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1.
Ying Yong Sheng Tai Xue Bao ; 30(9): 3215-3223, 2019 Sep.
Artigo em Chinês | MEDLINE | ID: mdl-31529897

RESUMO

The modified fly ash (MFA) was prepared through roasting the mixture of fly ash and NaOH/Ca(OH)2 at 250 ℃ for 1.5 h. The physicochemical properties of MFA were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), surface area analyze (BET), and Fourier transform infrared spectroscopy (FTIR) techniques. Results from BET analysis showed that the BET of MFA was enlarged by 20.6 times compared with FA. Results from SEM analysis showed that the glass phase was dissolved, with a rough surface and porous structure. Results from FTIR analysis demonstrated that -OH played an important role in Cd2+ adsorption. Results from the static adsorption experiment revealed that the removal efficiency of Cd2+ reached 97.3% when 0.2 g MFA was applied while the concentration of Cd2+ was 100 mg·L-1, the solution pH was 7.0, the adsorption temperature was 25 ℃ and the adsorption time was 90 min. In addition, the coexisting cations (K+, Na+, Mg2+, and Ca2+) might inhibit Cd2+ adsorption. Among all the cations, Ca2+ showed a most significant inhibitory effect on the removal of Cd2+. Langmuir isotherm and the pseudo-second-order kinetic models could well describe the adsorption behavior of Cd2+ on MFA, with the maximum adsorption capacity of 55.77 mg·g-1. Meanwhile, thermodynamic studies showed that Cd2+ adsorption onto MFA was spontaneous and endothermic process. MFA had better adsorption capacity than FA and had certain application pro-spects in wastewater treatment.


Assuntos
Cádmio/química , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias , Poluentes Químicos da Água/química , Adsorção , Cinza de Carvão , Concentração de Íons de Hidrogênio , Cinética , Espectroscopia de Infravermelho com Transformada de Fourier
2.
J Environ Sci (China) ; 85: 168-176, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31471023

RESUMO

Cadmium (Cd) and arsenic (As) are two of the most toxic elements. However, the chemical behaviors of these two elements are different, making it challenging to utilize a single adsorbent with high adsorption capacity for both Cd(II) and As(V) removal. To solve this problem, we synthesized HA/Fe-Mn oxides-loaded biochar (HFMB), a novel ternary material, to perform this task, wherein scanning electron microscopy (SEM) combined with EDS (SEM-EDS) was used to characterize its morphological and physicochemical properties. The maximum adsorption capacity of HFMB was 67.11 mg/g for Cd(II) and 35.59 mg/g for As(V), which is much higher compared to pristine biochar (11.06 mg/g, 0 mg/g for Cd(II) and As(V), respectively). The adsorption characteristics were investigated by adsorption kinetics and the effects of the ionic strength and pH of solutions. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR) revealed that chelation and deposition were the adsorption mechanisms that bound Cd(II) to HFMB, while ligand exchange was the adsorption mechanism that bound As(V).


Assuntos
Arsênico/química , Cádmio/química , Poluentes Ambientais/química , Carvão Vegetal , Óxidos/química
3.
Chemosphere ; 235: 1073-1080, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31561297

RESUMO

As one of emerging contaminants, microplastics (MPs) can enter the environment and adsorb toxic metals such as cadmium (Cd), thereby causing potential environmental risks. However, adsorption characteristics of MPs are poorly understood. Herein, batch experiments were performed to investigate the adsorption characteristics of Cd onto high-density polyethylene (HDPE) MPs with different particle sizes, that is, 1-2 mm, 0.6-1 mm, and 100-154 µm. The adsorption of Cd was quite rapid initially, and the equilibrium time was approximately 90 min. An increase in the pH of the Cd solution led to an increase in Cd adsorption. MPs with particle size of 100-154 µm had the highest adsorption capacity. Addition of 1, 10, and 100 mg/L NaCl all significantly decreased Cd adsorption. Adsorption kinetics fitted the pseudo-second-order model. Adsorption isotherm followed the Langmuir model and, to a lesser extent, the Freundlich model, with estimated maximum adsorption capacity of 30.5 µg/g. The adsorbed Cd easily desorbed from the MPs. Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed Cd adsorption to and desorption from MPs. Fourier transform infrared (FTIR) spectroscopy analysis showed no new functional groups formed during the adsorption and desorption processes, suggesting physical interaction may dominate the Cd adsorption onto MPs. The present study findings provide evidence that MPs can accumulate Cd, and the adsorbed Cd may be highly available, thus posing risks to the organisms exposed to these MPs.


