Removal of toxic chromium(VI) from aqueous solution by activated carbon using Casuarina equisetifolia

Highly activated carbon from the seed husk of Casuarina Casuarinas equisetifolia, a worldwide famous plant, have been prepared and tested for the removal of toxic Cr(VI) from its aqueous solution. The adsorbent was investigated for influences of initial chromium concentration (75, 100, 125, and 150 mg l^-1), pH, contact time, and quantity of carbon on removal of Cr(VI) from aqueous solution at room temperature (25±2 °C). The adsorption kinetic of Cr(VI) was studied, and the rates of sorption were found to conform to pseudo-second-order kinetics with a good correlation (R²≥0.99). The Langmuir and Freundlich models fit the isotherm data well. Furthermore, the Gibbs free energy was obtained for each system and was found to be-5.29 kJ mol^-1 for removal of Cr(IV). The negative value of Δ G° indicates the feasibility and spontaneous nature of adsorption. The results indicate that acidic pH (1.05) supported the adsorption of Cr(IV) on activated carbon. The maximum adsorption capacity of Cr(VI) on activated carbon was about 172.4 mg g^-1 at pH 1.05.     

Mass-transfer processes of chromium(VI) adsorption onto guava seeds

The chromium(VI) biosorption onto guava seeds, as an alternative method for Cr⁶⁺ removal from aqueous solutions, was investigated. The parameters affecting kinetics and equilibrium of Cr⁶⁺ adsorption onto guava seeds were studied. An external mass-transfer diffusion coefficient k and intra-particle diffusion coefficient k_i were determined to measure the rate-limiting step of adsorption. A single external mass-transfer diffusion model and intra-particle diffusion models were used. The effects of initial pH, sorbent mass, and initial Cr⁶⁺ concentrations on mass-transfer coefficients were investigated. The external mass-transfer coefficient has an average value of 7.2×10^-3 cm s^-1, while the intra-particle mass-transfer diffusion coefficient was 0.34 mg g^-1 min^-0.5. This indicates that external diffusion to the guava seeds surface and intra-particle diffusion are both involved in the sorption process. The isotherm equilibrium data were well fitted by the Langmuir and Freundlich models with an average correlation coefficient R²=0.98. The maximum removal of Cr⁶⁺ was obtained at pH 1 (about 100% for adsorbent dose of 15 g l^-1 and 25 mg l^-1 initial concentration of Cr⁶⁺). The results indicated that the guava seeds exhibit acceptable sorption capacity.     

Removal of cadmium(II), lead(II), and chromium(VI) ions from aqueous solution using clay

Removal of cadmium(II), lead(II), and chromium(VI) from aqueous solution using clay, a naturally occurring low-cost adsorbent, under various conditions, such as contact time, initial concentration, temperature, and pH has been investigated. The sorption of these metals follows both Langmuir and Freundlich adsorption isotherms. The magnitude of Langmuir and Freundlich constants at 30°C for cadmium, lead, and chromium indicate good adsorption capacity. The kinetic rate constants (K _ad) indicate that the adsorption follows first order. The thermodynamic parameters: free energy change (ΔG ^o), enthalpy change (ΔH ^o), and entropy change (ΔS ^o) show that adsorption is an endothermic process and that adsorption is favored at high temperature. The results reveal that clay is a good adsorbent for the removal of these metals from wastewater.     

Removal of chromium(VI) by ZnCl2 activated coir pith carbon

The adsorption of chromium(VI) onto ZnCl₂ activated carbon developed from coir pith was investigated to assess the possible use of this adsorbent. The influence of contact time, adsorbent dose, Cr(VI) concentration, pH and temperature were investigated. The two theoretical adsorption isotherms, namely, Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Q ₀) was found to be 120.5?mg Cr(VI) per g of the adsorbent. The adsorption followed the second-order kinetics and was found to be maximum at pH 2.0. The pH effect and the desorption studies showed that ion exchange mechanism might be involved in the adsorption process. The effects of foreign ions such as chloride, sulphate, phosphate, selenite, molybdate, nitrate and perchlorate on the removal of Cr(VI) have been investigated. The removal of Cr(VI) from synthetic ground water was also tested. The results show that ZnCl₂ activated coir pith carbon is effective for the removal of Cr(VI) from water.     

