Showing papers on "Chromium published in 2020"

Removal of chromium from wastewater by membrane filtration, chemical precipitation, ion exchange, adsorption electrocoagulation, electrochemical reduction, electrodialysis, electrodeionization, photocatalysis and nanotechnology: a review

Abstract: Chromium is a potentially toxic and carcinogenic metal originating from natural processes and anthropogenic activities such as the iron steel, electroplating and leather industries. Therefore, chromium should be removed from wastewater to avoid environmental pollution and to recycle chromium in the context of the future circular economy. Here we briefly review aqueous Cr species, their toxicity and methods to remove Cr such as membrane filtration, chemical precipitation, ion exchange, adsorption electrocoagulation, electrochemical reduction, electrodialysis, electrodeionization, photocatalysis and nanotechnology.

Chromium Pollution in European Water, Sources, Health Risk, and Remediation Strategies: An Overview.

Abstract: Chromium is a potentially toxic metal occurring in water and groundwater as a result of natural and anthropogenic sources. Microbial interaction with mafic and ultramafic rocks together with geogenic processes release Cr (VI) in natural environment by chromite oxidation. Moreover, Cr (VI) pollution is largely related to several Cr (VI) industrial applications in the field of energy production, manufacturing of metals and chemicals, and subsequent waste and wastewater management. Chromium discharge in European Union (EU) waters is subjected to nationwide recommendations, which vary depending on the type of industry and receiving water body. Once in water, chromium mainly occurs in two oxidation states Cr (III) and Cr (VI) and related ion forms depending on pH values, redox potential, and presence of natural reducing agents. Public concerns with chromium are primarily related to hexavalent compounds owing to their toxic effects on humans, animals, plants, and microorganisms. Risks for human health range from skin irritation to DNA damages and cancer development, depending on dose, exposure level, and duration. Remediation strategies commonly used for Cr (VI) removal include physico-chemical and biological methods. This work critically presents their advantages and disadvantages, suggesting a site-specific and accurate evaluation for choosing the best available recovering technology.

Chromium in Environment, Its Toxic Effect from Chromite-Mining and Ferrochrome Industries, and Its Possible Bioremediation

Abstract: Chromium has long been recognized as a toxic, mutagenic and carcinogenic metal It is toxic to microorganism, plants, animals and humans Chromium exists in environment in two stable forms: Cr(VI) and Cr(III) Cr(III) is less toxic and insoluble, while Cr(VI) is extremely toxic and highly soluble Chromium is used in many industrial applications, but it poses a threat to local environment The effluents and solid wastes from the mining, chrome-plating, leather-tanning, and dye-manufacturing industries are high in chromium concentration and identified as a major health hazard because of pollution to the environment Industrial waste is used in landfilling, which causes the seepage, and the leaching of toxic chromium from soil into water bodies poses a threat to the environment Ferrochrome industry is one of the biggest contributors of the chromium pollution to the water bodies South Africa has the world’s largest chromium reserve The waste materials produced by ferrochrome industry are slag, dust and processed water These wastes have high chromium concentration that can cause pollution to the environment Inhalation is the major exposure route of the Cr(VI) toxicity in humans The bioremediation of Cr(VI) to Cr(III) in the polluted site is a cost-effective and ecofriendly solution for preventing chromium detoxification Bioremediation can be in situ or ex situ, and choice of remediation method depends upon the extent of pollution and the nature of the site This paper summarizes the chromium pollution caused by ferrochrome industries, current remediation method adopted by ferrochrome industries, and the possible new methods for effective bioremediation This paper focuses mainly on bioremediation techniques to convert the high-toxic form of chromium to less-toxic and mobile form of chromium

A mechanistic approach of chromium (VI) adsorption onto manganese oxides and boehmite