Assuntos
Cádmio/química , Plásticos/química , Água/química , Adsorção , Cinética , Tamanho da Partícula , Polietileno/química , Soluções , Espectroscopia de Infravermelho com Transformada de Fourier
4.
Environ Pollut ; 254(Pt B): 113123, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31487672

RESUMO

Biochar has potential to control the bioavailability and migration of potentially toxic heavy metals in soil by adsorption. Natural ageing in the environment may change the physicochemical properties and adsorption function of biochar over the long-term. The present study compared the effects of different simulated ageing treatments on Cd adsorption of high and low temperature biochar from straw of corn (Zea mays). Fresh and aged biochars were systematically characterized by elemental analysis, FTIR, XPS, Zeta, SEM-EDS, XRD and the composition of their mineral ash. The adsorption of Cd to fresh and aged biochars was then assessed under the influence of pH. Drawing the results together the effects of ageing on the extent and mode of Cd adsorption could be elucidated. The results showed that the adsorption capacity of fresh biochar produced at 650 °C was higher than of biochar made at 350 °C, and that mineral co-precipitation plays a dominant role in Cd sorption. Leaching removed organic and inorganic ash components from biochars, markedly diminishing the capacity of the high temperature biochar to adsorb Cd. The adsorption performance of the low temperature biochar was dependent on surface complexation. The adsorption capacity of low-temperature biochar was markedly enhanced by oxygen-containing functional groups formed through acidification and oxidation. The long-term benefits of biochar in the management of polluted soil require a rethink, considering the contrasting ageing behavior of different temperature biochar and their response to different ageing environments.


Assuntos
Cádmio/química , Carvão Vegetal/química , Poluentes do Solo/química , Adsorção , Cádmio/análise , Temperatura Alta , Concentração de Íons de Hidrogênio , Minerais , Oxirredução , Solo/química , Tempo , Zea mays
5.
Chemosphere ; 226: 907-914, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31509920

RESUMO

The isomorphous substitution in the structure of phyllosilicate minerals plays an important role in regulating of surface chemical properties. In this work, iron muscovite nanoparticles with various Al species were successfully prepared to explore the structural Fe and Al species on the capture of Cd(II) from solutions. The synthesized nanocrystals have irregular shapes with diameters of 10-50 nm. The incorporation of Al(III) into the iron muscovite nanostructure has slight effect on the species of Fe and the crystal phase of the products. The degree of Al(III) substituting Si(IV) in the tetrahedral sheets of the minerals obviously increased with increasing of Al doping levels. For the samples with low Al doping levels (5% and 10%), the adsorption capacity of the iron muscovite nanoparticles for Cd(II) increased slightly. With increasing of Al doping ratio to 15%, the obtained iron muscovite nanoparticles exhibited a maximal uptake of 41.4 mg g-1 for Cd(II), which is about two times that of the undoped samples (22.8 mg g-1). The solution pH had a slight effect on the Cd (II) capture at a wide pH range from 4 to 8. The adsorption of Cd(II) is very fast and reached a steady state within 5 min. Desorption results showed that the binding strength between Cd(II) and iron muscovite nanoparticles was obviously enhanced by incorporation of Al at a high level. The ion exchange and surface complexation are principal mechanisms in the Cd(II) capture by the iron muscovite nanomaterials with various structural Al species.