1,3,5-triazine-triethylenetetramine polymer: an efficient adsorbent for removal of Cr(VI) ions from aqueous solution

The synthesis of 1,3,5-triazine-triethylenetetramine (TATETA), its characterization by infrared spectroscopy and elemental analysis, and its application for removal of Cr(VI) ions from aqueous solution is reported. The effects of pH, contact time, initial concentration of Cr(VI), sorbent dose, and temperature on adsorption were investigated and optimized by batch adsorption experiments. Adsorption was highest at acidic conditions with an equilibration time of 25 min. The adsorption followed a Langmuir model, with an adsorption capacity of 303 mg g^?1, was second order in its kinetics, and exothermic and thus spontaneous.     

Phytoextraction of Cr(VI) from soil using Portulaca oleracea

Cr(VI) represents an environmental challenge in both soil and water as it is soluble and bioavailable over a wide range of pH. In previous investigations, Portulaca oleracea (a plant local to the United Arab Emirates (UAE)) demonstrated particular ability for the phytoextraction of Cr(VI) from calcareous soil of the UAE. In this publication, the results of the evaluation of P. oleracea phytoextraction of Cr(VI) from UAE soil at higher concentrations are reported. P. oleracea was exposed to nine different concentrations of Cr(VI) in soil from 0 to 400 mg kg^?1. The uptake of Cr(VI) increased as its concentration in soil increased between 50 and 400 mg kg^?1, with the most efficient removal in the range from 150 to 200 mg kg^?1. The total chromium concentrations exceeded 4600 mg kg^?1 in roots and 1400 mg kg^?1 in stems, confirming the role of P. oleracea as an effective Cr(VI) accumulator. More than 95% of the accumulated Cr(VI) was reduced to the less toxic Cr(III) within the plant.     

Removal and recovery of uranium(VI) by adsorption onto a lignocellulosic-based polymeric adsorbent containing amidoxime chelating functional group

A new adsorbent (ABS) with amidoxime functional group was prepared through graft polymerization of acrylonitrile onto banana stem (BS) using ceric ammonium nitrate (CAN)/HNO₃ initiator system, followed by treatment with hydroxylamine hydrochloride in alkaline solution. Infrared spectroscopy, surface area analyzer, thermogravimetry, and potentiometric titration were used for the characterization of the adsorbent. Effective removal of U(VI) ions was demonstrated at the pH range 4.0–6.0. The mechanism for the removal of U(VI) ions by ABS was based on complexation adsorption model. Equilibrium was achieved in approximately 3 h. The experimental kinetic data were analyzed using first-order, second-order, and Elovich kinetic models, and are well fitted with second-order kinetics. The temperature dependence indicates an exothermic process. U(VI) adsorption was found to decrease with increase of ionic strength. The Freundlich isotherm model fitted the experimental equilibrium data well. The adsorption efficiency was tested using synthetic nuclear industry effluents. The maximum adsorption capacity for U(VI) removal was found to be 80 mg g^-1 at 20°C. Adsorbed U(VI) ions were desorbed effectively, about 99% by 0.2 M HCl. Repeated adsorption/desorption cycles show the feasibility of the ABS for the removal of U(VI) ions from water and nuclear industry effluents.     

Enhancement of extracellular Cr(VI) reduction for anammox recovery using hydrazine: performance,pathways, and mechanism

● N₂H₄ addition enhanced and recovered anammox performance under Cr(VI) stress. ● N₂H₄ accelerated electron transfer of Cr(VI) reduction for detoxification. ● N₂H₄ enhanced anammox metabolism for activity recovery from Cr(VI) inhibition. ● Extracellular Cr(VI) reduction to less toxic Cr(III) was the dominant mechanism. The hexavalent chromium (Cr(VI)) would frequently impose inhibition to anaerobic ammonium oxidation (anammox) process, hindering the efficiency of nitrogen removal in wastewater treatment. Hydrazine (N₂H₄), which is an intermediate product of anammox, participates in intracellular metabolism and extracellular Cr(VI) reduction. However, the roles of N₂H₄-induced intracellular metabolism and extracellular reduction in nitrogen removal under Cr(VI) stress remain unclear. The addition of 3.67 mg/L of N₂H₄ increased the anammox activity by 17%. As an intermediate, N₂H₄ enhanced anammox metabolism by increasing the heme c content and electron transfer system activity. As a reductant, N₂H₄ accelerated the reduction of c-Cyts-mediated extracellular Cr(VI) to the less toxic Cr(III). Extracellular Cr(III) accounts for 74% of the total Cr in a Cr(VI)-stressed anammox consortia. These findings highlight that N₂H₄-induced extracellular Cr(VI) reduction is the dominant mechanism for the survival of anammox consortia. We also found that N₂H₄ increased the production of extracellular polymeric substances to sequester excessive Cr(VI) and produced Cr(III). Taken together, the study findings suggest a potential strategy for enhancing nitrogen removal from ammonium-rich wastewater contaminated with Cr(VI).     

