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1.
Molecules ; 26(4)2021 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-33671782

RESUMO

CrCl3(thf)3 is a common starting material in the synthesis of organometallic and coordination compounds of Cr. Deposited as an irregular solid with no possibility of recrystallization, it is not a purity guaranteed chemical, causing problems in some cases. In this work, we disclose a well-defined form of the THF adduct of CrCl3 ([CrCl2(µ-Cl)(thf)2]2), a crystalline solid, that enables structure determination by X-ray crystallography. The EA data and XRD pattern of the bulk agreed with the revealed structure. Moreover, its preparation procedure is facile: evacuation of CrCl3·6H2O at 100 °C, treatment with 6 equivalents of Me3SiCl in a minimal amount of THF, and crystallization from CH2Cl2. The ethylene tetramerization catalyst [iPrN{P(C6H4-p-Si(nBu)3)2}2CrCl2]+[B(C6F5)4]- prepared using well-defined [CrCl2(µ-Cl)(thf)2]2 as a starting material exhibited a reliably high activity (6600 kg/g-Cr/h; 1-octene selectivity at 40 °C, 75%), while that of the one prepared using the impure CrCl3(thf)3 was inconsistent and relatively low (~3000 kg/g-Cr/h). By using well-defined [CrCl2(µ-Cl)(thf)2]2 as a Cr source, single crystals of [(CH3CN)4CrCl2]+[B(C6F5)4]- and [{Et(Cl)Al(N(iPr)2)2}Cr(µ-Cl)]2 were obtained, allowing structure determination by X-ray crystallography, which had been unsuccessful when the previously known CrCl3(thf)3 was used as the Cr source.


Assuntos
Cromo/química , Complexos de Coordenação/química , Furanos/química , Complexos de Coordenação/síntese química , Cristalografia por Raios X , Modelos Moleculares , Estrutura Molecular
2.
Ecotoxicol Environ Saf ; 213: 112003, 2021 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-33588188

RESUMO

A green rust-coated expanded perlite (GR-coated Exp-p) microelectrode was synthesized and incorporated into a column-mode three-dimensional electrokinetic (3D-EK) platform to effectively pursue a continuous Cr(VI) removal from the aqueous solution. Brucite-like layers of GR were decorated onto the Exp-p material. The molar ratio of Fe(II) to Fe(III) played a most vital role among the three synthesis factors in influencing the performance of the particle electrode. For the equilibrium adsorption experiments, the target maximum adsorption capacity of 122 mg/g was predicted by a target optimizer and desirability function at the conditions following the pH of 4.7, the initial concentration of 172.4 mg/L, the dosage of 0.28 g/L, and the temperature of 28.96 °C, respectively. SO42-, Cl-, and NO3- fiercely competed with Cr(VI) anions in the acidic conditions for the locally positive sites. A low concentration and a slow flow were favored in the column-mode 3D-EK platform. The pseudo-first-order and Langmuir models were suitable for describing the kinetics and isotherms of the adsorption process, respectively. Cr(VI) anions were electrostatically attracted to the silanol groups and GR surface of the adsorbent, subsequently reduced in both heterogeneity and homogeneity, and finally immobilized by coordinating with silanediol groups and silanetriol groups.


Assuntos
Cromo/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Óxido de Alumínio , Ânions , Eletrodos , Compostos Férricos , Concentração de Íons de Hidrogênio , Cinética , Dióxido de Silício , Temperatura , Água , Poluentes Químicos da Água/análise
3.
Artigo em Inglês | MEDLINE | ID: mdl-33560900

RESUMO

Removal of hexavalent chromium [Cr(VI)] from water was evaluated using a low-cost coated sand adsorbent for potential application in a flow-through filter system using permeable adsorption media. Manganese-aluminum coated sand (MACS) was investigated as a hybrid metal oxide based adsorbent due to the potential efficacy of manganese oxide and aluminum oxide for adsorption of Cr(VI) from water. Adsorbent characterization was performed using XRD, SEM/EDX, XPS and BET. Adsorption experiments were performed to determine adsorption capacity and kinetics. The effect of pH, common co-existing ions found in natural water, and the recyclability of adsorbent were investigated. Adsorbent characterization showed that the MACS sorbent contained aluminum oxide, manganese (III) oxide and manganese (IV) oxide. Adsorption followed the Langmuir and Freundlich adsorption equations, indicating favorable adsorption of Cr(VI) onto the MACS sorbent, while results from the Dubinin-Radushkevich equation were suggestive of physical adsorption of Cr(VI). Cr(VI) adsorption onto the MACS sorbent followed pseudo-second order kinetics. The adsorbent was effective in removing Cr(VI) over a broad pH range from 3 to 9.5, while surface charge analysis confirmed the adsorption of Cr(VI) onto the acidic surface of the MACS sorbent with a pHPZC of 9.72. The presence of co-existing ions bicarbonate, sulfate and phosphate in water resulted in a decrease in Cr(VI) uptake in the following order: phosphate > bicarbonate > sulfate. The presence of calcium resulted in a slight increase in Cr(VI) uptake. The MACS sorbent is a recyclable sorbent for adsorption and removal of Cr(VI) from water within 30 minutes of contact time.


