为例

可渗透反应墙（PRB）是一种高效的地下水污染原位修复技术。不同水文地质条件下,污染场地墙体位置布设合理性影响其修复效果,而利用地下水数值模拟可实现墙体位置优化。文章以某Cr6+污染地下水场地为例,基于Visual Modflow建立了研究区平面二维稳定流数值模型,并通过模型检验。根据墙体的设计尺寸（长20 m×宽2 m×深12 m）及填充材料的渗透系数（80 m/d）,利用所建模型分别计算了4种布设方案（墙体尺寸大小和填充材料渗透系数相同,布设位置不同）下墙体的捕获区宽度、粒子滞留时间和通过墙体的Cr6+通量。结果表明:4种布设方案模拟的滞留时间和捕获区宽度取值差异性不大,变异系数小于2%;Cr6+通量差别较大,变异系数高达76.32%,主要由地下水中Cr6+浓度空间分布不均引起。对比分析4种方案的各评价指标,方案2求得的捕获区宽度为21.9 m,粒子滞留时间为4.1 d,Cr6+去除量可达127.7 mg/d,可作为最佳布设方案。本研究建立的地下水流数值模型符合场地实际情况,可有效评估PRB截获污染羽的范围和去除目标污染物的能力,为铬渣类污染场地PRB原位修复工程设计与实施提供技术支撑和参考依据。     

零价铁去除Cr（Ⅵ）的批实验研究

零价铁去除Cr(Ⅵ)的一系列批实验结果表明：水溶液中发生的氧化还原反应符合准一级反应；对于相同粒度的铁屑(比表面积2．89m^2／g)，固液比由05g／100mL增加到2．0g／100mL，Cr(Ⅵ)质量浓度达到排放标准所需反应时间从26．7min降为3．6min；在固液比相同、原水中Cr(Ⅵ)质量浓度不超过30mg／L时，原水质量浓度增大，达到饮用水标准的反应时间增加；其他条件相同，升高温度可提高零价铁与Cr(Ⅵ)的反应速率。     

Adsorption of chromium (VI) from aqueous solution by the iron (III)-impregnated sorbent prepared from sugarcane bagasse

An iron (III)-impregnated sorbent was prepared from sugarcane bagasse and ferric chloride solution via carbonization/activation in a muffle furnace at 500?°C for 4?h. The adsorption removal of chromium (VI) from aqueous solution by the iron (III)-impregnated sorbent was then studied in a batch system. With increasing initial chromium (VI) concentration from 25 to 130?mg/L at an adsorbent dose of 300?mg/50?mL, the amount of adsorbed chromium (VI) increased from 4.15 to 12.20?mg/g at 20?°C, from 4.16 to 12.50?mg/g at 30?°C, and from 4.16 to 13.72?mg/g at 40?°C. The dynamical data fit very well with the pseudo-second-order kinetic model, and the calculated adsorption capacities of 4.16, 8.37, and 13.37?mg/g were equal to the actual values of the experiments at the initial chromium (VI) concentrations of 25, 50, and 100?mg/L, respectively. The Langmuir isotherm could yield better fits than the Freundlich isotherm. The calculated isotherm parameters confirmed the favorable adsorption of chromium (VI) on the iron (III)-impregnated sorbent.     

Biosorption of hexavalent chromium from aqueous solution onto pomegranate seeds: kinetic modeling studies

Hexavalent chromium has been proved to be the reason of several health hazards. This study aimed at evaluating the application of pomegranate seeds powder for chromium adsorption (VI) from aqueous solution. Chromium adsorption percentage (VI) increased with increasing the adsorbent dosage. Chromium adsorption capacity (VI), at pH = 2 and 10 mg/L initial metal concentration, decreased from 3.313 to 1.6 mg/g through increasing dosage of adsorbent from 0.2 to 0.6 g/100 ml. The adsorption rate increased through increase in chromium initial concentration (VI). However, there was a removal percentage reduction of chromium (VI). Chromium adsorption kinetics by different models (pseudo-first-order, modified pseudo-first-order, pseudo-second-order, Elovich, intraparticle diffusion, Boyd kinetic) was investigated as well. Studies on adsorption kinetic indicated that the experimental data were matched by pseudo-second-order model (R ² = 0.999) better. Obtained results demonstrated the pomegranate seeds can be used as an effective biomaterial and biosorbent for hexavalent chromium adsorption from aqueous solutions.     