Abstract: The concentration of chromium (VI) in the soil is an important environmental concern due to its mobility and acute toxicity. Due to its toxicity, removal of this species is very important. The mobility of Cr(VI) is highly governed by its adsorption onto the mineral surfaces. Manganese oxides are naturally-occurring scavengers and have a significant influence on the distribution, and transport of chromate species. Thus, to understand the fate of chromate species and its removal process, it is important to study chromium (VI) adsorption. In this study, birnessite (δ-MnO2), pyrolusite (β-MnO2), hausmannite (Mn3O4), manganite (γ-MnOOH), boehmite (γ-AlOOH), and Mn-Al binary oxide was used as adsorbents to adsorb Cr(VI) over a range of solution pH and initial Cr(VI) concentrations. A combined approach using the Langmuir and Freundlich models, proton stoichiometry and surface complexation model (SCM) have been used to describe the probable Cr(VI) adsorption process. Birnessite was the most potent adsorbent at low pH. The Langmuir model could describe the equilibrium isotherm data well, suggesting a uniform surface nature. Proton stoichiometry indicated that Cr(VI) adsorption involved more than one type of reaction. The findings confirm that Cr(VI) species bind to functional groups by the inner- and outer-sphere chromate complexes, with the extent of binding dependent on solution pH. The study presented herein can be applied to soils with a variety of surface properties, pH, and Cr (VI) concentrations. The study further advances our understanding of the interaction between Cr(VI) and minerals at the solid-water interface.

Multivariate optimisation of Cr (VI), Co (III) and Cu (II) adsorption onto nanobentonite incorporated nanocellulose/chitosan aerogel using response surface methodology

Abstract: In this study, tailor made Nanobentonite incorporated Nanocellulose/Chitosan aerogel (NCNB) has been used to study its metal adsorption capacity from simulated wastewater. The aerogel was characterised with FESEM, AFM, EDX, XRD, FTIR, Raman spectroscopy and found the successful conversion to the desired adsorbent in nano dimension. This NCNB was used for optimisation of Chromium, Cobalt and Copper adsorption. Response Surface Methodology (RSM) was implemented to derive the binary correlation between various experimental parameters such as initial metal concentration, pH, adsorbent mass and temperature using Central Composite Design (CCD). The regression coefficients were evaluated which validated second order polynomial equation for the remediation of Cr, Co and Cu with NCNB. The maximum adsorption efficiencies under the optimum condition of the process parameters for Cr, Co and Cu removal were found to be 98.90, 97.45 and 99.01 % respectively. Co efficient of determination, R2 for Cr, Co and Cu were 0.9796, 0.8973 and 0.9321 respectively. Halsey isotherm and pseudo-second-order kinetic model agreed well with the experimental data for all the three metals. Thermodynamics study showed the metal adsorption was spontaneous, endothermic and feasible in nature. These data imperatively show that use of this aerogel can be a good alternative to the expensive methods of heavy metal remediation.

Different Pathways for Cr(III) Oxidation: Implications for Cr(VI) Reoccurrence in Reduced Chromite Ore Processing Residue.

Abstract: Hexavalent chromium contamination is a global environmental issue and usually reoccurs in alkaline reduced chromite ore processing residues (rCOPR). The oxidation of Cr(III) solids in rCOPR is one possible cause but as yet little studied. Herein, we investigated the oxidation of Cr(OH)3, a typical species of Cr(III) in rCOPR, at alkaline pH (9-11) with δ-MnO2 under oxic/anoxic conditions. Results revealed three pathways for Cr(III) oxidation under oxic conditions: (1) oxidation by oxygen, (2) oxidation by δ-MnO2, and (3) catalytic oxidation by Mn(II). Oxidations in the latter two were efficient, and oxidation via Pathway 3 was continuous and increased dramatically with increasing pH. XANES data indicated feitknechtite (β-MnOOH) and hausmannite (Mn3O4) were the reduction products and catalytic substances. Additionally, a kinetic model was established to describe the relative contributions of each pathway at a specific time. The simulation outcomes showed that Cr(VI) was mainly formed via Pathway 2 (>51%) over a short time frame (10 days), whereas in a longer-term (365 days), Pathway 3 predominated the oxidation (>78%) with an increasing proportion over time. These results suggest Cr(III) solids can be oxidized under alkaline oxic conditions even with a small amount of manganese oxides, providing new perspectives on Cr(VI) reoccurrence in rCOPR and emphasizing the environmental risks of Cr(III) solids in alkaline environments.

