Fixed-bed Experiments Research Articles

Mercury Removal from Aqueous Solutions Using Modified Pyrite: A Column Experiment

Modified pyrite (MPy), which was obtained from calcination in an N2 atmosphere, was used as a sorbent for removing Hg(II) from aqueous solutions. Fixed-bed column experiments were conducted to determine the Hg(II) removal ability of MPy from aqueous solutions. MPy was found to be much better than natural pyrite for mercury removal. The concentration of Hg(II) in effluents was much lower than that of the emission standard used for Hg wastewater in China (0.05 mg/L), and the removal efficiency of Hg(II) was greater than 99% before breakthrough. When the capacity was 3274 times the column bed volume (1 bed volume = 25.12 cm3), the column breakthrough and the sorption amount of Hg(II) were 54.44 mg/g. The Hg(II) content in the used MPy sorbent was up to 24.79%. The mechanism was analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM), and X-ray Photoelectron Spectroscopy (XPS). The main mechanism of Hg(II) removal by MPy was the chemical reactions between mercury ions and mineral fillers, and HgS precipitated on the surface of MPy to remove Hg(II). The reaction was also accompanied by surface complexation and adsorption. The results of this work show that MPy can be used as a sorbent for continuous Hg(II) removal.

A novel nanocomposite based silica gel/graphene oxide for the selective separation and recovery of palladium from a spent industrial catalyst

A novel nanocomposite-based silica gel/graphene oxide (SG@GO-IIP) was prepared and applied to the recovery of palladium from a spent industrial catalyst. The nanocomposite material was characterized using Fourier-transform infrared (FT-IR), N2 adsorption-desorption, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG) techniques and a possible adsorption mechanism between Pd(II) ions and SG@GO-IIP was put forward. In addition, adsorption properties of SG@GO-IIP towards Pd(II) were investigated in detail via batch and fixed-bed experiments. The results showed that the adsorption process was well described by the pseudo-second-order kinetic and Langmuir models and that the maximum adsorption capacity achieved was 154.3 mg g−1, while adsorption equilibrium was reached within ~90 min. In the fixed-bed experiments, the effects of initial pH value, flow rate and fixed-bed height on breakthrough curves were investigated and the Thomas and Yoon-Nelson models were found to be more appropriate for describing the entire adsorption process compared to the Adams-Bohart model. The adsorption capacity of Pd(II) ions onto SG@GO-IIP reaches the maximum of 147.7 mg g−1 when pH of the solutions was 3.0, the flow rate was 0.6 mL/min and the fixed-bed height was 40 mm. The SG@GO-IIP material exhibited excellent affinity towards Pd(II) even in the presence of K(I), Na(I), Ca(II), Mg(II) and Al(III) ions, as well as possessing good regeneration and reusability properties, with its maximum adsorption capacity declining by only 8.9% after five adsorption/desorption cycles. The adsorption mechanism of Pd(II) onto SG@GO-IIP is considered to be via the formation of coordination bonds between the Pd(II) and iodine in the adsorbent. The study proposed a new method to recover palladium from a spent industrial catalyst via solid-phase extraction using SG@GO-IIP as a sorbent, sulfuric acid was chosen as the leaching liquor in the process and the technology may facilitate graphene oxide based nanocomposite materials begin to be applied by industrial applications to some extent.

Influence of different precursors on the characteristic of nitrogen-enriched biochar and SO2 adsorption properties

Biochars with different physicochemical properties will lead to different characteristics of nitrogen-enriched biochars obtained via modification, thereby affecting their SO2 capture characteristics. In this study, different feedstock types (peanut shells, corn stalks and corncobs), different activation condition were used to obtain the precursors for the preparation of nitrogen-enriched biochar via the methyldiethanolamine-methanol impregnation method to explore the influence of different precursors (raw biochar) on the characteristics of the nitrogen-enriched biochars and their SO2 adsorption properties. In addition, the SO2-adsorption process on nitrogen-enriched biochar in coal-fired power plants was simulated by fixed-bed experiments and the effects of the adsorption temperature, oxygen content, humidity and NO concentration on the SO2-adsorption capacities were investigated. The results show that the nitrogen content shows a stronger linear relationship with the micropore volume than that with the non-micropore volume, with the highest nitrogen content of biochars (CCAN850) reaching 9.50%. In the presence of O2 and a low concentration of NO (500 ppm), the SO2-adsorption capacity of CCAN850 increased to 216.19 mg/g at 120 °C. X-ray photoelectron spectroscopy (XPS) showed that the SO2-adsorption site of the nitrogen-enriched biochar is mainly quaternary nitrogen and the presence of NO promoted the combination of SO2 and NO that facilitated the adsorption of these compounds in the form of nitrogen and sulfur. This increased the SO2-adsorption capacity of the nitrogen-enriched biochar.

