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1.
Int J Prosthodont ; 33(4): 386-392, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32639698

RESUMO

PURPOSE: To investigate differences in the performance of polyether ether ketone (PEEK) frameworks vs traditional metal frameworks for removable partial dentures (RPDs) in terms of OHRQoL, patient preference, periodontal indices, and denture satistfaction. MATERIALS AND METHODS: Twenty-six participants were recruited to a randomized controlled crossover trial and were provided with either PEEK or cobalt-chromium (Co-Cr) RPDs. After 4 weeks, the participants were provided with the other RPD. After both 4-week testing periods, the participants chose their preferred RPD and were followed up again at 6 months and 1 year. The primary outcome measure was effect on OHIP-20 score, which was compared among patients using repeated measures ANOVA. Secondary outcomes were participant preference compared using chi-square analysis; Plaque Index and Gingival Bleeding Index (PI and GBI, respectively) compared using repeated measures ANOVA; and McGill Denture Satisfaction Questionnaire (MDSQ) score compared between the two 4-week follow-ups using paired-samples t test. RESULTS: Both Co-Cr and PEEK frameworks resulted in a significant improvement in OHIP-20 score (P < .001), but the material was not a significant factor in changes over 1 year (P = .87). There were no statistically significant differences in participant preference at 1 year (P = .491), nor between RPD materials in their effect on GBI (P = .476), PI (P = .967), or MDSQ (P = .368). CONCLUSION: Both Co-Cr and PEEK RPDs improved OHRQoL to a degree greater than the minimum clinically important difference at 4 weeks, 6 months, and 1 year compared to baseline. No significant preference or improved denture satisfaction score was seen for either material. PEEK frameworks seem to be associated with similar degrees of periodontal effects as Co-Cr frameworks.


Assuntos
Cromo , Cobalto , Prótese Parcial Removível , Estudos Cross-Over , Éter , Humanos , Cetonas , Projetos Piloto
2.
Water Sci Technol ; 81(9): 1840-1851, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32666939

RESUMO

A novel composite (nZVI@K-GCN) was firstly synthesized by liquid phase reducing nanoscale zero-valent iron (nZVI) on potassium-doped graphitic carbon nitride (K-GCN). The results of Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) suggested that nZVI@K-GCN possessed abundant active functional groups such as terminal amino-groups (-NH or -NH2 groups) and -OH, and the specific surface area and pore volume from BET of nZVI@K-GCN were 4.7 times and 3.7 times higher than that of graphitic carbon nitride (GCN), respectively. These properties showed that the composite was especially suitable for heavy metal treatment. The application of the composite in the removal of chromium(VI) from aqueous solution showed that the maximum adsorption capacity of nZVI@K-GCN towards Cr(VI) was 68.6 mg/g at 308 K when the initial concentration of Cr(VI) was 30 mg/L, and more than 99% removal was obtained at pH = 3. This adsorption was an endothermic and spontaneous process. XPS patterns and batch experiments proved that complexation, electrostatic attraction and reduction precipitation were the main adsorption mechanism for Cr(VI) on nZVI@K-GCN.


Assuntos
Ferro , Poluentes Químicos da Água/análise , Adsorção , Cromo/análise , Grafite , Compostos de Nitrogênio , Potássio
3.
Bone Joint J ; 102-B(7): 832-837, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32600130

