Efficient Removal Of Hexavalent Chromium Research Articles

Formation of active zero-valent iron by simple co-grinding with CaCO3 to protect fresh active surface for efficient removal of hexavalent chromium

A novel composite material consisting of zero-valent iron (ZVI) and CaCO3 was successfully prepared through a simple grinding operation. The as-synthesized ZVI/CaCO3 composites were applied to the reduction precipitation of hexavalent chromium (Cr(VI)) and a tremendous improvement in reaction capacity was obtained compared with raw ZVI and ground ZVI sample without CaCO3 addition. Many factors of the grinding operation and ZVI/CaCO3 mass ratios were investigated to evaluate material properties and to study reaction mechanism. A high removal efficiency of 99.68% within just 30 min on Cr (VI) (10 mg/L) was obtained by the ZVI/CaCO3 composite with ZVI mass ratio at 30 wt%. X-ray diffraction (XRD), Fourier transformed infrared (FTIR), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were used to investigate the chemical constitution and physicochemical properties of composites before and after the reaction. Addition of CaCO3 played very important role in both grinding iron particles into fine powders and protecting the fresh surface of active ZVI to enable the superior performance as zero-valent iron. Besides the environment-friendliness of the process itself without any pollutant emission, waste solid materials containing iron particles may serve as the starting sample to decrease the product cost.

Nanocomposites based on 3D macroporous biomass carbon with SnS2 nanosheets hierarchical structure for efficient removal of hexavalent chromium

In this study, a novel nanocomposite, carbon/SnS2 with 3D hierarchical macroporous (MCS), was successfully prepared for rapid photocatalytic treatment of hexavalent chromium (Cr(VI)). The 3D macroporous carbon (MC) can be obtained through a simple carbonization process of loofah. Since the MCS has a large specific surface area, it can provide numerous photocatalytic active sites and has excellent adsorption properties for the Cr(VI). In addition, the excellent electrical conductivity and unique hierarchical nanoarchitecture of macroporous biomass carbon could rapidly absorb the Cr(VI) from wastewater and provide electron transport tunnel for rapid charge separation/transport to suppress hole electron recombination. It is confirmed that such three dimensional photocatalytic material can quickly purify Cr(VI)-containing wastewater under mild visible light irradiation, with a efficiency of 63.2% Cr(VI) reduction within 120 mins. Besides the high visible light-driven photocatalytic activity, MCS also exhibits excellent cycling stability. In addition, the SEM images of MCS before and after photocatalytic removal of Cr(VI) indicate that the morphology of composite was perfectly maintained and no peeling-off of SnS2 was observed. More importantly, this study demonstrated that MCS can be used for practical applications due to its stability and economic availability.

Efficient Removal of Hexavalent Chromium from Wastewater with Electro-Reduction

Removal of hexavalent chromium had attracted much attention as it is a hazardous contaminant. An electrocoagulation-like technology electro-reduction was applied. The chromium (VI) in the wastewater was reduced to chromium (III) by the electron supplied by electricity power and Fe2+, formed from corrosion of steel electrodes in acidic conditions. The mechanism and parameters affecting the reaction were investigated. The results optimized by response surface methodology indicated that the influence of single factor on the reduction efficiency followed the order: A: dosage of H2SO4 > C: reaction time > D: reaction temperature > B: current intensity. The reduction efficiency was hardly affected by current intensity, while it was increased with the increasing of reaction time and acid concentration. The reducing agent, Fe2+ an and extra free electron, acted as a reducing agent and could easily reduce hexavalent chromium to trivalent chromium at high temperatures in an acidic medium.

Recyclable functionalized polymer films for the efficient removal of hexavalent chromium from aqueous solutions.