Co-monomer polymer anion exchange resin for removing Cr(VI) contaminants: Adsorption kinetics, mechanism and performance

Modified anion exchange resin (EDE-D301) was synthesized by mixing monomers: epichlorohydrin (ECH), dimethylamine (DMA), ethylenediamine (EDA) with the weakly alkaline anion exchange resin D301 through in-situ polymerization method. Adsorption performance of EDE-D301 for removing Cr(VI) contaminants was investigated in batch and column systems. Physicochemical properties of the anion exchange resins were characterized to determine the adsorption mechanism and regeneration ability. Characteristic results revealed that EDE-D301 showed enhanced surface area, positive charge and contents of N and Cl elements, indicating that the modifying reagents of monomers were successfully polymerized in the resin. The experimental adsorption data fitted well to the pseudo-second-order kinetic model and the Langmuir isotherm model. The fixed-bed experiments showed that the exhaustion time increased with increasing the bed depth, and decreased with increasing the flowrate and influent concentration. Adsorption capacity for Cr(VI) onto EDE-D301 was determined at a maximum level of 298 mg·g−1, and remained at 93% after four consecutive cycles. FTIR and XPS analysis indicated that the ion exchange and complexation were responsible for the Cr(VI) adsorption.

Ultra-High-Molecular-Weight polyethylene-based nanocomposite for removal of tetracycline in aqueous systems

The application of an ultra-high-molecular-weight polyethylene-based (UHMWPE) nanocomposite with nanohydroxyapatite (HA) and organophilic bentonite (OB) for adsorption of tetracycline (TC) was evaluated. The nanocomposite was prepared by combining the high energy grinding and the muffle heat treatment. Their formulation was investigated through complete experimental design (23), varying amount of OB, temperature and sintering time. The morphology and structure of the UHMWPE/HA/OB (ultra-high-molecular-weight polyethylene-based, nanohydroxyapatite and organophilic bentonite) were characterized using Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM) and Electron Microscopy Transmission (TEM). The adsorption of TC in the composite was investigated through batch and fixed-bed experiments. For the batch experiments, the UHMWPE/HA/OB nanocomposite adsorbed 8.72 mg∙g−1 TC at 328.15 K, at neutral pH and at 24 h of reaction. The experimental adsorption data for kinetics were best described by the pseudo second order model (R2 = 0.989) and the isotherms followed the Freundlich model (R2 = 0.996). The thermodynamic investigation indicated that the adsorption was an endothermic reaction and that there is an affinity between the adsorbent and the adsorbate. According to the results of the fixed-bed column experiment, the breakthrough curve was plotted and the characteristic column parameters were evaluated, and the experimental data were better described by the Yan model (R2 = 0.980). Based on the results of the work the UHMWPE/HA/OB nanocomposite is very promising for the removal of contaminants in aqueous medium.

Synthesis optimization and X-ray absorption spectroscopy investigation of polymeric anion exchanger supported binary Fe/Mn oxides nanoparticles for enhanced As(III) removal