Granulation of gibbsite with inorganic binder and its ability to adsorb Mo(VI) from aqueous solution

In this study, we prepared a new adsorbent and evaluated its ability to adsorb Mo(VI). Gibbsite was granulated with colloidal alumina or colloidal silica. The amount of Mo(VI) adsorbed onto granular gibbsite with a binder, effect of contact time and pH on the adsorption of Mo(VI), and column experiments were investigated. The amount of Mo(VI) adsorbed was greater in the order of ST12 (colloidal silica, 12%)?相似文献   

Carbon paste electrode modified with chromium thiopental for the potentiometric flow injection analysis of chromium (III)

A chemically modified carbon paste electrode for chromium (III) based on the formation of ion-association complex of chromium with 5-ethyl-6-oxo-5-pentan-2-yl-sulfanyl-pyrimidin-4-olate (thiopental, THP) as electroactive ion-exchanger (Cr-THP) was prepared and investigated. The electrode has a linear dynamic range of 1.7?×?10^?6–1.3?×?10^?2?mol?L^?1, with a Nernstian slope of 19.6?±?0.5?mV per decade and a detection limit of 9.0?×?10^?7?mol?L^?1. It has a fast response time of <15?s and can be used for at least 7 weeks without any considerable divergence in potential. The proposed sensor revealed good selectivity for Cr(III) over a wide variety of mono-, di-, and trivalent cations and could be used in the pH range of 2.3–6.5. The proposed electrode was used in batch measurements and in flow injection analysis. The Cr-CMCPE was successfully applied for the determination of Cr(III) in real samples (wastewater of hot dip galvanizing unit and alloys). The present electrode was also used as an indicator electrode in potentiometric titration of Cr(III). The results were highly satisfactory.     

Dual-functional sites for synergistic adsorption of Cr(VI) and Sb(V) by polyaniline-TiO2 hydrate: Adsorption behaviors,sites and mechanisms

• PANI/Ti(OH)_n^(4–n)+ exhibited excellent adsorption capacity and reusability. • Adsorption sites of Cr(VI) were hydroxyl, amino/imino group and benzene rings. • Sb(V) was adsorbed mainly through hydrogen bonds and Ti-O-Sb. • The formation of Cr-O-Sb in dual system demonstrated the synergistic adsorption. • PANI/TiO₂ was a potential widely-applied adsorbent and worth further exploring. Removal of chromium (Cr) and antimony (Sb) from aquatic environments is crucial due to their bioaccumulation, high mobility and strong toxicity. In this work, a composite adsorbent consisting of Ti(OH)_n^(4–n)+ and polyaniline (PANI) was designed and successfully synthesized by a simple and eco-friendly method for the uptake of Cr(VI) and Sb(V). The synthetic PANI/TiO₂ composites exhibited excellent adsorption capacities for Cr(VI) and Sb(V) (394.43 mg/g for Cr(VI) and 48.54 mg/g for Sb(V)), wide pH applicability and remarkable reusability. The adsorption of Cr(VI) oxyanions mainly involved electrostatic attraction, hydrogen bonding and anion-π interactions. Based on X-ray photoelectron spectroscopy and FT-IR analysis, the adsorption sites were shown to be hydroxyl groups, amino/imino groups and benzene rings. Sb(V) was adsorbed mainly through hydrogen bonds and surface complexation to form Ti-O-Sb complexes. The formation of Cr-O-Sb in the dual system demonstrated the synergistic adsorption of Cr(VI) and Sb(V). More importantly, because of the different adsorption sites, the adsorption of Cr(VI) and Sb(V) occurred independently and was enhanced to some extent in the dual system. The results suggested that PANI/TiO₂ is a promising prospect for practical wastewater treatment in the removal of Cr(VI) and Sb(V) from wastewater owing to its availability, wide applicability and great reusability.     

Selective separation and preconcentration studies of chromium(VI) with Alamine 336 supported liquid membrane

