Speciation dependent studies on chromium absorption using calcium alginate and iron doped calcium alginate biopolymer

Attempt has been made to develop methodologies for preconcentration of chromium in the biodegradable polymer beads. The uptake behaviors for chromium have been studied with Ca-alginate (CA) and Fe-doped calcium alginate (Fe-CA) beads. The work also aims to study the differential attitude of CA and Fe-CA towards Cr(III) and Cr(VI) so that, depending on the oxidation state of chromium effluent, environmentally sustainable methodologies can be prescribed for removal of chromium. Radiotracer ⁵¹Cr has been chosen as precursor of stable chromium throughout the experiment. It was found that Fe-CA beads are suitable for removal of Cr(III) and Cr(VI) while CA beads can be used for the speciation and separation of Cr(III) and Cr(VI) at pH 5.     

Design of BiOBr0.25I0.75for synergy photoreduction Cr（Ⅵ） and capture Cr（Ⅲ） over wide pH range

Conversion of hexavalent chromium (Cr（Ⅵ）) to trivalent chromium (Cr（Ⅲ）) is an effective way to reduce its environmental risk,especially via photoreduction process.However,over a wide range of p H values,it is still a great challenge to achieve a high removal rate,and the disposal of produced Cr（Ⅲ） should be concerned.In this work,we implemented a high removal rate at 98%for Cr（Ⅵ） and total chromium(Cr（T）) over a wide p H range （4–10） through the synergistic effect of adsorption,photoreduction an...     

Bioavailability, bioaccumulation and tolerance of chromium: consequences in the food chain of freshwater ecosystems

Many abiotic and biotic factors can influence the partitioning equilibrium of heavy metals, thus influencing metal impact on aquatic environments. Unicellular algal species release soluble organic substances able to complex metals. In our laboratory a Cr-tolerant strain was selected and isolated from a wild type strain of Scenedesmus acutus. The exudates released by the two strains counteracted the growth inhibition caused by Cr(VI) and the exudates of the Cr-tolerant strain were more effective. On the contrary, the exudates did not reduce chromium toxicity to the cladoceran Daphnia magna. The reduction of chromium effect on algae seems the consequence of an algae-specific interaction among Cr(VI), exudates and algal cells. Chromium uptake resulted to be energy-dependent since bioaccumulation rate in subdued light condition was lower than at high light intensity. The effect of Cr(VI) on algae changed depending on metabolism of the cells and in particular it seemed to be related to the bioaccumulation rate. Tolerance in the selected strain could not be ascribed to a lower uptake of chromium. The difference in sensitivity to chromium between the two strains was exploited to evaluate if tolerance acquired by algae could have consequences for Daphnia. After treatment with Cr(VI), the two strains of S. acutus were used as food source for D. magna. The results indicate that chromium is accumulated by algae in a form not available for daphnids and that Cr tolerance acquired by the algae can be of some advantage to the consumer organism.     

A comparative study of global hexavalent chromium removal by chemical and electrochemical processes

Direct electroreduction of Cr(VI) to Cr(III) has been widely proposed as an alternative for the treatment of effluents polluted with hexavalent chromium, however, no analysis is available on the cost of a global process, that considers both, the energy required to carry out the reduction reaction, and that associated with the operation of the process, to remove Cr(VI) via precipitation of Cr(OH)₃. This paper presents a study of the operation cost, considering raw material and electric power required by the electrochemical process, to remove Cr(VI) from real samples. A comparison between chemical reduction is presented, where both processes are followed by a step of alkaline chemical precipitation. The differences in pH required for each step are determinant in the overall cost of the process. Operating under optimal conditions the cost is almost 7 times higher for direct electroreduction process compared with the chemical method, and power consumption being secondary. The ratio decreases to 1.3 times when the electrochemical method is carried out at pH 2, but operating time is increased threefold, thereby increasing the cost of pumping the solution to be treated.     

XAS and XPS studies on chromium-binding groups of biomaterial during Cr(VI) biosorption

The reduction of toxic Cr(VI) to the less or nontoxic Cr(III) may be an useful detoxification technique for the treatment of Cr(VI)-contaminated waters. Recently, the protonated biomass of brown seaweed, Ecklonia, was shown to completely reduce Cr(VI) to Cr(III) in the pH range 1-5. The reduction of Cr(VI) to Cr(III) appeared to occur at the surface of the biomass. In this study, abiotic Cr(VI) reduction by the biomass was performed with various contact times, pHs and initial Cr(VI) concentrations, and surface and bulk characteristics of the Cr-laden biomass was then investigated using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The XPS spectra indicated that the Cr(VI) bound to the biomass was completely reduced to Cr(III) at tested various conditions. XANES and EXAFS spectra of the Cr-laden biomass were very similar to those of Cr(III)-acetate, which means that the Cr bound to the biomass during Cr(VI) reduction had an octahedral geometrical arrangement. The bonding distance of the chromium oxygen atoms was approximately 1.97-1.99 A. In conclusion, it was obvious that oxygen containing groups, such as carboxyl and phenolic groups, play a major role in the binding of the Cr(III) resulting from the abiotic reduction of Cr(VI) by the biomass.     