A macroporous anion exchange resin containing high density of positively-charged quaternary ammonium functional groups and supporting binary Fe/Mn oxides nanoparticles (HA502P-Fe/Mn) was synthesized for simultaneous As(III)oxidation and As(V) adsorption within a single bead. Various preparation parameters were investigated and optimized to achieve the highest As(III) removal efficiency, including metal oxides type, supporting materials, preparation solvents, and number of loading cycles. The results from five imaging techniques (SEM-EDX, TEM, XRD, XANES, EXAFS) confirmed that amorphous ferric and manganese oxides nanoparticles were successfully dispersed throughout the matrix of the parent macroporous anion exchanger. The changes in oxidation state of the Mn oxides from +4 to +2 and + 2 to +4 were observed by XANES during As(III) removal and regeneration runs, respectively. The EXAFS was used to investigate the neighborhood atoms surrounding arsenic during As(III) removal by HA502P-Fe/Mn. The bond distance between AsFe and AsMn of HA502P-Fe/Mn are 3.35 and 2.94 Å, respectively, suggesting that As(III) was oxidized to As(V) and adsorbed on the surface of Fe(III) and Mn(IV) oxide nanoparticles by formation of inner-sphere complex. As(III) was oxidized by MnO2 nanoparticles under the absence of oxygen environment and only As(V) was observed after adsorption. The equilibrium As(III) sorption isotherms, effect of pH, competing ions, and NOM were also evaluated. Fixed-bed column experiments using NSF challenge water standard 53 (300 μg As(III)/L, pH 6.5) were carried out and found that the material can remove As(III) equivalent to 4300 bed volumes (BVs) compared with 2000 BVs using commercial arsenic selective material (Layne-RT). The exhausted material can be regenerated using 10 BVs of regeneration solution and 98% of adsorbed arsenic can be recovered.

Removal of Cadmium from Aqueous Solutions by Saccharomyces cerevisiae-Alginate System.

The aim of this study was to determine the Cd2+ removal capacity of a biosorbent system formed by Saccharomyces cerevisiae in calcium alginate beads. The adsorption of Cd2+ by a S. cerevisiae–alginate system was tested either by batch or fixed-bed column experiments. The S. cerevisiae–alginate system was characterized using dynamic light scattering (DLS, zeta potential), size, hardness, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy. Beads of the S. cerevisiae–alginate system showed a spherical–elliptical morphology, diameter of 1.62 ± 0.02 mm, 96% moisture, negative surface charge (−29.3 ± 2.57 mV), and texture stability during storage at 4 °C for 20 days. In batch conditions, the system adsorbed 4.3 µg of Cd2+/g of yeast–alginate beads, using a Cd2+ initial concentration of 5 mg/L. Adsorption capacity increased to 15.4 µg/g in a fixed-bed column system, removing 83% of total Cd2+. In conclusion, the yeast–alginate system is an efficient option for the removal of cadmium at low concentrations in drinking water.

Catalytic Conversion of Biomass for Aromatics Over HZSM-5 Modified by Dawson-Type Phosphotungstic Acid

The multi-functional zeolites modified with different phosphotungstic acid (PW) ratios were prepared and characterized. Thermogravimetric tests coupled with kinetics analysis were performed to evaluate catalytic pyrolysis behavior of biomass; The presence of HZSM-5 inhibited the product diffusion, causing a slight delay of pyrolysis; The PW modification made the reaction more complex; reaction order increased from 1.96 to 2.12. The activation energy decreased from 53.32 to 31.15 kJ/mol with the increase of PW. Then, fixed-bed catalytic experiments were further conducted to investigate aromatics production; 10%PW modification gave the appropriate acidic distribution and pore structure, resulting in oxygen being more likely to be removed in the form of COx. Although the organic yield was only 10.73%, HHV reached 38.01 MJ/kg. The organic phase catalyzed by 10%PW/HZSM-5 exhibited higher aromatization degree, and the structures of benzene ring were mainly single-rings. The oxygenates (especially for phenols from 16.88% to undetected) reduced obviously with increasing PW loading, and the 10%PW modification gave the highest content (peak area, %) of desirable mono-aromatic hydrocarbons (52.29%). The GC/MS analysis results were basically consistent with the 1H/13C NMRs. Besides, the 10%PW/HZSM-5 had the highest catalytic stability and the spent catalyst could recover high activity after regeneration. Therefore, catalytic pyrolysis of biomass using Dawson-structured PW-modified HZSM-5 is a promising approach for production of light aromatic hydrocarbons.