Assuntos
Alumínio/química , Cromo/química , Manganês/química , Areia/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Compostos de Manganês/química , Concentração Osmolar , Óxidos/química
4.
Artigo em Inglês | MEDLINE | ID: mdl-33444076

RESUMO

Galvanizing industries generate large amounts of effluents rich in toxic and carcinogenic chromium(VI) species. Effective and sustainable treatments are required to comply with environmental regulations. This work focused on the development of innovative treatments for Cr(VI) by its removal from a galvanizing industry wastewater (pHinitial = 5.9) containing Cr (78 mg.L-1) and Zn (2178 mg.L-1) using the liquid surfactant membranes technique. The membrane phase carrier was Alamine® 336 in Escaid™ 110. For a synthetic solution (Cr(VI) = 353mg.L-1, pHinternal phase = 1.5), 99.9% of Cr(VI) was extracted in three stages ([KOH]internal phase = 0.27 mol.L-1). For the galvanizing wastewater, two selective extractions treatments were proposed: (1) 87% of Cr(VI) and 2% of Zn(II) were extracted in a single stage ([HCl]feed phase = 0.03 mol.L-1, [KOH]internal phase = 0.6 mol.L-1); (2) 95.6% of Cr(VI) and practically no zinc were extracted in a single stage ([HCl] feed phase = 10-6mol.L-1, [HCl] internal phase = 5mol.L-1). In another treatment condition ([HCl] feed phase = 2mol.L-1 and [KOH] internal phase = 1.2 mol.L-1), the simultaneous Cr(VI) and Zn(II) extractions (95% and 70%, respectively) were obtained in a single stage and more than 99% of both metals in three stages. This resulted in a depleted feed phase with 0.01 mg.L-1 of Cr(VI), that allows its discharge, according to the Brazilian legislation (≤0.1 mg/L).


Assuntos
Cromo/química , Tensoativos/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Zinco/química , Brasil , Resíduos Industriais , Metalurgia
5.
Ecotoxicol Environ Saf ; 208: 111552, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33396093

RESUMO

A novel material that nano zero valent iron (nZVI) loaded on biochar with stable starch stabilization (nZVI/SS/BC) was synthesized and used for the removal of hexavalent chromium [Cr(VI)] in simulated wastewater. It was indicated that as the pyrolysis temperature of rice straw increased, the removal rate of Cr(VI) by nZVI/SS/BC first increased and then decreased. nZVI/SS/BC made from biochar pyrolyzed at 600 °C (nZVI/SS/BC600) had the highest removal efficiency and was suitable for a wide pH range (pH 2.1-10.0). The results showed that 99.67% of Cr(VI) was removed by nZVI/SS/BC600, an increase of 45.93% compared to the control group, which did not add soluble starch during synthesis. The pseudo-second-order model and the Langmuir model were more in line with reaction. The maximum adsorption capacity for Cr(VI) by nZVI/SS/BC600 was 122.86 mg·g-1. The properties of the material were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) mapping, Brunauer-Emmett-Teller (BET), Fourier-transform infrared (FTIR), and X-ray diffraction (XRD). The results showed that the nZVI particles were uniformly supported on the biochar, and the BET surface areas of nZVI/SS/BC was 40.4837 m2·g-1, an increase of 8.79 times compared with the control group. Mechanism studies showed that soluble starch reduced the formation of metal oxides, thereby improving the reducibility of the material, and co-precipitates were formed during the reaction. All results indicated that nZVI/SS/BC was a potential repair material that can effectively overcome the limitations of nZVI and achieve efficient and rapid repair of Cr(VI).