RESUMO

AIMS: We have previously demonstrated raised cobalt and chromium levels in patients with larger diameter femoral heads, following metal-on-polyethylene uncemented total hip arthroplasty. Further data have been collected, to see whether these associations have altered with time and to determine the long-term implications for these patients and our practice. METHODS: Patients from our previous study who underwent Trident-Accolade primary total hip arthroplasties using a metal-on-polyethylene bearing in 2009 were reviewed. Patients were invited to have their cobalt and chromium levels retested, and were provided an Oxford Hip Score. Serum ion levels were then compared between groups (28 mm, 36 mm, and 40 mm heads) and over time. RESULTS: Metal ion levels were repeated in 33 patients. When comparing the results of serum metal ion levels over time, regardless of head size, there was a significant increase in both cobalt and chromium levels (p < 0.001). Two patients with larger head sizes had undergone revision arthroplasty with evidence of trunnion damage at surgery. Two patients within the 40 mm subgroup had metal ion levels above the MHRA (Medicines and Healthcare Products Regulatory Agency) threshold for detailed investigation. The increase in cobalt and chromium, when comparing the 36 mm and 40 mm groups with those of the 28 mm group, was not significant (36 mm vs 28 mm; p = 0.092/p = 0.191; 40 mm vs 28 mm; p = 0.200/p = 0.091, respectively). There was no difference, between femoral head sizes, when comparing outcome as measured by the Oxford Hip Score. CONCLUSION: This study shows an increase in cobalt and chromium levels over time for all modular femoral head sizes in patients with metal-on-polyethylene bearings, with two patients demonstrating ion levels above the MHRA threshold for failure, and a further two patients requiring revision surgery. These results may have clinical implications regarding longer term follow-up of patients and future implant choice, particularly among younger patients. Cite this article: Bone Joint J 2020;102-B(7):832-837.


Assuntos
Artroplastia de Quadril/métodos , Cromo/sangue , Cobalto/sangue , Prótese de Quadril , Adulto , Idoso , Idoso de 80 Anos ou mais , Artroplastia de Quadril/instrumentação , Feminino , Humanos , Íons , Masculino , Pessoa de Meia-Idade , Polietileno , Desenho de Prótese
4.
Bone Joint J ; 102-B(7_Supple_B): 116-121, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32600200

RESUMO

AIMS: This study aimed to determine if macrophages can attach and directly affect the oxide layers of 316L stainless steel, titanium alloy (Ti6Al4V), and cobalt-chromium-molybdenum alloy (CoCrMo) by releasing components of these alloys. METHODS: Murine peritoneal macrophages were cultured and placed on stainless steel, CoCrMo, and Ti6Al4V discs into a 96-well plate. Cells were activated with interferon gamma and lipopolysaccharide. Macrophages on stainless steel discs produced significantly more nitric oxide (NO) compared to their control counterparts after eight to ten days and remained elevated for the duration of the experiment. RESULTS: On stainless steel, both nonactivated and activated cell groups were shown to have a significant increase in metal ion release for Cr, Fe, and Ni (p < 0.001, p = 0.002, and p = 0.020 respectively) compared with medium only and showed macrophage-sized corrosive pits on the stainless steel surface. On titanium alloy discs there was a significant increase in aluminum (p < 0.001) among all groups compared with medium only. CONCLUSION: These results indicated that macrophages were able to attach to and affect the oxide surface of stainless steel and titanium alloy discs. Cite this article: Bone Joint J 2020;102-B(7 Supple B):116-121.


Assuntos
Prótese Articular , Macrófagos/química , Aço Inoxidável , Titânio , Vitálio , Ligas , Animais , Sobrevivência Celular , Cromo/análise , Meios de Cultura , Íons , Ferro/análise , Camundongos , Microscopia Eletrônica de Varredura , Níquel/análise , Óxido Nítrico/análise
5.
J Environ Manage ; 270: 110882, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32721321

RESUMO

Bitumen binders play a major role in reducing the aging and oxidation property of bitumen. Carbon nanomaterials act as an effective bitumen modifier due to its stiffness and strength. Thus, nano fibrous carbon (NFC) was prepared from Chrome Tanned Buffing Dust (a solidwaste generated from leather industries) with proper care of avoiding oxidation of Cr(III) to Cr(VI) through pulse pyrolysis system. Morphology analysis using TEM confirmed the nano fibrous structure of NFC. XRD pattern of NFC depicts the graphitic phases of carbon along with the Cr2O3. Prepared NFC has been used as bitumen modifier and the blending of NFC with bitumen were done using both conventional and microwave heating methods to study the proper blending methods to enhance the bitumen properties. Thermogram of the modified bitumen showed that the decomposition temperature increases by increasing the percentage of NFC (5-25%) in both the heating methods, but comparatively the thermal stability is more in microwave mixing than in conventional mixing. The morphology analysis of the modified bitumen showed that non-uniform blending in conventional type of heating and homogeneously blended mixture in microwave type of heating. The penetration value and ductility decreases while softening point and kinematic viscosity increases by increasing the quantity of NFC from 5 to 25% in modified bitumen. Microwave heat mixing method yielded better modified bitumen with NFC than conventional heating method in terms of stability, uniform blending and physical properties. The non-leachability of the Cr(III) in the NFC modified bitumen was confirmed through total chromium analysis in the leachate. But, chromium analysis in leachate of NFC immersed in acetate buffer for one month showed leaching of Cr(III) 5.5 µg/L in the 25% NFC modified bitumen block mixed using conventional heating method.