Assuntos
Silicatos de Alumínio/química , Alumínio/química , Cádmio/isolamento & purificação , Ferro/química , Nanopartículas/química , Adsorção , Cádmio/química , Concentração de Íons de Hidrogênio , Propriedades de Superfície
6.
Environ Monit Assess ; 191(10): 602, 2019 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-31478102

RESUMO

Globally, millions of tons of coal fly ash (CFA) are generated per year, and the majority of this material is usually stored in stock piles or landfills, and in a long-term, it can be an environmental hazard if rainwater infiltrates the ashes. Long-term leaching studies of Brazilian ashes are scarce. The purpose of this study was to evaluate arsenic, cadmium, molybdenum, lead, and zinc leaching behavior from a Brazilian CFA by a column experiment designed to simulate field conditions: slightly acid rain considering seasonality of precipitation and temperature for a long-term leaching period (336 days). All elements were leached from CFA, except lead. Elements leaching behavior was influenced by leaching time, leaching volume, and temperature. Higher leachability of As and Cd from CFA during warm and wet season was observed. Results indicate a potential risk to soil and groundwater, since ashes are usually stored in uncovered fields on power plants vicinity.


Assuntos
Cinza de Carvão/química , Monitoramento Ambiental , Metais Pesados/análise , Arsênico/análise , Arsênico/química , Brasil , Cádmio/análise , Cádmio/química , Água Subterrânea , Chumbo/análise , Chumbo/química , Molibdênio/análise , Molibdênio/química , Centrais Elétricas , Solo/química , Instalações de Eliminação de Resíduos , Zinco/análise , Zinco/química
7.
J Agric Food Chem ; 67(41): 11373-11379, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31539240

RESUMO

Cadmium bioremediation with metal-binding proteins is primarily conducted using metallothioneins (MTs). However, in the present study, we investigated a non-MT cadmium-binding protein from Lentinula edodes (LECBP) as a remediation tool for cadmium biosorption in Escherichia coli. The results indicated that the expression of LECBP significantly enhanced the cadmium biosorption capacity of transgenic E. coli. The secondary structure and conformation of LECBP were changed after binding with cadmium as evidenced by circular dichroism and fluorescence spectroscopy. The results of Fourier transform infrared spectroscopy indicated that carboxyl oxygen and amino nitrogen atoms were involved in the interaction between LECBP and cadmium. The results further demonstrated that glutamic acid and histidine residues are the potential binding sites. Our results have thus provided new insights into cadmium bioremediation in an aquatic environment.


Assuntos
Cádmio/metabolismo , Metalotioneína/metabolismo , Proteínas de Plantas/metabolismo , Cogumelos Shiitake/genética , Sítios de Ligação , Biodegradação Ambiental , Cádmio/química , Escherichia coli/genética , Escherichia coli/metabolismo , Expressão Gênica , Metalotioneína/química , Metalotioneína/genética , Proteínas de Plantas/química , Proteínas de Plantas/genética , Cogumelos Shiitake/metabolismo , Espectroscopia de Infravermelho com Transformada de Fourier
8.
J Photochem Photobiol B ; 198: 111580, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31394353

RESUMO

Heavy metal acclimation of bacteria is of particular interest in many aspects. It could add to our understanding of adaptation strategies applied by bacteria, as well as help us in devising ways to use such adaptive bacteria for bioremediation. In this study, we have explored the changes in the DNA of an aquatic Gordonia sp. acclimated to silver, cadmium, and lead. We have measured the changes in the DNA extracted from the acclimated bacteria by using ATR-FTIR coupled with unsupervised and supervised pattern recognition algorithms. Although whole-cell FTIR studies do reveal nucleic acid changes, the special care should be taken when considering marker nucleic acid bands in such spectra, as various other cell or tissue constituents also yield IR bands in the same region. An FTIR study on isolated DNA can be used to avoid this problem. The IR spectral profiles of the DNA molecules revealed significant changes in the backbone and sugar conformations of upon acclimation. We then further analyzed the DNA's global cytosine-methylation patterns of the heavy metal-acclimated bacteria. We aimed to find out whether epigenetic mechanisms operate in bacteria for survival and growth in inhibitory heavy metal concentrations or not. We found hypermethylation in Cd acclimation but hypomethylation for both Pb and Ag in Gordonia sp. Our results imply that changes in the conformational and methylation states of DNA seem to let bacteria to thrive in otherwise inhibitory conditions and mark the involvement of epigenetic modulation in acclimation processes.


