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Δευτέρα, 29 Απριλίου 2019

Hazardous Materials

Electrochemical removal of sulfide on porous carbon-based flow-through electrodes

Publication date: 5 August 2019

Source: Journal of Hazardous Materials, Volume 375

Author(s): Natalia Sergienko, Erdem Irtem, Oriol Gutierrez, Jelena Radjenovic

Abstract

Electrochemical oxidation of hydrogen sulfide and its separation from the waste stream in the form of sulfur was studied at low-cost carbon-based porous materials, activated carbon felt (ACF) and graphite felt (GF). Both materials were capable of selective HS oxidation to elemental sulfur in low-conductivity solutions (i.e., <1 mS cm−1), as well as in raw sewage. The HS removal rate was ten times faster at ACF compared with GF electrode due to the higher surface area and chemisorption of HS. To address the electrode passivation with the electrodeposited sulfur, different electrochemical recovery strategies were tested. GF could be only partially regenerated (i.e., 30% efficiency) using cathodic polarization. Also, both anodic and cathodic polarization improved the sulfide removal in the subsequent working cycle due to the introduction of new redox-active oxygen containing functional groups. Sulfur deposited at the ACF electrode could not be recovered by any of the investigated strategies. Thus, sulfur was incorporated into the carbon matrix and strongly bonded with the carbon functional groups at both GF and ACF electrodes. Although carbon-based electrodes have been widely investigated for electrochemical sulfide removal, this study demonstrates that their application is limited by low regeneration efficiency of the electrodeposited sulfur.

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Effective phosphorus removal using chitosan/Ca-organically modified montmorillonite beads in batch and fixed-bed column studies

Publication date: 5 August 2019

Source: Journal of Hazardous Materials, Volume 375

Author(s): Jiseon Jang, Dae Sung Lee

Abstract

In this study, phosphorus removal from aqueous solution was investigated using chitosan/Ca-organically modified montmorillonite (chitosan/Ca-OMMT) beads in batch and fixed-bed column systems. The XPS spectra confirmed that the calcium ions on the surface of the beads play a dominant role in capturing phosphate ions through surface complexation. The batch adsorption experimental data were fitted with pseudo-second-order kinetics and the Langmuir isotherm. The maximum adsorption capacity of the chitosan/Ca-OMMT beads was found to be 76.15 mg/g at an initial phosphate concentration of 100 mg/L at 25 °C. High phosphate uptake is achieved over the wide pH range 3–11, as well as in the presence of competing anions such as Cl, NO3, SO42-, and HCO3. Furthermore, the chitosan/Ca-OMMT beads can be easily regenerated using 0.1 mol/L NaOH as a desorption agent with more than 83.97% adsorption capacity remaining after five adsorption/desorption cycles. The Thomas, Yoon-Nelson, and Adams-Bohart models were applied to the experimental data to predict the breakthrough curves using non-linear regression; the Yoon-Nelson model showing the best agreement with the breakthrough curves. These findings demonstrate that chitosan/Ca-OMMT beads can be used as a cost-effective and environment-friendly adsorbent for the removal of phosphate from wastewater.

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Vanadium silicate (EVS)-supported silver nanoparticles: A novel catalytic sorbent for elemental mercury removal from flue gas

Publication date: 5 August 2019

Source: Journal of Hazardous Materials, Volume 375

Author(s): Zijian Zhou, Tiantian Cao, Xiaowei Liu, Shengming Xu, Zhenghe Xu, Minghou Xu

Abstract

Vanadium silicate (EVS) is a vanadium-substituted form of titanosilicate that has a high potential for use as a sorbent for mercury removal. In the present study, EVS with supported silver nanoparticles (EVS-Ag100) as the catalytic sorbent was synthesized for elemental mercury (Hg°) capture. The physical and chemical properties of the sorbents were investigated. The raw EVS exhibited a poor Hg° capture capacity (7.7 μg g−1), because most of the vanadium species in the structure of EVS were V4+. The loading of the silver could significantly enhance the Hg° capture capacity (63.4 μg g−1). EVS-Ag100 exhibited a superior Hg° capture performance at temperatures of approximately 150 °C. Silver nanoparticles that formed on the EVS were the active sites. In addition, the vanadium species of EVS-Ag100 exhibited higher Hg° oxidation activity than those in the framework of raw EVS. The XPS results revealed the activation of the vanadium species by the silver nanoparticles. After the capture of Hg° in the presence of O2, more V5+ was observed on the surface of EVS-Ag100. Exposure of EVS-Ag100 to a continuous simulated flue gas at 150 °C with a gas hourly space velocity of 220,000 h−1 led to Hg° removal efficiency of >96% in a 1 h test.