Assuntos
Cromo , Resíduos Sólidos , Carbono , Hidrocarbonetos
6.
Water Sci Technol ; 81(10): 2270-2280, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32701504

RESUMO

It is of great significance to remove Cr(VI) from water as a result of its high toxicity. Biochar from corn straw was modified by different acids (HNO3, H2SO4 and H3PO4) to remove Cr(VI) from aqueous solution. To estimate the removal mechanisms of Cr(VI) by the acid-modified biochars, batch experiments were performed in the light of contact time, Cr(VI) concentration, and pH, and the characteristics of acid-modified biochars before and after Cr(VI) adsorption were investigated by Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS). The adsorption kinetics of Cr(VI) by acid-modified biochars were consistent with the pseudo-second-order model, and the adsorption isotherm obeyed the Freundlich model. Furthermore, the acid- modified biochars could supply more oxygen-containing functional groups (-COOH and -OH) as electron donor (e-) and hydrogen ion (H+) to enhance the reduction of Cr(VI) to Cr(III), resulting in enhanced removal of Cr(VI). HNO3-modified biochar exhibited the highest removal efficiency of Cr(VI). In general, the acid modifition of biochar was an effective method to increase the removal of Cr(VI).


Assuntos
Poluentes Químicos da Água/análise , Zea mays , Adsorção , Carvão Vegetal , Cromo/análise , Concentração de Íons de Hidrogênio , Cinética
7.
Environ Pollut ; 264: 114804, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32559864

RESUMO

A large amounts of arable land is facing a high risk of hexavalent chromium (Cr(VI)) pollution, which requires remediation using a low toxic agent. In this study, the remediation effect of amorphous iron pyrite (FeS2(am)) on Cr(VI) in Cr(VI)-contaminated soil was evaluated by systematically analyzing the variation of the leachability, bioaccessibility, phytotoxicity, and long-term stability of the remediated soil. The effectiveness of FeS2(am) on the leachability was assessed by alkaline digestion and the toxicity characteristic leaching procedure (TCLP); the effect on the bioaccessibility was evaluated via the physiologically based extraction test (PBET) and the Tessier sequential extraction; the effect on the phytotoxicity was assessed via phytotoxicity bioassay (seed germination experiments) based on rape (Brassica napus L.) and cucumber (Cucumis Sativus L.), and the long-term stability of the Cr(VI)-remediated soil was appraised using column tests with groundwater and acid rain as the influents. The results show that FeS2(am), with a stoichiometry of 4× exhibited a high efficiency in the remediation of Cr(VI) and decreased its leachability and bioaccessibility during the 30-day remediation period. In addition, seed germination rate, accumulation and translocation of Cr, and root and shoot elongation of rape and cucumber of remediated soil are not significantly different from those of clean soil, illustrating that FeS2(am) is suitable for remediating Cr(VI) contaminated arable soil. The stabilization of Cr(VI) in contaminated soil using FeS2(am) was maintained for 1575 days. The long-term effectiveness was further confirmed by the increasing amount of free Fe and Mn in the effluent and the decreasing redox potential. In summary, FeS2(am) has an excellent efficiency for the remediation of Cr(VI), demonstrating it is a very promising alternative for use in the contaminated arable soil.