Assuntos
Metilação de DNA , DNA Forma Z/química , Gordonia (Bactéria)/química , Metais Pesados/metabolismo , Açúcares/química , Cádmio/química , Cádmio/metabolismo , Cádmio/toxicidade , Análise por Conglomerados , Análise Discriminante , Gordonia (Bactéria)/efeitos dos fármacos , Gordonia (Bactéria)/metabolismo , Chumbo/química , Chumbo/metabolismo , Chumbo/toxicidade , Metais Pesados/química , Metais Pesados/toxicidade , Testes de Sensibilidade Microbiana , Análise de Componente Principal , Prata/química , Prata/metabolismo , Prata/toxicidade , Espectroscopia de Infravermelho com Transformada de Fourier
9.
Ecotoxicol Environ Saf ; 182: 109431, 2019 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-31301593

RESUMO

The objective of this study was to examine the response of soil archaeal communities to saline stress in different types of Cd-contaminated soils from the North China Plain. Increased soil salinity by addition of 0.5% sodium salts (NaCl: Na2SO4: NaHCO3: Na2CO3 = 1:9:9:1) increased available Cd concentration, resulting in decreased ratios of Cd2+/CdT and CdSO4/CdT and increased ratios of CdCln2-n/CdT in soil solution. Soil saline stress decreased archaeal abundance and diversity and changed major soil archaeal taxa. For example, increased saline stress enriched taxa in the archaeal phyla Thaumarchaeota and Euryarchaeota, and these enriched tolerant taxa had much stronger correlations with soil properties, such as soil pH, EC or Na+. In addition, some microbes with low abundances like Bathyarchaeia (no rank) and Candidatus Nitrosotenuis were found to closely correlate with soil pH, EC, Na+, and Cl-, indicating they might play disproportionate roles in regulating ecological functions in stressed habitats. These results suggest that saline stress modified the effect of Cd toxicity on soil archaeal communities in different types of Cd-contaminated soils.


Assuntos
Archaea/efeitos dos fármacos , Cádmio/toxicidade , Estresse Salino , Microbiologia do Solo , Poluentes do Solo/toxicidade , Archaea/fisiologia , Cádmio/química , China , Solução Salina , Salinidade , Cloreto de Sódio , Solo/química , Poluentes do Solo/química
10.
Photochem Photobiol Sci ; 18(8): 2061-2070, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31339127

RESUMO

Firefly luciferases have been widely used for bioanalytical purposes during the last 5 decades. They usually emit yellow-green bioluminescence and are pH-sensitive, displaying a color change to red at acidic pH and higher temperature and in the presence of heavy metals. Besides the usual applications as bioanalytical reagents and as reporter genes, firefly luciferases' pH- and metal-sensitivities have been recently harnessed for intracellular metal and pH biosensing. Previously we cloned the luciferase of the Brazilian Amydetes vivianii firefly which displays the most blue-shifted color among known firefly luciferases. Here we purified it, characterized and investigated the kinetic properties and the pH, metal and thermal sensitivities of this firefly luciferase. This luciferase displays the lowest reported KM for ATP, the highest catalytic efficiencies, and the highest thermostability among the studied recombinant beetle luciferases, making this enzyme and its cDNA an ideal reagent for sensitive ATP assays and reporter gene. The blue-shifted spectrum, higher thermostability, lower pH- and thermal-sensitivities and protein fluorescence studies indicate a more rigid active site during light emission. This enzyme displays an unmatched selective spectral sensitivity for cadmium and mercury, making it a promising ratiometric indicator of such toxic metals. Finally, the weaker thermal-sensitivity compared to other firefly luciferases makes this enzyme a better ratiometric pH indicator at temperatures above 30 °C, suitable for mammalian cell assays.