Assuntos
Carvão Vegetal/química , Cromo/química , Poluentes Químicos da Água/química , Adsorção , Ferro/química , Pirólise , Amido , Temperatura , Poluentes Químicos da Água/análise , Purificação da Água , Difração de Raios X
6.
Ecotoxicol Environ Saf ; 208: 111734, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33396063

RESUMO

Hexavalent chromium [Cr(VI)] has strong mobility and it can enter into deep regions of soil. Cr(VI)-contaminated soil remediation is the process of removing Cr(VI) present in deep soils and any residual Cr(VI). In this study, the Cr(VI)-contaminated soil in Chongqing was investigated, and the remediation and economic feasibility of chemical leaching and reduction combined with a soil repairing approach was explored. The results showed that the leaching reagent, liquid-solid ratio, leaching time, reduction agent dosage, reduction temperature and reduction time had significant (P < 0.05) effects on the remediation of Cr(VI). At 0.02 mol/L oxalic acid and citric acid using a liquid-solid ratio of 5:1 and leaching time of 45 min, the removal rate of Cr(VI) was 62.7%, the residual Cr(VI) in soil was 126 mg/kg, and the soil pH was 4.09 after leaching. Between 25 and 90 °C, and at a molar ratio of 25:1 of FeSO4•7 H2O to Cr(VI), the reduction rate of Cr(VI) in soil after reduction was 54.0-98.4%, and the leaching concentration of Cr(VI) in soil was 0.01-0.29 mg/L. The optimal reduction was at 90 °C for 60 min, resulting in only 2.7 mg/kg of residual Cr(VI) in soil. The cost of this technology to treat the area studied was 826 ¥/ton of soil, which represents an economically feasible method for Cr(VI)-contaminated soil remediation.


Assuntos
Cromo/química , Recuperação e Remediação Ambiental/métodos , Poluentes do Solo/química , Ácido Cítrico , Poluição Ambiental , Ácido Oxálico , Solo , Poluentes do Solo/análise
7.
Ecotoxicol Environ Saf ; 208: 111735, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33396064

RESUMO

The transformation between hexavalent chromium (Cr6+) and trivalent chromium (Cr3+) has a significant impact on ecosystems, as Cr6+ has higher levels of toxicity than Cr3+. In this regard, a variety of Cr6+ reduction processes occurring in natural environments have been studied extensively. In this work, we investigate the reductive transformation of Cr6+ by ferrous ions (Fe2+) in ice at -20 °C, and compare the same process in water at 25 °C. The Fe2+-mediated reduction of Cr6+ occurred much faster in ice than it did in water. The accelerated reduction of Cr6+ in ice is primarily ascribed to the accumulation of Cr6+, Fe2+, and protons in the grain boundaries formed during freezing, which constitutes favorable conditions for redox reactions between Cr6+ and Fe2+. This freeze concentration phenomenon was verified using UV-visible spectroscopy with o-cresolsulfonephthalein (as a pH indicator) and confocal Raman spectroscopy. The reductive transformation of Cr6+ (20 µM) by Fe2+ in ice proceeded rapidly under various Fe2+ concentrations (20-140 µM), pH values (2.0-5.0), and freezing temperatures (-10 to -30 °C) with a constant molar ratio of oxidized Fe2+ to reduced Cr6+ (3:1). This result implies that the proposed mechanism (i.e., the redox reaction between Cr6+ and Fe2+ in ice) can significantly contribute to the natural conversion of Cr6+ in cold regions. The Fe2+-mediated Cr6+ reduction kinetics in frozen Cr6+-contaminated wastewater was similar to that in frozen Cr6+ solution. This indicates that the variety of substrates typically present in electroplating wastewater have a negligible effect on the redox reaction between Cr6+ and Fe2+ in ice; it also proposes that the Fe2+/freezing process can be used for the treatment of Cr6+-contaminated wastewater.


Assuntos
Cromo/química , Congelamento , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/química , Cromo/análise , Ecossistema , Galvanoplastia , Ferro/química , Cinética , Oxirredução , Águas Residuárias/química , Água/química , Poluentes Químicos da Água/análise
8.
J Mater Chem B ; 9(4): 1131-1137, 2021 01 28.
Artigo em Inglês | MEDLINE | ID: mdl-33432961