Assuntos
Recuperação e Remediação Ambiental , Poluentes do Solo/análise , Cromo/análise , Ferro , Solo , Sulfetos
8.
Water Sci Technol ; 81(5): 936-948, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32541112

RESUMO

A composite biosorbent (AC-TFR) prepared by encapsulating tannin-formaldehyde resin (TFR) into calcium alginate (AC) beads was used to remove Cr(VI) from an aqueous solution. Various influencing factors, such as TFR dosage, pH, initial Cr(VI) concentration, contact time, temperature and presence of co-ions in the medium, were investigated. The structures and adsorption performances of the adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Compared with other AC-TFR adsorbents, AC-TFR-2 (mass ratio of AC:TFR = 1:1) showed an excellent adsorption capacity based on the efficiency of Cr(VI) removal. The kinetic data fitted to pseudo-second-order and intra-particle diffusion models suggested that the adsorption process was subject to a rate-controlling step. The equilibrium adsorption data fitted well to the Langmuir isotherm model, and the maximum adsorption capacities of AC-TFR-2 were 145.99, 167.22 and 174.52 mg/g at 288, 298, and 308 K, respectively. The thermodynamic parameters revealed that Cr(VI) removal by AC-TFR-2 was endothermic and spontaneous, and the process was chemical adsorption. The mechanism of Cr(VI) removal consisted first of reduction to Cr(III), which has a low toxicity, and then chelation onto AC-TFR-2 via ion exchange.


Assuntos
Alginatos , Poluentes Químicos da Água , Adsorção , Cromo , Concentração de Íons de Hidrogênio , Cinética , Taninos
9.
Toxicol Lett ; 331: 178-187, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32569804

RESUMO

Chromium (Cr) (VI) compounds are known to be serious toxic and carcinogenic, but the mechanism is not clear. In our previous study, we found that Cr (VI)-induced ER stress plays an important role in the crosstalk between apoptosis and autophagy, while autophagy was apoptosis-dependent and subsequently prevents apoptosis cell death to keep A549 cells resistant to Cr (VI)-induced toxicity. In this study, we found that Cr (VI) could induce aerobic glycolysis in A549 cells. Both ER stress inhibitor, phenylbutyric acid (4-PBA) and the inhibitor of autophagy, 3-MA, repressed Cr (VI)-induced glycolysis, indicating that both ER stress and autophagy were involved in Cr (VI)-induced glycolysis in A549 cells. Co-treatment of the inhibitor of aerobic glycolysis, 2-DG and Cr (VI) for 24 h increased Cr (VI)-induced cleaved caspase-3, caspase-9 and the number of apoptotic cells, demonstrating that aerobic glycolysis played an important role in attenuating Cr (VI)-induced apoptosis. Furthermore, knockdown of ATF4 by siATF4 significantly decreased Cr (VI)-induced aerobic glycolysis and apoptosis, suggesting that ATF4 was involved in Cr (VI)-induced aerobic glycolysis and its effect of attenuating apoptosis in A549 cells. Taken together, our results demonstrated that autophagy-dependent glycolysis played a role in attenuating Cr (VI)-induced apoptosis. ER stress was involved in facilitating glycolysis, whose induction was mediated by ATF4. These findings open a window for the development of therapeutic interventions to prevent Cr (VI)-induced toxicity.


Assuntos
Fator 4 Ativador da Transcrição/metabolismo , Apoptose/efeitos dos fármacos , Autofagia/efeitos dos fármacos , Cromo/toxicidade , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Poluentes Ambientais/toxicidade , Glicólise/efeitos dos fármacos , Células A549 , Fator 4 Ativador da Transcrição/genética , Apoptose/genética , Autofagia/genética , Estresse do Retículo Endoplasmático/genética , Técnicas de Silenciamento de Genes , Glicólise/genética , Humanos
10.
J Environ Manage ; 268: 110711, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32510445