Assuntos
Trifosfato de Adenosina/análise , Técnicas Biossensoriais , Cádmio/metabolismo , Vaga-Lumes/enzimologia , Luciferases de Vaga-Lume/metabolismo , Metais Pesados/metabolismo , Temperatura Ambiente , Animais , Cádmio/química , Fluorescência , Concentração de Íons de Hidrogênio , Cinética , Luciferases de Vaga-Lume/química , Metais Pesados/química
11.
Bioresour Technol ; 291: 121868, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31357045

RESUMO

To clarify the adsorption behaviors of typical heavy metals onto sludge extracellular polymeric substances (EPS), the adsorption capacities and mechanisms, as well as the contributions of the different EPS components (proteins, humic acids and polysaccharides), to the adsorption of Zn2+, Cu2+ and Cd2+ were separately explored. Overall, proteins exhibited a relatively high adsorption capacity for the three metals ions, followed by humic acid, whereas least for polysaccharides. The adsorption of Cu2+ and Cd2+ onto proteins, humic acid and polysaccharides fit well to the Freundlich isotherm, whereas Langmuir model was the best fit for Zn2+ bindings onto polysaccharides/humic acid. The binding of Cu2+, Zn2+ and Cd2+ onto the three EPS components was exothermically favorable, and significant electrostatic interactions were observed for the heavy metals sorption onto humic acid and proteins. In addition, the effect of metal ions sorption on the spectrum of the proteins, polysaccharides and humic acid was also explored.


Assuntos
Cádmio/química , Cobre/química , Substâncias Húmicas , Polissacarídeos/química , Proteínas/metabolismo , Esgotos , Zinco/química , Adsorção , Cádmio/metabolismo , Cobre/metabolismo , Proteínas/química , Esgotos/química , Zinco/metabolismo
12.
Bioresour Technol ; 291: 121859, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31362200

RESUMO

The adsorption mechanisms of Pb(II) and Cd(II) in aqueous solution using camellia seed husk biochars pyrolyzed at different temperatures were studied. The adsorption of Pb(II) and Cd(II) on biochars are mainly controlled by ion exchange, oxygen functional groups (OFGs) complexation, Pb(II)/Cd(II)-π interactions, and precipitation with minerals. Compared to the raw biochars, both carboxyl and phenolic hydroxyl groups increased in the biochars washed with HCl. However, the previous research ignored the effect of the increased OFGs. Thus, a revised method was proposed from this study to more accurately calculate the contribution of four different mechanisms. Precipitation with minerals was the dominant mechanism for Pb(II) and Cd(II) removal, accounting for 80.61-89.03% and 53.57-75.84%, respectively, of the total adsorption as the pyrolysis temperature increased from 300 °C to 700 °C. As for oxygen functional groups complexation, the percentage of Pb(II) and Cd(II) removal were 4.76-8.55% and 11.34-29.59%, respectively.


Assuntos
Cádmio/química , Carvão Vegetal/química , Ácido Clorídrico/química , Chumbo/química , Oxigênio/química , Adsorção , Temperatura Alta , Oxirredução , Pirólise
13.
Sci Total Environ ; 690: 321-328, 2019 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-31299567

RESUMO

Cadmium (Cd)-contaminated paddy soil has become a global agricultural safety issue. The application of foliage dressing with mineral elements to alleviate Cd toxicity in rice might offer a cost-effective and practical strategy for safe food production. In this study, a pot experiment was conducted to optimize foliar composition and dosage. Field experiments in two consecutive rice seasons were performed to investigate the effectiveness and mechanisms of foliage dressing. Foliar spray of S, P, and a mixture of both were effective to reduce the Cd concentration in rice grain. The maximum decrease by leaf-grain translocation was achieved at 84%, and the maximum decrease of bio-concentration was 69% in the stem. The reduction of Cd concentration in rice decreased the direct damage to the photosynthetic system, and then increased the rice growth. Foliage dressing relieved the oxidative stress of Cd to rice by decreasing the MDA content, and increasing antioxidant enzyme activities. Foliar spray with S likely reduced Cd accumulation in rice by minimizing the production of reactive oxygen species, improving the activities of enzymatic and non-enzymatic antioxidant defense systems, and manipulating glutathione synthesis. The detoxification of foliar spray with P was originated from the decrease of Cd translocation and maintaining photosynthetic machinery. These results indicated that foliage dressing with S and P has great potential for the remediation of vast agricultural fields.