Polyaniline-TiO2 composite photocatalysts for light-driven hexavalent chromium ions reduction

Abstract: In order to develop efficient photocatalysts, great efforts have been made to reduce hexavalent chromium to trivalent chromium. The photocatalytic efficiency of this reduction depends largely on the adsorption and diffusion of hexavalent chromium ions on the surface of the photocatalyst. In this paper, polyaniline-TiO2 composite can effectively improve the photocatalytic reduction performance and stability of hexavalent chromium ion. The effect of polyaniline (PANI) thickness on Cr(VI) activity and stability of photocatalytic reduction was studied by adjusting the content of PANI on Mesoporous TiO2 (MT) surface. Under the irradiation conditions, the reaction results showed that the reduction rate was 100%, and the maximum reaction rate reached 0.62 min−1 when the PANI modification was 3.0%. Moreover, the results showed that the reduction performance remained 100% after ten cycles. The main reason is that the PANI modified on the surface of TiO2 is rich in positively charged amino group, which can efficiently adsorb the reactant Cr(VI), and make the product Cr(III) leave the reaction interface quickly, thus ensuring the performance of photocatalyst.

Single Chromium Atoms Supported on Titanium Dioxide Nanoparticles for Synergic Catalytic Methane Conversion under Mild Conditions.

Abstract: Direct conversion of methane to value-added chemicals with high selectivity under mild conditions remains a great challenge in catalysis. Now, single chromium atoms supported on titanium dioxide nanoparticles are reported as an efficient heterogeneous catalyst for direct methane oxidation to C1 oxygenated products with H2 O2 as oxidant under mild conditions. The highest yield for C1 oxygenated products can be reached as 57.9 mol molCr -1 with selectivity of around 93 % at 50 °C for 20 h, which is significantly higher than those of most reported catalysts. The superior catalytic performance can be attributed to the synergistic effect between single Cr atoms and TiO2 support. Combining catalytic kinetics, electron paramagnetic resonance, and control experiment results, the methane conversion mechanism was proposed as a methyl radical pathway to form CH3 OH and CH3 OOH first, and then the generated CH3 OH is further oxidized to HOCH2 OOH and HCOOH.

A review on the applicability of activated carbon derived from plant biomass in adsorption of chromium, copper, and zinc from industrial wastewater

Abstract: Metal ion contamination in wastewater is an issue of global concern. The conventional methods of heavy metal removal from wastewater have some drawbacks, ranging from generation of sludge to high cost of removal. Adsorption technique for copper(II), zinc(II), and chromium(VI) using activated carbon has been found efficient. However, it is not economical on a large scale. This, therefore, necessitates the search for economical and readily available plant biomass-based activated carbons for the sequestration of the metal ions. This review presents the state of the art on the adsorption of copper(II), zinc(II), and chromium(VI) from industrial wastewater. Based on the literature review presented, the groundnut husk and corncob based activated carbons were found to possess the maximum adsorption capacities for copper(II), zinc(II), and chromium(VI) removal, when compared with the other plant biomass-based activated carbons. The high values of the adsorption capacities obtained were as a result of the isotherms and pH of the adsorbent as well as the initial concentration of the metal solutions. From the review, the equilibrium data fitted better with Langmuir and Freundlich isotherms than with other isotherms. Research gaps were identified which include a need to investigate the kinetic and the thermodynamic behaviors of the metal ions onto the studied adsorbents. Furthermore, a comparative analysis of the three types of activation of the adsorbents should be investigated using single and multi-metals. The optimization of particle size, contact time, temperature, initial concentration, and adsorbent dosage for adsorption of copper(II), zinc(II), and chromium(VI) onto the studied adsorbents using response surface methodology is equally required.