Room temperature synthesis of Cu(Qc)2 and its application for ethane capture from light hydrocarbons

A facile and efficient room-temperature synthesis approach was proposed to prepare MOF material Cu(Qc)2 (henceforth called RT-Cu(Qc)2) with ultramicropores. RT-Cu(Qc)2 was successfully synthesized at room-temperature by means of (Zn, Cu) hydroxyl double salt as intermediate within 1–12 h. The resulting RT-Cu(Qc)2 exhibited excellent water vapor stability and its C2H6 uptake reached 2.19 mmol/g at 288 K and 1 bar. Its C2H6/C2H4 and C2H6/CH4 uptake ratio at 298 K and 1 bar were up to 3.70 and 22.67, superior to benchmark MAF-49, Cu(Qc)2 and ZIF-7. Its IAST-predicted C2H6/C2H4 and C2H6/CH4 selectivity reached 4.1 (1:1 v:v) and 35.9 (1:9 v:v) at 288 K and 1 bar, higher than most of ethane-capturing MOFs. Molecular simulation revealed well-defined host–guest match between Cu(Qc)2 and ethane. Fixed bed experiments confirmed that ethane/ethylene or ethane/methane mixtures can be completely separated using RT-Cu(Qc)2. RT-Cu(Qc)2 has great potential for separation of ethane/ethylene and the recovery of ethane from natural gas.

Mechanism study about the adsorption of Pb(II) and Cd(II) with iron-trimesic metal-organic frameworks

This study examined the effects of two kinds of iron-trimesic metal-organic frameworks (MOFs) [MIL-100(Fe) and Fe-BTC] on adsorption of Pb(II) and Cd(II). For both materials, adsorption of Pb and Cd nearly approached equilibriums in the initial 2 min with high pseudo-second-order kinetics rate constants (0.895 g·mg−1·min−1 for Pb and 1.416 g·mg−1·min−1 for Cd). Both materials showed better adsorption performance with the increase of solution pH (from 2 to 7). Adsorption processes were endothermic, entropy-increased and spontaneous. The higher enthalpy change (ΔH0) and entropy change (ΔS0) values for Cd adsorption reflected the more difficult adsorption of Cd compared with Pb, which is related with more negative hydration enthalpy (ΔHhydΘ) and larger ionic radius of Cd. Multilayer adsorption phenomena appeared with no maximum adsorptive capacity observed. Both Langmuir-Freundlich and Freundlich-BET models could well describe isotherms. Multilayer adsorption may be attributed to the formation of inner-sphere complexation and outer-sphere complexation. Bockris-Devanathan-Muller (BDM) electrical double layer theory was used for illustrating adsorption mechanism. The fixed-bed adsorption experiments with Fe-BTC showed outstanding elimination performance in initial operating period (>99.8% for Pb and >99.6% for Cd), with effective filtration volume of 980 mL for Pb and 300 mL for Cd. Recyclability test showed that Fe-BTC could be well regenerated by ethylenediamine tetraacetic acid disodium salt (EDTA-2Na). This study showed that MIL-100(Fe) and Fe-BTC are potential for practical heavy metal removal applications.

New insights from modelling and estimation of mass transfer parameters in fixed-bed adsorption of Bisphenol A onto carbon materials

The removal of Bisphenol A, 2,2-bis (4-hydroxyphenyl) propane (BPA) in fixed-bed columns was investigated by breakthrough adsorption tests at different operation conditions and further prediction by a mathematical model to describe the adsorption-diffusion process onto two synthesized carbon porous materials. In this study, a xerogel (RFX) prepared by an optimized conventional sol-gel method and a lignin-based activated carbon (KLP) obtained via chemical activation were used in batch and fixed-bed adsorption experiments. The materials were fully characterized and their adsorptive properties were compared to those obtained with a commercial activated carbon (F400). RFX and KLP materials reached the equilibrium adsorption in only 24 h, whereas F400 activated carbon required 48 h. In addition, F400 and KLP adsorbents showed higher equilibrium adsorption capacity values (qe = 0.40 and 0.22 kg/kg, for F400 and KLP, respectively) than that obtained for the xerogel (qe = 0.08 kg/kg). Both synthesized carbon-adsorbents were studied in fixed-bed adsorption tests, exploring the effect of the operation conditions, e.g., initial BPA concentration (0.005–0.04 kg/m3), weight of adsorbent (0.01–0.05 g) and volumetric flow rate (0.2 to 1.0 mL/min), on the adsorption performance of the column. All the tested adsorption columns reached the equilibrium in a very short time, due to the efficient dimensionless of the bed. Additionally, the regeneration of the exhausted adsorbent was studied, achieving the total reuse of the solids after three consecutive cycles using methanol as regeneration agent. Finally, a mathematical model based on mass conservation equations was proposed, allowing to efficiently fit the experimental BPA breakthrough curves and estimate the external and adsorbed-phase mass transfer coefficients with a high accuracy.