Cr(VI)吸附剂及其吸附机理研究进展

摘要 重金属污染已成为影响人们生活亟亟待解的问题,它不仅威胁着自然环境的持续发展,更是对人类身体健康提出了严峻的考验。其中,六价铬因为环境污染持续久,危害大,更是得到各国研究者的重视。研究者们研究了各种吸附材料,它们对于六价铬的移除能力以及移除机理不尽相同。本文介绍了Cr(VI)吸附材料分类及其特点,重点分析了聚合物吸附材料在吸附和分离Cr(VI)方面的应用进展。并简要介绍了Cr(VI)吸附过程中的吸附动力学模型和等温方程式,以著名的Langmuir和Freundlich模型为例加以说明,为解决重金属铬离子引起的环境污染尤其水污染问题提供一种借鉴。     

Ultrasonic assisted deep eutectic solvent liquid–liquid microextraction using azadipyrromethene dye as complexing agent for assessment of chromium species in environmental samples by electrothermal atomic absorption spectrometry

A novel type of solvent named deep eutectic solvent (DES) has been considered as a green ionic liquid analogue. A novel method was developed for enrichment and speciation of chromium ion from water and food samples based on deep eutectic solvent and ultrasonic extraction. The procedure for this method was comprised of Cr(III) complex formation with a hydrophobic complexing agent (Z)‐N‐(3,5‐diphenyl‐1H‐pyrrol‐2‐yl)‐3,5‐diphenyl‐2H‐pyrrol‐2‐imine (azadipyrromethene dye). Metal complex was entrapped in a deep eutectic solvent as an extracting solvent. While Cr(III) recovery was quantitative, the recovery of Cr(VI) was found 5%. After reduction of Cr(VI) to Cr(III), the method was applied for determination of total chromium(III) ion. The amount of Cr(VI) was calculated as subtracting of Cr(III) from total chromium ion. Various analytical parameters were optimized. The certified reference materials were analyzed and standard addition method also carried out to real samples to check the accuracy of the developed method. Preconcentration factor was found to be 50. The limit of detection of chromium(III) was found to be 4.3 ng l^‐1. The precision of developed method as the relative standard deviation (RSD) was found as 3.5 %. The developed method was applied successfully for the speciation of chromium ions in water and food samples.     

Biosorption of Cr(VI) from Water Using Biomass of <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>: Central Composite Design for Optimization of Process Variables

The potential use of biomass of Aeromonas hydrophila for biosorption of chromium from aqueous solution was investigated. The variables (pH, initial Cr(VI) concentration, biomass dose, and temperature) affecting process were optimized by performing minimum number of experimental runs with the help of central composite design. The results predicted by design were found to be in good agreement (R ² = 99.1%) with those obtained by performing experiments. Multiple regression analysis shows that uptake decreases with increase in pH and biomass dose, whereas it increases with increase in temperature and concentration. The maximum removal of Cr(VI) predicted by contour and optimization plots was 184.943 mg/g at pH 1.5, initial Cr(VI) concentration 311.97 mg/L, temperature 60 °C, and biomass dose 1.0 g. The removal of Cr(VI) was governed by adsorption of Cr(VI) as well as its reduction into Cr(III), which further gets adsorbed. The sorption capacity of biomass was calculated from experimental data using Langmuir sorption model and was found to be 151.50 mg/g at 40 °C and pH 1.5, which is comparable to other biosorbents. In addition to this, Dubinin–Radushkevich model was applied, and it was found that nature of sorption was chemisorption.     