Assuntos
Cádmio/química , Oryza/química , Agricultura/métodos , Recuperação e Remediação Ambiental/métodos , Fósforo/química , Solo , Poluentes do Solo , Enxofre/química
14.
Sci Total Environ ; 690: 900-910, 2019 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-31302554

RESUMO

Cadmium (Cd) is a toxic metal ion in pig manure impacting on the ecosystem, and hence the immobilization of Cd by green synthesis of iron nanoparticles (G-nFe) is a potential approach. In this study, transformation of Cd (II) during the pig manure thermophilic aerobic composting process in the presence of G-nFe was investigated. The results show that the addition of G-nFe promoted the composting process and release of available phosphorus (AP). In all six experiments, obvious passivation of Cd occurred during 15 days' composting. Particularly when 500 mL kg-1 of G-nFe was added and Cd (II) was added at 0.6%(w/w%), residual Cd increased from 0.0016% to 55.70% and exchangeable Cd decreased from 98.54% to 7.21%. Batch experiments revealed that the G-nFe promoted the transformation of Cd into a larger passivation fraction. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), SEM-Mapping and Fourier transform infrared (FTIR) analysis was used to characterize residual samples, where indicated that the passivation of Cd in compost was highly correlated with the increase of P, it can be concluded that fixing with compost resulted in the formation of Cd phosphate precipitation or co-precipitation with other phosphates.


Assuntos
Cádmio/química , Compostagem/métodos , Esterco , Nanopartículas Metálicas/química
15.
Environ Sci Pollut Res Int ; 26(25): 26254-26264, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31286369

RESUMO

In this study, magnetic bio-adsorbent based on chitosan with high molecular weight was prepared. To stabilize under acidic condition, the synthesized magnetic chitosan was cross-linked with κ-carrageenan (mChitoCar). The magnetic bio-adsorbent was characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicated that mChitoCar had desirable magnetic-sorption properties, and magnetic/bio-adsorbent was successfully synthesized and cross-linked. The present nanocomposite was applied to remove and immobilize Cd2+ from water and soil systems. Adsorption and desorption of cadmium by the chitosan bio-adsorbent were investigated using batch experiments. Isotherm data were described by using Freundlich, Langmuir, Dubinin-Radushkevich, and Temkin models, and better fitting was introduced by Freundlich model in both water and soil systems. The maximum adsorption capacity (b) of cadmium onto mChitoCar appeared to increase from the water system to the soil system, from 750.2 to 992.7 µmol/g, respectively. The adsorption mechanism with the help of potential theory indicates the adsorption of cadmium onto the mChitoCar surface is following chemical adsorption type. To evaluate the efficiency of the modified chitosan as a good bio-adsorbent in water and soil system, the difference between adsorption and desorption amounts, Δq, was calculated. By comparing the amounts of Δq, the bio-adsorbent is not economically feasible at high initial concentrations in the water system. But, the bio-adsorbent used can be relatively economic as a soil modifier.