Bimetallic BaFe2MAl9O19 (M = Mn, Ni, and Co) hexaaluminates as oxygen carriers for chemical looping dry reforming of methane

Chemical looping dry reforming of methane allows the continuous production of syngas and CO with decreased carbon footprint from two separated reactors, which provided system flexibility for various downstream applications, such as F-T synthesis or hydrogen purification. A key issue for this process is to find an appropriate oxygen carrier (OC) with high reactivity and recyclability. In this work, bimetallic BaFe2MAl9O19 (M = Mn, Ni, and Co) hexaaluminates were studied as OCs, with Fe-substituted BaFe2Al10O19 and BaFe3Al9O19 for comparison. The influence of Mn, Ni, and Co doping on structure, redox reactivity and stability was investigated by means of XRD, XPS, BET, H2-TPR, CH4-IR, SEM, CO2-TPO and fixed-bed experiments. Pure Fe-substituted OCs presented the coexistence of β-Al2O3 and magnetoplumbite (MP) hexaaluminate phases, which transformed from MP to β-Al2O3 during cyclic CH4/CO2 operation. Bimetallic BaFe2MAl9O19 (M = Mn, Ni, and Co) only crystallized in β-Al2O3 hexaaluminate due to the presence of +2 valent Mn, Ni, and Co, and the β-Al2O3 structure still remained stable during the CH4 reduction step. Mn doping inhibited the release of lattice oxygen, while Ni doping initiated significant CH4 pyrolysis. Among all dopants, the BaFe2CoAl9O19 OC exhibited good reactivity for syngas production with high CH4 conversion, high syngas yield, desirable H2/CO ratio (~2), and stable regenerability by CO2, taking advantages of the enhanced oxygen-donation ability and the preservation of hexaaluminate phase during successive CH4/CO2 redox cycles.

Synthesis of novel particle rice-based carbon materials and its excellent CH4/N2 adsorption selectivity for methane enrichment from Low-rank natural gas

Developing novel particle carbon adsorbents with excellent separation performance for recovering low concentration CH4 from coal mine gas remains great challenging. In this work, a novel and effective method was proposed for preparing particle carbon adsorbents with excellent separation performance of CH4/N2 mixtures. Rice was selected as carbon source to prepare carbon precursors in particle form by carbonization, followed by CO2 activation yielding particle rice-based carbon materials (PRCs) with narrow micropore distribution. Noteworthy, neither binding agent nor KOH was used in preparation process of particle PRCs. The resulting particle PRCs exhibited specific BET surface area of 776 m2/g. Its CH4 uptake and CH4/N2 adsorption selectivity were up to 1.12 mmol/g and 5.7 at 298 K and 100 kPa, which was superior to most of the reported powdery carbon materials and MOFs. Besides, computational simulation was applied to reveal the different contributions of the surface hydroxyl/carboxyl/aldehyde groups of the PRCs to the adsorption selectivity of CH4/N2. Calculation showed that the surface carboxyl groups played an important role in enhancement of the adsorption selectivity of PRCs toward CH4/N2 mixture. Fixed-bed experiments approved that CH4/N2 mixtures can be greatly separated at ambient condition. The particle PRCs are great potential materials for recovering low concentration CH4 from coal mine. This facile and effective method proposed in this work is great attractive in low cost preparation of particle porous carbon materials without binding agent and KOH.

Highly efficient and stable catalysis of p-nitrophenol via silver/lignin/polyacrylic acid hydrogel

As the second largest natural polymer in nature, lignin has a large amount of reserves and has important practical application value, which has attracted increasing attention. Ag@LPAH, a nanometer silver catalyst with a 3D structure, was successfully prepared in a simple operation. In batch experiment and fixed-bed experiment, it showed excellent catalytic degradation ability and stability of 4-NP. Thanks to the large number of carboxyl groups present in the lignin-polyacrylic acid hydrogel, the silver nanoparticles are well controlled to grow with no agglomeration. Ag@LPAH-20 exhibited optimal catalytic performance and stability, requiring only 123 s to complete the reaction and maintaining 99% catalytic efficiency after 10 cycles. In addition, the catalytic efficiency can be maintained over 90% for more than 120 min in fixed bed experiment.