Simultaneous removal of lead(II), chromium(III), and copper(II) heavy metal ions through an adsorption process using C-phenylcalix[4]pyrogallolarene material

Abstract: Heavy metal ion removal remains a serious challenge to the sustainability of our environment. In this work, a simple adsorbent, i.e., C-phenylcalix[4]pyrogallolarene bearing 12 phenolic functional groups, has been successfully synthesized and evaluated for the simultaneous adsorption of heavy metal ions in acidic media. Results showed that C-phenylcalix[4]pyrogallolarene exhibited good adsorption percentages for heavy metal ions, i.e., lead(II), chromium(III), copper(II), and nickel(II). Given that the adsorption of all metal ions was driven by the ion exchange mechanism, the adsorption process depends on the pH value of the aqueous phase, yielding the optimum pH values of 5.0, 4.9, 5.2, and 7.9 for lead(II), chromium(III), copper(II), and nickel(II) ions, respectively. The kinetics of heavy metal ion adsorption was governed by the pseudo-second order model, whereas the adsorption isotherm behavior was governed by the Langmuir model. The results also showed that the adsorption capacities for lead(II), chromium(III), copper(II), and nickel(II) were 60.97, 14.31, 8.14, and 16.86 mg g−1, respectively. The interaction between heavy metal ions and C-phenylcalix[4]pyrogallolarene was also investigated through UV–vis, FTIR, and 1H-nuclear magnetic resonance (NMR) spectroscopic studies. The findings showed that C-phenylcalix[4]pyrogallolarene is a potential adsorbent material for the simultaneous removal of heavy metal ions.

Redox mechanisms of conversion of Cr(VI) to Cr(III) by graphene oxide-polymer composite.

Abstract: Alternative methods of aqueous chromium removal have been of great research interest in recent years as Cr (VI) is a highly toxic compound causing severe human health effects. To achieve better removal of Cr (VI), it is essential to understand the chemical reactions that lead to the successful removal of Cr species from the solution. Recent studies have demonstrated that graphene oxide (GO) based polymer beads cannot only adsorb Cr (VI) via electrostatic attractions but also reduce it to Cr (III), which is a much less toxic form of chromium. This conversion and the functional groups involved in this conversion, until now, were not elucidated. In the present study, we employed X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy to investigate the conversion pathway of Cr (VI) to Cr (III) in graphene-based polymer beads. The results showed that alcoholic groups are converted to carboxylic groups while reducing Cr (VI) to Cr (III). The inclusion of GO in the polymer beads dramatically increased the potential of Cr (VI) uptake and conversion to Cr (III), indicating polymers and nanomaterials containing alcohol groups can remove and convert chromium in water. Other functional groups present in the polymer bead play an important role in adsorption but are not involved in the conversion of Cr (VI) to Cr (III).

Simultaneous Removal of Trivalent Chromium and Hexavalent Chromium from Soil Using a Modified Bipolar Membrane Electrodialysis System.

Abstract: In this study, a modified bipolar membrane electrodialysis system equipped with a ‘back-to-back’ soil compartment was fabricated for simultaneous removal of trivalent chromium (Cr(III)) and hexaval...

Comprehensive review of chromium deposition and poisoning of solid oxide fuel cells (SOFCs) cathode materials

Abstract: A solid oxide fuel cell (SOFC) is a clean and efficient energy conversion device. The development of intermediate-temperature SOFCs has made it preferable to use metallic interconnects (MICs) to greatly reduce the cost and significantly increase the efficiency compared to ceramic interconnect materials. However, gaseous chromium species will evaporate from the chromium-containing layer formed on the surface of commonly used MICs. Volatile chromium species have been shown to form solid deposits which poison the cathodes of SOFCs, causing drastic cell performance degradation and thereby limiting commercialization. In this review, we systematically summarize the status and progress of research on this topic and compare the variations in chromium poisoning phenomena under numerous SOFC operating conditions. Moreover, approaches to alleviate chromium poisoning are evaluated and discussed.

Chemoselective Cross-Coupling between Two Different and Unactivated C(aryl)-O Bonds Enabled by Chromium Catalysis.

Abstract: We report here the first example of cross-coupling between two different and unactivated C(aryl)–O bonds with chromium catalysis. The combination of low-cost Cr(II) salt, 4,4-di-tert-butyl-2,2-dipy...

Removal of chromium (VI) and lead from electroplating effluent using electrocoagulation

Abstract: The present study deals with the treatment of electro plating effluent (EPE) by electrocoagulation (EC) using iron as a sacrificial electrode. The initial concentration of chromium (VI) and...