RESUMO

In this study, Nb2O5 catalyst was applied in the photocatalytic process for the Chromium reduction. Cr (VI) is a compound classified as highly toxic and often found in industrial tannery effluents. The techniques used for the photocatalytic material characterization were: X-ray diffraction, Specific surface area (B.E.T method), photo-acoustic spectroscopy, Scanning Electron Microscopy (SEM) and X-ray Dispersive Energy Spectrometry (EDS). A comparison between Nb2O5 and TiO2 (widely used in photocatalytic reactions) indicated that Nb2O5 has 20% more Cr (VI) reduction than TiO2. Tests carried out with Nb2O5 calcined at 500 °C and with non-calcined Nb2O5 showed that the heat treatment did not favor the reaction. Parameters such as pH, radiation intensity, initial concentration of Cr (VI) and amount of catalyst were studied. The results indicated that the acid (pH 2), emitted radiation intensity (250 W), initial concentration Cr (VI) at 10 mg L-1 and 1.5 g L-1 Nb2O5 non-calcined are the process optimal conditions. In addition, the reuse tests for Nb2O5 in consecutive cycles four, were realized. Photostability was maintained at approximately 90% for all cycles when Nb2O5 calcined was used. On the other hand, when using Nb2O5 non-calcined reduced by 21% during the four tests. This behavior is possibly due to the greater adsorption capacity of the non-calcined material. Making the Nb2O5 catalyst attractive for considering larger scale tests.


Assuntos
Cromo , Adsorção , Catálise , Difração de Raios X
11.
Water Sci Technol ; 81(6): 1114-1129, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32597399

RESUMO

In this study, an efficient route to synthesizing polyethyleneimine-modified ultrasonic-assisted acid hydrochar (PEI-USAH) is developed and reported. Ultrasonic irradiation technique was used as surface modification method to shorten the crosslinking reaction for hydrochar and polyethyleneimine (PEI). The PEI-USAH showed an excellent adsorption capacity for Cr(VI) from aqueous solution. The physicochemical properties of this PEI-modified adsorbent were comparatively characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis and CNHS analysis. The effects of contact time, initial pH, and biosorbent dose on adsorption capacities were investigated. The batch adsorption experiments showed that PEI-USAH possessed the maximum adsorption capacities of 94.38 mg/g and 330.84 mg/g for initial Cr(VI) concentration of 100 mg/L and 500 mg/L, respectively. Furthermore, this adsorption process could be fitted to Langmuir adsorption and described by the pseudo second order kinetic model. Based on the above findings, PEI-USAH could be used as a potential adsorbent for removal of Cr(VI) from wastewater.


Assuntos
Sargassum , Poluentes Químicos da Água , Adsorção , Cromo , Concentração de Íons de Hidrogênio , Cinética , Polietilenoimina , Espectroscopia de Infravermelho com Transformada de Fourier , Ultrassom
12.
Chemosphere ; 257: 127112, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32474150

RESUMO

Given the millions of coal-fired power stations worldwide and the generalization of co-firing technologies in the near future, the aqueous extraction experiments were taken to study the effects of oxides on Cr mobility in ashes through SiO2-Al2O3-Fe2O3-CaO system. The results identify that both the component and the species of Cr in samples are vital factors to govern the fate of Cr during combustion. Although Cr-oxide hardly reacts with Al2O3, SiO2, and mixtures at 900 °C, the immobilization of Cr in Si-Al glass is ascribable to the heat-driven phase transformation of Cr-rich clay. The strong capture of Cr-oxide by CaO leads to the primary extraction of active Cr with the high toxicity and mobility; however, the opposite effect is found by Fe2O3. But the interactions of Al-/Si- oxides with others can trigger some changes in Cr mobility, wherein there is the lowest mobility of Cr in the case of Cr entering into the structures of Fe-rich SiO2/Si-Al glass during combustion. Thus, without regard to the sample source, it is effective to reduce the environmental risk of Cr in ashes through raising SiO2 and reducing MCaO/MFe2O3 < 5/4 prior to combustion.


Assuntos
Cromo/análise , Modelos Químicos , Cromo/química , Carvão Mineral/análise , Cinza de Carvão/química , Compostos Férricos , Óxidos/química , Dióxido de Silício
13.
Chemosphere ; 257: 127282, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32531491