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Mineralization of cefoperazone in acid medium by the microwave discharge electrodeless lamp irradiated photoelectro-Fenton using a RuO2/Ti or boron-doped diamond anode

Publication date: 15 July 2019

Source: Journal of Hazardous Materials, Volume 374

Author(s): Zhenjun Wen, Aimin Wang, Yanyu Zhang, Songyu Ren, Xiujun Tian, Jiuyi Li

Abstract

The mineralization of 125 mL of 50–300 mg L−1 cefoperazone (CFPZ) has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation (AO), electro-Fenton (EF) and photoelectro-Fenton (PEF) with a RuO2/Ti or boron-doped diamond (BDD) anode and an activated carbon fiber (ACF) cathode. A microwave discharge electrodeless lamp (MDEL) was used as the UV source in PEF process. CFPZ decays always followed pseudo-first-order kinetics and their constant rates increased in the order: AO < EF < MDEL-PEF, regardless of anode types. Higher mineralization was achieved in all methods using BDD instead of RuO2/Ti, while the most potent BDD-MDEL-PEF gave 88% mineralization under its optimum conditions of 0.36 A, pH 3.0 and 1.0 mmol L−1 Fe2+. The synergistic mechanisms were explored by quantifying the electrogenerated H2O2 and formed OH, in which 2.27 and 2.58 mmol L-1 H2O2 were accumulated in AO-H2O2 with RuO2/Ti or BDD anode, respectively, while 92.0 and 263.5 μmol L-1 •OH were generated in EF with RuO2/Ti or BDD anode, respectively. The oxidation power of EAOPs with different anodes was also compared by measuring the evolutions of NO3 and NH4+ as well as four generated carboxylic acids including oxalic, oxamic, formic and fumaric acids.

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Mono-and co-applications of Ca-bentonite with zeolite, Ca-hydroxide, and tobacco biochar affect phytoavailability and uptake of copper and lead in a gold mine-polluted soil

Publication date: 15 July 2019

Source: Journal of Hazardous Materials, Volume 374

Author(s): Altaf Hussain Lahori, Zengqiang Zhang, Sabry M. Shaheen, Jörg Rinklebe, Zhanyu Guo, Ronghua Li, Amanullah Mahar, Zhen Wang, Chunyan Ren, Shenshen Mi, Tao Liu, Ren Jing

Abstract

We assessed the efficacy of Ca-bentonite (CB) alone and combined with Ca-hydroxide (CH), tobacco biochar (TB), and zeolite (ZL) aiming to immobilize Cu and Pb and decrease their bioavailability and uptake by pak choi followed by maize in a mining contaminated soil. The CB alone was able to decrease the availability and uptake of Cu and Pb by pak choi and maize. The mono- and multi-combination of CH, TB, and ZL with CB showed contradictory impact on the availability and uptake of Cu and Pb as compared to the mono-application of CB. The combination of CB with ZL and CH + ZL reduced the uptake of Pb by pak choi and maize, while the combination of CB with TB and ZL reduced the uptake of Cu by pak choi and maize as compared to the mono-application of CB. The co-application of CB with CH increased the phytoextraction of Cu by maize and Pb by pak choi shoots as compared to the mono-application of CB. We conclude that modified clays such as CB alone or combined with ZL, TB, and/or CH might be suitable candidates for phytomanagement of Cu and Pb contaminated soils.

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Complex dielectric permittivity of metal and polymer modified montmorillonite

Publication date: 15 July 2019

Source: Journal of Hazardous Materials, Volume 374

Author(s): Ya Chu, Shaokai Nie, Songyu Liu, Changho Lee, Bate Bate

Abstract

Owing to its high surface area and high surface charge density, clay, either contaminated with heavy metal ions or modified with organic additives as barrier materials, is difficult to assess and monitor. Complex dielectric permittivity (κ*) showed promising potential in tackling the above issues. In this study, the complex dielectric permittivity (κ*) of clays modified with a surfactant, four polymers, and four metal ions was measured at frequencies from 0.2–20 GHz. With the addition of polymer and metal ions, increasing frequency caused a slight decrement in real permittivity but a significant decrement in effective permittivity. A modified linearity polynomial equation, which considered the particle conductivity, was developed to fit the relationship between effective conductivity (σeff) and porosity ranging from 0.7 to 1.0. A three-dimensional Cole-Cole plot (κ′-κeff″-w) shows Cole-Cole circle expansion at higher water content. The resonance strength of modified clays was observed to increase with water content, which suggests that the number of water molecules in the diffuse layer of polymer or metal ions saturated clay increased. However, sorbed polymer and metal ions have an insignificant influence on the resonance time τs and stretching exponent 1-α. κ* can provide nondestructive characterization of metal or polymer modified clays.