Chromium compounds have received considerable attention because these are used extensively in such industrial applications as electroplating, steelmaking, tanning of leather goods, and corrosion inhibition. The use of supported liquid membranes (SLMs) to remove metals from wastewaters has actively been pursued by the scientific and industrial community. In the present work, the selective separation and preconcentration of Cr(VI) ions has been studied by using a commercial amine as the membrane liquid on the porous polypropylene support. Permeation experiments were conducted on a laboratory scale batch reactor made up of perspex, with a memberane fixed amid the two chambers. The flux of Cr(VI) ions was found to be maximum (3.15?×?10^?5?mol?cm^?2?s^?1) around pH 1. Above and below this pH the flux decreases. Distribution studies show that an increase in the amine concentration leads to higher distribution coefficients at fixed pH values. At pH around unity, the distribution of Cr(VI) ions into the organic phase was found to be maximum, of the order of 56.3. The Cr(VI) transport through the membrane increases with rise in temperature. In order to check the long-term efficiency of the flat sheet SLM, an experiment was conducted with higher Cr(VI) concentration (5000?ppm) for 24?h, at optimised parameters. It was observed that in 24?h, about 1/5th of the feed Cr(VI) is left over while the rest is transported. However, minute organic droplets were also seen in the feed and strip compartments, after 1 day. This observation suggested the loss of membrane liquid. The feasibility of preconcentration of Cr(VI) by using the proposed SLM parameters, was also studied by using the hollow fibre (HF) system. Highest enrichment factor (E.F) value was obtained for 50?mg?L^?1 whereby all of the metal was transported to the stripping phase and the resulting Cr concentration was 688?mg?L^?1 (E.F?=?13.8). It was observed that while treating more diluted solutions, the enrichment factor decreases. The values of E.F equal to 8.9 and 11.3 were found for initial Cr concentration of 10 and 30?mg?L^?1.     

Removal of Mo(VI) from aqueous solutions using sulfuric acid-modified cinder: kinetic and thermodynamic studies

Removal of Mo(VI) from aqueous solutions was investigated using cinder modified by sulfuric acid. Various parameters such as pH, agitation time, Mo(VI) concentration, and temperature have been studied. The maximum adsorption of Mo(VI) occurred at pH between 4.0 and 6.0. Kinetic studies showed that the adsorption generally obeyed a pseudo second-order model. The activation energy was 31.4?kJ?mol^?1, indicating that the adsorption process was governed mainly by interactions of physical nature. Furthermore, application of Langmuir and Freundlich isotherm models to the adsorption equilibrium data showed that the adsorption behavior obeyed the Langmuir model. The adsorption capacity was found to be 10.8?g Mo(VI)?kg^?1 adsorbent. Finally, thermodynamic parameters such as ΔH ⁰, ΔS ⁰, and ΔG ⁰ were also evaluated, which showed that the adsorption of Mo(VI) on the treated cinder was endothermic, entropy increasing, and spontaneous. In conclusion, the sulfuric acid-modified cinder was shown to be an inexpensive, effective, and simple adsorbent for the removal of Mo(VI) from water.     

Fluorescence studies of dye displacement from DNA by chromium(III) complexes: Evidence for cation induced DNA condensations

The interactions of 10 different chromium(III) complexes with isolated calf thymus DNA have been analysed by studying the electronic and fluoresence spectra of intercalated ethidiumbromide. Triply charged cationic complexes including: [Cr(urea)₆]Cl₃.3H₂O, [Cr(1,10‐phenanthroline)₃](ClO₄)₃.2H₂O, [Cr(2,2'‐bipyridyl)₃] (ClO₄)₃.2H₂O, [Cr(ethylendiamine)₃]Cl₃.3.5H₂O and [Cr(NH₃)₆](NO₃)₃ displaced the dye from DNA. Similar effects were observed in experiments using the non‐intercalating dye bisbenzimidazole ("Hoechst 33258"). However, singly charged cationic, anionic and uncharged chromium(III) complexes such as: cis‐[Cr(1,10‐phenanthroline)₂Cl₂]Cl.2H₂O, cis‐[Cr(2,2'‐bipyridyl)₂Cl₂]Cl.2H₂O, [Cr(glutathione)₂]Na₂, [Cr(cysteine)₂]Na.2H₂O and [Cr(glycine)₃] were unable to displace both ethidiumbromide and bisbenzimidazole from DNA. There was no evidence for the formation of co‐ordinate bonds between chromium(III) and DNA for any of the above complexes. The charge and type of ligand are important in controlling the interaction of chromium(III) with isolated DNA in vitro. Our findings indicate that the outer sphere interaction of a chromium(III) complex with DNA is weak and unlikely to be the mechanism by which chromate causes DNA impairments in vivo and in vitro.     

基于氮掺杂碳量子点的制备及其对Hg2+的响应

以乙二胺和抗坏血酸为原料,通过一步水热法制备了水溶性的氮掺杂碳量子点(N-CQDs).研究了N-CQDs的形貌特征、光学性能和应用分析.表征结果说明,N-CQDs形态为均匀分散的球形,有明显的晶格条纹,抗光漂白性能良好,表面富有含氧官能团,具有良好的水溶性.此外发现N-CQDs还具有优良的荧光性能和荧光稳定性,量子产率可以高达12.29%.分析得出,Hg²⁺对N-CQDs在1.0—120μmol·L^-1范围内有一定的猝灭效应,可作为Hg²⁺的荧光探针,检出限达230 nmol·L^-1.     