RESUMO

The migration and redox transformation processes of toxic Cr(VI) in the upper and deep soil of chromate-polluted site are of great importance for the environmental risk control and soil remediation. In this study, soils from surface to deep (around 30-60 m) and the groundwater in a typical abandoned chromate production plant site which has experienced decades of contamination were both sampled and analyzed. The results show that the soil in the leaching workshop of Cr(VI), dichromate transformation workshop and chromium slag dumping ground exhibits severe contamination of chromium and the pollution has extended to the groundwater, causing serious pollution in groundwater too. The vertical migration and transformation of Cr(VI) in the soil layer are mainly affected by the soil permeability, organic matter content and the amount of water passing through the soil layer. During the downward migration, Cr(VI) tends to be retained by the clay layer and further accumulates around the depth of 5-10 m where the concentrations of both hexavalent and total Cr reach maximum values, and then continues to diffuse from the accumulation layer towards the deeper soil. Accompanying with the reduction of Cr(VI) by organic matter in the soil, the Cr(III) exists at various depths. When the depth is below the groundwater level of saturated aquifer, the distribution of chromium in the soil and groundwater reaches leaching and redox equilibrium due to the long-term interaction between the soil and groundwater.


Assuntos
Cromo/análise , Água Subterrânea/análise , Poluentes do Solo/análise , China , Cromatos , Oxirredução , Solo
14.
J Contemp Dent Pract ; 21(1): 11-16, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-32381794

RESUMO

AIM: To compare the antimicrobial effects of two different irrigation solutions activated with erbium, chromium-doped yttrium, scandium, gallium and garnet (Er,Cr:YSGG) laser or an ultrasonic system and a photodynamic therapy (PDT) on Enterococcus faecalis (E. faecalis). MATERIALS AND METHODS: The root canals of 72 single-rooted human permanent incisors were prepared with ProTaper Universal rotary instruments and incubated with E. faecalis (ATCC 29212) for 4 weeks. Then the teeth were randomly divided into seven experimental groups with 10 specimens for canal disinfection procedures. Group I, standard needle irrigation (SNI) with 2.5% sodium hypochlorite (NaOCl); group II, SNI with 2% chlorhexidine gluconate (CHX); group III, laser-activated irrigation (LAI) by Er,Cr:YSGG of NaOCl; group IV, LAI of CHX; and group V, passive ultrasonic irrigation (PUI) of NaOCl; group VI, PUI of CHX; group VII, PDT. The remaining two teeth were used as the control group. After the disinfection procedures were completed, the root canals were filled with phosphate-buffered saline and bacterial samples were taken with sterile paper cones. The cultivation was performed on Mueller-Hinton agar (MHA) plates. The live bacteria were calculated by counting the colonies on these plaques. The statistical analysis was performed using Kruskal-Wallis H test and Miller's multiple comparison technique. RESULTS: Both LAI and PUI of NaOCl and PUI of CHX were more successful than the PDT on root canal disinfection (p < 0.05). CONCLUSION: Within the limitation of the present study, the activation of NaOCl solution by Er,Cr:YSGG laser or an ultrasonic system can be useful in the elimination of the E. faecalis from the canal. The PUI of CHX also has similar results. Photodynamic therapy showed a lower performance compared to these methods. CLINICAL SIGNIFICANCE: The activation of the sodium hypochlorite with Er,Cr:YSGG laser or PUI may be useful for removal of the E. faecalis biofilm layer in the root canal.


Assuntos
Gálio , Fotoquimioterapia , Cromo , Cavidade Pulpar , Enterococcus faecalis , Érbio , Humanos , Irrigantes do Canal Radicular , Escândio , Ultrassom , Ítrio
15.
J Environ Manage ; 265: 110350, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32421549

RESUMO

The existence of leachable Cr(Ⅵ) in chromite ore processing residue (COPR) makes it hazardous waste. Therefore, resourceful utilization of COPR is necessary to protect the ecosystem and living biota from hazardous effect of Cr(Ⅵ) caused by its leaching. In this study, detoxification and immobilization of COPR was carried out through introduction of ascorbic acid (AA) in alkali-activated cementitious materials. Several dosages of AA were treated with water extractable/soluble Cr(Ⅵ) to achieve the optimum dosage which could be further utilized in solidification process. While, the compressive strength was developed through utilizing different modulus of water glass, liquid to solid ratios and curing temperatures. The results showed that 0.3% of AA was enough to reduce the Cr(Ⅵ) into Cr(Ⅲ), and highest compressive strength of 120 MPa was achieved after using the modulus of 1.6, liquid to solid ratio of 0.24 and curing temperature of 30 °C. The solidified samples having AA had not exceeded the toxicity limit up to 60% addition of COPR, and samples without addition of AA were effective for solidification of 20% COPR. Regarding mechanism, the compressive strength, leaching behavior and microscopic analysis i.e. X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR) and scanning electron microscope with energy dispersive spectrometry (SEM-EDS) showed that immobilization of chromium was carried out through physical and chemical means.