Synthesis of zerovalent iron from water treatment residue as a conjugate with kaolin and its application for vanadium removal

Publication date: 15 July 2019

Source: Journal of Hazardous Materials, Volume 374

Author(s): Adedayo Bello, Tiina Leiviskä, Ruichi Zhang, Juha Tanskanen, Paulina Maziarz, Jakub Matusik, Amit Bhatnagar

Abstract

This study was aimed at examining the possible utilization of iron-rich groundwater treatment sludge in the synthesis of zerovalent iron (ZVI) as a conjugate with kaolin clay (Slu-KZVI), and its application for vanadium adsorption from aqueous solutions. Iron was extracted from the sludge using 1 M HCl and was used in ZVI synthesis by the sodium borohydride reduction method. The characteristics and performance of Slu-KZVI were compared to a kaolin modified with synthetic iron (FeCl3·6H2O) (Syn-KZVI). Adsorption results showed a competitive performance by both classes of KZVI, with Syn-KZVI slightly outperforming Slu-KZVI. X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy confirmed the formation of Fe0 on the core-shell structure of both modified adsorbents. In addition, the surface analysis of Slu-KZVI indicated the presence of P and Ca to a small extent, originating from the sludge. Both classes of sorbents performed better in solutions with acidic and neutral pH values (3–7). Surface complexation was thought to be the primary mechanism whereas simultaneous V(V) reduction and Fe oxidation (redox) reactions may also have taken place to some extent. A sorption test with groundwater confirmed that adsorbents were able to reduce vanadium to a very low concentration.

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Exfoliated Ni-Al LDH 2D nanosheets for intermediate temperature CO2 capture

Publication date: 15 July 2019

Source: Journal of Hazardous Materials, Volume 374

Author(s): Aamir Hanif, Mingzhe Sun, Shanshan Shang, Yuanmeng Tian, Alex C.K. Yip, Yong Sik Ok, Iris K.M. Yu, Daniel C.W. Tsang, Qinfen Gu, Jin Shang

Abstract

CO2 capture is projected as one of the pragmatic approaches to deal with the global warming phenomenon. Adsorption-based CO2 capture is considered an economically attractive option to reduce CO2 emission. The success of the adsorption-based capture primarily relies on adsorbents and thus a variety of adsorbents have been investigated in the literature. We here report a high surface area (210.2 m2/g) exfoliated Ni-Al LDH nanoplatelet as a promising candidate for CO2 capture at an intermediate temperature of 200 °C applicable to integrated gasification combined cycle (IGCC) and sorption enhanced water gas shift (SEWGS) reactions. The materials were well characterized by PXRD, TGA, FTIR, TEM, ICP-OES, and N2 adsorption surface area, and pore size distribution techniques. A unique nanoflower morphology comprising of exfoliated LDH platelets of ca. 5 layer thickness was obtained. The CO2 capture capacity (0.66 mmol/g) of the exfoliated Ni-Al LDH nanoplatelet is comparable to that of the widely reported Mg-Al LDH-derived mixed oxides and MgO-based adsorbents. Provided that Ni-Al and other transition metal LDH materials are known to exhibit superior catalytic properties for CO2 methanation, this work could pave the way for development of dual-functional materials for CO2 capture and conversion.

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Decomposition behavior and mechanism of epoxy resin from waste integrated circuits under supercritical water condition

Publication date: 15 July 2019

Source: Journal of Hazardous Materials, Volume 374

Author(s): Kuo Li, Lingen Zhang, Zhenming Xu

Abstract

Integrated circuits (IC), a kind of widely used electronic component, is paid great attention to recover valuable materials and remove hazardous materials after being discarded. However, refractory epoxy resin as packaging material is tightly covered on waste IC. It is difficult to remove epoxy resin and recover metals environmentally friendly by traditional methods. In this study, decomposition of epoxy resin from waste IC in supercritical water (SCW) was investigated. The epoxy resin could be efficiently decomposed under SCW condition. High temperature and long operation time of SCW treatment was positive for decomposition efficiency. The main decomposition intermediates and products were phenol and its derivatives. The decomposition mechanism of epoxy resin in supercritical water belongs to complex free radical reaction. Seven proposed pathways for the formation of key intermediates were investigated, with the kinetic and thermodynamic parameters obtained by density functional theory calculations. The analyzation provided assistance in the optimization of SCW treatment. Epoxy resin conversion rate could reach 95.51% under the condition of 500 ℃, 23 MPa and 90 min, then metals could be easily separated and recovered from solid residue. Thus, SCW treatment presents an efficient and green process for the recycle of waste IC.

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Experimental study on vented explosion overpressure of methane/air mixtures in manhole

Publication date: 15 July 2019

Source: Journal of Hazardous Materials, Volume 374

Author(s): Pengliang Li, Ping Huang, Zhenyi Liu, Bingxuan Du, Mingzhi Li

Abstract

Gas explosion in manhole often occurs in cities. Many previous researches on gas explosion are not suitable for manhole explosion because of the particularity of manhole structure. To investigate the gas explosion in manhole, a full-scale manhole model was established, in which the explosion overpressure of methane/air mixtures were studied experimentally. The variation of blast wave overpressure with time at different distances was analyzed. In addition, the effects of methane concentration, ignition location and manhole cover weight on the external overpressure after manhole explosion were obtained. The results showed that at the experimental conditions in this paper, under the influence of vent mode and flame propagation, the maximum peak overpressure caused by manhole explosion was mostly at the third measuring point. And there were two peaks in the overpressure histories. It was also found that when the methane concentration was close to stoichiometric ratio, the ignition location was further away from the manhole head, and the weight of manhole cover increased, the peak overpressure of blast wave caused by explosion increased. Besides, some suggestions were put forward for the risk control of manhole explosion accident based on the experimental results.



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