陕西省渭河扩建电厂粉煤灰处理场土壤对Cr（Ⅵ）的吸附作用

粉煤灰处理区的环境地质调查表明:由于受地面排放的粉煤灰的影响,地下水中Cr（Ⅵ）浓度高出背景值4⁵倍.野外现场试验对Cr（Ⅵ）监测结果显示:在2m厚的灰体底部,下渗水中的Cr（Ⅵ）浓度已高达0.701ppm,超标14倍.很明显,Cr（Ⅵ）是粉煤灰中的主要污染质之一.老灰场的环境地质调查还发现:土壤对Cr（Ⅵ）的迁移有很大的阻滞作用.作者对此进行一系列野外及室内试验来研究粉煤灰中Cr（Ⅵ）的解吸,迁移及其与土壤之间的相互作用和有关的化学机理,并且评价了渭河扩建电厂新灰场区土壤包气带对粉煤灰中Cr（Ⅵ）的净化能力.     

Efficient removal of hexavalent chromium from aqueous solutions using autohydrolyzed Scots Pine (Pinus Sylvestris) sawdust as adsorbent

In this work, a low-cost lignocellulosic adsorbent with high biosorption capacity is proposed, suitable for the efficient removal of hexavalent chromium from water and wastewater media. The adsorbent was produced by autohydrolyzing Scots Pine (Pinus Sylvestris) sawdust. The effect of the autohydrolysis conditions, i.e., pretreatment time and temperature, on hexavalent chromium biosorption was investigated using energy-dispersive X-ray spectroscopy (EDS) and UV–visible spectrophotometry. The Freundlich, Langmuir, Sips, Radke-Prausnitz, Modified Radke-Prausnitz, Tóth, UNILAN, Temkin and Dubinin-Radushkevich adsorption capacities and the rate constant values for pseudo-first- and pseudo-second-order kinetics indicated that the autohydrolyzed material exhibits significantly enhanced hexavalent chromium adsorption properties comparing with the untreated sawdust. The Freundlich’s adsorption capacity K _F increased from 2.276 to 8.928 (mg g^?1)(L mg^?1)^1/n , and the amount of hexavalent chromium adsorbed at saturation (Langmuir constant q _m) increased from 87.4 to 345.9 mg g^?1, indicating that autohydrolysis treatment at 240 °C for 50 min optimizes the adsorption behavior of the lignocellulosic material.     

Sorption behavior of nine chromium (III) organic complexes in soil

Sorption data were obtained with a Matawan soil and the following chromium (III) organic complexes: chromium (III) ascorbate, chromium (III) glutamate, chromium (III) histidine, chromium (III) mandelate, chromium (III) citrate, chromium (III) cysteine, chromium (III) serine, chromium (III) pyruvate and chromium (III) oxalate. The influence of pH (2–12), ionic strength (0.005–1 M) and concentration of sorbate (1–10 mg/L) on the extent of sorption was evaluated. The pH value did not influence the percent sorption at environmentally relevant pH 7. Ionic strength between 0.005 and 0.01 M KNO₃ did not influence the sorption. Sorption and desorption data obtained at pH 7, 0.01 M KNO₃ and 1–10 mg/L for each chromium (III) organic complex were analyzed using Freundlich and Langmuir models. The Freundlich model provided good fits for all of the chromium (III) organic complexes. Sorption data for chromium (III) glutamate, chromium (III) pyruvate, chromium (III) oxalate, chromium (III) cysteine, chromium (III) ascorbate and chromium (III) citrate were described well by the Langmuir model. Estimates for the saturated sorption capacities were 141, 70.9, 36.5, 35.5, 28.6 and 4.4 μg/g, respectively. It was not possible to desorb significant amounts of the previously sorbed chromium (III) organic complexes. At the same pH, ionic strength and solid:liquid ratio, the order of the observed sorption to the Matawan soil from highest to lowest was chromium (III) mandelate, chromium (III) glutamate, chromium (III) histidine, chromium (III) cysteine, chromium (III) serine, chromium (III) pyruvate, chromium (III) oxalate, chromium (III) ascorbate and chromium (III) citrate.     