RESUMO

Persistent luminescence nanoparticles (PLNPs) emitting in the NIR window (700-1700 nm) have shown great promise in the field of fluorescence imaging due to their unique properties, including the absence of in situ excitation and low optical scattering in tissues. However, they are still facing some challenges, such as irregular shape, wide size distribution and poor persistent luminescence performance. Here, we report a facile mesoporous template method for synthesizing mSiO2@Zn0.6Ca0.4Ga2O4:Cr3+,Yb3+ (mSiO2@ZCGO) persistent luminescent nanoparticles, which show a regular morphology and a size of about 69 nm. In addition, these nanocrystals exhibit persistent luminescence in multi-NIR windows, the first infrared window (∼696 nm of Cr3+ emission) and second infrared window (∼1000 nm of Yb3+ emission). Under illumination of a 254 nm UV lamp for 10 min, the persistent time of Cr3+ ions and Yb3+ ions lasted more than 120 min and 10 min, respectively. In particular, the NIR persistent emission of mSiO2@ZCGO could be stimulated by soft X-ray, which is beneficial to long-term imaging in deep tissues. The optical penetration length of Yb3+ ions persistent luminescence was evaluated to be 2.8 mm. These results demonstrate the great promise of mSiO2@ZCGO for deep-tissue bio-imaging.


Assuntos
Luminescência , Nanopartículas/química , Imagem Óptica , Compostos de Cálcio/química , Cromo/química , Germânio/química , Raios Infravermelhos , Óxidos/química , Tamanho da Partícula , Dióxido de Silício/química , Propriedades de Superfície , Itérbio/química , Óxido de Zinco/química
9.
Chemosphere ; 262: 127733, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32763574

RESUMO

In this study, carboxymethyl cellulose (CMC) was employed to stabilize zero-valent iron nanoparticles (CMC-nFe0) to improve their dispersity and antioxidation for enhanced hexavalent chromium (Cr(VI)) removal. Scanning electron microscope (SEM) observation revealed that the nFe0 agglomerated in clusters, while the CMC-nFe0 connected as chains and presented higher dispersity. Therefore, compared with 54% of the nFe0, the Cr(VI) removal rate of the CMC-nFe0 increased by 0.8 time, reaching 97%. Besides, the nFe0 precipitated in 1 d and was obviously oxidized within 7 d under anoxic condition, leading to a rapid decease of Cr(VI) removal efficiency from 54% to 3% in 56 d. In contrast, the CMC-nFe0 showed no obvious subsidence and oxidized phenomenon within 14 d, which retained a relatively high Cr(VI) removal efficiency of 63% in 56 d, contributing to effective blockage of dissolved oxygen infiltrating from solution to nFe0 particles in presence of CMC. After reaction, the valence state distribution of Cr between solution and material surface indicated that Cr(VI) reduction was dominant comparing to physical adsorption to particles in the remediation process conducted by CMC-nFe0. In addition, lower initial pH and higher iron dosage facilitated Cr(VI) removal. Those results indicated that the dispersive and antioxidative characteristics of CMC-nFe0 were significantly superior to those of nFe0, and CMC stabilization thereafter can be a promising method to promote Cr(VI) elimination by nFe0.


Assuntos
Antioxidantes/química , Cromo/isolamento & purificação , Ferro/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Carboximetilcelulose Sódica/química , Cromo/química , Concentração de Íons de Hidrogênio , Nanopartículas Metálicas/química , Microscopia Eletrônica de Varredura , Oxirredução , Oxigênio , Poluentes Químicos da Água/química
10.
Chemosphere ; 263: 127898, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32828054

RESUMO

Advanced reduction process (ARP) has drawn an increasing interest as a new manner for removing oxidative pollutants in water. In this paper, we demonstrate the possibility of in-situ reduction of Cr(VI) by CO2·- produced from formate originally existing in leather wastewater by visible-light-driven ARP containing black TiO2 photocatalyst. The prepared black TiO2 with nanotube structure achieves remarkable enhanced the reduction rate of Cr(VI) as high as 96.2% (k = 0.0114 min-1) in the presence of formate, which is approximately 4.75 times than that of 56.3% (k = 0.0024 min-1) in the absence under 120 min visible-light irradiate at unadjusted pH. The results exhibit a distinct contrast with commercial TiO2 (P25). A series of control experiments are also performed, indicating that formate is able to convert the oxidative environment into a highly reductive one, and the formate concentration, black TiO2 dosage and pH may greatly impact on the Cr(VI) reduction rate. According to the electron spin resonance (ESR) measurement, CO2·- radicals can be directly verified as dominate radical in this system. Moreover, this system appears to be attractive for creating photochemical systems where in-situ production of CO2·- radicals may be realized by using formate. Then this in-situ ARP system will provide a new perspective for the Cr(VI) removing, which makes leather wastewater treatment much easier and more sustainable in the future.