Biosorption potential of Cr(VI) by Kocuria sp. ASB107, a radio-resistant bacterium isolated from Ramsar,Iran

Heavy metal pollution in soil and wastewater is a worldwide environmental issue in which microorganisms play a significant role for its removal. In the present study, biosorption of Cr(VI) by the live and dead cells of Kocuria sp. ASB107, a radio-resistant bacterium, was investigated. The effect of contact time, solution pH, initial hexavalent chromium concentration and adsorbent dose on biosorption efficiency was studied. Also, live cells were further immobilised on various matrices by different techniques and then were examined for tolerance to chromium biosorption. Experimental results indicated that the removal efficiency of chromium increased with decrease in pH, initial Cr(VI) concentration, and also increase in adsorbent dose and the contact time. The maximum removal efficiency of live and dead cells at acidic pH of 4–4.5, contact time of 24 hours, adsorbent dose 1.6?g/100?mL and initial chromium concentration 25?mg/L were 82.4% and 69.2%, respectively. The adsorption data was described well by Langmuir isotherm model. Among all immobilisation techniques tested, cross-linking showed the highest biosorption of Cr(VI). Results indicated that live cells of Kocuria sp. ASB107 were better than dead ones.     

Biosorption of chromium(VI), nickel(II) and copper(II) ions from aqueous solutions using Pithophora algae

The biosorption of heavy metals is considered to be one of the best alternatives for the treatment of wastewater. The metal binding capacity of algae and acid-treated algae is investigated to find out the removal characteristics of Cr(VI), Ni(II) and Cu(II) ions from single metal solutions. Batch experiments are conducted and the study is extended to investigate the effect of pH, amount of adsorbent and adsorbate concentration on the extent of biosorption. The results indicate that the adsorption capacity of algae depends strongly on pH. The maximum adsorption of Cr(VI), Ni(II) and Cu(II) occurs at pH values of 2, 7 and 4.3, respectively. The adsorption process follows first-order kinetic equation. The data obtained are correlated with Freundlich and Langmuir adsorption isotherms.     

二氧化钛改性油页岩渣对水溶液中亚甲基蓝和六价铬的吸附

以油页岩渣及其二氧化钛改性材料为吸附剂,探究它们去除水溶液中亚甲基蓝和六价铬的能力.通过实验,控制溶液的pH值、温度、初始浓度和接触时间,观察吸附效果变化特征,研究其动力学和热力学性能.实验表明,改性油页岩渣吸附亚甲基蓝和六价铬的吸附率是未改性的2—3倍,且改性油页岩渣对亚甲基蓝的吸附率可达97%,对六价铬的吸附率不到25%.吸附亚甲基蓝时,pH值越大,吸附效果越好;而吸附六价铬时,最适pH值为4.改性油页岩渣吸附亚甲基蓝实验符合准二阶动力学方程,计算得反应活化能为13.29 kJ.mol-1,表明此过程主要是物理吸附.在热力学方面,由范特霍夫方程计算得ΔG〈0、ΔH〉0,表明此过程自发吸热,可见此过程还伴有化学吸附.Langmuir和Freundlich等温模型拟合结果表明,Langmuir模型数据拟合甚佳,R2=0.9999,说明改性油页岩渣吸附亚甲基蓝是单分子层吸附.二氧化钛改性油页岩渣经7次回收利用后,对亚甲基蓝的吸附效果仅减少约1.5%.     

Development of pretreatment protocol for DNA extraction from biofilm attached to biologic activated carbon (BAC) granules

The biologic activated carbon (BAC) process is widely used in drinking water treatments. A comprehensive molecular analysis of the microbial community structure provides very helpful data to improve the reactor performance. However, the bottleneck of deoxyribonucleic acid (DNA) extraction from BAC attached biofilm has to be solved since the conventional procedure was unsuccessful due to firm biomass attachment and adsorption capacity of the BAC granules. In this study, five pretreatments were compared, and adding skim milk followed by ultrasonic vibration was proven to be the optimal choice. This protocol was further tested using the vertical BAC samples from the full-scale biofilter of Pinghu Water Plant. The results showed the DNA yielded a range of 40 μg·g^-1 BAC (dry weight) to over 100 μg·g^-1 BAC (dry weight), which were consistent with the biomass distribution. All results suggested that the final protocol could produce qualified genomic DNA as a template from the BAC filter for downstream molecular biology researches.