In this study, polyethylenimine-functionalized poly(vinyl alcohol) (PEI-PVA) films were prepared for the first time to remove aqueous Cr(vi). The results indicate that our PEI-PVA films have an excellent potential for Cr(vi) removal and their maximum removal capacity was 396.83 mg g−1. The optimized pH value was 2, the adsorption of Cr(vi) was fitted to the Langmuir model, and the kinetics of uptake could be described well by a pseudo-second-order rate model. Taking into account the simplified separation method of adsorbents and solutions, we used a PVA film as a carrier in which PEI-PVA microspheres were filled to obtain a PEI-PVA functionalized film (PPF). The PPF shows a great efficiency in the removal of Cr(vi) ions in solution, which can absorb and reduce the Cr(vi) ion concentration in the solution in 90 min. PPF has excellent selectivity and the removal efficiency of Cr(vi) ions in the presence of co-existing ions is not reduced. It also has good recycling properties; the removal efficiency remains at 77% over four cycles. The removal mechanism of Cr(vi) ions by PEI-PVA microspheres involves the reduction of the adsorbed Cr(vi) ions to Cr(iii) ions, which are less toxic.

Hydrogen ions and organic acids secreted by ectomycorrhizal fungi, Pisolithus sp1, are involved in the efficient removal of hexavalent chromium from waste water

Pisolithus sp1 is an ectomycorrhizal (ECM) fungi that was chosen during a screening test of six strains of ECM fungi due to its ability to tolerate and remove hexavalent chromium (Cr(VI)). The physiological responses of Pisolithus sp1 to Cr(VI) exposure, the relationship between Pisolithus sp1 and exogenously added organic acids (EAOAs) or Na3VO4 (H+-ATPase inhibitor) and the ability of Pisolithus sp1 to reduce Cr(VI) in liquid culture were also investigated. Hydrogen ions (H+), which were produced directly by Pisolithus sp1, reduced the pH of the medium and played an important role in Cr(VI) reduction; however, Na3VO4 significantly inhibited this process and resulted in a decrease in the Cr(VI) reduction rates. Organic acids were secreted after the reduction in Cr(VI) by Pisolithus sp1, and EAOAs did not significantly affect Cr(VI) reduction; those results revealed the secondary role of organic acids in Cr(VI) reduction. The Cr(VI) removal rate of Pisolithus sp1 approached 99% after Cr(VI) treatment for 12 days. Overall, 75% of the Cr(VI) removal was due to extracellular reduction and 24% was due to adsorption. The results of this study provide a strong basis for using Cr(VI)-tolerant and Cr(VI)-reducing fungi, as well as ectomycorrhiza, in the remediation of Cr(VI)-contaminated sites.

Zero-valent iron nanoparticles supported by functionalized waste rock wool for efficient removal of hexavalent chromium

A novel nanocomposite, named as ARWZ, was fabricated using zero-valent iron (ZVI) nanoparticles supported by acid-modified waste rock wool (ARW). ARW displayed a porous rod-like structure and could load plenty of ZVI nanoparticles. Meanwhile, ARW could effectively inhibit the aggregation and oxidation of ZVI nanoparticles because of steric-hindrance effect. ARWZ exhibited a large specific surface area and high removal capacity (197.69 mg/g) in 30 min for hexavalent chromium (Cr(VI)) from water and soil through adsorption and reduction, and the resulting ARWZ-Cr could be easily collected under a magnetic field because of the superior magnetic property. Importantly, when ARWZ was loaded in filter cotton with a micro/nano networks structure, the resulting system could be conveniently used as an excellent filter layer to control the migration of Cr(VI). This work provides a low cost and promising approach to remove Cr(VI), which also promotes the reuse of waste rock wool.

Efficient removal of hexavalent chromium from water by an adsorption-reduction mechanism with sandwiched nanocomposites.

Hexavalent chromium Cr(vi), one of the most toxic contaminants, is released in the environment due to various anthropogenic activities. This study presents a novel sandwiched nanocomposite synthesized using graphene oxide (GO), manganese dioxide (MnO2) nanowires, iron oxide (Fe3O4) nanoparticles and polypyrrole (PPy) to remove hexavalent chromium ion Cr(vi) from water by an adsorption–reduction mechanism. In the sandwiched nanocomposites, GO provided enough surface area, functional groups, and hydrophilic surface for efficient absorption. Fe3O4 nanoparticles with excellent magnetic properties make it easy to separate and recover from water. Under acidic conditions, MnO2 nanowires act as both template and oxidant to initiate the polymerization of pyrrole monomers on its freshly activated surface to obtain GO/MnO2/Fe3O4/PPy (designated as GMFP) nanocomposite. GMFP could effectively adsorb Cr(vi) through electrostatic attraction, and the adsorbed Cr(vi) ions were partly reduced to trivalent chromium Cr(iii) (62%), resulting in the efficient adsorption and high removal of Cr(vi) from water. Hexavalent chromium adsorption by GMFP is strongly pH dependent and the adsorption kinetics followed the pseudo-second-order model. The Langmuir isothermal model described the adsorption isotherm data well and the maximum adsorption capacity was up to 374.53 mg g−1 at pH 2.0. These experimental results suggested that GMFP had great potential as an economic and efficient adsorbent of hexavalent chromium from wastewater, which has huge application potential.