Assuntos
Cromo/análise , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Dióxido de Carbono/química , Catálise , Cromo/química , Luz , Oxirredução , Águas Residuárias , Água/química , Poluentes Químicos da Água/química
11.
Chemosphere ; 263: 127974, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32828060

RESUMO

CaCr2O4 (Cr (III)), mainly generated through the decomposition of CaCrO4 (Cr (VI)), is a significant intermediate for toxic Cr (VI) formation during solid fuel combustion. In this study, the formation, oxidation and sulfation kinetics of CaCr2O4 were analyzed to forecast the potential of CaCr2O4 oxidation during co-firing of coal and solid waste in a circulating fluidized bed boiler. The results indicated that the formation and oxidation of CaCr2O4 were fitted to a single step nucleation and growth model while CaCr2O4 sulfation was fitted to a shrinking core model. CaCr2O4 formation through CaCrO4 decomposition was favored in oxygen-lean atmosphere and considerably suppressed in the presence of oxygen. In contrast, CaCr2O4 oxidation was mainly determined by the contacts between CaCr2O4 and CaSO4/CaO, which influenced not only oxidation rates but also the product species. Moreover, the oxidation reactivity of CaCr2O4 was higher in the presence of CaO than that of CaSO4. On the other hand, CaCr2O4 sulfation can occur more easily than CaCr2O4 oxidation, the reaction rate of which was deeply affected by sulfate product layer. Findings in this study suggested that spraying calcium in furnace for desulphurization may increase the risk of CaCr2O4 oxidation. Measures including the adjustment of Ca/S ratio in blended fuel (with added limestone) and operating conditions (such as temperature and local atmosphere) in co-firing system could be taken to control CaCr2O4 formation and oxidation.


Assuntos
Cromo/química , Carvão Mineral/análise , Eliminação de Resíduos/métodos , Resíduos Sólidos , Leitos , Cromo/análise , Cinza de Carvão , Oxirredução , Oxigênio , Sulfatos , Temperatura
12.
Ecotoxicol Environ Saf ; 207: 111572, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-33254420

RESUMO

In this work, green tea extracts synthesized nanoscale zero-valent iron/nickel (GT-nZVI/Ni) was prepared and the Cr(VI) contaminated soil column was remediated by GT-nZVI/Ni suspension. The influence factors including the concentration, pH value and flow rate of GT-nZVI/Ni suspension were studied. Under the conditions of pH = 4, concentration of 0.15 g/L and flow rate of 1.25 mL/h, GT-nZVI/Ni suspension had the best reduction and immobilization effect on Cr(VI) in the soil column. Na+ and Ca2+ can promote the immobilization of Cr (VI) in soil, while humic acid weakened the immobilization of Cr (VI). After GT-nZVI/Ni is injected into the soil column, the content of weak acid extractable and reduced chromium is significantly reduced, and the toxic hazard of hexavalent chromium in the soil is greatly reduced. The 1D-CDE model was used to fit the breakthrough curves of Fe(tot), Fe(aq) and Fe(0), and the migration of GT-nZVI/Ni in Cr(VI) contaminated soil was simulated and predicted. Compared with the inert solute Cl-, the breakthrough curves of Fe (tot), Fe (aq) and Fe (0) in Cr (VI) contaminated soil column were significantly lagged, with delay coefficients of 2.465, 2.322 and 3.288, respectively. The reaction of GT-nZVI/Ni with Cr (VI) led to the decrease of Fe mobility. Finally, the outflow concentration of Fe (tot) was 0.064 g/L, and the loss was mainly due to reaction and retention in the soil. About 57.89% of GT-nZVI/Ni was retained in the soil.


Assuntos
Cromo/química , Recuperação e Remediação Ambiental/métodos , Poluentes Químicos da Água/química , Cromo/análise , Poluição Ambiental , Concentração de Íons de Hidrogênio , Ferro/química , Níquel , Solo/química , Poluentes do Solo/análise , Poluentes Químicos da Água/análise
13.
Chemosphere ; 262: 127806, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32750591