Adsorption of Azo Dye Methyl Orange from Aqueous Solutions Using Alkali-Activated Polypyrrole-Based Graphene Oxide.

The adsorption of methyl orange (MO) from aqueous solutions onto a KOH-activated polypyrrole-based adsorbent (PACK) was investigated using batch and fixed-bed column techniques. The structural, thermal, and morphological properties of the PACK, analyzed by various methods, support its applicability as an adsorbent. An adsorption kinetic study revealed a preferably pseudo-second-order (R2 = 0.9996) and rate-limiting step controlled by both film and intra-particle diffusions. The thermodynamic adsorption tests resulted in negative ΔG°, ΔH°, and ΔS° values, which decreased as the temperature and concentration increased, indicating the spontaneous and exothermic adsorption over 25–45 °C. The adsorption isotherms fit the experimental data in the order of Langmuir ≈ Freundlich > Temkin, with evidence of adsorption operating well via the monolayer physical adsorption process, and maximum monolayer adsorption ranging from 520.8 to 497.5 mg/g. The breakthrough curve of the fixed-bed column experiment was modeled using the Thomas, Yoon–Nelson, and Hill models, resulting in an equilibrium capacity of 57.21 mg/g. A 73% MO recovery was achieved, indicating the possibility of column regeneration. Compared to other adsorbents reported, PACK had comparable or even superior capacity toward MO. For cost-effectiveness, similar nitrogen-containing polymeric wastes could be exploited to obtain such excellent materials for various applications.

Interpretation of lead removal by two biomasses at different size via monitoring the solution environment

It is imperative to seek for a quick monitoring method in the sustainable cleanup of heavy metal contaminated water and in the efficient use of waste biomass resources. In this study, SMS (spent mushroom substrate) and CSMS (composted spent mushroom substrate) were processed into particles at different size for the lead removal from solution. The results indicate that biomass particles at different size are inconsistent in functional groups characteristics. In batch experiments, changes in pH and EC (electric conductivity) can explicate the lead removal process and the effect of particle size and dissolved matter on removal rate. The established removal rate models based on pH and EC value (p˂0.01) can be used to assess the efficiency of particles in lead removal. In fixed-bed experiment, lead removal rate is highly correlated with pH value (0.763–0.986, p˂0.01). The present study provides a quick method for monitoring the removal efficiency of waste biomass in the treatment of metal contaminated water.

Efficient removal of arsenic from groundwater using iron oxide nanoneedle array-decorated biochar fibers with high Fe utilization and fast adsorption kinetics

Although Fe-based biochar adsorbents are attractive for removing arsenic from water due to their advantages of costing little and being producible at a large scale, the practical applications of these granular adsorbents are mainly limited by low Fe utilization and slow adsorption kinetics. In this study, iron oxide nanoneedle array-decorated biochar fibers (Fe-NN/BFs) adsorbents have been prepared through a simple hydrothermal reaction. The vertical growth of iron oxide nanoneedle arrays on the surface of biochar fibers maximizes Fe utilization and shortens As diffusion distance, thereby increasing As removal kinetics and capacity. Batch experiments show that the adsorption capacities of Fe-NN/BFs for As(V) and As(III) reach to 93.94 and 70.22 mg/g-Fe at pH 7.0, respectively. As(V) levels (275 μg/L) in groundwater are rapidly reduced (less than 5 min) to below 10 μg/L using Fe-NN/BFs (1 g/L) at pH 6.7. Similar As(III) levels can be reduced to below 10 μg/L within 30 min by Fe-NN/BFs (1.5 g/L). In fixed-bed experiments, the treatment volumes of As(V) and As(III) spiked groundwater reach to 2900 BV (26.2 L) and 2500 BV (22.6 L), respectively, using two columns packed with Fe-NN/BFs in tandem (C0 = 275 μg/L, 2 g of adsorbents in each column). When the As concentration in the influent is reduced to 50 μg/L (As(V): 25 μg/L + As(III): 25 μg/L), the treatment volume using one column reaches up to 11000 BV. The Fe-NN/BFs packed column can be easily regenerated and reused many times. After four regenerations, the treatment volume of As(V) and As(III) were reduced by 10.4% and 22.8%, respectively.