Assuntos
Álcalis , Resíduos Industriais , Ácido Ascórbico , Cromo , Ecossistema
16.
Environ Sci Pollut Res Int ; 27(22): 28042-28052, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32410190

RESUMO

The current study deals with the adsorption of hexavalent chromium using acid (H3PO4)-activated water caltrop (Trapa natans) shell (PWCS) using an up-flow packed bed column. Characteristics of breakthrough curve was obtained by investigating the effect of several operating parameters viz. inlet flow rate (2-6 mL/min), initial metal ion concentration (50-150 mg/L), and adsorbent's column bed height (1-3 cm). Elevated time of breakthrough curve was reported with elevated adsorbent bed height and vice versa with enhanced initial metal concentration and inlet flow rate of sorbate solution. Process design and breakthrough curves under varying conditions were predicted by applying column models like Thomas model, Adams-Bohart model, Yoon Nelson model, and bed depth service Time (BDST). Column behavior was better described by the BDST and Thomas model and simultaneously gave a good fit with the experimental data of breakthrough curves. The percentage removal for Cr(VI) from aqueous solution having pH 2 and temperature 303.15 K was observed to be 52.46%. The maximum adsorption capacity was found to be 87.31 mg/g according to the Thomas model. Conclusively, phosphoric acid-modified T. natans shell (PWCS) showed better sorption potential for of Cr(VI) species from simulated wastewater.


Assuntos
Poluentes Químicos da Água , Purificação da Água , Adsorção , Cromo , Águas Residuárias , Água
17.
Environ Pollut ; 264: 114686, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32422517

RESUMO

Hexavalent chromium, Cr(VI), is a heavy metal contaminant and the reduction of Cr(VI) is accompanied by large isotopic fractionation. In this study, the sources of Cr were explored using the Cr isotopic composition of sediments from the Xiaoqing River, a heavily polluted river located in the Shandong Province of China, which flows into Laizhou Bay. The results show that δ53Cr values of the sediments are the highest upstream near the pollution source, and gradually decrease along the river toward the range for igneous reservoirs observed near the estuary. Based on the calculation of authigenic Cr isotopic composition (δ53Crauth) using the detrital index and leaching experiments, we suggest that the authigenic Cr in the sample near the pollution source with the highest δ53Crauth value mainly comes from the reduction of Cr(VI) discharged by anthropogenic activity, and authigenic Cr in other samples in the midstream with δ53Crauth values slightly higher than the range of igneous reservoirs may come from natural oxidative Cr weathering products. By introducing a Rayleigh model, we calculate that at least 31%-55% of Cr(VI) in the river water had been reduced to Cr(III) near the pollution source. Due to the self-purification ability of the river, Cr(VI) was reduced; thus, there is no record of high δ53Crauth values in the downstream of the Xiaoqing River and Laizhou Bay, indicating no obvious Cr pollution in these locations. The limited variation of δ53Cr values for samples from a sediment core in Laizhou Bay is also indicative of no obvious Cr pollution in the history. The Cr isotopic compositions of the river sediments are useful for the identification of Cr sources and can be used to advise environmental remediation on Cr pollution.