RESUMO

In the view of green and efficient removal of chromium pollution, uniform fiber ball loaded with Fe(OH)3 (UFB-Fe(OH)3), was firstly synthesized and successfully used in the photoreduction of Cr(VI) by oxalate acid (Ox). The Cr(VI) removal in UFB-Fe(OH)3+Ox + UV system was examined by the effect of concentration of Ox, initial Cr(VI) concentration, dosage of UFB-Fe(OH)3 and the reusability of UFB-Fe(OH)3. By studying the impact of the initial pH in the solution, the relationship between the change in pH during the reaction and the removal efficiency of Cr(VI), the effect of coexisting ion (NO3-), and the free radicals quenching tests, the Cr(VI) removal mechanism in UFB-Fe(OH)3+Ox + UV system was further deduced. The results showed that UFB-Fe(OH)3 could greatly enhance the photoreduction of Cr(VI) by Ox, 1.5 mM Cr(VI) was completely removed in 6 min by UFB-Fe(OH)3+Ox + UV system. UFB-Fe(OH)3 had the feasibility of multiple use, it still exhibited the excellent enhancement in Cr(VI) removal by Ox after six cycles of use. The Cr(VI) photoreduction mechanism was consist of three part: i) Ox generate a part of CO2·- under the ultraviolet (UV) to reduce Cr(VI); ii) the Fe(III) dissolved by UFB-Fe(OH)3 formed FeOH2+ in the solution, and then generated very little Fe(II) under UV to remove Cr(VI); iii) the synergistic effect of UFB-Fe(OH)3 and Ox rapidly generated a large number of CO2·- and Fe(II) under UV excitation to reduce Cr(VI).


Assuntos
Cromo/química , Oxalatos/química , Poluentes Químicos da Água/química , Cromo/toxicidade , Ferro , Compostos Orgânicos , Oxirredução , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/toxicidade
14.
Chemosphere ; 262: 127853, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32777616

RESUMO

Green rusts (GRs) are redox active towards contaminants but they are not stable for long distance transport during the soil and groundwater remediation. In this study, green rust chloride (GR) was stabilized by selected regents, including silicate (Si), phosphate (P), fulvic acid (FA), carboxymethyl cellulose (CMC) and bone char (BC), then these stabilized GR, collectively named GR-X, would be further applied for Cr(VI) removal from aqueous solution. The stabilization experiment demonstrated that the release of Fe(II) from GR was effectively suppressed by above reagents, enabling at least 50% lower Fe(II) leaching from the stabilized GR-X than that from the pristine GR. The intact hexagonal GR plates and crystallinity were also confirmed by the SEM images and XRD patterns after storage for 7 days, indicating the stable structure of GR-X was remained. In the Cr(VI) removal tests, Cr(VI) was eliminated by GR-X in seconds with a Fe(II) utilization efficiency over 90%. The Cr species examination demonstrated that the GR-X was able to transfer Cr(VI) into stable Cr(III)-Fe(III) precipitates (Fe-Mn oxides fraction). After Cr(VI) removal tests, all reactors were exposed to the air for 1 week to monitor pH fluctuation and evaluated the risk of acidification. The results indicate that, except for GR-Si system, the other post-remediation systems are stable and the pH buffering ability of GR-X could avoid acidification and lower the Cr leaching risk.


Assuntos
Cromo/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Carboximetilcelulose Sódica , Cromo/análise , Água Subterrânea , Ferro/química , Cinética , Oxirredução , Óxidos , Solo/química , Água/química , Poluentes Químicos da Água/análise
15.
Chemosphere ; 262: 127901, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32805660

RESUMO

In this work, Lysinibacillus sp. JLT12 was used to remove the Cr(VI)-induced passive layer on the magnetite. Mechanism study via dynamic kinetics, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy analyses revealed that Lysinibacillus sp. JLT12 could remove the passive layer (lepidocrocite and goethite) to facilitate the further Cr(VI) reduction by magnetite. For large-scale applications, porous ceramsite (PC) was prepared with magnetite, kaolin, and fallen leaves. Lysinibacillus sp. was then immobilized on the holes in PC. Slow-released nutrients were added to immobilized porous ceramsite (IM-PC) at a ratio of 1.5:10 (g/g) to supply carbon, nitrogen, and phosphorus to Lysinibacillus sp. JLT12 with low secondary pollution. The performance of IM-PC was evaluated via a column experiment. The results indicate that, in the presence of Lysinibacillus, the break-through time and maximum adsorption ability of IM-PC were 11.67 h and 121.47 mg/g, respectively. These values are higher than those of PC. Additionally, break-through curves detected at 5, 10, and 15 days demonstrated that the usage life of IM-PC was significantly longer than that of PC.