Heavy Metal Resistances and Chromium Removal of a Novel Cr(VI)-Reducing Pseudomonad Strain Isolated from Circulating Cooling Water of Iron and Steel Plant

Three bacterial isolates, GT2, GT3, and GT7, were isolated from the sludge and water of a circulating cooling system of iron and steel plant by screening on Cr(VI)-containing plates. Three isolates were characterized as the members of the genus Pseudomonas on the basis of phenotypic characteristics and 16S rRNA sequence analysis. All isolates were capable of resisting multiple antibiotics and heavy metals. GT7 was most resistant to Cr(VI), with a minimum inhibitory concentration (MIC) of 6.5 mmol L^?1. GT7 displayed varied rates of Cr(VI) reduction in M2 broth, which was dependent on pH, initial Cr(VI) concentration, and inoculating dose. Total chromium analysis revealed that GT7 could remove a part of chromium from the media, and the maximum rate of chromium removal was up to 40.8 %. The Cr(VI) reductase activity of GT7 was mainly associated with the soluble fraction of cell-free extracts and reached optimum at pH 6.0～8.0. The reductase activity was apparently enhanced by external electron donors and Cu(II), whereas it was seriously inhibited by Hg(II), Cd(II), and Zn(II). The reductase showed a K _m of 74 μmol L^?1 of Cr(VI) and a V _max of 0.86 μmol of Cr(VI) min^?1 mg^?1 of protein. The results suggested that GT7 could be a promising candidate for in situ bioremediation of Cr(VI).     

Electrode processes and their kinetic parameters in the reduction and oxidation of Cr(III) and Cr(II) in molten CsCl

The reduction of chromium ions in the CsCl-CrCl₃ melt in wide concentration and temperature ranges is reported. It is assumed that the melt contains polynuclear chromium complexes. The reduction of Cr(III) to Cr(II) is a reversible one-electron process. The electroreduction of divalent chromium to chromium metal is an irreversible process involving dinuclear and mononuclear chromium complex ions. The electron transfer rate constant has been calculated for various temperatures and chromium chloride concentrations in the salt melt. The activation energy of electron transfer and its dependence on the CrCl₃ concentration in the electrolyte have been determined for the Cr(III) ↔ Cr(II) process.     

An Opportunity for Recycling Semi‐dry Scrubber Residues Directly from Municipal Solid Waste Incineration Plants without Concern of Leaching Toxicity

The leaching behaviors of heavy metals from semi‐dry scrubber (SDS) residues of municipal solid waste incineration (MSWI) plants are re‐investigated. The most leachable heavy metals in semi‐dry scrubber residues from municipal solid waste incinerators are found to be chromium ions (Cr(III) and Cr(VI)), but neither lead nor cadmium. Both of the leachabilities of Cr(III) and Cr(VI) in MSWI scrubber residue are a function of the CaO/Al₂O₃ ratio of residues. The pH‐dependent leaching behaviors are only observed in the case of Cr(III), but not for Cr(VI). Our results show that it is worth recycling SDS residues which possess a lower chemical composition ratio of CaO/Al₂O₃, in order to reduce the potential risk of toxic leaching of chromium species.     

Comparison of chromium speciation by CZE and ion exchange followed by AAS

The hydrogen chromate anion (HCrO4-), which is the predominant species in acidic solutions and solutions with low chromium concentration, was determined by capillary zone electrophoresis (CZE) using UV detection on-column at 200 nm. A fused-silica capillary (55 cm x 50 microm i.d.) was employed with a high negative voltage of 20 kV. Total chromium was determined after reduction by H2O2 and its complexation by EDTA. The use of H2O2 as reducing agent is advantageous, as it does not increase the conductivity of the solution. Detection limits achieved (for 200 s injection time) were 30 and 8 microg/L for Cr(VI) and Cr(III), respectively. The CZE results obtained for Cr(III) and Cr(VI) were compared with those obtained by ion exchange with subsequent AAS.     

Thermodynamics of Chromium(VI) Anionic Species Sorption onto Surfactant-Modified Montmorillonite Clay

Batch sorption experiments performed on Cr(VI) species sorption showed a significantly enhanced removal of inorganic hexavalent chromium anionic species from aqueous solution by montmorillonite clays modified with quaternary amine, hexadecyltrimethylammonium (HDTMA) bromide. Unmodified clay had no affinity for chromium(VI) species. The sorption of Cr(VI) species has been carried out as a function of pH, contact time, adsorbate concentration (4.14x10(-5) to 8.62x10(-3) M), and temperature (5-45 degrees C). The surfactant-modified clay surface was stable when exposed to extremes in pH. The optimum pH for maximum sorption of Cr(VI) species was found to be at pH 1 and was constant between pH 2 and pH 6. The sorption data obtained was well described by DKR and Langmuir sorption isotherms. Sorption energy (E) for (i) surfactant sorption by montmorillonite clay and (ii) sorption of chromium(VI) species by surfactant modified clay have been computed from the DKR equation. Sorption energy evaluated for the sorption of both surfactant and Cr(VI) species showed that an ion-exchange mechanism was operative. The mechanism of retention appears to be replacement of counterion of the surfactant by Cr(VI) anionic species. Adsorbent capacity for the sorption of Cr(VI) species has been evaluated from the Langmuir sorption isotherm data. Thermodynamic parameters (Delta H degrees, Delta S degrees and Delta G degrees ) for surfactant sorption on montmorillonite clay and Cr(VI) sorption by modified clay have been evaluated. The specific rate constant for sorption of Cr(VI) species on modified montmorillonite was rapid during the first 10 min and equilibrium was found to be attained within 30 min. The sorption of Cr(VI) species onto modified montmorillonite clay followed first-order rate kinetics. Copyright 2000 Academic Press.     