Uniform and stable immobilization of metal-organic frameworks into chitosan matrix for enhanced tetracycline removal from water

Metal-organic frameworks (MOFs) have been attractive adsorbents for the treatment of antibiotic wastewater. However, in their powder form, the adsorbents suffer from the disadvantage of poor recyclability and complex operational process. Herein, we incorporated typical MOFs (ZIF-8, ZIF-67, HKUST-1, and Fe-BTC) into low-cost chitosan matrix for the tetracycline removal. Metal hydroxide(or metal oxide)/chitosan composite beads from the metal salt/chitosan solution were used as MOF precursor, which lead to the uniform and stable MOF loading into chitosan. This composition could not only shape MOFs into beads but also improve the adsorption capacity of the chitosan. As a result, ZIF-8-chitosan composite beads exhibited good adsorption performance toward antibiotic tetracycline. The adsorption processes followed pseudo-second-order model and Langmuir isotherm model. The maximum adsorption capacity could reach 495.04 mg/g, which is higher than most of the MOF-based or natural polymer-based tetracycline adsorbents. Moreover, the removal efficiency of ZIF-8-chitosan composite beads toward tetracycline was still above 90% after ten adsorption-desorption cycles. In the fixed-bed experiment, ZIF-8-chitosan column could treat ~887 bed volumes (BV) of tetracycline solution in real water sample. Both experimental characterizations and DFT calculations indicated that the adsorption mechanism involves in the electrostatic interaction, π-π stacking interaction and hydrogen-bonding interaction. This study provides a promising strategy for uniform MOF loading into the matrix and potential adsorbents for pharmaceutical wastewater treatment.

Simultaneous removal of cationic and anionic heavy metal contaminants from electroplating effluent by hydrotalcite adsorbent with disulfide ([formula omitted]) intercalation

Hydrotalcite materials are generally utilized for anionic pollutants due to its interlayered anion exchange ability. Their potentiality for cationic contaminants is rarely explored. In this study, disulfide (S2-) intercalated LDH material demonstrated capability to remove both heavy metal cations and oxyanions simultaneously from water. The S2- intercalation of LDH significantly improved its adsorption capability towards both heavy metal cations (Co2+ and Ni2+) and oxyanion (CrO42-). The adsorption amount of S-LDH towards Co2+ and Ni2+ reached 88.6mg/g and 76.2mg/g, which are 405% and 281% higher than that of pristine LDH. For CrO42- removal, the adsorption amount reached 34.7mg/g, 402% higher than that of pristine LDH. The cations capture mechanism mainly depends on the novel layer sheet cation substitution mechanism based on irreversible precipitation and the generation of metal sulfide precipitates. Meanwhile, the interlayered S2- can be easily replaced by CrO42- to realize the simultaneous removal of both heavy metal cations and oxyanions. In the fixed-bed column experiments, 448 bed volume (BV) (672 mL) of simulating electroplating wastewater can be efficiently treated by yielding only 1 BV(15 mL) of chemical sludge, which is practically acceptable. This work provided a highly practical adsorption technology based on the S2- modification hydrotalcite material for the purification of heavy metal ions contaminated wastewater.

Water flow resistance characteristics of double-layer vegetation in different submerged states

Abstract In a natural basin, the vegetation can change the slope convergence and affect the surface runoff. Vegetation height may vary in an area, showing a two-layer combination of high and low collocation. This study aimed to understand the effects of double-layer vegetation in different submerged states on flow resistance. Plantings of vegetation at different heights may control landslides and contribute to soil and water conservation. This study explored the water flow resistance characteristics of double-layer vegetation at different heights. A plastic bar was used to simulate rigid vegetation, and an indoor channel fixed bed experiment was used to simulate vegetation with different heights of 5 cm and 7 cm, 5 cm and 8 cm, 5 cm and 9 cm, and 5 cm and 10 cm. By analyzing the relationship between the Darcy–Weisbach resistance coefficient (f) and water depth (h), it was concluded that when the vegetation is in a non-submerged state, f and h satisfy f= 5.6427 h+ 0.0245. When the water depth just submerges the low vegetation, f changes abruptly, and f and h satisfy the relationship f= 3.4075 h + 0.0021. When the water depth is the same as the height of high vegetation, f attains the maximum value. In addition, the flow resistance f increases by 0.03 with a 1 cm increase in the vegetation height h. When the vegetation is completely submerged, f is negatively correlated with h.