Assuntos
Cromo/química , Óxido Ferroso-Férrico/química , Poluentes Químicos da Água/química , Adsorção , Bacillus , Biodegradação Ambiental , Carbono , Cromo/análise , Compostos Férricos , Concentração de Íons de Hidrogênio , Cinética , Espectroscopia Fotoeletrônica , Poluentes Químicos da Água/análise , Difração de Raios X
16.
Chemosphere ; 262: 127924, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32805661

RESUMO

Cr(VI) compounds at high temperature usually tend to decompose and reduce into Cr(III) due to thermodynamically instability for Cr(VI). This study found Cr(VI) could be reduced into Cr(V) instead of Cr(III) in the presence of CaO during heating solid waste containing Cr(VI). CaCrO4 is prepared and mixed with CaO as simulated solid waste containing Cr(VI). It was found that CaCrO4 reacted with CaO and formed a new product Ca5(CrO4)3O0.5 at temperature range of 800 and 1000 °C. The valence state of Cr in Ca5(CrO4)3O0.5 is determined to be +5 b y XPS analysis, and the color for new formed Cr(V) is observed in green, similar to Cr(III) compounds. The temperature and CaO are two keys to arouse the reduction reaction of Cr(VI) into Cr(V). In particular, the reduction of Cr(VI) into Cr(V) is strongly depended on temperature (800-1000 °C), this reaction can be balanced within 10 min, while prolonging sintering time has little help for promoting the reduction of Cr(VI) to Cr(V). Additionally, it was found Cr(V) can keep stable and not be re-oxidized into Cr(VI) at 800-1000 °C. Above results offers some new understanding and knowledge about the formation of Cr(V) in presence of much CaO or CaCO3 during heating solid waste containing Cr(VI).


Assuntos
Cromo/química , Eliminação de Resíduos/métodos , Hidróxido de Cálcio/química , Calefação , Temperatura Alta , Oxirredução , Resíduos Sólidos , Temperatura
17.
Molecules ; 26(1)2020 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-33379377

RESUMO

This study developed a nano-magnetite-modified biochar material (m-biochar) using a simple and rapid in situ synthesis method via microwave treatment, and systematically investigated the removal capability and mechanism of chromium (VI) by this m-biochar from contaminated groundwater. The m-biochar was fabricated from reed residues and magnetically modified by nano-Fe3O4. The results from scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterisations confirmed the successful doping of nano-Fe3O4 on the biochar with an improved porous structure. The synthesised m-biochar exhibited significantly higher maximum adsorption capacity of 9.92 mg/g compared with that (8.03 mg/g) of the pristine biochar. The adsorption kinetics followed the pseudo-second-order model and the intraparticle diffusion model, which indicated that the overall adsorption rate of Cr(VI) was governed by the processes of chemical adsorption, liquid film diffusion and intramolecular diffusion. The increasing of the pH from 3 to 11 significantly affected the Cr(VI) adsorption, where the capabilities decreased from 9.92 mg/g to 0.435 mg/g and 8.03 mg/g to 0.095 mg/g for the m-biochar and pristine biochar, respectively. Moreover, the adsorption mechanisms of Cr(VI) by m-biochar were evaluated and confirmed to include the pathways of electrostatic adsorption, reduction and complexation. This study highlighted an effective synthesis method to prepare a superior Cr(VI) adsorbent, which could contribute to the effective remediation of heavy metal contaminations in the groundwater.


Assuntos
Carvão Vegetal/química , Cromo/química , Óxido Ferroso-Férrico/química , Água Subterrânea/química , Poluentes Químicos da Água/química , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Magnetismo/métodos , Micro-Ondas , Nanopartículas
18.
Ecotoxicol Environ Saf ; 206: 111247, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-32890920