几种不同类型的FeOOH吸附水溶液中铬离子研究

采用两种显微结构不同的螺旋状和管状构造的天然铁细菌矿化针铁矿和化学合成的α—FeOOH及两种有机高分子模板矿化结晶的β-FeOOH作为吸附材料，分别在pH=5和6时对含Cr^3 和Cr(Ⅵ)废水进行了吸附实验研究，结果表明，天然生物矿化针铁矿对金属阳离子和阴离子均有明显的吸附作用，其显微结构、大小和形态影响其吸附能力；纯化学合成的针铁矿对铬离子的吸附能力较低；通过有机模板合成的纳米微晶β-FeOOH对Cr^3 和Cr(Ⅵ)均有极高的去除率，这与其表面存在与有机分子络合作用、增大了其表面对金属离子和铬酸根的化学亲合力有关。     

Aqueous heavy metals removal by adsorption on β-diketone-functionalized styrene–divinylbenzene copolymeric resin

An investigation was undertaken regarding the adsorption of different heavy metal ions from aqueous solutions using ??-diketone-functionalized styrene divinylbenzene resin under different experimental conditions such as initial concentration of metal ions, contact time, pH, and chelating capacity. The functionalization of resin was carried out by the condensation reaction of sodium salt of ??-diketones (pentane-1,3-dione) and chloromethylated styrene?Cdivinylbenzene resin in dichloromethane. Functionalized resin beads were characterized by Fourier transform infrared spectroscopy. The batch method was employed using different metal ions solution from 5 to 15?mg/L at different contact times. The adsorption kinetics was tested for the pseudo-first order, pseudo-second order reaction at different experimental conditions. The rate constant of adsorption kinetic models were also calculated and good correlation coefficient (R ²?>?0.9941) was obtained for pseudo-second order kinetic model. The maximum adsorption value obtain for lead (0.725728?mg/g), chromium (0.9199?mg/g), nickel (0.4974?mg/g), cobalt (0.6196?mg/g) and cadmium (0.6519?mg/g) at equilibrium condition, which shows that ??-diketone-functionalized styrene divinylbenzene resin is an effective adsorbent for toxic metal ions.     

Biosorption of lead from acid solution using chitosan as a supporting material for spore forming-fungal biomass encapsulation

Asexual spores of the filamentous fungus Rhizopus arrhizus were used as the resting biomass as they tolerate chitosan gelling for mycelia growing in chitosan beads. Biosorption of lead using the dead detergent pre-treated chitosan-immobilised and grown fungal beads was performed with initial lead (II) nitrate concentrations ranging from 9.02 to 281.65 mg/L. The adsorption data were best correlated with equilibrium adsorption isotherms in the order Redlich–Peterson, Langmuir, Freundlich and Fritz–Schlünder by non-linear regression. The biosorption kinetic model of pseudo second-order (R ² > 0.99) fitted better than pseudo first-order and modified pseudo first-order models. Among the four pseudo second-order kinetic models, the Blanchard model was the best fit for the experimental biosorption data. The rate-limiting step of biosorption of lead was shown to be intraparticle diffusion controlled according to Weber and Morris model fitting. The beads could be regenerated using 1 M nitric acid solution. This illustrated the good performance of the beads for regenerated sorption/desorption at least five cycles.