Assuntos
Cádmio/isolamento & purificação , Carragenina/química , Quitosana/química , Poluentes do Solo/isolamento & purificação , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Cádmio/química , Reagentes para Ligações Cruzadas/química , Concentração de Íons de Hidrogênio , Nanopartículas de Magnetita/química , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Poluentes do Solo/química , Poluentes Químicos da Água/química , Difração de Raios X
16.
Environ Sci Pollut Res Int ; 26(23): 23505-23523, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31197673

RESUMO

Bacteria-derived biochars from Bucillus sp. biomass under different pyrolysis temperature (250 °C, 350 °C, 450 °C, and 550 °C, respectively) were prepared, forming polyptychial, mesoporous graphite-like structure. The adsorption and sequestration efficiencies of Cd2+ by these biochars were evaluated, and the underlying mechanisms were then discussed. Cd2+ sorption data could be well described by Langmuir mode while the pseudo-second-order kinetic model and Elovich model best fitted the kinetic data. The functional groups complexation, cation-π interactions, and interaction with minerals (including surface precipitation with phosphorus and ion exchange) jointly contributed to Cd2+ sorption and sequestration on biochar, but the interaction with minerals played a dominant role by forming insoluble cadmium salt composed by polycrystalline and/or amorphous phosphate-bridged ternary complex. The maximum sorption capacity of BBC350 in simulated water phase of soil for Cd2+ was 34.6 mg/g. Furthermore, the addition of bacteria-derived biochars (1%, w/w) decreased the fractions easily absorbed by plants for Cd in the test paddy soils by 1.9-26% in a 10-day time. Results of this study suggest that bacteria-derived biochar would be a promising functional material in environmental and agricultural application.


Assuntos
Cádmio/química , Carvão Vegetal/química , Poluentes Químicos da Água/química , Adsorção , Bacillus , Biomassa , Cádmio/análise , Cinética , Metais Pesados , Minerais/química , Solo , Água , Poluentes Químicos da Água/análise
17.
Chemosphere ; 233: 17-24, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31163304

RESUMO

The 'focusing' effect has become a limiting factor for the removal of heavy metals from soils by electrokinetic (EK) remediation. A superimposed electric field EK (SE-EK) method is proposed to address this problem. Two sets of fixed electrodes placed at different positions were switched to move the 'focusing' region of Cd to the cathode by controlling the location of the pH jumping front. Moreover, a model was established to simulate and optimize the process of Cd transport in soil under the superimposed electric field. Results showed that, after 35 d of SE-EK remediation, Cd was mainly accumulated in the soil section near the cathode (S5), where the acid and alkaline fronts converged. The removal rate of Cd in the soil sections from S1 to S4 reached 87.60%, which was 6.13 times that in conventional EK remediation. Meanwhile, the energy utilization efficiency in SE-EK was 6.38 times that in conventional EK. The pH changes and Cd distribution during the SE-EK experiment were simulated well, with good agreement between the modeled and experimental data. The removal of Cd in SE-EK remediation could therefore be optimized through simulating the distribution of Cd in five situations with differences in switching time and electrode position. This research provides valuable technical support for effective EK remediation of heavy metal contaminated soil.


Assuntos
Cádmio/química , Recuperação e Remediação Ambiental/métodos , Poluentes do Solo/química , Cádmio/análise , Eletricidade , Técnicas Eletroquímicas , Eletrodos , Poluição Ambiental , Metais Pesados/análise , Solo , Poluentes do Solo/análise
18.
Chemosphere ; 233: 9-16, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31163310

RESUMO

The effects of cadmium (Cd) on wheat seedlings in the presence of graphene oxide (GO) were investigated. Parameters evaluated include root morphology, microtubule protein content, cytochrome P450 activity, and the microcellular structure of wheat seedlings. Compared with treatments with Cd or GO in isolation, treatments combining GO and Cd inhibited the total root length, total root surface area, average root diameter, and number of root hairs. GO combined with Cd also increased cytochrome P450 activity and reduced tubulin content. Cotransport of GO-loading Cd entered root tissues and was then transported to the mesophyll cells; this, in turn, triggered damage to cellular structures, including the cell membranes and chloroplast, leading to root blockage and reduced respiratory efficiency, decreased effectiveness of water and nutrient absorption, and ultimate inhibition of wheat growth and development. These effects of GO exposure were also concentration-dependent. The results indicated that GO amplified the phytotoxicity of Cd in wheat seedling roots. Given the worldwide exposure of the environment to Cd contamination, careful consideration should be given to the effects of GO in combination with Cd in agricultural management.