RESUMO

Palygorskite is a mineral widely applied for the removal of potentially toxic trace elements from the environment. This study aimed to identify the influence of pH (3, 4, 5, and 6) and humic acid (200 mg L-1) addition on the adsorption of hexavalent chromium (Cr (VI)) ions by the microparticles and nanoparticles of palygorskite. Therefore, the mineral was prepared as the micron- and nano-sized particles saturated with Ba2+ ions, and finally used in adsorption experiments. The results indicated that regardless of the mineral size, Cr(VI) adsorption was enhanced by increasing the contact time from 5 to 2880 min and the equilibrium conditions achieved after 1440 min from the beginning of experiments. With increasing the pH values from 3 to 6, the adsorption efficiency of Cr(VI) decreased significantly, and the highest rate of removal (64%) was found at pH = 3. The pseudo-second-order model best described the kinetics of Cr(VI) adsorption onto both micro- and nanoparticles of palygorskite. Also, the experimental data showed maximum consistency with the data calculated by the Freundlich isotherm model. The two processes of film and pore diffusion were recognized as the main mechanisms that controlled the adsorption of Cr(VI) by palygorskite microparticles and nanoparticles. A comparison of the maximum adsorption capacity of Cr(VI) in different treatments followed the order of nanoparticles > humic acid > humic acid + nanoparticles ≈ humic acid + microparticles > microparticles. Accordingly, the adsorption capacities of "palygorskite nanoparticles" and "humic acid" for Cr(VI) ions were 3.7 and 3.2 times higher than that of palygorskite microparticles, respectively. Moreover, the adsorption capacities observed in the simultaneous application of humic acid with palygorskite microparticles and nanoparticles were 20% and 45% lower than those without humic acid, respectively. To conclude, palygorskite nanoparticles were found to have a significant adsorption capacity for Cr(VI) ions, which is negatively affected by rise in the pH of the aqueous matrix.


Assuntos
Cromo/química , Poluentes Químicos da Água/química , Adsorção , Difusão , Substâncias Húmicas/análise , Concentração de Íons de Hidrogênio , Cinética , Compostos de Magnésio , Nanopartículas , Compostos de Silício , Poluentes Químicos da Água/análise , Purificação da Água/métodos
19.
Artigo em Inglês | MEDLINE | ID: mdl-32824851

RESUMO

Tannery sludge usually has high content of trivalent chromium (Cr(III)) and ammonium-nitrogen (NH4+-N). It is important to make a critical evaluation of the releasing behaviors of Cr(III) and NH4+-N from tannery sludge before its use on improving soil fertility in agricultural applications. For this purpose, static batch and dynamic leaching experiments with different mathematical models were carried out to simulate the Cr(III) and NH4+-N releasing kinetics from tannery sludge sampled in a typical tannery disposal site in North China, and their influencing factors were also discussed. The results showed that a larger solid-liquid ratio, a higher temperature, and a lower pH value of the leaching solution were beneficial for the release of Cr(III) and NH4+-N from the tannery sludge. The release kinetics of Cr(III) and NH4+-N followed parabolic diffusion and simple Elovich models both in the static and dynamic leaching conditions, indicating that the release was a complex heterogeneous diffusion process. The NH4+-N was easy to be leached out and its released amount reached 3.14 mg/g under the dynamic leaching condition (pH 7), whereas the released amount of the Cr(III) was only 0.27 µg/g from the tannery sludge. There was a positive correlation coefficient between dissolved Fe and Cr(III) in the leachate under different leaching conditions, and the calculated average ratio of Fe/Cr(III) concentration was 3.56, indicating that the small amount of the released Cr(III) came from the dissolution of Cr0.25Fe0.75(OH)3 minerals in tannery sludge.


Assuntos
Compostos de Amônio/química , Cromo/química , Resíduos Industriais , Curtume , China , Cromo/análise , Nitrogênio , Esgotos
20.
Chemosphere ; 261: 127824, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32755757

RESUMO

Adsorption-photo-reduction is considered as a potential route to remove Cr(VI) from wastewater. To explore the novel photocatalysts with efficient adsorption-photocatalytic activity, flower-like hierarchical ZnS-Ga2S3 heterojunction was prepared for the solar-light-driven reduction of Cr(VI). Its adsorption-photocatalytic capacity is greatly affected by the ZnS/Ga2S3 molar ratio, Cr(VI) content, pH values, and inorganic ions. Among these obtained composites, ZnS-Ga2S3-3 with a ZnS/Ga2S3 molar ratio of 3:1 exhibits the best adsorption-photocatalytic capacity. The adsorption capacity of ZnS-Ga2S3-3 is 54.42 mg g-1, and its total removal efficiency is 99.10% for 100 mg L-1 Cr(VI) solution after 160 min. In addition, the adsorption-photo-reduction performance of ZnS-Ga2S3-3 is slightly deactivated after nine cycle times. The Langmuir, pseudo-second-order, and first-order models well describe the adsorption isotherm, adsorption kinetic, and photo-reduction kinetic of ZnS-Ga2S3-3, respectively. The synergy effect of ZnS and Ga2S3 are favorable for the efficient transfer and separation of charge carriers, and provide sufficient vacant sites at the junction interface for the adsorption of Cr(VI).


Assuntos
Cromo/química , Poluentes Químicos da Água/química , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Sulfetos , Águas Residuárias/química , Compostos de Zinco
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