Performance and mechanism of Cr(VI) removal by zero-valent iron loaded onto expanded graphite

Zero-valent iron (ZVI) was loaded on expanded graphite (EG) to produce a composite material (EG-ZVI) for efficient removal of hexavalent chromium (Cr(VI)). EG and EG-ZVI were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and Brunauer–Emmett–Teller (BET) analysis. EG-ZVI had a high specific surface area and contained sub-micron sized particles of zero-valent iron. Batch experiments were employed to evaluate the Cr(VI) removal performance. The results showed that the Cr(VI) removal rate was 98.80% for EG-ZVI, which was higher than that for both EG (10.00%) and ZVI (29.80%). Furthermore, the removal rate of Cr(VI) by EG-ZVI showed little dependence on solution pH within a pH range of 1–9. Even at pH11, a Cr(VI) removal rate of 62.44% was obtained after reaction for 1hr. EG-ZVI could enhance the removal of Cr(VI) via chemical reduction and physical adsorption, respectively. X-ray photoelectron spectroscopy (XPS) was used to analyze the mechanisms of Cr(VI) removal, which indicated that the ZVI loaded on the surface was oxidized, and the removed Cr(VI) was immobilized via the formation of Cr(III) hydroxide and Cr(III)–Fe(III) hydroxide/oxyhydroxide on the surface of EG-ZVI.

Efficient removal of hexavalent chromium from water and soil using magnetic ceramsite coated by functionalized nano carbon spheres

A magnetic ceramsite (MC) coated by nano carbon spheres (MCCS) was fabricated, and then the MCCS was stabilized and functionalized by polyethylenimine (PEI) to obtain a nanocomposite named as MCCSP. The nano carbon spheres (NCS) possessed plenty of amino and oxygen-containing groups (OH, COOH) and distributed homogeneously on the surface of MC, meanwhile the size and dispersion of these NCS could be conveniently adjusted. MCCSP demonstrated a high adsorption capacity for Cr(VI) which could be then reduced to low toxic trivalent chromium (Cr(III)), and the obtained Cr(III) could be chelated on the surface of MCCSP by protonated amine groups. Importantly, the resulting MCCSP-Cr could be conveniently collected from water and soil by a magnetic separation system (MSS). Therefore, this work provides a promising approach to remediate Cr(VI)-contaminated water and soil and may have a high application value.

The use of Sn(II) oxy-hydroxides for the effective removal of Cr(VI) from water: Optimization of synthesis parameters

The development of a novel adsorbent based on Sn(II) oxy-hydroxide nanoparticles and the optimization of main synthesis parameters was examined for the efficient removal of hexavalent chromium at low residual concentration levels. The aqueous hydrolysis of Sn(II) salts in a continuous-flow process was evaluated as an effective method to synthesize an appropriate material able to operate both as an electron donor for Cr(VI) reduction, and provide a suitable crystal structure that favors strong complexation with the formed Cr(III) species. Experimental results revealed that the main hydrolysis parameters, such as pH value and tin origin/source, can be used to determine the chemical formula of the produced materials and thereby, eventually improve their uptake capacity for Cr(VI). Among the tested sorbent materials, the synthetic nanostructured hydroromarchite, Sn6O4(OH)4, prepared by the hydrolysis of SnCl2 in a highly acidic environment (pH2), was deemed the best sorbent material and it was further investigated for its Cr(VI) uptake performance under reliable conditions (column experiments) for drinking water treatment. Specifically, Rapid Small-Scale (laboratory) Column Tests indicated that aggregates of the Sn6O4(OH)4 nanomaterial can achieve a maximum uptake capacity of around 19mg/g, keeping the levels of outflow Cr(VI) below 10μg/L during the treatment of natural-like water at pH7. The high efficiency is mainly attributed to the stabilization of Sn(II) content in nanoparticles, as well as the improved surface charge density, reaching 1.0mmol[OH−]/g, whereas the obtained thermodynamic data indicate a combined reduction-sorption process. The latter aspect was further verified by XPS, showing that even in the highly-loaded sorbent materials with adsorbed chromium, its trivalent form is the predominant one. These specific characteristics suggest that the product is a more favorable candidate for wider applications in water treatment units, regarding Cr(VI) removal, compared to other examined sorbent materials.