Assuntos
Cádmio/toxicidade , Grafite/química , Poluentes do Solo/toxicidade , Triticum/efeitos dos fármacos , Cádmio/química , Compostos de Cádmio , Óxidos/química , Raízes de Plantas/metabolismo , Plântula/efeitos dos fármacos , Poluentes do Solo/química , Triticum/metabolismo
19.
Environ Pollut ; 251: 930-937, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31234259

RESUMO

Heavy metal stress in soil accelerates the plant root exudation of organic ligands. The degradation of exudate ligands can be fundamental to controlling the complexation of heavy metals. However, this process remains poorly understood. Here, we investigated the relationship between the transformation of glycine, a representative amino acid exudate, and cadmium/lead mobility in soils. Two 48-h incubation experiments were conducted after glycine addition to the soils. Parameters related to glycine distribution and degradation, Cd/Pb mobility, and the formation of glycine-Cd complex were analyzed. Glycine addition gradually decreased the Cd and Pb mobility throughout the 48-h incubation. By the end of the experiment, the CaCl2-extracted Cd and Pb concentrations decreased by 63.5% and 43.6%, respectively. The glycine mineralization was strong in the first 6 h, as indicated by a sharp decrease in CO2 efflux rates from 10.04 ±â€¯0.62 to 3.51 ±â€¯0.07 mg C-CO2 kg-1 soil h-1. The mineralization rates notably decreased after 6 h. The comparisons of dissolved organic carbon and hydrolyzable amino acid contents indicated that glycine mineralization in solution (95.6%) was much stronger than that in soil solids (49.3%). At the end of incubation, 0.22 mmol kg-1 glycine remained in soil solids. The remaining glycine provided sufficient sorption sites for Cd2+ and Pb2+, resulting in enhanced metal fixation via complexation. Comparisons of zeta potentials supported the formation of the glycine-Cd complex. The Cd and Pb immobilization processes could be attributed to metal-glycine complex formation, sorption re-equilibrium, and glycine degradation. These findings emphasize that the biogeochemical processes of glycine, derived from root exudates or protein degradation products, increased the sorption of heavy metals to soils and thus reduced their toxicity to plants.


Assuntos
Cádmio/química , Glicina/química , Chumbo/química , Poluentes do Solo/química , Solo/química , Biodegradação Ambiental , Fabaceae/metabolismo , Raízes de Plantas/metabolismo
20.
Water Sci Technol ; 79(8): 1511-1526, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31169509

RESUMO

This study aims to discover the impact of composting and pyrolysis on the adsorption performance of Auricularia auricula dreg (AAD) for Cd(II) in aqueous solution. Auricularia auricula dreg (AAD), Auricularia auricula dreg biochar (AADB) and Auricularia auricula dreg compost (AADC) were used to remove Cd(II) from aqueous solution, and their adsorption conditions and mechanisms were compared. The adsorption quantity of three adsorbents reached the maximum (AAD: 80.0 mg/g, AADB: 91.7 mg/g, AADC: 93.5 mg/g) under same conditions (adsorbent dosage of 1 g/L, pH 5.0, biosorption temperature of 25 °C, and biosorption time of 120 min). All Cd(II) biosorption processes onto three adsorbents complied with the Langmuir isotherm model and the pseudo-second-order kinetic equation, and spontaneously occurred in an order of AADC > AADB > AAD. The difference in biosorption quantity relied on variation in surface structure, crystal species and element content caused by composting or pyrolysis. Composting enhanced the changes in surface structure, crystal species, functional groups and ion exchange capacity of the AAD, resulting in AAD had greatly improved the biosorption quantity of Cd(II). Pyrolysis increased the adsorption of Cd(II) mainly by increasing the Brunauer-Emmett-Teller (BET) surface area, the particle size and pH, in the same time, providing more oxygen-containing functional groups.


Assuntos
Cádmio/química , Compostagem , Poluentes Químicos da Água/química , Adsorção , Concentração de Íons de Hidrogênio , Cinética , Pirólise
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