ENAA studies of chromium uptake by Arthrobacter oxydans

To study chromium uptake by Arthrobacter oxydans [Cr(VI)-reducing bacteria isolated from Columbia basalt rocks, USA] the instrumental epithermal neutron activation analysis (ENAA) was applied. It was established that chromate accumulation is dose-dependent and it is most intensive in the interval of Cr(VI) concentrations (10-50 mg/l). At lower concentrations of Cr(VI) (up to 50 mg/l) the most intensive formation of Cr(V) was found using ESR method. Besides, it was established that reduction from Cr(VI) to Cr(V) is a faster process than the uptake of Cr(VI). According to ENAA measurements, in contrast to Cr(VI), Cr(III) is not accumulated in Arthrobacter oxydanscells up to concentrations of 200 mg/l. Using epithermal neutron activation analysis the background levels of 17 major, minor and trace elements were determined in Arthrobacter oxydans. This revised version was published online in August 2006 with corrections to the Cover Date.     

The use of 5-(4-pyridyl)nonane for the separation of chromium(vi) from fission products in hydrochloric acid media

The distribution of chromium(VI) between 5-(4-pyridyl)nonane in benzene and hydrochloric acid media has been studied as a function of the concentration of the acid, extractant, chromium(VI), chloride and a few other ions. The extraction mechanism and the composition of the extracted complexes of Cr(VI) have been proposed. The separation of Cr(VI) from uranium, thorium and fission products in 3M hydrochloric acid has been achieved.     

Application of ionizing radiation to environmental protection: removal of toxic Cr(VI) metal ion in industrial wastewater: preliminary study

Hexavalent chromium, a major contaminant in most wastewater sites, is a potential health threat inducing cancer to humans while trivalent chromium is an essential element for the metabolism of sugar. The radiation-induced reduction of Cr(VI) metal ion to Cr(III) by the perhydroxyl radical (HO₂ ^?) and carboxyl radical anion (CO₂ ^??) produced by continuous radiolysis of water was investigated by steady state radiolysis of O₂, Ar and N₂O-saturated pH 3 solutions in the presence of formate. In all cases the removed Cr(VI) was a linear function of the absorbed dose. The added formate was favorable for removing Cr(VI). Its presence protects the solution from reverse radiolytic oxidation of Cr(III) to Cr(VI). The measured and calculated yield of removal of Cr(VI) do agree quite well at low formate concentration but at high formate concentration the measured yield was higher than the expected. When all formate is exhausted no recovery of Cr(VI) from Cr(III) was observed in case of O₂- and Ar-saturated solutions whilst in the case of N₂O-saturated solutions Cr(VI) recovers. The results obtained in this study highlight the potential of this technology for industrial wastewater treatment.     

Analytical speciation of chromium in in-vitro cultures of chromate-resistant filamentous fungi

In this work, different analytical speciation schemes have been used to study the reduction of Cr(VI) by a chromate-resistant strain of filamentous fungi Ed8 (Aspergillus sp), indigenous to contaminated industrial wastes. As demonstrated previously, this strain has the capability to reduce chromate present in the growth medium without its accumulation in the biomass, yet the reduced chromium end-products have not been characterized. Liquid growth medium, initially containing 50 mg L(-1) Cr(VI), was analyzed for Cr(III)/Cr(VI) and for total Cr at different time intervals (0-24 h) after inoculation with fungi. Three hyphenated procedures, based on the Cr(III)-EDTA formation and species separation by anion-exchange or ion-pairing reversed-phase chromatography with ICP-MS or DAD detection were used. The results obtained for Cr(VI) in each case were consistent, demonstrating efficient reduction of chromate during 24 h of Ed8 growth. However, pre-column complexation with EDTA did not ensure complete recovery of the reduced forms of chromium in the above procedures. An alternative speciation scheme, based on extraction of Cr(VI)-benzyltributylammonium bromide (BTAB) ion pairs into chloroform and subsequent determination of residual chromium by ICP-MS has provided evidence on the effective conversion of chromate into reduced chromium species in the growth medium. The results indicate the feasibility of using Ed8 strain for chromate bioremediation purposes. Analytically it can be concluded that speciation of chromium in biological systems should not be limited to its two most common oxidation states, because the actual reduced chromium species are not converted quantitatively to Cr(III)-EDTA.     