Efficient removal of hexavalent chromium and lead from aqueous solutions by s‐triazine containing nanoporous polyamide

s‐Triazine containing dicarboxylic acid was synthesized. Then, it was reacted with 1,3‐phenylenediamine in molten tetrabutylammonium bromide to formed soluble aromatic polyamide with good yield and moderate inherent viscosity of 0.35 dL g−1. The solubility and flexibility of polyamides are low. So, we used ether group such as di(4‐aminephenyl) ether in building polyamide. The structure of monomer and polymer was confirmed by Fourier transform infrared spectroscopy, elemental analysis, and proton nuclear magnetic resonance techniques. Thermogravimetric analysis was used to evaluate the thermal properties of synthesized polyamide, and their results show that this polymer had a good thermal stability. The surface morphology of s‐triazine containing polyamide was studied by field emission‐scanning electron microscopy and transmission electron microscopy, and the results show that it has a porous morphology and moderate Brunauer–Emmett–Teller specific surface (367 m2 g−1). It was further investigated for Pb (II) and Cr(VI) ion removal by optimizing the parameters including pH and contact time. The maximum uptakes of Pb(II) and Cr(VI) at pH 5.0 and pH 4.0 are 57% and 76%, respectively. Also, sorption kinetics of this polymer was investigated. Copyright © 2017 John Wiley & Sons, Ltd.

Highly efficient removal of hexavalent chromium in aqueous solutionsviachemical reduction of plate-like micro/nanostructured zero valent iron

The plate-like micro/nanostructured zero valent iron has exhibited the significantly enhanced ability to remove Cr(vi) from the real electroplating wastewater compared with the commercial zero valent iron.

Fabrication of Unique Magnetic Bionanocomposite for Highly Efficient Removal of Hexavalent Chromium from Water.

Biotreatment of hexavalent chromium has attracted widespread interest due to its cost effective and environmental friendliness. However, the difficult separation of biomass from aqueous solution and the slow hexavalent chromium bioreduction rate are bottlenecks for biotechnology application. In this approach, a core-shell structured functional polymer coated magnetic nanocomposite was prepared for enriching the hexavalent chromium. Then the nanocomposite was connected to the bacteria via amines on bacterial (Bacillus subtilis ATCC-6633) surface. Under optimal conditions, a series of experiments were launched to degrade hexavalent chromium from the aqueous solution using the as-prepared bionanocomposite. Results showed that B. subtilis@Fe3O4@mSiO2@MANHE (BFSM) can degrade hexavalent chromium from the water more effectively (a respectable degradation efficiency of about 94%) when compared with pristine B. subtilis and Fe3O4@mSiO2@MANHE (FSM). Moreover, the BFSM could be separated from the wastewater by magnetic separation technology conveniently due to the Fe3O4 core of FSM. These results indicate that the application of BFSM is a promising strategy for effective treating wastewater containing hexavalent chromium.