Assuntos
Baías , Poluentes Químicos da Água/análise , China , Cromo/análise , Monitoramento Ambiental , Sedimentos Geológicos , Isótopos
18.
Bioresour Technol ; 311: 123553, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32454422

RESUMO

Black liquor (BL) is an agro-industrial residue with high number of lignocellulosic components which could be recognized as a biomass feedstock. In this work, BL coupled with red mud (RM), were applied to prepare cost-effective zero-valent iron (ZVI) embedded in biochar. The oligomers in BL acted as reductants for RM to generate ZVI, while the organic components could be converted into biochar during pyrolysis. The RM/BL demonstrated excellent performance in the removal of Cr(VI) (349.5 mg/g), as the mechanisms were reduction and adsorption. The fixed-bed column study was conducted and 1.7 L simulated wastewater could be treated by 1.0 g RM/BL. After reaction, 95.5% ± 0.8% and 82.5%±3.2% Cr-loaded adsorbents could be recovered by an external magnet for batch and fixed-bed experiments, respectively. All these results shed light on valorizing these two widespread agro-industrial byproducts, and bridged the knowledge gap between magnetic bio-adsorbent preparation and its industrial practicality on wastewater purification.


Assuntos
Ferro , Poluentes Químicos da Água , Adsorção , Biomassa , Carvão Vegetal , Cromo
19.
J Environ Manage ; 268: 110584, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32383665

RESUMO

It is proposed a closed-loop treatment cycle for Cr(III) removal from contaminated soils (2080 mg/kg). The treatment includes the use of lactic acid as washing agent, and the recovery of both Cr(II) and lactic acid from the spent solution. Results indicate that Cr(III) removal efficiency can be very high, passing 70% in all tested operative conditions. The metal forms strong complexes with lactic acid, and therefore cannot be eliminated through direct precipitation simply increasing the pH value. Therefore, lactic acid is preliminarily extracted from the solution using n-butanol at very acidic pH. The obtained extraction degree is generally high, varying between 0.5 and 1 according to the amount of used n-butanol solution. After lactic acid extraction, almost 100% of chromium can be recovered through precipitation in alkaline conditions. Lactic acid, in turns, can be purified and reused for a new washing treatment, separating it from n-butanol solution through water extraction. The extraction efficiency is once more satisfying (around 0.5), and not dependent on the operative pH.


Assuntos
Poluentes do Solo , Cromo , Poluição Ambiental , Ácido Láctico , Solo
20.
Water Res ; 181: 115923, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32422451

RESUMO

Natural organic matter (NOM) can influence the toxicity and speciation of chromium (Cr) in subsurface through redox reactions and complexation. Under anoxic conditions, NOM can be reduced by microorganisms or geochemical reductants, and the reduced NOM (NOMred) represents a large reservoir of organic matter observed in anoxic sediments and water. While the current body of work has established the kinetic of Cr(VI) reduction by oxidized NOM (NOMox) under oxic conditions, much less is known about the rates and mechanisms of Cr(VI) reduction triggered by NOMred under anoxic conditions and the colloidal properties of the reaction products. This study provided new information regarding the NOMred-mediated Cr(VI) reduction and colloidal stability of reduced Cr(III) particles over a wide range of environmentally relevant anoxic conditions. We show that under dark anoxic conditions reduced humic acid (HAred) moieties (e.g., quinone) can quickly reduce Cr(VI) to Cr(III), and the reduced Cr(III) can subsequently complex with carboxyl groups of HA leading to the formation of stable HA-Cr(III) colloids. Rates of Cr(VI) reduction by HAred are 3-4 orders of magnitude higher than those by oxidized HA (HAox) due primarily to the higher reducing capacity of HAred. The stable HA-Cr(III) colloids are formed across a range of HA concentrations (8-150 mg C/L) and pH conditions (6-10) with hydrodynamic diameter in the range of 210-240 nm. Aberration-corrected scanning transmission electron microscopy (Cs-STEM) and X-ray photoelectron spectroscopy (XPS) confirmed that the particles are composed of HA-Cr(III). The high colloidal stability of HA-Cr(III) particles could be attributed to the enhanced electrosteric stabilization effect from free and adsorbed HA, which decreased particle aggregation. However, the presence of divalent cations (Ca2+ and Mg2+) promoted particle aggregation at pH 6. These new findings are valuable for our fundamental understanding of the fate and transport of Cr in organic-rich anoxic environments, which also have substantial implications for the development and optimization of subsurface Cr sequestration technology.


Assuntos
Cromo , Substâncias Húmicas , Coloides , Oxirredução
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