水溶液中六价铬在碳纳米管上的吸附

针对用碳纳米管对水溶液中六价铬的吸附净化进行了研究, 考察了溶液浓度、溶液pH值、共存的三价铬离子等因素对吸附行为的影响. 实验结果表明, 碳纳米管在室温下对于六价铬的吸附量随着平衡浓度的增大而升高, 在铬浓度为493.557 mg•L−1时碳纳米管吸附量达到最大值为532.215 mg•g−1; 六价铬的浓度在300~700 mg•L−1的范围内, 碳纳米管对铬的吸附量变化不大；大于700 mg•L−1时, 随着铬的平衡浓度的升高碳纳米管对铬的吸附量降低, 铬浓度为961.074 mg•L−1时, 碳纳米管吸附量降至194.631 mg•g−1. 在pH值为2~7的范围内, 碳纳米管对六价铬的吸附量随着溶液pH值的减小而增大; 而在碱性条件下, pH值对碳纳米管吸附六价铬的影响不大. 溶液中存在三价铬时, 碳纳米管对六价铬的吸附量明显降低, 表明三价铬与六价铬有竞争吸附. 此外, 活性炭的对比吸附实验表明, 在低浓度时, 譬如在六价铬浓度为190 mg•L−1吸附时, 碳纳米管对铬的吸附量约为活性炭的6倍；而在高浓度下, 譬如六价铬浓度为493 mg•L−1时, 碳纳米管对铬的吸附量约为活性炭的2倍.     

Comparative Study of Chromium Biosorption by Mesorhizobium amorphae Strain CCNWGS0123 in Single and Binary Mixtures

The appearance of chromium in the aqueous effluent is a major concern for the modern industry. In this work, Mesorhizobium amorphae strain CCNWGS0123 was investigated as a biosorbent to remove chromium from aqueous solutions. The optimum pH for Cr(III) and Cr(VI) biosorption were 4 and 2, respectively. This isolate showed an experimental maximum Cr(III) adsorption capacity of 53.52 mg?L^?1, while the result was 47.67 mg?L^?1 for Cr(VI), with an initial 100 mg?L^?1 Cr ions and 1.0 g?L^?1 biomass. In terms of time equilibrium, Cr(III) ion was more readily adsorbed than Cr(VI) by this isolate. The biosorption data of both ions fit the Langmuir isotherm better than that of Freundlich model. Meanwhile, this organism exhibited a good capability to release Cr ions, with desorption efficiency of 70 % for Cr(III) and 76 % for Cr(VI). Fourier transform infrared spectroscopy analysis showed that –OH, –COO, –NH, amide I, and C=O were involved in Cr(III) and Cr(VI) binding. The biosorbent was further characterized by scanning electron microscopy and energy-dispersive X-ray spectrometry, which indicated an accumulation of chromium on the cellular level. In the binary mixtures, the removal ratio of total Cr and Cr(III) increased from pH?2 to 4. The highest removal ratio of the total Cr was observed in the 25/25 mg?L^?1 mixture at pH?4. In addition, the removal efficiency of Cr(VI) was closely influenced by Cr(III) in the mixture, decreasing to 23.57 mg?g^?1 in the 100/100 mg?L^?1 mixture system, due to the competition of Cr(III). The potential usage of the chromium-resistant rhizobium for the remediation of chromium-contaminated effluents has been demonstrated based on the above results.     

Removal of hexavalent chromium from wastewaters by bone charcoal

The adsorption of hexavalent chromium onto bone charcoal was studied as a function of time, amount of charcoal, pH, concentration of chromium and sample volume. The cross interference with other elements was also investigated. Tests were carried out with solutions of chromium(VI) at concentrations between 5 and 25 mg · L^–1. Chromium removal efficiencies higher than 90% were achieved at pH = 1 using 2 g of bone charcoal and a stirring time in the order of 30 min. Acid and alkaline pretreatments of bone charcoal did not improve the sorption capacity of bone charcoal against Cr(VI). The presence of other ions had practically no influence on the chromium removal. The presence of a matrix of tannery effluents did not reduce the removal capacity of bone charcoal for Cr(VI), but it was confirmed that only 47% of Cr(III) can be removed using these conditions. Received: 20 July 1998 / Revised: 4 October 1998 / Accepted: 10 October 1998