Microchannel-embedded metal–carbon–polymer nanocomposite as a novel support for chitosan for efficient removal of hexavalent chromium from water under dynamic conditions

A blend of micron-sized chitosan and carbon nanofibers (CNFs)-supported iron (Fe)-oxide nanoparticles (NPs) was dispersed in a modified polyvinyl alcohol to produce an approximately 1mm-thick metal–carbon–polymer nanocomposite film. The film was laser-ablated to create microchannels (150μm-wide, 100μm-deep and 30mm-long), thereby exposing the in situ dispersed chitosan and Fe-oxide NPs to the surrounding liquid through the porous walls of the fabricated microchannels. The prepared micro-textured nanocomposite film was used as a novel contactor for the remediation of hexavalent chromium (Cr(VI))-contaminated water under flow conditions. The material showed a high metal-uptake (∼80mgperg of chitosan/Fe-CNF composite), which was approximately the same as the equilibrium adsorption capacity determined under batch conditions. The spent nanocomposite film could be successfully regenerated and reused four times. The prepared material cum contactor in this study provides a potential solution to the difficulty of supporting all such micron- and submicron (nano)-sized metal/polymer particles that are prone to elution in liquid flow, by providing them a mechanically and thermally stable support for their practical use in separation and purification applications.

Highly efficient removal of hexavalent chromium from electroplating wastewater using aminated wheat straw

Highly efficient aminated wheat straw had high adsorption and selectivity for Cr(vi) in electroplating wastewater, and some adsorbed Cr(vi) were reduced to Cr(iii) and released into solution.

Efficient removal of hexavalent chromium by high surface area Al2O3rods

High surface area Al2O3rods were develped and exhibited high adsorption capacity of 39 mg g−1for hexavalent chromium.

Cu-Zn powders as potential Cr(VI) adsorbents for drinking water

This work examines the possibility of applying CuZn alloys as a reducing medium for the efficient removal of hexavalent chromium from drinking water. In an effort to develop a route for producing powders of CuZn alloys under mild conditions and investigate the optimum composition for such application, a series of alloys in the form of powders were prepared, by a sequence of Cu and Zn ball-milling and low temperature annealing. Batch Cr(VI) removal tests, performed to evaluate and compare the efficiency of the products under typical natural water parameters (pH 7 and natural-like water), indicated that the best performing material have a composition around 50wt% Cu. The dominant reduction mechanisms are both the corrosion of the alloy surface and the electron transfer to the solution. The behavior of granulated CuZn media was tested in rapid-scale column tests using the commercial KDF which verified the high potential of CuZn alloys in Cr(VI) removal. Nevertheless, Cu and Zn leaching problems should be also considered.

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, Toth, 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.

Evaluation of Consortia of Microorganisms for Efficient Removal of Hexavalent Chromium from Industrial Wastewater

The Chromium (Cr) uptake ability of Cr-resistant bacterium Bacillus thuringiensis, yeast Candida etschellsii, and a protozoan Stylonychia mytilus, isolated from industrial waste water, was evaluated individually and in different combinations. It was found that the three types of microorganisms grown together in a culture medium could collectively uptake 90% of Cr(6+) from the culture medium as against 82% by bacterium + protozoan or yeast + protozoan combined culture, each. Consortium of bacterium, yeast and ciliates therefore could make much more efficient inoculum for remediation of Cr-contaminated industrial waste water.

Efficient removal of hexavalent chromium by a tolerant Streptomyces sp. affected by the toxic effect of metal exposure

To isolate and analyse chromium-resistant micro-organisms suitable for bioremediation. Strain CG252, with a minimal inhibitory concentration of 500 microg ml(-1), was isolated from contaminated soils and identified as a Streptomyces sp. by 16S rDNA sequence analysis. Assays carried out at various Cr(VI) concentrations indicated that chromium removal was more efficient at lower concentrations and that this activity resulted in accumulation of Cr(III). Atomic adsorption analysis indicated that the chromium removed was not associated with cell mass and activity assays showed that the capacity to reduce Cr(VI) was most probably due to a soluble cytosolic enzyme. Cells grown as biofilms showed enhanced removal of Cr(VI) with respect to planktonic cells, while analysis of growth and colony morphology indicated that Cr(VI) had a toxic effect on this strain. Streptomyces sp. CG252 tolerated heavy metals and elevated levels of chromium, despite its negative effect on growth and development, and was efficient at removing Cr(VI) by promoting reduction to Cr(III). Strain CG252's capacity to tolerate heavy metals and to reduce Cr(VI) to the less toxic Cr(III), especially when forming biofilms, makes it a promising candidate for detoxification of sites containing this heavy metal.